季节冻土区路基土的损伤本构模型研究

Study on constitutive model of subgrade soil in seasonally frozen area

为探索不同冻融循环次数和围压作用对季节冻土区路基土在不同含水率条件下的应力-应变关系及损伤机理,以辽宁阜新市某公路区间为试验路段,采用环刀法选取试验路段路基土样,通过冻融循环及三轴压缩试验,得到在不同冻融循环次数及围压作用下路基土的应力-应变曲线变化规律;根据损伤力学及统计学原理,将Weibull分布与Lemaitre有效应力原理相结合,建立了季节冻土区路基土损伤本构模型。结果表明:冻融循环作用可导致路基土试件强度降低,且随着试件含水率的增加,应力-应变曲线呈现由应变软化逐渐表现为应变硬化特征,试件最优含水率为应变软化与应变硬化的分界点;随着围压的增大试件强度增加,在冻融循环次数较少且围压较低时,试件的应力-应变曲线出现峰值应力,曲线表现出应变软化特征,在冻融循环次数较多且围压较大时容易出现应变硬化现象;经对比分析,所建立的损伤本构模型与试验应力-应变曲线吻合度较好,且模型所需参数均可通过三轴试验获得,说明该模型能够较好地描述季节冻土区路基土的应力-应变关系,具有实用性。另由试验结果可知,为降低东北地区冻融循环作用对季节冻土区路基强度的影响,提前做好路基的防排水工作对于路基冻融病害防治是非常重要的。

In Northeast China,the annual temperature difference is relatively large,and the subgrade soil pres⁃ents freeze-thaw cycle with the change of temperature,belonging to seasonal frozen soil,which is easy to cause serious deformation of subgrade in Northeast China during service,the occurrence of subgrade diseases such as frost heave,frost heave and mud heave leads to the change of soil structure,the reduction of subgrade stiffness,and the deterioration of bearing capacity.The stress-strain relationship can effectively represent the law of stress and deformation of soil,and the establishment of a reasonable freeze-thaw damage model has guiding signifi⁃cance for the structural design of seasonally frozen soil subgrade.Consequence,in order to explore the stress strain relationship and damage mechanism of subgrade soil in seasonal frozen area under different water content under different freeze-thaw cycles and confining pressure,choosing a highway section in Fuxin City,Liaoning Province as the test section,using the ring knife method to select the subgrade soil sample of the test section and freeze-thaw cycle and triaxial compression test,the experiment obtained the relation of the stress-strain curves of subgrade soil under different freeze-thaw cycles and confining pressures.According to the damage mechanics and statistics principles,the Weibull distribution is combined with Lemaitre effective stress principle to establish a damage constitutive model of subgrade soil in the seasonal freezing zone.The results show that the optimum moisture content of subgrade soil in seasonally frozen area is the limit moisture content of its stress-strain curve from strain softening to strain hardening.When the moisture content is less than the optimum moisture content,the peak stress of the curve increases with the decrease of the moisture content,and decreases with the increase of the number of freeze-thaw cycles.When the moisture content of the test piece is greater than the optimum moisture content,the curve has no peak stress with the increase of the moisture content,showing obvious strain hardening characteristics.When the number of freeze-thaw cycles is small and the confining pressure is low,the stress-strain curve of the specimen shows a peak stress,and the curve shows a strain softening feature with the in⁃crease of confining pressure,the strength of the specimen increases.Strain hardening is easy to occur when there are many freeze-thaw cycles and large confining pressure.Through comparative analysis,the established dam⁃age constitutive model is in good agreement with the test stress-strain curve.It can reflect that the stress-strain curve of subgrade soil in the seasonally frozen area shows a change rule of first increasing and then tending to be stable.And the parameters required by the model can be obtained through triaxial tests,which shows that the model can better describe the stress-strain relationship of subgrade soil in seasonal frozen area,and is practical.In addition,it can be seen from the test results that in order to reduce the impact of freezing and thawing cycles on the subgrade strength in the seasonal freezing area in Northeast China,it is very important to do a good job in the waterproof and drainage of the subgrade in advance for the prevention and treatment of subgrade freezing and thawing diseases.