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Proceedings of 1949 Civilian Soil Mechanics Conference
ASSOCIATE COMMITTEE ON SOIL AND SNOW MECHANICS
TECHNICAL MEMORANDUM NOo 17
PROCEEDINGS OF 1949
CIVILIAN SOIL MECHANICS CONFERENCE
OTTAWA,
CANADA
May, 1950
Section No. 1 2 TABLE OF ｃｏｾｔｅｎｔｓ Title Foreword Introductory remarks FOUNDATION PROBLEMS Page No. 1 2 ( L) 3 4 5 6
W. F. Riddell: "Fc undat Lon conditions in 3 Winnipeg andl immediate vicinity".
R. Peterson: "Foun da tion condit ions
in Saskatchewan" . 10
I.
F. Morrison andR. M.
Hardy: ｉｾｯｵｮﾭdation conditions in the Edmonton area" ]2
Discussion on foundation problems 15
HIGHWAY PROBLEMS
7
8
G. B. Williams: "Status of highway soils investigation in Manitoba."
w.
E. Winnitoy: "Soils problems in highway construction in Saskatchewan"21
27
9 L. H. McManus: "Soils problems
encoun-tered in highway construction in ａｬ｢･ｲｴｾｴＳＰ 10
11
12 13
J. D. Mollard: "Application of photo-analysis to the determination of soil conditions"
Discussion on highway problems WATER DEVELOPMENTS AND DAMS
S. Rutledge: "The Spr-ay Lake s Power Project"
R. Peterson: "Soil Mechanics as re-lated to the P.F.R.A. water develop-ment program".
33
44
49
Section No. Title Page No. 14
15 16 17
C. F. Ripley: "Procedure s and equip-ment used by the P.F.R.A. in the
investigation, design and construction of water development projects"
Discussion on water developments and dams
Visit to St. Mary and Pothole Dams Closing Dinner
54 61 64
68
Appendix A - List of those attending the Conference
Appendix B - Program for 1949 Civilian Soil Mechanics Conference. Appendix C = The St. ｍ｡ｲｾ - ｬｾ｡ｬｫ River Irrigation Project.
NATIONAL RESBARCH COUNCIL OF CANADA
ASSOCIATE COmMITTeE ON SOIL AND SNOW NiliCHANICS
Proceedings of 1949 Civilian Soil Mechanics Conference, Lethbridge 9-10 September, 1949
This is the record of the third annual conference held in Canada on the subject of Soil Mechanics and Foundation
Engineering under the auspices of the Associate Committee on Soil and Snow Mechanics. These conferences were initiated in 1947 to bring together those Canadians working in this field to dis-cuss problems and exchange information of mutual interest.
The first two conferences were held in Ottawa and
attended by delegates from all parts of the country. This year's Conference was held at Lethbridge, Alberta, on 9-10 September by kind invitation of the Prairie Farm Rehabilitation Branch (P.F'.B.A.) of the Depar-trnent of Agriculture, whose staff generously made all arrangements for the meeting. This time and place were chosen so that the delegates might see construction operations uncier way on the st. Mary Dam, the largest earth-fill structure so far built in Canada. The Conference also provided a suitable opportunity for discussion of those particular soil mechanics problems en-countered in Western Canada.
A list of those who attended the Conference accompanies this report as Appendix A.
Section 2
INTrtODDCTURY
ｈｾｎｾｒｨｓThe Conference was opened by the Chairman, R. Mo Hardy, Dean of Applied Science of the University of Alberta, ｅ､ｭｯｮｴｯｮｾ
who welcomed those present and explained that, as in previous ｹ･｡ｲｳｾ the meeting would provide an informal opportunity to dis-cuss work, problems and ｩｮｦｯｲｾ｡ｴｩｯｮ related to Soil Mechanics and Foundation .2:ngIne er-ing. He read a telegram from lVIr. R. B'. Legget, Chairman of the Associate Cormnittee on Soil and Snow Mechanics, expressing his regret at being unable to attend and wishing for the success of the meeting.
The Chairman announced that the program at this Con-ference was planned somewhat differently than in former years, since a prime object of holding the Conference in Lethbridge was to visit the site of the st. Mary Dam. The first day would there-fore be occupied by technical sessions; the second would be taken up with a field trip to the dam, returning in time for an informal dinner in the evening at which business would be discussed.
Technical matters were to be dealt with on the first day in three separate sessions on foundation problems, highway problems, and water developments and dams, respectively. Papers had been prepared by chosen speakers under each of these subjects to form a general review as a background for discussion.
The Chairman emphasized that although those presenting prepared discussions had been chosen from the west, ample op-portunity for any of those present wi shing to speak would be provided in the form of open discussion periods.
The Agenda of the Conference accompanies this report as Appendix
B.
3.
Section 3
F 0 U N D A T ION PRO B L EMS
FOUNDATION CONDITIONS IN WINNIPEG AND 11@w.:DIATE VICINITY
by W. F. Riddell
Winnipeg seems to have gained the rather dubious
reputation of having douotful and difficult foundation conditions. This reputation is not warranted. Good foundations can and are being constructed for all classes of buildings from medium cost residences to major commercial and industrial projects. If good foundation practice is observed, then adequate, trouble-free support should be assured to a structure at a cost reasonably in keeping with the total cost of the structure.
WinnipeG Soil Conditions
The site of Winnipeg city is part of the bed of old Lake Agassiz, which thousands of y ear-s ago covered a great part of ｾ｡ｮｩｴｯ｢｡ Province. Evidence indicates that, at one time, water to a depth of over 500 feet covered the city site. Great quan-tities of mineral sediments from in-flowing rivers were deposited in stratified layers on the bottom of this lake. With the re-cession of the northern ice barrier and gradual release of the impounded water of Lake Agassiz, the site for the future city of Winnipeg was provided.
Prair ie grade, the bed 0 f the 1ake , in Winnipeg averages
60 to 70 feet above limestone bed-rock, which slopes downward slightly from the south to the north boundaries of the city. At the south boundary the soil depth is 4C to 50 feet and at the north boundary, about 5 miles away, the depth is 75 to 90 feet.
Be-tween the surface and bed-rock are found typical layers of soil, which often vary considerably even over a rather limited area. These layers ana the bearing values permitted upon them
by
the Winnipeg Building Coae are shown in Figure 1.FIGURE 1
(a) APPROXIMATE WINNIPEG SOIL CONDITIONS
(Depths of strata quite variable) Layer
6 ino=4 ft. A treacherous soil Remarks Much organic matter
Normally dense, firm
Often soft and soupy Fairly dense material
Mixed grave19 boulders; may have artesian water Good foundation soil
Good foundation soil
ｄ･ｮｳ･ｾ firm layer. Soil somewhat similar to Go
2 - 4 ft.
2 ｾ 4 ft.
1 - 2 ft,
5 - 10 fto Hard, cemented gravel
20 ft. average 20 fto average 1 = 3 fto 1 - 3 ft" Total Thickness Depth -
--
" Brown clay Yellow, silty clay Loam Description Silty clay Dark grey to chocolate clay Hardpan Semi-hardpan---'---
...ＭｾＮＬＭ---c
B A I J H D G F E K(b) SOIL BEARING ｖａｌｕｅｾ PERMITTED
WINNIPEG BUILDING CODE
Ｗｾ 30 Determine by load Value Bearing 1 2' 1 2 (Tons per Industrial Building Soil
Soft wet clay, or silt Mixed clay, moderately dry
Blue clay, with no substrata of yellow or brown
Hardpan
Rock (solid limestone) Any doubtful soil
5.
