Development of a Coupled BCHM-Model for Numerical Investigations of MICP treatment of Soil

近年来的研究表明，微生物诱导方解石沉淀（Microbially induced calcite precipitation，MICP）可以显著改变土壤的力学性质，增加土壤的机械刚度，降低土壤的渗透性。因此，它提供了一个潜在的替代环境友好的解决方案，以广泛的工程问题，如。G.软土地基加固、水土流失控制、地震控制、核素和重金属污染修复。由于大面积的MICP特别是耦合生物-化学-水力-机械（BCHM）过程尚未被探索，迄今为止，应用MICP改善土壤性质只能在实验中证明。近年来，人们对土壤中的MICP进行了大量的实验研究。然而，作为分析多孔介质中BCHM耦合问题的重要工具，MICP的数值框架仍处于早期阶段。特别是关于MICP的力学本构模型和力学耦合效应的数值模型的研究工作还很少。虽然对MICP处理土力学特性的试验分析已经为MICP处理砂力学模型的建立提供了足够的数据，但考虑到目前MICP的研究现状，本课题的目的是研究MICP处理砂的力学本构特性，建立完全耦合的BCHM模型，为MICP的应用提供科学依据。具体目标包括：1）发展力学本构模型2）将我们现有的BCH模型扩展到完全耦合的BCHM模型3）发展一个鲁棒的和计算有效的耦合问题的解决策略4）基于实验数据校准和验证数值模型;四、分析模型参数的敏感性，希望通过本研究能够加深对MICP中耦合BCHM过程的理解可以得到改进，可以合理地预测不同尺度下的长时间和MICP行为，可以确定相关的未来研究领域。此外，耦合模型的概念和求解策略有望在多孔介质中进一步耦合问题的建模框架中得到采纳和应用。

According to some recent research, microbially induced calcite precipitation (MICP) can obviously change soil properties in term of increase of mechanical stiffness and reduction of permeability. Therefore it provides a potential alternative environmental friendly solution to a wide range of engineering problems e. g. reinforcement of the soft underground, soil erosion control, seismic control, remediation for nuclides and heavy metal contamination. Since a large area in MICP especially the coupled bio-chemo-hydro-mechanical (BCHM) processes are unexplored, to date applying MICP to improve the soil properties can only be demonstrated in the experiment. Recently many experimental investigations have been conducted on MICP in soil. However as an essential tool for the analysis of the coupled BCHM issues in porous media the numerical framework for MICP is still at its early stage. Especially, research work with regard to the mechanical constitutive model on MICP and numerical model dealing with the mechanical related coupling effects is rare. Although the experimental analysis on the mechanical behaviour of the MICP treated soil have provided sufficient database for the development of the mechanical model for MICP treated sand.Considering the current research state of MICP the aim of this project is to investigate the mechanical constitutive behaviour of MICP treated sand and develop of a fully coupled BCHM model and herewith extend scientific basis for the MICP application. The specified objectives include: 1) to develop the mechanical constitutive model; 2) to extend our current BCH model to a fully coupled BCHM model 3) to develop a robust and computational efficient solution strategy for coupled problem 4) to calibrate and validate numerical model based on experimental data; 4) to analyse the sensitivity of model parameters.It is expected that through this proposed research the understanding of the coupled BCHM processes in MICP can be improved, the long-time and MICP behaviour in different scales can be reasonably predicted, the related future research area can be identified. Besides, the concept of coupled model and the solution strategy are expected to be adopted and applied in the modelling framework of further coupled issues in porous media.