- o. .0- - r ' ""‘“°“""°"?‘”~“““""-M"’_"m« SOIL TEMPERATURE REGIME AND. ITS INTERACTION. WITH SUBMERGED TILE Thesis for the Degree of M. S. L" MICHIGAN STATE UNIVERSITY .j SIROUS HAJI-DIAFARI 197.2 0 o 0‘ u c n .; u u o o-- o o 0 . _ o .' . .- ‘ ‘ I o ','.l. 0.0' 'l't' '.' . , . . .... O O ' y. - - v ._ . c -a .‘1 , - o- . - .. V'. - . . v "' 1.x” ' -.. .- .- v ‘ . .3.“ . .4 — - . ,.-' c g..- , .. 0.!“ . -'-." o-v’ 33") .‘I - -. I “p, o . :‘l .h'. ‘ o , v. - , - - .’.4!:. _ - 3k”- ' - - ‘.- ‘ _ r‘: - - — _ e, ..... ‘.‘| _' , _ ‘:o" - o' _ . _ . ' w"! o “‘ _ , . r o - _ 3,“. , V _ - . - - fl ‘. '. . . ‘ ' ‘ ‘ . . ' ‘ ‘ -. . ' ' ' - .'. . ‘ . ' . ' ' v — ' - . A , ' ‘ ‘ -'_.. . ‘ ' ‘ .: V ’ - ~ , , ~ . . _ -. V ' -. . _ , - . " . 'o - °. 0 . - c r 4 . . . . - . , - . . ‘ _ ‘ . . _ - _ I ' , ' - - ‘ ' ‘ ‘ ‘ ' ’ '. _ o 0'- ~ . ‘ ‘4 V . c ; .l . '. ‘ '0 . ‘ ’ - O - I 00000 , V l 0 ;' . T ‘ .r. ‘ .Q - < . O r . _ I.' - ‘‘‘‘‘‘ - - ;: . _ ‘ , I r v. r ' — A - . I ‘ a 0"“. 4' . o a . ’7 T t I I . ’ . ' d ’ 0' ' - v , _ r ' - h. ..... - o . ‘o 1 , . r f I - - .“ -O o t a o . . . , , . I ’ a . - f a r -. .. -}. , . o I 'l n .' ‘ . r -' ' c g ’ . , ’ . ‘_ .'.- t - n , I - r ' l l .'-'. 4'. .-’- - . . _, _ - ‘ u . o ' - .- - r . ,1 . - '--.,' -o.-. — . _ _ - - - _ ~'. - r o 1‘ ’ ' A- ,1' . I "‘ o - - . o . - v . . 4 . I "‘,.‘.‘ \ ‘ ‘ ' - ' ~ . - . - . ,, .' — e —_ ‘ 7 4- ‘ ’ ' “"' "~‘ -0 o- o -9 u 0—- 0.. o-.‘ o so‘I‘CIOOOM IHISII " BINDING av ' 800K BINDERY INC. I m. :I'RIEIERORT. HIBIIIGA] HUM; & SBNS' LIBRARY BINDER I NWWWN ABSTRACT SOIL TEMPERATURE REGIME AND ITS INTERACTION WITH SUBMERGED TILE By Sirous Haji—Djafari The purpose of this study was to investigate the effect of thermal environment on submerged drain tile and the conditions causing the cracking of clay tile due to the freezing of part of water within the tile. The loca- tion of interest for the investigation was near Saginaw, Michigan. A new technique was used to obtain soil tem- peratures from air temperatures. In order to ascertain the behavior of‘a crack resulting from freezing the water within a drain tile, an experiment was conducted in the laboratory. The result of this experiment led to the determination of realistic conditions for solving the mathematical model of the freezing. In order to investigate the effect of sub- merged drain tile on the Ebrmal environment, a computer model was developed and utilized to study four, six and eight inch submerged drain tile burried at 36, 42 and 48 inches depth. Sirous Haji-Djafari The investigation led to following results: the average soil temperature varies as a function of depth but the average soil temperature is always greater than the average air temperature. When the soil temperature sur- rounding a submerged tile is reduced to less than 32°F for a period of time, the water inside the tile will freeze. Cracking will occur when about 1/3 of the water has frozen and the location will be at the interface of the ice water Approved Aégéfiifl,fl/ é? ;EZ%Z;%”“\ Ma or Professor Approved 45 A W Head of Department phase and the tile wall. SOIL TEMPERATURE REGIME AND ITS INTERACTION WITH SUBMERGED TILE By Sirous Haji-Djafari A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Agricultural Engineering 1972 ACKNOWLEDGMENTS The author wishes to express his sincere apprecia- tion to Dr. George E. Merva, who served as his Major Professor for the entire graduate program. His experience and inspiration were a constant source of assistance during the study. It has been a great privilege to work with him. The author is indebted to Professor E. H. Kidder of the Agricultural Engineering Department, Michigan State University, for his unfailing guidance. Sincere acknowledgment is due to Professor J. E. Adney, Mathematics Department, Michigan State University, for his cooperation and assistance. Appreciation is also extended to Associate Profes- sor J. V. Beck, Mechanical Engineering Department, Michi- gan State University, for his helpful suggestions. The author expresses his thanks to the Hancock Brick and Tile Company, Finley, Ohio, for furnishing the required funds to complete this project. The author is also thankful to his wife, Azizeh, for all the efforts put forth by her during the period of this study. ii TABLE OF CONTENTS» ACKNOWLEDGMENTS . . . . . . . . . . . . . LIST OF TABLES LIST OF FIGURES . . . . . INTRODUCTION Chapter I. REVIEW OF BASIC POINTS . . . . . . . . . . . . 1.1 Introduction . . . 1.2 Source and Amount of Heat . 1. 2.1 Latitude and Slope of Land . 1.2.2 Vegetative Cover . . . . . . 1.3 Thermd.Pr0perties of Soils 1.3.1 Heat Capacity of Soils 1.3.2 Thermfl.Conductivity and Soil Factors Affecting It 1. 4 General Differential Equation for the Temperature Field .‘. . 1.5 Daily and Seasonal Changes in Soil Temperature . . . . . . . . . . . 1. 5.1 Damping Depth . . . . . . . . . II. DEFINITION OF THE PROBLEM 2.1 Background. . . . 2.1.1 Tile for Over- size Trenches 2.1.2 Clay Tile and Frost Action 2.2 EXperimental Set-up . . . 2.2.1 Procedure 2.2.2 Observations . 2.3 Mathematical Model . . 2.3.1 General Assumptions 2.3.2 Specific Assumptions 2.3.3 Determination of Initial and Boundary Conditions . . . . . . 2.4 Solution of the Model . . 2.4.1 Formula and Method of Solution. 2.4.2 Numerical Solution . 2.4. 3 Applying the Boundanrand Initial Conditions in Solution of Related Formulas iii Page ii vii I-IH oooouxza 4:- 19 22 25 28 28 28 31 31 32 35 35 37 41 57 59 59 62 Chapter III. 3.1 Results . . . . . . . . 3.1.1 Results of Experiments 3.1.2 Results of Soil Temperature Study . . . . . . . . . . . . . . 3.1.3 Results of Computer Modeling 3.2 Discussion of Results . . . . . IV. CONCLUSIONS . . . . . . . . . V. RECOMMENDATIONS FOR FURTHER STUDIES LIST OF REFERENCES Appendices I. FOURIER SERIES MODELING OF PERIODIC PHENOMENA . . . . . . . . II. COMPUTER MODELING FOR STUDY OF SOIL TEMPERATURE WITH SUBMERGED DRAIN TILE III. CONVERSION FACTORS iv Page 66 66 66 67 70 77 79 81 83 85 92 108 Table 1-3 1-4 1-5 1-6 2-1 2-3 2-4 2-5 LIST OF TABLES Specific heatvalues<3 densities p, and specific heat per unit volume C of several soil minerals and rock materials Specific heat values c, densities p, and specific heat per unit volume C of several organic soils and soil materials . . . . Specific heat values c, densities p, and specific heat per unit volume C of several soils after Kersten (1949) . . . . . . ThermalprOperties of some typical soils and of the common soil constituents (at 10°C) Comparison of thermalproperties of frozen and unfrozen soil Damping depths oftemperature fluctuation having various periods for several values of thermal diffusivity Recorded daily soil temperature (°FJ at different depths in East Lansing Horti- culture Farm in 1963 . . . . . . . . Annual average of soil temperature (°F.) for East Lansing Horticulture Farm Station . Annual average soil temperature (°F.) at the University of Minnesota, St. Paul Station. Soil is under sod cover Effect of soil coverage on yearly average soil temperature (°F.) at different depths O O O O o O O O 0 Difference between air temperature and soil temperature at different depths in °F. Effect of soil cover on. soil temperature at different depths in the cold season Page 12 13 14 20 21 27 42 43 43 46 48 69 Table Page 3-2 Effect of soil cover on soil temperature at different depths in the warm season . . . . 69 3-3 Time and required duration of submergance for cracking to take place in clay drain tile . . . . . . . . . . . . . . . . . . . 76 I-l The calculated fourier coefficients for 8 inches depths of soil . . . . . . . . . . . 88 I-2 The calculated fourier coefficients for 20 inches depths of soil . . . . . . . . . . . 89 I-3 The calculated fourier coefficients for 40 inches depths of soil . . . . . . . . . . . 90 I-4 The calculated fourier coefficients for 80 inches depths of soil . . . . . . . . . . . 91 vi Figure 1-1 2-2 2-3 2-8 LIST OF FIGURES Extrinsic factors which influence frost action . Intrinsic factors which influence frost action Frost penetration in bare and grass-covered soils. Heat conductivity and diffusivity in coarse ' quartz sand Linear heat conduction . Location of thermocouples in the experi- mental setup . . . . . . A picture of the cracked tile showing the general appearance. Note the thermo- couple wires entering from the right Temperature variation for each thermo- couple . . . . . The shape of ice causing cracking of a drain tile. The location of the crack is shown in the picture at the lower right of the tile Grid system Effect of soil coverage on soil temperature. Variation of monthly average air and soil temperature by depth The average monthly air temperature for East Lansing, Saginaw and Evart in 1968. Air temperature of East Lansing and Saginaw for the year 1963 vii Page 18 19 33 33 34 36 39 45 47 50 51 Figure 2-9 2-10 2-11 2-12 3-1 3—4 3-6 Calculated soil temperature for Saginaw, 1963 . Recorded soil temperature for East Lansing, Horticulture Farm Station, 1963 Recorded soil temperature for East Lansing, Horticulture Farm Station, 1968 Approximation of drain tiles in grid system for cumputer model Frost penetration in bare and sod surface soil Temperature history in the soil around a four inch submerged drain tile burried at 36, 42, and 48 inch depths Temperature history in the soil around 6 inch drain tile burried at 36, 42, and 48 inch depths . Temperature history in the soil around eight inch submerged drain tile burried at 36, 42, and 48 inch depths The effect of water within the four-inch drain tile on soil temperature. (Iso- thermal lines are shown in the figure) A photograph of an 8 inch clay tile removed from a field located near Saginaw, Michigan.. viii Page 54 55 56 58 68 71 72 73 74 78 INTRODUCTION Drainage plays an important role in agricultural production, both in arid regions as well as in regions where the primary role of drainage is in the removal of excess ground water from the plant root zone. A well-designed drainage system requires high quality material which, for a plastic conduit system is synonymous with a material capable of supporting the over- burden load. For a rigid conduit system a crack-free tile is required which is capable of supporting the loading which may occur due to trench and/or over-burden, since a cracked tile, if disturbed, may collapse, thus causing blockage of the tile line and failure of the System. Although progress has been made toward providing safe design criteria, a source of damage to buried tile lines remains uninvestigated, i.e., the cracking of tile due to water freezing within the conduit. Such a condi- tion may occur in areas where good tile outlets are not available and pump drainage is utilized. Under these con- ditions, tile lines are often installed with minimum cover and submerged outlets are used. A large portion of the drainage system may be submerged during the cold season, and penetration of severe cold weather can cause freezing of a portion of the water within the lines and subsequent cracking of the buried clay conduit. A knowledge of the condition conductive to freezing damage would lead to the establishment of design criteria which would ultimately increase the reliability of the drainage installed under these conditions. In this thesis, a study has been made to investi- gate the effect of thermal environment on submerged drain tile and the conditions causing cracking of clay tile due to the freezing of part of the water within the tile. In