A more detailed description of the various layers is as follows:
(A) Roughly 2 feet of loam with clay subsoil; very sticky
and plastic when wet. This material provides the surface for our gumbo-like mud roads.
(B)
About 3 feet of silty clay. This provides a fairfoun-dation material for light structures so long as it retains its normal moisture. Under moisture reduction, it cracks and becomes brittle, while with abnormal moisture cuntent it becomes very plastic and easily subject to flow.
(C) About 3 feet of brown clay. In its normal state this is
a dense, firm fine-grained, practically impervious layer of soil. It becomes readily plastic with excess moisture, dries slowly but cracks considerably in the process of dehydration.
(D) The so-called Ｇｾｹ･ｬｬｯｷ strip". This is a mixture of clay and silt, mostly silt. It is bright yellow in colour and varies ｩｾ thiakness from a few inches to about 4 feet; 12 to 18 inches is a fair average. It is highly pervious, shrink. and swells con-siderably with varying moisture content, becomes s oft and slippery when wet and fair].y brittle when dried out. This strip is quite frequently intermixed with the brown layer and has been at least a con tri but ing fac tor to muc h of the founda tion trouble in Winnipeg.
(E) Approximately 20 feet of dense dark grey to chocolate
coloured clay. ｩｖｾＸｮｙ of the larger Winnipeg buildings have f'o un-daticns in this stratwn. Where rationally designed, conservatively loaded arid with moisture co nt e nt of the soil not unduly changed, such foundations have in general been highly satisfactory.
(F) Some 20 feet of dense clay of the type ｣ｯｾｮｯｮｬｹ known
as blue clay. Its characteristics are similar to that c'f (E). The clay content of both layers
(E)
and (F) is over 80 per cent, with colloidal clay nearly 50 per cent. Normal moisture content is somewhat over 50 per cent.(G) About 2 feet of sandy, grey clay material containing
ground-up limestone and some boulders. Usually this stratum
carries consia.erable water, but not often in sufficient quantities to cause serious trouble. The bottom of this layer is the usual limit to which an auger boring can be carried.
(H) About 2 feet of material somewhat similar to, but harder
than (G), containing more crushed limestone and embedded bou l
c
er-s 10 to 30 inches in diameter. For want of a better name, this mayis a very and containing Its crushing concrete, It can be be classed as semi-hardpan.
(I) Five to 10 feet or more of hardpano This
dense ｲｲｾｴ･ｲｩ｡ｬＬ sometimes described as boulder clay a high percentage of broken limestone and boulders. strength in its normal state is that of poor quality but a piece iwnersed in water disintegrates readily. excavated with a hand pick.
(J) Layer (I), or hardpan may extend to limestone be d-ir-o c k , but a water-bearing layer of uncemented gravel and boulders
several feet in depth may be encountered. The water is often found to be under considerable pressure and for concrete piers going to b e d-cr-oc k there may be serious difticul ty in controlling the water flow in an excavation.
(1\) The limestone rock may be tissured and fractured to a
considerable depth at times. Due care must therefore be exercised that the solid limestone bed has been reached when using the al-lowable bearing value for this material.
Foundation Horizons
Winnipeg has four commonly used foundation horizons9 the last three of which may be classed as good to excellent. The first is always doubtful. These are:
(1) Any elevation" in or above the "yellow strip"
(A - D)
(2) The grey-chocolate, or blue clay strata (E or F) (3) Hardpan (I)
(4) Limestone rock (K)
The foundation conditions presented by these various horizons may be considered in detail.
(1) A foundation on soil in or above the so-called "yellow ｳｴｲｾＢ｣｡ｮｮｯｴ be classed as stable, and affected during its lii'etime solely by normal settlements. These soils change in moisture content quite readily illld frequently in very localized areas, causing differential swelling ffild contraction in these
areas. Lightly loaded footings of the same foundation" e.g0 residence footings, may move vertically in opposite directions.
Spread footing foundations in or above this "yellow strip" are those which have caused nearly all the foundation trouble in Winnipeg and provided most of the extensive repair
7.
work required, mainly on better class homes and on apartment bloCKS, churches, schools, etc.
There are only two satisfactory cures for this trouble-some condition:
(a) A rigid foundation unit, or (b) Deeper foundations
(a) When a rigid foundation, constructed as a unit, without
separate interior footings, is subjected to differential moverrent ,
the structure rotates as a unit and there is no damage to the
superstructure. This type of foundation is becoming commonly used, employing steel beams from wall to wall of basements to support the first floor in residence ｣ｯｮｳｴｲｵｾｴｩｯｮ especially, and
re-inforcing the basement walls and their footings to act substantial-ly as a single unit. For larger buildings this method is usually not practicable.
(b) Deeper foundations imply proper spread footings in soils
(E) or (F), or less ｣ｯｭｭｯｮｬｹｾ the use of bored or driven piles. An arrangement to compensate for differential motion of interior footings is the use of variable length ｰｯｳｴｳｾ in which a screw jack arrangement is incorporated in the post. By checking with datum points on the foundation walls and posts, all points may be kept approximately level by adjustment with the jack, as differential settlement of the posts takes place, so that minimum structural damage occurs. This requires regular checking by an interested party, usually the owner. This method is a maintenance arrangement and cannot be classed as a satisfactory solution of a foundation problem.
(2) Foundations in dense clay layers (E) and (F) may be: (a) Spread footings
(b) Driven piles (mostly timber) (c) Spread-bore piles (concrete)
These latter are about 14-inch auger bored holes, belled out at the bottom in conical shape by a special tool to about
twice the 'hole diameter in order to obtain sufficient bearing area. 1hey are not considered reliable for permanent footings.
(3) Foundations on hardpan are obtained by using: (a) Driven piles
(b) Auger bored piles
(c) Auger bored piles belled out at hardpan, which may be classed as piers.
(a) Driven piles are mostly timber, driven to refusal with automatic hammers.
(b) Piles which are bored only without belling will not likely
reach true hardpan but reach auger refusal in the semi-hardpan layer. Experience has shown that this gives satisfactory results for the accepted pile loadings ..
(c) Auger bored piles with bottoms belled on hardpan vary
from 26 to 60 inches in diameter in the shaft and are belled out to the required ｳｩｾ･ by hand to rest ｾｮ firm hardpan. Water from the "yellow strip" or in the layers just above the hardpan may cause considerable trouble at times. Normally, pumping can take care
of the inflow and belling is accomplished without undue difficult Yo (4) Foundations on limestone rock are usually of the pier type, machine bored or manually excavated to hardpan. From this point, excavation is completed by hand, using jack-hammers of picks, until the limestone is reached. The most serious trouble likely
to be encountered is water in volume under the hardpan.
All bored piles and bored piers are reinforced with ｶ･ｲｾ tical steel rods and horizontal ties, usually placed in the hole before any concrete Is poured. Concrete is generally poured in from the top of the hole until the required elevation for the pile top is reached.
