基于压水试验的地层渗流场反分析

Inverse analysis of seepage field from packer permeability test

地下工程建设过程中,地下水分布以及岩体渗透参数确定至关重要。基于对解决欠定反分析问题的目标函数分析,通过利用适应度函数、地质统计原理和变差函数等优化,得到了解决地层渗透系数一类水文地质问题的罚函数,为解决欠定的反分析问题提供了一个优化评判准则,并结合粒子群算法建立优化反分析数学模型;提出利用压水试验钻孔水头变化反分析得到地层渗透系数的新方法。对南京地铁上元门车站,进行现场压水试验得到钻孔水头高度,利用经过罚函数优化的反分析数值计算获得地层渗透系数,对压水试验区域的电阻率跨孔CT探测验证了该方法区域上的正确性,该区域的钻孔原位渗透系数测试验证了该方法在数值上的准确性。结果表明,经过罚函数优化的反分析计算的准确率达到90%,说明该方法有助于得到全面的地层水文地质信息,对后续的治理具有指导作用,希望能对类似工程有一定的借鉴意义。

Groundwater distribution and determination of rock mass permeability parameters are very important in the process of underground engineering construction. Based on analysis of the objective function of underdetermined problem, and through the use of fitness function and the principle of geological statistics and variation function optimization, we obtain a class of hydrogeological problems＇ penalty function for solving formation permeability coefficient, which provides an optimized evaluation criterion to solve the problem of inverse analysis of underdetermined problem. Also, a mathematical model of optimized back analysis combined with particle swarm optimization（PSO） algorithm is established, and a new method to evaluate formation permeability coefficient is proposed using back analysis of the drilling head change from packer permeability test. At Nanjing Shang Yuanmen subway station, we conduct packer permeability test to get drilling head height on-site, and obtain permeability coefficient of the layer by using back analysis numerical calculation to optimize the penalty function. Detection of the resistivity cross-hole CT is conducted to verify the accuracy of the method, and drilling in-situ permeability tests verify the accuracy of the method to obtain numerical results. The results show that calculation accuracy reached 90% after analysis optimization by a penalty function, which proves that the method helps in getting comprehensive formation hydrogeological information. The method is important for the follow-up governance, which is expected to have certain reference significance for similar projects.