this study the location of interest is near Saginaw, Michi- gan, where extensive areas of soil had been laid bare during the cold months. These areas are in large part pump drained and the drainage system pumps may not be Operative during the winter season. For this study soil temperatures were calculated from air temperatures based on a new technique which has been presented in the body of this thesis. The data re- quired to support the hypothesis leading to the technique was obtained from United States Weather Bureau records from stations in Michigan, Minnesota, and Wisconsin. It is felt that if it is demonstrated experimen- tally that cracking does occur under certain temperature conditions, and if a similar set of conditions can be predicted for a field location through application of the selective modeling technique, then one could expect that tile drainage due to cracking can be anticipated for the location of interest. An experiment was conducted in the laboratory. The result of this experiment led to a deter- mination of realistic conditions for solving the mathematical model of tile freezing. In order to investigate the effect of submerged drain tile on thermal environment, a computer model was developed and utilized in the theoretical analysis. CHAPTER I REVIEW OF BASIC POINTS 1.1 Introduction In studying soil temperature and frost action around drain tile, many influencing factors must be considered. The factors which influence the soil temperature are divided into two groups: extrinsic and intrinsic factors (Kavianpour 1971). Extrinsic factors are those which determine the ambient conditions. The extrinsic factors are summarized in the block diagram of Figure 1—1. Intrinsic factors are those inherent to the soil material and include the thermal properties of soil, such as; the thermal conductivity, k, the specific heat, c, and the thermal diffusivity, a. The intrinsic factors are given in Figure 1-2. In order to develOp the basic concepts relating to thermal properties of soil, it is necessary to review some of the work which has been carried out with respect to the major factors and their influence on the overall thermal diffusivity of the soil. 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Hfiom one mo moHuHoQOMQ Hespoab cofiufimomEou zmmommzz zmmomm szommz: zmmomm 1.2 Source and Amount of Heat According to Baver, 1965, the temperature of the soil is primarily dependent upon the amount of radiant energy that is received from the sun. .The quantities of heat reaching the earth's surface by conduction from within the earth, or resulting from chemical and biological proces- ses, are so small that such sources have a negligible effect upon soil temperature. The amount of radiation reaching the earth from the sun depends upon the amount emitted by the sun and the absorption of the radiation by the atmosphere. In addition to the atmospheric conditions, there are several characteristics of the earth's surface that greatly affect the amount of radiation that is retained. (Baver 1965). These may be grouped as follows: 1.2.1 Latitude and slope of land The angle at which the sun's rays meet the earth greatly influences the amount of radiation received per unit area. Radiation reaching the earth at an angle is scattered over a wider area than the same radiation striking the earth's surface perpendicularly. Conse- quently, in the former case the amount of heat received per unit area is decreased in proportion to the increase in area covered. The amount of radiation reaching the earth per unit area is proportional to the cosine of the angle made between the perpendicular to the surface and the direction of the incoming radiation. Therefore, the radia- tion received per unit area decreases with an increase in this angle. 1.2.2 Vegetative cover The major effect of vegetation of soil temperature is the insulating quality of plant cover on temperature fluctuations. Bare soil is unprotected from the direct rays of the sun and becomes very warm during the hottest part of the day. When cold seasons arrive, unprotected soil rapidly loses its heat to the atmosphere. In winter the vegetation acts as an insulating blanket to reduce the rate of heat loss from the soil. Consequently, a pro- tected soil is cooler in summer and warmer in winter than one that is bare. The investigation of Petit (see Baver, 1965, pp. 365-366) has shown that frost penetrates deeper and disappears slower under bare conditions than under grass or surface mulches. This is illustrated in Figure 1-3. It may be seen that the sod cover decreased the rate and depth of penetration of frost as compared with bare soil. When thawing occurred, frost disappeared from the pro- tected soils sooner than from the bare soil owing to the fact that the latter soil was frozen to a greater depth. Temperature - °C I N -10 -12 -14 Figure Grass Cover . / I- \\ I \{ //// Bare Surface \ - -’- \ ‘- - \\__ \ ‘ \ Ix. \w’ \\\. _ _. " \ \a' I— - Temperature 1 ’L l L L L k L n n L n I Nov.Nov.Dec.Dec.Dec.Jan.Jan.Jan Feb Feb Feb.Mar. O O H O O H O O O) O I I I l I I I H N H N H N H N 1—3. Frost penetration in bare and grass-covered soils [Petit (1893)]. Redrawn from Baver 1965 p. 366. 10 1.3 Thermal Properties of Soils The temperature of a soil depends not only on the quantity of energy transported to it, but also on its ability to absorb this energy (Geiger 1965). The basic factors which control soil temperature are the thermal prOperties of the soil. Other factors such as intensity of absorption of energy (related to soil color) also affect this ability. Two independent thermal prOperties enter into a quantitative description of the heat transfer by conduc- tion, viz., the thermal conductivity, k, and the heat capacity per unit volume, C = pc. In many equations the ratio of these two quantities appears. The ratio is called the thermal diffusivity and is denoted by the symbol 77 pc' DeVries (van Wijk, et a1. 1963), Geiger (1965), and Baver (1965) present a detailed discussion relating to thermal pr0perties of soils. 1.3.1 Heat capacity of soils The specific heat of any substance is defined as the number of calories of heat required to raise one gram of the substance one degree on the centigrade scale (Baver 1965). The heat capacity per unit volume of a given material C as defined above is equal to its specific heat, c, times its 11 mass density, p. The specific heat of water is 1.00 calorie per gram per °C at 16°C (one BTU/lbm per °F at 60°F). All other constituents of soils have much lower specific heats. It may be seen from the data in Tables 1-1 and 1-2 that quartz has the lowest specific heat of the major soil constituents and humus the highest, excepting water. The aluminosilicate kaolin has a slightly higher specific heat than quartz. Since the major constituents in most soils are quartz, aluminosilicates, water ahd humus, it is evi- dent that humus and water will affect the heat capacity considerably. The heat capacity per unit volume of soil can be found by adding the heat capacities of the different soil constituents in one cm3 (DeVries, see van Wijk, et al., 1963). Thus, if x5, xw, and x3 denote the volume fractions of solid material, water (or ice) and air, respectively, one has C = x C + x C + x C s s w w a a The third term in the right-hand side can usually be neglected. The value of CW = 1.00 cal cm-3 °C'1 in the 3 -1 case of water, 0.45 cal cm- °C in case of ice at 0°C and .43 cal cm.3 °C-1 for ice at -20°C. The specific heats of twelve different mineral soils and material were measured by Kersten (van Wijk, et al., 1963) (see Table 1-3). 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HwthV memg oN.H -- . 55¢.o means H Do Eu Hmov monopomom H Eu wv away A Uo m Hmov HmHhoumz H- m- m- asap :woz H- H- u a o «.mHeHnoumE HHOm cam mHHOm oHcmMHo Hmho>om mo 0 oEDHo> “Ha: Hog use: onHoomm use .a moHuHmaop .o mosHm> pmo: onHoonm .N-H oHan 14 Table 1-3. Specific heat values c, densities p, and specific heat per unit volume C of several soils after Kersten (1949).* c1 . p C (cal g 1 $23: 1 (cal cm-S Soil °c 1) (°C) (g cm 3) °c 1) Northway fine sand 0.197 61.0 2.76 .543 Northway sand 0.171 - 6.7 2.74 .468 0.185 18.8 -- 0.191 60.2 -- Northway silt loam 0.168 -10.4 2.70 .453 0.176 20.4 -- 0.193 60.4 -- Chena river gravel 0.194 61.0 2.70 .523 0.196 60.4 -- Fairbanks silt loam 0.164 - 8.4 2.70 .442 0.183 18.8 -- 0.194 61.3 -- Graded Ottawa sand 0.157 - 9.5 2.65 .416 0.164 18.5 -- 0.176 37.7 -- 0.189 60.3 -- 20-30 Ottawa sand 0.183 37.8 2.65 .48 0.189 59.9 -- Lowell sand 0.159 - 9.5 2.67 .420 0.188 19.7 -- 0.188 60.9 ~- Crushed quartz 0.190 60.9 2.65 .503 Crushed trap rock 0.193 59.9 2.97 .573 Crushed feldspar 0.190 59.3 2.56 .486 Crushed granite 0.161 -13.3 2.67 .429 0.174 19.4 -- 0.189 60.9 -- (Adopted from van Wijk, et al., 1963 page 212) *See Appendix III for conversion factors from metric to British units. 15 -1 linearly from .16 i .01 cal cm.3 °C at -l8°C to .19 i .01 cal cm.3 °C-1 at 60°C. Since the specific mass of these minerals is about 2.7 g cm.3 an average value of GS of about .46 holds for a mineral soil at 10°C. The specific heat of soil organic matter was determined by several authors (see van Wijk, et al., 1963), the most probable value being .46 cal g'1°C-1 (extremes 1 are .42 and .48 cal g'1 °C- ). An average value of spe- cific mass of the organic materials in soil is 1.3 g cm.3 and therefore, GS = .60 is a good average value in the case of organic soils. DeVries concludes that if the volume fractions of soil minerals and of organic matter are denoted by xm and x0 respectively, the heat capacity per unit volume.equals 3 1 C = .46 x + .60 x0 + xw cal cm C . 1.3.2 Thermal conductivity and soil factors affecting it Geiger (1965) defines the thermal conductivity k as the amount of heat in calories that will flow through a one cm. cube of substance in one second, when the tem- perature difference between opposite faces is one degree centigrade, and there are no variations in temperature. In natural soils, k varies not only from place to place, but also in one place as the water content of the soil changes (van Wijk 1965). 16 1.3.2.1 Soil composition and porosity Von Schwarz and others (Baver 1965) have shown that the heat conductivity of different soils follows the order: sand > loam > clay > peat. The degree of packing and porosity of the soil seems to be the major factor determining the thermal trans- fer. Smith and Byers (1938) arrived at the following approximate expression for the thermal conductivity of a dry soil, k = kzp + k1 (l-p) where k2 and k1 are the conductivities of dry air and of the soil material respectively, and p is porosity. This expression shows that the conductivity of the soil decreases as the porosity increases. Skaggs and Smith (1968) con- clude that the thermal conductivity of different soils can be calculated in terms of soil porosity. 