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为提高地应力反演的精度,提出了FLAC3D中利用偏最小二乘回归方法拟合地应力场及将地应力场精确加载至计算模型并实现平衡的方法,首先对各应力分量分别进行回归,以提高局部异常应力区域的拟合精度。然后依据FLAC3D的计算原理,分析了单元应力与节点不平衡力的关系,将回归所得的单元初始地应力加载至模型并计算节点不平衡力,在节点施加与不平衡力反向的节点荷载,实现力的平衡,完成地应力场的加载。当采用弹塑性模型时,假定平均应力不变,根据屈服条件修正偏应力大小,对不满足强度条件的单元地应力进行修正,以满足弹性假设条件,修正后的单元地应力满足平衡条件及强度条件,并能精确满足地应力场回归估计值,接着介绍了一种将模型单元地应力张量表示成各单元坐标的函数,通过求取插值函数获得任意坐标的地应力张量的三维超曲面样条插值方法。最后以工程实例证实,改进方法可以有效提高局部地应力异常区域的拟合精度,解决了边界应力奇异分布的问题。
In order to improve the precision of in-situ stress inversion, a method of partial least-squares regression in FLAC3D to fit the in-situ stress field and accurately load the in-situ stress field into the calculation model and to achieve balance is proposed. Firstly, the stress components are regressed respectively, In order to improve the fitting accuracy of the local abnormal stress region. Then according to the calculation principle of FLAC3D, the relationship between unit stress and node unbalance force is analyzed. The initial stress of unit obtained by regression is loaded into the model and the node unbalance force is calculated, and the node load opposite to unbalance force is applied to node. Achieve the balance of power to complete the stress field loading. When the elastic-plastic model is adopted, the average stress is assumed to be constant, and the deviatoric stress is corrected according to the yielding condition. The unit ground stress that does not meet the strength condition is corrected to satisfy the elastic assumption, and the corrected unit ground stress satisfies the equilibrium condition and strength Conditions, and can accurately meet the in-situ stress field regression estimates, then introduced a model unit stress tensor expressed as a function of each unit coordinates, obtained by interpolation function to obtain arbitrary coordinates of the stress tensor of the three-dimensional hypersurface Spline interpolation method. Finally, an engineering example shows that the improved method can effectively improve the fitting accuracy of the local anomalous area and solve the problem of the singular distribution of the boundary stress.