含硫酸钠盐冻结粉砂强度与变形指标的试验研究

对硫酸钠盐含量为0.5%的冻结粉砂在-2℃的温度下和0.3~17 MPa围压范围内进行了三轴压缩试验.试验结果表明,含硫酸钠冻结粉砂强度随围压的增大呈先增大后降低的规律,强度的增大阶段可分为两个阶段,第一阶段为0.3~4 MPa,增大速率为1.775;第二阶段为4~8 MPa,增大速率为0.753,围压8 MPa时强度最大,其值为13.10 MPa,与0.3 MPa围压处的最小强度值3.52 MPa相差9.58 MPa;在8~17 MPa的围压范围内,强度整体呈现下降趋势,强度在13.10~12.19 MPa波动.为在冻土工程计算中选取合理的变形指标,对比分析了初始切线模量E0与0.5倍强度处割线模量E0.5、初始切线泊松比μ0和0.5倍强度处割线泊松比μ0.5随围压的变化规律.分析结果表明,两种方式确定的弹性模量和泊松比的变化规律均可按围压分为0.3~4 MPa、4~10 MPa和10~17 MPa三个阶段,弹性模量E0与E0.5在第一阶段和第二阶段均随围压的增大而增大,但第二阶段的增加速率比第一阶段低,在第三阶段E0随围压的增加呈现明显的减低趋势,从最大值1 022.39 MPa降低到490.27 M Pa,而E0.5在在该阶段受围压影响不大;泊松比μ0与μ0.5在第一阶段与第二阶段均随围压的增大而减小,但第二阶段的降低速率比第一阶段小,在第三阶段μ0与μ0.5随围压的增大而增大.对变形指标随围压的变化规律分析表明,冻土初始变形行为对围压敏感,数据离散性大,在工程计算中选取0.5倍强度处对应的割线变形指标在数据上更为稳定、可靠.

Experimental study on strength and deformation indicators of frozen silty sand with sodium sulfate

Triaxial compressive tests at a temperature of -2 ℃ have been carried out in terms of saline frozen silty sand with Na2 SO4 of 0.5%,while the confining pressure changes from 0.3 MPa to 17 MPa.The results showed that the strength of saline frozen silty sand first increased and then decreased as with increasing confining pressure.The increasing process of strength was divided into two stages,the decreasing rate was 1.775 for first stage while the confining pressure ranged from 0.3 MPa to 4 MPa and 0.753 for second stage while the confining pressure ranged from 4 MPa to 8 MPa.The maximum strength reached 13.10 MPa when σ3 =8 MPa and differed by 9.58 MPa from the minimum strength when σ3 =0.3 MPa.Variation of the strength was within 13.10 MPa to 12.19 MPa and showed down trend wholly while the confining pressure was within a range from 8 MPa to 17 MPa.To select the reasonable deformation indexes for engineering calculations,the variation of ini-tial tangential modulus E0 ,secant modulus E0.5 ,initial tangential Poisson′s ratio μ0 and secant Poisson′s ratio μ0.5 with confining pressure have been studied,respectively.The change laws of elastic modulus and Poisson′s ratio with confining pressure were both divided into three stages by confining pressure (0.3 -4 MPa,4 -10 MP and 10 -17 MPa).As a result,initial tangential modulus E0 increased as the confining pressure increased in the first and the second stage and decreased from 1 022.39 MPa to 490.27 MPa as the confining pressure increased in the third stage.As to secant modulus E0.5 ,it increased along with the increasing of confining pressure in the first and the second stage but fluctuated nearby the corresponding value when σ3 =10 MPa in the third stage.Poisson′s ratio μ0 and μ0.5 decreased with confining pressure increasing in the first and the second stage and increased with confining pressure increasing in the third stage.The initial deformation capacity was more sensitive and the data has intensive discreteness throughout the process.Therefore,being nearly independent of the confining pressure,μ0.5 was suggested to perform engineering computation.