1.3.2.2 The influence of soil moisture in thermal conductivity Earlier investigations have shown that the heat conductivity of soils and soil materials increases with the moisture content. Patten (see Baver, 1963, pp. 376- 379) studied the conductivity of various soils at differ— ent moisture contents. He found that the conductivity of dry quartz particles, as well as of soil, was only about l7 one-half to one-third that of water (.005 calorie per sq. cm. per second per degree change in temperature gradient) and about one-fifteenth to one-twentieth that of a solid quartz block. Thus, the conductivity of quartz, for ex- ample, is greatly decreased when it is divided into parti- cles. The reduction in conductivity is due to the small amount of surface contact between particles through which heat will readily flow. The presence of water between the particles increases the conductivity to values higher than that of pure water. The presence of a water film at the points of contact of the particles replaces the air which is a poor heat conductor and thus improves the thermal contact between the particles. A typical example of Patten's curves is given in Figure 1-4. It is seen that heat conductivity increases with moisture content. It is also to be noted that the greatest rate of increase in conductivity takes place at the lower moisture contents. On the other hand, with fine quartz powder and fine-textured soils, Patten's original curves indicate that the greatest rate of change of heat conductivity apparently occurred at the higher moisture contents. Also, it can be seen from Figure 1-4 that the diffusivity a = EE increases rapidly at first with in- creasing moisture to a maximum, and then decreases. This is due primarily to a greater rise in conductivity at the 60 ~ 55 P 18 10 5 I- 0 I 1 l I 10 20 30 40 50 Moisture Percentage l = Heat conductivity, K, c.g.s. x 104 plotted against H20 in per cent by wet weight 2 = Same as l but with H20 expressed in per cent by volume 3 = Diffusivity, K/C x 102, plotted against H20 in per cent by wet weight 4 Same as 3 but with H20 expressed in per cent by volume 5 = Total porosity in per cent by volume Figure 1-4. Heat conductivity and diffusivity in Coarse quartz sand . (Redrawn from Bevar, 1965, p. 377.) 19 lower moisture contents, as compared with the increase in heat capacity. As the moisture content becomes larger, however, the value of c becomes greater and diffusivity decreases. Thermal properties of some typical soils and the common soil constituents are given in Tables 1-4 and 1-5. 1.4 General Differential Equation for the Temperature Field The basic law which quantitatively defines heat conduction is generally attributed to the French mathema- tician Jean Fourier (1768-1830). With reference to Figure 1-5 Figure 1-5. Linear heat conduction. the one dimensional form of the Fourier law states that the quantity of heat dQ conducted in the x-direction of a homo- genous solid in time dt is a product of the conducting 20 .mNHa: gmNpHNm ou oHNuoE Eonm mNouomm :OHmNo>coo Now HHH wanomm< meme HmomH .Hth am> Eoumv o.o NN.m om.H Na. N.H N. N. H.o Nm.m mm.H Nm. N. N. N. N.m No.4 NH.H NH. NH. N. o. Beam N.NH HN.HN NN.m N. N.N o. N. N.NH N.NN o.m m. N.N o. N. e.N N N m. o. c. o. NmHu 0.4H om.om N.N N. N.m o. N. N.mH o.mm N.N m. N.N o. N. o.N mm.m NN.N m. N. o. o. eemm NN.©N om.HH me. N.m Hooov ouN cow NON mooo. co. NH< Ne.m NN.H oo.H NN.H page: e H o. c. Nopume Uchmuo NN.Nm Nm.NH Ne. N mHeNosz NmHu o.mNH mN.NN NN.OH HN Nppmso mmewmw m-OH x_lmw m-OH x wmm HoovmeU AvoVomm so mmwwme Noumz oocmpmHSm So N N Hmo HmoHHHHE mo mGOHuomNm oasHo> a a a U 2 mx 3x «.HUOOH New muemspHpmaou HHOm coEEoo may mo paw mHHOm Hmonxw osom mo mothomoum HmENoae .q-H oHHMH 21 .Oo>HNoO ohm whoauo map mmhmuosmawm somoco prcowmomowcH ohm pomzoO pm: One .ucoucoo ousumHoE .pmo: onHoomm oHNuoESHo> .>HH>Huo:O:oo Hweuone "muoposmnmm«« .muHcs gmHHHNm op oHNumE Scam mnouomm HOHmNo>noo Now HHH wanoam< meme .HO .m .ch HmHsouHo >0>Nsm HmonoHooO Echmv v.NO O.H NHOO. OO.H N.H OOH OOH Nu N.Om OOH mo mo m.mm v.Om NHO. mOO. me. mm. v.m m.N OOH O.H OOO. mm. O.v NHH NHH w.H O.H O.HN OOO. NHO. um. Ne. v.m O.m How so Hem nHO zuHmcoO p02 Hmso hon EwO kuHmcoO pm: HoEDHo> kn uqoo -NomO unopcoo ounpmHoz HucmHoz HMO “coo -Nomv ucopcoo ohzumHoz uanoz we: pcoo -Nomv pcognoo ousumHoz Hmso you HmuO ossHo> .ans you new; unopmH Hoom you NEUO NpHsHmsmmNe HNEN0;N five mEo Hog Hmov “mo: onHoomm oHNNoesHo> HOo oom Eu Non HmoEO kuH>Huoswaoo Heapoge U03N£H :oNohm Oozmgh :oNonm Oaxaca coNon ooH\Noumz Hucoonmm moO HmHu Hpcmuemm NNH-NHO NHHm ««NouoEmNmm ¢.Hflom GONOHMHS fifim GONOHM mo moHuNomonm HwENoHp mo :omHNmmEou .m-H oHan 22 area A normal to the flow path x, the temperature gradient %; along the path, the thermal conductivity k. Expressed analytically: d _ dT ’ 35%- - kAa-i- [1.1] The Equation [1.1] defines the transient heat flow in a linear conductor, and from this is derived the general partial differential equation satisfied by the transient temperature field in a three-dimensional volume. Schneider (1955) derives the equation for three- dimensional and obtains: finer-511%)+g§CkT§§3+g§CkT§§3+é=cp§§ [1.21 where O = rate of generation or utilization of energy per unit volume. The most general partial-differential equation for heat conduction is the same form, but with kT, c, p, and O replaced by k(x,y,z,T), c(x,y,z,T), p(x,y,z,T) and O(x,y,z,T,t) to include spatial and temporal as well as temperature dependence. 1.5 Daily and Seasonal Changes in Soil Temperature The movement of heat into or out of the soil depends upon the difference in temperature between the surface of the soil and lower layer of the soil, i.e., the soil 23 temperature gradient. Much information regarding the tem- perature regime of the soil can be obtained by solving the differential equation of heat flow for the soil. For a homogenous and isotropic 5011, assuming no significant generation or utilization of heat occurs in the soil, equation [1.2] can be written (Merva 1970) 32T 32T 32 _ + + - 311' 357’ 327 [1.3] 9 he wlo: H-I-I where: T = temperature x,y,z = Cartesian coordinates, 2 increasing downward q = thermal diffusivity = k/pc t = time With the further assumption that no gradient of tem- perature exists in the x,y directions, equation [1.3] reduces to 2 8 1 8T ——7 = —'—- p [1.4] 82 a at The solution of equation [1.4] will describe the behavior of the temperature in the soil mass. Merva (1970) solves this equation with the following initial and boundary conditions: T(z,t) = some quasi-steady state condition (a) T(o,t) = a known periodic function of time (b) T (w,t) = a finite value (c) 24 and obtains: : : /nn 2 - at = Znnt _ nn T(z,t) A0 + n=le [En COS( E?~z) T ~ 2nnt nn + bn 51n C-FF_" /E?'z)] [1.5] where: r is the maximum period of time for which the solution is valid. For a diurnal temperature variation T is 24 hr. or 86,400 sec. while for the annual temperature variation, 1 = 365 days. 2 = depth of 5011. A0, an, and bn are Fourier series coefficients that can be obtained from T _ 1 A0 - 1F] f(t)dt . [1.63] o T 2 _ 2 nwt. an - ?’/ f(t) cos 't dt [1.6b] o T _ 2 a Znnt bn _ TEff“) s1n 1: d1; [1.6c] o where f(t) is the surface temperature. In many cases the surface temperature data is available from ESSA, Weather Bureau. 25 For any soil A0 is the average temperature of the soil surface for a period of time equal to one complete cycle of the longest periodic component of the Fourier Series solution, and in practice AO would be determined by averaging temperatures over a length of time equal to the length of record used to obtain for the Fourier series representation. The interpretation of Equation [1.5] as Merva states is: The exponential multiplier therefore tells us to what depth a fluctuation with a frequenc of 2nn/r will enetrate. It is immediately apparent that the lowest requency components of the Fourier Series expansion influence temperature at greater depths than do high frequency components. Thus, one would expect the yearly temperature fluctuation to be detectable at far greater depths than the daily fluctuations. Also from the Equation [1.5] we note that the argument of the sinusoidal fluctuation contains an angular frequency which is a function of time, and a phase shift which is a function of depth. The result of the phase shift is that the time of occurrence of She maximum or minimum temperature is shifted with ept . 1.5.1 Damping depth The depth to which fluctuation will penetrate to soil mass before being reduced by a factor of e'1 is called the damping depth and can be calculated (van Wijk et al., 1963) from: D = -—- [1.6] 26 The physical explanation of the damping and retarda- tion of the temperature variation with depth lies in the fact that a certain amount of heat is stored or released in a layer when the temperature in that layer increases or decreases respectively. The damping depth depends on the period of tempera- ture variation. It is /365 z 19 times larger for the annual variation than for the diurnal variation in a given soil. Table 1-6 presents damping depths for several values of thermal diffusivities. 27 Table 1-6. Damping depths of temperature fluctuation having various periods for several values of thermal diffusivity.* Damping Depth D (cm) Dif2::?31ty Period of Fluctuation in cmZ/sec hourly daily yearly .001 1.07 5.24 100.19 .002 1.51 7.42 141.69 .003 1.85 9.08 173.54 .004 2.14 10.49 200.38 .005 2.39 11.73 224.03 .006 2.62 12.85 245.42 .007 2.83 13.87 265.08 .008 3.03 14.83 283.38 .009 3.21 15.73 300.57 .010 3.39 16.58 316.83 .011 3.55 17.39 0 332.30 .012 3.71 18.17 347.07 .013 3.86 18.91 361.24 .014 4.01 19.62 374.88 .015 4.15 20.31 388.04 .016 4.28 20.98 400.76 .017 4.41 21.62 413.10 .018 4.54 22.25 425.07 .019 4.67 22.86 436.72 .020 4.79 23.45 448.07 *See Appendix III for conversion factors from metric to British units. CHAPTER II DEFINITION OF THE PROBLEM 2.1 Background Drain tiles in common use are clay, concrete or plastic. A well-designed drainage system requires high- quality material as well as proper installation to insure a long-lasting drain for the more severe exposure condi- tions that are likely to be encountered in ordinary farm drainage. 2.1.1 Tile for over-size trenches Many tests have been made (Manson, in Luthin, 1957) to determine experimentally and theoretically the loads to which drain tile are subjected in service. These tests look to design of tile systems which will avoid cracking of the tile from overloading after installation. The effect of numerous factors have been studied, such as soil type, depth of cover, width of trench, and bedding conditions of the tile as laid. Based on these studies, tables (for example see Luthin, p. 316 or Standards for Drainage, p. 34) have been prepared to show safe allowable depths of trench for drain tile of different diameters. 