The authors have developed practical and simplified reliability analysis procedures for geotechnical structures recently. Since reliability analysis has originally developed by structural engineers, there are a number of issues to be customized or specialized for geotechnical reliability problems. By integrating the authors' recent studies, a whole framework of a proposed procedure GRASP (Geotechnical Reliability Analysis by a Simplified Procedure) is explained in this paper. In addition, examples of pile foundation design are presented to demonstrate the effectiveness of the proposed procedure. Furthermore, by summarizing quantitative reliability results by GRASP, future challenges in geotechnical design are pointed out.

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 A multiple steel pipes bridge pier integrated by pile foundation without a footing has been proposed to design a rational foundation of the bridge pier structure. Based on the past achievements, the proposed substructures possess an excellent advantage of reduction of strain at the column through strain decentralization at footing point. In addition, reduction in footing weight contributes to decrease pile strain. On the other hand, the proposed substructure has some disadvantages i.e. increase in strain and displacement of piles. But it has been revealed that the strain generated at piles can be minimized by using underground beams around pile heads in the ground. In this paper, the seismic performance of the proposed bridge pier structure grounded in dry sand and liquefiable sand is evaluated based on the large-scale shaking table tests using bridge pier and foundation models with the scale of 1/20. As with the past achievements, the proposed structure has advantages of strain reduction of column by strain decentralization at footing point. It is recognized that it has high seismic performance and high toughness in view of the fact that the main members (columns and piles) hold a large residual strength after yielding of the shear panels.

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 In the current concept of repository for radioactive waste disposal, compacted bentonite as well as bentonite-based material will be used as an engineered barrier mainly for inhibiting migration of radioactive nuclides. However, mechanical properties including swelling properties are also important because these assure low hydraulic conductivity of the compacted bentonite. In this paper, a microstructural model of saturated bentonite and its condition of change are proposed. Microstructural mechanism of swelling pressure is also proposed based on the model and its conditions of change. Numerical simulation of a one-dimensional unloading and reloading test is conducted using the modified Cam-Clay model considering microstructural change of soil. It is revealed that the results of the test can be simulated approximately by the model.

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 In Japan, where mountainous districts occupy 70% of the land, a lot of shallow landslides caused by heavy rain have occurred each year. It is important to identify soil hydraulic parameters in order to simulate rainwater infiltration processes. Recently, much attention has been paid to the inverse analysis based on in-situ measurements, to identify the soil hydraulic parameters. In this study, the particle filter, which is one of the data assimilation methods, was applied as the method of inverse analysis. Firstly, the soil hydraulic parameters, which are used in the water retention curve proposed by van Genuchten, were identified through the inverse analysis of the particle filter. Then, the numerical simulation, in which the identified parameters are used, was performed to verify the reproducibility to soil moisture behavior. As a result, the analytical results, which simulated with time for the condition of heavy rainfall, were in excellent agreement with in-situ measurements. Therefore, the particle filter was available to identify the soil hydraulic parameters based on in-situ measurements.

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 The study was conducted to understand the slope collapse behaviour due to rainfall of decomposed granite soils with fines. The small slope model was prepared to perform the collapse tests by rain. The model was made of the decomposed granite soil “Masado” with various contents of fines. The measurement was obtained by accelerometers, water pressure transducers and image analysis. The characteristics were evaluated by collapse pattern, collapse size and pore water pressure generation. Firstly two collapse patterns were found which are “permeation failure” and “slip failure”. Masado with higher content of fines occurred the slip failure. Also the Masado showed higher generation of pore water pressure and larger collapsing size. A new index with permeability and rainfall could be proposed to evaluate the collapse behaviour.

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 We have developed a rapid measurement method to the paper disc groundwater velocity meter which uses no electricity. The paper disc groundwater velocimeter can measure the groundwater velocity and direction in one borehole using the trajectory of the ink transported by the groundwater water on the paper disc. The smallest measurement time of this device is 5 min. However, it should have the image analysis of the paper and should take much time to get the result. If the device could measure the result immediately after the measurement, the total performance of the velocimetry will be more rapid. We have developed a ruler to convert the tailing length to groundwater velocity and flow direction.
 We evaluated the measurement accuracy after the application of the sensory analysis. As a result of the sensory analysis, in the range between 0.3 to 1.5 cm/min, the accuracy of the velocity and direction were within 33% and 10 degrees respectively. Though the measurement accuracy of the velocity was lower than the existing calorimetry device, the measurement accuracy of the flow direction was as same degree of the existing calorimetry device.

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 Wooden piles had been applied to foundations of railway viaducts and station architecture since later 19th century, Meiji Era. It is well known that wooden piles have not been decayed and durable for over 100 years in case they exist in groundwater or clay soil layers by past studies and reports. On the other hand, wooden piles might be decayed in case that they exist above groundwater level, and in sand soil layers. This report says that wooden piles have not been decayed severely by the real wooden piles dug in reconstruction work Tokyo Marunouchi Station building, even though they exist above groundwater level, where clay or soil layers lie. And we try to identify the producing area of wooden pile for foundations of Tokyo Station by the record of construction and timber production report. This study says the probability that wooden piles for Tokyo Station had been made in Noheji District in Aomori , and the kind of wood is so called “Kacchi-Matsu (pine)” is very high.

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 Solidification of clayey soil by adding quick lime or cement materials may be inhibited due to the soil properties such as types of clay minerals, water quality of porewater. In this study, in order to investigate the mechanical property of lime and cement stabilized clay containing magnesium salts, unconfined compression test was conducted. Subsequently, accelerated deterioration test which was simulated seawater environment was performed to investigate the effect of concentration of magnesium salts on deterioration behavior of stabilized clay. As a result, it is verified that magnesium salts have functions to decrease the strength and accelerate the progression of deterioration of stabilized clay. Additionally, a new parameter that can evaluate the deterioration rate of stabilized soil containing magnesium salts regardless of stabilizer types was proposed.

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