我国地面沉降模拟现状及需要解决的问题

Present status of modeling land subsidence in China and problems to be solved

我国现有模型有下列特点:水流模型都是准三维模型,模型中的参数都是常数,沉降模型采用线弹性模型,水流模型和沉降模型的耦合分二步进行。因此,模型还存在难以精确刻画由弱透水层释水引起的地面沉降,不符合准三维模型的应用条件。水流方程应是一个变系数的动态水流方程,渗透系数、贮水率不应视为常数。土层压缩非线性,有蠕变、塑性变形存在,沉降模型采用线弹性模型不适合,对土层厚度变化大的地区沉降模型必须是三维的,滞后现象必须克服。如何描述引起地裂缝的水平位移,分两步进行的耦合不合适,要做到水流模型与沉降模型的真正耦合等八个方面的步骤。本文提出分三步进行的解决方案:首先采用三维水流模型,以便不仅给弱透水层建立方程,还能考虑它的各向异性,参数值能随着土层的变形沉降而不断改变。沉降模型为能考虑蠕变、塑性变形的非线性模型;水流模型和沉降模型要做到能真正耦合。其次,解决滞后问题。最后,建立三维沉降模型,考虑水平位移和地裂缝问题。

Characteristics of present land subsidence models in China were as follows: (1)flow models were quasithree dimensional models; (2) parameters in models were constants; (3)subsidence models were linear elastic models; (4) couple of flow model and subsidence model had two steps. Hence, there were eight disadvantages for present models. (1) They can not precisely described land subsidence caused by drainage of aquitards; (2) They do not agree with conditions of quasithree dimensional model; (3) Flow equation was a dynamic equation in which coefficients vary with time. So hydraulic conductivity and specific storativity should not be constants; (4) It was improper to use linear elastic model for a subsidence model, because soil showd nonlinear stressstrain relation, and there exited plastic deformation and creep;(5) Three dimensional subsidence model was necessary for area with large variation of thickness of soil layer (Quaternary sediments); (6) Problem of delay must be treated; (7) How to described the horizontal displacement which induced ground fissures; (8) It was improper to couple flow model with subsidence model by two steps, and real couple need to realize. A plan with three steps was present. Firstly, three dimensional flow model should be adopted so as to establish equations for aquitards and consider heterogeneity of aquitards, in which the values of parameters vary with subsidence of soil layers. Subsidence model should be a nonlinear model considering plastic deformation and creep.Real couple of flow model with subsidence model is necessary. Secondly, problem of delay should be solve. Finally, three dimensional land subsidence model should be develope in which horizontal displacement and ground fissures are considered.