In the construction project of breakwater in Sakai-Minato Port, the determination of the shear strength of the upper intermediate soil layer and the necsssity of ground improvement became an engineering problem. Both the unconfined compression strength q_u and the triaxial undrained compression strength s_u(SCU) after the consolidation with the mean in-situ effective stress were obtained. By comparing the values of q_u with that of s_u(SCU), it was known that the quality of soil samples used for the unconfined compression test was classified as “very poor”. It was considered that the unconfined compression strengths of intermediate soil were reduced seriously by the characteristic that the even the samples taken by undisturbed sampling method cannot keep the effective stress inside. By evaluating the shear strengths of intermediate soil as 75% of s_u(SCU), the breakwaters were constructed safely without any ground treatment.

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Unsaturated drained triaxial tests were carried out previously to elucidate deformation behavior, the effective stress path, and water retention properties of Loam, volcanic soil, during shearing processes. We clarified the relation between the void ratio and van Genuchten parameters using water retention curves under drained and undrained triaxial tests conditions. Furthermore, we predicted the unsaturated shearing behavior by considering the void ratio dependence of water retention curves under drained conditions by applying the Nova model and Modified Cam-Clay model. Comparing results obtained with the Nova model with those of the Cam-Clay model, the former showed a slightly larger value. For axial strain of less than 5-10%, Nova model agreed well with laboratory test results.

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Landslide deformation process was analyzed by comparing inclination rate and displacement rate in rotational-movement type two landslides. In addition to the Shionokawa Landslide, measuring about 250 m in width, we focused on the Toi Landslide, which is an about 40 m wide colluvial landslide with an inclination rate a digit greater than the former and conducted comparison and analysis of the inclination rate measured with IT ground tiltmeter (PWRI et al. 2009) and the displacement rate measured with extensometers installed on the landslide scarp to make comprehensive evaluation. It then allowed us to arrive at the correlation of y=kx for the inclination rate, x (rad/day), by the backward rotary motion measured with ground tiltmeters installed in the landslide and the displacement rate, y (m/day), obtained from ground extensometers or moving stakes placed at the landslide head. Assuming the correlation is produced by the rotary motion of the radius, r₂’ (m), on the ground surface, it then leads to r₂’=k=14.6 - 18.0 for the Toi Landslide and r₂’=k=35.4 - 42.2 for the Shionokawa Landslide. On the other hand, the rotary motion of the radius, r₂ (m), estimated based on the estimation from the landslide geometry, r₂ = about 16 and r₂=36 respectively, leading to almost the same results with r₂’. For a landslide with rotary motion predominantly observed, it is suggested that the comparison and analysis of the displacement rate and inclination rate contributes to clarification of the deformation mechanism of the landslide. Further improvement in precision of estimation of the deformation process of a landslide that has an arc-shaped slip surface or of the shape of the slip surface is expected by those analyses and the method to estimate slip surfaces obtained from moving stake observation.

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In recent years, cases where reinforced earth walls were adopted in the construction of expressways are increasing. On the other hand, damages and deformations of these walls have been reported. In this paper we will take up deformations that had developed in a geotextile reinforced earth wall using mudstone. Deformations to this earth wall developed one year after construction, and consequently, the wall was rebuilt. Various tests were carried out at the time of the reconstruction to study the case and find the cause of the deformation. Testing and research showed low relative weaknesses of the wall, such as high water content at the upper wall and around the front face of the upper wall, and low shear wave velocity. From the results, we have concluded that the deformation was caused by water penetrating from the road surface and drainage facilities of the reinforced earth wall backfill. In the testing, we were able to confirm the validity of the surface wave exploration and that the strength of the geotextile reinforcements used in the deformed area had lowered.

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The high accuracy and the adaptability to the construction control of the strength prediction method of cement-treated soil with volume solid content was shown by the discussion using the mixing test data of the actual project. The strength-time relationships of 3 cement-treated marine clays were obtained by laboratory experiments, and it was shown that the strength increase process can be divided into two stages, the first stage within 3 days after mixing and the second stage 3days after the mixing. For both stages, the equations of the relationship between strength increse and curing time, which have 5 parameters, were proposed. The parameters of proposed equations were determined using the mixing test data of 12 marine clays. Comparing the measured strength with the predicted by the proposed, it was concluded that the equations successfully predicted the relationship of strength-increase with time.

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It is of great importance to understand temporal and spatial changes in the hydraulic and transport properties of rock mass mediated by the mineral dissolution controlled by temperature and stress conditions. In this work, a suite of flow-through experiments in a single fracture in granite has been conducted under temperature and stress conditions controlled. Specifically, the two different experiments of the short-term and the long-term experiments are performed to examine the influences of loading time on an evolution of the fracture permeability. The measured changes of the fracture permeability show reversible and irreversible behaviors under short-term and long-term conditions, respectively.

