This paper presents a simple methodology for determination of in situ shear strength parameters by recently developed lightweight dynamic cone penetrometer. A series of laboratory calibration lightweight dynamic cone penetration tests, and direct shear tests with pore water pressure measurements were conducted at different void ratios and degrees of saturation. Based on the laboratory calibration test results, a method of determining void ratio, e from the data of cone resistance, q_d was established for different degrees of saturation. A method of determining shear strength parameters from the data of q_d was proposed based on the correlations developed between void ratios with q_d and shear parameters.

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This paper discusses the reinforcement effect of geogrids on the improvement in the brittle tensile strength of stabilized property soil based on laboratory test results. Triaxial tests were conducted under consolidated undrained conditions using specimens made of stabilized soil and stabilized soil with a geogrid. The test results showed that the use of a geogrid in stabilized soil increases the failure strain, as compared to the case where a geogrid is not used, and can prevent the continuous development of cracks. In addition, it was observed that the interaction between the geogrid and the stabilized soil can increase the tensile strength of the soil. The results also showed that the increase in the tensile strength due to the use of the geogrid does not change with the confining pressure; therefore, the increase in the tensile strength can be modeled as quasi-cohesion.

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The mechanical behavior and the strength characteristic of quasi-brittle inhomogeneous solids such as rock and concrete are strongly governed by the behavior and failure process, such as cracking within the microstructure involved in them. In order to predict such strength characteristic of the body containing a microstructure, utilizing the multiscale analysis method with micro-crack propagations, a numerical method for evaluation of macroscopic strength of cracked bodies is proposed. Numerical analysis of an uniaxial loading test show that the predicted strength agrees fairly well with that of experiments and demonstrates the performance of the proposed method for evaluating the strength of quasi-brittle solids.

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This paper comprehensively describes the characteristics of undrained shear behavior of partly saturated sandy soils, in which flow failure due to liquefaction in alluvial deposits is generally caused. In this study, in order to obtain the relationship between shear stress and strain under partly saturated condition, undrained triaxial compression tests of reconstituted Toyoura sand samples and undisturbed Koshigaya sand samples at various B-values were conducted. It is found that the different evaluation of in-situ flow failure of partly unsaturated sandy soil layers can be revealed because the undrained shear behavior was influenced by relative density and partly saturated condition.

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Most of old fill-dams (H≧15m) was mostly accumulated with the muddy soil in reservoir that caused the water pollution and the reservoir capacity loss. In order to make efficient use of the muddy soil as the embankment soil for improving the damaged embankment, we have developed a new type method to improve the old small earth dam embankment (H<15m) by means of the cement-mixed muddy soil. This method is applicable to the improvement of the fill-dam embankment larger than the small earth dam embankment.
In this paper, we propose the design method using the strength parameters (c’ ,φ’) by triaxial compression tests to improve the old fill-dam embankment.

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Most of old fill-dams were accumulated with a muddy soil in reservoir that caused the pollution and the shortage of reserved water. This muddy soil is generally high-water-content and very soft clayey soil. In order to make efficient use of such a problematic soil as embankment soil, we have developed a new type method to repair the damaged embankment by the cement-mixed muddy soil. The strength and strain behavior of the cement-mixed muddy soil is influenced considerably by the grading and the water content of muddy soil including the cement amount and curing period.
We propose the strength control method considering the effect of the grading and the water content of muddy soil on the strength of cement-mixed muddy soil.

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Most back-analyses in geotechnical engineering are based on field displacement monitoring data. In the present study, a novel method is developed to back-calculate rock mass strength parameters from AE monitoring data in combination with an FEM analysis. The method is based on the important concept of generalized AE initiation threshold of rock masses, established from comprehensive data analysis of laboratory tests and underground AE monitoring programs. One example is given to demonstrate the back analysis process using AE monitoring data recorded from the Kannagawa powerplant cavern. The rock mass strength parameters identified from this approach compare well with field test data.

