145
255
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Use at the Ahney Level in
highway leashes

Thesis her the degree of Bi.

STUART D. LONG

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Use of the Abney Level in

Highway Location

A Thesis Submitted to
?he Dean of the Graduate School of
UICHIGAN STATE “OLLEGE
of
AGRICVLTURE AYD APTLIED SCIENC*

by

Stuart D. Long
Candidate for Degree of

Civil Engineer

Hersh 1937

THESIS

 

/5§%35%%ZEZ7

Qince this thesis is a study of the high-
way location methods of the Vnited States Forest
Service in Yegi n Five, it might be well to consider
part of the specifications under which these roads
are constructed.

"eats performed with loaded pick-up trucks
(% ton) on gravel surfaced roads pointed out that
the maximum grades which could be economically
climbed in various gears were: let gear, 15%; 2nd
gear, 10¢; and high gear,5fl. Grades between these
values, as a VZ grade, are to be avoided for a long
duration for they present too much pull to be made
in high gear and in 2nd gear the motor is not work-
ing at full capacity. This is an important detail,
for in location work a balance of yardage must not
be made by altering the grade. The grade must re-
main the same and the location must be changed to
produce a difference in the involved yardage. In
other words, the grade remains at the ruling speci-
fied grade for all parts of the road except on

curves of 90 feet in radius or less. This, Of course,

1. “9104

pertains to highways designed to overcome elevation,
as a road from a canyon bottom to the top of a ridge.
Roads in whiCh distance is to be overcome at no
great change in elevation the conventional undulating
grade location is used.

Two types of grade compensation are used.
A grade compensation for curvature is used so that
loaded trucks may me ntain a uniform Speed on any
part of the grade. Also improvement and reconstruc-
tion of an uncompensated curve always results in a
curve of steeper grade than the ruling rrade which is
highly undesirable. 0n the other hand a compensated
curve from 3 to SS lower than the ruling grade can
be reconstructed at a larger radius and the resulting
grade will still remain at or below the ruling grade.

A compensation for elevation is also
employed. As the grade climbs in elevation above the
3,000 foot level a devrease in grade of lfl is made
on the ruling grade for every 1,500 feet additional
rise. Thus a 105 ruling grade becomes a Qfl at 4,500
feet, a; at 6,000 feet, 7; at 7,500 feet, etc. This
is based on the fact that as the motor climbs into
the higher altitudes the efficiency is reduced. The
above compensations are designed to allow a uniform
speed on any part of the grade regardless of align-

ment or elevation.

INTRODVCTI N

Within the past ten years the western
Regions of the United States Fores Service have
embarked upon an extensive road building program.
”he steadily increasing weStern travel, bringing
crowds into the almost vacant National Forests,
created a need for roads and parks. But greater
than this public utility need was the need of roads
for fire protection. Along with these strangers to
the mountains came t;e ever increasing fire hazard.
Carelessly tossed cigarettes and forgotten camp—
fires commenced to turn huge areas of valuable brush
country and timber lands into burns. As the frequency
of these fires increased it became apparent that an
extensive road building program must be developed
to facilitate placing men into a fire region in a
minimum of time.

As the program began, fire surveys were
made on all of the Hational Forests in the west and
roads planned which would put men from fire suppres-
sion camps located throughout the forest into a fire
zone within forty-five minutes after detection. To
one who knows of the few roads in the almost virgin
mountains this was an extremely ambitious program.
In roughing out the Specifications for these roads,

two things became at once apparent. First, since

l

the roads woubd be used most for offiCial business,
the actual car-miles of travel would be much lower
than on county and state highways. Hence there was
no economical juSLification for a high cost per mile.
Secondly, if lower cost per mile were to be realized,
entirely new methods of construction and surveying
must be develoyed.

