摘要:

Experimental evidence is produced to show that it is reasonable to assign a unique strength to all soils when at their respective liquid limits, and to redefine the plastic limit as the water content at which the strength is 100 times that at the liquid limit. Combining these assumptions with ideas of critical state soil mechanics it is then possible to relate the compression index of the remoulded soil to its plasticity index, and to suggest a unique relation between remoulded strength and liquidity index, irrespective of actual values of liquid and plastic limits. Field data from the Gulf of Mexico and from the North Sea are presented in support of these relations. The predictions of strength are best for overconsolidated clays, having water contents near the plastic limit.Recently in the United Kingdom the cone penetrometer has become the recommended test for determination of the liquid limit, in preference to the Casagrande test. Having redefined the plastic limit it would be logical to use the cone penetrometer to determine this too, by using cones with different weights. Experimental data are shown to illustrate and support this proposal.

ISSN:0008-3674    

DOI:10.1139/t78-014

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The results from a testing program designed to simulate the problem of lifting an object embedded in the ocean floor are presented and examined herein. The breakout force, defined as the force in excess of the submerged weight required to dislodge the object, was found to depend on the shear strength of the soil or sediment. The maximum breakout force occurs for undrained conditions and can be estimated from bearing capacity equations.The uplift pressure is transferred to the sediments by a reduction in pore-water pressure. If the reduction in pressure is limited by infiltration of water, or any other process, then a reduction in the breakout pressure will result.The reduction in breakout pressure that occurs when time for infiltration is allowed can be estimated from available solution curves from theory of consolidation.

ISSN:0008-3674    

DOI:10.1139/t78-015

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The paper presents a two dimensional mechanical model for the deformation and creep of polycrystalline ice that takes into account the elastic and plastic deformations of each crystal.The model applies to many cases of creep so that the different types of creep curves have been defined during the transitory, permanent and accelerated phases and the corresponding creep laws have been derived. The mechanics of cracking are not analyzed in this paper.The expression for the plastic deformation in this model is based on the principle of multiplication of mobile dislocations and Glen's law for permanent creep. The corresponding mathematical expression for creep without cracking, called α creep, is shown to represent, at the lower limit, the flow of glaciers and is shown to verify a large variety of measured creep curves either in monocrystals or in polycrystalline ice.The elastic deformations in this model bring to light the important role played by delayed elasticity, which is shown by experimental data but has never been elucidated previously.

ISSN:0008-3674    

DOI:10.1139/t78-016

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The paper summarizes investigations on jacked and driven piles in non-uniform soils consisting of clay and sand. Part 1 deals with the bearing capacity of piles penetrating through clay into sand whereas Part 2 discusses the case of piles in a sand stratum overlying clay. Preliminary tests on small model piles have been undertaken to study the effects on the point resistance of parameters such as the strength and thickness of a clay stratum, the strength ratio of soils in the two layers and the geometry of the layers. Based on these results, tests on a 76 mm diameter instrumented steel pile and a 36 mm diameter static cone penetrometer have been carried out for selected combinations of the variables involved.The test results are analysed to determine the influence of clay thickness and strength on the point resistance of piles in sand, expressed by a non-dimensional clay strength factor λ, and parameters influencing λ are discussed. The effect of layering on the shaft friction in sand and the radial stresses along the pile length are studied. The efficiency of small groups of model piles in layered soils is obtained. Field data are analysed, including scale effects, and simple design rules are suggested to estimate the bearing capacity of piles in layered soils.

ISSN:0008-3674    

DOI:10.1139/t78-017

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The previous Part 1 of this paper deals with the bearing capacity of piles penetrating through clay into sand. In the present Part 2 the case of piles penetrating into a sand stratum overlying clay is discussed. As the pile points approach the sand–clay interface, the piles may fail by punching through the sand into the underlying clay. Test results on instrumented model piles and field data are analysed to estimate the punching resistance of piles in layered soils.

ISSN:0008-3674    

DOI:10.1139/t78-018

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

A study is reported of experiments on model plane strain footings subject to repeated loading. The load was returned to zero at the end of each cycle. This is characteristic of a train wheel load passing over a railroad tie.Four series of tests were conducted. Series A consisted of static tests, which provided a comparison with series B. Series B consists of applying a cyclic load on the footing between zero load and a constant upper value. The upper value was varied from test to test and ranged from 13.5 to 90% of the static failure load. Series C was acyclic test that was a continuation of series B after a considerable deformation had occurred. The berms caused by the cyclic load test of series B were removed and a second cyclic test was conducted on the same foundation soil as the original test. Series D was a static test that was done as a continuation of series B. After removing the berms, as in series C, a static test was conducted in a manner similar to that for series A.The results have been quantified by the use of a hyperbolic fit and show that wider footings should perform better than narrower ones. This has been substantiated by examination of experimental railroad tests conducted by the Association of American Railroads.

