摘要:

The Statnamic (STN) load test is characterized by a relatively long duration and low pile velocity and acceleration compared with the dynamic load test. The estimation of the static capacity of piles and their static performance characteristics from dynamic loading tests usually requires a signal matching process. In this process, the soil parameters are varied until an acceptable match between the computed and measured responses is achieved. The soil properties obtained are then used to characterize the static behaviour of the pile. In this paper, an approach is presented to analyze the response of flexible and rigid piles during the STN load test. In this approach, a one-dimensional model is used to represent the pile-soil system accounting for nonlinear soil behaviour, slippage at the pile-soil interface, and energy dissipation through wave propagation and different types of damping. The postpeak resistance of certain types of soils is also considered in the analysis. An automatic matching technique (AMT) was developed to facilitate the signal matching process for the analysis of pile response during the STN load test. The proposed AMT has several advantages, including reducing the bias in the results due to the initial selection of the soil parameters; increasing the accuracy and reliability of computed pile capacity; and reducing computational time, thus allowing for the analysis of the test results in the field. It is then possible to compute the pile capacity and make a timely decision on its suitability. The proposed approach was used to analyze the results of six STN load tests, and the comparison between the measured and computed results was good.Key words: piles, Statnamic, pile load test, signal matching, transient load, capacity.

ISSN:0008-3674    

DOI:10.1139/t00-028

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Researchers have shown that properties of fine-grained soils such as hydraulic conductivity change significantly when the pore fluid is replaced with organic liquids. In general, such changes have been reported as a function of the dielectric constant of the pore fluid and attributed to changes in soil structure. However, mechanisms causing changes in soil structure are yet to be understood. In this paper, the physicochemical properties of kaolinite, bentonite, and a local soil are determined as a function of the dielectric constant of pore fluids to evaluate the mechanisms causing changes in soil structure and, in turn, hydraulic conductivity. The physicochemical parameters determined in this study are cation exchange capacity (CEC), zeta potential (&zgr;), surface charge density, pore-size distribution, and Atterberg limits. Results show that physicochemical properties change as the dielectric constant of the pore fluid changes, such that as the dielectric constant of the pore fluid approaches that of the soil, the repulsive and attractive forces diminish; yet, there is a net increase in the attractive forces, causing aggregation of the particles. Based on the results of this study, it is suggested that as repulsive forces decrease the soil particles tend to flocculate and form aggregates due to attractive forces among particles, leading to a net increase in the effective flow area, resulting in increased hydraulic conductivity of the soil - pore fluid system.Key words: fine-grained soils, diffuse double layer, attractive forces, physicochemical parameters, CEC, zeta potential.

ISSN:0008-3674    

DOI:10.1139/t00-023

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

This paper presents the prediction of horizontal load-displacement curves of pile groups based on the results of single pile tests. Although the same basic model is employed, two different approaches are taken: one assumes soil to be linear elastic-plastic, and the other assumes it to be elastic nonlinear. The model is calibrated on the basis of the results of a full-scale single pile test. Special emphasis is placed on model calibrations, since the success of any prediction method depends on a careful characterization of the soil. Some new approaches for determining the soil parameters are presented. Two methods for predicting load-displacement curves, one from each model approach, are then proposed and discussed. Special emphasis is placed on group efficiency in the elastic-plastic method and on the boundary conditions of the single pile and the pile group in the elastic nonlinear method. Using the soil characteristics from the model calibrations, the load-displacement curves for a given pile group are then predicted. These predictions are compared with the results of a full-scale pile group test carried out at the same site as that of the single pile test. Agreement between the predictions and the test results tends to validate the methods proposed.Key words: displacement predictions, pile groups, model calibration, pile tests.

ISSN:0008-3674    

DOI:10.1139/t00-022

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The implementation of unsaturated soil mechanics into geotechnical engineering practice requires that there be a paradigm shift from classical soil mechanics methodology. The primary drawback to implementation has been the excessive costs required to experimentally measure unsaturated soil properties. The use of the soil-water characteristic curve has been shown to be the key to the implementation of unsaturated soil mechanics. Numerous techniques have been proposed and studied for the assessment of the soil-water characteristic curves. These techniques range from direct laboratory measurement to indirect estimation from grain-size curves and knowledge-based database systems. The soil-water characteristic curve can then be used for the estimation of unsaturated soil property functions. Theoretically based techniques have been proposed for the estimation of soil property functions such as (i) coefficient of permeability, (ii) water storage modulus, and (iii) shear strength. Gradually these estimations are producing acceptable procedures for geotechnical engineering practices for unsaturated soils. The moisture flux ground surface boundary condition is likewise becoming a part of the solution of most problems involving unsaturated soils. The implementation process for unsaturated soils will still require years of collaboration between researchers and practicing geotechnical engineers.Key words: unsaturated soil mechanics, soil suction, unsaturated soil property functions, negative pore-water pressure, matric suction, soil-water characteristic curve.