It might be well at this point to mention
the type of construction equipment used in the con-
struction of these roads, for the survey must be
made with a thorough knowledge of what is to be
expected and what is possible with the equipment
at hand. The bulldozer was decided upon as the major
piece to be used for excavation. This piece of equip-
ment is a heavy model tractor with a cast steel blade
mounted in front on a heavy A-frame. Along the cut-
ting edge is bolted a tough mole board, which with
the aid of two cutting points at the ends, carries
the brunt of the excavation york. mhis blade is
equipped with a quick acting oil pressure pump which
activates the blade for vertical movement. It has
the advantage of carrying a down pressure on the
blade so that the entire weight of the tractor may
be brought to bear on the blade. ”he bulldozer
proved very efficient on mountain slopes as high
as forty-five degrees on the cross section slope.

In normal excavating with average 510pes it is

1

capaole of excavating and placing 300 yards during

an eight hour shift. On the writer's location of
Oak Opening Road, where an estimated 30,000 cu.
yds. were involved in 55 miles of road, and where
approximately 30S of the volume was rock and de-
comp.sed granite, the bulldozer averaged nearly
200 cu. yds. excavrted and placed in an eight
hour shift.

The choice of the bulldozer was due to
its ease in handling in rough terrain. It has the
advantage of being able to excavate from the up—
hill side of the section and side-cast the material
immediately to make the fill on the down hill side.
One of the advantages of grade location is based
on this advantage. ”he efficient end-haul was rather
limited being about 75 to 100 feet. However, this
made possible the economical construction of a 200
foot through cut or fill by working the yardage from
the center of the cut or fill mass. This short end-
haul limit did not interfere materially with the
location for rarely was it necessary to located
a through out or fill longer than 200 feet.

In the field of location and surveying,
Mr. 0.1. Young, Chief Surveyor of Region Five,
California, developed the Abney level method of loca-
tion. It was apparent from previous experience that
the cost of transit surveys was out of all proportion

to the cost of construction. Cost being the import-

ant item to reduce it became necessary to deoart

widely from previous surveying methods in the
development of a system that would prove itself
efficient.

Primary in the development. was the princi-
ple that office work was to be eliminated so far as
possible. This in itself would be a major saving but
it meant that some metlcd for working out problems of
grade, alignment, and yardage, must be perfected for
field use. With grades it meant that the engineer
must learn to fit the grade to the ground and not
to an office profile. It meant that alignment and
yardage must be worked out coincidently with the
grades. If computations of yardage were to be made
in the field it meant that the end-area and mass dia-
gram method must be replaced.

All of this was to be accomplished under
extremely difficult conditions. The types of roads
on which this method was to be used were, by virtue
of their need, always in rough country. These
roads must cut through heavy brush country, rocky
ridges, and canyons, to reach points of fire advant-
age. In most cases the mountain slepes are from
25 to 40 degrees and some go as high as 50 degrees.
Below these mountain lepes are the fertile valleys
of California. "oo many times have the effects of
heavy rains falling on burned over areas resulted in

damaging flo ds in the valleys below. So it is that

the best location for fire protection is the worst
possible from an engineering standpoint.

To meet the required Speed in this rough
country the Abney level method of road location was
developed. The writer's position in this work was
that of Junior Civi anineer whose duty it was to
carry on the complete work of location, surveying,
and engineering details necessary to the construction
of the roads.

In the presentation of this method acknow-
ledgement is hereby made to Fr. C.L. Young for cost
figures and to the Vnited States Forest Service for

tables.

THE ABNEY LEVE

The Forest Service type Abney level is in
many respects similar to the hand level. Its major
parts are: (See ?late No. 1, page 7) the barrel, "A",
which has a horizontal crosshair, "B"; eyepiece, "C”,
which telesc0pes for focusing purposes; level bubble
"D", which has a single cross mark etched at the level
position and is attached to movable arm "E". This arm
swinging from a pivot slides over scale "G" which is
graduated in percent of grade plus and minus. Directly
below the bubble is a prism mirror "H" which allows
the level bubble to be visable coincidently with the
cross hair in the end of the barrel.