28 29 2.1.2 clay tile and frost action The frost resistance of clay products is largely dependent on the quality and handling of the raw clay or shale previous to, and during burning. In order to obtain factual information regarding the durability of clay tile under actual service condi- tions in a cold region, Miller and Manson (Luthin, 1957, pp. 321-322) dug up some tile which had been installed for an average of 33 years and concluded that: 1. The shale tile examined were all in first-class condition even where the depth of cover averaged but 1.7 feet. 2. Many of the surface clay tile were in poor condi- tion where the depth of cover was 2.00 feet and less. Frost penetration is an important factor in tile line freezing. There are a number of factors other than depth of penetration that influence the effeCts of frost action on drain tile. Manson summarizes them as: 1. Quantity and source of water carried by the tile during cold weather. Vegetative cover. Physical condition of the soil cover--fa11 plowed, etc. Depth and duration of snow cover. Frequency and duration of winter temperatures. U14:- CNN Considerable attention should be paid to factor one, especially in areas where good tile outlets are not available and pump drainage is utilized, because tile lines are often installed with minimum cover and submerged outlets are used. Thus a large portion of the drainage system may 30 be submerged and close enough to the surface that severe cold weather can cause freezing of the water within the lines, with subsequent cracking of the buried conduct if the pump is not operated during the winter period. In this thesis, a study has been made to investi- gate the temperature history around submerged drain tile to determine the reasonable depth at which cold weather will not result in freezing of the water inside the drain tile. It is noted that the presence of water within the tile is expected to inhibit the cooling action and thus the freezing of the water. To determine if freezing will occur, therefore, it is necessary to ascertain the penetration and duration of the 32° front in soil at the desired location. It is felt that if it can be demonstrated experimentally that cracking does occur under certain temperature condi- tions, and, if a similar set of conditions can be predicted for a field location through selective modeling techniques, then one could expect that tile damage due to cracking can be anticipated for the selective location. In the present study the location of interest is near Saginaw, Michigan, where extensive areas of soil lay bare during the cold months. These areas are in large part pump drained and the drainage system pumps may not be operative during the winter season. 31 2.2 Experimental Set-up In order to ascertain the behavior of a crack result- ing from freezing of the water inside a drain tile, an experiment was conducted in the Physical Properties Labora- tory at Michigan State University. The result of this experiment led to a determination of realistic conditions for solving the mathematical model of tile freezing. 2.2.1 Procedure Two four-inch clay drain tiles were selected for the experimental phase of the study. The ends were blocked with wood sealed to the tile with silicon rubber sealer. Four thermocouples located midway between the ends of the tile were placed one inch apart on a diameter inside one of the tiles, while a second experiment was performed using only three thermocouples. When the silicon rubber seal was dry, the tiles were soaked in water for 24 hours and were then filled with 40°F. water. A No. 40 Constantan wire was wrapped around the second tile and the ends of wire were fixed with a nail to the wood used to block the tile ends. The wire was attached to a strain gauge amplifier indicator in order to determine the exact time of cracking so that when the tile cracked, the wire broke and the meter on the amplifier tvent to full scale. 32 Both tiles were embedded in a box of dry soil and additional thermocouples were located on each of four sides of the tiles as shown in Figure 2-1. The whole system was placed in a freezer with the average ambient temperature maintained at 0°F. The thermocouples were connected to a self-balancing potentiometer recorder. In addition the temperatures of the thermocouples were checked with a Millivolt potentiometer. The instruments used were: 1. Strain gage amplifier from Daytronic, model 300 D, with type 90 strain gage input model.' 2. Self-balancing potentiometer from Texas Instrument, point Multiriter. 3. Millivalt potentiometer from Leeds 8 Northrup Company Catalog No: 8686. 2.2.2 Observations The temperature readings of thermocouples corre- sponding to the points 1,2,3,4 are given in Figure 2-2. The other experiment showed a similar behavior. Since the tOp surface of tile was exposed to ambient air with average temperature zero degrees F., points 1,2,3 cooled in this order respectively. Point 4 cooled faster than other points because the thermal dif- fusivity of the soil was greater than that of water. 33 Thermocouples 4 inchVClay Drain Tile Figure 2-1a. Location of thermocouples in the experimental setup. Figure 2-1b. A picture of the cracked tile showing the general appearance. Note the thermo- couple wires entering from the r1ght. 34 4:00PM- Crack occurred at. 3:35 PM -3:00PM- ~---- Point 1 — —.— Point 2 2:00PMF- Point 3 ,1 ,/ _. .. Point 4 i’.’ I 3 : o . E 1:00PM - / 2% I :1 E I... 12:00PMr 11:00AM~ 10:00MW- 9:00AM ‘ 30 31 32 33 34 35 36 37 38 39 40 41 42 Temperature in °F Figure 2-2. Temperature variation for each thermocouple. 35 When the temperature of point one reached 32°F. it remained constant at this value. The temperature of points 2,3 decreased respectively until they reached 32°F. and then they also remained constant. The temperature of point 4 dropped below 32°F. When the temperature of all of the water inside the drain tile became 32°F., the forma- tion of ice started. Ice was formed in the upper portion of the tile. The formation was crest-shaped and occupied about one-third of the volume inside the tile at the time of cracking. The shape of the ice and location of the crack are shown in Figure 2-3. Thus, it has been demon- strated that cracking of a clay tile due to freezing of water within the tile is possible provided the tile system remains at 32°F. for a sufficiently long duration of time. It is probable that the condition indicated will occur if the temperatures surrounding the tile drop to less than 32°F. on all sides. 2.3 Mathematical Model 2.3.1 General assumptions Heat is transported in the soil mainly by conduc- tion, i.e., the transfer of thermal energy on a molecular scale. To facilitate the mathematical treatment the fol- lowing general assumptions are made: 36 Figure 2-3. The shape of ice causing cracking of a drain tile. The location of the crack is shown in the picture at the lower right of the tile. 1. The soil is almost saturated in the winter, therefore, the thermal conductivity is uniform throughout the soil mass. This assumption has a deficit in that the thermal properties of frozen soil are different from those of unfrozen soil. Consequently, when the soil starts freezing there will be a moving boundary within the soil mass across which the thermal properties differ with time and temperature. Since we are interested only in a critical temperature around a drain tile for simplification we assume that the soil is homogenous and isotropic and therefore the 37 thermal properties are independent of space and time coor- dinates. The thermal diffusivity of frozen soil is used in the calculations since frozen soil has the higher value. The resulting temperatures will thus be conservative. 2. The latent heat of fusion of water can be ignored in the model during the phase change. 3. The medium is at rest, i.e., that no motion of matter on a macroscopic scale occurs. 4. The heat flow is in the vertical and horizontal directions only. 5. No heat is generated or utilized within the soil medium. 2.3.2 Specific assumptions The surface of the soil is subjected to a seasonal variation in temperature. The temperature fluctuation is sinusoidal and its daily and yearly fluctuation decreases with depth. At the damping depth the temperature is almost constant for a period of one cycle (see Sec. 1.5). The damping depth is a function of the thermal diffusivity and differs for different soils. The damping depth for daily temperature fluctuations for most soils normally is less than 12 inches (see Table 1-6). The upper coordinate boundary for the present solu- tion of the mathematical model is located at 13 inches below the soil surface so that daily temperature 38 fluctuations can be ignored (see Figure 2-4). For a soil having a different thermal diffusivity, this depth should be calculated and the upper coordinate boundary chosen accordingly. It is assumed for the purposes of the model that T(x,z,t) represents the temperature of the soil at depth 2 and distance x from the center of the tile at time t. In the solution, for the upper boundary it is assumed that one inch above the first x coordinate line the temperature is constant at some value G. The assumption is necessary to facilitate solving of the tridiagonal matrix associated with the solution. In the computer solution it is possible to change the value of G at every time increment, thus, a slow temperature variation of the upper boundary is possible. Since the soil is a semi-infinite body, it is assumed that at infinite depths soil temperature remains constant, i.e., T(x,m,t) = constant for each period of time where m represents the maximum grid point, which in the present problem is 68 inches. Since the soil temperature at the yearly damping depth usually is nearly constant, it is desirable that the value of m be equal or greater than the yearly damping depth. It is assumed that at the right hand side of the soil system there exists a boundary beyond which the tem- perature of the water in the tile will not effect the soil temperature. This point is taken 68 inches from the center 39 8011 Surface‘* j—t .------....C..........f.'.d............'............ 0 n o . u . u o o . a . n . o . c . o . u . o . o . u . . c n . o . o . o . c 1 . . + . - OJ C H X H . ........... —. .‘. .J . o x IIIIIIIIII JO‘IO . . II ....... ‘.~.. 1 . . . . . . . OJ C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . O . , 0 1 1 . + .1 .1 Z Z .1 Z ll. IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO m,m Grid system. Figure 2-4. 40 of the drain tile. Mathematically, the assumption can be stated as T(m,z,t) = T(z,t), a known temperature at every depth and time. Due to symmetry, the vertical line passing through the center of the tile is an insulated boundary, i.e., aT/ax = 0 for T(0,z,t). Finally it was assumed that the tile line was sub- merged by 32°F. water, and that the temperature in the tile remains constant at 32°F. until a point one inch below the tile line reaches 32°F. (see Sec. 2.2). Formation of ice will begin from the coldest point and will extend downward in the tile as was demonstrated by experiment. Because of the complexity of solution for a two phase, moving boundary, ice-water problem, the entire system is considered as a single phase system. It is assumed the cracking will occur when the temperature one inch below the bottOm of the tile reaches 32°F. The assumption is justifiable since experi- mental evidence shows only about one-third of the water must turn to ice to initiate cracking of the tile. It is thought that the time required to attain 32°F. at one inch below the bottom of the tile is more than adequate to allow for conversion of one-third of the water to ice. 41 2.3.3' Determination of initial anddboundarygconditions 2.3.3.1 Determination of soil temperature The soil temperature readings to a depth of 36 inches in Miami fine sandy loam soil under fescue grass at the East Lansing, Horticulture Farm were obtained from the U.S. Weather Bureau Climatological records for 1963, the coldest year of record at this station for the past 15 years. The temperature of the soil for eleven days (from February 21 until March 4, 1963) was chosen (Table 2-1) and by interpolation the temperature for every inch of soil depth was estimated and used as the daily temperature data. Because the annual average of soil temperature and soil cover and soil characteristics differs from location to location, the temperature reading of the East Lansing Station can not be assumed to be representative of the soil temperature for other locations. Since the recorded temperature for an arbitrary location is not available, the soil temperatures were estimated using a Fourier series technique as follows. The annual average soil temperature A0 is not equal throughout the soil profile, it varies with depth. Tables 2-2 and 2-3 give annual average values of soil temperatures .zmegon .mumm HmonoHouweHHO .swohzm Hogumoz .m.: Scum :oxmu ohm mama .O ogon mo oonwom .mmmhw odomom.HoO:= EmoH szmm oaHm HEmHz 42 :oHpmHommNuxm NN NN . mm mm NN NN NN NN NN NN NN NN menuaH NN NN NN mm mm mm mm NN HN NN HN HN NN NoeucH NN NN HN HN HN HN HN NN NN NN NN mm mm mogueH 4N HN NN NN NN NN NN NN NN HN NN NN NN NoguaH NH NN NN NN NN NN NN NN NN NN NN NN NN mogueH N NN NN NN NN NN NN NN NN NN NN HN NN mogueH N NN NN N H- NH N N- N NH N N H- .nHe .NENN NN NN NN NN NN NH NH NN NN 4N NH HH .xee HHN NNN NNN NNN HNN NNNN NNNN NNNN NNNN HNNN NNNN NNNN HNNN gamma mxmm .mcmH :H sham ohouH50HpNo: wchcwH pmmm :H maumow uqonommHO Hm H.moO ouzpmyomEou HHON HHHHO wouhooom .H-N oHan 43 Table 2-2. Annual average of soil temperature (°F.) for East Lansing Horticulture Farm Station. Depth 1967 1968 1969 1970 Air 46.7 47.9 47.4 48.1 2 in. 53.3 53.2 53.2 52.4 4 in. 51.8 51.5 51.3 51.0 8 in. 50.1 49.6 49.9 50.1 20 in. 49.3 49.1 49.5 49.5 40 in. 49.3 49.2 49.4 49.5 80 in. 49.1 49.0 49.4 49.1 Data from U.S. Weather Bureau, Climatological Data for Michigan. Table 2-3. Annual average soil temperature (°F.) at University of Minnesota, St. Paul Station. Soil is under sod cover. Depth 1963 1964 1965 Average air temp. 45.9 46.9 43.6 1 cm. 51.2 51.7 47.9 g S cm. 50.6 51.0- 47.2 10 cm. 49.8 50.2 46.4 20 cm. 48.2 48.7 45.4 40 cm. 47.9 48.0 45.0 80 cm. 47.2 48.2 45.1 120 cm. 47.5 48.2 45.6 160 cm. 47.7 -- 46.4 320 cm. 47.3 -- 46.9 480 cm.