基于变模量本构模型的三维地基沉降计算分析

Calculation for 3-D soil foundation settlements based on variablemodulus constitutive model

对于地质条件复杂的基础工程,传统的解析方法难以获得合理的地基沉降和应力结果,此时数值方法的可靠性显得尤为重要,而数值方法的关键是选择合适的本构模型。为此,选择参数少且较易准确获取的变模量本构模型,通过二次开发将其嵌入到FLAC3D中,依托荔湾大厦基坑工程,分析了大面积、大荷载、复杂地质条件下基底沉降、应力及底板弯矩分布特征,并与弹性本构模型结果和实测沉降值进行对比,证明变模量本构模型在三维地基沉降分析中的优越性和适用性。同时分析了基础形状、刚度、荷载大小和地层条件等对地基沉降和应力分布特征的影响。所得结论主要有:①复杂地质条件下,基于变模量本构模型所得三维地基沉降结果与实测结果吻合较好;②基础刚度或荷载较大时,弹性本构模型因无法考虑屈服后的应力释放问题,所得基底应力端部集中显著,结果失真,所获得的底板弯矩也过大,这容易造成地基承载可行性和基础结构可靠性的误判。变模量本构模型模量随应力水平实时调整,可有效模拟端部应力释放,可以提供较合理的地基沉降和应力分布结果;③对于不等厚不均匀地层,其沉降和应力分析时应避免采用弹性本构,确保工程评估的准确性。

The traditional analytical method has some limitations for the three-dimensional foundation settlement and stress results with complex geological conditions.The reliability of numerical methods is particularly important in these conditions.An appropriate constitutive model is critical for the reliability of numerical methods.In order to accurately solve the three-dimensional foundation settlement under complex geological conditions,the variable modulus constitutive model,in which the number of parameters is relatively few and easy to obtain,is applied to the foundation pit engineering of Li-wan building with the FLAC3D software to analyze the characteristics of basement settlement and stress distribution.These results are compared with the measured data and results calculated by elastic constitutive model.It proves the superiority and applicability of the variable modulus constitutive model in the three-dimensional foundation settlement analysis.Influences of foundation shape,stiffness,loads and stratum condition on the foundation settlement and stress distribution are analyzed with the elastic and variable modulus constitutive models.Main conclusions are as follows:①the settlement results of three-dimensional foundation under complex geological conditionsbased on the variable modulus constitutive model are in good agreement with the measured results.②When the foundation stiffness or load is large,the stress at the end of the foundation is distorted with the elastic method because the elastic constitutive model fails to simulate the stress release while zones yield.The bending moment of foundation plate is bigger than the value.These will lead to the misjudgment of the bearing feasibility of the foundation and the structure reliability.In the variable modulus constitutive model,the modulus can change with the stress level.Thus it can simulate the stress release process and provide the reasonable settlement and stress results.③The elastic model is not recommended to analyze the foundation settlement and stress when the stratum is inhomogeneous.