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Compaction grouting, an in-situ static compaction technique by means of grout injection, has been increasingly adopted for improving the liquefaction resistance of loose sandy ground in recent years. An increase in the lateral confining pressure and densification are considered as the main factors for the increase in the liquefaction resistance of sand caused by compaction grouting. The advantage of this method is that the construction can be conducted without disturbing the existing and servicing structures such as airport runways and taxiways. However, several issues, such as high cost of construction compared to another liquefaction countermeasure such as sand compaction pile method or damaging pavements caused by unexpected ground surface heaves, has also been reported. The present study addresses these issues by investigating the effect of the improvement ratio or grout pile spacing of compaction grouting on the liquefaction resistance by model tests using a geotechnical centrifuge and X-ray tomography and numerical simulations. The findings indicate that the densification can be archived mainly in the lateral side of a grout pile and an earth pressure coefficient value, K, of more than 1.5 provides effective liquefaction resistance to the sandy ground.

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Recently, a shortage of soil disposal area has been serious in Japan, and there has been a demand to dispose the dredged soil as much as possible in the disposal area with limited capacity. To meet this demand, the vacuum consolidation method with horizontal pre-fabricated drains has been applied to the soft ground formed by dumping of dredged soil. Horizontal drains of 100cm wide, 10mm thick and 117-171m long were installed at the horizontal interval of 0.8m on the bottom surface and a middle section of the disposal area. Then, soft soil was improved by the vacuum pressure of over 75-80kN/m². The volume of dredged soil converted in the original sedimentation condition was 1.1 times as much as the capacity of the disposal area, though all of the dredged soil was successfully accepted in the disposal area because of bulk reduction of the soil by the vacuum consolidation method.

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Chemical injection method is one of the soil improvement procedures in urban area and is very effective for the countermeasure against the liquefaction of the loose sand foundation of the existing superstructure in the coastal area. The reasonable evaluation of mechanical characteristics of chemically stabilized sand is required to conduct the successful soil improvement. Although significant numbers of unconfined compression tests of sand specimens stabilized with liquid glass have been carried out, the mechanical and chemical interpretation of the strength increase of chemically stabilized sand has not been fully given. The equivalent granular void ratio of the mixed soil including sand and fine soil particles has been found to be uniquely related to the shear modulus of the mixed soil specimen. In this study, unconfined compression tests and elastic wave velocity measurement tests are carried out on the sand specimens improved by the liquid glass solutions. The unconfined compression strength, the shear wave velocity and the propagation velocity of the improved sand specimens are found to be uniquely related to the equivalent granular void ratio.

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The geotechnical investigation was carried out at 4 valleys, which are designated as landslide risky valleys in heavy rainfall time by Hiroshima Prefectural Government. Using the models of valleys, the rainfall seepage analysis, the calculation of ground water level and the slope stability analysis were carried out, making the risk assessments of valleys in heavy rainfall time. The practical geotechnical investigation method using lightweight dynamic cone penetration test was also proposed, with which the geotechnical investigation of one valley can be completed by 2 personals in a day. By the laboratory rainfall seepage test and the one-dimensional analysis, it is found that the volumetric water content and degree of saturation and the descent velocity of high water content band (HWCB) is determined by the rainfall intensity. The method for calculating the groundwater level after HWCB reaches the base layer is newly obtained. Using the findings, the risk assessments of 4 valleys were made by comparing the safety factors calculated for continuous rainfalls with several intensities.

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Based on results of triaxial or torsion cyclic loading tests on a variety of soils containing organic matters such as highly organic soil or organic clay obtained from Hokkaido or Akita prefecture, empirical equations for elastic shear modulus G₀ and reference strain γ_r are proposed. Density of soil particles, which exhibits good correlation to ignition loss, is introduced as a parameter reflecting content of organic matter in the equation for G₀. In case of saturated soil, this equation is roughly consistent with other researchers’ equation proposed so far by parameters being replaced into water content. Based on a relationship between γ_r and G₀ derived by formula of Hardin-Drnevich model, the empirical equation for γ_r is successfully expressed as a function of water content and consolidation stress. Compared with prediction from equations proposed, test results fall in a range of 0.7 to 1.5 times for G₀ and of 0.5 to 2.0 times for γ_r.

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When constructing embankment on soft ground, shallow soil stabilization method and/or earth reinforcement method with geotextile are often used as a countermeasure against lateral displacement of the toe of the embankment.
Sometimes, embankments on soft ground are also constructed with wire net matting horizontally laid. The wire net matting in the embankments is considered to be effective to restrain the lateral displacement. In this paper, results of a field observation are first described in relation to the behavior of the embankment on soft ground with wire net matting. The effectiveness of the two layered wire net matting is then discussed from the mechanical point of view for protecting the horizontal movement of the embankment based on the observation results. It was clear that the two layered wire net matting results in reducing the horizontal displacement in the toe of the embankment, which might be named as a restraint effect of wire net matting.

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The Sweden weight sounding test is commonly used as a geotechnical investigation method for detached houses in Japan. However, a weak point of this testing machine is located in the difficulty of control of the load scuttled. Consequently, there is a problem in terms of reliability for estimate the undrained shear strength. In the other hand, it is believed that there is a relationship between the resistances by rotation of screw point with the shear resistance of the cohesive soil. In this study, as laboratory experiments, a special vane with the same screw point height and width (diameter) was prepared to evaluate and clarify the relationship of undrained shear of the cohesive soil from the torque of the screw point and special vane. As a result, there are a closely relation for the undrained shear strength of cohesive soil between special vane and screw point. Also, it proposes an equation to estimate the undrained shear strength of cohesive soil by torque value. By field experiments, it can be verify the validity and apply of estimated expressions.

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