Migration of Light Non-Aqueous Phase Liquids (LNAPLs) in porous soils was studied experimentally, using one-dimensional and two-dimensional laboratory tests. The movement of crude oil under constant pressure was observed in vertical and horizontal transparent columns filled with sand. It was found that in both cases the average oil saturation does not change during the oil propagation. Its value depends on the initial water saturation in sand and the mobility of air in front of the oil front. The hydraulic conductivity to oil was found to be constant along the vertical column, while it decreased exponentially when oil was spreading along the horizontal column. Two-dimensional experiments were carried out in a sand tank with simultaneous water flow and the oil migration. Oil leaked into the sand from a thin feeder above the water table with constant oil level. The experiments were conducted with three types of LNAPL: crude oil, vegetable oil, and engine oil. Evolution of the oil mound was recorded through the transparent front wall of the sand tank, while the water table was monitored using a series of piezometers. Presence of the water table had a major effect on the oil mound shape and size. Downwards movement of the oil front slowed down around the top of the capillary fringe and completely stopped near the water table. The depth of penetration into the capillary fringe depended on the oil viscosity and the pressure at the oil source. Lateral spreading was more pronounced in the direction of the water movement.

View full abstract

This paper examines the nonlinear hysteretic characteristics of load transfer between soil and piles for random loading. First, we demonstrate that in past experiments the mobilized lateral soil resistance to piles varies with cyclic loading patterns. The soil resistance mobilized against one-sided cyclic loading is smaller than that mobilized against fully-reversed cyclic loading. We then establish that the stress-dilatancy behavior of soil causes such a loading pattern dependency, based on the mechanical property of soil elements subjected to cyclic compression-extension deformation. Finally, the hysteretic characteristics of load transfer between soil and pile associated with the stress-dilatancy effect is modeled as a function of cyclic loading pattern.

View full abstract

The applicability of three previous empirical correlations proposed for estimating relative density of sandy soils based on the SPT N-value, effective overburden stress and soil gradation characteristics was investigated in the present study by using a data base of relative density obtained from high quality undisturbed samples of fine to medium sand with F_c≦20%, D₅₀≦1.0 mm and D_max≦4.75 mm. All undisturbed samples were recovered by in-situ freezing method. The relative density estimated by Meyerhof's method (1957) was in the range of +15%~−45% of the measured values. Meyerhof's method (1957) was modified by Tokimatsu and Yoshimi (1983) by considering the effect of fines content on the SPT N-value. The relative density estimated by Tokimatsu and Yoshimi's method (1983) is in the range of +25%~−20% of the measured values. The underestimation of relative density of Meyerhof's method (1957) was modified. On the contrary, the overestimation of relative density is more significant than Meyerhof's method. The relative density estimated by the method proposed by Kokusho et al. (1983) is in the range of +20% to −35% of the measured values even for dense sand with a relative density larger than 60%. Meyerhof's method (1957) and the method proposed by Kokusho et al. (1983) have a common disadvantage that they will extremely underestimate the relative density of fine to medium sand for SPT N-value lower than about 8. The errors in estimation of relative density by these methods are large. A simple empirical correlation (Eq. (10)) was proposed in the present study to estimate the relative density of fine to medium sand based on the normalized SPT N-value, N₁. The relative density estimated by the proposed method is in the range of +15% to −30% of the measured values for N₁ in the range between 0 and 50. As a whole, the proposed method is less in errors for estimating relative density compared with those estimated by Meyerhof's method (1957) and the method proposed by Kokusho et al. (1983). Based on a data base of undisturbed samples with data of fines content obtained from the SPT spoon samples, the method proposed by the authors is again compared with the three previous methods. The relative density estimated by the proposed method based on the above data base is in the range of +15% to −10% of the measured values. Among four methods, as a whole, the proposed method shows the least errors in estimation of relative density. The proposed method was also modified (Eq. (16)) by taking into account of the effect of fines content of SPT samples. The relative density estimated by the modified method based on the fines content is almost in the range of +10% to −10% of the measured values. Two empirical correlations proposed in the present study are less in errors of estimating relative density compared with three previous methods. The range of relative density estimated by the proposed method is well consistent with the range of the measured values (40% to 90%). The empirical correlations proposed in the present study should be applied to fine to medium sand with F_c≦20%, D₅₀≦1.0 mm and D_max≦4.75 mm.

View full abstract

It has been revealed from the long term consolidation test that the e-logp relation is linearly shifted with decrease in the strain rate in logarithm scale. The minimum strain rate measured by the conventional long term consolidation test is at most in the order of 10⁻⁹s⁻¹. Question arises whether such a shift of the e-logp relation continues at even the infinite small strain rate, for example, smaller than 10⁻⁹s⁻¹. To investigate the strain rate dependency of cohesive soil, the relaxation test was carried out for Osaka Pleistocene clays. It may be considered that in relaxation test, recoverable strain decreases due to decrease in acting pressure, and the irrecoverable strain equally increases, because the total strain remains constant. In this paper, assuming that the isotaches model can be applied to the irrecoverable strain, the strain rate dependency at very small strain rate was obtained from a series of relaxation tests. In this investigation the “strain rate dependency ratio” (SRDR) is defined as the ratio of the stress in the same ε or e under the objective strain rate, based on the strain rate of 3.3×10⁻⁶s⁻¹. It is revealed that the SRDR at infinite small strain rate is about 0.7.

