COOPERATIVE RESEARCH ON THE PREDICTION METHODS AND EVALUATION OF DEFORMATION OF EARTHSTRUCTURES FOUNDED ON SOFT FOUNDATIONS DURING EARTHQUAKES

本文首次对新近发生的三陆春冈地震、久路地震、兵库县南武地震等地震引起的地表变形破坏进行了研究。通过室内三轴压缩试验、中空圆筒试验和环形剪切试验，对砂土的变形特性进行了研究。据报道，每一种类型的地球结构都有特定的地面变形机制，需要在每一个案例研究中推导出适当的机制来分析它。特别报道了神户港岛大面积液化的大颗粒土样的三轴压缩试验结果。研究发现，土体的变形特性取决于沉积构造，当剪应变超过5%后，土体的孔压在卸荷时突然升高。通过振动台试验，研究了液化地基中埋地管道上浮及周围地面变形的防治措施。研究发现，管道的上浮量在很大程度上依赖于周围土体的运动，并提出了相应的防治措施，并进行了实验验证。提出了一种基于能量原理的侧向地面流变形分析方法。它能够处理各种边界条件。本文将其应用于研究受填土重量影响的板桩护岸河堤的变形机理。研究结果表明，该分析方法在大面积地面流中得到了验证。

Case histories and studies of damages caused by ground deformation due to recently hit earthquakes, e.g. Sanriku Haruka-Oki Earthquake, Kushiro-Oki Earthquake and Hyogo-Ken Nanbu Earthquake, are first made in this study. Laboratory tests, such as triaxial compression apparatus, hollow cylinder appartus and ring shear apparatus, are conducted to investigate deformation behavior of sandy soils. It is reported that each type of earth structures possesses a specific mechanism governing the ground deformation, and it is desirable to deduct an appropriate mechanism involved in each case study for analyzing it. Especially, triaxial compression test results on soils containing large grains sampled from the Kobe Port Island which experienced extensive liquefaction are reported. As a result of this study, it is found that deformation characteristics of soils depend on the depositional structures and the pore water pressure suddenly rises upon unloading immediately after the shear strain exceeds 5 %. Shaking table tests are carried out to examine countermeasures against floatation of buried pipes in liqiefied ground and deformation of surrounding ground. it is found that the amount of the pipe floatation depends heavily on the movement of the surrounding soil, and the countermeasures against such soil movement is devised and experimentally verified. A deformation analysis method on lateral ground flow is proposed, based on the energy principle. It is capable of coping with a variety of boundary conditions. In this study, it is applied to solve the deformation mechanism occuring at the river dikes protected by sheet piles subject to earthfill weight. As a result of this study, this analytical method is verified for the ground flow involving a large area.