ISSN:0008-3674    

DOI:10.1139/t00-026

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

To prevent the appearance of localized sinkholes under roads and railway lines in areas at risk, a research program testing a geosynthetic reinforcement solution was carried out by a group of laboratories. The aim of the reinforcement is to limit surface deformation after the appearance of a sinkhole by making the surface settlement as compatible as possible with the geometrical safety criteria of the road or railway line until earth filling and repair works can be scheduled. Full-scale tests were carried out on reinforced, instrumented road and railway structures subjected to localized collapse. At the same time, a numerical study was carried out to gain a better understanding of the mechanisms involved (arch effect, membrane effect, and collapse mechanisms). The experimental results of the full-scale tests were analyzed and compared with the results of three-dimensional finite element modeling.Key words: localized sinkhole, karstic cavity, reinforcement, geosynthetic.

ISSN:0008-3674    

DOI:10.1139/t00-002

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The paper describes the results of a statistical analysis of failures and accidents of embankment dams, specifically concentrating on those incidents involving piping and slope instability. The compilation of dam incidents includes details on the characteristics of the dams, including dam zoning, filters, core soil types, compaction, foundation cutoff, and foundation geology. An assessment of the characteristics of the world population of dams was also carried out. By comparing the characteristics of the dams which have experienced failures and accidents to those of the population of dams, it was possible to assess the relative influence of particular factors on the likelihood of piping and slope instability.Key words: dams, failures, piping, instability database.

ISSN:0008-3674    

DOI:10.1139/t00-030

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

A method for estimating the relative likelihood of failure of embankment dams by piping, the University of New South Wales (UNSW) method, is based on an analysis of historic failures and accidents in embankment dams. The likelihood of failure of a dam by piping is estimated by adjusting the historical frequency of piping failure by weighting factors which take into account the dam zoning, filters, age of the dam, core soil types, compaction, foundation geology, dam performance, and monitoring and surveillance. The method is intended only for preliminary assessments, as a ranking method for portfolio risk assessments, to identify dams to prioritise for more detailed studies, and as a check on event-tree methods. Information about the time interval in which piping failure developed and the warning signs which were observed suggest that the piping process often develops rapidly, giving little time for remedial action. In the piping accidents, the piping process reached some limiting condition allowing sufficient time to draw down the reservoir or carry out remedial works to prevent breaching.Key words: dams, failures, risk, probability, piping.

ISSN:0008-3674    

DOI:10.1139/t00-029

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

A series of three-dimensional finite element analyses has been carried out to investigate the effect of the removal of sections of an earth berm supporting an embedded retaining wall. For the particular wall-berm geometry and ground conditions considered in these analyses, relationships between the wall movement, the length of berm section removed, the spacing between successive unsupported sections, and the time elapsed following excavation are presented and discussed. The analyses show that, for a given elapsed time, wall movements are proportional to the length of the excavated berm section provided that the unsupported sections are sufficiently widely spaced. If the spacing between unsupported sections is reduced below some critical value, wall movements then depend on both the length of and distance between the excavated berm sections.Key words: finite element analyses, diaphragm walls, earth berms, construction sequence, three-dimensional effects.

ISSN:0008-3674    

DOI:10.1139/t00-033

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The paper presents some findings from recent laboratory research aimed at improving ground-movement predictions in a hard, heavily overconsolidated lodgement till. These findings are subsequently applied to a new three-dimensional version of the BRICK soil model to investigate the suitability of this model for the till. It is shown that BRICK captures the essential features of the material's behaviour under triaxial conditions and is capable, when incorporated in a finite element code, of providing realistic predictions for the settlement of shallow foundations.Key words: glacial till, stiffness, strength, BRICK model, footing settlement.

ISSN:0008-3674    

DOI:10.1139/t00-032

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Vane shear test data obtained by a number of researchers show that the excess pore pressures generated within the soil surrounding the vane by vane insertion and rotation and their effects on the measured vane shear strength have been misinterpreted for many years. The accepted model developed by Blight of field vane testing and the accepted criteria for determining undrained and fully drained vane shear strengths are based on this misinterpretation. Consequently, estimates that are based on this model of the degree of drainage that has been attained at the time the vane shear strength is measured may be significantly in error, and the measured undrained shear strengths may be unconservative. A revision of Blight's approximate theory of field vane testing is presented which is consistent with the available experimental data. Revised practical criteria for determining the undrained and fully drained shear strengths are also presented, and a simple revision of current standard vane shear test methods is proposed which would eliminate, for all but those soils with very high coefficients of consolidation, the possibility that estimates of the undrained vane shear strength may be unconservative.Key words: vane shear, undrained strength, drained strength, excess pore pressure.

ISSN:0008-3674    

DOI:10.1139/t00-035

出版商:NRC Research Press    

年代:2000

数据来源: NRC