View full abstract

The Deep Mixing Method (DMM), a deep in-situ soil stabilization technique using cement and/or lime as a binder has been often applied to improve soft soils. Group column type improvement has been extensively applied to foundations of embankment or lightweight structures. A design procedure for the group column type DM ground has been established in Japan mainly for application of embankment, in which two failure patterns are assumed: sliding failure in the external stability and rupture breaking failure in the internal stability. The internal stability of the improved ground has been investigated experimentally, and it was found that the DM columns show various failure modes: shear, bending and tensile failure, depending not only on the ground and loading conditions but also on the location of each column. However, the current design does not incorporate the effects of these failure modes, but only that of shear failure mode. For the external stability, it is known that a collapse failure pattern, in which the DM columns tilt like dominos, could take place instead of sliding failure. The current design method, which does not take into account this failure pattern, might overestimate the external stability. In this study, a series of centrifuge model tests and elasto-plastic FEM analyses were performed to investigate the external stability of group column type DM improved ground under embankment loading. The centrifuge model study has revealed that the improved ground does not fail with a sliding failure pattern but with a collapse failure pattern in the model test condition. The FEM analyses confirmed the model test results and showed that the improved ground could fail with sliding failure in a certain type of ground conditions such as a floating type improved ground. A simple calculation incorporating the collapse failure pattern gave reasonable estimation of the embankment pressure at ground failure. This paper demonstrates the importance of simulating appropriate failure pattern for evaluating the external stability accurately.

View full abstract

In unsaturated soil mechanics testing, total volume change of the specimen is related to both water and air volume changes and cannot be measured with the same techniques as in conventional saturated soil mechanics. Over the years, several methods have been developed with various degrees of accuracy and complexity. The intention of this paper is to describe some of the problems involved with volume measurement in unsaturated triaxial tests, together with the apparatus and techniques developed to solve these problems.

View full abstract

Laboratory and field strength development of cement stabilized coarse-grained soils are studied in this paper. A phenomenological model to assess the laboratory strength development is developed. The model is divided into the dry and the wet sides of optimum water content. At the optimum and on the wet side of optimum, the strength development in cement stabilized soils at a particular curing time is dependent only upon the soil-water/cement ratio, w/C, which can reflect the combined effects of water content and cement content. It is moreover premised that the relationship between strength and water content is symmetrical around the optimum water content (OWC) in the range of 0.8 to 1.2 times the OWC. The proposed model is useful for assessing the strength development wherein water content, cement content and compaction energy vary over a wide range. Only the test result of a single laboratory trial is needed. From the field study, it is found that the field roller-compacted strength, q_ufr is lower than the laboratory strength, q_ul under the same dry unit weight, soil-water/cement ratio and curing time due to several field factors. The ratio q_ufr/q_ul varies from 50 to 100%. Non-uniformity in mixing soil with cement is realized by the ratio of field hand-compacted strength to laboratory strength, q_ufh/q_ul ranging from 0.75 to 1.2. For most data, the field roller-compacted strength is 55 to 100% the field hand-compacted strength. This might be caused by the difference in compaction method and curing condition between laboratory and field stabilization. From this field observation and the proposed model, a practical procedure for repairing damaged roads using the pavement recycling technique is introduced. The procedure consists of the determination of cement content, the execution of the field stabilization and the examination of the field strength. It can save on sampling and laboratory testing and hence cost.

View full abstract

The Hyogoken-Nambu Earthquake in 1995 caused extensive damages to the foundations of bridges. Ever since, methods to improve the bearing capacity of existing foundations have become an important aspect of foundation engineering in Japan. Micropiles are considered to provide promising solutions. The mechanism which enhances the bearing capacity of surface footings reinforced with micropiles is the subject of investigation in this study. As an initial phase, model tests were conducted to understand the load-displacement behavior of surface footings with and without micropiles on loose, medium dense, and dense layers of sands. Salient factors which influence the behavior of the footings were selected and their influence on bearing capacity was examined through a comprehensive series of model tests. Notable improvements in the bearing capacity of surface footings reinforced with vertical micropile groups were observed in the case of dense sand which is dilative during shear. To assess quantitatively the degree of improvement in the bearing capacity of surface footings reinforced with micropiles, an index R called “Network Effect Index” was introduced in this study. The index R of unity means that the bearing capacity of footings reinforced with micropiles is simply equal to the summation of the individual value of the surface footing and that of the micropile group. An index R of more than two is achieved in this study where surface footings reinforced with a group of vertical micropiles bear on a dense layer of dilative sand. By contrast, with loose and medium dense sand, which are contractive in nature, the index R is found to be less than unity.

View full abstract

This paper describes a new ductility design method of abutment foundations in soil liquefaction situations under large earthquakes. The proposed method was developed for introducing it to the 2002 Japanese Specifications for Highway Bridges. Based on past damage case histories, several failure scenarios were assumed that are, as a result, associated with soil liquefaction. Then the proposed design method was made to control damage against soil liquefaction situations. The load combinations considered in the proposed method are based on one of the assumed failure scenarios. A practical seismic earth pressure evaluation for high peak ground acceleration levels, as observed in the 1995 Hyogo-ken Nanbu (Kobe) earthquake, has been newly introduced. Back-analyses of 14 damage case histories of abutments were conducted using the proposed method, and a design threshold value was explored accounting for the performance-based design concept. The back-analyses also unveiled remaining issues and the current status of abutment design against large earthquakes.

View full abstract