When the arm is set at zero on the scale the
instrument is handled as the ordinary hand level. If the
sliding scale is set at ~10fl and the instrument placed
to the eye and the level bubble brought to the level
position, the line of sight through the barrel will
be on a —lOfl grade.

If it is desired to run a given grade, ir-
respective of elevations, distance between stations,
and alignment, the following is the procedure: The
instrumentman first determines his personal H.I. as
with a hand level. "hen to set any other point on a

given grade no matter what the distance to that point

 

 

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8

may be, he has but to set that grade on the Abney level
scale and locate the rodman until his personal H.I. is
read on the rod as the level bubble shows level. The
point under the rod is then at the given grade from

the point on which the instrumentman was standing. In
this manner the grade is actually run out on the ground,
each point being an grade and not having a cut or fill
to reach grade.

The decided advantage in running a highway
grade with the Abney level in this manner is that the
sight distance is not limited as when computing grades
at even stations. If the sight distance is 40 feet,
well enough, but if it be 250 feet, so much the better.
Since no measurement need be taken to determine the
distance to the rodman the flevibility of the system
is easily seen. The disadvantage of using this method
for running a grade line is that alignment resulting

is sinuous in nature.

GRADE STAYING

Grade staking in this thesis shall be
defined as: Setting a stake on the grade of the
road which is irrespective of the centerline of the
road; that is with neither cut nor fill at that point.

Tangent shall be defined as: Any part of
a location wherein the radius of curvature is £933
than 80 feet.

A curve shall be defined as: Any part of
a location wherein the radius of curvature is 80
feet or liifiv

The usual meaning of tangent as referring
to long straight lines between successive P.T?s. and
P.C's. does not apply in Abney level surveys since
tangent as defined applies to all curves over 80
feet in radius.

Referring to Tlate No. 2, page 10, it will
be noted that most roads constructed in mountainous
country will be of this Balanced Section type. It
will also be noted that it is possible to set a stake
on the grade of the road irrespective of the center-
line of the section. This is at point "3". It is
this stake which is referred to when the term "grade
staking" or "staking the location on grade” is used.

If the cut bank has a slope of %:l, the
fill slope os 1%:1, and the angle 9 is known, it is

ossible to set u e nations for the end areas of cut
P Q

 

 

Fill Slopes

 
     

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10

Ils‘r “a. 2
BALANCED SECTION

Normal 810pe -
of ground “

 

 

L.
[V

 

——-———————-—1 b-

 

9 Angle of 310pe of grdund in degrees
x 310pe distance measured on slepe of ground
w Width of rondbed
a Width of roadbed in the solid
A Area in Cut
A' Area in Fill
V Volume
. 8' o g '.'.'-a
9 Cot 3'1 A 2 co; a-s
1.“52A x . 2A
a 3‘... 3
a-LF-" ILL

 

 

 

 

__r_

11
and fill. Viz:

A = a2 and A' : w-a _
2 cote - l 2 cot 0-5

By solving these formulae for various
values of O by approximating a value for a; and if
A is equated to A' (Balanced section, cut equals fill)
then:

A a A' and V g 1.852A and the slope dis-

tance x = 2A
a sin 9

 

Therefore with tables computed for various
values of road width and cross section slope it
becomes quite simple to locate a stake on grade and
tape the distance up the slope to locate the cut stake.

The end areas used in the developement of
the formulae do not take into account a shrinkage
factor. This detail is left to the Judgement of the
locating engineer for the soil conditions change so
rapidly as the survey progresses that any constant
shrinkage factor introduced into the formulae would
not be consistant with operating conditions.

