冻融及加卸荷条件下川藏交通廊道典型岩石力学特性的劣化规律

Degradation Law of Mechanical Properties of Typical Rock in Sichuan-Tibet Traffic Corridor under Freeze-Thaw and Unloading Conditions

为了探究川藏交通廊道沿线典型岩石冻融循环条件下的劣化规律,选取昌都-林芝段的花岗岩、片麻岩和砂岩为试验对象,开展冻融循环条件下岩石加卸荷试验,结果表明:(1)随着冻融循环次数的增加,岩石抗压强度损失率达30%,粘聚力降幅达18.4%,内摩擦角降幅达10.5%,弹性模量逐渐下降,泊松比逐渐增加;(2)三轴压缩试验中,岩样的变形模量呈现与抗压强度类似的劣化趋势,但是变形模量的劣化幅度比抗压强度劣化幅度大;冻融循环作用下岩石抗压强度越大劣化程度越低,对砂岩的劣化最明显,片麻岩次之,花岗岩最小;(3)与三轴压缩试验相比,在卸围压试验中,冻融循环作用对岩石的卸荷量同样有劣化作用,卸荷程度较小时岩石劣化并不明显,随着卸荷量的逐渐增加,卸荷量大于80%时,岩石的变形模量呈指数型下降,泊松比呈指数型增加;(4)随着冻融循环次数的增加,三轴压缩试验中由拉张和剪切破坏造成的裂纹数量增多;卸围压试验中岩石以拉张破坏为主;岩石微裂纹数量增加的同时,不平整度增加,矿物颗粒之间的胶结状态变差;(5)综合试验结果分析,冻融作用对岩石劣化作用最强的为砂岩,其次是片麻岩,最弱为花岗岩.

In order to explore the degradation law of typical rock along Sichuan-Tibet traffic corridor under freeze-thaw cycles,granite,gneiss and sandstone of Changdu-Linzhi section of Sichuan-Tibet traffic corridor were selected as the test objects,and the loading and unloading tests of rock with different freeze-thaw cycles were carried out.The results show follows:(1) With the increase of freeze-thaw cycles,the loss rate of rock compressive strength is 30%,the cohesion decreases by 18.4%,the internal friction angle decreases by 10.5%,the elastic modulus decreases gradually,and the Poisson’s ratio increases gradually.(2) In triaxial compression test,the deformation modulus of rock sample presents the degradation law similar to compressive strength.Freeze-thaw action has the most obvious degradation effect on sandstone,followed by gneiss and granite,which is proportional to the compressive strength of rock,and the degradation range of deformation modulus is larger than that of compressive strength.(3)Compared with compression test,in unloading confining pressure test,freeze-thaw cycle also has degradation effect on unloading amount of rock,and the rock degradation is not obvious when the unloading degree is small.With the gradual increase of unloading amount,when the unloading amount is greater than 80%,the deformation modulus of rock decreases exponentially and the Poisson’s ratio increases exponentially.(4) With the increase of freeze-thaw cycles,the number of cracks caused by tensile and shear failure increases in triaxial compression tests.The rock of unloading confining pressure test is mainly tensile failure.When the number of micro-cracks increases,the degree of irregularity increases,and the cementation state between mineral particles becomes worse.(5) According to the comprehensive test results,freeze-thaw action has the strongest deterioration effect on sandstone,followed by gneiss,and the weakest is granite.