高填方地基不排水稳定性分析强度指标研究

Study of strength indices for undrained stability analysis of high filled ground

目前国内工程界对高填方地基的排水稳定性关注较多,然而针对地下水位较高、排水性能较差的原状地基,由快速填筑引起的不排水稳定性问题更为突出。综述了现行规范中关于边坡不排水稳定性分析的相关条文及国内外常用方法。通过分析总应力摩擦角的应力路径相关性以及计算原状地基典型点位的总应力加载路径,解释了采用三轴固结不排水(consolidated-undrained,简称CU)总应力强度指标进行不排水分析,会高估高填方地基的不排水稳定性,该方法存在理论缺陷和工程隐患。以简单假想边坡模型和某高填方机场实际工程为算例,利用简化Bishop法,选用5种不排水分析指标或模型,分别计算其不排水稳定性安全系数。结果表明:CU总应力法会高估高填方地基的不排水稳定性;其余4种方法计算得到的不排水稳定性安全系数比较接近,相对适用。

Domestic geotechnical engineers paid more attention to the drained stability of high filled ground;however,the undrained stability brought by rapid constructions was more of a problem for ground with a high groundwater level and poor drainage performances.The relevant standards existing in current specifications and the common methods about undrained stability analysis of slopes were reviewed.By analyzing the relationship between total stress friction angles and stress paths and by calculating the typical total stress paths of original ground in high-fill projects,an explanation was given why the undrained stability of high filled ground was overestimated when strength indexes of total stress from consolidated-undrained(CU)triaxial tests were applied to undrained analysis,which brought theoretical defects and engineering hidden dangers.Taking a simple hypothetical slope model and a real case of a proposed high-fill airport as example,the factors of safety(FOS)of the undrained stability were calculated through five undrained analysis parameters or models using simplified Bishop method respectively.The results show that the undrained stability of high filled ground is overestimated by the CU total stress method all the time;the FOS of undrained stability by other four methods are close,which verifies the relative applicability of these methods.