Particular Problems
The foundation conaitions and procedures thus far des-cribed are those most commonly encountered and accepted as
standard in current practice, in and immediately adjacent to the City of Winnipeg. The soil conditions are reasonably constant
over most of the area, excepting adjacent to the river banks. Herey
the upper layers of the soil predominate and cause rather hazardous conditions by reason of their more pervious and unstable nature. During spring floods, water under pressure saturates these soils for a considerable distance from the bank and then drains gradually
as the river level drops, first from the flood stage and then again in the fall as the water level is lowered for the winter by opening the control gates of the Red River dam below the City.
Special precautions must be taken with all river bank foundations, or trouble invariably occurs. A number of fine old residential buildings in these locations have already been torn down, partially due to the high cost of foundation and structural maintenance in these areas.
9 •
One of Winnipeg's perennial problems is a satisfactory solution for a low cost residence ｦｯｵｮ､｡ｴｩｯｮｾ to protect adequately the cheaper class of residence construction and to prevent the
structural damage which almost invariably occurs wi th the ordinary non-rigid foundation unit and interior footings. So ｦ｡ｲｾ not much of real value has been accomplished except to stiffen foundation walls with a minimum of reinforcing ｳｴ･･ｬｾｩｮｳｵｦｦｩ｣ｩ･ｮｴ to provide rigid foundation units.
In better class ｣ｯｮｳｴｲｵ｣ｴｩｯｮｾ more basement floors are being kept clear altogether of any direct clay support by using beam and sl ab construction 0 n top of c onc nete piles. This
eliminates the possibility 'of basement floor heaving or settle-ment due to variations in moisture content in the clay directly under the slab, which is one of the common Winnipeg difficulties.
Foundation underpinning and repair work on shallow foundations is almost a major industry in ｗｩｮｮｩｰ･ｧＭＮＭｾ｡ｮｹ of the older spread footing foundations are being affected, both by settlement and slow changes in soil moisture content, with the general trend in the direction of moisture reduction. With so many ｦｯｵｮ､｡ｴｩｯｮｳｾ and particularly ｲ･ｳｩ､･ｮｴｩｾｬ ones, still in a
dubious condition, the foundation companies in Wiru1ipeg will have no lack of work in the foreseeable future. Practically all under-pinning support is now of the bored pile type, to h ar-dpan , and ｮｾ｡ｲｬｹ all parts of the city are equally affected. It is hard to convince home owners to spend more ｴｨｾｮ a nominal sum for foun-da tiun support. Most of them pr- efer to take the chance that nothing serious wi11 happen in their particular case, and quite frequently the unhoped-for happens.
'In the case of lighter foundations it looks rather doubtful if any ｨ｡ｰｰｹｾ simple solution of this probleill will be found. Better ｦｯｵｮ､｡ｴｩｯｮｳｾ at somewhat increased ｣ｯｳｴｾ seem to be the only logical answer.
Except for lighter foundationsy Winnipeg has a good
reputation with respect to its foundation support, especially for construction within the last two decades. There is now little reason for any serious foundation trouble on new construction if normal precautions are taken to see that good foundation practice is followed. Winnipeg engineers and architects should now be
sufficiently aware of local conditions to make reasonably sure that all important new c mstruction is adequately protected in this re-gard.
Section 4
POUNDATION CONDITIONS IN SAShATCrlBWAN
_ _ _ _ _ _ _ _ _ _Ｚ Ｎ Ｎ Ｚ Ｚ Ｚ Ｎ Ｎ ［ Ｎ Ｚ Ｚ ［ ［ Ｎ Ｎ ［ ［ ［ ｣ Ｍ ］ Ｍ ］ Ｇ Ｍ Ｂ Ｍ Ｎ Ｎ ［ Ｎ Ｎ Ｚ Ｚ Ｎ Ｎ Ｍ Ｚ Ｚ Ｚ Ｚ Ｍ Ｇ Ｍ Ｍ Ｍ Ｍ ｃ Ｍ Ｚ ｾ ｟ ｟ Ｚ ｣ Ｚ Ｇ ｟ ｟ Ｇ _
by Robert Peterson
In considering foundation conditions in Saskatchewan9
mention should be made of ｴｨｾ general geology of the area. General-ly speaking, in the populated area of Saskatchewan, varying depths of glacial deposits overlie the bed-rocK formation but bed-rock out-crops in some areas and also along the banks of the deeper river
valleys. For the most part the bed-rock is of sedimentary origin and consists of soft shales and sandstones, the shales being almost clay-like and the sandstones no more than weakly cemented sands. The
glacial deposits are in some areas unsorted, lliid in other areas they are sorted by wind and water.
In the Saskatoon area very dense unsorted glacial clay oc-curs in the river bed and beneath the low-lying downtown area. At higher elevations the glacial material is somewhat sorted possibly due to the formation of old laKes, with the result that fine sands, silts and clays are common. The unsorted glacial clay is ar. excellent foundation material and foundation pressures of 2 to 4 tons per square foot are c ommori where structures are erected on this type of material. It is believed that during the construction of the Broadway Bridge
(the ｾｩ･ｲｳ of which are designed for Ｓｾ tons per square foot) an
eccentric loading produced a foundation stress of about 7 tons per square foot with no detrimental settlement.
The Regina Plains region is probably our best example of sorting by water and the entire area consists of a highly plastic laKe clay. Generally speaking, this is a fairly good foundation material if foundation stresses do not exceed 2 tons per square foot, and if the footings are placed sufficiently deep so that the underlying soil does not change in moisture content due to seasonal cycles of wetting and drying. The most troublesome property of this material is its high change in volume with changes of water ccntent, and consequently, shallow footings and the basements of homes are damaged by differential movement due to changes in water content of the soil either annually or over a period of years. This same problem has been described by Professor Riddell as being troublesome in the Winnipeg area.
Considering the province of Saskatchewan generally, it would seem that the farm home located in highly plastic lake clay is by
far the most important problem. In many cases a farmer constructing a home does not have the information that is available to the city dwellers and quite frequently serious mistakes are made in dealing
11.
with tais type of soil. Frequent inquiries are made at the
University of Saskatchewan in connection with such probloms. Only recently a farmer ｲ･ｰｯｲｴ･ｾ that it was necessary to cut 4 inches off the interior column in his basement because he thought that the outside footings had settled the same amount. The truth of the
matter was that a cistern in his basement had saturated the material below the footing of" the interior column and had caused 4 inches of swelling. ｍｩｳｾ｡ｫ･ｳ such as this are all ｴｯｯ｣ｯｾｮｯｮ and it is felt that some agency such as the Division of ｂｵｩｬ､ｩｲｾ Research of the National Research Council should tackle this problem and attempt to prepare a bulletin dealing with building construction on this very treacherous clay soil.
Section 5
(a) FOUNDATION CONDITIUNS IN
THE
EDMONTONAREA
by I. F. Morrison
The general building ground at Edmonton consists of two general classes of soil: (a) Glacial deposits, primarily boulder clay, which occur generally in the region except in the river valley; (b) River ､･ｰｯｳｩｴｳｾ which are essentially non-cohesive, including silt, and wnich rest on bed-rock which, at the City Power Plant location, is shale, or hard clay, with a high bentonite content.
