岩溶区建筑场地桩基平均入岩高程预测

嵌岩桩入岩位置在岩溶场地具有很大的不确定性，成桩难度和桩基方案技术经济性论证缺乏可靠依据，这是目前岩溶场地桩基础、筏板基础和复合地基优选时的常见问题。本文将基桩入岩起始位置处的高程定义为基桩入岩高程，岩溶场地所有基桩入岩高程的平均值称为场地桩基平均入岩高程。场地桩基平均入岩高程决定了场地基桩入岩深度的变化范围，反映了场地桩基成桩难度及其技术经济性。以柳州市金盛广场4#楼桩基工程为背景，基于岩溶区已有的桩基入岩概率模型建立了场地桩基平均入岩高程预测模型，所需数据来源于岩溶场地丰富、廉价的勘察钻探资料，无需补充其他额外测试或勘测数据，合理考虑了岩溶地基溶蚀特征和桩径大小等两个影响因素。研究表明，岩溶场地桩基平均入岩高程预测值与实测值误差一般不大于0.5 m，满足岩溶地区嵌岩桩技术经济性论证的精度要求，可作为岩溶场地基础方案优选和成桩工艺选择的基本依据。

An analysis of the average entering-rock height of grouped piles at building sites in a karst terrain

The depth of socket piles is often uncertain in karst areas, and there is lack of reliable basis to evaluate the difficulty of pile formation and economical efficiency for pile foundation, which is a frequent issue encountered when an optimal scheme can only be produce among pile foundation, raft foundation and composite foundation. In this paper, the elevation at which a single pile starts to enter rock is defined as the elevation of the single pile entering rock. The average elevation of all single piles entering rock in a karst site is called the average elevation of pile entering rock in site (abbreviated as AER hereafter). The AER can be used to predict the variation range of the rock-entry depth and rock-socket thickness of all piles, which reflects the difficulty and technical economy of pile-forming in site. Taking the pile of the No.4 Building of the Jinsheng Plaza in Liuzhou as the engineering background and based on an existing analytical method of the entering-rock probability of piles, this paper establishes an analytical model for predicting the AER at karst building sites. All obligatory data for the model is abundant and inexpensive, which come from investigation and without additional work of test or survey. Two factors affecting the parameter AER, the dissolution feature and pile diameter, are reasonably considered in this model. The results show that the predicted ARE derivates from the measured value within 0.5 m and this precision satisfies the requirement of technical and economic demonstration of rock-socket piles, and can be used as the basis for optimizing foundation schemes and selecting pile-forming methods in karst areas.