基坑底分层回弹量的实用计算方法

基坑开挖后的卸载会引起基坑的回弹,基坑开挖越深,则回弹量越大,较大回弹量会造成各种工程问题。现有回弹量计算方法需要进行专门的回弹试验或特定应力路径试验以确定回弹计算所需的模量。为了避免进行专门试验,特研究了应用常规试验所得模量与常用Mindlin解和Boussinesq解相结合,得到一种计算回弹量的简便可行方法。通过对Mindlin解和Boussinesq解计算所得应力,与e-lg p模型和Duncan-Chang模型的变形计算方法进行组合,得到4种计算方法,然后应用分层总和法计算求解基坑的回弹量,通过与实测值对比,比较4种组合计算方法的精度,得出更适合于工程实际应用的、准确性更高的基坑回弹量计算方法。经3个工程实例检验,推荐采用Mindlin解和e-lg p模型分别计算应力和模量,再应用分层总和法累加变形量,可得到与工程实测值非常相近的坑底总回弹量和坑底分层回弹量。

A practical method for calculating layerwise rebound at the bottom of foundation pit

Excavation of the pit will cause the rebound, the deeper the excavation is, the greater the rebound will be; the large amount of rebound will cause a variety of engineering problems. Existing rebound calculation methods require specialized rebound experiment or a particular stress path experiment to determine the unloading modulus. The application of modulus obtained from conventional laboratory tests and commonly used Mindlin solution and Boussinesq solution combined in a simple and practical way to get the rebound is studied in this paper. Four calculation methods for different combinations between the stress calculation of the Mindlin solution and Boussinesq solution and the deformation calculation of e- model and Duncan-Chang model, are obtained; and then the amount of rebound is calculated by the application of the layerwise summation method; and the accuracies of four methods are explored respectively. A more practical method for the application of engineering excavation rebound calculation is obtained. Compared with the measured values, the Mindlin solution and e- model are recommended respectively to calculate the stress and modulus; and then a calculated rebound which is very accurate to the measured values can be obtained with the application of the layerwise summation method.