‘ 47.5 -- 47.1 640 cm. 48.0 -- 47.9 800 cm. 48.7 —- 47.7 960 cm. 48.0 48.2 47.8 1120 cm. 47.8 48.1 47.7 cm. 48.0 47.9 47.8 1280 for Minnesota. Data from U.S. Weather Bureau, Climatological Data 44 for the East Lansing, Horticulture Farm Station from 1967- 1970 and annual average soil temperatures for different depths and related annual air temperatures for the University of Minnesota, St. Paul Station, respectively. The recorded soil temperatures reveal that the soil surface has the highest yearly average temperature. Annual average soil temperature rapidly decreases with increasing depth to a certain depth. Beyond this depth gradually A0 increases as shown in Table 2-3. At any depth the yearly average soil temperature is greater than annual average air temperature for a given location. Soil temperature is also highly affected by surface cover. AC has a greater value for bare soil than for grass or sod-covered soil as is shown in Figure 2-5 and Table 2-4. As discussed above, since each depth of soil has a different annual average temperature, the annual air tem- peratures can not be used in a Fourier series to obtain the boundary conditions to be substituted for the soil surface temperatures to obtain a solution using Equation [1.5]. Indeed, if one analyzes data for the soil temperature, the air temperature and the temperature one inch above the ground, the results show that the annual average temperature at one inch above the ground is greater than the annual air temperature. This fact is illustrated in Figure 2-6. H.coHpmum Hsmm .um .mwomoncHz mo kuHmHo>HGD .mumw HmonoHoumEHHu .HmomHO :mopsm Hoaumoz .m.: Eoum :onp «puma .ohnumhomfiop HHom co ommHo>oo HHom mo uoommm .m-N oNSMHm .ooO .>oz .uoo .mom .w:< HHSO mash. km: .HQ< .Hmz .nom .qu T l 1 I d d- 4 I I I I J o A OH , eunumpomEoH LON ommho>< Hmsqc< 1 O L0 45 do exniexedmal mangmuomsoh HH< ommpo>< ON mmmho Nova: HHom ohmm News: Table 2-4. Effect of soil coverage on yearly average soil temperature (°F.) at different depths. under bare under soybean Depth under sod soil covered soil Air 45.9°F. 1 centimeter 51.2 55.8 53.1 5 centimeters 50.6 55.8 51.6 10 centimeters 49.8 53.0 50.8 20 centimeters 48.2 49.9 48.9 40 centimeters 47.9 48.1 47.2 80 centimeters 47.5 47.5 47.1 Data from U.S. Weather Bureau, 1963. Climatological Data, University of Minnesota, St. Paul Station, Minnesota. In order to calculate the soil temperature at dif- ferent depths, a Fourier series was fit to the soil tempera- tures at each depth as recorded at the East Lansing Horticulture Farm. Such a technique gives a function which describes the temperature fluctuation at each depth in the soil for the above mentioned station. In order to obtain the soil temperatures for another location in Michigan it was postulated that the same general nature of temperature fluctuation would be present; however, the mean soil tem- peratures A0 for each depth would be different depending upon whether the corresponding average annual air tempera- tures were greater or less than the average annual air temperature at the East Lansing location. Thus, the 47 .Hm< .Nmz .nom .cmO .numow >9 mop: «HomEou HHom One NHN ommpo>m zchcoE mo :oHumHHm> mo OH NOOH .ooO .>oz .uoo .mom .m:< >H3O .csw Hm: .HQ< .Hmz .nom .cmO a q .\ t \‘0/ d d d 1‘ J ‘- ohspmhomEms ohzumhomEoH ommho>< Hmsc< HH<- d 4 o>onm O:90Nm .:H H .N-N 6NsNHN ON om OQ om O0 O5 OO do einieiedmal 48 correct value of Ao must be determined. At the present time, calculating A0 is difficult, because soil temperature is recorded in only a few locations in every state, and the relation between soil temperature and-air temperature has not been determined. Therefore, to get an estimate of annual average soil temperature at different depths, the following procedure was applied. The difference between the annual average air and soil temperatures at selected depths was calculated from Tables 2-2 and 2-3 and the results are given in Table 2-5 for the Minnesota and Michigan data. Table 2-5. Difference between air temperature and soil temperature at different depths in °F. University of Minnesota East Lansing St. Paul Horticulture Farm Depth 1963 1964 1965 average 1968 1969 1970 average cm. 6.3 5.8 4.3 5.5 -- —- -- -- cm. 4.7 3.6 4.1 5.3 5.8 4.3 5.1 10 cm. 3.9 2.8 3.3 3.6 3.8 2.9 3.4 20 cm. 2.3 1.8 2.0 ' 1.9 2.5 2.0 2.1 40 cm. 2.0 1.4 1.5 -- -- -- -- 50 cm. - -- -- -- 1.2 2.1 1.4 1.6 80 cm. 1.3 1.3 1.5 1.4 -- -- -- -- 100 cm. - -- -- -- 1.3 2.0 1.4 1.6 120 cm. 1.6 1.3 2.0 1.6 -- -- -- -- 200 cm. - -- -- -- 1.8 2.0 1.0 1.6 49 As can be seen from Table 2-5, the annual average soil temperature at 8 inches is about two degrees F. higher than air temperature for any given year, and between 20-80 inches depth the difference reduces to 1.5 degrees F. It is worthwhile to note that this difference depends on soil coverage as well as kind of soil, and soil moisture content. For example, for bare soil the variation is greater than sod-covered soil (Table 2-4). Based upon the above reasoning it is felt that adding two F. degrees to the annual average air tempera- ture, will with good accuracy yield an estimate of the annual average soil temperature at 8 inches for a soil that has a sod cover. Similarly, adding 1.51h degrees to the annual average air temperature will give an estimate of the average annual soil temperature between 20-80 inches depth. The temperature fluctuations for every soil depth are dependent upon weather conditions, surface coverage, type of soil and soil moisture content. It is assumed in the present study that if the daily air temperature varia- tion of a region has a similar pattern in comparison with another region, then the soil temperature fluctuation for the two regions with the same kind of soil will also have a similar shape. The daily air temperature variations for East Lansing, Saginaw and Evart (Central Lower Michigan) for 1968 are given in Figure 2-7. In Figure 2-8 a similar H.2meHOHz .mumO HNOHmoHoumEHHo swohsm Hosumoz .m.: EONH coxmu apnea .OOOH :H ppm>mm One .Bmchmm .qumcmH pmmm pom oysumhomsop NHN HHaucoE ommpo>m one .N-N oHSNHm Hm HOMO: ON >9m39nom Hm zhmscmh om mN ON mH OH m om mN ON mH OH . m Om mN ON mH OH - q q - H d u I- H. H- - I-I. . T I H H OHI O upm>m N n. zmchmm \ OH 5 l 9 .w ONG I 9 ON m. mchcmH umwm N m NHL. O U) 51 .mOOH Ham; map How smaHmmm Ocm mchcmH ummm mo oNSHNNoQEou NH< .O-N oNSNHm Huge: L- thspnom NAHNHENO m mN ON mH OH -fi mN ON mH OH m mN ON mH OH d d 1 J a a W d a a “I u d-I I— JI CHI. > . N- / 1 O \\ 1 m I I- - , m1 ZNCHmmm. \// \\ , . OHw \ \\> \N 7 x x, . NH m //< x .. ON m 7., \/ . N m \ I .I.\ 40” .10 N I \ .d NN /\ mchcmH ummm . mm N - N O... N -me O U) 52 graph is given for the air temperature of East Lansing and Saginaw for 1963. It can be seen from Figures 2—7 and 2-8 that air temperature of Saginaw has almost the same shape as for East Lansing, except for a few days in February 1963 (from 14-25), which were much cooler. Accordingly, the reasoning discussed above was applied to calculate the soil temperature for Saginaw. To obtain the temperature fluctuations, the Fourier coeffi- cients were calculated for each depth at which the tempera- ture was recorded and available. Since the recorded daily soil temperature in East Lansing is not complete for 1963, the recorded soil temperature at depths 8, 20, 40 and 80 inches of 1968 were used to calculate the Fourier coeffi- cients. For accuracy the first 73 coefficients for 8, 20, 40 and 80 inches were calculated and the results are given in Appendix I. In the present study the temperature distribution for Saginaw for 1963 at 8, 20, 40 and 80 inches depths were estimated, based on average values of soil temperature as calculated above, and soil temperature fluctuations which are characteristic of Central Lower Michigan as determined from the East Lansing data. The annual average air temperature at Saginaw in 1963 was 45.5 degrees F. The annual average of soil tem- perature at 8 inches was taken to be equal to 47.5 degrees F. 53 and at 20, 40 and 80 inches depths the calculated value of AC was found to be 47.0°F. The calculated Fourier coefficients for 8, 20, 40 and 80 inches and the assumed annual average value of soil temperature estimated as above were used in the Fourier series model to estimate the daily temperatures for the above depths. The calculated temperatures for Saginaw are given in Figure 2-9 and the recorded temperatures for East Lansing in 1963 and 1968 at different depths are given in Figures 2-10 and 2-11. By interpolation, the temperature for every inch of soil depth was estimated and used as the daily tempera- ture data where such information was required as initial condition to the computer solution. 2.3.3.2 Thermal diffusivity Since the temperature readings in East Lansing are obtained in fine sandy loam, a thermal diffusivity was chosen equal to .006 cmz/sec and with interpolation a = .009 cmz/sec is used for frozen soil (see Table 1-5). In calculating the soil temperature for Saginaw, a = .009 2 . . . cm /sec was used assum1ng a frozen s1lt loam $011. .mOOH .chmem Now ohsumhomEou HHom OopmHsonu ON cope: ON mH mN ON L H . . Huangnom - mH Hm Ahmscmh ON Om mN b h mH ’ OHM .N-N opsNHN OH 54 Agnew ‘I ‘ NNNNN .cH N Npgoe .:H on ON .mN .ON -NN .ON -ON .Om .Hm er .mm -vm .mm .om .hm -wm -Om go ainiexedmel 55 .coHpmum Ehmm oHSHHsoHuHo: Hm .mOOH .mchamH ummm Now oNSHNNomEop HHom Oowhouom .OH-N onstm Hm thshnom - . Humzcmh - seem: NN NN NN NH NH ‘Em ON 0w «m N ON mH OH m mm mN ON mH OH ICIIIII H ‘- : L fi' m m M “19.1 meow .:H «N -4 KN :E:» -I- < .0m 6 meow .cH cm L ..... H r. mm A I O 03 Q' N) M q. .OOOH Hm m ON ON 4 .coHpmpO ENmm ONDHHsquHo: .OchsmH pmmm Now oNSHNNomEou HHom OmONoooO Ouemz OH I. Q. NHOSHnom mH xhwsch mN OH .HH-N whszm -I7./ N . ...-....u. N../L Qmmfi 4.3.” ON III-III.-.- momw .c H cede-0.0.0.. \n- I OO N) >. ....»