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This article presents a case history of the performance of a full-scale test embankment constructed on a marine soft clay deposit improved by prefabricated vertical drains (PVDs) in the east of China. For analyzing the subsoil behavior, a 2D FEM model is established, in which the PVD-improved effect is considered by a simplified method of equivalent vertical hydraulic conductivity. The calculated results can predict the settlement behavior well; however, the FEM gives an underestimate for the value of excess pore pressures and it predicts similar values for the dissipation rate of excess pore pressures. The measured undrained shear strength of subsoil,Cu, is compared with the predicted value based on Ladd’s empirical equation and the Modified Cam-Clay model (MCC). The shear strength predicted by Ladd’s equation agrees well with the measured value, whereas the MCC overestimates the ability to improve subsoil shear strength during consolidation. The undrained shear strength of subsoil,Cu, increased as the construction progressed, and the shear strength incremental ratio, ΔCu/Δp′, decreased slightly with the degree of consolidation,U. [ABSTRACT FROM PUBLISHER]

This article presents a testing study on the strain-rate effects on the stress--strain behavior of natural, undisturbed Hong Kong marine deposits (HKMD) from three Hong Kong locations, including a one-dimensional (1-D) compressibility in a confined condition, and undrained shear strengths in triaxial compression and extension modes. The influences of the strain rates on the one-dimensional compressibility are studied by means of constant rate of strain (CRS) tests and multistage loading oedometer (MSL) tests, and those on the undrained shear strengths are studied by K o -consolidated undrained compression and extension tests with step-changed axial strain rates (C K o UC and C K o UE tests), and with both step-changed axial strain rates and relaxation processes (C K o UCR and C K o UER tests). The strain-rate effects on the stress--strain behavior are generally examined by “apparent” preconsolidation pressures in the 1-D compressions and undrained shear strengths in the triaxial compression and extension stress states. The stress--strain behavior of the natural, undisturbed HKMD exhibits considerable viscous characteristics. In the CRS and MSL tests at a given strain, the higher the strain rate, the higher the effective stress, the higher the porewater pressure. In the undrained shearing tests, the higher the strain rate, the higher the undrained shear strength, but the lower the porewater pressure. For the C K o UC and C K o UE tests on the Tsing Yi site samples, the undrained shear strength increases by 8.5% and 12.1% for one order increment of axial strain rate of 0.2%/hr (i.e., ? 0.2 ) for the compression and extension modes respectively. For the C K o UCR and C K o tests on the Tung Chung site samples of different compositions, average ? 0.2 is increased by 6.2% for the compression and 9.5% for the extension, but by 18.8% for the extension on a higher plastic sample. The present study shows that the strain-rate effects on the stress--strain behavior of the undisturbed HKMD are larger for specimens in extension than those in compression. [ABSTRACT FROM AUTHOR]

China is arguably one of the countries where the most tunneling and underground projects are being performed. Recently in China, it has often been necessary to construct tunnels under many types of conditions and to develop new techniques. Currently, some advanced construction techniques cannot be appropriately applied to different types of underground conditions, and many traditional methods are still often used. However, because of the progress in tunnel boring machines(TBM), innovations are required for the construction method. This article introduces the current situation of TBM both in western countries and in China, and examines the future of TBM in China. [ABSTRACT FROM AUTHOR]