岩溶地区复合地基承载力的计算

CALCULATION OF BEARING CAPACITY OF COMPOSITE FOUNDATION IN KARST AREA

在广东省岩溶地区工程实践的基础上,总结出4个方面岩溶地质特征,分析其对岩溶地区复合地基工作机理及地基承载力的影响,给出了各主要参数的取值原则,提出了考虑岩溶发育程度的岩溶地区复合地基承载力计算方法,并用该方法对某实际工程进行不同桩型复合地基承载力的试算比选。借助岩溶地区现场3组预应力高强混凝土管桩(PHC桩)+高压旋喷桩复合地基大压板静载试验,通过布置土压力盒,测定并分析PHC桩桩顶、高压旋喷桩桩顶和桩间土体应力及其承载力特征值,计算桩土荷载分担比,分析静载试验中桩、土的受力特性。试验结果与设计计算得出的岩溶地区复合地基承载力特征值基本吻合,表明岩溶地区复合地基承载力计算方法安全可靠;在复合地基中,PHC桩桩土应力比为15～48,高压旋喷桩为1. 5～8,PHC桩桩顶应力集中显著; PHC桩承担了70%以上的荷载,高压旋喷桩和桩间土承担荷载总计不超过30%。

On the basis of engineering practice of karst area in (Guangdong, four characteristics of karst geology were summarized. The influence on the working mechanism and bearing capacity of composite foundation were analyzed. The principles for determining the main parameters were given. The calculation method for the bearing capacity of composite foundation considering karst development degree was presented. The calculation method was applied to calculate and compare the bearing capacity of different composite foundations treated with different kinds of pile or piles combination. Three static load tests with large pressure plate on PHC pile + high pressure jet grouting pile composite foundation were carried out in karst area. The earth pressure cells were arranged to measure the bearing capacity of PHC, high pressure jet grouting pile and soil between piles. The load sharing ratio of pile-soil was calculated. The mechanics of pile and soil were analyzed. It was shown that the calculated result of bearing capacity of composite foundation in karst area was similar to the test results. The load sharing ratio of pile-soil of PHC pile was between 15 to 48 and the load sharing ratio of high pressure jet grouting pile was between 1. 5 to 8. The stress concentration on the top of PHC was significant. The load shared by PHC pile was over 70%. The load shared by high pressure jet grouting pile and soil was less than 30%.