摘要:

A practical science has not been fully developed for unsaturated soils for two main reasons. First, there has been the lack of an appropriate science with a theoretical base. Second, there has been the lack of an appropriate technology to render engineering practice financially viable.This paper presents concepts that can be used to develop an appropriate engineering practice for unsaturated soils. The nature of an unsaturated soil is first described along with the accompanying stress conditions. The basic equations related to mechanical properties are then proposed. These are applied to practical problems such as earth pressure, limiting equilibrium, and volume change.An attempt is made to demonstrate the manner in which saturated soil mechanics must be extended when a soil is unsaturated. Two variables are required to describe the stress state of an unsaturated soil (e.g., (σ –ua) and (ua–uW). There is a smooth transition from the unsaturated case to the saturated case since the pore-air pressure becomes equal to the pore-water pressure as the degree of saturation approaches 100%. Therefore, the matrix suction (i.e., (ua–uW) goes to 0 and the pore-water pressure can be substituted for the pore-air pressure (i.e., (σ –uW)).The complete volumetric deformation of an unsaturated soil requires two three-dimensional constitutive surfaces. These converge to one two-dimensional relationship for a saturated soil. The shear strength for an unsaturated soil is a three-dimensional surface that reduces to the conventional Mohr–Coulomb envelope for a saturated soil.The manner of applying the volumetric deformation equations and the shear strength equation to practical problems is demonstrated. For earth pressure and limiting equilibrium problems, the unsaturated soil can be viewed as a saturated soil with an increased cohesion. The increase in cohesion is proportional to the matrix suction of the soil. For volume change problems it is necessary to have an indication of the relationship between the various soil moduli.There is a need for further experimental studies and case histories to substantiate the proposed concepts and theories.

ISSN:0008-3674    

DOI:10.1139/t79-011

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

A common occurrence in cuts or fills of swelling soils is their reduction in strength with time. At the time of compaction, the clay generally has a high matrix suction. Correspondingly, it has a high strength and will stand at relatively steep side slopes. With time, the soil generally tends towards saturation and the matrix suction reduces towards zero. There is a reduction in total strength and if the gravitational forces are too large, the slope fails.During the past several years, numerous cut and fill slopes have been observed in the Regina area of Saskatchewan. Many of these slopes have remained stable for 4–6 years and then failed. There has been a 20 year history of observations on the Belle Plaine overpass west of Regina. Field and laboratory investigations have been conducted.With a knowledge of the geometry of the slope and failure plane, the simplified Bishop method of stability analysis was used to perform a 'back-analysis' to assess the shear strength parameters. The shear strength parameters from the laboratory program are compared with those calculated from the stability analyses. The analyses indicate that the peak shear strength parameters from triaxial tests on the softened Regina clay (i.e.,c' = 5 kPa and), with the appropriate pore water pressures, give a factor of safety of 1 for the failed surface. The effect of spring thawing appears to be to produce the condition of most serious pore water pressures.

ISSN:0008-3674    

DOI:10.1139/t79-012

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The method of down-hole seismic surveying is described. This method was successfully used to a depth of 50 m in a cased borehole and these results are presented. The method may be used to find thein situlow strain shear modulus for use in theoretical response studies.Structural changes and changes in the stress state of samples usually result from sampling, handling, and testing procedures. Large changes in soil properties may result from these processes. An assessment of the change in soil properties is presented, which is of importance for the use of laboratory derived soil properties in theoreticalin situdynamic response studies.The magnitude of sample disturbance is assessed by comparingin situand laboratory measured shear wave velocities.In situdown-hole shear wave velocities are compared with low strain (1 × 10−6) laboratory dynamic torsion test results. The large differences found may be correlated with thein situshear wave velocity.A procedure is presented to correct the laboratory established shear modulus–strain relation–ship for the effects of sample disturbance. The adjusted laboratory curve is then suitable for use in theoretical response studies and will be a more accurate representation of thein situdeformation characteristics.

ISSN:0008-3674    

DOI:10.1139/t79-013

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Cyclic loading tests were performed on many undisturbed specimens and a few compacted specimens of two samples of very sensitive clay from an earth dam site on the Outardes River in Quebec. Failure occurred when one or more thin shear zones developed in which the remolded soil was reduced to a liquid, while the rest of the specimen remained intact, strong, and brittle. The cyclic strength of this clay was high in comparison to that required for the foundation of a planned earth dike and was relatively strong in comparison with other clays. However, simplified analyses indicate that under some conditions dynamic loading can be expected to induce instability in this type of soil.

