A typhoon wind disaster prediction model was used to investigate three typhoons: T9719 (Oliwa), T9807 (Vicki), and T9810 (Zeb) that struck the main islands of Japan, and the surface wind and the rate of damaged wooden houses were estimated. The estimated distribution of the surface wind approximately agreed with that of the observed surface wind, and the damage rate distribution agreed with that of the actual damage incurred. Two main problems remain; underestimation of the strong wind to the rear of the center in Typhoon 9807 and the accuracy of the estimated damage rates.
Analysis of the strong winds of Typhoon 9807 showed that a phenomenon similar to a cold front had occurred in the rear area of this typhoon.

View full abstract

Landslides are common geomorphic events on fragile, steep slopes of the granitic mountains in southern Thailand. The ensuing catastrophes have resulted in considerable economic losses to the country as well as to its people, and the disastrous consequences have significantly reduced the pace of sustained social and economic development. Although the occurrence of landslides can not be prevented, it is possible to reduce their effects on lives and property through prevention and mitigation measures. We used GIS and remote sensing to identify landslide hazard and risk areas in southern Thailand to ensure that appropriate measures are used to prevent and/or mitigate the negative impacts of landslides. Results showed that 73, 21 and 5 percent of the total land areas respectively faced low, moderate, and high landslide hazards. Areas facing high hazards lie on mountainous terrain, indicative of the pressing need for effective land use zoning and sustainable agricultural practices to maintain slope stability. Further analysis showed that 553, 971 hectares, equivalent to 8 percent of the total land area, was subject to high risk. The prevention and mitigation measures required to reduce the risks of future landslides are discussed.

View full abstract

Liquidized landslides have caused many disasters because of their high mobilities and long travel distances. The 1995 Takarazuka Golf Course landslide is a typical liquidized landslide with a runout of 180 meters. A series of undrained speed-controlled ring shear tests and another series of undrained strain-controlled triaxial compression tests were conducted on weathered granitic sands to determine the conditions under which liquidized landslides are generated in order to investigate the process of liquefaction and shear behavior in the steady state as key phenomena in such landslides. Test results showed that liquefaction was generated in loose to dense specimens in the ring shear tests, whereas in triaxial compression tests liquefaction occurred only in loose specimens. The apparent friction angles in the steady state obtained by the ring shear tests after grain crushing terminated were smaller than the values for the Takarazuka Golf Course landslide. Because that landslide showed a clear shear surface, grain crushing in that surface must have been complete or almost complete. The direct shear state with large shear displacement reporduced in the ring shear tests corresponds to the state of shearing in the sliding surface of the landslide. The small apparent friction angles obtained in the ring shear tests therefore provide a good understanding of the high mobility of liquidized landslides.

View full abstract

The grain crushing character of sandy soil greatly affects its excess pore pressure generation behavior during rapid landslide motion. Ring-shear apparatuses were used in an experimental study of the relationship between grain crushing and excess pore pressure generation by sandy soils. Three samples with different grain crushing susceptibilities were used. Drained tests were conducted to investigate these samples' grain crushing susceptibilities. Undrained tests (speed-controlled and cyclic-loading ones) were conducted to investigate excess pore pressure generation behavior. Based on the findings for sample-height change in the drained tests and for the excess pore pressure ratio in the undrained tests together with shear displacement, dilatancy characteristics of sandy soils could be divided into three phases: “initial negative dilatancy”, “initial positive dilatancy”, and “negative dilatancy due to grain crushing”. The first two phases were mainly affected by the initial structure, whereas the last one was affected by the grain crushing susceptibility. Once the steady state was reached, excess pore pressure apparently was determined by grain crushing susceptibility, whereas the initial density did not have this effect. In the undrained cyclic-loading tests, the effect of the frequency of cyclic-loading on excess pore pressure also was found negligible.

View full abstract

The seismic observation network in Shiga prefecture is composed of four systems. All the observation data obtained were used to estimate the dynamic characteristics of the surface soils around the lake and the seismic hazard for Hikone City. Since 1995, 21 records have been obtained at the USP site of which those for the 1999 Shigaken-Hokubu Earthquake and 1999 Wakayamaken-Hokubu Earthquake were used in this study. Transfer functions of the surface soil in each ward of Shiga Prefecture based on the Mt. Kojin site (KJY), which has relatively hard soil, were calculated from the records of the two earthquakes. Assuming a scenario earthquake at the Hyakusaiji fault close to Hikone City, maximum ground motions were obtained for 15 city blocks in order to establish a damage estimation for that city. The number of collapsed wooden houses and the damage ratio were calculated based on the distribution of construction of wooden houses by year. Blocks with a larger ratio of old, wooden houses in Hikone showed a close correlation with blocks with a large ratio of aged persons in them, indicative that weak persons, such as the elderly, may find themselves in a severe situation during a natural disaster.

View full abstract