冻融循环下低液限盐渍化粉土力学特性研究

Study on the Mechanical Characteristics of Salinized Silt Soil with Low Liquid Limit under Freeze-Thaw Cycle

为了研究冻融作用对低液限盐渍化粉土强度的影响,对不同初始含水率低液限盐渍化粉土进行冻融循环试验后,开展不固结不排水(UU)剪切和扫描电镜(SEM)试验,从宏微观角度揭示低液限盐渍化粉土强度的劣化机理。结果表明:未冻融时,含水率的改变不会引起低液限盐渍化粉土应力-应变曲线形态发生变化,均表现为软化型;在冻融作用下,含水率小于14%时试件的曲线形态不会发生改变,呈现软化型,高含水率的试件其应力-应变曲线形态会向着硬化性转变;通过分析冻融和含水率与破坏强度的关系,发现低液限盐渍化粉土破坏强度随含水率的提高呈现线性衰减,破坏强度随冻融循环次数的增加呈现指数型衰减,前3次冻融过程中破坏强度的衰减速率和幅度最大,随后趋于稳定;随着围压的增大,试件的应力-应变曲线会由软化型向硬化型过渡;在微观结构方面,冻融作用会改变土颗粒之间的接触形式,造成孔隙和裂隙的发育,冻融过程中微观结构的变异规律和宏观力学指标的劣化具有一致性。结合土体损伤力学,构建了冻融作用下的低液限盐渍化粉土黏聚力损伤劣化模型,冻融过程中的劣化度符合双曲线关系,最终劣化度A_(c)与含水率呈指数型关系,劣化速率B_(c)与含水率呈线性关系。

In order to study the effect of freeze-thaw on the strength of low-liquid limit salinized silt,after the freeze-thaw cycle test of salted silt with different initial moisture content,non-consolidating and non-drainage(UU) shear and scanning electron microscopy(SEM) tests were carried out to reveal the deterioration mechanism of the strength of low-liquid limit salinized silt from macro-micro perspectives.The test results show that the change of moisture content does not cause the stress-strain curve morphology of low-liquid limit salinized silt to change when it is not freeze-thawed,and all of them are softening.Under the action of freeze-thaw,the curve shape of the specimen will not change when the moisture content is less than 14%,showing a softening type,and the stress-strain curve shape of the specimen with high moisture content will change to hardening.By analyzing the relationship between freeze-thaw and moisture content and failure intensity,it is found that the failure intensity of low-liquid limit salted silt decays linearly with the increase of moisture content,and the failure intensity decays exponentially with the increase of freeze-thaw cycles,and the attenuation rate and amplitude of the failure intensity are the largest in the first three freeze-thaw processes,and then tend to be stable.With the increase of confining pressure,the stress-strain curve of the specimen will transition from softening type to hardening type.In terms of microstructure,freeze-thaw will change the contact form between soil particles,resulting in the development of pores and fissures,and the variation law of microstructure and deterioration of macroscopic mechanical indicators in the freeze-thaw process are consistent.Combined with the soil damage mechanics,a low-liquid limit salinized silt cohesion damage deterioration model under freeze-thaw action was constructed,and the deterioration degree during the freeze-thaw process conformed to the hyperbolic relationship,and the final deterioration degree A_(c) had an exponential relationship with the moisture content,and the deterioration rate was B_(c) linear relationship with the moisture content.