摘要:

The shear strength of an unsaturated soil is written in terms of two independent stress state variables. One form of the shear strength equation isThe transition from a saturated soil to an unsaturated soil is readily visible. A second form of the shear strength equation isHere the independent roles of changes in total stress σ and changes in pore-water pressureuware easily visualized.Published research literature provides limited data. However, the data substantiate that the shear strength can be described by a planar surface of the forms proposed. A procedure is also outlined to evaluate the pertinent shear strength parameters from laboratory test results.

ISSN:0008-3674    

DOI:10.1139/t78-029

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

A high clay strength and apparent preconsolidation may be a result of chemical processes such as cementation at the contact points of the clay particles. In order to study some of the mechanical properties of a cemented clay two artificially cemented simple shear samples were produced and tested. Their engineering properties were compared to those of non-cemented clay samples with a real preloading. The cementing agent that was introduced into the sample was CaCO3. This was achieved by a sequence of treatments of CaCl2, Na2CO3, and original pore water. The different solutions were transported into the samples by diffusion. The cementation process took 90 days. The average amount of CaCO3introduced into the two samples was 3.3 and 4.2%, respectively. By electron microscope techniques it was revealed that calcium carbonate was precipitated in spots of 5–10 μm diameter. One of the samples was run with undrained static loading. The other sample was first subjected to undrained cyclic loading and then to undrained static loading. Cementation increased the horizontal shear stress at failure by 35–40%. This corresponds to an apparent overconsolidation ratio of about 1.75. Both for static and cyclic loading the engineering properties were essentially independent of whether their high strength was achieved by cementation or by a real preloading.

ISSN:0008-3674    

DOI:10.1139/t78-030

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Two parallel tunnels were built in 1976 as part of the first phase of the Edmonton Rapid Transit System. The tunnels, approximately 250 m long, 6 m in diameter, and having centres 11 m apart have been driven in downtown Edmonton with an average of 7.5 m overburden above the crown. The tunnels were located entirely within a dense, jointed till sequence of Wisconsin age.The tunnels were advanced using a mole followed by two systems of soil support. The temporary supporting system consisted of steel ribs and timber lagging while the permanent lining was cast-in-place reinforced concrete. To reduce drag friction, the cutting profile of the mole is about 20 mm larger than the diameter of the shield. The steel ribs are expanded into place by hydraulic jacks.Two finite element analyses were performed. One predicted surface settlements and the other predicted lining stresses. The settlements predicted for a single tunnel agreed closely with observed values but the observed amount was considerably more than predicted for both tunnels. The reasons for this are suggested as being due to a cross tunnel connecting the two main tunnels and to a decrease in stiffness of the soil mass brought about by the moling of the first tunnel.insituassessment of stresses in the ribs was not successful due largely to the fact that the ribs were not expanded entirely against the soil. Thus comparisons with predicted values could not be made and values of the earth pressure at rest could not be established. However, rib deformations were essentially complete within a few days thus confirming the essentially time-independent character of the deformational behavior of the till.

ISSN:0008-3674    

DOI:10.1139/t78-031

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Soil disturbance due to the driving of two groups of 116 concrete piles each in sensitive marine clay was studied on a construction project in eastern Canada. Pore-water pressures, heave, and lateral movement of soil and piles, and tests of strength, compressibility, and consistency limits of the soil were observed prior to and up to 3 months after pile driving whereas observations of pore-water pressures were continued for an additional 5 months. Driving of the piles had little effect on the compressibility and consistency limits of the marine clay, but theinsitushear strength and cone penetration resistance were reduced by about 15 and 30%, respectively. Soil heave within the group of piles decreased linearly with depth from a maximum of 450 mm (18 in.) at the ground surface to about zero at the pile tips, and in volume amounted to approximately 55% of the soil displaced by the piles. The vertical heave outside the pile group was confined to a horizontal distance of 12 m (39 pile diameters). During pile driving, the lateral movement of previously driven piles was as much as 175 mm (7 in.). Horizontal soil movements measured by inclinometers varied up to 125 mm (5 in.). Pore-water pressures generated during piling exceeded the total overburden pressure by 35–40%. The excess pore pressures dissipated in about 8 months after the piling was completed.

