考虑冰膜厚度的桩–土界面剪切特性及冻拔计算

Shear behavior of pile-soil interface considering ice film thickness and frost jacking calculation of piles in frozen soil regions

冻土–桩基接触界面的剪切力学行为是冻土区桩基冻拔计算模型建立的重要依据。开展一系列不同界面冰膜厚度的冻结砂土–混凝土负温直剪试验,分析冰膜厚度对界面剪切力学变形特性的影响,结合多元回归方法建立多因素影响的三折线剪切本构模型。基于剪切位移法,引入三折线剪切本构模型,构建季节性冻土地基单向冻结过程中单桩冻拔效应的理论计算模型,并进行算例分析。研究表明:冰膜厚度对界面的剪切行为影响显著,峰值剪切强度及残余剪切强度与冰膜厚度的关系可近似为双曲线函数关系;构建的剪切本构模型可较好地反映界面温度、法向应力及冰膜厚度对冻土–混凝土界面剪切行为的影响;桩周土体冻结过程中部分桩土界面会产生滑移,切向冻胀力的峰值位置随冻深的发展而下移;冰膜厚度对桩基的冻拔效应影响显著,冻拔力随冻胀率的增大并非呈线性增大,主要受桩土界面剪切强度的影响。

The shear behavior of the contact interface between frozen soil and pile is an important basis for establishing the frost jacking calculation model of piles in frozen soil regions.A series of negative temperature direct shear tests of frozen sand soil and concrete with different ice film thickness at the contact interface were carried out to analyze the influence of the ice film thickness on the shear mechanical deformation characteristics of the interface.Combined with multiple regression method,a trilinear shear constitutive model with multiple factors was established.Based on the shear-displacement method,the trilinear shear constitutive model is introduced to establish a theoretical calculation model for the frost jacking behaviour of single pile during the process of unidirectional freezing of seasonal frozen soil,and an example is analyzed.The results show that the ice film thickness has a significant effect on the shear behavior of the interface,and the relationship between the peak shear strength and the residual shear strength and the ice film thickness can be approximated as hyperbolic functions.The shear constitutive model can better reflect the effects of interface temperature,normal stress and ice film thickness on the shear behavior of frozen soil-concrete interface.Some pile-soil interface will slip during the freezing process of the soil around pile,and the peak position of tangential frost heaving force moves downward with the development of frost depth.The thickness of ice film has significant influence on the frost jacking effect of pile foundation.The frost jacking force does not increase linearly with the increase of frost heaving ratio,which is mainly affected by the shear strength between pile and frozen soil.