Applicability of tube sampling for Niigata sand deposits is discussed through bender element and cyclic triaxial tests for samples obtained from two-chambered hydraulic piston samplers (Shogaki, 1997) with inner diameters of 48 mm and 50 mm, a one-chambered 70 mm diameter sampler, a 125-mm rotary triple-tube sampler and the frozen (FS) sampling method (Yoshimi et al., 1989). The relationship between the relative density (D_r) and normalized SPT N-value (N₁) obtained from small diameter samplers with inner diameters of 45 mm and 50 mm samplers was close to that of the FS and the N₁ coefficient was greater than those of the 70-mm and other tube samplers. The stress ratio at 20 cycles (R_L20) and the initial modulus of rigidity (G_CTX) of samples obtained from the 45-mm and 50-mm samplers were greater than those of the 70-mm, 125-mm rotary triple-tube and other tube samplers. However, the R_L20 values obtained from the 45-mm and 50-mm samplers were smaller than those of the FS sampler in the area of N₁>24. The G_BE and G_CTX values obtained from the 45-mm and 50-mm samplers were close to those of the FS sampling. Therefore, the 45-mm and 50-mm samplers can take equally high quality samples for Niigata sand deposits.

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The shearing behavior of a soil-structure interface governs the response of many geotechnical systems, in particular piled foundations. The shaft resistance of piled foundations is known to degrade with cyclic loading, although the governing mechanism is not well understood. This paper presents the results of a laboratory soil-structure investigation in which internal specimen deformations were obtained using particle image velocimetry (PIV) and the normal confining stress was permitted to vary according to a constant normal stiffness (CNS) condition. The PIV measurements showed the shear deformation and volume change to be concentrated within a shear band with a thickness of 5-7 particle diameters adjacent to the interface. During a single cycle the volume change within the shear band began with an initial contraction, followed by dilation to the failure envelop. For the cycling amplitude investigated this response led to a net specimen contraction. The benefit of quantifying the thickness and contraction of the shear band using PIV is that the progressive decrease in void ratio of the shear band can be linked to the limiting value imposed by the minimum void ratio. This provides a framework in which the contraction of the specimen depends on the potential contraction expressed as the difference between the current and minimum void ratio. A model for this contraction is presented, and linked to the decay in normal stress and the limiting loss of interface friction. This framework clarifies the mechanism of friction fatigue during installation and loading of displacement piles in sand.

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This paper demonstrates the application of computational contact mechanics in geotechnical engineering. It first presents a general formulation of kinematic constraints for frictional contact and a general description of the associated numerical algorithms. These numerical algorithms are then used to analyse the stability of cantilever sheet-pile walls. It is shown that the finite element method incorporated with the modelling capacity for frictional contact is indeed very useful in geotechnical analysis and can provide solutions to problems that are otherwise difficult to solve.

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This paper discusses a reinforcement method for pouring high-pressure non-dispersive mortar into underwater piers of riprap, and an integrated detection method for the effectiveness of the reinforcement. For verifying the high-pressure grouting enforcement quality, we apply comprehensive non-destructive geophysical methods including ground penetrating radar (GPR) and elastic wave tomography, incorporating with wave velocity test and point loading strength test for core samples. Elastic wave tomographic results show that the velocity of high-quality pouring region increases and that of the low-quality pouring region is low. GPR profiles indicate that the reflection strength from the interface between solid and hollow concrete layers becomes weak after pouring. Core samples verify these phenomena.

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To evaluate the effects of a clay layer on the performance of pump-and-treat remediation, an advection-dispersion analysis assuming non-sorption was calculated by changing five parametric variables, namely, the length of the clay layer, the thickness of the clay layer, the hydraulic conductivity of the clay layer, the effective molecular diffusion coefficient of the contaminants, and the contamination duration. The simulation procedure consisted of firstly contaminating the analysis domain, and then cleaning up this contaminated domain by a pump-and-treat system in order to consider strictly the contamination conditions of a clay layer at a real contaminated site. From the calculation results, the pump-and-treat remediation was found to be effective if at least one of the following two conditions was satisfied, namely, the hydraulic conductivity of the clay layer was greater than 5.0×10⁻⁵ cm/s or the thickness of the clay layer was less than 3 m. In addition, the contamination duration was an important parameter in evaluating the applicability of this pump-and-treat remediation to contaminated sites. For cases in which the contamination duration was short, the contamination conditions of the clay layer easily became heterogeneous such that the remediation duration was much longer than the contamination duration. It is necessary to note that contaminated sites may not always be remedied in a short period of time, even if the sites are discovered early.

