摘要:

Biot coupled consolidation numerical analyses have been applied to a stage-constructed embankment on soft clay in the centrifuge. In the test, the sand embankment was constructed during flight on a clay foundation consisting of an overconsolidated crust overlying a normally consolidated layer. Measurements were taken of pore pressures, dissipation rates, and displacements in the foundation clay. Predictions of these were made using a simple Cam-clay model for the clay and the Cambridge CRISP computer program. A linear elastic idealization was used for the embankment. With some exceptions, pore pressures and dissipation rates were very well predicted, as were maximum values of both horizontal and vertical displacements. However, displacement profiles with depth were not so well predicted. Particular attention is given in the paper to the determination of relevant values of shear modulusGand the difference in behaviour resulting from using constant permeability and permeability varying with void ratio.Key words: embankments, soft clay, centrifuge test, numerical analysis, Biot consolidation, Cam-clay model.

ISSN:0008-3674    

DOI:10.1139/t86-020

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

A model is proposed for the behaviour of flow slides in loose, cohesionless materials in which the debris spreads out as a uniform sheet. Excess pore-fluid pressures are assumed to be generated, for example by undrained loading arising from the collapse of metastable structure, in the source area of the flow slide. Under the influence of these, the leading element of the debris moves downslope by basal sliding, consolidating as it does so by single, upward drainage. As a result, the pore pressure at the base of the element eventually decays to a value that brings the element to rest, hence defining the run-out of the flow slide. The model is applicable, in principle, to subaqueous and subaerial flow slides and to pore fluids consisting of water, gas, or both of these. The predictions of the model are tested against the observed behaviour and measured properties of the 1966 flow slide at Aberfan, South Wales. The results show that a sliding–consolidation model provides a possible mechanism for that event.Key words: Cohesionless material, loose metastable structure, partial liquefaction, excess pore-fluid pressure, basal sliding, consolidation, flow slide, acceleration, velocity, run-out.

ISSN:0008-3674    

DOI:10.1139/t86-021

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

An investigation is made of the eccentricity and inclination factors for estimating the ultimate bearing capacity of rigid single piles in homogeneous soils under eccentric and inclined loads. For combined eccentric inclined loads the corresponding theoretical factors are obtained by combining inclination factors and eccentricity factors, which are derived from extending the theory of inclination factors for shallow strip footings. The theoretical values of inclination factors, eccentricity factors, and eccentric inclination factors are compared with some experimental results of model piles in sand and clay.Key words: bearing capacity, clay, eccentricity factors, eccentric inclination factors, inclination factors, rigid piles, sand, ultimate load.

ISSN:0008-3674    

DOI:10.1139/t86-022

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

The erosion of clayey soils is a complex phenomenon that includes various types of erosive actions. A tentative classification of erosion processes is proposed. This paper concentrates on the scour resistance of solid clays. Available prediction methods are reviewed. Generally they propose relationships between physical or mechanical parameters and the critical hydraulic shear stress,c, that defines a boundary between "no erosion" and "erosion". It became apparent that the physicochemical parameters of both the clay and the eroding water control the erosion process. However, subsequent studies on these parameters have yet to yield reliable predictions of natural clay erodibility from indirect measurements. An erosion testing program was therefore performed on three Quebec clays with the improved rotating cylinder technique. In this test, intact or remolded samples can be tested, physicochemical parameters can be controlled, and the hydraulic shear stressand the erosion rateėcan be adequately determined. A relatively complete and accurate graph ofėversus, includingėvalues forvalues lower than critical can be established. Previous and present research underline the need to exert a strict control of all clay and water parameters, including that of sample preparation, in order to adequately simulate a field problem.Key words: erosion, clay, scour resistance, physicochemical properties, rotating cylinder te

ISSN:0008-3674    

DOI:10.1139/t86-023

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

With the growing interest in peat as an energy fuel, the need for better inventories of this resource becomes increasingly important. Although conventional imaging sensors can provide information on the areal extent of peatlands, depth measurements must still be taken in the field in order to estimate the volume of material present. A recently completed program conducted in eastern Newfoundland suggests that impuse radar systems can provide depth information and volume estimates comparable to those obtained with manual measurement techniques. Ground-based data were acquired using 80- and 400-MHz radar systems and airborne data were collected using 80- and 120-MHz systems. For ground-based profiles, peat thickness of up to 8.1 m was clearly measureable. The airborne profile data were generally poorer in quality; however, depths of up to 4.8 m were successfully profiled from an altitude of 1.5 m. No significant seasonal variations were observed. Impulse radar techniques seem to be particularly useful for reconnaissance level surveys. Additional research is needed in order to develop a system suitable for airborne profiling.Key words: impulse radar, peat resources, peatlands, Newfoundland, depth, volume, profiling, airborne profiling, radar propagation.