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Most of old fill type dams were accumulated with a muddy soil in reservoirs that caused the pollution and the loss of reservoir capacity. This muddy soil is generally high-water-content and very soft clayey soil. We have developed a new type method to repair the old embankment by the cement-mixed muddy soil in order to make efficient use of such a problematic soil as embankment soil. In this paper, we investigate the grading and the plasticity characteristics of the muddy soil accumulated in areservoirs to apply this reparing method adequately to improve the old fill type dam embankments. From our results, we concluded that the strength management of cement-mixed muddy soil required to concider the effects of the grading and the water content of the muddy soil in case of the fill type dam reservoirs because there is very much change of the grading.

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A nonlinear elastic constitutive model that describe the increase of a secant Young's modulus by the crack closure is proposed and incorporated into the homogenization method to evaluate the mechanical properties of discontinuous rock mass. The homogenization analysis involving this “weak layer model” simulates an unconfined compression test of a specimen with a single crack and the results are compared with those of the experiment, and the effectiveness of the weak layer model is shown. Then, the proposed method is applied to an evaluation of strength of a rock mass simulating an actual rock shear test. The predicted peak shear stress agrees with those of the real test well, and the potential of the homogenization method with the proposed weak layer model in the field of rock mechanics and rock engineering is shown.

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A numerical procedure using crack tensors is one method of analyzing a jointed rock mass. In this study, excavation analyses for a circular cavern, hood type cavern, and a large-scale underground power station cavern are carried out with finite element analysis modeling of the jointed rock mass by crack tensors. The purpose of analyses is to investigate the influence of the joint stiffness ratio (i.e., ratio of normal stiffness to shear stiffness) and the stress dependency of joint stiffness on the stress and deformation around the caverns. The numerical results reveal that the numerical procedure newly taking into account the stress dependency of joint stiffness can be used to predict the deformation of a jointed rock mass more accurately than the conventional method.

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For the purpose of developing the design method for pile foundation subjected to the liquefaction-induced lateral flow, the authors have conducted a series of both small and large scale tests as follows: first, model piles installed into model ground formed inside shear container mounted on shaking table was vibrated to be liquefied; then, the shear container was sheared by external force while vibration being applied. Based on the test results, the formula of evaluating the maximum forces applied to a single pile through non liquefied and liquefied layers have been proposed as a function of the pile layout. Moreover, the coefficient of subgrade reaction and compressive strain of layers have been clarified.

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We are suggesting a simplified design method for pile foundations subjected to lateral flow due to soil liquefaction considering spacing effects between piles, which was established based on the results of small and large scale shaking table tests. The proposed method is effective for predictions and examinations of pile foundations whose limit states of the seismic performance are limited in terms of allowable displacements, because nonlinearities in both soils and piles are taken into consideration. Finally, using the proposed method, single pile behaviors in the large-scale shaking table tests are simulated to show its validity in practical situations.

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Accidents due to slope failure frequently occur at excavation sites. About 20 workers die annually in accidents attributed to slope failure or rockfall during slope-cutting work in Japan. Lives of the workers and property could be saved if early predictions of failure could be made. Many instruments had been developed to measure the movement of slope just before the failure such as landslide, mainly. But most of them are either difficult to set up in the field or are expensive to opt. By the way of prevention of the labor accidents due to slope failure, it is necessary to develop the system which are utilized for small-to-medium-sized slope-cutting sites. In this report, the development of two-dimensional displacement sensor system for the measurement of early response of failure just before the failure and the application of it are explained.

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Authorized reasonable design method for steel pipe sheet pile reinforcement method for existing caisson foundation in water has not been established, because reinfrocement effect and lateral load ratio transferred to SPSP wall are not clear. In this research, the detail of mechanical behavior of caisson foundation reinforced by steel pipe sheet piles are explained using three dimensional elasto-plastic finite element method. The main parameters are caisson-SPSP connection condition and pile length. From this result, it can be seen that the complete connection between caisson and SPSP, and pile installation to the bearing layer are not necessary.

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To study the failure criteria for cohesive granular material, the true triaxial test was simulated with three dimensional DEM analysis. The interglanular adhesive force was introduced between sphere particles, and the specimens of rectangle aggregate were applied to shear process with stress path on the octahedral plane. The specimen shows more isotropic characteristic for deformation than that of real granular material. From the obtained simulation results, it was found that the Lade failure criterion governed the failure stress state for dilative and contracted specimens, and that the contours on the octahedral plane for equivalent octahedral shear strain showed similar shape with that of the Lade failure criterion.

