made it useful as a canal lining material, where a good quality bentonite
is available at reasonable cost. Bentonite has been used as a buried
membrane; by pre-mixing it with soil to form a 2- to 3-inch thick im-
permeable layer, usually compacted into place; and by mixing it in place
with the subgrade materials.

Bentonite Membranes

As a membrane, bentonite has been very effective in re-
ducing seepage losses. Like asphaltic membranes, it is believed these
installations will prove effective as long as the membrane is protected
from drying out, weathering, and erosion, Protection usually consists
of a loose cover of earth and/or gravel. One of the oldest bentonite
membranes has been in service for 13 years. The bentonite used has
been raw pit run or commercially ground and dried material.

Bentonite-soil Mixtures

Either pit run orcommercial grades of bentonite may be
mixed with soil and both have been very effective over a period of sev-
eral years in providing water tightness to canals and laterals. The op-
timum amount of bentonite to be used with a particular soil must be de-
termined by laboratory tests. Essentially, the bentonite is a filler or
binder for coarser silty and sandy soils, which alone would neither be
stable nor water-tight. Usually, placed as a 3- to 4-inch thick layer,
it is recommended that a protective cover of stable earth or gravel be
placed over the lining.

This type of bentonite lining is generally more costly than
the membrane, due to compaction on the side slopes. Maintenance costs
should be about the same as for other types of earth linings.

Mixed-in-place bentonite-soil mixtures

Mixing bentonite with the subgrade materials by spreading
it over and plowing or discing it into the subgrade material to depths of
6 to 12 inches has been effective in reducing seepage through the bottoms
of canals and laterals. It is difficult to place and mix in this manner on
the side slopes with existing equipment and hand placement is costly.
After mixing, the subgrade should be compacted to reduce the possibility
of erosion,

Soil-Cement

Soil-cement has been used as a canal lining material in local-
ities where subgrade soils or those adjacent to the canal are of a sandy
character and suitable earth materials are not readily available. In-
stallation costs in trial installation have been relatively low. Two types
of soil-cement have been used; the standard type and the plastic type.
Few soil-cement linings have been placed in recent years although per-
formance has been reasonably satisfactory in some locations in the south-
west,

13


CONCRETE LINED FARM DITCHES

In water short areas of North-eastern Colorado, the farmers
are attempting to conserve every possible drop of irrigation water by
the installation of concrete linings in their farm ditches. Construction
varies, but for the most part, like those shown below, they are cast-
in-place linings, utilizing ready-mixed concrete wherever a ready-mix
plant is in the close vicinity. The linings are unreinforced.

The lining above has a bottom width of 18 inches and a 10-
inch depth. Instead of providing outlets in the lining, 6-inch siphon
tubes are used to get water to the land,

The above lining has a 13-inch base width and 12-inch depth,
Reusable forms were employed and at frequent locations a section of
lining was placed having grooves for the installation of check boards.

4


and lateral distribution systems having hydrostatic heads up to about 8
feet maximum. The recent installation made will provide additional
information regarding serviceability and cost. Preliminary data in-

dicates the pipe to be competitive with precast pipe in the smaller
sizes and with concrete linings.

2k Ok kk

Don't forget we need your O&M ideas.

17 GPO 847633


Although many miles of shotcrete linings have given years
of satisfactory service, particularly in the southwestern states, in
general, it is not considered as desirable or as economical as slip-
formed concrete linings for large jobs. Not only is the rate of place-
ment for shotcrete lining ery slow in comparison to slip-form op-
erations, but shotcrete 13 inches in thickness usually costs as much
as 2 inches of concrete, if conditions are favorable for slip-form
placement,

Asphaltic Concrete

A combination of asphaltic cement and aggregate; mixed,
placed and compacted in a hot and plastic state, asphaltic concrete
is most satisfactorily placed by slip-forms of the subgrade guided
type because of the resulting economy and uniform high density.
This lining is particularly well adapted to smaller canals and lat-
erals, although it has been used for larger facilities.

