摘要:

A state-boundary surface defines a boundary in stress – void-ratio space above which no stress state can exist. The applicability of the state-boundary surface for sand has not gained widespread attention primarily because sand is not generally considered to be a difficult soil from a design point of view apart from liquefaction. Liquefaction is a phenomenon usually encountered in very loose cohesionless materials. An experimental study relating the drained and undrained behavior of very loose saturated sand is presented. It is shown that the post-peak portion of undrained stress paths travels along the state boundary and that the state boundary can be approximated by a straight line. The slope of this straight line appears to stay constant for very loose sand. There are potentially an infinite number of these lines, which form a three-dimensional surface in deviator stress – effective mean normal stress – void-ratio space. Previously published results by various researchers are used to confirm the existence of the state boundary. This surface is mathematically defined in deviator stress – effective mean normal stress – void-ratio space. Loose saturated sand samples loaded drained from a stress state on or very close to the state boundary surface essentially travel along the state boundary surface.Key words: sand, collapse, liquefaction, stress path, state boundary, triaxial test.

ISSN:0008-3674    

DOI:10.1139/t94-040

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

A recent effective stress model of vane shear strength testing in soils can relate measured torques to vane shear strengths using theoretical analysis in terms of effective stress parameters. The strength estimates are based on known in situ stresses and soil parameters derived from laboratory testing. The model may be applied, for example, in obtaining theoretical estimates of conventional undrained vane shear strengths for comparison with field data and for use in stability analyses. However, the model incorporates a correction factor μv, analogous to Bjerrum's field vane shear strength correction factor μ, intended to compensate for pore-pressure and shearing-rate effects. This correction factor must be evaluated before reliable torque or shear strength estimates can be made in any given case. To facilitate this, the paper presents correlations of μvwith both liquid limit and plasticity index, based on world-wide data from clays and silts. The correlations are compared with independent data from Norwegian clays.Key words: clay, correction factor, effective stress, liquid limit, plasticity index, silt, vane shear strength.

ISSN:0008-3674    

DOI:10.1139/t94-041

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The Becker penetration test (BPT), through correlations with the standard penetration test (SPT), is widely used for foundation design and liquefaction assessment in gravelly soils. Most of the existing correlations, however, do not adequately account for the variable energy output of the diesel hammer used in the Becker system, and shaft friction on the Becker casing is ignored. An alternative and more rational approach to BPT–SPT correlations is presented, based on experimental and numerical studies conducted at the University of British Columbia. The research involves performing SPT, BPT, and other in situ tests at several sites in British Columbia and includes dynamic measurements of energy transfer in the SPT and BPT. Stress-wave measurements and wave-equation analyses are used to evaluate the effect of friction on the BPT blow count. New BPT–SPT correlations are proposed that consider the energy transfer in both tests and explicitly consider casing friction in the BPT. A recommended procedure for estimating equivalent SPTN60from BPT blow count is presented.Key words: Becker penetration test, standard penetration test, dynamic measurement, pile driving, stress-wave propagation.

ISSN:0008-3674    

DOI:10.1139/t94-042

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Centrifuge modelling of the lateral spread of a conservative solute in a partly saturated fine sand has been accomplished in a 3 m radius centrifuge at simulated gravitational accelerations of 25 and 50 g. The distributions of the contaminant after 2 months, 6 months, and 1 year of prototype time were found experimentally by dissection of models. The results support the contention that centrifuge modelling does correctly recreate prototype transport phenomena, including transport due to matrix suction, in partly saturated fine sand. For the conditions modelled, it was found that all of the contaminant introduced at the soil surface became immobilized, for at least 1 year, inthe upper 2–3 m of the 6 m deep soil profile.Key words: centrifuge modelling, contaminant fate, vadoze zone, matrix suction, diffusion.

ISSN:0008-3674    

DOI:10.1139/t94-043

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

A numerical decomposition technique, which has resulted from a linking between joint-geometry modeling and generation schemes, and a distinct element code (UDEC), is used to study the effect of joint-geometry parameters of finite-size joints on the deformability properties of jointed rock at the two-dimensional (2D) level. The influence of joint-geometry parameters such as joint density, ratio of joint size to block size, and joint orientation on the deformability of jointed rock is shown. Relations are established between deformability properties of jointed rock and fracture-tensor parameters. An incrementally linear elastic, anisotropic constitutive model is developed to represent the prefailure mechanical behaviour of jointed rock at the 2D level. This constitutive model has captured the anisotropic, scale-dependent behaviour of jointed rock. In this model, the effect of the joint-geometry network in the rock mass is incorporated in terms of fracture-tensor components. Some insight is given related to estimation of representative elementary volumes for deformability properties of jointed rock.Key words: rock masses, deformability, distinct element method, fracture tensor, anisotropy, scale effects.

