摘要:

The design of a new laboratory facility for evaluating the structural response of small-diameter buried pipes (e.g., leachate collection pipes in landfills) is presented. The pipe is tested within a 2.0 m wide, 2.0 m long, and 1.6 m high prism of soil, subject to large vertical pressures (1000 kPa), with only minimal roughness and deflection of the lateral boundaries. Results from finite element analyses are presented to examine the effect of proximity, roughness, and stiffness of the lateral boundary on the soil and pipe response and how reasonable the laboratory idealizations are relative to the deep burial conditions expected to prevail in the field. Shear stresses arising from the roughness of the lateral boundaries alter the stresses acting around the pipe and reduce the proportion of the applied surcharge reaching the pipe. Outward deflection of the lateral boundaries also alters the stress state around the pipe, predominantly resulting from decreases in horizontal stresses within the soil. Reducing boundary friction to less than 5° and limiting the boundary deformation to less than 1 mm at a vertical surcharge of 1000 kPa provide a good idealization of field conditions for a deeply buried pipe.Key words: buried pipes, soil-structure interaction, laboratory testing, boundary friction

ISSN:0008-3674    

DOI:10.1139/t99-104

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The importance of the surface charge of clay minerals (fixed or variable) and the effect of H+ions on the adsorption and removal of Pb2+ions from contaminated soil are investigated using kaolinite (variable charge) and two illitic (fixed charge) soils with pH 3.9 and 9.2. The adsorption-desorption characteristics of Pb2+ions were determined using batch equilibrium tests and acid leach tests with various acids used to leach the soils. Under the same adsorption conditions, illitic soil adsorbed much more Pb2+ions than kaolinite. The difference is largely due to the surface charges on the clay minerals. Removal of Pb2+ions from variable-charge minerals (e.g., kaolinite) requires much less effort than removal of Pb2+ions from constant-charge minerals (e.g., illite). The surface charge of a clay mineral has an important effect. By increasing the number of H+ions available in the soil system with a buffer solution such as NaOAc-HOAc, heavy metals adsorbed on the clay surface are expelled to pore water. The increase in H+ions in the soil system also assists in dissolving any metal carbonates, thereby increasing the solubility of heavy metals in illitic soil. The more H+ions available in the pore fluid, the more Pb2+ions can be released from the system.Key words: clay minerals, sorption, desorption, heavy metal, hydrogen ion, electrokinetic, acid leach.

ISSN:0008-3674    

DOI:10.1139/t99-106

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Thermomechanical couplings in the consolidation of an unsaturated clayey silty sand are investigated. The couplings are analysed through the influence of the temperature (relative to the total vertical stress) on the mechanical characteristics (relative to thermal) of the consolidation. They are evidenced by means of two types of tests (thermal consolidation and mechanical consolidation). The two types of tests lead to quantitative results comparable with regards to characteristic parameters of both types of consolidation. Some elements of interpretation are proposed to integrate all of the experimental results within a framework of thinking resorting to the thermoelastoplastic behaviour of the soil under study and to the thermal and mechanical hardening phenomena.Key words: unsaturated soils, consolidation, thermal, mechanical, coupling, hardening.

ISSN:0008-3674    

DOI:10.1139/t99-112

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The initial support and tie foundation problems of a railroad track built in 1974 to carry axle loads 21% greater than presently (1998) permitted under interchange laws at a speed of 88 km/h are presented. Some of the concerns related to and affecting the final rehabilitation that resulted in a final satisfactory performance are documented. The foundation engineer's interest is directed to the ballast, the tie, and to a lesser extent the rail's behaviour. Cobble-sized (75-150 mm) river gravel was used as the source for the ballast in the rehabilitation. The ballast's satisfactory performance has permitted the establishment of guidelines for future use of this type source of material where suitable quarried rock is not available. The railroad's satisfactory performance after rehabilitation has proven that the design concepts involving 36 t (40 tons) axle loads operating on 60 kg/m (119 lb/yd) continuously welded rail, concrete ties, and ballast manufactured by crushing from a river aggregate were achievable.Key words: railway track, concrete ties, ballast aggregate, aggregate, crushed face, rail, 36 t (40 tons) axle loads.

ISSN:0008-3674    

DOI:10.1139/t99-108

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The purpose of this research was to obtain a better understanding of the nonlinear stress-strain behavior of the typical gravel of Santiago, Chile, due to the increasing needs for construction of high-rise buildings, multilevel underground constructions, and new subway lines to be built under historical city landmarks. A finite-element computer program to perform incremental stress-strain analyses of soils was developed on the basis of a modified version of the hyperbolic elastic model. The changes herein proposed to this well-known constitutive model were based on triaxial tests carried out on 150 mm diameter specimens of compacted sandy gravels which involved various stress paths. A comparison was performed between the observed and calculated load-settlement relationship in a plate-load test that included unloading-reloading cycles. From the good agreement obtained it is concluded that the modified version of the hyperbolic model proposed represents reasonably well the behavior of the Santiago gravel.Key words: constitutive relations, finite-element model, laboratory tests, field tests, soil properties, case history.

