薄表土层覆盖区双层介质地基附加应力传递模型

Additional stress transfer model of double layer dielectric foundation on thin topsoil covered area

  • 摘要: 在采空区对应地表兴建建筑物,地基附加应力的作用可能引起采空区已稳定结构的活化并产生地表残余移动变形,影响建筑物的安全使用;针对薄表土层地区的地基附加应力、荷载影响深度计算模型较少且不完善的特点,需从计算过程简单、参数较少且易获得等角度出发,进一步探索双层弹性介质地基附加应力传递模型。首先将薄表土层地区的地基简化为上部厚度较薄、力学强度较弱的表土层,下部为厚度较大、力学强度较大的岩石层地基模型;其次基于Boussinesp弹性解,假定双层地基的各分层分别为横观各向同性弹性体且地基附加应力传播过程中无动能的变化;再次基于岩土层分界面表土与基岩微单元层的弹性应变能守恒和竖向附加应力平衡条件,建立平衡方程,并借助Matlab对方程中的各分项式进行积分求解与化简,推导出适用于薄表土层地区矩形与圆形均布荷载作用下的基础中心点正下方地基附加应力求解方程;然后根据建筑物地基附加应力影响下的采空区稳定性分析方法,基于C#语言编写出薄表土层地区拟建工程对采空区场地稳定性影响分析软件,实现了地基附加应力计算与采空区稳定性评价的科学与高效化,同时对双层介质地基附加应力求解模型进行了验证并与广泛应用的均一介质模型计算结果进行了对比;最后对双层介质参数E1μ1E2μ2对地基附加应力及影响深度规律进行了分析。结果表明:薄表土层地区双层介质地基附加应力传递模型求解简单、结果科学准确;薄表土层双层弹性地基内竖向附加应力在表土层中传播过程中存在一定程度衰减;相对于均一介质体,双层介质地基附加应力影响深度减少5.3%~10.3%;基岩与表土层的弹性模量E2/E1越大,基岩内部沿深度方向的地基附加应力衰减越明显、传递深度越小;地基附加应力对于表土与基岩的泊松比敏感性较差,但仍表现出μ1/μ2越小,基岩内部沿深度方向的地基附加应力越小、传递深度越小的特点。

     

    Abstract: When constructing some buildings on the surface of mine goaf, the additional foundation stress may cause the activation of the stable structure in goaf, and in turn the residual movement and deformation of surface may affect the safety of buildings. In view of the few and imperfect models for calculating the additional stress and the depth of load effect on thin topsoil layer area, it is necessary to further investigate the additional stress transfer model of double layer elastic medium foundation from the perspective of simple calculation process, fewer parameters and easy access. Firstly, the foundation of thin topsoil area is regarded as the upper layer with thin thickness and weak mechanical strength, and the lower layer is the rock layer with larger thickness and high mechanical strength. Secondly, based on the Boussinesp elastic solution, it is assumed that each layer of the double-layered foundation is a transversely isotropic elastomer and there is no change of kinetic energy during the propagation of additional stress in the foundation. Thirdly, based on the conservation of elastic strain energy and the balance condition of vertical additional stress between the micro cell topsoil layer and bedrock layer on the interface of rock and soil layer, the balance equation is established, and each component of the balance equation is solved and simplified in its integral domain with help of MATLAB. The equation for solving the additional stress under the center point of foundation with rectangular uniform load and circular uniform load in thin surface soil layer is derived. Then, according to the stability analysis method of goaf under the influence of additional stress of building foundation, an analysis software of the influence of proposed construction project on the stability of goaf is written using the C# language, which realizes the scientific and efficient calculation of the additional stress of foundation and the stability evaluation of goaf. The model for solving additional stress of double layer medium foundation is verified and the calculation results are compared with those of the widely used homogeneous medium model. Finally, the effect of parameters E1, μ1 and E2, μ2 on additional stress and depth of foundation are analyzed. Results show that the additional stress transfer model of double layer medium foundation with thin topsoil area is simple to be solved and can be used to guide the comprehensive utilization of mining subsidence area. For the coal mining subsidence area with thin topsoil layer, the vertical additional stress of foundation attenuates to a certain extent in the process of propagation in topsoil layer. Compared with homogeneous medium, the depth of additional stress on the foundation of double layer medium decreases by 5.3%−10.3%. The higher ratio of elastic modulus E2/E1 between bedrock and topsoil layer is, the more obvious attenuation of additional stress along the depth direction in bedrock is, and the smaller transfer depth is. Additional stress is less sensitive to the Poisson's ratio of topsoil and bedrock, but the smaller μ1/μ2 ratio, the smaller additional stress and the smaller the transfer depth in bedrock.

     

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