关于饱和软土地基堤坝边坡稳定分析总应力法的讨论

在饱和的软土地基上修筑堤坝，由于孔隙水压力不易准确测定，需采用“φ=0”的总应力法进行稳定分析。这一做法在国外已明确纳入设计规范，在国内工程界较少受到重视，导致过高地估计了安全系数。本文首先系统地回顾了临界状态土力学中的伏斯列夫强度理论，在理论上阐述了饱和软土地基快速填筑时采用总应力法的原因，同时引用了Bishop和Bjerrum、美国联邦公路局、美国陆军工程师团与我国水电水利工程边坡设计规范的相关条文，确认在饱和软土地基采用总应力法进行稳定分析的合理性。以花敖泡土石坝和拉哇水电站围堰为工程实例，分别采用对土的固结不排水剪的两种做法开展稳定性分析，结果表明，直接将土的固结不排水剪强度指标ccu与φcu作为填筑后的强度参数，将严重高估其安全系数。因此建议正在修订的碾压式土石坝与边坡设计规范增加相应条文，并期望引起工程界对这一问题的重视。

Discussion on total stress method for stability analysis on slope of embankment and dam on saturated soft soil foundation

Due to the relevant pore water pressure is difficult to be correctly measured，the total stress method of“φ = 0”is necessary to be adopted to the stability analysis on the embankment and dam built on the saturated soft soil foundation． This method is already and clearly specified in the relevant design specifications at abroad，but less attention is paid to it within the engineering field at home，which leads to the overestimation of the safety factor concerned． At first，the Hvorslev strength theory in critical state soil mechanics is systematically reviewed herein，and then the reason of adopting the total stress method to the rapid filling of saturated soft soil foundation is theoretically described． Meanwhile，the relevant provisions of Bishop ＆ Bjerrum， FHWA，the U． S． Army Corps of engineers and the Design Specification for Slope of Hydropower and Water Conservancy Project issued in China，are cited to confirm the reasonability of adopting the total stress method for the stability analysis of saturated soft soil foundation． Taking Hua’aogou earth-rockfill dam and the cofferdam for Lawa Hydropower Station as the study cases，two methods of consolidated-undrained shear test are used to analyze the stability of the dam body． The results show that if the strength indexes ccu and φcu from the consolidated-undrained shear test are directly taken as the strength parameters after the filling，the safety factor is to be seriously overestimated． Therefore，it is suggested to add corresponding provisions to the design code for roller compacted earth-rock fill dams and slopes under revision and is expected that more attentions are to be paid on this issue within the relevant engineering field．