Formulations are developed to compute the consolidation behaviour of a clay soil containing multiple thin sand layers. One-dimensional loading and two-dimensional flow are considered. The formulations are based on the transfer matrix approach, which is found to be very convenient and efficient for analysing the consolidation of a multi-layered soil system. Special attention is given to accommodating thin sand layers in a computationally efficient way. The formulations developed are verified by using available field observation records and a formulation that is based on a different approach. Coupling of the consolidation of clay soil and the discharge flow in sand layers is found to be primarily governed by the parameter λ, defined herein. Based on this finding, a design criterion is proposed for designing multiple thin sand layers to accelerate the consolidation of a constructed clay ground. An example is provided to use the above design criterion.

View full abstract

The objective of this paper is to examine the material properties of paper sludge (PS) and construction sludge (CS) as landfill cover materials. Compaction, shear strength, consolidation, and hydraulic conductivity tests are carried out to evaluate the material properties as well as the engineering behaviors of PS and CS. Furthermore, the long-term behavior of these two types of sludge is evaluated by centrifuge tests. The basic properties of PS and CS indicate their suitability for use as cover materials, and the PS results agree well with previously documented data. The leaching properties of heavy metals from both types of sludge satisfy the Japanese Environmental Quality Standards for reusing them as cover materials. The compacted CS shows hydraulic conductivity in the range of 1.2 × 10^-8 to 6.5 × 10^-8 cm/s, which can satisfy the requirements for hydraulic conductivity of landfill covers distributed by USEPA. In the case of compacted PS, there is no remarkable difference in the hydraulic conductivity (in the range of 3.5 × 10^-7 to 9.0 × 10^-7 cm/s) for a wide variation of water contents ranging from 50 to 150%. Compacted PS and CS maintain a hydraulic conductivity of 10^-7 and 10^-8 cm/s order of magnitude, respectively, under a centrifugal field of 60 G over 24 hours. Thus, the PS and CS can maintain these levels of hydraulic conductivity for about 9.86 years when used as barrier materials.

View full abstract

The use of a compressible layer such as expanded polystyrene blocks behind a rigid retaining wall and geogrid layers embedded in a dense granular backfill is examined as a reinforcement technique for retaining wall structures. The mobile model retaining walls adjacent to reinforced model specimens are subjected to different surcharge pressures, and are caused to move laterally to measure the lateral earth pressure during the wall movement. The coefficients of earth pressure at rest and active earth pressure are carefully inferred from test results. Three series of tests are conducted; one test series with expanded polystyrene blocks installed behind the wall, another with geogrid layers embedded within model specimens, and the last series with expanded polystyrene blocks installed behind the wall and geogrid layers fixed between two adjacent expanded polystyrene blocks and embedded within model specimens. The reductions in the earth pressure at rest and the active earth pressure due to various patterns of reinforcement are interpreted in relation to the concept of controlled yielding of compressible expanded polystyrene blocks, tensile strains induced along geogrid layers, fixity between expanded polystyrene blocks and geogrid layers, and a facing unit consisting of expanded polystyrene blocks.

View full abstract

The current practice of estimating bearing capacity usually employs the conventional bearing capacity formula originally developed for strip footings under vertical central loading. In order to account for the effect of footing shape and eccentricity and inclination of loads, correction factors are introduced in the formula, which are derived based on a number of small-scale model test observations. This paper describes research on the bearing capacity of rectangular footings on sand subjected to vertical eccentric loading. Two aspects, namely the effects of footing size and of footing shape on the bearing capacity and deformation characteristics, are focused on. A series of loading tests was conducted in a centrifuge on rectangular footings with aspect ratios from 1 to 5, at two different centrifugal accelerations. In addition, finite element analyses were performed in which factors influencing the angle of shear resistance including stress level dependency, anisotropy and coefficient of intermediate principal stress, were taken into account. It was found that the shape factor of footing apparently increased with increasing footing width. This indicates that the shape factor used in the current practice underestimates bearing capacity of footings. This was also the case for failure locus in the M/B-V (moment-vertical) load plane. Normalized failure locus for wider footings with a smaller aspect ratio is considerably larger than that reported in the literature. The stress level dependency of the angle of shear resistance appeared to be responsible for the scale effects of footings on the failure locus.

View full abstract

An earthquake of magnitude 7.6 occurred in the south-east coast of El Salvador on January 13, 2001, causing widespread damage to buildings and several kinds of civil engineering structures due to ground shaking and earthquake-induced ground failures, including several large-scale landslides. This paper discusses the results of the damage investigation conducted in the area after the earthquake, with emphasis on the general features of the earthquake and its effects on the ground damage, specifically the landsliding which occurred in natural slopes and the liquefaction of soil deposits. The occurrence of liquefaction in the alluvial plain exhibited several characteristics in common with those observed in other areas of similar condition. On the other hand, the main cause of slope failures in volcanic deposits was not clearly identified, and several possible sources of slope instability were pointed out.

View full abstract

The resistivity tomography, the horizontal electrical profiling, and the elastic wave tomography methods were used for evaluating an improved area in gravelly soils by chemical grouting. The first and second methods are basically the same; however, the second method is much easier to perform. The availability of the second method is also investigated. The improved area was confirmed by excavation after grouting. The actual improved area was compared with the area estimated by using the above three methods. Among them, the resistivity tomography method could nearly estimate the grouted area in cooperation with the analytical method used by Komine et al. It was, however, difficult to evaluate the grouted area by either the horizontal electrical profiling nor the elastic wave tomography method in the present case.

View full abstract

The Gujarat earthquake in India occurred in January, 2001, and caused significant damage in the province of Gujarat. The Japanese Geotechnical Society sent a small reconnaissance team to the damaged region after the quake. The present text presents the report from this activity. The major attention of the team was focused on geotechnical aspects of the damage which were related to earthfill dams and harbor land fills. It was found that a significant portion of damage was concentrated in fills resting on soft natural soils. Swedish weight soundings which were conducted at two places demonstrated the existence of such a soft subsoil. From this, it was concluded that amplification of earthquake shaking as well as the permanent deformation in the soft foundation soil induced such kinds of damage as subsidence, cracking, and lateral spreading in overlying artificial fills. For the better seismic resistance of those affected fills during future earthquakes, the improvement of soft subsoil seems essential.

View full abstract

The rate dependent nature of liquefied sand was investigated by laboratory shear tests. Since previous experience has revealed the many difficulties inherent in maintaining the state of liquefaction of a sandy specimen, new measures were attempted. The test results indicate that the measured shear stress consists of frictional and rate dependent components, and a viscosity coefficient was assessed from the latter component. The measured viscosity varies with the rate of strain as well as the magnitude of strain itself. A similar test on a dry specimen revealed less viscosity and implied that a major part of rate dependency comes from the behavior of pore liquid in the case of water-saturated sand. It was interesting, moreover, that sand with fines was of less viscosity. Finally, a numerical analysis was conducted on a real liquefaction-induced ground deformation and the results were consistent with the observation.

View full abstract