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

最近的一些研究表明，微生物诱导方解石沉淀(MICP)可以明显改变土体的性质，使其力学刚度增加，渗透性降低。因此，它为软基加固、土壤侵蚀控制、地震控制、核素修复和重金属污染等广泛的工程问题提供了一种潜在的环境友好的解决方案。由于MICP法，特别是生物-化学-水力-机械耦合(BCHM)工艺的大面积应用尚未被探索，因此，应用MICP法改良土壤性质目前还只能在试验中得到证实。近年来，人们对土壤中的MICP值进行了大量的实验研究。然而，作为分析多孔介质中耦合BCHM问题的重要工具，MICP法的数值框架仍处于初级阶段。尤其是关于MICP力学本构模型和处理与力学相关的耦合效应的数值模型的研究工作还很少。虽然对MICP土的力学性能的试验分析为MICP砂的力学模型的建立提供了足够的数据。鉴于MICP土的研究现状，本课题的目的是研究MICP土的力学本构关系，建立完全耦合的BCHM模型，从而为MICP土的应用提供科学依据。具体目标包括：1)建立力学本构模型；2)将我们现有的BCH模型扩展到完全耦合的BCHM模型；3)开发一种稳健且计算高效的耦合问题的求解策略；4)基于实验数据对数值模型进行校准和验证；4)分析模型参数的敏感性。希望通过这项研究，可以提高对MICP中耦合BCHM过程的理解，合理地预测不同尺度下的BCHM行为，并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.