At the Government grain elevator, wooden piles were driven and in one spot a nest of boulders ｷ｡ｾ encountered. The clay came up between the piles to a beight of about 3 feet. The speaKer believes that it does not pay to drive piles into this clay.
There are also, in various parts uf the city, "soft spots" which are evidently old sloughs. These have relatively poor bearing capacity and the ground just belpw the surface is quite wet indicating that the sloughs, although dried up, have not been !ully drained. The conditions of the building ground vary from place to place; sand and silt pockets occur here and there in the boulder cla]. Bed-rock may be higher up than just the bottom of the river valley which ｾｳ roughly 200 feet below the general level of the city. An outcrop occurs part way ｾｯｷｮ the bank below the Macdonald Hotel.
In the valleYi at the City Power Plant location, there is a layer of silt about 30 feet deep lying on a layer of sand which rests on a thick bed of gravel. The gravel in the river
bed c han ne L is relatively thin. When the pump-vhous e at the plant was built, a yit 20 feet deep into the bed-rock was excavated. Due to the obviously high swelling value of the shale, it was thought that the material would make a very tight contact with the thick bottom slab of the structure; nevertheless, small pockets were excavated and filled with sand. To these a
manometer tube was COllilected. Water has been observea to stand at a height in this tUbe very nearly at the level of the river, indicating that the building is supported on a thin film of water under considerable pressure.
13.
( b)
by R. H1. Hardy
A procedure has been evolved for u.axLng foundation investigations for bUildings in the Eamonton area. This pro-cedure has resultea from a survey of foundation conditions in Edmonton, starting in 1945, and extending over several years. This survey was financed by the National Research Council with the work being done in cooperation witn a number of local con-tractors and the Edmonton Branch of the Engineering Institute of Canada.
The general investigation shows that the great major-ity of troubles encountered with foundations in the area are caused by changes in mo Ls t.ur e content, resulting in the shrink-age or s we Ll Ln.t of the soil immediately below the base of
footings. Some trouble was reported with seepage water which was also due to the effect of drying of the soil to a aepth of the same order as that of the foundations.
The general soil conaition in the area consists of a boulder clay to a depth considerably greater than that which is appreciably affected by foundation loadings. The clay is some-wh at variable in character. It co ntains sand pockets and also
layers of rOCK which are frequently cemented t og e t.he r with hard clay. The clay varies in plasticity from medium to nighly
plastic.
It is possible to identify the characteristic structure of a soil which has been previously dried out since its deposi-tion. This is true even though the grounawater table at the present time may be practically at the surface of the ground. Such dried soil m8.Y be identified by a "nugget structure". 'I'h e significance of this term can readily be appreciated by ｯ｢ｾ
serving the structure of a piece of clay which has been allowed to dry in the air after being removed from an excavation.
Positive evidence has been secured that the surfaces between adjoining nuggets of a clay having such a structure are not sealed off to the passage of water when the material later tahes up water after having been dried. The result is that seepage water can move through the soil along these sur-faces at a rate that is many times greater than it could move through the natural soil. This ·fact results in frequent cases of trouble with seepage water in basement excavations and has also caused trouble from seepage into basements after com-pletion of the buildinGo
Damaging movements may be produced in buildings in the area by either shrinkage or swelling of the soil immediately below the foundations. The essential point, therefore, in
examining condit Loris a t a potential building si te is to determine the d e pth to which the foundation should be carried to be reason-ably sure that no appr-e c La b Le change in moisture content will occur below the foundations. Evidence has been collected of previous drying to a depth of 10 feet, but in general it will vary from a depth of 2 feet down to a maximum of about 10 feet.
In arriving at a safe bearing pressure, Terzaghi's solution is used, assuming that the material is a saturated cohesive soiJ. Safe bearing pressures are ｲ･｣ｯｄｾ･ｮ､･､ on the basis of about twice the unconfined compressive strength of the soil as determined from laooratory unconfined compression tests. An attempt is made to predict the worst moisture content that may exist below the foundations from an analysis of a soil
moisture profile as determined during a survey of the conditions at a site, and also by using the moisture content-compressive strength curve as established by unconfined compression tests on the material at various moisture contents.
15.
Section 6
DISCUSSIGN UN F'CUNDATIUN PROBLEMS
Professor Morrison initiated the discussion on this topic by making a brief comment on a German paper by Hruban en-titled "The Yield Point in the Semi-infinite Solid in the Case of Local Loading". An abstract of the paper was read and it was summarized as follows:
The paper is of a theoretical or technical character and mathematical equations are developed for the transition of the material below a footing from the elastic to the plastic state. Two plastic regions develop, ｢ｲ｡ｮ｣ｨｩｲｾ out from each edge of the footing. These regions increase in size due to increased loading on the footing, until they merge on the vertical centre line. Further increased load causes continuous settlement of the foot-ing due to plastic flow of the material. This is quite apart from the development of the usual rupture shear surfaces and occurs at a load considerably below the rupture load. The per-missible unit loading is defined as the unit loading which just causes the two plastic regions to meet.
Two single formulae, each having three terms which in-clude coefficients taKen from tables, and which take into account the size of the footing, its depth, the Coulomb cohesion, the specific weight of the soil, and the angle of internal friction, are given. These enable one to compute directly the safe bear-ing capacity of the soil as defined above. The values so obtained are reasonable and agree well with current practice.
In additi6n, it is pointed out that the angle of inter-nal friction is not a soil constant, but rather a parameter which depends on the stress conditions unaer which it was determined. In using it, therefore, the value corresponding to the stress conditions which fit the application ｾｨｯｵｬ､ be used. The value for ¢l which corresponds to the condition of plane strain should be used for retaining walls and strip footings; ¢2 should be used for spread footings, rectangular, circular, etc. It is the value determined by the triaxial test. ¢3 is determined in the triaxial test, but by the process of increasing the mantle
pressure to failure rather than the axial pressure. It is easy to obtain the value of the other two values of
¢
when one is given. There may be a considerable difference in these three values for the internal friction.Mr.
McRostie expressed his interest in the papers
which had been presented on prairie foundation conditions,
and mentioned some problems encountered in Ottawa.
For some time the need for settlement observations
on actual structures has been recognized, and over the last
five years several buildings have been under observation.
From the results of these observations, and from the results
of consolidation tests recently performed on typical soils,
the conclusion has been reached that the computed settlements
are c9nsiderably less than those actually observed.
This
phenomenon has been observed by others, and some have
｣ｯｮｳｩｾdered that the effect of pre compression of the clay soils
might be a cause.
As far as can be
ｴｯｬ､ｾthe Ottawa clays
were not pre compressed in their past history, but there may
have been ancient drying which would have had a similar effect.
It is hoped at least to obtain a constant relationship, if one
exists, between computed and actual settlements.
The other important point gathered from settlement
observations is the lack of agreement between measured
､ｩｦｦ･ｾrential settlements and signs of failure.
On some brick
buildings differential settlements of
005inches have occurred
between points 15 feet apart with no cracks in evidence where
at other places in the same building, differential settlements
of
002inches have resulted in cracks at least
Oq2inches in
width.
This seems to bear out the conclusions of laboratory
experiments by observers from Palestine that brickwork fails
in shapes which are often inconsistent with settlement.
