硬壳层非饱和软基路堤的填土高度研究

INVESTIGATION ON FILLING HEIGHT OF EMBANKMENT ON UNSATURATED SOFT GROUND WITH STIFF CRUST

硬壳层在软土路堤工程中具有很好的承载传递特性,应充分发挥其有利作用以优化路堤填土高度设计与施工管理.考虑硬壳层的应力扩散作用和自重反压护道作用,基于非饱和土平面应变抗剪强度统一解与吸力角双曲线模型,推导了实际地应力状态下硬壳层非饱和软土地基的临塑/临界载荷计算公式,进而建立了路堤临塑/临界填土高度的解析解,并给出解析公式的适用条件与应用步骤,最后探讨了各因素对路堤临界填土高度的影响规律.所得解析公式能综合反映4种因素的影响,具有很好的可比性,且对比验证了解析公式的正确性及给定公式适用条件的必要性与合理性.研究结果表明:硬壳层的影响具有整体性,应同时考虑其厚度和弹性模量的变化,可忽略路堤等效宽度的影响;侧压力系数的影响明显,侧压力系数为1.0对应的路堤填土高度明显偏大,应原位测试确定地基土的真实侧压力系数;采用不同强度准则的计算结果差异显著,应充分考虑中间主应力对公式适用范围及路堤填土高度的影响;高、低基质吸力的影响特性不同,低吸力时路堤填土高度线性增加且与截距无关,高吸力时路堤填土高度受双重作用相对大小的控制,或先逐渐减小后缓慢增大、或逐渐增大,并与截距密切相关.

The stiff crust commonly distributed in the soft ground area has a good capacity for load transmission in embankment engineering, and its beneficial effect should be brought into a full play. Analytical formulae for both the critical edge load and critical load of unsaturated soft ground are deduced with taking into account of the stress dispersion and self-weight berm of stiff crust. It is assumed that the strength of unsaturated soils is governed by the unified shear strength formulation and a hyperbolic model of suction angle. Then, analytical solutions of the critical edge filling height and critical filling height of embankment are presented, whose applicable conditions and implementation steps are also proposed. Finally, the influences of various parameters involved are conducted on the critical filling height of embankment. The obtained analytical formulae have good comparability and are validated. In addition, the necessity and rationality of the proposed applicable conditions are highlighted. The findings of the study illustrate that, the stiff crust has an overall influence, and the changes about thickness and Young＇s modulus of stiff crust could be simultaneouslyconsidered; the effect of lateral pressure coefficient is remarkable, and thus a real lateral pressure coefficient would be determined by in-situ test; moreover, the differences are significant with different strength criteria, and the effect of intermediate principal stress should be fully considered on the applicable conditions of formulation and filling height of embankment; the effect of high suction is different as compared with that of low suction.