摘要:

Spatial variability of undrained strength (Cu) has been modelled in several ways in the past. In particular, concepts of time series such as autoregressive moving average models have been used to model the analogous "spatial series" of the values of depth versus undrained strength. It should be noted that the very purpose of such modelling studies is to provide estimates of the values of undrained strength at a given value of depth. In the present paper, the main prerequisite to apply these models, viz. the complete removal of trend present in the spatial series of depth versusCu, has been focussed. An accurate modelling procedure is recommended which can estimate the values ofCuat a given value of depth better than any other model in this class of models existing in the literature. Sensitivity in the trend patterns of the depth versus Cudata is well taken care of. A computer program has been developed inFORTRAN77to fit the model in conjunction with a standard nonlinear least-squares routine taken from the literature. One of the advantages of the present model is the speed of convergence of the computer program. Two case studies appearing in the literature have been successfully solved to demonstrate the efficacy of the model developed.Key words: spatial variability, time series analysis, spatial series, nonstationarity, autoregressive moving average models, regression, nonlinear least squares, error sum of squares.

ISSN:0008-3674    

DOI:10.1139/t92-080

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Numerous studies have been completed in recent years on the alteration of the hydraulic conductivity of clayey soils as a result of exposure to concentrated organic or inorganic permeants. These hydraulic conductivity changes have been attributed to either changes in microstructure, due to contraction of the diffuse double layer, or to the alteration of the macrostructure, as a result of volume changes leading to shrinkage fractures or fissures. In this paper, the change in hydraulic conductivity of a highly plastic natural clay during exposure to a concentrated sodium chloride (NaCl) solution is described. The performance of samples with three different initial soil structures, prepared by slurry, static compaction, and kneading compaction, were investigated under various levels of confining stress. Hydraulic conductivity tests were carried out before and after the samples were exposed to the NaCl solutions. Scanning electron microscope photography was used to compare the soil structures before and after brine permeation. The test results show that the alteration of hydraulic conductivity is strongly related to the initial soil structure and the level of confining stress. No significant change in the microfabric of the clay was observed; however, the size of the interaggregate pores appeared to increase as a result of the physicochemical volume change that occurred during brine permeation. The increase in hydraulic conductivity that occurred during brine permeation could be prevented by increasing the level of confining stress. The stress levels at which significant increases in hydraulic conductivity occurred appeared to be coincident with low levels of vertical stress which allowed the sample to undergo lateral shrinkage and a subsequent loss of confinement.Key words: hydraulic conductivity, clay soils, osmotic consolidation, sodium chloride brine, soil structure, scanning electron microscope.

ISSN:0008-3674    

DOI:10.1139/t92-081

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

In the vicinity of an excavation in a saturated soil, ground settlements are often caused by the combined effects of stress release and drawdown of the water table. These settlements may be crucial if the excavation is carried out in a congested area. A case history of excavation adjacent to closely constructed blocks of buildings is discussed in this study. Ground settlements and water-surface levels were monitored during the excavation period, as the settlement of the surrounding area was of concern. The authors have previously developed a fully coupled numerical method that allows the computation of the displacements and pore pressures in a soil taking account of the drawdown of the water table which may accompany excavation. This method is used here for back-analysis of a full-scale excavation that has been comprehensively documented. Comparisons between the field measurements and the calculated results are given in this paper.Key words: consolidation, excavation, finite element, seepage, transient unconfined flow.

ISSN:0008-3674    

DOI:10.1139/t92-082

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The paper describes a new field testing method, called the sharp cone test, intended forin situdetermination of creep properties of frozen soils and ice. The method consists of pushing a smooth, low-angle, cone into a predrilled conical portion of a borehole. The creep properties of the material are determined by applying a constant axial load on the cone, and by observing its time-dependent axial displacement as it penetrates and enlarges the conical hole. The paper describes the test, gives its theoretical interpretation, and shows the results of a series of tests carried out in a frozen sand.Key words: frozen soil, ice, sharp cone, field testing, creep properties.

ISSN:0008-3674    

DOI:10.1139/t92-083

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The theoretical model for predicting the cyclic response of soils is extended to handle the generation and dissipation of pore-water pressures and to predict the rutting of the subgrade of a flexible pavement. The model utilizes multiyield surfaces and the concepts of critical state mechanics to predict the permanent deformation of the subgrade under vehicular loading. The theoretical solution also considers the effects of the drainage characteristics of the subgrade soil on the rate of development of the permanent deformation. Experimental verification of the model concepts are presented for a drained cyclic load test on Ottawa sand and for undrained cyclic loading on Newfield clay using published experimental data. An illustrative example is given for the prediction of rutting in a silty clay subgrade. The model parameters for the silty clay are obtained from triaxial and consolidation tests. These parameters are then put into a computer program that determines the rut depth, pore-water pressure, and the ratio of the vertical deformation and the rut depth as functions of the number of vehicular loads for a flexible pavement for various conditions of drainage ranging from undrained to fully drained. The role of the coefficient of consolidation of the subgrade in controlling the rate of development of the rut depth is highlighted.Key words: critical state soil mechanics, multiyield surfaces, rutting, silty clay subgrade, drainage, vehicular loading.