The
strength of mortar seems to be a major factor and other
work-manship factors are importanto
Settlement observations in the past were performed
by optical levelling methods but this method does not lend
itself to observation on interior points of a buildingo
To
overcome this difficulty a simple hydraulic levelling apparatus
has been designed by Mro Peckover, patterned after other
equipment in useD
This hydraulic equipment is now in use and
is very effectiveo
Any mention of settlement observations raises the
question of bench markso
It has been found extremely
diffi-cult to obtain satisfactory bench marks in large areas in
Ottawa covered by compressible deposits over 80 feet thick.
The only alternative is to carry in a line of levels for
three-quarters of a mile from bench marks on rock, at considerable
expenditure of time and some loss of accuracyo
Any suggestions
17.
In Ottawa there is, as in Winnipeg and Edmonton, con-siderable damage done by changes in soil volume due to moisture content variations in the soil beneath light ｾｬｩｬ､ｩｮｧｳ with shallow foundations. The causes of these moisture content variations would ｳ･･ｾ to merit more examination. Everyone
recognizes that seasonal variations in the water table can cause local differences in moisture and hence differential ｭｯｶ･ｭ･ｮｴｾ
but the general lowering of the water table in a whole city due to increased run off from impervious construction co e s not seem to be as obvious a cause of differential settlements; it would rather tend to cause total settlements. Any actual observations on water table variations would shed needed liGht on this problem.
In Ottawa it is definitely felt that vegetation can be and is a cause of serious moisture fifferences and hence dif-ferential settlements. The effect of sewer cuts
ii
not as well determined but there are signs which point to the fact that poorly backfilled trenches, all on suitable grades and all connected to an ｯｵｴｬ･ｴｾ lower the water table across the front of buildings and cause differential settlements between front and rear.It is interesting to note that the effect of an im-pervious cover such as a paved yard or driveway in raising or lowering the water table is not universally agreed upon. Cooling observes in Great Britain that a walk placed around a house in-creases runoff and recommends it as a means of preventing a rise in moisture content of the soils beneath footings and resultant swelling and cracking. On the other ｨ｡ｮ､ｾ it is widely observed in highway practice that a rise in moisture content of soils be-neath an impervious pavement actually occurs and decrease of evaporation losses is considered the cause. It is possible that each view mijY be correct under different conditions.
Remedies for settlements due to moisture content
changes a:ce still c e Lng sought. An inexpensive method of short bored piles is to be tried in an effort to ｴｲ｡ｮｳｦ･ｾ the load to a d.epth 10 feet greater than ｵｳｵ｡ｬｾ where changes :!-n moisture do not occur. An emergency remedy is the ｡ｰｰｬｩ｣｡ｴｾｯｮ of water to the soil merely by watering in holes dug to footing levelj
or even on the surface. Cracks often close 60 per cent over-night on the addition of water by this method but it is not a cure. The possibility of killing or discouraging tree roots or other vegetation by means of chemicals added to this water is being explored. In many cases where damage is being done by a large tree, owners will prefer to repair the building continually rather than destroy the tree which is often the only shade.
Hence any method which would spare the tree and yet save the foundation would be welcomed.
Mr.
McRostie concluded his review of these problems encountered in Ottawa with a hope that some of the points he had mentioned would raise some discussion.Mr. Peckover supplemented Mr. McRostie's remarks with a brief description of the soil responsible for most of the problems which he had mentioned -- the Leda Clay. This is a marine deposit,
inorganic, and of high compressibility. Some of its characteristic properties are a water content of 35 to 80 per cent, a liquid limit of 40 to 70 and a plasticity index of 20 to 40. The water content is almost always higher than the liquid limit. The unconfined compressive strength ranges from 17 pounds per square inch in the "undisturbed" condition to 1.5 pounds per square inch after re-moulding at the same water content, and the soil is therefore extremely sensitive to disturbance.
This data has resulted from a recent study of samples of this 2aterial taken to a depth of 35 feet.
Dean Hardv made reference to the behaviour of a uniform silt material in ｴｨｾ vicinity of Kamloops, British Columbia. The material was a loess and existed in its natural state at a dry density of only 65 pounds per cubic foot and at a natural moisture content of 5 to 8 per cent. The material was characterized by a very uniform particle size of about 0.01 millimeter. Settlements were observed in a number of buildings at one location on this material, sufficient in some cases to cause the complete collapse of walls. The actual amounts of differential settlement in build-ings about 30 feet wide by 150 feet long were from 6 to 12 inches.
The topography in the area was characterized by steep slopes resulting in rapid runoff. "Sinkholes" had also been ob-served to develop in the area. The usual explanation of "sink-holes" by geologists is that they are the result of underground erosion. However, at this site investigation showed the existence of holes almost at the crest of high shoulders in which it would be impossible to contemplate their formation by underground
erosion.
An investigation at the site showed that the develop-ment of the "sinkholes" and also the settledevelop-ment of the buildings was the result of a reduction in volume of the soil following
appreciable amounts of surface runoff water coming in contact with the soil for the first time in its geological history. Laboratory consolidation tests showed that the addition of water to an un-disturbed sample of the soil could result in a settlement of the order 1-3/4 inches per foot depth of soil becoming saturated.
The situation in the area seemed to be that a thin skin of weathered soil protected the underlying dry loess from water. A penetration of this skin protection by an animal hole or an auger hole or some such similar mechanism might result in surface water flowing underground at that spot. The surface water would saturate the underlying soil which would then consolidate under its own
190 The settlements of the buildings were the result of the surface runoff characteristics being altered when flat areas upon which to place the builuings were dug out from side hills. In so doing the surface soil was removed and the runoff characteristics naturally altered. The result was that surface water in these flat areas tended to flow down into the soil rather than to run off. The resulting increase in moisture content of the underlying soil resulted in the process of consolidation occurring, which permitted settlement of the buildings.
Mr. Peterson mentioned an experience which the P.F.R.A. had with this same loess soil at Kamloops.
About one year ago they constructed a small irrigation project on a silt bench adjacent to the South Thompson River. Shortly nfter the water was turned into the system, a very exten-sive washout occurred beneath one concrete structure and another area in which a turnout was locateu subsided approximately 8 inches over an area of about 75 feet in diameter. The engineer in the area felt that there must be extensive cavities in the underlying material. The material before irrigation apparently was in a very dry loose state as it probably had been deposited by wind. After saturation the material consolidated, accounting for the subsidence.
" Similar experiences hav e oeen described by !Vir'. W. J.
Turnbullv • He describes settlements of the ground surface of 2 or 3 ·feet after 15 years of irrigation on loess soil.
Dr. Allan contributed a few comments on the application of geology to foundation problems. In the prairie provinces, foun-dations are chiefly associated with unconsolidated ､ｾｰｯｳｩｴｳＬ the originy composition and methods of deposition of which are
im-portant to the foundation engineer. There is a need f'or- the study of Pleistocene and ｒ･｣ｾｮｴ deposits and the mapping of these
deposits of various originsy particularly in Alberta. Only a start
on the study of these deposits has been made by the geologist and by the soils engineer.
In the Winnipeg.area, the foundation problems so clearly described in the paper Given by Professor Riddell occur in quite uniform deposits in the basin of Lake Agassiz. The deposits ｯｵｴｾ
side of old Inke basins are much more complex and less uniform from east to west across the prairie provinces .
.::..
