考虑孔隙比的冻胀弱敏感性土修正PCHeave模型研究

Study on Modified PCHeave Model for Weakly Sensitive Soils to Frost Heave Considering Void Ratio

针对我国严寒地区高速铁路路基填料和机场填方等工程具有严格的压实度要求,而考虑孔隙比的冻胀弱敏感性土冻胀影响研究尚未有系统性的理论分析,采用理论与经验分析相结合的方法,基于冻胀弱敏感性土的孔隙比与渗透系数和未冻水含量之间的关系,建立考虑孔隙比的修正PCHeave模型。基于该模型分析孔隙比与冻胀量、冻结深度和冻胀率之间的关系,并进行试验对比验证。研究结果表明:孔隙比与冻胀弱敏感性土的未冻水含量之间存在很好的线性关系;冻胀弱敏感性土的冻胀量和冻胀率均随孔隙比先增大再减小,即存在一个最不利孔隙比使得冻胀量和冻胀率均达到最大值;冻胀弱敏感性土的冻结深度随孔隙比增大而逐渐增大;若仅考虑孔隙比对饱和渗透系数的影响,冻胀量和冻胀率均随孔隙比显著增加,若仅考虑孔隙比对未冻水含量的影响,冻胀量和冻胀率均随孔隙比减小,但减小幅度很小。冻胀弱敏感性土通常被认为不能产生显著冻胀,在一定孔隙比下也能产生较大冻胀,同时考虑孔隙比对饱和渗透系数与未冻水含量的影响要更合理。冻胀弱敏感性土的冻胀不能忽略孔隙比的变化,与试验结果对比,该模型能够较好地描述孔隙比对冻胀弱敏感性土的冻胀影响。

In response to the strict compaction requirements for high-speed railway subgrade filling and airport filling projects in severe cold regions,and lack of systematic theoretical analysis on the frost heave effects of weakly sensitive soils considering void ratio,a modified PCHeave model considering void ratio was established based on the relationship among pore ratio,permeability coefficient and unfrozen water content of weakly sensitive soils by combining theoretical and empirical analysis.Based on this model,the relationship between void ratio and frost heave,freezing depth and freezing rate was analyzed,and the experimental comparison was carried out.The results show that there is a good linear relationship between pore ratio and unfrozen water content of soils with weak sensitivity to frost heave.The frost heave and frost heave rate of weakly sensitive soil increase first before decreasing with the void ratio,that is,there is a most unfavorable void ratio that maximizes the frost heave and frost heave rate.However,the freezing depth of weakly sensitive soil to frost heave increases with the increase of pore ratio.If only the effect of void ratio on saturation permeability coefficient is considered,both the frost heave and frost heave rate increase significantly with the pore ratio.If only the effect of void on unfrozen water content is considered,both the frost heave amount and the frost heave rate decrease with the void ratio,but with minor decrease range.Weakly sensitive soils to frost heave,which are generally considered to not produce significant frost heave,can also produce large frost heave at a certain porosity ratio level.Therefore,it is more reasonable to both consider the influence of porosity ratio on saturation permeability coefficient and unfrozen water content.The change of void ratio cannot be ignored in the frost heaving of weakly sensitive soil.The comparison with the freezing tests shows that this model can better describe the effect of void ratio on frost heaving of weakly sensitive soil.