Plate No. 3, page 12, shows a section of
a table developed from the above formulae. The cross
section angle 9 is measured at the station by means
of a slope rule or inclinometer reading in degrees.
Under "a" is found the distance from the grade stake
to the heel of the out. A use for this will be shown
later. "x" gives the distance measured along the
.ngRE of the ground from the grade stake to the

cut stake or the toe of the cut. Under "V" is the

12

PLATE NO. 5
SlOpe Stakes and Volumes
Width of Road 16' Cut Slope %:1 Fill 810pe 1%:1

Balanced Excavation Table

69 x. ‘V a;
10 9.4 12.9 9.4
is the cross section
11 9.5 14.6 3.4 slope angle in degrees
12 0.8 16.”i 8.5 13 the width of the
road bed in the solid
13 9.9 18.2 8.6
is the volume in cu.
14. 10.9 20.2 8.7 ydshper 50' section
15 10.5 22.2 8.7 is the distance meas-
ured up the slope from
16 10.7 24.1 8.9 grade stake to the
cut stake.
17 11.0 26.4 8.9
18 11.3 28.9 9.0
19 11.6 31.7 9.1
20 11.9 34.6 9.2
21 12.3 37.9 9.3
22 12.7 41.4 9.4
25 13.1 45.5 9.5
24 15.6 49.6 9.7
25 14.2 54.5 9.8‘
26 14.7 60.0 10.0
27 15.4 66.4 10.2
28 16.? 73.8 10.5

15

volume of a 50' section. Since this table was com-
puted by equating the cut and fill end areas it follows
that all of the cut is required to make the fill in

the section, making due allowance for shrinkage.

Other tables for various values of road widthsand

cut bank slopesare at the engineer's hand when differ-
ent soil conditions are encountered. It was found

that if the slope angle was taken intelligently (usually
averaged over the section) splendid résults were
obtained in the balancing of yardage when grade and
proper road width were obtained.

In Plate No. 4, page 14, is shown a stake
line location which has been set on a plus 5% grade
contour. That is to say, each stake has been set at
50 foot stations on a plus 5% grade. As noted in the
field notes, ground elevationsand grade elevations are
identical. ”his method of location was used wherever
alignment of the grade contour was in good keeping
with proper location and curves of radius less than
80 feet did not result. In other words, grade loca-
tion was used on tangents. Plate No. 5. page , 15
shows the location afiter excavation.

The grade contour curves which result are
parabolic in nature and have good driving easement.

Thotographic evidence of grade location may be seen

 

 

 

 

 

 

 

[] 50.50

I 51.00

 

 

 

 

 

 

 

 

 

 

7ta 3 Rod Cd.E . Grade i1 lorfipflGrade
.07 0.0 100.0 100.0 7.1 pl-s t
.10 ‘.‘ 102.5 102.5 “.0 "
‘0 o.‘ 105.? 105.0 ?.0 "
l 0.7 10”.F 107.5 ‘.7 ”
3‘ 0.‘ il‘.0 115.0 ' ‘ "
Ft". 3. 4

A“.

re

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Plate he

 

 

 

 

 

 

 

16

in the Appendix, page 1, Figs. 1 and 2.

A study of the limits of grade location
will be discussed. There are three cases when loca-
tion by the grade point must be abandoned: First,
where a through out is necessary to provide fill or
to materially better alignment; second, where a
through fill will materially better the alignment;
and lastly where the grade alignment results in a
curve of less than 80 feet in radius.

Since the grade method produces a road
sinuous in nature it would be expected that in some'
cases short through cuts and through fills would
straighten out a location through country out up by
many sharp ridges and gulches. In this case an econ-
omical balance must be drawn by the engineer between
better driving ease and cost of additional excavation.

In like manner when the location approaches
a gulch the grade contour will produce a hair-pin
curve. This may be seen in the plan view of a minus
grade contour shown in Plate No. 63 page 17. The
stations are at 25 foot intervals and the grade is
minus 4%, scale being 50 feet to the inch. It is
obvious that the grade contour curve is useless in
this case. Superimposed over this grade contour
curve is a circular curve which is located on center-
line in the conventional method. The cut from the

canyon walls furnishes the fill over the drainage

 

 

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h
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radc ,

flan ?10W 0f
and
Circular Curves

 

 

 

 

 

    

_—‘_. h a

(

.__._~—--?rade Contour
__ —-—— Circular C-zrve
Scale 1"! Sn'

 

 

