煤系地层人工挖孔桩承载特性现场试验研究  

Field test study on bearing characteristics of manual digging piles in coal strata

作　　者：缪云 王贵彬 徐福建 王发旭 MIAO Yun;WANG Guibin;XU Fujian;WANG Faxu(School of Civil Engineering,Jiangsu Open University,Nanjing 210036,China;Nanjing Dongda Self-balanced Pile Testing Co.,Ltd,Nanjing 210018,China;Guizhou Sino Rock Engineering Testing Co.,Ltd,Guiyang 550009,China)

机构地区：[1]江苏开放大学建筑工程学院,江苏南京210036 [2]南京东大自平衡桩基检测有限公司,江苏南京210018 [3]贵州中岩工程检测有限公司,贵州贵阳550009

出　　处：《建筑结构学报》2020年第7期124-130,共7页Journal of Building Structures

基　　金：江苏省建设系统科技项目(2018ZD272);江苏高校自然科学基金项目(18KJB220001)。

摘　　要：为获得煤系地层的桩基承载特性,利用荷载箱放于桩底的自平衡静载试验,直接测得了大直径人工挖孔桩的桩侧摩阻力和桩端承载力。试验结果表明:侧阻的荷载传递函数为双曲线,位移4~5 mm时的侧阻可达极限值的90%;煤层侧阻发挥特性更加接近破碎岩层而非土层;极限侧阻的大小落于JGJ 94—2008《建筑桩基技术规范》中强风化软质岩一档的较低值(干作业钻孔桩)。端阻的荷载传递函数为理想弹塑性双折线,充分发挥端阻所需位移约为桩径的1%;煤层端阻发挥特性既不同于土层,也有别于岩层;极限端阻的大小高于规范强风化软质岩的上限值(干作业钻孔桩),接近中密粗砂的上限值(干作业挖孔桩)。桩位附近靠近孔口高程的煤层岩基载荷试验表明,该法可用于确定短桩的桩端刚度,但用于确定桩端极限承载力则会得到明显偏小的结果。To obtain the bearing characteristics of pile foundation in coal strata,the self-balanced method with the loadcell placed at the pile bottom were used. The shaft resistance and the end resistance of large diameter manual digging piles were measured directly. The test results show that the load transfer function of the shaft resistance is hyperbolic. With displacement of 4-5 mm,the shaft resistance can reach up to 90% of the limit value. The shaft resistance characteristics of the coal strata is close to the fractured rock rather than the soil. The ultimate shaft resistance matches the lower value of the strong weathered soft rock( dry-bored pile) in JGJ 94—2008 ‘Technical code for building pile foundations’. The load transfer function of the end resistance is an ideal elastoplastic double-fold line. The displacement required to fully mobilize the end resistance is about 1% of the pile diameter. The end resistance characteristics of the coal strata is different from the soil or the rock. The ultimate end resistance is higher than the upper limit of the strong weathered soft rock( dry-work bored pile),and it is close to the upper limit of the medium-density coarse sand( dry-dug pile) in the code. The plate load testing on rock at the dug-hole top elevation were carried out near the piles. The results show that the plate load testing can be used to determine the coal strata’s end stiffness of the short piles,but it will significantly underestimate the ultimate end bearing capacity.

关 键 词：煤系地层 人工挖孔桩 自平衡法 岩基载荷试验 侧阻 端阻 荷载传递函数 

分 类 号：TU473.1[建筑科学—结构工程] TU317.2[建筑科学—土工工程]