ISSN:0008-3674    

DOI:10.1139/t94-044

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

A series of column experiments were conducted to evaluate three methods to determine sulphide oxidation rates in mine tailings. Measurements were made of (i) the flux of oxygen across the surface of the tailings, (ii) the oxygen consumption rates at the tailings surface, and (iii) the total sulphate produced in the pore water over time. Two columns were prepared with a mixture of quartz sand and pyrrhotite and overlain with varying thicknesses and grain sizes of a nonreactive layer. The impact of nonreactive layers with varying water-table depths on the overall oxidation rate was also evaluated. Modelling was applied to verify the importance of diffusion and kinetic control of the different column configurations. The results indicate that the overall rate of oxidation is reduced when fine-grain layers are applied. This is due to the high water saturation conditions generated by the fine material regardless of the depth to the water table. The consistency and precision of the methods used to measure relative oxidation rates were noted and a new practical field mapping tool is recommended. The new method provides rapid measurements of relative oxidation rates that can be applied to existing tailings rehabilitation with soil-type covers to show spatial and temporal trends.Key words: sulphide oxidation, tailings, laboratory experiment, oxidation rate methods, water saturation, cover materials.

ISSN:0008-3674    

DOI:10.1139/t94-045

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

A large (est. volume 2.8 × 106 m3) landslide occurred in sensitive Leda clay on the east bank of the South Nation River at Lemieux, Ontario (45.4°N, 75.06°W), on June 20, 1993. The earthflow involved an area of about 17 ha and retrogressed a total of 680 m, 555 m into the flat plain above the river. No lives were lost but a motorist was injured when he drove into the landslide crater. The 1993 landslide occurred 4.5 km downstream of the well-known 1971 South Nation River landslide along a stretch of river that had experienced other historical landslides in 1895 and 1910. A band of earlier, undated, retrogressive sliding, between 100–130 m in width, was present at the base of the slope that failed in 1993, and the earthflow was probably triggered by a reactivation of these failures. Borehole information obtained in 1986 and 1987 in the vicinity of the landslide indicates that a zone of soft, sensitive marine clay existed beneath the flat farmland, which was overlain by a stiffer cap consisting of laminated marine-estuarine sands and deltaic silts and sands. The morphology of the debris suggests a mechanism that involves the fluidization of much of the landslide mass and subsidence, translation, and rotation of cap blocks. The stability number for the site was approximately 9.6, suggesting that the flow could have occurred as a result of extrusion of the soft sensitive clay layer due to undrained cap loading. Landslide debris temporarily blocked the South Nation River, causing flooding upstream and adversely affecting water quality downstream.Key words: landslide, earthflow, sensitive clay, debris hazards, water quality.

ISSN:0008-3674    

DOI:10.1139/t94-046

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The findings of a laboratory study on the time-dependent displacement of model piles in saline frozen soil are reported. The short-term time-dependent pile deformation in ice-poor saline silty sand was best described using a simple power law of time, whereas the long-term time-dependent deformations were best described using a flow law formulation similar to that used to describe the long-term time-dependent deformation of ice or ice-rich permafrost. The use of cementitious grout as a backfill resulted in doubling of the pile load carrying capacity for a given displacement rate. The laboratory test results compare well with other laboratory and field studies.Key words: frozen soil, saline, model pile, time-dependent deformation, sand backfill, grout.

ISSN:0008-3674    

DOI:10.1139/t94-047

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

This paper presents the results of a laboratory investigation of shaft resistance of rock-socketed piers using constant normal stiffness (CNS) direct shear tests. In this context, an experimental program is conducted in which small-scale piers are loaded in compression, and specimens having the same pier-surrounding medium interface geometry and components as those found in the small-scale models are subjected to direct shearing. Pseudorock materials were used for the construction of the model piers and shear specimens. These materials were chosen to simulate rocks of very weak to medium strength to investigate the influence of relative stiffness of pier and surrounding medium construction materials on the shear resistance. Furthermore, predicted values of side shear resistance using empirical relationships are compared with experimental results to examine the validity of these relationships.Key words: rock, socketed piers, shaft resistance, direct shear, model pier, constant normal stiffness.

ISSN:0008-3674    

DOI:10.1139/t94-048

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Small-scale testing under 1 gconditions as well as in the centrifuge presupposes that a model and prototype have comparative behavior. The chief condition for agreement between model and prototype is that the initial soil states of both must be at equal proximity to the steady state line. Then, when stresses are normalized to the initial mean stress, the model will in all aspects behave similarly to the prototype. Scaling rules are presented that indicate the relations between stress, strain, and displacement for the model and the prototype in terms of geometric scale and stress scale. An obvious limit of scales is imposed by that the soil in the model can be no looser than the maximum void ratio. Similarly, it must not be denser than a value that corresponds to a prototype soil at the minimum void ratio. Three main areas of application of the approach in engineering practice are identified: design of representative 1 g small-scale model tests; reanalysis of data from conventional small-scale tests; and improving the versatility of centrifuge facilities in recognition of the fact that the centrifuge test does not need to be performed at equal levels of stress, when designed according to the new approach.Key words: physical modeling, sand, scaling relations, steady state, centrifuge testing.

ISSN:0008-3674    

DOI:10.1139/t94-049

出版商:NRC Research Press    

年代:1994

数据来源: NRC