ISSN:0008-3674    

DOI:10.1139/t99-109

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

When a mass of saturated clay is heated, as in the case of host soils surrounding nuclear waste disposal at great depth, the thermal expansion of the constituents generates excess pore pressures. The mass of clay is submitted to gradients of pore pressure and temperature, hydraulic and thermal flows, and changes in its mechanical properties. In this work, some of these aspects were experimentally studied in the case of Boom clay to help predict the response of the soil, in relation to investigations in the Belgian underground laboratory at Mol. Results of slow-heating tests with careful volume change measurements showed that a reasonable prediction of the thermal expansion of the clay-water system was obtained by using the thermal properties of free water. Despite the density of Boom clay, no significant effect of water adsorption was observed. The thermal consolidation of Boom clay was studied through fast-heating tests. A simple analysis shows that the hydraulic and thermal transfers are uncoupled. Experimental results from fast-heating tests showed that the consolidation coefficient does not change significantly with increased temperature, due to the opposite effect of increasing permeability and decreasing porosity. The changes of permeability with temperature were investigated by running constant head measurements at various temperatures. An indirect analysis, based on estimation of the coefficient of volume changemv, showed that the indirect method of estimating the permeability from consolidation tests should be considered carefully. Intrinsic permeability values were derived by considering the change of the viscosity of free water with temperature. A unique relationship between the intrinsic permeability and the porosity was observed, with no dependence on temperature, confirming that the flow involved in the permeability test only concerns free water.Key words: clays, thermal consolidation, adsorbed water, permeability, temperature effects, radioactive waste disposal.

ISSN:0008-3674    

DOI:10.1139/t99-105

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The results of laboratory column tests conducted to assess the effect of the mass loading on the clogging of porous media are presented. The tests were conducted using actual leachate from the Keele Valley Landfill under saturated, anaerobic conditions. It is shown that clogging is greatest where there is the greatest mass loading (near the inlet in this case, but likely near the collection pipes in a field situation). An empirical relationship between the hydraulic conductivity and drainable porosity is presented. Even though it is shown that higher flow rates give rise to less efficient bioreactors, the columns with high flow still experience greater rates of clogging than those with low flow. The columns were found to be severely clogged when the drainable porosity had decreased to about 10% of the initial value. The bulk (wet) density of the clog material is found to range between 1.6 and 2 Mg/m3and, on a dry mass basis, 27% of the clog is calcium and 47% is carbonate. The columns were colonized by a diverse consortium of bacteria including methanogens, sulfate-reducing, and denitrifying bacteria, with methanogens being dominant in the portion of the column where clogging was most severe.Key words: leachate collection, clogging, porous media, mass loading, flow rate, anaerobic, microbial.

ISSN:0008-3674    

DOI:10.1139/t99-107

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

This study uses several approaches to examine whether calcium-containing aggregate such as dolostone is a suitable drainage material for landfill leachate-collection systems. The thermodynamic stability of carbonate drainage materials has been assessed using published leachate data from landfills in the United Kingdom and leachate sampled from four large landfill sites of variable age in southern Ontario. Electron-microbeam techniques have been used to check for dissolution in dolomitic stone exhumed from the drainage layer of the Keele Valley Landfill leachate-collection system and from experiments that simulated landfill conditions. The mineralogy of cover soils applied daily to the landfill has been compared to the drainage stone and detrital material occluding pore space in the leachate-collection system to evaluate their relative contributions to clogging. The data suggest that dissolution of dolomitic drainage stone is not significant and contributes little to the clogging of landfill leachate-collection systems. However, crystallization of secondary calcite occurs about the dolomitic stones and sizeable quantities of inorganic fines, including dolomite, were present within some samples of "clog material" exhumed from the Keele Valley collection system. Most of the dolomitic fines probably were generated during construction of the collection system; such creation of fines ought to be minimized in future landfill developments.Key words: leachate-collection system, landfills, clogging, mineralogy, leachate chemistry.

ISSN:0008-3674    

DOI:10.1139/t99-110

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

This paper presents the results of a full-scale field experiment on the stability of a slurry-filled diaphragm wall trench. The objective of this experiment was to observe the failure pattern of a slurry-supported trench excavated in sandy ground. Ground responses, including settlement and lateral deformation of the surrounding ground adjacent to the experimental trench, were carefully monitored during the experiment. The stability of the trench was examined by lowering the slurry level in stages. The trench was deliberately failed. Field observations indicated that the experimental trench failed in 2 h in a progressive sliding pattern that resulted in a near-hemispherical cave-in of the adjacent ground. In this paper, a failure mechanism of the trench is proposed and an analytical method is adopted to back-analyze the stability of the trench. The stability of the trench and the failure pattern can be accurately analyzed using the method of Tsai and Chang.Key words: full-scale experiment, field test, slurry trench, stability analysis.

ISSN:0008-3674    

DOI:10.1139/t99-122

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The objective of the present research is to quantitatively evaluate the compression that can occur during the evaluation of pore-size distribution of cohesive soil using mercury intrusion porosimetry (MIP). A new experimental procedure was developed that can be routinely used to evaluate the corrections associated with the compressibility for porous solid samples using MIP. The approach used in this study involves performing mercury intrusion tests on dehydrated kaolin samples using freeze-dried and oven-dried techniques, and on identical samples confined by low-porosity latex membranes. Corrections for latex intrusion and issues related to dehydration of samples are addressed. The measured contact angle of mercury with kaolin clay using the sessile drop technique was used in the data reduction. Repeatable test results were obtained throughout the testing program. The procedure for obtaining volume-change behavior under isotropic conditions for a large range of pressures using the mercury porosimeter is also presented for oven-dried samples. Scanning electron micrographs for intruded and compressed specimens are presented along with a discussion on the observed hysteresis in MIP test data. The test results for kaolin samples show substantive initial compression before the occurrence of actual intrusion. This resulted in errors associated with the interpretation of pore sizes with diameters in the range of 0.4-200 µm.Key words: mercury intrusion, clay, compression, correction, pore-size distribution, high pressure.

ISSN:0008-3674    

DOI:10.1139/t99-121

出版商:NRC Research Press    

年代:2000

数据来源: NRC