Since no curing is required, the lining is ready for immed-
iate use after placement and cooling.

The cost of asphaltic concrete lining is comparable with
that of slip-formed concrete lining and offers a saving in installa-
tion cost only where suitable concrete aggregates are not available.
Because of the plastic nature of this lining, some types of weed
will penetrate it. In fact, weed growth is actually promoted by the
heat absorbing property of the black surface, Treating of the sub-
grade prior to placement of the lining is advisable, especially when
it is placed in areas where such weeds as tules, cattails, or willows
are firmly rooted. A harder asphalt is now specified for use in hot-
mix asphaltic linings today, to obtain better resistance to water ero-
sion and weed puncture.

Buried Asphaltic Membranes

Two types of buried asphaltic membrane linings have been
used to good advantage in Bureau construction. One is composed of
hot asphalt cement applied directly to the subgrade and the other is
a prefabricated material similar to rolled roofing which is laid upon
the subgrade,

Buried Hot-Applied Asphaltic Membranes

Essentially, the hot-applied buried asphaltic membrane lin-
ing is one in which the asphalt layer, 1/4- to 3/8-inch in thickness, is
sprayed upon the subgrade, and this barrier to the passage of water
is held in place and protected against injury and weathering by cover-
ing with a layer of earth and/or gravel. A special catalytically blown
asphaltic cement is nowused for the membrane, and has been found to
be superior to other types of asphalts.

This type of lining is third in volume installed on Bureau


A REPORT ON THE LOWER-COST CANAL LINING PROGRAM

In a paper presented at the annual meeting of the National Rec-
lamation Association in Portland, Oregon, November 8-10, 1954,
A. B. Reeves, Chief, Irrigation Operations Division, Bureau of Recla-
mation, reviewed the Bureau of Reclamation's Lower-cost Canal Lining
Program. The accomplishments of the program since its inception in
1946, the advantages and limitations of various types of linings, and
the future investigations planned were discussed. Copies of Mr. Reeves!
paper, "Linings for Irrigation Canals", may be obtained by writing the
Commissioner's Denver Office, U. S. Bureau of Reclamation, Denver
Federal Center, Denver, Colorado, Attention:- Code 400.

Approximately 26, 000, 000 square yards of lower-cost linings
have been placed in more than 750 miles of canal and laterals on Bureau
Projects since 1946. The table on the following page is a summary of
the various type of linings placed and their representative cost. The
cost of a lining to meet a given condition will vary with the individual
job.

Selection of a Lining

No one lining is satisfactory for all conditions to be encountered.
Selection of a lining to meet given conditions was discussed by Mr. Reeves
and a summary of his remarks follow.

Canal Linings are Expensive

Even the lower-cost canal linings are expensive. In good ter-
rain, a lined canal will generally have first costs 2 to 3 times that of an
equivalent unlined earth canal because of the cost of the lining. The
costs presented on the following table, with few exceptions, are repre-
sentative installation costs for the various types of linings placed under
contract by the Bureau of Reclamation. The exceptions are for experi-
mental installations made by contractors or by Government forces and
reflect the cut-and-try costs associated with this type of work.

In the selection of a lining, the location of the canal or lateral,
the character of the subgrade and construction materials available, and
the cost of maintenance and probable useful life must be considered.
Accurate maintenance costs are difficult to obtain and in many instances
the probable useful life must be estimated, as few experimental linings
have been in use more than six to 8 years.

Concrete Linings

The tabulation does not include the more costly reinforced con-
crete linings. In general, they are now used only where structural safety
is imperative or where other factors such as frost action, high hydrostatic
pressure, etc., must be considered, There is no reason to believe that
reinforced concrete will outlast unreinforced concrete, if the latter is
properly designed, constructed and selected for a suitable location.

