冻土区土石混合体冻融交界面剪切性能研究

Study on shear performance of soil-rock mixture at the freezing-thawing interface in permafrost regions

随着全球气候变暖,多年冻土加速退化,冻土区土石混合体边坡稳定性问题日益突出。为探究不同含水率和碎石含量对土石混合体冻融交界面剪切强度的影响。开展土石混合体冻融交界面直剪试验,得出含水率(21%、24%、27%、30%)和含石率(0%、10%、20%、30%、35%、40%)对土石混合体冻融交界面抗剪强度变化的影响规律。试验结果表明:含水率对土石混合体冻融交界面强度的影响可分为快速下降和缓慢下降两个阶段。当含水率从21%增加到27%的过程中,土石混合体冻融交界面强度下降迅速。当含水率从27%增加到30%的过程中,界面抗剪强度继续下降,但下降速率减慢,即含水率对界面强度影响的阈值在27%左右。随着碎石含量增加,界面抗剪强度一直处于增长趋势。当含石率为10%的交界面强度相比不含石的交界面强度有明显增加,最大增长幅度为33%。当含石率大于30%时,土体抗剪强度增长迅速,即含石率对界面强度影响的阈值在30%左右。当含石率一定时,交界面处摩擦角随着含水率增加逐渐减小,在含水率达到27%后变化缓慢,而交界面黏聚力在含水率达到27%前快速减小后趋于缓慢下降。当含水率一定时,随着含石率增加,交界面摩擦角一直处于增长,尤其在含石率超过30%后增长迅速。当含石率从0%增加到30%的过程中,黏聚力先有小幅度下降后处于平缓增长趋势,在含石率超过30%后迅速增加而后又趋于平缓。

With the accelerated degradation of permafrost caused by global warming, the problem of slope stability of soil-rock mixture in permafrost regions has become increasingly prominent. To investigate the effects of different water contents and rock contents on the shear strength of soil-rock mixture at the freezing-thawing interface, direct shear tests were carried out on the freezing-thawing interface of soil-rock mixture, and the effects of water content(21%, 24%, 27%, 30%) and rock content(0, 10%, 20%, 30 %, 35%, 40%) on the shear strength of the interface were obtained. The test results show that the effect of water content on the shear strength of the freezing-thawing interface of soil-rock mixture can be divided into two stages: rapid decrease stage and slow decrease stage. The shear strength of the interface decreased rapidly as the water content increased from 21% to 27%, but the decreasing rate slowed down when the water content continued increasing to 30%, suggesting that the threshold value of the water content affecting the shear strength of freezing-thawing interface can be considered to be around 27%. The shear strength of freezing-thawing interface increased with rock content. The shear strength of freezing-thawing interface with the rock content of 10% significantly increased compared to that without rock, with the maximum increase of 33%. When the rock content exceeded 30%, the shear strength would increase rapidly, suggesting that the threshold value of the rock content affecting the shear strength of freezing-thawing interface can be considered to be around 30%. When the rock content was constant, the friction angle of interface gradually decreased with the increase of the water content, and the change tended to be stable after the water content reached 27%. However, the cohesive force at the interface decreased rapidly before the water content increased to 27%, and then decreased slowly.When the water content was constant, the friction angle at the interface increased with the increase of rock content especially when the rock content exceeded 30%. The cohesive force decreased first and then increased slowly with rock content ranging in 0%-30%, but the cohesive force increased rapidly and tended to be flat when the rock content exceeded 30%. When the rock content increased from 0% to 30%, the cohesion force first decreased slightly and then increased gently. After the rock content exceeded 30%, the cohesion force increased rapidly and then leveled off.