含盐量及冻融条件对冻融氯盐粉质黏土静动强度特性影响研究

Effects of salt content and freeze-thaw conditions on static and dynamic strength characteristics of freeze-thawed chloride silty clay

沿海地区隧道建设中人工冻结法加固越来越多,而冻融氯盐粉质黏土静动强度及弹性模量特征是人工冻结法加固解冻融沉预测与稳定性设计的重要依据。为深入研究氯盐粉质黏土静动强度及弹性模量变化规律,开展了冻融前后、不同含盐量及冻融温度的固结不排水静三轴试验和动三轴试验。研究结果表明:不同试验条件下静三轴应力-应变曲线及动三轴骨干曲线均呈现应变硬化特征;冻融前试样曲线初始线性阶段更明显。静强度随含盐量增加先降后升,存在一对应最低强度的临界含盐量为1%;-10℃冻融后,含盐量≤3%时动强度无明显变化,含盐量为4%时动强度显著增大至其余含盐量试样的1.8倍;含盐量增加使弹性模量增加1.1~2.0倍。对弹性模量进行E/E_(max)归一化处理,并可用双曲线模型进行描述。冻融后,2%含盐量试样静、动强度损伤率分别为52%~66%、69%~78%,峰值静、动弹性模量损伤率为90%、81%。冻融温度对静、动强度及弹性模量影响不明显。研究结果可为人工冻结法在海相含盐地层应用、预测与控制工后融沉提供理论依据,保证隧道安全运营。

Artificial ground freezing technology is commonly used in tunnel construction in coastal soil regions.The static and dynamic strength characteristics,as well as the elastic modulus of freeze-thaw chloride silty clay,are crucial for predicting thaw settlement and designing the stability of artificial ground freezing technology.Hence,consolidated-undrained triaxial compression tests and cyclic triaxial tests were conducted with varying salt content,freeze-thaw cycles,and temperatures to investigate the static and dynamic strength as well as the elastic modulus in more detail.The results indicated that all static triaxial stress-strain curves and dynamic triaxial backbone curves exhibited strain-hardening behavior.The initial linear stage of the curve was more pronounced in specimens without freeze-thaw.The static strength initially decreased and then increased with rising salt content.A critical salt content of 1%corresponded to the minimum static strength.When the salt content was≤3%,the dynamic strength showed no significant change.However,it increased significantly to 1.8 times that of other salt content specimens when the salt content reached 4%after undergoing freezing-thawing at-10℃.The increase in salt content led to a 1.1-2.0 times increase in the elastic modulus.The elastic modulus can be normalized as E/E_(max)and described using a hyperbolic model.For specimens with 2%salt content after freeze-thaw cycles,the damage rates of static and dynamic strength were 52%-66%and 69%-78%,respectively.The damage rates of static and dynamic peak elastic modulus were 90%and 81%,respectively.The impact of freezing temperature on static and dynamic strength and elastic modulus was minimal.This research can establish a theoretical foundation for the utilization of artificial ground freezing technology in marine saline formations,as well as for the prediction and control of post-construction thaw settlement to ensure the safe operation of tunnels.