6


Full advantage has been taken by the installation of the above
lining to cultivate and irrigate all possible land in the field. Located
along the fence line, the steel fence posts have been set in the concrete
of one side of the lining.

Concrete lining from an abandoned ditch has been salvaged
and is being replaced in a new ditch. The unreinforced concrete lin-
ing withstood the handling very well.



Again with reference to the tabulation, the lower-cost con-
crete linings are first in volume placed since 1946. These linings
can be included in the lower-cost category because of improved
techniques in placement, liberalization and simplification of spec-
ifications, elimination of reinforcement steel, development of sub-
grade-guided slip-forms, and standardization of canal shapes and
sizes,

Even the lower-cost concrete linings are higher in first
cost than many other types of canal linings, but they are probably
lower in maintenance cost and longest in useful life; that is they
are longest in useful life from the point of experience. We do not
have comparable records of useful life for other types of linings.

Concrete is more resistant to erosion than most other
types of linings and because of its beam strength, it will usually
bridge short reaches of poor subgrade support. Therefore, it is
preferable where high velocities exist or where safety is of pri-
mary importance. Concrete linings eliminate weed growth and
burrowing animals cannot penetrate the lining as they can unlined
or earth-lined canals; hence, lower maintenance costs.

Failures of concrete linings are generally due to adverse
subgrade conditions, excessive hydrostatic pressures beneath the
lining, frost heaving, poor quality concrete, faulty design or con-
struction, etc. In northern climates, frost heaving is the greatest
factor contributing to the destruction of concrete linings,

Shotcrete Linings

Shotcrete (pneumatically applied portland cement mortar)
continues to be successfully used in the Southwest, where the climate
is not severe. It can be placed on irregular surfaces obviating the
necessity for fine trimming of the subgrade prior to application. It
has been used satisfactorily for resurfacing badly cracked and leaky,
but reasonably sound old concrete linings.


Department of the Interior

Bureau of Reclamation

OPERATION AND MAINTENANCE

EQUIPMENT AND PROCEDURES

RELEASE NO. 10
October, November and December 1954.

bigVG

t

iM
NW

ba

ol - “p00

Sloper Speeds Canal Bank Maintenance

Silicone Resins as Waterproofers

Glyptal Solution Prolongs Life of Tags

Turntable on Motor Graders Lubricated During Operation
Concrete Lined Farm Ditches

A Report on the Lower-Cost Canal Lining Program


Prime Asphalt Membranes

Prime asphalt membrane linings were the forerunners and led
to the development of the hot-applied, buried asphaltic membranes.
Few of the prime membrane linings have withstood the test of service
or exposure. More recently, prime membranes have been considered
for use in stabilizing sandy soils, rather than making them water-tight.

Heavy Compacted-Earth

The second largest volume of lining placed by the Bureau has
been heavy compacted-earth. It might more appropriately be called
"thick, compacted-earth lining", as compared with the thin, compacted-
earth linings discussed below. Constructed of selected impervious soils,
placed with the bottom and side slopes compacted in horizontal layers
6 inches in thickness, the lining thickness is about 3 feet on the side
slopes (with the thickness measured normal to the slope) and 2 feet on
the bottom,

Where suitable material is available with a minimum of haul
and the job is large enough to utilize mechanized equipment fully, this
lining has proved to be one of the lowest in first cost. Because of the
high uniform density, stability, and thickness a protective cover is not
required, except at curves or other points of high water-velocity.

Properly constructed, the lining has been found by field tests
to be highly impermeable; with losses comparable to those of a good con-
crete lining. In areas where high ground water or expansive soils pre-
dominate, heavy compacted-earth linings may be preferred to concrete
linings. The rigid concrete linings have been disrupted by the expansion
on wetting of expansive subgrade soils or by hydrostatic pressures from
a high ground water table; whereas, the compacted-earth linings, charac-
terized by greater weight and flexibility, are not ordinarily damaged by
these forces.

