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This Paper describes the results of a series of large-scale triaxial tests conducted on greywacke rockfill, used in dam construction in Southern Thailand. The tests are conducted at low to moderate confining stresses to relate their findings to the stability of rockfill dams. Considering the current test results in conjunction with previous laboratory data, revised failure criteria for rockHI are proposed in nondimensional form. For both low and hieh confining stresses, lower and upper bounds of strength envelopes have been established, based on a wide array of granular materials. The influence of the coofining stress on the shear strength of rockfill is studied in depth, and the implications of a non-linear envelope at low normal stress levels on the stability of rockfill dams are discussed. Although two parallel rockfill gradations for specimens compacted to similar porosities are considered, the exact role of particle size effect on shear strength is not examined in detail, as the difference in maximum particle sizes tested in this study is not sufficiently large.

This paper presents the performance of a full-scale test embankment constructed on soft Bangkok clay with prefabricated vertical drains (PVDs) at the site of the new Bangkok International Airport in Thailand. The embankment was square in plan with a maximum height of 4.2 m, 3H:1V side slopes, and base dimensions of 40 m by 40 m. The piezometric level with depth is characterized by negative drawdown starting at around 8-10 m depth caused by excessive withdrawal of groundwater. Instrumentation was provided to monitor both horizontal and vertical movements of the test embankment. The measured increases in undrained shear strengths with depth are in agreement with the values calculated from the SHANSEP technique. The secondary compression ratio, Cα, was 0.018, or within the normal values for marine clays. The coefficient of horizontal consolidation measured in the field, Ch(field), was higher for soil at 4 and 10 m depths than for the weakest soil at 6 m depth. The back-calculated Ch(field) values range from 3 to 8 m2/year, and the ratio of Ch(field) to Ch(lab) ranges from 4 to 5, where Ch(lab) is the coefficient of horizontal consolidation measured in the laboratory. The degree of consolidation estimated from the pore-pressure dissipation measurements agreed with those obtained from settlement measurements. The water-content reductions from field measurements were also in good agreement with the values computed from the consolidation settlements. The full-scale study confirmed that the magnitudes of consolidation settlements increased with the corresponding decrease of PVD spacing at a particular time period. Lastly, the results of the full-scale study have proven the effectiveness of PVDs for the improvement of soft Bangkok clay.Key words: soft clay, consolidation, prefabricated vertical drain, preloading, test embankment.

This paper describes the observed and the predicted performance of a full·scale trial embankment built to failure on a soft Malaysian marine clay. Predictions of the subsoil deformation, the critical height of fill and the corresponding slip surface are made and subsequently compared to the field measurements. It is of importance to realize that all the predictions were made prior to the actual failure of the embankment. The comparison with measurements was possible only after the International Symposium on Trial Embankments on Malaysian Marine Clays, was held in Kuala Lumpur, Malaysia, in November 1989, during which the field data were made available to the invited predictors (including the second writer) by the Malaysian Highway Authority. Finite-element codes based on the modified Cam-clay theory (CRISP) and hyperbolic stress-strain model (ISBILD) were utilized to investigate the behavior of the embankment and the foundation soil until failure. The type of numerical modeling includes purely undrained, fully drained, and a coupled consolidation analysis. The finite-element solutions are subsequently compared with the conventional stability analy.sis.

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