18

channel. When sufficient out has been obtained to
make the fill the location returns to grade again.
In concluding the discussion on grade
location it may be said that in gently sloping
country (cross section slopes up to 55 degrees, the
natural angle of repose) which is not cut up by
short sharp ridges and gulches, grade location pro-
duces excellent results from the standpoint of
costs, alignment, and construction ease. When the
cross section slepe is greater than 53 degrees the
grade point cannot be staked for the entire section
must be of the bench type, all of which is in cut.
When the terrain becomes of such a nature that the
location is a series of curves of less than 80 feet
in radius the survey must be run on the conventional

centerline.

19

CENTERLINE LOCATION

As pointed out in the previous chapter
grade location cannot be used in all cases. For use
with centerline location, tables similar to those
described under the Balanced Section have been pre-
pared. One may enter these tables with a cut on
centerline and.the cross section lepe in degrees
and find the yardage involved for excavation and for
fill (if the section is not a through out); or the
yardage involved if the section is in cut. Similar
tables give the fill yardage for sections part in cut
and part in fill as well as for sections all in fill.
A separate table gives the distance to the cut stake
and the cut at that point. It was the writer's pract-
ice when dealing with through cuts and fills to slope
stake them in the conventional manner. For in most
cases considerable yardage was involved and a good
balance desired.

In this problem of centerline location the
case of tangent through cuts and fills will be first
taken up. See Appendix, page 2, Fig. 5. As in all
discussion it will be assumed that a preliminary
survey line has been established. In which case the
through out or fill may have been roughed out with

preliminary stakes. In any case in approaching a

20

problem of this type it must first be determined
where the location is to leave grade and enter

upon centerline. Plate No. 7, page 21, gives a
graphic representation of grade contour replaced by

a centerline location to give a tangent with through
cuts and fills. Here the location has been progress-
ing on grade from the righthand side and has been
ended at Sta. A, the point which has been chosen as
one suitable for entering upon centerline location.
At Sta. A must be determined the true centerline of
the section. Referring to Plate No. 2, page 10, it
may be seen that the centerline may be established by
measuring from "G" a distance equal to(a - w/ZL The
distance "a" may be found in the tables, page 12, for
any s10pe and roadwidth. From this is subtracted one-
half of the width and the result is the distance from
the grade point to the centerline of the section.
This is the distance "y" on Plate No. 7 and Sta. A'
is then on the centerline of the section.

When the engineer has in mind the point at
which the location is to return to grade, the center-
line location is carried to that point in the conven-
tional method. The station stakes are set in line and
elevations run with the Abney set at the level posi-
tion. At the final station the reverse operation is
done to locate the grade point, or it may be done by

merely setting the rod on grade by reading the com-

 

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rs“, .' e
'_:1.;f: u. 1- a!” n‘ 7., ' I,
I .Jsd [X
Y "
- .
-‘f..r .. o O
o -. ' p
. O
. 1.; ‘f I:
o 0 “OC
- O

 

 

 

 

 

puted grade rod.

The next step is the determination of yard-
ages which is done by taking cross section slepes and
entering the tables. Since in most cases the grade
is predetermined and should not us changed, any dis-
crepancy in yardage oalance should be adjusted by a
change in location rather than in a change in grade.
As in all other cases, where care and judgment were
employed in the selection of the prOper slope for the
section (average slope) an excellent balance in yard-
age was obtained when grade and road width were ob-
tained. 10% over fill yardage was a common figure but

was varied as the geological formations differed.

CENTERLINE LOCATION

Curves

When a location progressing on grade
resulted in curves of less than 80 feet in radius
the method of surveying was of the centerline type
and accurate circular curves were staked. As
pointed out previously sight distance was generally
limited and this necessitated curve location by the
middle ordinate method.

