基于电阻率孔压静力触探的浅层气可靠度识别

Reliability identification of subsurface shallow gas based on resistivity piezocone penetration tests

地下浅层气的存在会对地铁项目的勘察、施工以及后期正常运营构成安全隐患。采用基于地质统计学和可靠性分析的概率方法,对杭州某地铁站场地的电阻率静力触探测试数据进行分析。通过回归分析移除电阻率数据的趋势项,以变差函数为工具,描述电阻率残差在竖向和水平向上的各向异性,采用克里格插值对未采样点参数值进行最优线性无偏估计,采用一阶可靠度方法获取基于电阻率的地下浅层气分布三维概率图。分析表明:电阻率残差具有显著的各向异性,在竖直和水平方向的自相关距离分别为5.1 m和55.6 m。在考虑不同土体电阻率背景值不同的前提下,采用一阶可靠度方法建立了浅层气三维概率分布图。该场地竖直方向上浅层气分布于25m附近及30~35m深度区间内,水平方向上则集中分布于RCPTU1点位附近。可基于该结果提出针对性的防治对策,为布设排气孔、浅层气监测等治理措施提供依据。

The existence of underground shallow gas will pose significant hazard and risk to the investigation, construction, and subsequent operation of subway projects. In this study, the probabilistic method based on geostatistics and reliability analysis is used to analyze the resistivity piezocone penetration test data of the Tangxinline station site of Hangzhou Metro Line 7. Regression analysis is performed to remove the trend term of resistivity data, and the variogram function is used to describe the anisotropy of the resistivity residuals in the vertical and horizontal directions. Kriging interpolation is used to obtain the optimal linear unbiased estimation of non-sampling points. By considering the resistivity background values of different soil types, three-dimensional probability maps of the subsurface shallow gas are obtained using the first-order reliability method. The results show that the resistivity residual has significant anisotropy, and the autocorrelation distances in vertical and horizontal directions are 5.1 m and 55.6 m,respectively. In the vertical direction, the shallow gas is distributed in the vicinity of 25 m and the depth interval of 30-35 m, and in the horizontal direction, it is mainly distributed around RCPTU1 point. The results of this paper can provide basis for shallow gas monitoring plan, exhaust hole layout and other treatment measures.