< N..... ON mH I‘II‘I I .CH ON / .,%/ -.N.../I |.N.:. L ON ON ON NN ON ON -Om Nm mm «m mm om mm Om Om ON HO NO ON v elnieieuma; do 57 2.3.3.3 Depth and diameter of drain tile The most often used drain tile in drainage systems are four, six, and eight inch tile. 'Depths vary depending upon the type of soil and drainage conditions. The most- recommended depth for drainage of Michigan soils is from 36 to 48 inches (Standards for Drainage of Michigan Soils, 1963). In the computer solution the tile boundaries are delineated by grid points as shown in Figure 2-12. Solu- tions obtained by applying the model using the boundary and initial conditions determined above were examined for four, six and eight inch tile for depth of 36 in., 42 in., and 48 in. 2.4 Solution of the Model Based on the concepts advanced in preceeding sections, the temperature distribution around a tile and the cracking of a submerged tile due to freezing of the water inside the drain can be studied using the following approach. The cross section of soil which is our problem Space is covered with a grid as shown in Figure 2-4. The left boundary of this grid passes through the center of the tile. Since the solution is symmetrical about a vertical line passing through the center of the tile, only the right half of the solution need to be computed. The grid lines 58 1 3 4 1 r I J———’ 31- I: 2. 33 32r- 33 ’ 33- i 34- 34- 35' V 35» 36 ' 36- 37 ‘ 37f "’( Four inch tile (48 in. Six inch tile (48 in. depth) depth) I 29 30— 31w 32- T 1“33 34 T 35 36 37w Eight inch tile (48 in. depth) Approximation of drain tiles in grid system for computer model. 59 are spaced one inch apart and cover a square of 68-inch width and depth. Grid points corresponding to the tile boundary vary depending upon the diameter and depth of the tile. 2.4.1 Formula and method of solution The general heat conduction equation is (see section 1.4): a ’ 8T 3 8T 3 3T _ 8T 'a‘i(kT ‘53?) + fickr '5?) + Vickr "57) - DC "55 [2'1] With the assumptions stated above, the equation can be written: 32T+32T=1_B_T_ [2 2] 8x Oz a at where: T = Temperature z,x = Cartesian coordinates, z increasing downward, and x increasing horizontally from the center of the tile to the right Thermal diffusivity of the soil Q II time H II 2.4.2 Numerical solution The analytical solution of Equation [2.2] is com- plicated. A numerical approximation to the solution of 60 Equation [2.2] may be obtained by the step-wise solution of an associated difference equation. Three approaches are possible. They are: a. The explicit difference method, which yields equatiOns that are simple to solve, but require an uneco- nomically large number of time steps of limited size. b. The implicit difference method, which yields equations that do not possess a singularity to limit the time step, but which require at each time step the solu- tion by iteration of large sets of simultaneous equations. c. The alternating-direction implicit method (Cranahan, 1969) has been presented by Peaceman and Rachford (1955), and Douglas (1955) and is used in this paper. The alternating-direction implicit procedure re- quires the line-by-line solution of small sets of simultaneous equations that can be solved by a direct, non-iterative method. Essentially, the principle is to employ two dif- ference equations which are used in turn over successive time-steps, each of duration At/Z. The first equation is . implicit only in the x-direction and the second is implicit only in the y-direction. Let T(i,j,n) represent T(z,x,t) where Z = iAz and X = ij (Figure 2-4). Thus if Ti’j is an intermediate value at the end of the first time-step (see Appendix II for detail), we have: 61 * -T. +21 1* * 1-l,j (T + 3 Ti,‘ ’ T J i+l.j followed by: -T 1 a t 3 i'lej J i+10j where: a = Thermal diffusivity; At Time increment; Ax 1 i,j-1,n+l * ZCX * 1) Ti,j,n+l ‘ _ 1 ' Ti,j-1,n + 2(7 ‘ 1) Ti.j.n * Ti.j+1.n [2'3] Ti,j+1,n+l = [2.4] [2.5] Distance-increment in the horizontal direction; A2 = Depth increment in the vertical direction. 2(% + 1) Let b and f = 2c% - 1) [2.6a] [2.6b] Equations [2.3] and [2.4] can then be written in the form: t at k -T + bT. . - T + T i-1.j 1.: 1+1.j = Ti.j-1.n + fT. . 1:3,“ i.j+l.n [2.7] 62 and 'Ti,j-l,n+l + bTi,j,n+l ‘ Ti,j+1,n+1 = * f* 3‘: Ti-1.j * Ti,j * Ti+l,j- [2.8] In general the equation [2.7] is solved for the * intermediate values T, which are then used in Equation [2.8], thus leading to the solution T. at the end of 19j9n+1 the whole time interval At. A tridiagonal coefficient matrix is used in the solution of Equations.[2.7] and [2.8] (Carnahan, et al., 1969, pp. 441-446). 2.4.3 Applying the boundary and initial conditions in solution of related fOrmulas Based on the preceeding sections, the behavior of soil surrounding a submerged tile will be predicted by solving Equations-[2.7] and [2.8]: 9: * 1: 'Ti-1.j * bTi.j ‘vTi+1.j = Ti.j-1.n * fTi.j.n * Ti,j+l,n [2.7] 63 -T + bT - T i,j-1,n+l i,j,n+1 i,j+1,n+1 = * * * Ti-l,j * fTi,j * Ti+1,j N [2.8] t where T and T refer to temperature at the beginning and end of half time step At/2; and with the following boundary and initial conditions: Time Temperature Condition at t=0 and at multiples T = known throughout the of 24 hours soil mass T = known 2 = -1 0 < x i m at t > 0 T = known z = m 0 < x < m T = constant x = m 0 > z 2 m 3T - 0 1 h 'd - 0 5;-- a ong t e 51 e x-0 s z < m The temperature of water in the tile will be held constant at 32°F., for t > 0, until a grid point one inch below the tile line becomes 32°F. 64 Equation [2.7] was applied to each point i = 1,2, ---m-l in the j column and the following tridiagonal system for the j column was obtained: 1 i" b'I‘ i“ d = - + . - = 1 0.3 1.1 2.1 l 2 31": b'I‘ i" d = - . + — . = 1 1.1 2.1 3.1 2 """"""""""""""""" [2.7a] - T + bT T - d I 1 - 1 - 1'19j lej i+193 - 1 * b * - d 1 " "“2 ' Tm-3,j m-2,3 Tm-—1,3 ‘ m-z * bT - d I 1 - m-l - Tm-2,j m-l,j m-l ) with 1‘ W d0 = 2T0,1 + me0 + G for 1 = 0 1>for j = 0 d1 = 2Ti,l + fTi,0 for 1 - l,2,---m-l“ d0 - T0,j-1 + fT0,j + T0,j+l + G for 1 = 0 d1 = Ti,j-l * fTi,j + Ti,j+1 for 1 = 1,2,3---m-1 [2.7b] for j = 1,2,---m-l d0 = 2T0,m-1 + fTO, + G for i = 0 for j = m d1 = 2Tim-l + fT1,m for i = l,2,---m-l 65 Comparing the coefficients of Equation [2.7a] with coefficients of the tridiagonal matrix (see Carnahan, et al., 1969, pp. 441-446) it can be seen that a = -1, b = b, c = -1 except for the first equation where a = 0, and for the last equation where c = 0. This procedure is valid except for points that have a constant temperature (for example water in the tile). At such locations the tridiagonal matrix must be modified. This has been done through consultation with Dr. J. V. Beck, Associate Professor of Mechanical Engineering, Michigan State University, as follows. When one of the unknowns in the tridiagonal system becomes known and constant, the value of the b coefficient is given a magnitude of unity and the other coefficients are taken equal to zero in the equation. The known value was substituted instead of the value d (value of the right hand side of Equation [2.7a]. The other coefficients in the column of the tri- diagonal matrix related to this.point will be zero. For detail see sample computer program in Appendix II. The procedure is repeated for successive columns j = 0,1,---,n-l until all the Ti’j are found at the end of the first half time-step. The temperatures at the end of the second half time step are found similarly, by applying EquatiOn [2.8] with related boundary and initial conditions, to each point in a row (j = 0,1,---,n-1), for successive rows (1 = 0,1,---,n-l). CHAPTER III 3.1 Results The results of this research have been outlined in three headings: 3.1,1 Results of Experiments An experiment was conducted in order to deter- mine the realistic condition for solving the math- ematical model of freezing water inside a drain tile. The results of this experiment can be sum- marized as follows: 1. In the process of cooling the water inside the drain tile there was a gradient between the water and the ambient temperature and it was greatest between the water and the upper sur- face of the tile. Water started to freeze when the temperature throughout the water inside the tile reached 32° F., and the temperature surrounding the tile was less than 32° F. The conversion of only a portion of the water to ice caused the cracking of the tile. 66 4. 67 The location of the crack was at the water—ice interface on the interior tile surface in the lower third of the tile (see Figure 2-3). 3.1.2 Results of Soil Temperature Study 1. The annual average soil temperature is not equal throughout the soil profile; it varies with depth. Annual average soil temperature rapidly de- creases with increasing depth to a certain depth. Beyond this depth gradually its value decreases. At any depth the yearly average soil temperature is greater than annual aver- age air temperature for a given location. The highest annual average temperature has been observed at one inch above the ground of given location. Annual average temperature of bare soil at certain depth is greater than sod-covered soil (see Figure 3-1) and the frost penetra— tion is deeper in bare 5011 than sod covered soil. In the winter the bare soil is much colder than sod or grass covered soil. In the summer the bare soil is warmer than soil under sod. This fact is illustrated in Tables 3-1, 3—2. 68 . .HHom oONWHSN Oom Ocm opmp :H coHpmNpocom umopm .H-m oNSOHm «OOH gown: «OOH .nom «OOH .cmO mOOH .oom . mOOH .>oz H.NNHNNNN HNNN .NN .NNoNoccHz Now wpmw HmoHOoH0poEHHo EONL coxmu manna . U M N 1 N N. ‘ w . 1 NH M w N .I ohspwhomEOH . mH / 7 E .1 . w x w 2 . ./ .7/. M. H _ M~ K - NN.m ...>..\. ..1/.1.: / .... /x ..\/ \ /.s x\ /. \ / \ MN x. a u .. mN m J.\ / \x IK\\.// Wxx/ \u /¢/\u K. g M. »\/s 96 \.\ x... (.11. \/. < <\ /. .NN a N 1 mm mnpmow Eu OO um ONSHONOQEoH HHOOO ounwg O wwmm-- JON maumow Eo OO pm opsuwHomEoH HHoOO oommNsm Oom 1m¢ .Om 69 Table 3-1. Effect of soil cover on soil temperature at different depths in the cold season. January February Ave e 'r T . rag al emp 6.2°F 14.8° Average Soil under under under under under under tem at sod bare soybean sod bare soybean p. soil soil 1 centimeter 24.5 9.9 18.2 22.0 19.7 19.8 5 centimeters 24.9 11.2 18.7 21.9 20.5 19.4 10 " 25.7 12.0 19.4 21.9 19.7 19.5 20 " 26.8 12.2 20.6 24.1 18.0 19.5 40 " 30.4 14.5 23.9 27.5 17.3 20.4 80 " 34.2 22.5 30.7 32.8 20.1 24.4 Source: Data are taken from Climatological Data, University of Minnesota, St. Paul, 1963. Table 3-2. Effect of soil cover on soil temperature at different depths in the warm season. June July Average air Temp. 70.4°F 73.5 Average Soil under under under under under under temp at sod bare soybean sod bare so bean ° soil soil Y 1 centimeter 73.5 89. 89.1 80.6 94.6 84.8 5 centimeters 72.5 87.1 82.7 79.3 93.1 79.9 10 " 70.5 81.5 79.4 76.8 87.8 78.6 20 " 66.5 74.0 73.3 72.6 82.0 75.8 40 ” 62.3 68.5 66.2 68.2 76.9 71.8 80 ” 57.5 61.8 59.8 63.6 71.5 67.0 Source: Data are taken from Climatological Data, University of Minnesota, St. Paul, 1963. 