Turnbull, W. J.: "Utility of Loess as a Construction iVlaterialll ,
Proceedings of Second International Conference on Soil Mechanics and Foundation Engineering, Vol. 5, page 97, Rotterdam, 1948.
made at
He
There are many foundation problems which c annot yet be fully explained, but wnich are related to the variation in 6e-position, post-deposition movements, and composition of the
unconsolidated aeposits and the underlying relatively soft bed-rock. In Alberta, there are at least two Kinds of bentonite. There are perched water tables; there are burie6 eskers and old erosion surfaces, to mention only a few of the problems related to foun-dation studies.
In Alberta many coal seams are ｴｨｩ｣ｫｾｲ where they out-crop along the sides of valleys than at bO or 100 feet in from the outcrop. This suggests movement since the valley was eroded.
Dr. Allan wished to support strongly the suggestion
by Nil'. McR ostie that there should be bench marks established
various points in the prairies to record any change in level. stated that it is a fact that there has been uplift of several hundred feet in south western Alberta in post-glacial time, and was of the opinion that there are tectonic movements present now in parts of Alberta, especially in the proximity of the foothills belt, and that these movements might be indicated by precise
21.
Section 7
H 1 G H WAY PHCBL.L:.lilS
STATUS OF HIGHWAY SOILS INV.c.;STIGA'rION ｮｾ N!ANITOBA
. by Go B. Williams
I am very pleased to have the opportunity of attending this Conference. I feel, however, that I am someNhat out of my class, since for the last four years I have been out of direct contact with the soils work undertaken by our Department. I ､ｯｾ however, retain my interest and can see the effects of the inves-tigational work undertaKen. My remarks are oased on an evening
discussion with Messrs. Sharpe and Jonecky of the Materials Section. I have a feeling that investigational work on soils in our Department has lagged. Our procedures and information are much the same as they were four years ago. There has been little ad-vancement. There is one reason for ｴｨｩｳｾ and that is that we have been so busy undertaking actual construction projects that we have been unable to cievote any time to investigational work. Fo r the past four years we have done nothing but attempt to apply the ｰｲｯｾ cedures developed ･｡ｲｬｩ･ｲｾ and to utilize the information gained from previous investigations and study.
Soil Survey
Our soil surveys are now conducted in almost exactly the same way that they were undertaken four years ago. Our procedure roughly is to take soil borings along the centre line9 at a ｭ｡ｸｩｾ
mum spacing of bOO feet and to a depth of at least 2 feet below the anticipated cut line. Soil samples are t ake n and submitted to the testing laboratory. The recurrence and depths of layers of the type soils are recorded for each boring. A new set of soil samples is taken at a maximum distance of every three mileso Earlier9 it
was our hope that we would be able to utilize the agricultural soil ｭｾｰ and obviate the necessity of the field boring. The Province has relatively recently been mapped in detail. In order to use
these maps, it was necessary for us to co-ordinate all of the borings which the soil surveys had made for some years before to the agri-cultural soil types. This is a job which we have never c omp Le t.e d , and for this reason the agricultural map can only be used as a general guide when considering preliminary location plans for ｨｩｧｨｾ ways.
Samples from the soil surveys are submi tted to our testing laboratory where a standard physical analysis is made covering liquid ｬｩｭｩｴｾ plastic ｩｮ､･ｸｾ shrinkage limit, volume cha nge, field moisture e q ui va Le nt , and the hydrometer analysis, rreviously it was our hope to eli!'1inate most of these ｴ･ｳｾｳＬ
and possibly substitute the perr.J.eability test and the capJ.lla-rity ｴ･ｳｴｾ in order to utilize the soil classification ｳｵｾｧ･ｳｴ･､
by the Public Roads Administration, To do so meant that lie had to run ｰ･ｾｮ･｡｢ｩｬｬｴｹ and capillarity tests on soils which were in service under our ｰ｡ｶ･ｾ･ｮｴｳＳ and check these against the original laboratory testsa This again is something that we have never completeda I wouldi however, like to know from
this conference if anyone else has made use of this proposed modified soil classification as reported in the Highway
Research Board Proceedings early in 19440
With our present tests we make little or no use of the field moisture equivalenti shrinkage lirr.i t and volume change vB"ues in judging soil characteristicso ａｧ｡ｩｮｾ our present tests do not give us the answers we need, for example, whether or not frost heaving wlll occura Naturally this con= dition is dependent also on drainage conditions and soil
ｳｴｲｵ｣ｴｵｲ･ｾ but we frequently hit a frost boil area and after testing connot be sure whether under=drainage can solve the ｰｲｯ｢ｬ･ｭｾ or whether to excavate and use gravel backfillo If the grade line will ｰ･ｲｭｩｴｾ I usually favour a couple of feet of extra fillo I realize that soil tests alone in such cases are of little value unless ｣ｯｾｯｲ､ｩｮ｡ｴ･､ with field boringsj the profile and drainage9 but it was this problem
which made the capillarity and permeability tests look so attractivea We felt that a little experience in interpreting
the numerical values of these tests would be a great help in arriving at a solutionc
In addition to the tests ｾ･ｮｴｩｯｮ･､ tefore, in the laboratory we also run the standard Proctrr compaction test on the predominant soil typeso If there ure several ｳ｡ｾｰｬ･ｳ
of a clay which have a slightly different appearance in the fieldp but on analysis show the same major characteristicsp
only one Proctor is run for this type; that is, the soils to be covered by a compaction test are selected after the physical analysis is made , and also on a basis of their recurrence in
tne field. On completion of the laboratory ｴ･ｳｴｳｾ the results aI'3 t"I"11Flted and included in the field book of soil recordingso
23.
Soil Reports
For each project a soil report is submitted by the Materials Engineer. in making his report he refers his soil borings to the cross ｳ･｣ｴｩｯｮｳｾ usually in cooperation with the resident engineer for the project. This 1s done at the stage waere tentative embankment grade line and cut quantities are
balanced. In the soils report recommendations include sub-cuts where poor material is encountered, the wasting of unsuitable material (such as some top soils and silts in an excavation area) with the necessary revisions in excavation ｱｵ｡ｮｴｩｴｩ･ｳｾ and sug-gestions for the best possible borrow materials. Areas of shallow fill are recorded where compaction below natural ground line will be required, and an estimate of the quantity is made for inclusion in the over-all quantities estimate. Compaction quantity for one foot in cuts is estimated to be included in the quantities estimate.
In some instances we run into difficulties with compaction in cuts as in an effort to obtain compaction, sometimes by disturbing the soil we produce a condition of ｩｮｳｴ｡｢ｩｬｩｴｹｾ rather than improving the situation. This is a point which requires special consideration and can best be determined in the field at the time of construction.
The specified minimum density for the project is listed for each section, and the optimum moisture. These values, how-･ｶ･ｲｾ are taken with a grain of salt. In the field we are actually obtaining the densities we specify. The optimum moisture content, however, is frequently at variance with what our laboratory test requires. wher e difficulties occur in the field in obtaining the specified density, a sample ｩｾ submitted to the laboratory.