ISSN:0008-3674    

DOI:10.1139/t79-014

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

This paper deals with the choice, calibration, and use of earth pressure cells in the measurement of the contact stress distribution across a strip footing. The footing was 30 cm wide, rough, and rigid; the measurements were made in a laboratory with the footing bearing on compact to dense, air dry, uniform, crushed quartz sand.Typical test results are compared with the theoretical distributions of both shear and normal stresses that have been proposed by various authors.

ISSN:0008-3674    

DOI:10.1139/t79-015

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Measurements were made on a 4.3 m (14 ft) bored diameter, 3.0 m (10 ft) finished diameter tunnel for a sewer in Mississauga, Ontario. Measurements included deformation of the flexible temporary lining, pressures on the temporary and rigid concrete permanent linings, soil deformations and surface settlements as the tunnel was excavated, and the effect of the tunnel on groundwater levels.Because of the stiffness of the very dense till and the method of construction it was found that during the period of measurement the tunnel opening deformed and was largely self-supporting. Some increase of loads on the linings with time was observed, but the rate of increase was almost negligible after 6 months. The water table around the tunnel was lowered as the tunnel and the surrounding pea gravel fill acted as a drain.Indications are that the tunnel has nearly uniform all-around pressure on it, considerably less than the overburden pressure, and, therefore, that it could be considered in ring compression without bending moments in either lining. If bending moments are not present, the permanent lining could be reduced from the 460 mm (18 in.) used to half that thickness or less and still be quite conservative in supporting all-around loads equal to the overburden pressure and providing for wear.

ISSN:0008-3674    

DOI:10.1139/t79-016

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

A positive double cutoff wall was used to control the foundation seepage and to minimize the danger of piping, for a 107 m (350 ft) high earthfill dam founded on 126 m (420 ft) of pervious and highly compressible alluvial deposits.At the end of the first year of operation (Dec., 1976), the cutoff walls had deflected 285 mm (11.2 in.) downstream and had been vertically compressed by 140 mm (5.5 in.). These deformations were caused by the combined action of the weight of the dam and the reservoir load and were monitored by a comprehensive instrumentation.The reading of the instruments indicates that 85% of the vertical deformation in the walls is mainly due to the load transmitted by the negative skin friction between the walls and the surrounding compressible alluvium, whereas the compression induced by the dam's weight, transferred directly through the inspection tunnel (acting as a pile cap), is only 15%. A large part of the wall's compression is attributed to the creep of the concrete.The presence of an arching effect in the foundation due to the particular shape of the canyon has been confirmed by the instrument readings. This phenomenon was previously brought to light by the finite element analysis.The structural analysis of the behaviour of the cutoff walls confirms the necessity of the twin walls, because the stresses induced in the single wall (negative friction on both sides) would have been dangerously close to the ultimate strength of the concrete.

ISSN:0008-3674    

DOI:10.1139/t79-017

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Sample analytical and numerical thermal solutions for problems involving insulated pad designs on permafrost are presented. Other aspects of pad design on permafrost are considered, including the required depth of cover for insulation subjected to different wheel loadings and the use of insulation on sloping terrain to improve pad stability.

ISSN:0008-3674    

DOI:10.1139/t79-018

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Many recent publications on the influence of sampling techniques indicate that, generally speaking, the quality of the samples increases with the diameter of the sampling equipment. However, all studies also conclude that even the large diameter samplers available on the market substantially damage the structure of the clays of eastern Canada, as compared to the sample quality obtained by block sampling. In addition to the difficulties associated with the excavation of the trenches necessary for block sampling, the depth of block sampling is limited, at least in soft clays.The sampling technique described in the present paper allows the retrieval of deep blocks, working from the ground surface and using a cutting method quite similar to that used for conventional block sampling. The large diameter borehole is filled with water or bentonite slurry to reduce the possibility of bottom heave. By comparing the results of unconfined compression tests it is shown that the samples obtained by this method are of a quality equal or superior to that of blocks sampled conventionally at the bottom of open cuts.

ISSN:0008-3674    

DOI:10.1139/t79-019

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Bellow-hose settlement gauges were used to measure vertical soil heave during the installation of concrete piles in sensitive marine clay. The equipment is described and the sources of error are discussed.

ISSN:0008-3674    

DOI:10.1139/t79-020

出版商:NRC Research Press    

年代:1979

数据来源: NRC