ISSN:0008-3674    

DOI:10.1139/t78-032

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Deposits of the Quaternary Period in the Edmonton area consist of a lower and an upper till, in places separated stratigraphically by a sand, with lacustrine clays, silts, and sands overlying this sequence. Detailed field investigations suggest the possible existence of complexities that have not been fully integrated into an understanding of the Quaternary history of the Edmonton area.The lower till is a moderately stony sandy silt till. In places the upper portion has been reworked or sheared by the ice that deposited the upper till producing a thin zone of slightly lower strength. The upper till is a moderately stony sand till. Regionally it appears to be quite variable lithologically and contains inclusions of sand and gravel; therefore it is more reasonable to think in terms of an upper till unit composed of till and genetically related material. In some localities this upper unit is one single bed of till; in other places, however, it is a layered sequence of paratills, sands, and silts resulting probably from deposition in standing water. The lenses of sand and gravel associated with this unit have caused problems in tunnelling operations and other construction as they contain water, which can cause flooding when encountered during excavation. The paratills known from the examination of outcrops consist of sequences of interbedded till-like material and sands. These sequences are probably the result of turbidite deposition in an ice-marginal lake. These materials would resemble till when encountered in drilling operations.Problems associated with the Quaternary deposits of the Edmonton area include borehole interpretation to develop site stratigraphy, and the determination of geotechnical properties of the deposits and an assessment of their local variation over a specific site. Also of concern are the joints and fractures in the deposits, which affect slope stability and permeability of the soil mass.An understanding of the Quaternary history and the intrinsic variability of the deposits formed predominantly under the influence of ice is necessary for an understanding of potential sources of variability in geotechnical properties. Interaction between the geologist and the geotechnical engineer can only enhance their mutual comprehension of potential problems and their solutions.

ISSN:0008-3674    

DOI:10.1139/t78-033

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Some structures built in different rock formations in Southern Ontario have been subjected to various degrees of distress. These case histories include heaves of quarry bottoms, buckling of concrete lining of canal floors, cracking of concrete lining of tunnels at the springline, and long term movement of the walls of unsupported excavations.Inference from these case histories, together with direct measurements ofinsitustresses, indicate that high horizontal stresses exist in the Silurian and Ordovician rocks. The magnitude of the maximum stress in the horizontal plane varies from 6–14 MPa depending on the depth and rock type.Excavations in rock relieve thein situstresses. The stress relief serves as an initiating mechanism for time-dependent deformation to occur leading to the process loosely termed as 'rock squeeze'. It appears, therefore, that due consideration must be given to this prevalent phenomenon for the design of underground structures in rock in this region.

ISSN:0008-3674    

DOI:10.1139/t78-034

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Case histories of failure of water-retaining structures on highly plastic clay indicate that the intact strength of the clay does not reliably predict the stability condition. A study of the foundation conditions revealed the presence of structural discontinuities such as nugget and blocky structure, joints, fissures, and slickensides. A re-analysis of the failures, using the normally consolidated strength of the soft highly plastic clay, as suggested by Skempton and Hutchinson for stiff fissured clays, gives a more reliable prediction of the in situ stability condition.

ISSN:0008-3674    

DOI:10.1139/t78-035

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The geotechnical characteristics of compacted soils used by the Prairie Farm Rehabilitation Administration in earth embankments were correlated with easily obtained soil properties.Relationships were established between Standard Proctor maximum density and optimum water content versus liquid limit for clay soils. In addition, a relationship was established to determine the Standard Proctor maximum dry density and optimum water content using the results from the one-point Proctor test for clay, and sand and silt soils.Effective shear strength parameters and consolidation characteristics of compacted samples were related to liquid limit, water content, and dry density. The results of field and laboratory measurements of pore pressure were used to relate the pore pressure coefficientsU/σ3andU/σ1to the deviation of water content from optimum water content and applied stress. A relationship was established between embankment compression and embankment height using field measurements of embankment settlement.The data suggest that similar geotechnical characteristics will be obtained for laboratory and field compacted alluvial and glacial soils when they are placed with Standard Proctor compactive effort at similar water contents, densities, and liquid limit. In this paper 'alluvial clay' is used to describe clays deposited in lacustrine or fluvial environments and 'glacial clay' is used to describe clays deposited by a glacier.

ISSN:0008-3674    

DOI:10.1139/t78-036

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

To fill an important gap in the knowledge of creep phenomena, the creep behaviour of the intact, overconsolidated Saint-Alban clay has been investigated by means of drained and undrained triaxial tests as well as of odometer tests.Creep deformations can be broken into volumetric and shear components. The development with time of both volumetric and shear strains can be represented by means of the phenomenological equation proposed by Singh and Mitchell in 1968. However, the stress function in that equation must be defined separately for each strain component and by reference to the limit state of the clay.A general model of the time dependent behaviour of clays might be obtained by combining the concepts of limit state and isotaches, as implied in the YLIGHT model proposed by Tavenas and Leroueil in 1977 but the effect of overconsolidation on the shape of the isotaches requires further investigation.

ISSN:0008-3674    

DOI:10.1139/t78-037

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Data from creep tests on frozen sands show that the strain at the onset of tertiary creep, ϵpr, can depend strongly on the applied stress. This observation is supported by data published previously for a frozen clay and a frozen sandy loam. Thus, the effect of stress on ϵprcannot be ignored in either theoretical or applied considerations.

ISSN:0008-3674    

DOI:10.1139/t78-038

出版商:NRC Research Press    

年代:1978

数据来源: NRC