Yasuhito Sasaki

Characteristics of wind pressures on basic structures with curved surfaces and their response in turbulent flow

Abstract Long-span and lightweight structures tend to vibrate in strong winds. Their dynamic behaviour in strong winds is very important at their design stage. We first investigate the characteristics of wind pressures on spherical and cylindrical domes through wind tunnel experiments. We then simulate the response of a hemispherical pneumatic dome as a buffeting problem using the modal analysis method.

Soil creep process and its role in debris slide generation—field measurements on the north side of Tsukuba Mountain in Japan

We measured the ground inclination movement, moisture content, and amount of rainfall on a valley-head slope and a side slope along the valley on the northern side of Tsukuba Mountain, and elucidated the process and role of soil creep in debris slide generation. Soil creep usually occurs during and after rain. The amount of creep caused by one rainfall has a positive correlation with the amount of rain and increase in soil moisture. For the valley-head slope, soil creeps down and accumulates at the bottom bottleneck part of the head hollow, in which soil is compressed and forms a wavy landform. The lower end of the head hollow gradually becomes steeper and unstable. Side slopes along a valley-head slope show differences in topsoil thickness and creep speed between sections near and below a knick line. The amount of soil creep per year is larger in a section near a knick point than that below it. Soil gradually concentrates directly below the knick point, and the slope becomes steeper and unstable. The total amount of soil movement in 1 year was several millimeters for both the valley-head and side slopes. This means several liters/year of soil squeeze out for every slope section of 1 m in width. This value is similar to the general speed of erosion caused by debris slide (mainly topsoil failure, or shallow landslide) in Japan. Furthermore, neither surface erosion nor internal erosion has been observed in this site. Soil creep seems to carry most of the debris to places where debris slides will occur in this site. Soil creep prepares future debris slides and dominates the cycle of debris slide as well.

Comparison of wind pressure measurements on tower-like structure obtained from full-scale observation, wind tunnel test, and the CFD technology

Abstract Full-scale measurements, wind tunnel tests and CFD calculations have been carried out on pressure measurements on a tower-like structure. This paper presents the comparison of pressure measurements among these three methods. The mean wind pressure coefficients obtained from the wind tunnel tests are fairly close to those of the full-scale measurements after the reference pressure is taken into consideration. RMS wind pressure coefficients obtained in the wind tunnel tests were smaller than those in the full-scale measurements. In the application of the results of wind tunnel test to real designs, at least the turbulent intensity of approaching wind should be taken into consideration, at least. As regards mean wind pressure coefficients of the comparisons among the three methods, CFD calculated results showed good agreement with those of wind tunnel tests and full-scale.

Formation of Earthquake Faults by the Fukushima Hamadori Earthquake and an Estimation of Displacement Distribution Around the Faults Using Airborne LiDAR Data

A series of earthquake faults was produced by the 2011 Fukushima Hamadori Earthquake (Mw 7.1), which broke out one month after the Great East Japan Earthquake. Two lines of earthquake faults appeared extending 30 km in length. They were inferred to be located partly on the active faults and partly on its extended line. The purpose of this presentation is to analyze these faults. We made use of a new method of airborne LiDAR data in the investigation of the displacement distribution by the earthquake. The results obtained fit generally well with the distribution data of net fault displacement produced by field investigation. Furthermore, the results suggest that the earthquake caused block tilting and land subsidence. Our new method makes available information difficult to obtain by the conventional method of field research of displacement distribution and it is useful for investigation immediately after the earthquake.

Mitsuhiro SHIBATA, Shunsuke SHINAGAWA, Yasuhito SASAKI

鉱山はしばしば環境汚染を引き起こす一方, 鉱山の存在やその地質特性は, 岩石に由来する環境汚染リスクの予見のための情報とな.本研究では, 岩石中に天然に含まれる重金属等による環境汚染リスクを建設工事にあたって事前に把握するために, 全国の鉱山分布図や鉱山データベースを作成し, 主な重金属等の種類ごとに鉱床に起因する環境汚染リスク箇所を整理した.