Maintenance of compacted-earth linings should be about the
same as an unlined canal. We have only meagre information concern-
ing the useful life of these linings, but one lining in a northern project
has been performing well for a period of 13 years, with recent tests
indicating it has been little affected. Linings installed more recently
are now being examined,

Heavy compacted-earth linings appear more suitable for the
larger canals; however, some adaptations have been attempted for
smaller facilities. A narrower lining having a horizontal width of only
3 to 4 feet, as compared with the 7 to 8 feet in the larger canals, has
been placed using smaller equipment; compacting with a single sheeps-
foot roller pulled by a small crawler or farm type tractor. Another lin-
ing was placed in a small lateral by first filling the canal prism with
compacted-earth and later reexcavating with a plow-type ditcher.

Thin, Compacted-earth linings

Thin, compacted-earth linings ordinarily 6 to 12 inches in

11


projects since 1946. Availability of suitable asphalt throughout the
western states has contributed to the extensive use of this lining,
which can be placed at costs less than half that of most hard surface
linings. The lining can be installed in much less time that a hard
surface lining with a minimum of interference to regular operations,
and also can be satisfactorily installed in cold or wet weather, fre-
quently encountered during the non-operating season in northern cli-
mates.

The maintenance of asphaltic membrane linings is slightly
more than that for an unlined canal. The soil or gravel cover over
the membrane is subject to beaching and weed growth in much the
same manner as earth lined or unlined canals, and the membrane must
be kept covered at all times.

As for useful life, it is believed it is a matter of how long
the membrane will last. Recent tests of the membranes indicate very
little deterioration with age, and good service is expected.

Buried, Lightweight, Prefabricated Asphaltic Membranes

Prefabricated asphaitic membrane linings were developed to
permit use of an asphalt membrane, but to eliminate the use of hot
asphalt requiring skilled personnel and special equipment for place-
ment. The lightweight prefabricated linings resemble and are handled
and placed in much the same manner as rolled roofing; lapping and ce-
menting the joints. These linings also must be protected from damage
by a cover or earth and/or gravel, and maintenance problems are simi-
lar to those of the hot-applied buried membranes,

Because of the hand labor involved in placement, the prefabri-
cated membrane is more costly to install than the hot-applied membrane,
but is particularly adapted for placement in remote locations and by
maintenance forces, where the amount of lining required is not great.

Exposed, Heavy, Prefabricated Asphaltic Membrane

To eliminate the need for a protective cover over the prefab-
ricated membrane, several manufacturers have now developed a thicker,
heavier type of material, 1/4- to l-inch in thickness, which we term
"Heavy, Prefabricated Membrane". Several trial installations have
been made on small laterals, and the cost for installation will vary with
the thickness of the material used.

Asphalt Macadam

Asphalt macadam has been used only in a limited way in Bu-
reau work, Few macadam linings have been constructed, but it has
been used as a cover material for other types of linings quite success-
fully, primarily where suitable cover material of other types is scarce
or obtainable only at high cost.

10


CANAL LININGS PLACED
and their
REPRESENTATIVE COST

(Since December 31, 1946)

