北京地区多层含水层中施工降水诱发地面沉降的实时预测

摘要

Subsidence induced by groundwater lowering in construction is one of the major risks in the geotechnical engineering currently,which is particularly prominent in Beijing area,whose hydrogeology is characteristized by multi-layered aquifers.In order to predict the problems accurately and conveniently,firstly,based on seepage theory and effective stress principle,the main influencing factors on the compaction of individual layers during groundwater lowering in construction through multi-layered aquifer were analyzed,and the corresponding coupled mathematical model of seepage and compression of subsidence was established.According to the principle of groundwater occurrence and movement,combined with the hydrogeological characteristics of Beijing area,a novel method to determine the bottom boundary of coupled model with major aquifer was proposed,which made the two physical & mechanical processes of seepage and compression coupled under the specific geological conditions,ensured that the that model was scientific and had engineering precision,reduced the difficulty of the actual work of analysis,and improved the practicability of the model analysis.In the aspect of specific storage value of interbed,which was an key paramerter in the model,with hydraulics of groundwater and measured data,the error and its main reason of existing calculation formula was studied,and was combined with the local experience in Beijing area.The correction formula for the specific storage of interbed was introduced,which improved the accuracy of model analysis.Finally,taking a practical project in Beijing area as an example,the detailed simulation of subsidence induced by groundwater lowering in construction through multi-layered aquifer was carried out,and the rationality of the numerical results was analyzed.%施工降水诱发地面沉降是当前主要岩土工程风险之一,对于以多层含水层为典型水文地质特征的北京地区,这类问题尤为突出.为准确而便捷地进行该类问题预测,首先基于渗流理论和有效应力原理,分析了多层含水层区降水过程中不同层位的压缩量变化规律及主要影响因素,并建立了相应的渗流-压缩耦合数学模型;根据地下水赋存与运动原理,结合北京地区水文地质特征,提出了采用主控含水层来确定耦合模型下边界的新方法,实现了渗流和地层压缩2个物理力学过程在特定地质条件下的耦合,在保证模型科学性和工程精度的同时,降低了实际分析工作的难度,提高了分析模型的实用性;在弱透水层释水率这一重要模型参数取值方面,根据地下水动力学和相关实测资料,研究了既有计算公式存在的误差及其主要原因,并结合北京地方经验,提出了相应的修正方法,进一步提高了模型分析精度.最后,以北京地区某实际工程为例,进行了多层含水层中降水诱发地面沉降的精细模拟,并对数值结果合理性进行了分析.