This paper is an extension of earlier papers (Wong et al., 2008a, b) which sought to investigate the poroelastic and poro-viscoelastic behaviour of a ground medium following the closing of a spherical cavity, whereas the focus here is for a long horizontal tunnel with a circular section. It presents Laplace transform analytic solutions for the time dependent hydromechanical responses of a decommissioned and backfilled deep tunnel drilled into a poro-viscoelastic host medium. Both the backfill, which is assumed as poroelastic, and the host medium are supposed saturated with water. The solutions developed and inverted numerically to obtain the responses in time domain are used to study the effects of lining support deterioration, the backfill stiffness and of the host medium viscosity. The convergence of the tunnel leads to the expulsion of water from the backfill into the host medium resulting in corresponding transient responses. Each of the key parameters studied can have the effect of either attenuating or accentuating the transient and long term hydromechanical responses by delaying or shortening the dissipation period depending on the direction of change taken by the parameter value. The solutions presented in this paper permit an assessment of the relative importance of these parameters. Comparisons are also drawn between a tunnel and a spherical cavity of identical radius. Generally speaking, the implications of lining support, backfill stiffness and viscosity of ground medium are more significant in terms of the resulting hydromechanical responses, for the tunnel than for the spherical cavity.

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To investigate liquefaction properties of sandy soils, undrained cyclic loading tests are usually performed. However, it would be difficult to simulate fully the actual soil behaviour through the laboratory tests because the tested sample can be disturbed even though it is taken by in-situ freezing technique. In this study, by using three kinds of in-situ frozen sandy soils which were taken from Holocene and Pleistocene deposits and their reconstituted samples, their volume change properties were measured during freeze and thaw processes at different confining pressures of 30 kPa and 98 kPa. In order to investigate the effects of the possible sample disturbance on the liquefaction resistance, small strain characteristics were measured as well, which would reflect the soil structure. Decreases in the small strain characteristics and the liquefaction resistance were observed in case of the Holocene specimens that were thawed at the confining pressure that was lower than the in-situ overburden stress. On the other hand, in case of the Pleistocene specimens, the effects of the confining pressure during the thaw process on the small strain characteristics and the liquefaction resistance were small. Such contrastive feature between the Holocene and the Pleistocene samples could be linked with the difference in the types of their natural aging effects.

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An investigation into the base capacity of piles in passing through loose, liquefiable sand and founded in underlying dense sand is presented based on the results of a series of dynamic centrifuge tests on instrumented model pile groups. Excess pore pressures equal in magnitude to the initial effective vertical stress were observed to be generated in the bearing layer of dense sand at both shallow (15 m) and deep (26 m) depths. This induced a dramatic reduction in base capacity and consequently, large settlements of the piles by as much as ~5D₀. A spherical cavity expansion solution for base capacity was validated against measured values showing good agreement, provided that excess pore pressure and dynamic shear stiffness in the bearing layer are known. A simple closed-form relationship, applicable to end-bearing piles, between the degree of liquefaction and the initial pile static safety factor was then developed against plunging failure at the pile base which can be used in design.

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All rigorous methods of slices, i.e., those satisfying all equilibrium conditions, have numerical problems under some conditions, and the worst is “failure to converge” even if the solution exists. This is considered to be the unique reason that those simplified slice methods, i.e., those satisfying part of equilibrium conditions, are still in use. The purpose of this study is to develop a solution procedure for those rigorous methods such as Morgenstern-Price's method. The procedure is so robust that it is able 1) to detect whether the solutions exist within a specified domain; 2) to find out all possible solutions; 3) and to trace all branches of equilibrium curves in the domain.

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The initial, linear elastic range of a soil stress-strain curve is often defined by the small-strain elastic modulus E₀ or shear modulus G₀. In the present study, simpler and effective methods are proposed for the estimation of the small-strain stiffness of clean and silty sands; these are based on triaxial compression test results and the CPT cone resistance q_c. In the method based on stress-strain curves obtained from triaxial compression tests, an extrapolation technique is adopted within the small-strain range of a transformed stress-strain curve to obtain estimates of the small-strain elastic modulus. Calculated small-strain elastic modulus values were compared with the values measured using bender element tests performed on clean sands and sands containing nonplastic fines. The results showed that the method proposed produces satisfactory estimates of the small-strain elastic modulus for practical purposes. In the CPT-based method, two G₀-q_c correlations available in the literature were evaluated. For isotropic conditions, both correlations produced reasonably good estimates of G₀ for clean sands but overestimated it for silty sands. A G₀-q_c correlation which is proposed takes into account the effect of silt content of the sand and stress anisotropy.

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The liquefaction potential assessment under the framework of simplified procedure that involves the use of cone penetration tests (CPT) typically relies on empirical correlations between the soil cyclic resistance ratio, CRR and cone tip resistance q_t. For sands that contain fines (particles passing #200 sieve), an adjustment based on fines content in the CRR-q_t correlation is called for in currently available procedures. Earlier laboratory calibration tests in reconstituted silty sand specimens performed by the authors have indicated that partial drainage in CPT played an important role in the CRR-q_t correlations. A series of laboratory tests on undisturbed samples and field piezocone penetration tests (CPTU) were carried out in an alluvial soil deposit at two test sites in Central and Southern Taiwan. The results indicated that unlike the uniformly mixed specimens reconstituted in laboratory, the tested natural alluvial silt/sand soils can be heterogeneous with closely spaced clean sand layers embedded in a matrix of silty material. This stratification can render the CPTU a drained test even at fines contents well in excess of 50%. The ignorance of free draining effects on CPTU due to stratification in alluvial soils may lead to overestimation of CRR. Because of these factors, calibration of the CRR-q_t correlations by performing tests in local soil and field procedures to ascertain the drainage conditions in CPTU are important to the proper application of the CRR-q_t correlations in the liquefaction potential assessment.

