摘要:

Experimental studies on unsaturated soils are generally costly, time-consuming, and difficult to conduct. Shear strength data from the research literature suggests that there is a nonlinear increase in strength as the soil desaturates as a result of an increase in matric suction. Since the shear strength of an unsaturated soil is strongly related to the amount of water in the voids of the soil, and therefore to matric suction, it is postulated that the shear strength of an unsaturated soil should also bear a relationship to the soil-water characteristic curve. This paper describes the relationship between the soil-water characteristic curve and the shear strength of an unsaturated soil with respect to matric suction. Am empirical, analytical model is developed to predict the shear strength in terms of soil suction. The formulation makes use of the soil-water characteristic curve and the saturated shear strength parameters. The results of the model developed for predicting the shear strength are compared with experimental results for a glacial till. The shear strength of statically compacted glacial till specimens was measured using a modified direct shear apparatus. Specimens were prepared at three different water contents and densities (i.e., corresponding to dry of optimum, and wet of optimum conditions). Various net normal stresses and matric suctions were applied to the specimens. There is a good correlation between the predicted and measured values of shear strength for the unsaturated soil.Key words:soil-water characteristic curve, shear strength, unsaturated soil, soil suction, matric suction.

ISSN:0008-3674    

DOI:10.1139/t96-060

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Water mains are important lifelines of modern urban infrastructure. However, in most developed countries, the average life of these cast or ductile iron pipes approaches 50–75 years. In recent years, the disruption of water sevices as a consequence of water main breaks is on the rise in most Cadadian cities. This paper describes the developement of a simplified Winkler model to stimulate the responses of a jointed water main subjected to differential temperature change and water pressure. The simplified Winkler model accounts for axial and radial restraints offered by the surronding soil. In spite of its simplicity, the Winkler model is able to predict the overall response of strains and stresses, which confirms satisfactorily some of heuristic and documented observations on water main breaks.Key words:water main breaks, pipe–soil interaction, temperature influence, Winkler mode

ISSN:0008-3674    

DOI:10.1139/t96-061

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Results from field and laboratory tests illustrate the influence of vertical effective stress and temperature on the secondary compression of peat from Middleton, Wisconsin, U.S.A. A large fraction of the total settlement of the peat is due to secondary compression. The coefficient of secondary compression, Calpha, generally increases with time, and settlement predictions using a constantCalphamay underestimate field settlement. Laboratory step-stress and step-temperature tests indicate that the rate of void ratio change during secondary compression varies exponentially with both temperature and vertical effective stress. A stress coefficient of creep,Ctheta, and a temperature coefficient of creep,CT, are defined to characterize these relationships. For Middleton peat, the logarithm ofCthetadecreases linearly with void ratio andCTis constant. The results suggest that laboratory stress and temperature conditions should match those in situ for accurate determination of secondary compression parameters. Cooling also has an important effect on the secondary compression of peat. For large decreases in temperature, an overconsolidated condition is created for which additional secondary compression is greatly reduced. Settlement data from two test embankments on peat illustrate the effect of staged construction and subsurface heating on secondary compression in the field. The temperature changes achieved in situ were not large enough to cause a strong thermal precompression effect.Key words:peat, organic soil, secondary compression, consolidation, settlement.

ISSN:0008-3674    

DOI:10.1139/t96-062

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Chloride and sodium migration in an unsaturated stone collection system underlying a compacted soil liner was examined for three different flow rates ranging between 2.5 and 0.017 m/a. Relatively high and uniform concentrations were observed in the unsaturated stone layer. The groundwater velocity played a significant role in contaminant transport through unsaturated stone even at a flow of 0.017 m/a. Experimental observations were accurately predicted using one-dimensional advective–diffusive–dispersive theory. Transport parameters were reduced by modelling the test data.Key words:soil liner, unsaturated flow, diffusion, landfill, collection syste

ISSN:0008-3674    

DOI:10.1139/t96-063

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Modern underground mining methods often call for the excavation of large, often unsupported voids called stopes. In many cases, these are nonentry stopes, with the removal of broken rock (mucking) performed by remote control. With the risk to human safety thus reduced, stability concerns within the stopes are primarily driven by the economics of unplanned overbreak and waste rock dilution of the mined ore. In this context, it is appropriate to speak of acceptable risks of instability and to optimize design by balancing risk costes with productivity potential. Larger individual stopes generally increase productivity while reducing stability. The modified stability graph is a popular empirical mine design tool that has been calibrated to provide discrete recommendations for maximum stope dimensions based on a rock quality index. It seems appropriate to extend the method to account for variability in the calibration data and also for variability in each new set of input parameters. A risk template and associated probabilistic techniques are proposed to supplement the discrete design limits currently established.Key words:risk, mining, stability, design, emperical.

