砂土中松动土压力及松动区位移破坏形式的试验研究

Trapdoor model tests on loosening earth pressure and failure mode of loosening zone in sand

针对经典的Trapdoor问题,设计室内挡板下落模型试验装置,进行不同埋深比(埋深比为上覆土体高度与松动区宽度之比)的挡板下落模型试验,采用微型土压力盒量测试验全过程中挡板上方松动土压力的变化,对土体松动土压力及松动区位移破坏形式进行研究。将试验结果与文献既有解析解进行对比,进一步提出考虑挡板上土压力分布的修正松动土压力解析解。研究结果表明:由于土拱效应的存在,松动土压力小于土体自重土压力,松动土压力在试验初期迅速达到最小值,随后略有增长并达到稳定。利用颗粒图像测速技术研究松动区土体内部滑裂面发展规律,所得松动土压力与挡板上各位置松动土压力均吻合良好。松动区土体下移过程中均首先出现初始三角形滑裂面,随着松动区土体位移的增大,滑裂面发展呈现2种不同形式:当土体埋深比小于等于2时,呈逐渐张开展开形式;当土体埋深比大于2时,呈逐渐张开并塔型上升形式。

A trapdoor apparatus was designed to study the classic Trapdoor problem.Micro earth pressure cells were used to measure the loosening soil pressure on the trapdoor during whole period of tests.A series of trapdoor tests with different soil depth ratios(depth ratio is defined as the ratio of soil depth to trapdoor width)were conducted to analyze the loosening soil pressure and the failure mode of loosening zone.Tests results were compared with analytical solutions from literature and a modified analytical solution considering the stress distribution on trapdoor was proposed.The results show that because of soil arching effect,the loosening soil pressure is less than the soil weight.The loosening pressure quickly decreases to the minimum at initial stage of tests,then increases slightly and remains stable at last.Particle image velocimetry(PIV)method was used to analyze the development of slip surfaces in the loosening zone.Results calculated by proposed analytical solution fit well with the tests results.The initial slip surface is triangle slip surface.When the deformation of soil in loosening zone increases,there are two different forms of slip surfaces:it is called expansion form for condition that depth ratio is less than or equal to 2;or called expansion and tower raise form for condition that depth ratio is more than 2.