There is a ground anchor technique as one of the earth reinforcements to sustain the stability of the slope, which has been widely used for stabilizing cut slopes in Japan for the last thirty years. As ground anchors are anticipated to be deteriorated by geological environments such as ground water and natural disasters such as earthquake and typhoon, it is recommended to evaluate its performance by regular survey and tests. Moreover, it is believed that old-type anchors have a low protection performance against the corrosion on the surface of old-type anchors. Consequently, it is necessary to evaluate appropriately the damage of anchors as well as the stability of slope reinforced by deteriorated ground anchors. The performance of ground anchors is generally checked by soundness diagnosis, which is the visual check of anchor head, and lift-off tests, which is the loading test to measure a residual stress in anchor. The soundness diagnosis and lift-off test are effective for evaluating the performance of single anchor itself, however, the reliability of the safety assessment between the entire reinforced slope and the performance evaluation for single ground anchor has been questioned. This paper analyzed the reliability of soundness diagnosis based on the past regular surveys and lift-off tests statistically, proposed a deterioration model for single ground anchor using the Weibull distribution and finally assess the stability of reinforced slope with the proposed model.

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In order to investigate the instability mechanism of caisson-type composite breakwater under tsunami condition, a scale of 1/100 model experiment was performed in laboratory. Loading tests were also carried out to investigate the reduction of bearing capacity under the existence of seepage flow. From the results of laboratory experiment and finite element analysis, it was confirmed that the bearing capacity of rubble-mound can considerably decrease due to the tsunami-induced seepage flow. It is concluded that the effect of seepage flow in the rubble-mound should be taken into account when making a design of the caisson-type composite breakwater against tsunami. The following conclusions are drawn from this study; (1) The occurrence of seepage failure of the harbor-side rubble-mound under tsunami condition is experimentally confirmed. The rubble filled gabion on the harbor-side rubble-mound is useful for preventing from the seepage failure. (2) In this study, the reduction of bearing capacity due to seepage flow attains no less than 40% of the bearing capacity without the seepage flow. The rubble filled gabion on the harbor-side rubble-mound is not effective improving the bearing capacity of breakwater since the effective weight of rubble filled gabion is not large enough to increase the strength of harbor-side rubble-mound. (3) In the design of caisson type composite breakwaters against tsunami, the influence of seepage flow and seepage force on the stability should be taken into account. (4) The failure plane and plastic zone in the rubble-mound under tsunami condition become shallow by the effect of seepage flow and force.

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Hazardous sinkholes started to emerge as a new problem that threatens the safety of the people in Korea. In this study, sinkhole simulation and monitoring in centrifuge test were designed to make environment for related research. Electrical resistivity monitoring system was built in centrifuge facility and 1g preliminary test was performed using ice blocks in order to ensure the simulation of underground cavities in centrifuge model. Subsequently, 20g centrifuge test was performed simulating two types of underground cavities such as existing cavity and water leakage from sewage pipeline. After reaching target centrifugal g-level, groundwater was injected from the base of model box to simulate the groundwater level change. Electrical resistivity survey was conducted continuously to monitor the underground anomalies. The electrical resistivity results from the centrifuge test corresponds well to expected process of sinkhole generation by showing the definite resistivity difference between underground cavities and adjacent soils. From the underground cavity simulation in centrifuge, it is noticed that electrical resistivity survey could monitor the process of underground cavity generation effectively, and developed monitoring system can be applied to further the parametric studies in sinkhole research.

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This paper describes the case study in which hazard maps for heavy rainfall induced slope failure were developed for the villages located in the mountainous area close to Median Tectonic Line. The purpose of creation of the hazard map is to discuss evacuation system at the village. The risk for slope failure was evaluated for 10m grids of the villages as a safety factor based on the mechanical model which is an infinite length slope with ground water. For the analysis of the risk for slope failure field survey were carried out to obtain the parameters for different geological conditions close to Median Tectonic Line. The created hazard maps were used effectively to discuss the evacuation rules at the villages.

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A new macro-element method with water absorption and discharge functions proposed by the authors was incorporated into a soil-water coupled finite deformation analysis code capable of accounting for inertial forces and verified by simulating an actual ground behavior observed in a peaty ground improved with vertical drains and vacuum consolidation. It was found that the proposed method was capable of simulating a range of ground behaviors including the temporal change in pore water pressure, horizontal displacement, and the settlement of the surrounding ground. Because a continuous middle sand layer was found to exist spanning the entire improved area at the actual site, additional simulations were performed to elucidate the effect of this layer. Furthermore, based on a series of simulations with a particular focus on the influence of drain spacing, it was revealed that although the vacuum consolidation method is effective in cases where it is necessary to limit deformation of the surrounding ground, the same reduction in residual settlement can be achieved using vertical drains alone, provided that the drains are deployed at a sufficient frequency.

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Sediment transport is the natural phenomenon which is occurred along river stream. Many factors are influencing on this process, but the main parameters are current velocity and flow discharge. The velocity and flow discharge are two river components which intercorrelated each other. Current velocity may cause scouring at the river stream continuously. The materials from scouring process would be become the primary sources of sediment load. There are two sediment load types, suspended load and bed load. The quantity of sediment load that expressed by sediment concentration plays an important part in river morphology changing. This study is focused to assess the sediment concentration affected by current velocity. The sediment samples were taken from Kanor village-Bengawan Solo River during the dry and monsoon seasons. Suspended load samples were taken by suspended trap equipment. River water current was measured by current meter magnetic. This paper is mainly investigated the differences between the quantity of sediment concentration affected by river water current during the dry and monsoon seasons. The investigation results were sediment concentration in milligram per liter (mg/L) and river water current. Based on the data analysis result, the sediment concentrations and current velocities shows the linear correlation. During dry season the sediment concentration and current velocity are lower than in the monsoon season. The highest sediment concentrations were at 0.8 of water depth. This phenomenon is thought be due the effect of particle settling process, so the sediment concentrations are accumulate at the lower point of water column.

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Steep natural terrain in Hong Kong, combined with deep weathering profile and high seasonal rainfall, is highly susceptible to rain-induced, shallow landslides. With over 35 years of practice in landslide risk management, Hong Kong has progressively built up a series of important databases that facilitate conducting state-of-the-art research and development works on landslides. Amongst others, there is a dense network of raingauges that provides state-of-the-art rainfall records, a high-resolution inventory of historical landslides and a LIDAR-based digital terrain model for natural terrain. This paper will firstly discuss the previous landslide susceptibility map for natural terrain in Hong Kong, and then present a new territory-wide rainfall-based landslide susceptibility analysis for natural terrain that takes cognizance of effect of slope angle. The year-based susceptibility model correlates landslide density with normalized maximum rolling 24-hour rainfall for eight different slope angle classes. The potential applications of the outcomes of the landslide susceptibility analysis will also be discussed.

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