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A device is presented for reconstituting sand specimens directly onto the triaxial apparatus by pluviation in air, water or under vacuum. The sand is delivered by means of an uniform rain covering the whole specimen cross section and target density is achieved by changing fall height and depositional intensity. The apparatus was calibrated using Ticino River sand, for which water and vacuum pluviations provided the lowest and highest densities, respectively. Whilst the density of loose samples was similar to that obtained using Kolbuszewski (1948) and ASTM minimum density methods, much denser specimens were obtained with vacuum pluviations as compared to vibration compaction methods (similar to ASTM maximum density method). The resulting maximum relative density, referred to the limits from standard tests, was as high as 140%. Water pluviation density is independent of both depositional intensity and fall height. For other target density best results in terms of sample uniformity are achieved by vacuum pluviation with an appropriate selection of depositional intensity and fall height. This also provides an extremely high reproducibility of target density.

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The pumice sand found in the North Island of New Zealand has properties which lie beyond those usually associated with cohesionless soils. The grains are very soft and the sand has a high void ratio, thus forming a compressible material. This paper presents the results of a series of drained triaxial and K₀ tests on dry pumice sand. The tests were conducted to evaluate the geotechnical properties, particularly the critical state parameters, of the sand and also to provide background information for interpretation of cone penetration tests in the material. The K₀ tests were used to evaluate the compression envelope under conditions of no lateral strain and to determine values of constrained modulus. Significant grain crushing was found to occur during testing even at low confining stress, in fact the stress-strain-strength behaviour of the material is dominated by particle crushing. Routine soil testing techniques were found to be inadequate for the evaluation of the specific gravity of pumice sand particles and a different technique was used for this purpose. The angle of friction of pumice sand was found to be larger than that of quartz sands, however pumice sand required very large shear strains to mobilise the peak and critical state shear strength and, for several tests, critical state conditions were not reached.

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An unprecedented local downpour occurred in Niigata Chuetsu region on 13 July 2004. The total amount of rainfall reached 250 mm in an area 20 km in a north-south direction and 100 km east-west direction including Sanjo, Mitsuke, Nagaoka and Tochio cities. The Niigata Prefectural Government have reported that the heavy rainfall caused 11 dike breaks and over 300 landslides. Consequent damage included 15 deaths (2 out of 15 were killed by landslides) and over 26,000 houses flooded. This paper first presents an outline of this disaster. A detailed investigation was carried out on a dike break and a natural slope failure to clarify the failure mechanisms. Then a series of direct and ring shear tests was conducted to examine the shear strength considering moisture content and existence of a discontinuity plane. Strength parameters obtained from the experiments were used for slope stability analyses. Finally, new simple analytical and estimation methods using an unsaturated seepage and slope stability analyses are presented.

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A stress-strain model called TESRA (Temporary Effects of Strain Rate and Acceleration), described in a non-linear three-component framework, has been proposed to simulate the effects of viscous property on the stress-strain behaviour observed in drained plane strain compression (PSC) tests on clean sands. According to the TESRA model, the current viscous stress component is obtained by integrating for a given history of irreversible strain increments of viscous stress component that developed by respective instantaneous irrecoverable strain increment and its rate and have decayed with an increase in the irreversible strain until the present. The TESRA model was implemented into a generalized elasto-plastic isotropic strain-hardening non-linear FE code. The integration scheme to obtain the viscous and inviscid stress components according to the TESRA model in FEM analysis needs some specific considerations including the relevant choice of the suitable rate parameter. The shear stress—shear (or axial) strain—time relations from five drained PSC tests on saturated Toyoura sand and air-dried Hostun sand were successfully simulated by the FE code embedded with the TESRA model. It is shown that the FE code can simulate the time-dependent stress-strain behaviour of sand accurately without spending any significant extra computational time or storage. The results of simulation using one element and multi-element are essentially the same.

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