This paper reviews laboratory methods for measuring the stress-strain-strength-flow behaviour of soft clays for determination of design parameters. It describes three levels of testing from simple classification tests to advanced testing for measurement of design parameters. The paper traces some of the major practical contributions of experimental research to our understanding of soft clay mechanical behaviour. Recommendations are given for implementation of these research results in practice with the goal of improving the engineering state-of-the-practice, which often lags well behind the research state-of-the-art. Significant advances in the understanding of clay behaviour have been realized in the past few decades including such issues as the influence of anisotropy, stress history, rate effects, and sample disturbance. Of these issues, sample disturbance remains by far the most difficult one to deal with in practice and in fact is often ignored. It is recommended that evaluation of sample disturbance be considered an essential aspect of any site characterization program.
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This paper reviews the causes of sample disturbance and its impact on laboratory measured design parameters for soft clays. It is the most significant issue affecting the quality and reliability of laboratory test data. All key design parameters such as compressibility, yield stress and undrained shear strength are adversely influenced by sample disturbance. Each stage of the sampling process, from initiation of drilling to final preparation of laboratory test specimens, causes potential disturbance to samples and is described in the paper. Several practical solutions are presented, which if properly implemented can reduce the degree of sample disturbance. These include the use of weighted drilling mud, special tube sample geometry, fixed piston samplers, and proper sealing and handling of samples. Qualitative and quantitative methods of assessing sample quality are also presented together with examples from case studies.
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