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Authors have developed a technique, called the cement-mixing and mechanical dehydration (CMD), as one of waste recycling and pollutant stabilization techniques. In order to investigate the strength properties and elution characteristics for contaminated sediments containing heavy metals, tri-butyl tin (TBT) and tri-phenyl tin (TPT), unconfined compression test and a series of elution tests were performed for contaminated sediments treated by the CMD. The main conclusions obtained form this study are as follows; 1) CMD is effective for increasing the unconfined compressive strength of contaminated sediments. 2) Heavy metals eluted from contaminated sediment treated by CMD can be satisfied with the Japanese national environmental quality standard. 3) Elution of TBT and TPT can be expressed by an exponential function of the potential of hydrogen, pH, in alkaline pH range.

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This paper proposes a new practical method to evaluate soil parameters for performance based design. The characteristic value of soil parameter is the expected value in principle, but it is not the mere average. We should take into account of errors statistically estimated, errors in derived values associated with testing methods, inhomogeneity of the soil itself, and limited number of test data. The new method uses a correction factor based on the variation coefficient derived from the soil data. In this method, the characteristic value automatically reflects the variability of derived values associated with the testing method and the reliability of the data interpretation.

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The compression tests and the bending tests are performed to study the moduli of deformation of frozen sand and clay. As a result, the measurement method of the compression tests is improved to exclude the influence of disturbance of the near ends of specimen, and the appropriate range of specimen height is shown to remove the influence on moduli of deformation. Also, it is explained that the influence on the moduli of deformation by strain rate and by dry density of the specimen is small, and that little difference of the moduli of deformation between compression tests and bending tests is found. Moreover, the experimental formula of the moduli of deformation as a function of temperature are proposed. Finally, the constitutive equations of frozen soil including breakage point are proposed for the elasto-plastic analysis of composite structure which includes frozen soil and other materials.

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Micro pile foundation is applicable as a measure such as a rock fall barrier to stabilize slopes. Combination piles as a set of micro piles normally driven into the ground that is an inferior condition such as a slope of talus cone at cold regions; an excessive displacement of the foundation is highly likely due to the pressure of snowfall. However, the behavior of a foundation with combination piles on such ground is not sufficiently clear. In this report, we proposed an analytic model for the structure of foundation composed of a vertical pile, a slant pile and a footing, and applied this analytic model to relationships of road and displacement it got from a result of experiments, and verified that validity. Furthermore, we discussed the relationship of load and deformation characteristic, as obtained from analytic results concerning combination piles applied as a foundation of the rock fall barrier on the slope of talus cone, we showed examples of the application to the design for the combination micro piles loaded by accumulated snowfall.

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It is indispensable to understand the phenomena and to store the fundamental data for establishing a highly reliable criterion to judge the possibility of seepage flow failure. Experiments on upward seepage flow failure were conducted using a parallelepiped container with glass beads. It was observed that small size particles jump up and down at the surface of the specimen before the failure and then the specimen starts to shrink or swell depending on the initial void ratio while the coefficient of permeability also begins to re-enlarge. It means that local piping necessarily occurs as the sign of failure due to boiling or global piping except the case with a uniformity coefficient of nearly 1.0.

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The daily inspection of the stability of water-sealing function is one of the most important items in the operating procedure for underground oil storage. The simplified criteria for the daily on-site judgement are strongly needed for the speedy evaluation and the expedient countermeasures. In this paper, the methods based on the simple statistical model are proposed for the daily judgement and their effectivenesses are verified by using the observed data concerning groundwater. The effective rainfall method is adopted to evaluate the data fluctuation due to seasonal precipitation. And, the method based on the cross-correlation structure of multiple groundwater table measurements is also discussed.

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In constructing an embankment on clay ground trapping local sand layers, the generated excess pore water pressure is propagated to the surrounding ground through the sand layers. In the present study, a series of model loading tests was conducted to investigate the propagation of the excess pore water pressure and consolidation behavior. The test results showed that the excess pore water pressure in the sand layers delayed the consolidation in the surrounding clay ground and that in some cases the clay ground was heaved by the excess pore water pressure propagated from sand layers. In addition, the effect of the time difference of loading and number of sand layers on consolidation behavior was experimentally investigated.

