Mechanism of germination of underground cavities and its influence on pavement

本项目以下列主题为对象，使用实验和分析程序：主题-1通过实验室实验模拟由于水渗透而在砂层中形成空洞的过程。主题-2道路挖掘回填材料稳定性测试方法的开发，以及避免因人行道下面出现空洞而导致道路下沉的压实度指南。主题--开发用于土壤模型试验的离心机，带有模型变形和离心机内应力分布的观测系统。Theme-4离心模型性能试验模拟了自重作用下含空洞粘性路面的破坏过程。主题-5带空洞粘土地基的承载力试验。主题-6含空洞粘土地基的承载能力分析。首先，通过一系列模型试验验证了空洞的形成过程。然后用…压实模进行回填材料的稳定性试验在底板上开发了直径为10 mm的h 13个孔。结果表明，材料的抗压实性能基本上取决于材料的粒度分布，85%以上的材料压实度对防止压实是有效的。在这项资助的支持下，研制了一台容量为400g·t、有效半径为1.55m的新型离心机。研究了顶板抗拉强度与塌陷洞室宽度的关系，提出了顶板塌陷形状的预测公式。在Theme-5和Theme-6中，对有空洞和无空洞的人工粘土地基在重力场中进行了承载力试验，得到了地基承载力与空洞深度和宽度的关系图；对模型粘土进行了基础试验分析，得出了当空洞位于基础宽度的3倍以上时，地基的承载力与没有空洞的粘土地基的承载力相同的结果。在人工地基上进行的承载力试验也得到了相同的结论。在此基础上，以大阪市为例，给出了路下空洞风险图。较少

The following themes were objects in this project using experimental and analytical procedures: Theme-1 Simulation of a process to form a cavity in a sandy layer due to water permeation by experiments in laboratory. Theme-2 Development of Stability Test Method of back filling materials for a road excavation, and a guideline of the degree of compaction to avoid subsidence of a road due to a cavity underneath pavements. Theme-3 Development of a centrifugal apparatus for soil model tests with observing systems for deformation of models and distribution of stresses in the centrifuge. Theme-4 Performance of centrifugal model tests to simulate a process of failure of a clayey pavement with a cavity by self-weight. Theme-5 Bearing capacity tests of a clay ground with a cavity. Theme-6 Analyses of bearing capacity of clay ground with a cavity.Firstly, the process to form a cavity was demonstrated in a series of model tests. Then Stability Test of back-fill materials using a compaction mold wit … More h 13 holes measuring 10 mm in diameter at the bottom plate was developed. The results showed that the resistance of materials for de-compaction depended on basically grain size distribution, and that over 85 % of the degree of compaction of material is effective to prevent de-compaction.A new centrifuge apparatus with a 400 g-t capacity and an effective radius of 1.55 m was developed with a support from this grant aid. The relationship between the tensile strength and the width of collapsed underground cavities was investigated and an equation to predict the shape of collapsed ceiling was proposed. In theme-5 and 6, bearing capacity tests for model ground on an artificial clay with/without a cavity were performed in the gravitational field, and a chart was obtained, which shows a relationship of bearing capacity to depth and width of a cavity in the ground.Analyses for the footing tests on model clay were performed, and obtained result that if a cavity locates over three times of a footing width, bearing capacity of the ground is, the same as that on a clay ground without any cavity. The same conclusion was obtained in the bearing capacity tests on the artificial ground. According to the conclusions, a risk chart for under-road cavity was presented based on data sampled in Osaka city area. Less