岩溶地基嵌岩桩桩基特性分析与试验研究

【作者】 王革立；

【导师】 彭振斌；

【作者基本信息】 中南大学 ， 地质工程， 2002， 博士

【摘要】 目前，国内外对于岩溶地区嵌岩桩的工作特性的研究一直不很充分，其承载力特性、剪应力分布模式、最佳嵌固深度和岩溶顶板厚度、岩质性状对桩基特性的影响等有待进一步研究与完善。针对岩溶地区嵌岩桩特性的模拟模型试验研究相关报道比较少。本文就解决岩溶地区，桩基竖向荷载作用下岩溶顶板安全厚度以及嵌岩深度问题进行了深入的探讨，并研制了相应的物理模型进行了试验研究，取得了较为满意的结论。 本文首先在参考大量的国内外文献资料的基础上，对竖向荷载下基桩的荷载传递机理进行了深入的分析与讨论，并对基桩荷载传递性状的变化规律进行了归纳与总结。同时对单桩的荷载-沉降特性的机理进行了探讨，将单桩荷载-沉降曲线综合为六种，并列举了四类缺陷形成的异常P-S曲线。对于基桩竖向承载力的确定，提出了按桩身结构强度确定、按土的强度与变形确定以及按静力分析法确定等几种方法。在基桩的深度效应方面，研究了桩端阻力和和桩侧阻力的深度效应，从理论上提出了端阻力的临界深度以及深度效应的内在机理；讨论了岩溶地区桩基的负摩擦力问题。 通过对岩溶地区嵌岩桩工作性状和破坏模式的理论分析，认为在岩溶发育地区桩基的稳定性问题主要决定于嵌岩桩的竖向荷载，顶板厚度以及顶板的抗弯强度等有关的强度指标。 在对课题进行充分论证的基础上，运用相似理论，针对岩溶地区嵌岩桩的工作特性，提出了建立室内桩基模拟实验台的试验方案，自主设计并研制了模拟试验模型，同时结合模型编制了相应的数据采集与分析软件。 要进行相似模拟试验，模拟材料的选择是试验成功的关键，通过室内小样试验分析了模拟材料的内在作用机理，选择了以砂、水泥、石膏为原材料的试验配方，推导了水泥石膏砂模拟材料抗压强度和抗弯强度的经验公式。通过室外模拟试验，验证了其合理性，得出了模拟岩样的强度范围。并采用不同的试验方案，运用改进的均匀设计法用不同的配比有效地模拟了灰岩的岩性。研究了岩性、嵌岩深度、顶板厚度、侧摩阻力对模拟顶板极限荷载的影响，提出了以普通水泥、石膏为胶结材料，细砂为骨料的模拟材料配比方案。 通过对大量试验结果的综合分析，提出了岩溶顶板安全厚度验算方法，得出岩溶顶板和桩基垂直荷载的半经验半理论公式如下： σ_max=3γL²/4h+（3F（2L-D）/4bh²）=ξ[R-t]其中经验系数ξ取0.8～1.3。 通过嵌岩桩模拟嵌岩深度的试验，给出了岩溶地区嵌岩灌注桩嵌岩深度建议值。在岩溶发育地区，嵌岩深度的选取应综合考虑侧摩阻力和顶板结构内力，一般岩溶地区，当岩面较为平整且上覆土层较厚时，嵌岩深度宜采用0.2d或不小于0.2m。更多还原

【Abstract】 The .international studies on the performance of the socketed piles in karst subgrade show still insufficient at present. Therefore, succeeding research is essential on improving the loading mechanism, shear distribution v- socket depth, bedrock thickness and properties. Up to now , the references concerning the simulated test are rarely reported . In this paper , an extensive study on socket depth, and bedrock thickness is carried out and some satisfactory results have been obtained.Based on various international papers, a deep investigation for vertical load transfer has been carried out to propose 6 varieties of load-settlement curve and 4 types of defective P-S curve. 4 approaches have also been suggested in the paper to determine vertical capacity in light of the pile strength, strength and deformation of" surrounding soil and static analysis. In addition, the study touches upon the depth effect of end- bearing and lateral resistance, negative friction to extract the theoretical critical embedded depth and its mechanism.The theoretical analysis for the performances of the socketed pile in karst region and their failure patterns shows the pile stability is mainly due to the vertical load, bedrock thickness and its bending resistance.With the performance of the socketed pile in karst region and Simulate theory . simulated model test plan lias beer. marked out moluding the test equipment ana computing system for collecting daces and results analysis.The choice of similar material is ; key problem- in the simulated model cest. With. the improved "Limited uniform design methods" .the mixture of cement with gypsum and sand is treat as similar material :r. test. Though, a deep analysis of the mterna; interaction in mixture, empirical cropcrtionmg is suggested to effectively simulate limestone . the regressive equation of compression strength and. bending strength prove reasonable. Performing various test C’..Y.~.S . simulate; model tests have beep. earned out to investigate the factors affecting e critical loading capacity including limestone properties - socket depth, bedrock thickness and lateral friction et al.According to the test results and theoretical analyses ,the paper has proposed the approach to examine the safety bedrock thickness, half-theory and half-experience formula associated with vertical load is suggested as followed: ?In karst subgrade, the embedded depth seems difficult to deternine. considering synthetically the correlation, between the pile skin friction resistance and the bedrock internal cohesion and also the influences on loading capacity of pile,-. the mine. socketed length is suggested 0.2 pile diameters or at least 0.2m when the rock surface is level and the upper soil is thick relatively.更多还原