70 3,1,; Results of Computer Modeling In order to investigate the effect of thermal en- vironment on submerged drain tile 3 computer model was developed. The calculated soil temperature for Saginaw, Michigan for 1963 was used in the model, and the boundary and initial conditions were based on the experimental re- sults. The results of the computer program modeling soil temperature around four, six and eight inch submerged drain tile buried at 36, 42 and 48 inch depths are given in Figures 3-2, 3-3, and 3-4. Figure 3-2 represents the temperature history of the soil around four inch drain tile. It can be observed that on February 9, the soil temperature at the 31 inches depth was 32° F. and at 37 inches depth the temperature was 32.4° F. On this day for the purposes of the model, water was assumed to have entered the drain tile at a constant temperature equal to 32° F. The effect of water within the four-inch drain tile on soil temperature has been shown in Figure 3-5. The model results indicate that the presence of water inside the drain tile inhibited rapid cooling of the soil around the tile, and 7 days were re- quired before soil one inch below the drain tile reached 32° F. or less. On this day the soil one foot from the drain tile at the 37 inch depth had a temperature equal to 31.54° F. Since the ambient soil temperature was less than 32° F. it is 71 cm space .efl m4 .mgpgoe noun m4 can .Nq .om on weapons mans cflmhw pomuoEnSm nocfi psom m pasosm Hfiom on“ GM kHOpmfi: opspmnomEoH sumac .cfl N4 - em P D . . mm om mm mo oHSumhomEoH samba .cfi om .N-m ousmfld L l O N) omom ow C) O O Ln \0 l\ O <- seqouI ut qideq om OH 72 um poprsn oHHu :Hmhw :mmoe .cfi we .meodme sue“ me can .Ne .om nocH o panchm HHom may :H >noumH: oHDHMHomEoH endow .aH Ne Nm om mm mo eunumuomth L — mfi om .m-m mhnmflm 4H new endow . OH F em now an om om om on oo om ow om om OH seqouI ut qideq oHHp cHwhu womuoEnsm nocH pzmHo wcsoum HHom map :H xuoumH: oHSHmhomth om sumac .qfi we vm Nm om mm - P CN 0 .mepmoe coca we use .Nq .om on emeusn r em samba .nfl N4 mm on wN mo othMHoQEOH om om gnome .:H om ON Dom cm pom cm .4-m ossmfim ow oH seqouI ut qideq Depth in Inches 27+ 74 30.40 28. 29.- 30r 31» 32. 33- 341 35» 36- 37- 38- 39. 4o- 41- I l A A . J 44 Figure 3-5. 2 3 4 5 6 7 8 9 10 11 12 13 14 Distance from Center of Tile in Inches The effect of water within the four-inch drain tile on soil temperature. (Isothermal lines are shown in the figure.) 75 felt, in accordance with the experimental evidence, that the water inside the drain tile would begin to freeze. At a point one inch below the four inch drain tile buried at 42 inch and 48 inch depths the temperature reached 32° F. or less on February 21 and on February 25, respectively. One inch above the six inch drain tile the tempera- ture was 32° F. on February 10, while one inch below the tile the temperature was 32.22 degrees F. and on February 19 (after 9 days) one inch below the six inch tile the temperature attained a value of 32° F. or less. On Feb- ruary 22, and March 1, the temperature one inch below the six inch tile buried at 42 and 48 inch depths reached 32° F. or less, respectively. Similar observations were noted for the eight inch drain tile buried at 36, 42, and 48 inch depths except more time was required to cool the eight inch tile. February 20 and February 23 and March 3 were the dates at which the temv perature one inch below the drain tile became 32° F. or less respectively. Other results are summarized in Table 313 and can be stated as follows: 1. The tile which had been buried deeper, froze later in the season than shallow-buried tile. 2. Tile which had less diameter froze faster than big diameter tile. 76” .m:0HpHu:oo onSmmm map Hood: oomHm oxen on mconmpu How owuoEQSm wo :oHuwhsw wouHscom Ho .oHHu :H wosnom o>m£ op poESmmm mm: ooH noan pm ouma mm .m ONN monumou oHHH m>onm HHom HuHez Hm moan H< ”:OHumHhomomg NH NH mane OH o m\m NN\N ON\N . m N mH\N HH\N OH\N < OH . .HH made a u H\m NN\N mH\N m o mH\N HH\N OH\N < o OH mane A u mN\N HN\N NH\N m H mH\N HH\N OH\N < NH NH om Hmoeuch HmoaoeHv spawn oHHH *eoHHmHNumma oHHH :Hmun mo pouoEmHm .oHHp :Hmhv meo aH oomHm oxmu op mconmHo How oocmeoEnsm Ho coHumHSp wohHSUou paw oEHH .m-m oHan 77 3.2 Discussion of Results The results of this research give a useful tool for determining the behavior of water inside submerged drain tile as it may relate to the cracking of clay tile. This research investigates the variation of soil temper- ature and its relation with air temperature as a means of determining the soil temperature at every depth. As in- dicated previously, the results are conservative, because: 1. The recorded soil temperatures for Saginaw were not available, therefore the soil temper- ature for Saginaw for 1963, the coldest year on record, had to be calculated based on assump- tions relating soil temperature and air temper- ature, and the general nature of soil tempera- ture fluctuations. 2. The latent heat of fusion of water and varia- tion of thermal diffusivity of frozen and un- frozen soil and also ice and water were not taken into account due to the complexity of the required model. However, it is believed the results of the pres- ent study are logical and in agreement with field observa- tions. Figure 3-6 is a photograph of an 8 inch clay tile removed from a field located near Saginaw. The tile had been buried at 48 inches. Note that the position of the 78 cracks are in agreement with the general location of cracks noted in the experimental investigation. Also, the fact that the model suggests that freezing can occur in such tile buried at 48 inches gives support to the hypothesis that cracking of this tile resulted from freezing of water since our model indicates that for 1963 at Saginaw, Michigan, especially for bare soil, the soil temperature up to 48 inch depth had reached 32° F. or less, and cracking due to freez~ ing could result. Figure 3-6. A photograph of an 8 inch clay tile removed from a field located near Saginaw, Michigan. Compare the location of cracks with that shown in Figure 2-3. CHAPTER IV CONCLUSIONS The following conclusions are based on the inves— tigation conducted on soil temperature and effect of ther- mal environment on submerged drainage conduits. l. The annual average soil temperature is not equal throughout the soil profile; it varies with depth. Annual average soil temperature is always greater than annual average air temperature. When the temperature of soil surrounding a submerged drain tile is reduced to less than 32° F. for some period of time, the water in- side the drain tile will freeze and as a result of the phenomena when about 1/3 of the water has been changed to ice the clay drain tile will crack. The primary crack will occur at the water-ice interface on the interior tile surface, which usually is located in the lower half of the tile. 79 80 The tile which has been buried deeper will freeze later in the season than shallow— buried tile. Tile of less diameter will freeze faster than big diameter tile. The time which is required to freeze the water inside the drain tile in order to crack the clay tile depends upon the temperature gradient between water and ambient. When the temperature gradient increases the water will freeze faster than with a low temperature gradient. CHAPTER V RECOMMENDATIONS FOR FURTHER STUDIES 1. This study is the first step in evaluating the effect of environment temperature and frost penetra— tion on submerged drain tile. Further research is needed in order to utilize the result of this study in developing a complete model for predicting soil temperature around drain tile. 2. Soil temperature reading should be extended for more locations in every state under different soil cover, such as bare soil, grass covered soil, and sod covered soil. 4 3. The process of data recording should be accom- panied by the measurement of the solar radiation, which is a governing factor in increasing the soil surface temper- ature. Solar radiation data are required in studying the relationship between surface and air temperature. 4. The soil temperature measurement should be ac- companied by the measurement of the moisture content of soil. Variation of soil moisture is required in the esti- mation of thermal properties of soil as well as the study of the migration of moisture in the soil. 81 82 5. Investigation should be continued to complete the mathematical model in order to determine the soil tem- perature at every depth with respect to soil surface tem- perature or air temperature. This study should include effect of the latent heat of fusion, and the variation of thermal diffusivity in moving media (i.e., frozen and un- frozen soil as well as water and ice) in determining the soil temperature, and water inside the drain tile in differ- ent seasons . LIST OF REFERENCES LIST OF REFERENCES Barakat, H. Z. and J. A. Clark, 1966. On the solution of the diffusion equation by numerical methods. Journal of Heat Transfer, Transactions of ASME, Series C. 88:421-427. Baver, L. D., 1965. Soil physics. 3rd ed. John Wiley and Sons, Inc., New York. 362-384. , Carnahan, B., H. A. Luther and J. O. Wilkes, 1969. Applied numerical methods. John Wiley and Sons, Inc., New York. 429-761. 1963. Climatological data of Michigan. U.S. Department of Commerce. Monthly Summaries. 1967-1970. Climatological data of Michigan. U.S. Depart- ment of Commerce. Annual Summaries. 1963. Climatological data of Minnesota. U.S. Department of Commerce. Monthly Summaries. 1963-1965. Climatological data of Minnesota. U.S. Departs ment of Commerce. Annual Summaries. 1962-1963. Climatological data of Wisconsin. U.S. Depart- ment of Commerce. Annual Summaries. Douglas, J. Jr. 1955. On the numerical integration of 2 2 3 U + 3 u = 33 by implicit methods. J. Soc. Indust. 3X2 3y 3t App. Math. 3:42-65. Geiger, R. 1965. The climate near the ground. Harvard University Press, Cambridge. 26-33. Kavianpour, A. 1971. Analytical estimation of thermal properties and variation of temperature in asphaltic pavements. Ph.D. Thesis, Michigan State University, East Lansing. 6-9. 83 84 Lachenbruch, A. H. 1970. Some estimates of the thermal effects of a heated pipe line in permafrost. Geological Survey Circular. 6-32. Luthin, J. N. 1957. Drainage of agricultural lands. American Society of Agronomy. Madison. 315-339. Merva, G. E. 1970. Physical principles of the plant en- vironment. Unpublished class notes. Agricultural Engineering Dept., Michigan State University, East Lansing. 95-121 and Appendix I. Peaceman, D. W. and J. H. H. Rachfor. 1955. The numerical solution of parabolic and ellyptic differential equations. J. Soc. Indust. App. Math. 3:28-41. 1963. Recommended standards for drainage of Michigan soils. Bulletin of Agricultural Experiment Station and Cooperative Extension Service. Schneider, P. J. 1955. Conduction heat transfer. Addison- Wesley Publishing Company, Inc., Cambridge. 1-5. Skaggs, R. W. and E. M. Smith. 1968. Apparent thermal con- ductivity of soil as related to soil porosity. Transactions of the ASAE. 11(4):504-507. Smith, W. O. and H. G. Byers. 1938. The thermal conduc- tivity of dry soils for certain of the great soil groups. Soil Sci. Soc. Am. Prod. 3:13-19. van Wijk, W. R., et a1. 1963. Physics of plant environ- ment. North-holand Publishing Company. Amsterdam. 102-132 and 210-213. van Wijk, W. R. 1965. Soil microclimate, its creation, observation and modification. Meterological Mono- graphs. 