基于岩基载荷试验成果对岩石地基承载力特征值计算式的讨论

Discussion on formula of characteristic value of rock foundation bearing capacity based on rock foundation loading test results

针对岩基载荷试验获得的岩石地基承载力特征值远高于《建筑地基基础设计规范》(GB 50007—2011)计算值的情况,分析了造成偏差较大的原因,提出了解决方法,并结合工程实例验证了解决方法的合理性、经济性和安全性。研究结果表明,造成岩石地基承载力特征值的岩基载荷试验值大于计算值的主要原因是地基规范中计算式未考虑岩体围压效应提高系数,该系数随岩石饱和单轴抗压强度的增大而减小;引入岩体围压效应提高系数修正计算公式,提出重庆地区软质岩、较软岩、硬质岩的岩体围压效应提高系数取值分别为1.5,1.2,1.0;对于岩层胶结程度差、取样困难地层,岩体完整性折减系数应取规范中的低值;对于构造裂隙发育、区域地质较破碎地区,即使定性为较完整地层,岩体完整性折减系数仍不能取高值。

The rock foundation loading test characteristic value based on rock foundation loading test is higher than the calculated values in Code for design of building foundation（ GB 50007—2011）,and the reason of large deviation was analyzed and solutions were proposed.Combined with the engineering practice,rationality,economy and security of the solution were verified.The research results show that the main reason for a larger rock foundation loading test value than calculated result of rock foundation loading test characteristic value is that calculated formula in code does not consider the improvement coefficients of confining pressure effect in rock,and the improvement coefficient is in inverse proportion to uniaxial compressive strength of rock.And calculation formula of the improvement coefficients of confining pressure effect in rock was introduced and it proposed that improvement coefficients of confining pressure effect of soft rock,slightly soft rock and hard rock in Chongqing are suggested to adopt 1.5,1.2 and 1.0 respectively.For the rock layer with poor degree of rock formation and the difficulty of sampling,the rock body integrity reduction coefficient should take the lower value in the code.For the region with structural fracture development and the regional fragmented geology,the rock body integrity reduction coefficient still cannot take higher value even if the rock layer is complete.