ISSN:0008-3674    

DOI:10.1139/t92-084

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The behaviour of a pipeline embedded in a creeping medium is examined. Approximate solutions for a beam in a creeping foundation are developed, and characteristic nondimensional load–displacement relationships are presented. A comparison of these approximate solutions provides upper and lower bound solutions that are consistent with finite element analyses. Furthermore, the simplified solutions can be readily adapted for analyzing the uplift behaviour of shallow pipelines. These solutions can also be used to analyze the creeping behaviour of laterally loaded piles. The results are presented in the form of nondimensional charts that permit hand calculations and rapid verification of the structural design of the pipelines and piles. An approximate three-dimensional solution that accounts for embedmentis proposed.Key words: creeping behaviour of pipelines, creeping foundation, laterally loaded pile.

ISSN:0008-3674    

DOI:10.1139/t92-085

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Available design methods for anchored bulkheads do not allow easy optimization of design. To facilitate optimization, generalized parameters were developed to characterize the design situation and analytical results. Design aids were formulated as graphs and tables which show the relations among input data (anchor location, surcharge pressure, dredge depth, depth to water, and soil characteristics) and design output (maximum moment, anchor force, and embedment).Key words: bulkhead, anchored, design, dredged, sand.

ISSN:0008-3674    

DOI:10.1139/t92-086

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

In recent years dynamic compaction (DC) has become a popular method for deep improvement of loose cohesionless soils and man-made fills of disposed waste and rubble. One of the main problems facing design engineers and contractors is the assessment of the number of tamper drops, grid spacing, and layout of passes required to attain satisfactory improvement depth in the soil strata. Many DC sites have irregular subsurface conditions where it is difficult to interpret results from site exploration and verification tests. The industry has long been using a simple relationship to estimate the depth of improvement (influence depth). The estimates obtained from that empirical method may vary considerably and in many cases may be rendered useless for DC design. The paper describes a new, rational, and more comprehensive DC design method based on results from an extensive experimental model study of impact response in dry sand. Analysis of normalized impact energy and the resulting densification in the sand in terms of normalized dimensions of volumetric strain contours shows unique correlations that are used for the proposed design method for dynamic compaction in unsaturated sandy soils. Data from several DC sites fit well with the new method. With future studies of field results the proposed approach could eventually be calibrated and used for other types of soil conditions.Key words: dynamic compaction, design, impact, sandy soil, energy, plastic strains

ISSN:0008-3674    

DOI:10.1139/t92-087

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The study of the physicochemical properties of pure amorphous materials (complexes) consisting of Fe2O3and SiO2in various proportions indicates that the amorphous complexes will exhibit different properties and characteristics depending on the proportions of Fe2O3and SiO2. Addition of the amorphous complexes with illitic clay studied shows that the properties of the clay admixture will also vary according to the properties of the amorphous complex, albeit to a lesser degree. The properties and behaviour observed for the amorphous complexes and the clay admixtures can be linked directly to the large specific surface area and high surface charge of the amorphous complexes. The contribution of amorphous complexes to the clay – amorphous complex mixtures (clay admixtures) is twofold: firstly, by the amount of amorphous complex in the clay admixture, and secondly by the composition of the amorphous complex used. The contribution from the amorphous complex is in two forms: water-holding capacity and bonding action. The presence of pH-dependent surface charges associated with the amorphous complexes makes the physicochemical properties and behaviour of the clay admixtures (e.g., liquid limits and zeta potential) sensitive to the pH environment. Coating of amorphous colloids onto clay particle surfaces, shown by scanning electron microscopy, appears to, be enhanced by a decrease in pH of the system, indicating that the enhancement is likely due to the increased electrostatic attraction resulting from the increased amounts of positive charges on the amorphous colloids.Key words: amorphous materials, mass ratio, zeta potential, Bingham yield stress, clay admixtures, hydrogen bonding, specific surface area, cation exchange capacity, anion exchange capacity, fabric and soil structure.

ISSN:0008-3674    

DOI:10.1139/t92-088

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The pore-pressure generation and dissipation around shallow tunnels excavated in both normally and overconsolidated clays are investigated. The influence of the diameterD, depth of cover to diameter ratioH/D, coefficient of earth pressure at restK0, and strength and modulus variations with depth on pore-pressure generation are examined. The effects of immediate support on pore pressure are also studied by defining a quantity termed effective stiffness ratio (ESR). A two-dimensional, nonlinear finite element analysis is performed to obtain the pore-pressure generation behav-iour. Strength, modulus, initial stress field, and unloading due to excavation are reflected in this analysis. The pore-pressure dissipation behaviour is investigated by employing an uncoupled consolidation theory using finite elements. A dimensionless time factor is used to present the results of pore-pressure dissipation. These results are presented using nondimensional quantities and in normalized forms. The results are directly applicable to estimation of pore pressures for determining long-term stability of tunnels.Key words: clay, pore pressure, tunnels, uncoupled consolidation, finite elements, stress-strain.

ISSN:0008-3674    

DOI:10.1139/t92-089

出版商:NRC Research Press    

年代:1992

数据来源: NRC