ISSN:0008-3674    

DOI:10.1139/t96-064

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The measurement of soil parameters, such as the permeability and shear strength functions, used to describe unsaturate soil behaviour can be expensive, difficult, and often impractical to obtain. This paper proposes a model for predicting the shear strength (versus matric suction) function of unsaturated soils. The prediction model uses the soil-water characteristic curve and the shear strength parameters of the saturated soil (i.e., effective cohesion and effective angle of internal friction). Once a reasonable estimate of the soil-water characteristic curve is obtained, satisfactory predictions of the shear strength function can be made for the unsaturated soil. Closed-form solutions for the shear strength function of unsaturated soils are obtained for cases where a simple soil-water characteristic equation is used in the prediction model.Key words:soil suction, soil-water characteristic curve, shear strength function, unsaturated soil.

ISSN:0008-3674    

DOI:10.1139/t96-065

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Stress-dependent hydraulic conductivities of weathered fractured clay till were measured in a flexible-wall permeameter. Measured conductivities were in the range 10–7to 10–8cm/s, of the same order as the clay matrix (10–8cm/s), and representing equivalent hydraulic apertures in the range 0–5 &mgr;m. In general, the isolated fractures exhibited strongly nonlinear closure characteristics and hysteric behaviour under stress reversal. Some fracture samples exhibited only weak stress dependency, representing observable features of only nominal conductivity. Results of the investigations suggest fractures are closed to residuel aperture for an overburden load of the order of 12 m, this defining an effective closure depth and the degree of maximum useful compactive effort that might be applied to "seal" fractures and reduce fluid migration.Key words:fracture permeability, till, stress permeability, landfi

ISSN:0008-3674    

DOI:10.1139/t96-066

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The evaluation of well yields conventional time–drawdown methods is based on the assumption of infinite-acting radial flow (IARF) of groundwater to a well. However, long-term well yields are controlled by heterogeneities and, as suggested here, by the presence of linear features and aquitard leakage, and the subsequent departures from IARF. Accurate prediction of long-term well yields therefore requires an evaluation of aquifer heterogeneities. Derivative techniques combined with aquifer geology and conventional methods aid in the evaluation of long-term well yields in the heterogenous aquifers. Our case study involves the estimation of long-term well yields from relatively short-term aquifer tests in an aquifer near Calgary, Alberta. The wells are completed in a gravel-floored cahnnel incised into bedrock. On the regional scale, the floor gravels appear to form a continuous and homogeneous aquifer. Aquifer-test responses indicate internal heterogeneity at a scale below the resolution attainable with the available well control. Reliable estimates of aquifer parameters are obtained by applying a derivative technique to the analysis of time–drawdown data. Derivative analysis allows us to isolate test segments for which the assumption of IARF is valid. Characteristic time–drawdown and derivative curves are then integrated with geology to identify the nature of heterogeneities and assess their impact on long-term aquifer response to pumping.Key words:aquifer-test, derivative, heterogeneity, well yield, buried valley aquif

ISSN:0008-3674    

DOI:10.1139/t96-067

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Tailings produced by milling for one extraction from hard rock mines, which range in size from clay to fine sand, have relatively low hydraulic conductivity,k. The value ofkmust be known with a certain degree of certainty to analyze consolidation and seepage conditions in and around tailings ponds. In this paper, the authors present the results of a laboratory investigation on hydraulic conductivity of homogenized tailings from hard rock mines. After describing some of the basic properties of four different materials, including mineralogy, grain size, Atterberg limits, compaction characteristics, and consolidation curves, permeability test results are given. The hydraulic conductivity value usually varies between 10–4and 10–5cm/s. The effect of various factors on this value, including void ratio and grain size, is then discussed in relation to predictive models. It is shown that a modified version of the Kozeny-Carman equation, in which a tortuosity factor and a grain-size distribution function are included explicitly, can represent the data very well. The equation is also checked against results taken from the literature on similar types of materials.Key words:tailings, hydraulic conductivity, laboratory tests, void ratio, grain size, tortuosit

ISSN:0008-3674    

DOI:10.1139/t96-068

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Self-boring pressuremeter tests are presently used to assess in situ deformation characteristics of sand. To reach the desire testing depth with minimum disturbance, a consistent self-boring procedure is commonly adopted. High lateral stresses developed during insertion of the pressuremeter has led, in the past, to the adoption of a lantern to cover and protect the expandable rubber membrane section of the probe. This note summarizes an investigation of the influence of different lantern designs on the predicted shear modulus of the sand. Distinct steel strip lanterns were used and compared with the standard lantern used in the Camkometer. It is demonstrated that the interstrip friction of the steel lantern can affect the shear modulus from unload–reload loops of the test. The importance of this investigation is viewed as more practical than technical, since steel lanterns are less expensive, quicker, and simpler to construct than the standard Camkometer lantern.Key words:self-boring procedure, lanterns effect, unload–reload, interstrip friction, shear modulus, san

ISSN:0008-3674    

DOI:10.1139/t96-069

出版商:NRC Research Press    

年代:1996

数据来源: NRC