Predicting deformation of multipropped excavations in soft clay with a modified mobilizable strength design (MMSD) method

Although serviceability (i.e., deformation) governs the performance of deep excavations in urban areas with soft clay deposits, the common design methods are only able to check the potential of base stability, rather than the deformation. This limitation has led to the development of an analytical approach entitled the mobilizable strength design (MSD) method, which can predict both serviceability and safety in a single step of calculation. The modification of the MSD method (i.e., the MMSD method) was recently made by the authors, by implementing a more realistic plastic deformation mechanism into the calculation. The objectives of this study are (a) to validate the MMSD method by comparing its predicted deformation with eight well-documented case histories in Shanghai and Hangzhou soft clay and (b) to quantify the influence of some potentially important factors on the deformation of deep excavations in Shanghai and Hangzhou. The accuracy of the MMSD predictions for the maximum lateral wall displacement (δh-max) have been found to fall within 35% of the field data in most of the cases. This accuracy is more satisfactory than the accuracy (i.e., 120%) of the MSD predictions for the corresponding case histories, suggesting the effectiveness of the modified plastic deformation mechanism considered in the MMSD calculation. Based on the verified MMSD method, preliminary design charts that predict δh-max of narrow excavations (specifically for a metro station) considering different geometries and strength mobilization characteristics have been developed.