How-ever, we are not using field compaction tests, and usually by the time confirmation, or another value, is received from the labora-tory, the work has been done and accepted because it looks right. TNhere immediate surfacing is proposed, a r-e e ommend at Lon is made as
to the type. Where bituminous mat is to be used, the depth uf base course is recommended.
construction Procedure
Under our grading specificatiuns, provision is made for the remuval and disposal of unsuitable material from the embankment or in the excavation area. In deter:nining what material is un-suitable, the inspector is governed by the soils repurt. With experience, he comes to depend upun u Ls own eye and feel to p Lc k up the unsuitable :naterial identified in the repurt. ＧｩｾｾｬＱ･ｲ･ unsui t-able material is encountered below natural ground line with a light 1'ill to g r-ade, a sub-cut is made and the arnount of the s ub-i c ut is
immediately measured by the inspector before the baCk fill is under-taken in order that the contractor may receive the excavation
In compaction, our specifications call for the placing of fills in a maximum of 12-inch layers up to the top foot, where two 6-inch layers are required. The contractor is required to roll with an approved sheepsfoot, or pneumatic-tired rollerj as requir3d
to provide the density. In our specifications he is required to provide a minimum of one double-drum sheepsfoot for every 40 yards of excavation capacity, or fraction thereof. As mentioned beforej
our specified density is 95 per cent of the standard Proctor
density determined in our laboratory for the ,nain soil types. We do not have very much difficulty in obtaining this. Probably we are not compacting enough. ,We have found, however, that we are obtaining much better compaction than ever before, and we are getting a reasonably uniform compaction. Except for the way the
specification is written in so far as what the contractor has to do, the specified density hos not been changed in four years. It is, however, a long step from the original compaction we required in 19399 when all that was requirea was the operation of a
sheeps-foot rollero At that time on some of our projects on heavy clay, we recorded densities of 67 to 75 pounds per cubic foot; whereas now, for the same soil, we are consistently getting 90 to 95 pounds per cubic foot.
In addition to specifying the density in placing a
minimum requirement for the amount of compaction equipment, we do pay for water added as a contract item. As mentioned before, we do
have some difficulty in correlating the laboratory optimum density with what is the optimum in the field. It usually causes an ｡ｲｧｵｾ ment between the grade foreman and our inspector, and I believe
that I can safely say that the decision is usually made by rolling, to the moisture content at wnich the specified density is most
easily obtained. Our inspection staff has observed that with dif-ferent soils the oontractors seem to get along a little better with different weights of rollers. A further practice sometimes agreed upon by our inspection staff and the contractor is to reduce the depth of layer if difficulty is encountered in obtaining density. Base C'ourse
In considering soil investigations for highway work, it is impossible to omit base courses.
In the field of base coursesj in the last three years the
opinion of the Department has changed somewhat from our original idea of a well-designed, stabilized mix. We have now reached the point where we are pretty nearly ready to accept anything we can get locally. Our specifications as to grading vary considerably for every job we handle. In some instances we call for crushed material because it suits the local pit; in others we just call for screening. Our usual practice is to obtain samples from the local pits, and where we get an unexpected bid on an untested source we
25.
go out and sample that pi t and then try to l)roduce the mos t stable mix we can from that aggregate SOJrce. This sometimes gets our inspection staff in quite
a
jam. They really lIs we a t it outll alongwith the contractor to ｾ｡ｋ･ the thing work. In addition, it some-times gets the r-ost of us involved from an adminis'trative point of view, with squabbles over whether extras should be allowed be-cause the pits 6id not turn out as ｰｬ｡ｮｮ･､ｾ or whether all the work finally necessary to provide a base course was actually ｣ｯｮｾ
templated wne n the contract was drawn. ',I';hi18 this causes a lot of trouble, I believe it is the only thing we can ao. With the
quantity of base course .nat.er La I we are now using we cannot afford to pass up any local deposit of material which has a possibility of being more stable than the material in the embankment itself. I
am qUite convinced that we will have to go still further and utilize other methoas of stabilization than our present standard process of using a mixutre of clay and gravel or sana. At present we have a
job under consideration wuich will require some 9U,OOO yards of
base course. At an averape haul of 6 miles we can obtain blow sand, or at 10 miles we can obtain quantities of sand plus small quantities of stone; or at 28 miles haul we can obtain a graded aggregate, It has not been decidea yet which we will use, but I do know that we
cannot afford to pass up the deposits at the shorter haul and take only the 8raded aggregate. If we did so I am quite sure that with-in five or six years from now, when other construction projects open in that area, we will have to use the sand pits, so we might as well use sand now with a short naul .
I will not attempt to give you any standard for depth of base course. The use of the cone bearlng test on our subgrades to arrive at base course design is another investigation we have
neglected. At present our maximum depth is 12 inches for flexible pavements, vVhere we feel that more depth of base is required due to soil conditions, drainage and traffic, we use an 8-inch reinforced concrete pavement instead of flexible pavement and base. Our
reasoninr, is based on the fact that these are the areas in which we llave limited gravel resources, and the rigid reinforced slabs make DOSt effective use of the minimum quantity of aggregate.
ｃＨＩｬｾｃｌｌｊｓｉｏｎ
Fr-om my r-emar-ks one might gather that 1 am pessimistic about the progress of soils investigation in our Department. 1 feel that we have not provided enough staff to carryon investi-gations along with cunstruction. There is one Lt1ing, however, that has impressed me in our last few years of construction work and that is the universal acceptance of soils investigation as a normal part of highway construction. Compaction and optimum'moisture are everyday facts to any grade foreman. tie measures moisture content by the feel of the soil and has it pretty well gauged to fit his own equipment. lie knows that certain soils will not compact and
oisposes of them outside the embankment proper in flattening
slopes. For different soils he changes his compaction equipment. While he may have opinions of his own on the need for it, in all
instances he accepts the fact that not all soil excavated is suit-able for fill and discards it as directed.
My point is that while we have lagged on new investi-gation, at least we have r'e a che d the stage where soil studies are accepted as part of the design and the results incorporated as normal construction procedures.
Section 8
SOILS PROBLt£i.1S ｉｬｾ BIGtfNAY CONSTHUC'l'ION .Ll\ SAShATCHEWAN
by
w.
E . 'v'iinni toyIn dealing with the matter of soils problems as they are encountered in highway construction in the Province of Saskatchewan, 1 may say that our problems are not nearly as difficult as they are in most other provinces. This is because of our low annual rain-fall and predominance of good subgrade soils. Nevertheless, we still have soil problems, such as they are, and special precautions have to be taken in h8ndling some soils.
(1) Subgrade Soil Moisture
Low as our annual rainfall may be, we still have to contend with excessive subgrade moistures. In the case of gravelled roads, excessive ｳｵ｢ｧｲｾ､･ moistures accumulate in the spring of the year to such an extent that heavy truck traffic tends to cut up and rut the low-lying sections of roads so that all surface gravel is
churned up with the mud. The result is that we are forced to ban for a time all heavy truck traffic on our highways during a period when the ground begins to thaw in the springtime. This accumulation of moisture in the subgrade of roads that are paved also weakens
the structure; the pavement would fail badly if we allowed heavy truck traffic to continue travelling on it during the spring ｢ｲ･｡ｫｾ up.
During the ｓｕｩｬｾ･ｲ and fall of the year, however, the
evaporation of ground moisture is generally far greater than the ac-cumulation of such moisture, with the result that the subgrades
become quite dry. Under such conditions our paved roads function very well with a minimum of base course construction, but the
gravel roads become very rough and dusty. Due to lack of moisture it is a difficult task to properly maintain gravelled roads.