ISSN:0008-3674    

DOI:10.1139/t86-024

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

A fundamental experimental study of sand behaviour under low stress ratio proportional loading wherein all strain components are contractant is presented. Experimentally observed behaviour under stress conditions of the triaxial test led to a coherent framework for representing proportional loading stress–strain response. The stress–strain relationship formulated incorporates relative density as an inherent independent state variable and does not require appeal to material isotropy.Key words: triaxial test, proportional loading, sand, relative density, energy density, stress increment, strain increment.

ISSN:0008-3674    

DOI:10.1139/t86-025

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Potential exploitation of the 500 m thick coal deposit at Upper Hat Creek, British Columbia, required detailed investigation of the sequence of Tertiary tuffaceous rocks surrounding the coal and the overlying surficial materials. Studies have shown that extensive bentonitic slide deposits partially cover the coal body on the west side of Hat Creek valley; part of this area is currently active. A translational debris slide of approximately 17 × 106 m3volume and 2 km length is moving across the northwest boundary of the proposed pit into the valley bottom.Detailed field investigations complemented by laboratory testing have defined the basal plane of sliding and permitted a back-analysis to be made. From measured piezometric pressures, the mobilized shear strength on the failure plane is calculated to be,cr′ = 0, which is largely in accord with laboratory test results.Slope stability in thick montmorillonite-rich claystones/siltstones is known to present difficulties, as evidenced by the Panama Canal excavations. Consideration is given to the engineering significance of bentonitic slides and preventive measures that might be adopted in their control.Key words: active slide, Tertiary, claystone, montmorillonite, open pit, coal, monitoring, residual strength, piezometric pressures.

ISSN:0008-3674    

DOI:10.1139/t86-026

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Four case histories where important changes in pile capacity were observed with time are presented. Two show an increase of pile capacity for shaft bearing piles driven into deep sand deposits. The increase occurred over a period longer than needed for pore pressure dissipation. In one case, increases of 33 and 85% in pile capacity were measured 2 and 51 days, respectively, after pile driving. The other two case histories deal with the decrease of pile capacity of close-toe pipe piles driven to shale bedrock. The decrease, determined using dynamic monitoring during initial driving and at restriking a few days later, ranged from 11 to 25%. It is concluded that restriking should be currently practiced on all construction sites to investigate any change in pile capacity after driving. This procedure is particularly recommended for toe bearing piles on shale bedrock.Key words: pile capacity, shaft bearing piles, toe bearing piles, relaxation, soil setup, pile dynamic analysis, shale, time factor, case histories.

ISSN:0008-3674    

DOI:10.1139/t86-027

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

A geotechnical investigation of the Pierre Shale near Hayes, South Dakota, was conducted by the U.S. Geological Survey as a basis for evaluating problems in deep excavations into that formation. The physical and mechanical properties of the shale were determined through use of core holes drilled to a maximum depth of 184 m.In situborehole determinations included a gravimeter survey, pressuremeter testing, thermal profile measurements, and borehole velocity measurements. Onsite and offsite laboratory measurements included rebound measurements, sonic velocity measurements of shear and primary waves, X-ray mineralogy and major element determinations, size analyses, fracture analyses, fabric analyses, and determination of thermal properties.Below 15–22 m, the shale is an unweathered, saturated, overconsolidated, underpressured clay shale with a clay-mineral content ranging between 50 and 100%, dominantly composed of mixed-layer illitic smectites. The physical and mechanical properties vary widely. The variation is related to the clay mineral content (especially in bentonite zones), a large transverse mechanical anisotropy, and zones of fractures and microfractures, which may result from rebound caused by erosion. These may contribute to slope instability over large areas. The thermal and mechanical properties change markedly if the shale is permitted to dry out. The state of stress and overconsolidation appear to be functions of the depositional and erosional history of the deposit. Both are markedly affected by the large fracture zones. The properties of the clay shale indicate problems that may be encountered in excavation and use of deep underground facilities.Key words: anisotropy, characterization, clay shale, consolidation state, physical properties, rebound, relaxation, stress state, thermal properties.

ISSN:0008-3674    

DOI:10.1139/t86-028

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

A new stress characteristic solution has been developed for two-dimensional strip footings on the surface of a sand layer. The analysis uses sand properties defined by a critical state model. This analysis takes account of different stress levels, different placement densities, the sand compressibility, and the transition from strain softening to strain hardening behavior that accompanies increased stresses. The results show linear relationships between log (Nγ) and log (footing breadth) that depend on the details of the sand model used. The results have been compared with available summaries of laboratory- and field-scale results. Although the critical state models for the sands used in the experimental studies cannot be fully developed from published information, nevertheless the trend of the results is encouraging. Additional information on validations of the critical state sand model is needed.Key words: surface footings, stability, capacity coefficients, self-weight, plasticity, stress characteristics, critical state.

ISSN:0008-3674    

DOI:10.1139/t86-029

出版商:NRC Research Press    

年代:1986

数据来源: NRC