Hidetoshi Ochiai

THE PULL-OUT RESISTANCE OF GEOGRIDS IN REINFORCED SOIL

Abstract Pull-out resistance has been evaluated using pull-out tests on geogrids in soils. Both field and laboratory pull-out tests were carried out in order not only to make clear the pull-out mechanism but also to determine the parameters for design and analysis of the reinforced soil structures. When the geogrid in the soil is subjected to a pulling force, the geogrid is pulled out of the soil as the grid itself elongates. In order to evaluate the pull-out resistance, two elevation methods which are called ‘Mobilizing Process Method’ and ‘Average Resistance Method’ are newly defined. These are implemented using the test results. Recommendations for laboratory pull-out tests are also proposed.

Bearing capacity analysis of reinforced foundations on cohesive soil

Abstract The bearing capacity of geosynthetic reinforced cohesive foundation loaded by aflexible uniform strip footing is analysed using a rigid plastic finite element formulation. This method is based on the upper bound theorem of the theory of plasticity and the bearing capacity is obtained as a load factor at the ultimate limit state. The reinforcing material and the surrounding sand are modelled as a single composite material with an equivalent cohesion. The underlying soft ground was also assumed to be purely cohesive and hence, both the reinforced soil and soft ground were modelled using the vos-Mises failure criterion. The method of analysis used here in is firstly verified for the case of unreinforced ground by comparison with the Prandtl solution. For the case of reinforced cohesive foundation ground, a series of analysis are conducted by changing the depth and length of the embedded geosynthetics as well as its number of layers. Based on these results, the reinforcing effect on the bearing capacity of the cohesive foundation grounds is quantitatively evaluated.

Advanced Direct Shear Testing for Collapsible Soils with Water Content and Matric Suction Measurement

At natural, in-situ water content, collapsible soils have high strength and relatively high void-ratio with low compressibility. These soils could easily collapse when wet. If the differential deformations and slope stability effects have been neglected in the design and construction processes, they could cause damage to constructions. Ther efore, the identification of collapsible soils with estimation of the collapse potential and shear strength become major components in appropriate engineering for these moisturesensitive soil sites . To deal with shear strength of unsaturated soil or collapsible soil, the direct shear box apparatus for measuring in water content with matric suction must be modified. The electrical sensors for water content measurement are installed near the shear plane. Due to low friction material, Teflon sheets are then used as a spacer to control the water content of the specimen during testing.

Mobility Characterization of Planetary Rover in Reduced Gravity Environment

This paper describes effects of gravity on mobility performance of wheeled rovers for future lunar/planetary exploration missions. A series of model tests of a wheel‐terrain system were performed on an aircraft during variable gravity maneuvers, and it became clear that slip of the wheel becomes high when the gravity is less than 1/2G. In addition to the flight experiments, the same model tests were performed in a laboratory on the ground (1G condition). The experiments were demonstrated with variable wheel loads by using counterweights. As a result of the on‐ground experiments, the mobility performance under low wheel load conditions was found to be improved contrary to the flight experiments. In case of the flight experiments, not only the wheel load but also bearing in the terrain changes with respect to the gravity level, while only the wheel load changes in case of the on‐ground experiments. Thus, running under a reduced gravity condition becomes difficult because the terrain generates higher rolling...

An empirical relationship for predicting soil collapsibility due to soaking under compression and shear

Collapse and direct shear box tests on an unsaturated compacted soil with suction and water content measurements due to soaking are first presented. The compressibility, strength and dilatancy characteristics are discussed on the basis of the experimental results, paying attention to the initial water contents and the normal stresses. Then, a simplified relationship for rationally predicting the collapse settlement under one-dimensional compression condition is presented based on the experimental considerations. The applicability of the empirical relationship presented is finally discussed by comparison with the experimental data obtained by one-dimensional compression tests.

Ferrite-Induced Immobilization of Pb-Contaminated Soil and Application of Magnetic Separation

The ferritization method is applied to Pb-contaminated soil. In order to confirm the immobilization effect by ferritization, artificial Pb-contaminated soil was prepared and batch tests were performed. From the test results, it was confirmed that the insoluble effect of the ferritization-treated soil for Pb-contaminated soil is much higher over a wide range of pH levels. Furthermore, the superconducting magnetic separation was applied to feirritization-treated soil with magnetite. It is suggested that the combination of ferritization treatment and magnetic separation may be one of the techniques for the remediation of contaminated soil containing heavy metals.

Development of Geo-materials for rooftop gardening by using Heat Compressed Crushed recycled EPS with volcanic ash clayey soils

発泡スチロールの約30 ％が埋立や単純焼却により処理されており，有効なリサイクル方法の開発が望まれている。本研究では，廃棄発泡スチロール減容材を基盤材料として用い，これと火山灰質粘性土を再利用して軽量性，保水性を有する屋上緑化植栽基盤の開発を目指した。具体的には, 粒状化した廃棄発泡スチロール減容材に, 軽量性・保肥性を有する火山灰質粘性土(黒ぼく)を混合し，屋上緑化基盤材料への適応性を評価した。

Failure analysis of cement-treated soil by FEM implemented with particle discretization

The authors conducted failure analysis of cement-treated soil by using the finite element method (FEM) implemented with particle discretization. The analysis results were compared with laboratory test results. To predict the tensile failure of the cement-treated soil, the material properties of cementtreated soil dependent on confining stress dependent were introduced into the FEM. The results of the numerical simulation were in good agreement with the value that had been obtained by laboratory tests.

EVALUATION OF THE PREVENTION POTENTIAL AGAINST LANDSLIDE DISASTERS

本文では, 自然的・社会的因子が複雑に絡み合った地すべりの災害・防災ポテンシャルを評価するために, マルチプルリスクの概念に基づく多重ロジスティックモデルを適用した方法を提案する. そして, その評価法を利用した災害・防災ポテンシャルマップの作成手法を示す. 提案した方法はポテンシャルを発生確率で示すもので, それを用いたマップは, 防災対策の効果を表す有効な手段となり得る.