路基土动态回弹模量预估进展与展望

路基动态回弹模量是路面结构设计的重要参数,而路基土回弹模量MR的预估是确定路基回弹模量的基础。基于此,总结分析国内外路基土动态回弹模量预估模型的主要成果,并根据预估模型变量的不同,将典型预估模型分成了3类:第1类(A类)是以应力为变量的预估模型;第2类(B类)是将基质吸力耦合到应力变量中的预估模型;第3类(C类)是将基质吸力作为独立应力变量的预估模型。进而,从每类模型中选取2个被广泛接受的代表性模型,并采用3种土样的重复加载动三轴试验数据,对各类模型的适用性和特点进行分析。结果表明:A类模型形式简单,考虑了体应力、偏应力、八面体剪应力等应力变量对路基土动态回弹模量的影响,但对路基湿度状态的反映仅体现在k1,k2,k3等模型参数中;B类模型是基于微观力学理论和热力学定律或基于Bishop非饱和土的有效应力原理提出的,若通过试验确定有效应力参数,成本高且设备不易操作,若通过经验公式来确定则误差较大;C类模型又分为将基质吸力作为应力的增量和乘积2种形式,增量形式导致MR随基质吸力的变化不受围压、循环偏应力的影响,与实际情况不符,而乘积形式可避免该现象的产生;建议采用乘积的形式来反映基质吸力对路基土动态回弹模量的贡献。此外,为提出适用于中国路基路面设计体系的路基土回弹模量预估模型,应在加载序列、基质吸力测试、预估模型构建、干湿循环影响等方面开展进一步研究。

Progress and Prospect of the Prediction Model of the Resilient Modulus of Subgrade Soils

The resilient modulus of the subgrade is a fundamental parameter for flexible pavement design. Therefore, the prediction of the resilient modulus of subgrade soils, M_R, is the basis for determining the resilient modulus of the subgrade. Here, the resilient modulus prediction models of subgrade soils proposed in the literature were reviewed and the models were summarized into three groups according to the model variables:Group A, the constitutive models were built with stress states; Group B, the constitutive models incorporated the matric suction into applied shearing or confining stresses; and Group C, the constitutive models expounded the independent stress state variable approach. Two equations selected from each of the groups were used to predict the resilient modulus for three compacted subgrade soils. The results indicate that the models of Group A are simple in form, considering the effects of stress variables such as bulk stress, deviatoric stress, and octahedral shear stress, but the reflection of the subgrade humidity state is only reflected in the regression coefficients (k₁, k₂, k₃). Models of Group B were based on the micro-mechanical theory and the laws of thermodynamics or the Bishop effective stress principle based on unsaturated soil. Experimental determination of the effective stress parameters is costly and challenging, while determination of these parameters an empirical formula will result in a significant error. Models of Group C were characterized as forms of increment and product. The incremental form does not consider the influence of matric suction affected by the confining pressure and deviatoric stress. Therefore, adopting the product form for coupled matric suction was suggested. In order to propose the subgrade soil resilient modulus prediction model suitable for China's subgrade pavement design system, further research should be carried out in terms of the loading sequence, matric suction test, prediction model building, and the dry and wet cycles.