花岗岩孤石发育地区桩基勘察优化技术研究

Study on Investigation and Optimization Technology of Pile Foundation in Granite Area

通过研究孤石的空间发育规律,创见性提出特征地质钻孔、特征土层厚度等概念,首次提出以场地见孤率、线孤石率划分孤石发育程度,同时进行了以孤石直径为变量的桩基受力模型理论研究,给出相应的计算公式。绘制出荷载(承载力)-深度(桩长)关系图,提出了安全深度、危险深度以及介于两者之间的平衡深度等概念,进一步统计后,提出危险见孤率、安全见孤率、优化指数等指标;关系图揭示,安全深度与危险深度与孤石直径大小存在线形关系,当孤石直径d变化范围窄时,平衡见孤率相对较小,优化指数相对变大,场地勘探工作量可优化空间高;基于此理论,给出了工作量优化的分析步骤;不同孤石发育等级下,根据计算的优化指数,提出孤石空间发育的3种情况及相应工作量布置建议,得出了在不同孤石发育等级下,优化指数大于一定数值可不进行逐桩勘探的结论;利用上述理论研究成果,在某项目进行了相应实践,为孤石发育地区的桩基勘察工作量布置提供了建议,为项目节省了投资,取得较好的社会经济效益。

By studying the spatial development law of boulder,the concepts of characteristic geological borehole and characteristic soil layer thickness are creatively put forward,and the development degree of boulder is divided by the rate of spot spot and linear boulder rate for the first time.At the same time,the theoretical study of pile foundation stress model with boulder diameter as variable is carried out,and the corresponding calculation formula is given.The load(bearing capacity)-depth(pile length)relationship diagram was drawn,and the concepts of safe depth,dangerous depth and balance depth between the two were proposed.After further statistics,the indexes such as dangerous isolation rate,safe isolation rate and optimization index were put forward.The relationship diagram reveals that there is a linear relationship between the safety depth and the danger depth and the diameter of the boulder.When the variation range of the boulder diameter D is narrow,the equilibrium apparent isolation rate is relatively small,the optimization index is relatively large,and the optimization space of the site exploration work is high.Based on this theory,the analysis steps of workload optimization are given.According to the calculated optimization index,three kinds of spatial development of boulder and corresponding workload layout suggestions are put forward under different development grades of boulder.It is concluded that pile by pile exploration can not be carried out when the optimization index is larger than a certain value under different development grades of boulder.Based on the above theoretical research results,the corresponding practice is carried out in a project,which provides suggestions for the workload layout of pile foundation investigation in the Gush stone development area,saves investment for the project,and obtains better social and economic effects.