Tables for various radii and chords were
computed from the formula middle ordinate = éCZ/R.
See table on Plate No. 8, page 24. In locating a
circular curve the points A and 8 must be located on
the centerline of the section and not on the grade
point. If for example an 80 foot radius curve is to
be staked, the points A and B are determined by
consulting the tables under the prOper cross section
lepe and road width. The curve tables give the
ordinate for an 80 foot curve with 25 foot chords as
3.9'. This is the full ordinate to be used on the
circular curve. Since in locating the first point
on the curve only half the distance from A to C is on
the curve, only half the ordinate or 1.95' is used
and is set off at point B. The line of sight establ-
ished along AB' and point C is located. At C the full

ordinate is set off and a line of sight established to

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

‘-

 

 

 

 

 

25

D. When the curve approaches tangency again the
half value of the ordinate is again used. The
middle ordinate method is not out of the ordinary
and consequently no more time will be devoted to
it. However, the location as it pertains to the
Abney level will be discussed in some detail.

Curve location is quite naturally the back-
bone of driving ease on mountain roads. Major points
to be considered in the design of curves are: Driv-
ing ease, cost of construction, drainage, and cost of
the survey. Curves of the type shown in Appendix,
pages 2 and 3, Figs. 4 and 5, show how the grade runs
from cut on the canyon walls to fill over the natural
drainage channel and back to cut on the far side of
the canyon. Good location calls for well designed
approach tangents, a curve which will fit into the
natural terrain, and a good balance of yardage. Since
in most cases the survey is run on grade at each end
of the curve it follows that the cut from the canyon
sides must make the necessary fill in the center over
the channel. Borrow pits are never used.

The engineer experienced in Abney level
surveys approaches the curve problem in the follow-
ing manner: First he must visualize the grade points
on each tangent. Then he must be able to picture the

proposed curve in place between the two grade points

26

and the approximate yardage involved. When the
location is set to the best of knowledge it is
staked as described by the ordinate method. When
this has been accomplished with good alignment the
ground elevations are run between the grade points
in conventional method. Grades and cuts are
computed for 25 foot stations and the yardage
determined from the tables. If a balance is
obtained the curve as staked becomes final. If
there is a discrepancy in the cut and fill yard-
age the curve must be relocated for it must be
borne in mind that in most cases the grade is fixed
and can not be changed to accommodate a change in
yardage. If there is an excess of cut the curve may
be pulled down the canyon to decrease the cut and
increase the fill. Possibly a change in radius will
give the desired results. Various problems occur
and in most cases each is different and the solution
of them depends on the topography. No rule can be
fixed for their solution. Skill and past experience
in Abney level surveys will give the engineer un-
canny judgment which results in good fast locations.
As in all other branches of the Abney level method
the ability to picture the constructed grade in the
rough terrain is the key to good surveys.

It was the writer's experience that after a

few months of this type of surveying it was possible

to locate a well designed curve on the first attempt

in most cases.

27

28

CONCLUSION

In the writer's Opinion the Abney level
method of surveys has solved the problem of high-
way location on secondary mountain roads. It has
extremely flexible characteristics. When starting
a new job it was the writer's practice to obtain a
U.S.G.S. map of the district and plot in the pro-
posed grade by means of dividers set to the proper
scale. This proved very helpful in determining
whether the road could be designed as a 5% or a 10%
ruling grade. It also brought out whether the
grade could be carried directly to the proper term-
ini without the use of switchbacks. With this know-
ledge in mind and the U.S.G.S. map in hand one day
or two in the field would generally suffice for a
good reconnaissance survey. During this survey the
primary control points were fixed. Secondary control
points, that is, possible switchback locations, sad-
dles through which the grade must pass, and crossings
over bad canyons were also fixed. An altimeter
proved very helpful in this survey. A two-man party
working in average country could cover about five
miles of reconnaissance in two days.

