冻土与结构接触面次峰值冻结强度试验研究

为探究冻土与结构接触面次峰值冻结强度影响因素、影响规律及其预估方法，选取南京河西地铁施工区域典型粉细砂为试验土样，利用改进后的大型多功能冻土直剪仪，开展多影响因素条件下的冻结强度直剪试验研究。在对次峰值冻结强度定义和量化标准约定的基础上，研究发现极限峰值后剪应力陡降、峰后剪应力周期性变化、软化衰变等典型变化规律。将次峰值冻结强度与接触面温度、粗糙度、法向应力拟合后发现其分别呈反比例线性、二次抛物线、正比例线性关系。通过关系数据库管理软件数据挖掘，得出次峰值冻结强度关键影响因素及大小依次为接触面法向应力、粗糙度，而接触面温度为非关键影响因素。经多元非线性回归，构建了耦合接触面温度、法向应力及粗糙度三因素的次峰值冻结强度预估模型，可为人工冻土区或天然冻土区冻结加固设计、盾构法施工、地下结构物设计等提供冻结强度参数选取依据。

Sub peak adfreezing strength at the interface between frozen soil and structures

To study the influence factors of sub peak adfreezing strength at the interface between frozen soil and structure, the typical fine sand located in the Hexi area of Nanjing subway construction site was selected as test sample. The large-scale multi-functional frozen soil-structure interface shearing instrument was optimized and improved to conduct direct shear tests of adfreezing strength considering multi-influencing factors. Based on the specific definition and the agreement of quantitative criteria for sub peak adfreezing strength, it was found that the shear stress was typical of steepness after the limit peak, and the peak post shear stress changed periodically . The relationships among sub peak adfreezing strength, interface temperature, roughness and normal stress were fitted and found to be inverse proportional linearity, quadratic polynomial, proportional linear relationship respectively. Through the database management software, it was found that the normal stress and roughness were the key influencing factors, but the interface temperature was non-critical influencing factors. The three-element sub peak adfreezing strength prediction model coupled with interface temperature, normal stress and roughness was constructed by multivariate nonlinear regression. It can provide important adfreezing strength parameters for artificial freezing reinforcement design, shield construction and underground structure design in artificial freezing reinforcement area or permafrost area.