6(28):59-73. APPENDICES APPENDIX I FOURIER SERIES MODELING OF PERIODIC PHENOMENA APPENDIX I FOURIER SERIES MODELING OF PERIODIC PHENOMENA In engineering analysis and design it is often necessary to work with environmental parameters which change with time such as the temperature of the earth's surface or the relative humidity within a plant canopy. The parameters may vary continuously and the function which describes the process, i.e., the mathematical model, may not be known. As a first step in the description of the process one has instead a sequence of data obtained over some interval of time, for example, the series of average daily temperatures for each day of the year. In many cases, much information could be obtained about a process from a continuous mathematical model. (Merva 1970). For most environmental parameters (temperature, relative humidity, partial pressure of C02’ etc.) directly related to the plant environment, there exists a consider- able amount of periodicity. The presence of periodicity suggests that some type of periodic function could be con- structed to fit the observed data. Such a function would be useful in that it would serve to model the behavior of these parameters. Fourier Series will furnish such a func- tion. 85 86f A Fourier series approximation of this function can be written: k anCoswnt + Zn=1 f(t) = A0 + 2:: bnsinwnt (I-l) l where f(t) = T = temperature at some point of interest; A an and bn are all constant scaler coefficients. 0’ It is necessary to determine the coefficients A0, an and bn and the arguments wnt up to a value of k such that the function is sufficiently accurate. To determine the arguments wnt it is necessary only that as t varies from zero to t where c is the interval of time over which the model is desired,L the,argument must vary from zero to some integer multiple of Zn. The necessary conditions are fulfilled if (on = 3&1 . Equation (I-l) for a function being modeled over the interval t can be written: f(t) = A0 + 2k 1 (ancos 3%1 t + bn sin Q31 t) (1-2) n: AO , an and bn can be obtained from 1 . A0 = «E 7‘; f(t) dt (1-3) t 2 H an = g [0 f(t) Cos 1% t dt (1-4) 1: . 2 11 bn = t3- IO f(t) sm Ti} t dt (1-5) The function f(t) can now be approximated to the desired accuracy by performing the integrations indicated in equations (1—3), (I-4), and (I-S). In most cases only 87 A0, a1, a2 and b1 and b2 must be found to obtain a reason- able approximation to the function f(t). Determining more coefficients will usually give a better representation of f(t) although not necessarily a better model for the fluc- tuations of the parameter being investigated. The accur- acy will depend on what one uses for f(t) in the integra- tion. - The first 73 Fourier coefficients for 8, 20, 40, 80 inches depth of soil have been computed by equations I-3, I-4, and I-5 and the results are given in Tables (I-l), (I-Z), (1-3), and (1-4). (See section 2.3.3.1). 88 TABLE I-l THE CALCULATED fOURlER COEFFICIENTS FOR 8 INCHES DEPTHS OF SOIL N0 A COEFF. B COEFF. NO A COEFF. B COEFF. 1 “180552 “110084 38 '0041 0004 2 .451 1.179 39 .074 .296 3 1.018 .759 40 .134 .086 4 0163 10335 41 -0000 -0091 5 “.510 .278 42 .190 “.130 6 “0239 -0932 43 -0132 0101 7 .169 .224 44 .069 .240 8 “.767 .464 45 .257 “.420 9 0379 -0507 46 '0151 -0046 10 -9248 .420 47 '0479 0408 11 10626 “0266 48 0568 .016 12 “.972 0299 49 0147 -0169 13 '0316 “0113 50 0061 -0001 14 0519 0375 S1 -0148 “0104 15 “.098 “.418 52 .027 .022 16 ’0024 -0460 53 ’0017 -0094 17 -0397 0275 54 -0116 -0159 18 .013 “.004 55 “.128 .135 19 .261 .546 56 .201 .031 20 .357 “.517 57 “.121 .085 21 -0417 0020 58 0104 0009 22 -0345 . -0011 59 -0005 "0081 23 0097 -0008 60 -0046 .052 24 '0042 0234 61 0019 0017 25 .454 -0122 62 0312 -0105 26 “.282 “.222 63 “.149 “.094 27 0096 0090 64 -0240 -0054 28 .199 .285 65 .060 .182 29 “.357 “.361 66 .154 “.033 30 0180 0002 67 -0108 0075 31 -0185 0003 68 0080 -00Q8 32 0115 0098 69 -0037 .005 33 0048 “0109 70 0149 ‘0187 34 “.068 .065 71 “.142 .037 35 -0201 “0172 72 .-0248 -0217 36 “.108 .151 73 .039 .172 37 -0115 0119 ' 89 TAEUEI-Q THE CALCULATED FOURIER COEFFICIENTS FOR 20 INCHES DEPTHS OF SOIL NO A COEFF. B COEFF. NO A COEFF. B COEFF. 1 -150583 -110904 38 ‘ 0007 0038 2 .293 1.043 39 .017 .262 3 0560 0884 40 -0054 0115 4 “.212 .856 41 “.001 “.096 5 “.614 “.103 42 .179 “.022 6 0089 “0704 43 -0015 -0033 7 0181 0475 44 0042 0167 8 -0683 0299 4S 0408 -0203 9 0387 -0257 46 ”0010 -0054 10 “.255 .252 47 “.305 “.014 11 1.106 .230 48 .268 .171 12 -0737 0030 49 0015 -0103 13 “.076 “.187 50 .041 .070 14 0389 0264 51 -0021 “0100 15 0047 -0273 52 0089 0122 16 0081 -0249 53 -0052 -0060 17 -0375 0104 54 0019 -0209 18 .037 “.035 55 “.003 .007 19 “.017 .458 56 .037 .059 20 0320 -0218 57 -0099 -0040 21 -0265 -0066 58 0028 '0036 22 -0036 -0143 59 .075 -0047 23 0041 0088 60 -0074 -0124 24 “.281 .184 61 “.037 .039 25 .290 .136 62 .068 .153 26 -0076 -0189 63 -0014 -0028 27 0084 0106 64 0045 '0054 28 -0080 0203 65 0031 0002 29 “0149 -0232 66 0052 0018 30 0164 0120 67 -0048 0045 31 “.074 .065 68 .037 .093 32 -0064 0192 69 ’0044 -0030 33 .051 .054 70 .114 “.038 34 0001 -0070 71 -0068 0046 35 “0043 -0175 72 0034 ‘0103 36 “.055 .123 73 ' .090 .011 37 -0092 0027 90 TABLE I-3 THE CALCULATED.FOURIER COEFFICIENTS FOR 40 INCHES DEPTHS 0F SOIL NO A COEFF. B COEFF. NO A COEFF. B COEFF. 1 ”110044 “120678 38' -0004 -0017 2 .399 .750 39 .020 .094 3 .289 .763 40 “.104 “.006 4 -0330 0736 41 0098 -0059 5 “.421 “.174 42 “.004 .035 6 0343 -0452 43 -0063 ”0161 7 .077 .295 44 .034 .109 8 “.520 “.037 45 .158 “.044 9 0282 -0053 46 0001 0036 10 -0228 “0060 47 0027 -0147 11 .548 .416 48 “.059 .047 12 -0295 ”0232 49 0015 -0022 13 ' -0052 -0093 50 -0045 0051 14 .030 .301 51 .085 “.070 15 -0028 0006 52 -0005 -0001 16 .082 .026 53 .060 .001 17 -0180 ‘0082 54 0018 -0026 18 .067 “.115 55 .005 .032 19 ’0108 0029 56 1"’001'34 0020 20 0122 0108 S7 '0062 -0039 21 -0072 ‘0031 58 0025 -0013 22 0023 -0066 59 -0001 -0009 23 .019 .180 60 “.017 “.111 24 -0143 -0077 61 0036 -0043 25 -0014 0083 62 -0063 0027 26 0110 -0125 63 “0045 -0063 27 -0034 -0022 64 -0036 0073 28 “.097 “.081 65 “.040 .025 29 0114 0027 66 -0068 -0029 30 .010 .148 67 “.023 .008 31 “.092 .017 68 .010 “.017 32 -0045 0141 69 0004 0031 33 -0029 0017 70 0032 0024 34 0010 -0047 71 -0043 -0010 3S 0062 -0086 72 , 0033 0046 36 -0003 -0053 73 “0044 -0063 37 .023 “.025 I11 11.....- 91 TABLE I-h THE CALCULATED,FOUR1ER COEFFICIENTS FOR 80 INCHES DEPTHS OF SOIL N0 A COEFF. 8 COEFF. N0 A COEFF. B COEFF. 1 ”70894 ”120433 38' 0066 0010 2 0017 0747 39 0020 ”0036 3 ”0186 0615 40 ”0047 0000 4 ”0424 0398 41 0048 ”0004 S ”0426 ”0269 42 ”0045 0058 6 .323 “.221 43 “.030 “.025 7 ”0026 0206 44 ”0044 0066 8 ”0310 ”0014 45 ”0025 0072 9 .221 .040 46 .003 .070 10 ”0068 ”0042 47 0067 ”0039 11 0215 0306 48 ”0037 0053 12 ”0076 ”0208 49 0054 0013 13 ”0041 ”0166 50 ”0027 0027 14 “.122 .119 51 .016 “.002 15 .061 .067 52 .041 .023 16 ”0036 0102 53 0075 0020 17 “.045 ”0063 S4 ”0069 ”0067 18 0048 0086 55 0037 ”0084 19 ”0058 ”0017 S6 ”0070 ”0043 20 0081 0073 S7 ”0023 ”0018 21 ”0118 ”0026 S8 0088 ”0005 22 0015 0015 59 0042 ”0058 23 “.063 .194 60 .062 “.054 24 ”0021 ”0125 61 0029 ”0008 25 ”0004 0045 62 ”0007 ”0129 26 0127 0044 63 ”0017 ”0061 27 ”0043 ”0004 64 0015 0052 28 “.097 “.086 65 “.004 .060 29 .012 .095 66 .103 .006 30 0045 0010 67 0000 ”0027 31 0024 ”0021 68 0061 ”0058 32 0034 ”0047 69 ”0063 ”0033 33 ”0012 0007 70 ”0029 ”0030 34 ”0071 ”0100 71 ”0039 0020 35 ”0055 0012 72 ”0018 0010 36 0050 ”0071 73 ”0047 ”0037 37 ”0017 ”0064 APPENDIX II COMPUTER MODELING FOR STUDY OF SOIL TEMPERATURE WITH SUBMERGED DRAIN TILE APPENDIX II COMPUTER MODELING FOR STUDY OF SOIL TEMPERATURE WITH SUBMERGED DRAIN TILE II.l Differential Equation Unsteady heat conduction equation in the soil is given by aZT + BZT = 1 TL (11.1) 8x2 322 a at Let T(i,j,n) represent T(z,x,t), where Z = iAz and x = ij (Figure 2-4). The finite difference approximate derivative of partial differential equation by the Taylor's expansion is given T. . -T. . 31 = 1,Jip+1 1.1 + 0(At) (II.Z.a) 3t At 2 - . . . 3_; = Ti.j'1;n 2T13J9n+T143+19n + O[(AX)2] (II.2.b) 3x (Ax)2 2 . . -2T. . + . . §_l = 1‘1’J:n 1,1,n» 1*1zJ:n + O[(Az)2] (II.Z.c) 822 (A2)2 Ifihere O ( ) represents the discretization error. For convenience let define 6: Tiaj,n = i0j'1LEEZTiaj;E+Ti:j+l:n (II-3-a) (13:02 and 2 T. . -2T. . +T. . 62 Ti,j,n = 1-1iJLn 111)“ 1+1,J,n (11.3.b) (A2)2 92 93 Essentially, the principle of the implicit alter« nating-direction method (Cranahan, 1969) has been used in this paper to employ two difference equations which are used in turn over successive time-steps, each of duration At/Z. The first equation is implicit only in the x-direc- tion and the second is implicit only in the y-direction. Thus, if Ti j is an intermediate value at the end of the 9 first time-step, the Equation (II-l) can be written i. . - T- - 2 T. . Z T. . (11 4 a) 1’] 1,3,1}. = 6X1’J 62 1,3,n ° ° At/Z followed by: T i i’j’n+1 iij = 2 i. . + 2 T. . At/Z 5x 1:3 52 1,J,n+1 (II.4.b) Written in full and rearranged, with x = z for simplicity, the equations (2-3) and (2-4) can be obtained. II.2 Expansion of the Formula and Applying Related Boundary and Initial Conditions The Equations (2-7) and (2-8) with the related boundary and initial conditions are used in computer model- ing. The expansion of the Equation (2-7) is given in sec- tion (1.2.4.3). The expansion of the Equation (2-8) in the tridiagonal system for the 1 rows is as following. 94 j = l "Ti,0 + bTi,1 ‘ Ti,2 = d1 J = 3 —T 1 + bTi 2 - T1 3 = dz __ ......... (II.5.a) J = 3 “T1 J-l + bTi J - T1 3+1 = dj j = m-Z 'Ti,m-3 + bTi,m-2 - Ti,m-1 = dm_2 j = m-l “Ti,m-1 + bTi,m‘1 = dm'l with * * . d0 = T1,j + fT(o,J) + G k 1: 1': dj - Ti-1’j + fTi,j + Ti+1,j (II.5.b) d T fT * * _ = '_ ° + - - m 1 1 1:3 1,3 + Ti+1,j + Ti,m The coefficients of the tridiagonal matrix (see Cranahan, et al., pp. 441-446) are: a1 = O and ak = -l k 2,3,--e,m bk = b k 1’32-"9m cm = O and ck = -1 k = l,---,m-l (II.6) 2 (% + 1) (See equation 246a). where b 95 When one or two or more points attain a constant temperature the tridiagonal matrix should be modified. This condition happens when the temperature inside the drain tile remains constant for a period of time. For simplicity let us assume that only one point, for example point (9.5), has a known constant temperature, say Tc' In tridiagonal system for j = 5 column the equa« tions are . * * * ’ 1 = 8 -T7,5 + bT8,5 ‘ T 9,5 =d8 (II.7.a) * * * ’ i = 9 ‘T8 5 + ng 5 ' T10 5 =d9 (II.7.b) . * * * ’ 1 = 10 -T9,5 + leO,5 F T11,5 =d10 (II.7.C) 1: Since the T9 5 is constant, the condition of (II-6) no longer ’ can be used in determining the coefficients of Equations (II-7). Equation (II,7.a) can be written a * _ d’ * ‘T7,5 + bT8,5 ‘ 8 + T9,5 d8 hence c8 = 0; d8 = Tc+d8 = Tc + (T8,4+fT8,5+T8,6) I . . . * * _ * _ 81m11arly 1n Equation (11.743 leO,S - Tll,5 - d10 + T9,5-d10 hence alo = 0; d8 = Tc+di = TC+(T10,4+fT10,5+T10,6) and The 96 finally the Equation (II-7.b) can be modified equations of tridiagonal system for i = 9 row are = 4 -T9,3 + bT9,4 — T9,5 = d4 (II.8.a) = s -T9,4 + bT9,5 - 19,6 = d5 (11.8.b) = 6 ‘T9,5 * bT9,6 ' T9,7 ’ d7 (II.8.c) A similar procedure should apply to Equation (II-8). 2-11 For two or more constant temperatures (see Figure ) more equations are involved (see computer program). 11.3 List of Principal Variables ProgramSymbol Definition A,B,C,D coefficient vectors of tridiagonal matrix DTAU time step At DX space increment, Ax (one inch) F f = 2(1/A-1) I,J raw and column subscripts, i,j ICOUNT counter on the number of time—steps IFREQ number of time-steps between successive printings of temperatures G constant temperature at one inch above x coordinate M RATIO TAU TMAX TPRIME TRIDAG TSTAR ZERO 97 number of space increment (68) A=a At/(Ax)2 matrix of temperatures T at each grid point Time, t. 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