The preliminary survey was carried on with
a five-man party. This survey was usually run with-

out setting station stakes. With the ruling grade

29

having been picked this grade was carried out by
tying red flagging at every Abney station regard-
less of distance. At points of grade changes, and
at points where the location changed from center-
line to grade and vice versa, double flagging was
placed. Since most cases of circular curves and
through cuts and fills were roughed in on the pre-
liminary survey this method proved ample when the
final location was made. In average country where
brush conditions were not too bad a five-man

party could do a mile of preliminary survey a day.
In this connection it might be said that a good
reconnaissance and a good preliminary survey are
invaluable to the engineer when he sets about
staking the final location. This method gives
ample opportunity to make alternate preliminary
surveys in an endeavor to pick the route, for as
might be expected in mountainous country a great
many alternate routes are generally available. A
preliminary roughed in by flagging can quickly and
inexpensively determine which is the prOper loca-
tion.

Final location work varies widely with
the type of country. In heavy brush country which
has not been cleared after the preliminary makes loca-
tion work slow. But in cases where the brush has been

cleared it progresses with marked rapidity.

30

To take a complete example of the flexibil-
ity of the system the case of the writer's location
survey of the Oak Opening Road in the Sequoia National
Forest will be used.

The completed length of this road was 5.5
miles, with the lower terminus at elevation 2,500 feet'
and the upper at elevation 4,500 feet. The general
route of the road was along a ridge and its purpose
was for fire protection in a country of high fire
hazard. It was a segment of the Ponderosa Way, a
road which will ultimately traverse the entire length
of the Sierra Mountains.

The reconnaissance survey was completed in
two days with a two man party. During this survey
the primary and secondary controls were established.
This survey together with an hour or two of office
work with a U.S.G.S. map showed that the road
could be constructed with proper grades between the
major control points. 0n the morning of the third day
the construction equipment and brush crew were wait-
ing at the lower major control point. The preliminary
survey was worked out to the first saddle, a distance
of about 1,000 feet, in several hours. By noon of the
same day grade and slope stakes were in and the ground
cleared of brush and timber. By night the grade had
been roughed out and was ready for blading. Under no

other method of surveying is such speed attainable.

31

When the grade is staked the bulldozer
Operator can plainly see the grade point and on
shallow cuts can start the blade digging at grade.
0n steeper cuts the blade is started digging at the
upper cut stake and,works down until grade is reached.

Costs of these surveys, as prepared by
Mr. C. L. Young, Chief Surveyor of Region Five, show
some interesting savings.

Open timber, slopes uniform and not more
than 30 degrees (easy country) ........ $75 per mile

Average heavy timber, heavy slopes.3150 per mile
Dense brush, heavy lepes..........$275 per mile

0n the northern forests the costs average
around $150 per mile while on the southern forests
the cost per mile is about average at $250. These
costs include traversing the road after completion
but do not include office work. This may be explained
in the system where' days of bad weather and other
work are charged off as office work. In this connec-
tion it may be stated that the only office work re-
quired in this method is the preparation of monthly
reports, profiles for use by the construction foreman,
and making traverse maps. In this connection a man-
day per mile of road would seem a fitting figure to
charge against office work.

With present day trends toward longer radius

curves, more through cutting ridges and filling gulches

the balanced section will be used less and less in
rough cut up country. However, it will never be
entirely replaced. It has had a great part in
highway location by developing a type of location
wherein the road grade is literally fitted to the
surrounding terrain. Curves are laid into natural
gulches and canyons. But perhaps most of all it has
sought to develop the engineer to a skillful designer.
He has been forced to picture both plan and profile

in his mind at once. He has been forced into making
quick and accurate estimates of yardage involved in
cuts in steep country. It was the writer's exper—
ience that after eight months of this type of survey—
ing uncanny judgment was developed. In rough country
centerline location could be staked for a distance

of 1,000 feet at a time and have the yardage on

all cuts and fills balance when the ruling grade was
applied to the ground elevations. Which, of course,
is the outcome of working with the grade on the ground
instead of an office profile.

The system, as to be expected, has its
disadvantages. Men going into this work must be
trained to the new surveying standards. Yardage com-
putations, though giving excellent balancing, would not
suffice for contract purposes according to eastern
practices. However, after seeing it in operation,

seeing the results, and using it for some time, there

is no question but what there is valuable food for
thought for the engineer. There are doubtlessly
. numerous places where this type of surveying might

be employed to great advantage.

