冻融循环下南阳膨胀土直剪试验

我国南水北调中线工程沿线的部分膨胀土渠道处在季节性冻土地区。为了探究冻融循环对膨胀土抗剪强度 和体积变化的影响规律, 对经历冻融循环的膨胀土和非膨胀性黏土试样进行尺寸测量和直剪试验。试验结果表明: 在冻融循环初始阶段, 土体抗剪强度的降低较为明显, 随后由于含水率的降低, 土体的强度逐渐增强; 在冻融循环的 过程中, 非膨胀性黏土的体积变化表现为/ 冻胀融沉0 , 而膨胀土的体积变化表现为/ 冻缩融胀0 。干密度的改变不影 响膨胀土的抗剪强度和体积变化的规律形态, 干密度大的膨胀土最终体缩量较小。采取防蒸发措施的膨胀土在冻 融循环前3 次抗剪强度逐渐减小, 随后趋于稳定, 其最终体积几乎不受干缩的影响。 Par t of ex pansiv e clay channel in the M iddle Route o f South2to2Nor th Water T ransfer Project ( SNWTP) in China is located in the seasonal fr ozen so il r egion. In or der to inv estigate the effects of fr eeze2thaw cycle o n the shear st rength and vol2 ume chang e of ex pansiv e clay, direct shear test w as conducted o n the ex pansiv e and non2ex pansive clay samples w hich had expe2 r ienced the freeze2thaw cycle, and then the sizes o f sam ples w ere measur ed. The results showed that ( 1) the shear str eng th de2 cr eases g radually at the initial st age of f reeze2thaw cy cle and then incr eases g radually with the decr easing of w ater content ; ( 2) during the pr ocess o f fr eeze2thaw cycle, t he vo lume chang e of no n2ex pansiv e clay appears as " fr ost heav ing and thaw collap2 sing ", while the v olume chang e of ex pansive cla y appears as " fr ost shr inking and thaw ex panding "; ( 3) the var iatio n o f dr y den2 sit y does no t aff ect the shear str eng th and volume chang e of clay, and the ex pansiv e clay w ith higher dry density has smaller fi2 nal volume shrinkage; and ( 4) the shear strength of ex pansive clay w ith w at er retentio n measur e decreases g radually at the fir st three freeze2t haw cycles, then tends to be stable, and its final v olume is not affected by dr ying shr inkage. 中央高校基本科研业务费专项资金( 2014B36614)