冻融循环对不同塑性指数路基土弹性模量的影响研究

Influence of freeze-thaw cycles on elastic modulus of subgrade soil with different plasticity indices

在季节性冻土区,不同状态(塑性指数,围压等)路基土在通车运营期间经历冻融循环后,其物理力学性质会发生变化,但目前针对冻融循环对其的影响研究还不够广泛和深入,不能给季冻区路基设计提供准确的数据支持,故路基设计时并未将这种变化考虑其中,只取设计前期所采土样的试验值。取季节性冻土区3种不同塑性指数路基土,在室内采用最佳含水率制备成最大压实度试样,在封闭条件下经历0～7次完整冻融循环过程后,进行不同围压下的三轴压缩试验,在偏应力-应变曲线中通过直线段应力-应变关系得到弹性模量数据,结果表明,同种土相同冻融循环次数下,弹性模量随围压增加而增加;相同围压下弹性模量随冻融循环次数基本呈下降趋势。采用指数函数对所有弹性模量数据进行多元非线性拟合,建立不同塑性路基土弹性模量与围压及冻融循环次数的关系,拟合效果理想,可为缺乏相关资料的季冻区路基设计提供参考。

In seasonally frozen soil region, the physico-mechanical properties of subgrade soils with different states （plasticity index, confining pressure, etc.） will change after freeze-thaw cycle during the traffic operation; but the study of effects of freeze-thaw cycle is not extensive and intensive and can not provide accurate data to support the roadbed design in roadbed design of seasonally frozen soil region. So this change has not been taken into account. Three subgrade soils with different plasticity indices are selected from seasonal frozen soil region. Static triaxial test is executed on the samples exposed to 0-7 times closed-system freeze-thaw cycles under different confining pressures. Elastic modulus is obtained from the line segment of deviator stress-strain curve. The results show that the elastic modulus increases with confining pressure increase for the same kind of soil under the same freeze-thaw cycles. Elastic modulus with the same confining pressure decreases with the of freeze-thaw cycles; Under the same confining pressure and the same freeze-thaw cycles, elastic modulus increases with the plasticity index. The exponential function is adopted for multiple nonlinear fitting. The relationship between elastic modulus and confining pressure, plasticity index, freeze-thaw cycles is obtained and shows a good correlation..