A strength estimation formula for cement-solidified soil made from dredged soil with different liquid limits, initial water content, and sand content is proposed. Strength tests were conducted under various conditions (initial water content, sand addition rate, cement addition rate) using three types of clay with different liquid limits. The applicability of the proposed formula was examined using the experimental results and the results of the compounding test actually used in the field. Focusing on the relationship between the parameters of the proposed formula and the liquid limit of clay, we created a strength estimation formula with the liquid limit, the initial water content ratio, and the cement addition rate as parameters.

Effectiveness of crushed stone layer with geosynthetics on mitigation of liquefaction-induced deformation of the embankment is examined by a series of dynamic centrifuge model tests. Bending tests of the crushed stone layer with geosynthetics are also performed to understand the contribution of the geosynthetics on increase in the bending stiffness of the crushed stone layer as a slab. The experiment reveals that the crushed stone layer with geosynthetics can minimize the liquefaction-induced lateral stretching of the foundation ground and the deformation of the embankment. The high permeability crushed stone layer also contributes to minimizing the build-up of the excess pore water pressure during shaking and helps faster dissipation of the excess pore water pressure after shaking. These effects also contribute to minimizing the liquefaction-induced lateral stretching of the foundation ground and the deformation of the embankment.

As a countermeasure for the road cave-in’s, it is effective to find and treat subsurface cavities under the road pavement before their collapses. Recently, thanks to the Ground Penetration Radar technology, a lot of subsurface cavities within 1.5m deep are being detected in the practice of road maintenance and management. Repair works for the cavity should be prioritized according to its collapsing risk. The appropriate way for the risk evaluation of cavity collapse is therefore urgently required. In this study, the mechanism and process of cavity generation, expansion and surface collapse were investigated by a series cavity model tests including loading tests above a cavity. The condition for surface soil collapsing was examined and it was found that the surface collapse can be evaluated by the ratio of cavity depth and width. The threshold value for the cavity collapse obtained from the model tests almost agrees with the value for cave-in cases in the national road.

In recent years, fully automatic test methods have been widely used for the Screw Weight Sounding (SWS) test, in which the machine controls load and rotation and records the test results. By the fully automatic test method, it is possible to control the load at the time of scuttling and to investigate at a depth of about 20m, which is difficult by the hand-controled method. Since 2010, we have conducted SWS tests using fully automatic test method throughout Japan and compared results of them with SPT and indoor mechanical test (unconfined compression test and box shear　constant volume test). As a result, it was found that the correlation between the W_sw・N_sw value in SWS test and N value in SPT is low in sandy soil. On the other hand, in cohesive soil, it was found that the correlation is relatively high, and the correlation between the W_sw・N_sw value and value of the undrained shear strength (q_u/2 , s_ub) is high. In addition, according to the test results, it is considered that the formula by Inada, which is often used in practice, equivalent to the lower limit. In this paper, we propose a new correlation fomula showing the relationship between W_sw・N_sw value and N value, s_u value of cohesive soil, based on the test results conducted at all survey sites using a specific testing machine.

The R_L20,5% is generally used as the liquefaction strength of soil in Japan where the liquefaction is decided by basing on generated strain. However, when applying this method to evaluating the liquefaction strength of the ground improved by the permeable grouting method, the method may not fully evaluate the characteristics of the improved soil including the toughness against cyclic shearing load and the suppression of residual deformation. In this study, a series of cyclic torsional shear tests on the hollow cylinder specimen of improved ground with the permeable grouting method were conducted at a high shear stress ratio assumed with a strong earthquake. By observing its resistance against cyclic shear load, it was found that in order to appropriately evaluate the characteristics of improved soil, it is necessary to decide the liquefaction strength by considering both the strain and the excess pore water pressure. In addition, even when the soil is judged as non-liquefied soil, its excess pore water pressure still increases under cyclic shear load. Therefore, by confirming the undrained strength deformation characteristics of the improved ground at a high water-pressure state after a cyclic shear load, the undrained shear strength of improved soil was confirmed the same with that before applying the cyclic load.

It has recently been urgent to deal with various deterioration of support structures on tunnels particularly in urban areas. Serious cracks on support segments of shield tunnels in soft clay deposits as well as deterioration phenomena such as free lime and rebar corrosion that is illustrated in the literature¹⁾ are observed. It is true they have many previous studies of consolidation induced problems due to change load condition but there are some cases where problems occur in the absence of remarkable external factors. As one of these problems, the influence of shield tunnel excavation on the long-term deformation of the soft alluvial clay deposits is discussed based on triaxial compression and extension tests and numerical analyses in the present paper. Both experimental and calculated results show that long-term compressive deformation possibly occurs induced by compression and extension shear forces in the stress state lower than p_c due to tunneling excavation. The reason why this phenomenon occurs is found to be that the extension shear stress causes great damage to the structure of the quasi-overconsolidated clay.

