Ryohei Ishikura

EXCESS PORE WATER PRESSURE ACCUMULATION AND RECOMPRESSION OF SATURATED SOFT CLAY SUBJECTED TO UNI-DIRECTIONAL AND MULTI-DIRECTIONAL CYCLIC SIMPLE SHEARS

This paper is to investigate the effect of cyclic shear direction (or phase difference) on the accumulation of excess pore water pressure during cyclic shear and on the recompression after cyclic shear. Several series of uni-directional and multi-directional cyclic simple shear tests under undrained condition were carried out for normally consolidated Kaolin. From the test results it is shown that the accumulation of pore water pressure and the post-cyclic settlement increase with the shear strain amplitude and the phase difference. The values of the shear strain amplitude at which the effect of cyclic shear direction is most significant, decrease with the increase of the number of cycles. The change of the void ratio in the recompression stage increases approximately in proportion to the logarithm of the stress reduction ratio and is not affected by the shear strain amplitude. For multi-directional cyclic shear, this change of the void ratio depends on the phase difference and the number of cycles. The cyclic recompression indices in the recompression stage were obtained for uni-directional and multi-directional cyclic shears. The cyclic shear induced settlement can be calculated by using these indices.

Behavior of Breakwater Foundation Reinforced with Steel Sheet Piles Under Seismic Loading

Waterfront structures such as breakwater, coastal dike, sea wall, etc., suffer serious damage from the earthquake and tsunami. The breakwaters are designed to protect coastline and seaport from the devastation effect of wave and current of tsunami by absorbing their wave energy and reducing overtopping. The port of Kamaishi (Iwate Prefecture, Japan) suffered heavy causalities due to the Great East Japan Earthquake in March 2011 mainly due to the damage of breakwater mound/foundation which was caused due to collapse of the breakwater. On the other hand, mitigation of compound disaster due to predicted future earthquakes such as Tokai earthquake, Nankai Earthquake, and Tonankai-Nankai Earthquake is a matter of great concern. The stability and safe performance of breakwater is very important for the protection of structures and population living near to coastline. It is, therefore, necessary to develop a new earthquake and tsunami resistant reinforcement technique for breakwater foundations which will make the breakwater resilient against the earthquake and tsunami forces. This paper deals with the development of an effective reinforcement technology for breakwater foundation which provides resiliency to the mound against earthquake. The technique involves use of steel sheet piles and gabion type mound (gravel wrapped up in steel wired mesh), which is effective in preventing breakwater subsidence and horizontal displacement. As a part of the study, a series of shaking table test in 1 g of gravitational field were performed and through the tests, the reinforcement effect by the steel sheet pile and gabion under earthquake loading and its influence on breakwater performance was made clear.

Numerical Study on the Seismic Response of Waterfront Retaining Wall Reinforced with Cushion

This paper describes the findings on the effectiveness of waterfront retaining structure reinforced with cushion made of tire chips, which has been analyzed using commercial software, PLAXIS 2D. The numerical model was subjected to the real earthquake recorded during the 1995 Hyogo-ken Nanbu earthquake. The results of the numerical analysis were presented in term of the deformation of the mesh, the displacement of the quay wall horizontally and vertically, and the settlement of the soil behind the quay wall. In general, the utilization of tire chip as a cushion behind a waterfront retaining wall was able to improve the behavior of the wall against an earthquake loading.

Evaluation of rainfall erosivity and impact forces using strain gauges

Rainfall erosivity and impact forces are key meteorological parameters for predicting rainfall-induced hazards and disasters. Erosivity of rainfall is widely indicated by its kinetic energy or momentum that is widely derived from drop diameters or drop size distribution and velocity of raindrops. Raindrop velocity and impact forces describe the rainfall erosivity dissipated to impacting surface. These parameters are not commonly evaluated and available in practice due to cost and capability of measuring instruments. A strain gauge-based device was developed for automatic and continuous measurement of the parameters in laboratory. The strain sensor, with the aid of a portable, dynamic, and high frequency data acquisition, was calibrated to capture the falling velocity of a 4.00 mm diameter waterdrop with varying heights. Results of the falling velocities of a waterdrop against heights in this study showed a close agreement with results from literature data and equations for the falling velocity and its impact force of a waterdrop were derived. In addition, results of using the equations to derive terminal velocities and impact forces as a function of drop diameters were presented.

Evaluation and Optimization of the Granulated Blast Furnace Slag-Natural Sand Mixture Hardening Properties

The granulated blast furnace slag is classifies as a high permeable stiff material with sand size particles that when it interacts with water it shows a time dependent self-hardening behavior. The previously mentioned properties indicates that the slag is a promising material that can be effectively utilized in various geotechnical aspects where it was reported that it has been used as earth reinforcement technique in harbor construction projects. However, onshore utilization of slag material is limited. It was reported that utilizing sand compaction pile (SCP) method imposes crushing the slag particle resulting in significant education of the hydraulic permeability. This study aims at evaluating the strength development of slag material under various curing times. In order to prevent the significant drop of the hydraulic permeability as a result of early hardening of the crushed particles, the slag particles were mixed with sandy soil sand and subjected to various curing durations then were examined by evaluating the strength development of the adopted mixtures.

Study on the Effect of Union Basement on Decreasing Destruction During Liquefaction

One of the greatest earthquakes in human’s history (9.0 Mω) occurred in Japan on March 11, 2011, which also took a tsunami sweeping the Tohuku region. In this major disaster, around 27,000 personal houses were damaged by liquefaction. On the principle of higher safety and lower cost for the engineering of preventing liquefaction, a new structure form, Three-Union house with basement, is introduced in this study. Aiming at liquefaction inhibition and the increasing of stability of foundation, the function of basement for preventing liquefaction is evaluated by shaking table tests. The factors considered in the test are as follows, with or without substructure, individual basement or union forms, the weights of different model. The test result showed that higher stability can be achieved by Three-Union house with basement.

Analysis of the Lateral Force on Stabilizing Piles in c-φ Soil

In the past, the lateral force on stabilizing piles has been studied by many researchers. In this study, the lateral force loading on stabilizing piles per unit thickness is analyzed in a semi-infinite c-φ soil ground (φ > 0, c > 0). The soil arching effects between two neighboring piles are considered. A new formula is proposed to estimate the lateral load acting on the stabilizing piles. When the proposed approach is applied on some kinds of c-φ soil, an invalid value would be obtained on the failure plane. However, the invalid value can be ignored since it has little impact on the solution. The in situ observed tests from the literatures are introduced to validate the proposed approach. The comparison charts illustrate that the prediction from the proposed approach shows a better agreement with the test results comparing with the solution from plastic deformation theory.

COMPARISON OF CONSOLIDATION CURVES FOR REMOLDED MUD VOLCANO OF SIDOARJO, INDONESIA

Sidoarjo mud volcano (Lusi) is one of the most challenging problems regarding to the compressibility of fine grained soils in Indonesia. Understanding about compressibility behavior is essential to construct appropriate remediation program for this problems. Consolidation test has been conducted to investigate the compressibility behavior of Lusi mud volcano. In this study, the laboratory test result is compared with estimated value derived from several empirical equations. A simple equation can be used to predict e-log σ’ curve very well by using the correlation between initial void ratio (e0) and void ratio corresponding to unit pressure (e1); and correlation between compression index (Cc) and physical properties of soils, such as liquid limit (wL) or natural water content (wn). This equation predict better than other available equations in literature when compared with laboratory test of Lusi mud volcano.