33

APPENDIX

Photographs in the appendix are by the writer
and depict roads constructed on the writer's Abney

level surveys.

 

Appendix

 

 

Fig l

The sinuous nature of a grade
location is well shown here with the
resulting long graceful parabolic
curves. Oak Opening Road in the
Sequoia National Forest.

 

 

 

Fig 2

A nortion of the Oak Opening
Road in Sequoia Forest showing a
typical stretch of grade location
using the balanced section.

Appendix 2

This center
line thru out and
fill eliminated a
bad double reverse
curve had the loca-
tion been surveyed
on grade. San "
Jacinta Ridge Rd,
San Bernardinn ‘
National Forest.

 

 

 

Fig 4

A typical long radius curve
located on centerline across a
gulch. Grade location used on
approach tangents. Oak Opening
Road, Sequoia National Forest.

 

Appendix

 

 

Fig 5

A center line location of
a switchback followed by series
of reverse curves. Note open-top
culvert and spillway. Kramer
Gulch Road, Sequoia Forest.

 

 

'... these types of roads,
by virtue of their need, were
always in perplexing terrain."

ADDendix

 

 

 

A culvert being set to proper
grade with the abney level. Grade
stakes can be set for long culvert
.installations quickly when the abney
is set at the proper grade. San
Jacinta Ridge Road. San Bernardino
National Forest.

 

 

Fig 8

A switchbsck graded over the
above culverts by center line method.

Sta
74+50
75+00
5n
7fi+00
50
77+on
PC 25
50
75
7R+00
25
50
75
79+00
25
PT 50
75
80+00

50

iRod

+5.7
+6.4
-1.4

-23

-1.3

-3.2

Appendix

Gr. E1
3117.0
3119.5
3122.0
3124.5
3130.2
3136.6
3135.2
3132.9
3131.6
3128.4
3125.0
3128.9
3133.7
3137.6
3141.3
3140.0
3138.3
3139.5

3142.0

Eote: 0

Gfii?e

3117.0
3119.5
3122.0
3124.5
3127.0
3129.5
3130.3
3131.0
3131.8

3138.3
3139.5
3142.0

refers

TYPICAL FIELD NOTES

Gr'd

45%

b
S C or F
21 9
17 9
24 9
24 G
22 C 3.2
25 C 7.1
20 C 5.2
20 C 1.9
17 F 0.2
17 F 4.1
15 F 8.3
16 F 5.1
19 F 1.1
22 C 2.1
22 C 5.0
20 C 3.0
25 G
28 o
28 0

to "grade".

Yardage

Cut
37.9
26.4
49. 6
49.6
190.0
210.0
96.0
\37.0

8.5

5.0
41.0
93.0
54.0
27.3
56.0
74.0

F111

Appendix

The field notes on the precedhgg_ page
were taken from a section of road progressing on grade,
through a curve section on centerline, and back to
grade again. From Sta 74+50 to Sta 76+00 the location
is on grade with ground and grade elevations identical
and no out or fill at the grade stake. The cross sec-
tion slope appears under "S" and the cut yardage to
balance the section is entered in the yardage column.

From Sta 76050 a short tangent on center-
line was run to Sta 77925, the P.C. The column under
the plus and minus Rod are the elevation differences
between the stations.

From the P.C. the curve runs to Sta 79L50,
the P.T. on centerline. The location returns to grade
at the next station.

The yardames envolved on the curve,‘that is
between Sta 76+50 and Station 79+50, are:

Cut 664.5 and Fill 603.5
which with a 10% allowance for fill will give a good
balance of the yardage. The yardages were computed from
tables similar to those shown on page 12 and tables
of similar nature for sections in excavation and em-

bankment.

 

1.4.; .1

. . . .K it" 7
pin/iku (Cu-ll. II.
.........I. ..

 

1

”tr.

 

m

h