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Fick's law has been used to simulate gas systems within soil, although this law can be applied only to binary gas systems and the effect of the Knudsen diffusion is not considered. By contrast, the dusty gas model can be applied to multi-component gas systems with Knudsen diffusion. Blanc's law is a simplified version of the dusty gas model, but it can be used only for gas systems in which the tracer gas is dilute. Although the dusty gas model is superior to other methods for simulating gas systems within soil, it is not generally used because of its complexity. Numerical techniques such as the Eulerian-Lagrangian method for solving the advection-dispersion equation can be used to simulate the migration of chemical substance in the water or gas phases of soil within the range of every Péclet number. We derived the compound diffusion coefficient and compound velocity from the dusty gas model and formulated the advection-diffusion equation with these values by using the characteristic finite element scheme. Results of the model developed here were consistent with the results of column experiments conducted in this study, and the precision of the developed model was verified.

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In this paper, a new thermo-elasto-viscoplastic model is proposed, which can characterize thermodynamic behaviours of soft sedimentary rocks. Firstly, as in the Cam-clay model, plastic volumetric strain which consists of two parts, stress-induced part and thermodynamic part, is used as hardening parameter. Both parts of the plastic volumetric strain can be derived from an extended e-ln p relation in which the thermodynamic part is deduced based on a concept of ‘equivalent stress’. Secondly, regarding soft sedimentary rocks as a heavily overconsolidated soil in the same way as the model proposed by Zhang et al. (2005), an extended subloading yield surface (Hashiguchi and Ueno, 1977; Hashiguchi, 1980; Hashiguchi and Chen, 1998) and an extended void ratio difference are proposed based on the concept of the equivalent stress. Furthermore, a time-dependent evolution equation for the extended void ratio difference is formularized, which considers both the influences of temperature and stresses. Finally, it is proved that the proposed model satisfies thermodynamic theorems in the framework of non-equilibrium thermodynamics.

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In order to discuss the flow through a rough surface rock fracture, direct shear and flow coupling tests on various rock fractures are carried out. Through the experimental results, the flow on the fracture and the validity of the cubic law are discussed and estimated. As a result, it is understood that the cubic law cannot sufficiently explain the experimental results, although it can partially take into account the experimental results in the Re range of 0.02 to 0.2. Moreover, a simulation by a 2D model, including the inertia term, has been carried out. The 2D model has been found to show a good performance of the fracture flow in comparison with the representative fracture flow model, namely, LCL (local cubic law). The flow on the fracture shows the channeling flow and a higher Re value. Consequently, the flow on the fracture is thought to be caused by the influence of the inertia term.

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It is shown that the use of visco-plastic shear or volumetric strain as the stress history-independent hardening parameter in an elasto-viscoplastic model for sand may result in inaccurate numerical simulations of geotechnical boundary value problems. A new elasto-viscoplastic constitutive model for sand is proposed, formulated based on a stress path-independent irreversible (or visco-plastic) strain energy-based hardening function. The function was derived based on results from drained plane strain compression (PSC) tests on saturated dense Toyoura sand along a wide variety of stress path. The model is coupled with an existing isotropically work-hardening and -softening, non-associated, elasto-plastic model for sand. The constitutive model takes into account the effects of loading rate due to viscous properties on the stress-strain behaviour as well as those of pressure level, inherent anisotropy and void ratio and work softening associated with strain localization into a shear band. It is shown that the proposed model can much better simulate the effects of stress history on the deformation characteristics of sand than many previous models. The FEM code incorporating the model is validated by simulating physical PSC tests and bearing capacity model tests of a strip footing on sand performed by previous studies.

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This report summarizes the results of international parallel test on the measurement of the elastic shear modulus at very small strains, G_max, using bender elements which was carried out from 2003 to 2005 by technical committee, TC29 (Stress-strain and Strength Testing of Geomaterials) of the International Society of Soil Mechanics and Geotechnical Engineering. The purpose was to evaluate the consistency of the bender element test results obtained by applying the exactly similar test material as well as the test method besides identifying the various existing hardware and software being used in this test. It was decided that the domestic TC29 group of Japanese Geotechnical Society (TC29-JGS) was expected to lead this international co-operation. By 2005, reports of the test results were obtained from 23 institutions from 11 countries. This report has been prepared by TC29-JGS taking a leading role from the beginning. A standard test method is proposed here in order to obtain more accurate data from the bender element test by examining various test methods adopted at different institutions worldwide and the effects of various factors on the test results.

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Kashiwazaki City and Kariwa Village, located in the north central part of Japan, were the major areas damaged during the 2007 Niigataken Chuetsu-oki Earthquake (M_w 6.6). Ground motion records for the area indicate the effects of a deep subsurface structure. Microtremor array observations were performed at three sites and gravity surveys at 120 sites in the Kashiwazaki area. The gravity basement estimated from the gravity surveys exists at a depth of about 1000 m around Kariwa Village Hall, and becomes shallow in the southwestern direction around Kashiwazaki City Hall. The gravity basement is compared with the results estimated by the microtremor array observations and validated at two sites, namely, KST and KVH (Kariwa Village Hall). The peak period of the calculated response spectra at Kashiwazaki Village Hall corresponds to the peak period of the observed H/V spectra during the main shock.

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