Lining Installed
Placed Cost per
Sq. Yds. Miles Sq. Yd.
Unreinforced Concrete. . . .. . . 17,406,210 389.0
3 to 4 inches in thickness. .... $2.50
13 to 2 inches in thickness . . . . 1.30
Shotcrete Linings Pa soe oe ee » 1,054,221 115.6
14 inches in thickness se GS ew a 2.00
2inches inthickness. ...... 2.30
Asphalt:-
Asphaltic Concrete .. i 0 228, 416 31.9 2.40
Buried Asphaltic Membranes:
Hot-applied (sprayed) .... . 2,152,391 102.3 1.14
Light prefabricated ...... 15, 376 1,2 1,50
Exposed, heavy asphaltic
membrane. . es 3, 434 0.5 1.54
Asphalt Macadam oe ie oe ee 3, 500 0.1 *
Prime asphalt membrane . a iat 0 13, 591 1. 8' bs
Earth: -
Heavy compacted ........ 4,176,235 72,0
Large Canal. . . a6 8 #G 0.55
Small canal or lateral sha we 1.00
Thin Compacted. . . oo 131,519 5.9 0.40
Loosely placed earth blankets - oa 351, 146 19.1 0,24
Silted or sediment lined ..... ee ial 0.14
Bentonite: -
Raw or processed membrane , . 123, 282 9.5 1,01
Bentonite-soil mixture. .... 6, 080 0.8 1.60
Mixed-in-place ........ 24, 664 1.8 *
Soil-Cement:-
Standard type... 1... . ae 69, 020 8.0 0.76
Plastic type 2... we se 10, 018 Lod 0.89
Miscellaneous. . é 22, 399 2.5 *

(Includes grouting, asphalt under-
sealing, asphalt emulsion concrete,
asphalt emulsion-mortar shotcrete,
etc.)

Total 35,791,502 763.1
*The small amount of lining installed on an experimental basis
**Not applicable.



SILICONE RESINS AS WATER PROOFERS

Advertising literature has been received in which silicone
resins have been described as useful in waterproofers for concrete,
cinder blocks, wood, etc. Requests have been received by the Bu-
reau's Denver Paint Laboratory from various branches within the
Denver Office and from the field for information on the value of sili-
cone resin for these purposes.

Conclusions drawn from the Denver Paint Laboratory re-
search program in which these materials were evaluated indicated
that the unpigmented silicone resins, in their present state of develop-
ment, are unsatisfactory as waterproofers for below grade use and
are unsatisfactory as waterproofers for uses where a hydrostatic
head exists. It was further concluded that on porous surfaces, above
grade, low solids content silicone resin based clear coatings could
not be considered water repellents and thus would have little use in
Bureau Construction,

These findings have now been confirmed by one of the pro-
ducers of the silicone resins used by manufacturers of waterproofers,
In literature describing one of their newest products in this field,
they state that the resin can be used in the manufacture of coatings
designed to "impart water repellancy to above-grade brick, concrete,
mortar, cinder block, stucco, etc.".

He ok ok ok

GLYPTAL SOLUTION PROLONGS LIFE OF TAGS

An employee suggestion by Robert E. Morris, Region 1, U. S.
Bureau of Reclamation, saves time in making out safety and equipment
marking tags. By dipping the tags in a 40 percent Glyptal solution, they
remain legible for a longer period of time as well as being more durable.

ak ok ok ok ok

TURNTABLE ON MOTOR GRADERS LUBRICATED DURING OPERATION

A. H. Carlson, Region 1, U. S. Bureau of Reclamation, saves
time and eliminates the need for a separate supply of lubricant in lubri-
cating the circle (turntable) on motor graders during operation,

A 1/4-inch copper tubing is run from a shut-off valve connected
to a fuel tank to a control valve inside the grader cab. The tubing is con-
tinued from the control valve along the frame to the front of the drawbar.
At that point a short length of flexible tubing is connected to copper tub-
ing leading back along the drawbar to the circle, Using the control valve,
the operator can clean and lubricate the circle from the cab while the
grader is in motion.

Hk


Standard Type

Standard soil-cement is a compacted mixture of soil and
cement in which the moisture content of the mixture is maintained at
time of placement at about the optimum as determined by laboratory com-
paction tests. Mixing has been accomplished by discing and blading
the mixture into place, but it is best accomplished by use of a pulvi-
mixer. The spreading and necessary compaction on canal side slopes
as steep as 13 or 2 to 1, is difficult to accomplish, and early deterior-
ation of the lining on the side slopes is believed due to lack of density.
An installation in which a special compaction machine was used in a
small lateral was made this past winter. The cement companies and
the Portland Cement Association also collaborated in this installation.