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The new Radio-isotope density cone penetrometer (Nuclaer Density Cone Penetrometer; ND-CP) has been developed. The gain in robustness of cone shaft is achieved by introducing special steel with high strength to avoid bending and/or broken due to encountering hard stratum with gravels. A set of inclinometers as well as thermometer have been incorporated to ND-CP to confirm the degree of vertical penetration and monitor the temperature around sensors for q_c, f_s and u. The effect of temperature on measured strain is large enough for the measured values to be corrected, particularly a due consideration is required for cone tip resistance, q_c for very soft clays because possible error can not be ruled out for the shear strength derived from q_c. The newly developed ND-CP is a so-called double probe type that facilitates an ordinary density probe unit consisting of ¹³⁷Cs gamma ray source and NaI scintillation detector together with natural gamma ray (background value; BG) detection probe unit consisting only of NaI scintillation detector in one cone. Cost saving has been achieved with the new ND-CP for Tekong reclamation project in Singapore by being free from additional penetration to detect the natural gamma ray in the ground.

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Although the stability of the working-face is one of the most important issues during the excavation of a tunnel, the mechanism of working-face collapses and their causes have not been sufficiently discussed. This situation may lead to improper countermeasures against working-face collapse. For example, in projects such as tunnel excavation with only a thin overburden, improper measures may greatly affect the surface structures, resulting in significant societal loss. This paper presents a case-study of a large box excavation and traction project right under a railway, examines the collapse mechanism of the working face, and discusses the role of face bolts as one of the countermeasure works. It was conclusively confirmed that a large-scale collapse is highly likely to happen at the working face, resulting from an equivalent strain of geo-materials induced by tensile stress during excavation, and that the installation of face bolts would limit tensile stress and effectively prevent a large-scale collapse of the working face.

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The partial factors format, which is one of the reliability design methods, needs to be applied to open-type wharfs on vertical steel pipe piles in harbor structures in order to perform performance checks. In this study, the serviceability limit states, repairability limit states and ultimate limit states for vertical steel pipe piles of an open-type wharf are defined, then partial factors of design formulae are provisionally calculated based on reliability theory. Twenty existing open-type wharves are used, and limit states for the ground bearing capacity and bending moment of the piles are examined. Considering the uncertainties of basic variables such as the lateral subgrade reaction coefficient, the yield stress of the steel pipe piles and the ground bearing capacities of pile tips and shaft friction, the reliability of existing structures that were designed using previous methods is evaluated using the advanced first-order second-moment method, and a set of partial factors is estimated based on the sensitivities of basic variables. Finally, the reliability index in the design section is calculated by the partial coefficient method, and the validity of the proposed technique is verified.

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The 2004 Niigataken-Chuetsu Earthquake caused not only heavy casualties but also serious damage to infrastructures such as electric-power, water-supply, and transportation facilities. Power generation facilities, including three fill-dam reservoirs of the Shinanogawa Hydroelectric Power Plant were also heavily damaged; this plant is owned by the East Japan Railway Company. Differences in level caused by fissures along the fill-dam were brought about at the Asagawara Reservoir, one of the three reservoirs. Investigations of the site were carried out by trench-cut and boring methods, and showed that cracks and fissures were mainly superficial, and posed no major problem to the overall structure. The core also showed no damage. There was no damage to the function of the dam, therefore restoration was enabled despite the severity of the earthquake itself. Moreover, the cause of such damage was considered based on the investigation result.

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It is common practice to cover railway embankment slopes with protective materials to prevent rain-induced slope failure. Although slope covering of this type is designed mainly for erosion control, it also has the effect of helping prevent the groundwater level rising through the embankment body in the event of heavy rain. This study investigates the groundwater level lowering effect of protective covering over the upper half of the slope of a railway embankment made of sandy material, and the factor of safety of the slope that can be achieved by such slope covering. A numerical analysis parameterizing such factors as embankment height and slope covering length is conducted, and the effect of slope covering on slope failure due to heavy rain is investigated quantitatively. The study has revealed that upper surface covering over an embankment slope helps prevent rain-induced slope failure. This paper also proposes a procedure for applying these results to a risk evaluation method based on critical rainfall.

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