ISSN:0008-3674    

DOI:10.1139/t78-019

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The Athabasca Oil Sands are largely within the McMurray Formation, which is a transgressive blanket quartz sand of Lower Cretaceous age. Millennia of erosion have resulted in extensive exposures of oil sand along river valleys in the vicinity of Fort McMurray. Study of these slopes has contributed to understanding the nature and behavior of oil sands. Oil sand slopes with active toe erosion are characteristically high and steep (up to 70 m at slopes over 50°), have an indurated outer face and display a stress–relief exfoliation joint system that controls slope recession phenomena. Bitumen does not contribute mechanically to slope stability. The major agents affecting slope morphology are the lithology, the aspect and the basal stratigraphy. Ravelling along exfoliation fractures is the major failure mode, block falls are a minor failure mode and rotational landslides have not been observed. Remolded oil sand may flow viscously, but intact oil sand displays an unusually high strength.

ISSN:0008-3674    

DOI:10.1139/t78-020

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Previously published data are inadequate to explain the high natural shear strength of oil sand. Dissolved gas comes out of solution when confining stresses are removed rapidly, and this results in an internal pressure that expands the oil sand specimens disrupting their fabric. Geophysical logs indicate thatinsitudensities are much higher than those determined from conventionally cored specimens.Although the behavior of slopes in oil sands suggests that the shear strength is high, the source of strength of the oil sand has not been explained. Therefore detailed oil sand strength testing was undertaken on samples obtained in a special manner. Down-hole refrigeration of cored sections resulted in relatively high-quality specimens, and these were shaped on a lathe to provide triaxial and shear-box test samples.Strength tests on dense Ottawa sand, oil sand tailings and densely recompacted oil sand were performed: standard behavior was observed throughout. A series of triaxial and shear-box tests on undisturbed oil sands demonstrated a Mohr failure envelope that is highly curved, which displays no cohesion intercept and which is extremely steep for the initial portion of the envelope. Optical and scanning electron microscope investigations have revealed a dense interpenetrative structure and a considerable degree of grain surface rugosity. These factors give rise to a very high dilation rate before failure, and the dilation rate is suppressed as normal stress increases. The suppression of dilation results in shear of grains and grain asperities, giving rise to an apparent cohesion intercept at higher normal stresses. The curvilinear failure envelopes may be conveniently expressed as power-law relationships, and this form of expression will prove useful in stability analysis.

ISSN:0008-3674    

DOI:10.1139/t78-021

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

This study explores several aspects of the 'discontinuous' approach to prediction of settlements of foundations on jointed rock. The first part presents the results of experiments with numerical and analytical solutions. It is shown that solutions of continuum elasticity cannot be used without introducing errors due to method alone, which could be serious for sensitive structures.The second part of the study describes measurements of joint stiffness on samples of natural joints in limestone and sandstone. Normal and shear stiffness coefficients were measured. It was found that the unit shear stiffness coefficient varies greatly with displacement, and an empirical relationship was derived that might be useful in analysing other rocks.

ISSN:0008-3674    

DOI:10.1139/t78-022

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The foundation soils for an embankment in New York State constructed on preconsolidated varved clay were instrumented to determine pore pressures and settlements during and after construction. Four embankment cross sections, three of which had sand drains, are analyzed in this paper. Predictions of theinsituundrained pore pressures, initial settlements and final consolidation settlements are presented and compared with the results of field measurements. Undrained pore pressures and initial settlements are predicted using the finite element program FEECON for plane strain embankment conditions and elastic theory for three-dimensional embankment conditions. Final consolidation settlements are predicted using a modification of the Skempton–Bjerrum approach. At cross sections with sand drains, predicted undrained pore pressures are adjusted to account for the effect of the sand drains. In addition, vertical and horizontal coefficients of consolidation are determined from the field measurements and compared with laboratory values of vertical coefficients of consolidation. The results of the investigation indicate that the proposed prediction techniques yield reasonable predictions of undrained pore pressure and initial settlement. Additional case studies are required in order to evaluate the predictive methods for the rate and amount of consolidation settlement.

ISSN:0008-3674    

DOI:10.1139/t78-023

出版商:NRC Research Press    

年代:1978

数据来源: NRC