Plastic Type

Plastic soil-cement having a higher water content than
that of the standard type, and a consistency comparable to concrete may
be placed by means of a slip-form similar to that utilized in the place-
ment of concrete linings. This overcomes the difficult slope compac-
tion of the standard type soil-cement. The plastic linings, however,
exhibit low resistance to weathering and erosion.

Experimental Linings and Related Studies

The linings discussed above are for the most prrt either those
tried and approved for construction or abandoned because of inferior re-
sults or excessive installation or maintenance costs. Renewed interest
in some of the linings is possible because of improved techniques or the
development of better methods and equipment for placement. In addition,
the Lower-cost Canal Lining Program continues to foster studies of
other materials and methods for use in the lining, stabilization and wa-
terproofing of canal subgrade materials and perform related studies.
Some of the studies underway which have not been advanced sufficiently
for general field application are described below.

Physical Stabilization and Compaction of Subgrade Soils

Some subgrade materials can be made sufficiently dense by
compaction alone to improve their impermeability. Also the suitability
of either clayey or granular soils may be improved and the imperme-
ability increased by combining them in proper proportions in the place-
ment of a thin or heavy compacted-earth lining. Just recently, this
latter has been attempted on a large canal. It offers possibilities at
reasonable cost only if a large amount of lining is required, and where
large mechanized equipment can be used.

Resin and Chemical Stabilization

Resins and chemicals have been used in roadway construction
for stabilization and waterproofing. They have also been used experi-
mentally in canal linings. However, further study is necessary before
field application can be made. Some chemicals are toxic and in leach-
ing tests the waters have also been found to be toxic.

14


Asphalt Emulsion

The cold-mix asphalt emulsions have been used in a man-
ner similar to hot-mix asphalts in concretes, with the aggregate and
asphalts being thoroughly mixed and compacted in place. These linings
require curing, which in turn requires time and favorable weather con-
ditions. Some of the mixes remained soft and others contracted upon
drying and curing, thereby creating cracks that must be filled. Cold
mixes so far placed exhibit low resistance to erosion and lack stability
for an appreciable length of time. The addition of a filler and portland
cement to overcome this deficiency has been tried.

Pneumatically Applied Asphalt Mixtures

Several experimental linings have been constructed in the man-
ner of portland cement shotcrete linings. The pneumatic method of place-
ment is particularly advantageous in covering exceptionally rougn sur-
faces, but the slow rate of application, cost, and low resistance to ero-
sion and weathering have so far been unfavorable for its wide use. The
addition of portland cement to the mixture has added stability and pro-
vided for additional resistance to erosion,

Undersealing of Old Concrete Canal Linings

Although not strictly a lining in itself, the undersealing of
old concrete linings by forcing hot asphaltic cement under the lining has
been successful in preserving the original concrete lining in several lo-
cations. This is not a new process, but recent techniques have provided
for better results.

Plastic Linings

Canal linings of synthetic plastic are under consideration,
A number of manufacturers have furnished samples of their products for
laboratory testing and field installations. Presumably, the plastic lin-
ing would be of the buried membrane type, covered with earth and gravel
for protection, although field experiments with plastics of greater thick-
ness have been made in which the plastic is used as an exposed lining.
In the past the cost of the plastics has made their use prohibitive. Lower
material costs are promised by the manufacturers.

Monolithically Cast-in-place Concrete Pipe

Included in the Lower-cost Canal Lining Program because
it replaces a lined canal, monolithically cast-in-place concrete pipe
was installed experimentally during the past year. This type of pipe
has been previously used by private irrigators in California and has a
record of serviceability. Its cost, compared to the placement of some
types of linings has been high and this has been one reason it has not
been previously considered. Its structural strength has been another
factor.