(2) Slough-Bottom MUCk and Organic Matter
During the early construction of roads in this Province, very little attention was given to the matter of selecting soils.
In the early days, the elevating grader was a popular piece of equipment for building dirt roads. In using such a piece of ･ｱｵｩｰｾ ment there was no means of carrying away undesirable soils or
sections of road where there was a great deal of bush leaf iliold, or in depressions containing accumulations of washed-in organic matter, the undesirable leaf mold and organic matter would be
elevated and dumped on top of such same materials already existing in place and then this was sandwiched with a light cover of good suil that was scooped up from the bottom of the ditch. Such sections of road are still giving us trouble even though some of them have been rebuilt to some extent. Where sloughs became dry dJring the summer, the slough-bottom muck was also dumped into the core of the road. A great aeal of such construction was done on municipal roads which were later incorporated into the provincial highway system. Where such sections of r-oad are at a higher
elevation and remain dry, we are troubled with the breaking up of surface crusts in the case of gravelled roads and bituminous
ｳｵｲｦｾ｣･ｳ in the case of paved roads. This is due to the springing action of such subgrades under heavy loads. In low sections
where moisture accumulates we are troubled with frost boils in the spring.
(3) Alkaline Soils
Alkaline.soils are very innocent-looking9 whether they
occur in an alkaline area, or whether they border a stagnant slough in a non-alkaline area. These soils, containing a large percentage of deliquescent salts, have often been unsuspectingly incorporated into the subgrade. Such soils simply will not dry and form soft spots on the road. We have had to dig out the spots or provide extra reinforcement over long stretches of such soils.
(4) Frost Boils
In spite of our low annual ｲ｡ｩｮｦ｡ｬｬｳｾ we still have
numerous frost boils occurring during the spring thaw. A wet fall will aggragate this situation. Frost boils are most numerous in low lying roads that are composed of shallow, fine sandy or silty learn soils. Although our soils are predominantly glacial tills, tney also contain pockets of very fine sandy soils that yield to frost action.
It should be mentioned that in the past few years we believe that we have been able to overcome a large number of our soil problems in an indirect manner. In order to Keep our roads free of snow we have had to elevate our subgrades weIr above the
surrounding area. By doing so and by selecting the soils9 we have
been covering up sections containing organic soils with an appreci-able fill and so far such sections have held up well. Also, by raising the grade line well above the ditch line we are getting away from frost boils in areas that used to frost boil badly in the past. In this type of construction the roadbed soil moisture con-tent is lowered and pavements stand up better.
2ov •
(5) Compaction Problem
The impracticability of being able to compact soils at optimum moisture is one of our biggest problems. This is due to the hot dry climatic conditions that exist on the prairies from about the beginning of July until late fall. During the greater part of the construction season our soils are quite dry and powderyo A large amount of water has to be adoed only for the purpose of
bringing the existing moisture to the required optimum moisture. However, when extra water ｨ｡ｾ to be adaed to ｾ｡ｫ･ up for evapo-ration losses, the cost of the water alone will easily amount to one-half of the grading cost.
The problem comprises not only the cost of water, but the controlling of the proper moisture at all times at all spots on the road. Moisture control for compaction on airports is relatively easy where all work is confined to the same area. In highway work, however, where work progresses along the road rapidly
and soils of greatly varying moisture contents are encountered, moisture control becomes a very difficult matter. At least, we have not been able to cope with it satisfactorily.
Section 9
SOMb; SOILS ｐｒｏｂｌｾＱｖｬｓ ENCOUIiTEhJ::D IN HIGlmAY CONSTRUCTION IN ALBERTA
by
L.
H. McManusIt appears that we all have much the same troubles with soils in the Prairie Provinces, but due to c lirnatic conditions
and other factors, we in Alberta consider them in a different order of importance.
(1) Topsoil
From the point of view of everyday difficulty, from its volume in construction, from the number of pavement failures di-rectly attributed to it and from the cost in dollars and cents, our number one problem is topsoil. This soil yields our valuable field crops but is a very poor road building material. This ｴｯｰｾ soil extends over the top of the borrow area and also under the fill. With an average width of section of 80 feet we have 1200 cubic yards per mile per inch of depth. A layer of 10 inches of topsoil, which is not uncommon, will yield a total of 12,000 cubic yards per mile. To waste all of this material would be very expensive even if we just consider the cost of excavation alone. It is sometimes difficult to find a place where it can be wasted.
An alternative solution to the problem is to use the topsoil to flatten out the side slopes. This improves the safety on the highway and gives us a better soil for seeding. We also attempt to use this type of material in the base of deeper fills, taking care to always have a fair depth of compacted sUb-soil on top. The topsoil as placed in any fill must be compacted. This is sometimes expensive since it is often quite dry and may have an optimum moisture around 35 per cent. There are sonle cases where our grade line parallels the ground surface on a gentle slope where we do not have anything ｢ｾｴ topsoil in our standard sections. In this case it is necessary to waste the topsoil from the ditches and to obtain some suitable material with which to construct our fill. To get rid of the topsoil here we use an Irish trick; that is, we dig a hole and bury it. Actually, we remove the topsoil from our ditches and pile it up out of the way.
We
then go down below grade and obtain material suitable for ｣ｯｮｾ structing the highway fill. These borrow pits are then back=us with suitable construction material and with a place to waste the unusable soil without leaving an unsightly borrow pit or waste pileo This is all done within our right of wayo
(2) Compaction
The next problem which we run into most frequently is that of obtaining proper compactiono I do not intend to go into the subject of compaction except to say that it is generally ac= cepted as desirable in the construction of all first class highways and that very often it is difficult to achieveo Our troubles here can be divided roughly into two types:
(1) Specifications$ and
(2) Meeting these specificationso
Most of us who have to do with construction are in the unhappy position of having to write specifications and then to
see that they are meto Consequently, the one has a very important effect on the othero At the present time we are considering this phase of the grading operations separately and paying by the hour for sheepsfoot rollers and by the 1,000 gallons for water addedo
I believe that it would be more satisfactory if some part of the operation was included in the unit price for earth worko In this way the contractor would gain by careful organization of his equipment0 If, for instance, the supplying and operating of ｳｨ･･ｰｳｾ
foot packers was included in the excavation price, then the con-tractor would be interested in obtaining compaction in the least possible operating timeo Such unpredictable factors as additional water could be paid for as a separate contract itemo
(3)
MuskegAnother problem which faces us is construction over
muskego This problem is becoming more important and more apparent as we construct and improve our ｨｩｧｨｷｾｹｳ in the north and north= western part of the Province where we encounter considerable areas
of muskego An attempt is made to avoid these sections but this is not always possibleo Up until the present we have been able to construct more or less satisfactory subgrades over these areas, particularly if the road is to have only a gravel surface0 It is
then possible to repair any small unevenness which may developo The height of fill which can be carried depends on the strength of the muskego With ･ｶ･ｲｾｩｮ｣ｲ･｡ｳｩｮｧ truck loads, it is necessary to build higher and stronger fillso The added weight of these fills tends to increase the unequal settlement of the muskego This uneven settlement might greatly increase the maintenance cost of an