The specimen of triaxial test used for the soil properties in design of the important fills is prepared by tamping uniformly in a steel mold in which deformation is restrained in laboratory. On the other hand, in the field construction, the compaction machine passes on the fill materials, so a large density distribution is observed in the depth direction in each compaction layer. In addition, since the surface of fill has a small restraining pressure, disturbance due to local shear failure occurs during compaction. In this paper, test fill specimens were retrieved from a full-scale test fill compacted by a small compaction machine in large steel vessel. Result of triaxial test for unsaturated specimen, strength and deformation properties were compared between the specimens compacted in the field and in the laboratory as the same fill material. It is argued that the vertical non-uniformity specimen of strength and deformation properties compacted soil in the field and in the laboratory can be evaluated in the same way by taking into account the effects of shear failure in the field compaction in addition to ρ_d and S_r.

In the two-dimensional effective stress analysis code FLIP, users need to determine input parameters which can reproduce liquefaction strength curves obtained from laboratory tests, and it usually requires lots of element analysis and much time. In this study, we propose an automatic estimation method of liquefaction parameters that can reproduce a given liquefaction strength curve. First, we showed an outline of the proposal method with a flowchart. Second, parameter estimation was carried out for several liquefaction strength curves prepared analytically, and the effectiveness of the proposal method was confirmed. At the same time, using previous research, we proposed initial input parameters which can be used in proposal method, and its versatility was confirmed. Finally, it was confirmed that the proposal method can reproduce the liquefaction strength curve obtained from laboratory tests.

The main section of Yamatogawa Route of Hanshin Expressway is consisted of mud-pressure shield tunnel structures, and the appropriate disposal of a large amount of soil in the form of sludge generated from the excavation is an issue since the tunnel is located in urban area. Here the sludge is recycled as material of sea reclamation utilizing the official recycling promotion scheme. Under this recycling project, the establishment of quality control technology is required and undertaken during the recycling process to ensure the stable production of qualified reclamation materials (cone index: 400 kN/m² or more, and pH = 6.0 - 9.0) while not hindering the progress of tunnel excavation. This paper reports that, by strictly practicing the quality control manual, which defines the frequency of geotechnical and chemical tests and the related methodologies to guarantee the making of appropriate reclamation materials, the total volume of approximately 950,000 m³ of reclamation material meeting the soil contamination standard can be supplied. Also, not only the achievement of constant generation and supply of qualified materials out of muddy soils, it is proved that this recycling project can extend the life of existing soil disposal sites, reduce the impact on the surrounding environment of reclaimed land, and lower the recycle cost.

Japan Geotechnical Society has implemented proficiency tests for more than a decade. In the present report, the following two topics are focused on; homogeneity of distributed samples and validity of the evaluation methods. Regarding the former one, possible influence of changing the homogeneity criterion in JIS Z 8405 and sample preparation methods suitable for geomaterials are explained. Regarding the later one, with showing properties of the assigned values and normality of the test results, solutions for existing problems in the proficiency tests of geomaterial testing are discussed. And it is recommended that the repeating tests should be applied to the test for particle size distribution of soils.

While groundwater drainages are taken against them on expressway embankments, methods for verifying the effects of countermeasures have not been unified. Therefore, we have collected water level data and rainfall data observed by geotechnical investigations nationwide, and analyzed them by three calculation methods that represents the relationship between rainfall and the water level in the embankment. Next, we have also considered how to verify the effect of countermeasures using the method with the highest correlation among the three methods. In addition, since the water level in the embankments depending on the season, we have examined a new method called “water level condition” based on the concept of the evaluation of river level. As a result, we propose a method to verify the effects of countermeasures by using the effective rainfall, which had the highest correlation with rainfall, and using the water level condition.

Surveys and analyses of frost heave damage rely on frost susceptibility tests that reproduce the density as well as the grain size distribution of natural ground. When dealing with ground that has a high gravel fraction, however, it can be difficult to prepare suitable test samples, meaning that the tests must be performed under conditions different from those of natural ground. Moreover, the fine fraction is a factor in ground heave, and if the gravel fraction is neglected, the fine fraction under testing becomes higher than it would be in reality. Consequently, frost heave performance will be overestimated. In this study, we focused on electrical conductivity, which has a mechanism similar to that of frost heave, and examined a grain size distribution correction method for frost susceptibility test results by utilizing the correlation between electrical conductivity and frost heave. We found a close correlation between frost heave rate and electrical conductivity, suggesting the possibility of using electrical conductivity to infer frost heave performance. We also found that using gravel volume fraction was effective as a grain size correction method for frost susceptibility test results.