The pipe has been used primarily to replace small laterals

16


SLOPER SPEEDS CANAL BANK MAINTENANCE

Several projects have reported that the Briscoe Sloper is sav-
ing time and money in the maintenance of canal banks. Engineered
primarily for the purpose of maintaining irrigation system canals, lat-
erals and drains, and designed for mounting on several sizes and makes
of tractors, the sloper is a welcome addition to any project's mainte-
nance equipment.

The sloper is regularly
furnished complete ready for
mounting and includes a spoil
wing which attaches to the rear
of the tractor and spreads ma-
terial brought up the slope.
This reduces but does not elim-
inate the amount of work neces-
sary to keep operating roads
graded. The sloper can be op-
erated with or without the
spoil wing. It is important
that the tractor have sufficient
power for the work contem-
plated; the larger or deeper
the canal, the lary:er the trac-
tor needed.

Even in rough going, the
sloper has been found excel-
lent for the removal of weeds,
silt berms, and in the general
leveling of the bank slopes.
The sloper operates efficiently
with water in the canal, pulling
the berms, grass, weeds, and
debris to the top of the bank,
where it will not float into and
clog headgates or outlets.
Where there are no obstruc-
tions, 3 miles of canal bank
can be cleaned per hour. With
obstructions, the progress is
slower, but the blade can be
quickly and easily swung up to
pass over or around outlet headwalls, bridges, etc, with but a minimum
of bank remaining to be cleaned by other means.

Further information regarding the cable controlled sloper shown
in the lower photograph on this page, or the hydraulically operated one
shown on the cover can be obtained from the manufacturer, E. V. Bris-
coe and Sons, Route 2, Box 118, Kerman, California, or by contacting
distributors located in many cities.



INTRODUCTION

This release, Release No. 10 of the Operation and Mainten-
ance Equipment and Procedures Bulletin, has been delayed in publi-
cation because of several uncontrollable circumstances, one of which
was the assembly of information from the field.

The Bulletin is receiving wide distribution in the United States
and Overseas and your contributions are being very well received. Re-
cently our attention has been called to several worthwhile suggestions
that were included in the Incentive Awards publication for which em-
ployees were recognized for making the suggestions, Several of these
are included in this issue of the Bulletin, but the detail that makes this
Bulletin more attractive is lacking in the award bulletin. In the future,
it is suggested that material of interest to readers of this Bulletin also
be forwarded to the Commissioner's Denver Office, Attention:- Code 400,

In a paper presented at the Annual Meeting of the National Rec-
lamation Association last fall in Portland, Oregon, A. B. Reeves, Chief,
Irrigations Operations Division, Bureau of Reclamation, Denver, Colo-
rado, reviewed the Bureau's Lower-cost Canal Lining Program accom-
plishments. Mr. Reeves' paper is briefly summarized, beginning on
page 6.

The O&M Equipment and Procedures Bulletin is circulated for
the benefit of irrigation project operation and maintenance people. Its
principal purpose is to serve as a medium of exchange of operating and
maintenance information. Reference to a trade name does not consti-
tute an endorsement of a particular product and omission of any com-
mercially available item does not imply discrimination against any man-
ufacturer, It is hoped that labor saving devices or less costly equip-
ment developed by the resourceful water users will be a step toward
commercial development of equipment for use on irrigation projects in
continued effort to reduce costs and increase operating efficiency.

de ook ok ok


thickness and composed of cohesive soil thoroughly compacted and
protected by a coarser soil or gravel have been used considerably in
the past. Recently, the Bureau has not employed the thin-compacted
earth linings on a large scale, because of the relatively high cost of
side slope compaction.

These linings should have maintenance costs comparable with
other types of earth linings if adequately protected from damage by
erosion or during cleaning operations,

Loosely Placed Earth Linings

Probably the most widely used of all in the past, is the loose
earth lining which consists of a blanket of soil cast on the subgrade of
a canal or lateral or pushed into place by mechanical means or by hand,
Generally, they are not as effective or as permanent as compacted-earth
linings and are used very little by the Bureau except in case of emergency.

Little trimming or reshaping of an existing canal is necessary
and equipment requirements are exceptionally simple. Seepage has
been effectively and economically reduced only if the blanketing soils
are impervious in a loose state and are adequately stable to resist ero-
sion. Soils containing sand and gravel have been placed on some Bureau
projects in this manner and are performing well. Low first cost of lin-
ing makes use of the loosely placed earth blanket attractive, but main-
tenance may be high, if erosion is to be controlled.

Sediment Linings or Silted Canals

The deposition or relatively thin layers of clay or silt over the
wetted perimeter of an unlined canal usually reduces seepage signifi-
cantly. This may be a natural process if the flowing water carries sed-
iment, or a sediment may be added. The effectiveness of the sediment
lining is dependent upon the material used, the velocity of the water in
the canal, and the structural formation of the subgrade material through
which the seepage occurs.

These linings are highly susceptible to erosion, puncture, de-
terioration by weathering, and destruction during cleaning operations.
Experience in the field has shown that unless it is possible to secure
penetration of the sediment into the voids of the subgrade material,
linings of this type will have a very short life. Except for the fact that
they are low in first cost and the treatment can be repeated from time
to tirne with little additional cost, the linings as such have been very in-
effective over a period of time. Repeated treatment increases the a-
mount of cleaning that is necessary and therefore increases the cost of
maintenance.

Bentonite Linings

Bentonite is an earth material containing a large percentage of
montmorillonite-type clay. It is characterized by high water absorption,
accompanied by swelling and imperviousness. This characteristic has

12


Bentonite Sedimenting

Being a very fine colloidal material when mixed with water,
some bentonites can be kept in suspension in waters flowing within a
canal. It is reasonable to assume that with the particles kept in sus-
pension, water seeping from the canal will carry the suspended ben-
tonite into the voids of the canal subgrade materials, If it is possible
to fill the voids of this subgrade material with the colloidal clay toa
sufficient depth to prevent its eventual erosion, it will provide an im-
permeable barrier to the passage of water.

This study is a continuation of the general study of silting
and sediment lining. Bentonite is being used as the sedimenting ma-
terial because of its very fine colloidal characteristics and general
chemical uniformity. Our present study is directed toward (1) se-
curing stable suspensions of the colloids in given canal waters, the
chemical nature of which affects this stability; (2) determining the
depth to which the colloids penetrate the voids of various types of
subgrade materials; (3) making limited field demonstrations under
controlled conditions; and (4) determining the permanence of the
field treatment in providing impermeability to a given subgrade ma-
terial.

Although there is existing literature on the subject to the con-
trary, it is emphasized that the permanence of the method has not been
proven. From three installations made this past spring, there is an
indication that seepage has been reduced considerably in a sandy soil,*
some limited benefits with a loess, and little benefit in fractured bed-
rock, This leads to the conclusion that in very fine grained soils, in
very coarse grained soils, and in large fissures and cracks, the ben-
tonite has either not penetrated or has passed on through the void space.

There are other problems in using bentonites that make further
study necessary. There are high-swelling and low-swelling bentonites.
The character of the particular bentonite, the chemical composition of
the canal water and that of the subgrade material must be known. The
incompatability of the chemical composition of these materialscan re-
sult in flocculation of the bentonite and result in its settling out of the
canal water within a very short distance; benefitting only this short
reach and forming a thin coating which is easily eroded.

Other Types of Asphaltic Canal Linings

The variety of asphalt mixtures, their combination with other
materials, and their method of use have led to other developments in
the treating of canals and laterals to secure imperviousness, stability,
and waterproofing. The asphalt producers have cooperated in the ap-
plication of their products to the Lower-cost Canal Lining Program.
Some of the newer applications to the problems, or some that have not
found wide usage to date are asphalt emulsions; pneumatically applied
asphalt, sand, and cement mixes; prime asphalt stabilizers; and the
injection or grouting of canal materials with asphalt.

15