Degradation Law of Mechanical Properties of Typical Rock in Sichuan-Tibet Traffic Corridor under Freeze-Thaw and Unloading Conditions
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摘要: 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.Abstract: 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.
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图 1 川藏交通廊道昌都-林芝段交通位置
Fig. 1. Traffic location map of Changdu-Linzhi section of Sichuan-Tibet traffic corridor
图 2 抗剪强度参数随冻融循环次数变化曲线
a.粘聚力变化趋势；b.内摩擦角变化趋势
Fig. 2. Curves of shear strength parameters versus freeze-thaw cycles
图 3 加载试验峰值强度随冻融循环次数变化曲线
a.花岗岩; b.片麻岩; c.砂岩
Fig. 3. Curves of peak strength of loading test changing with freezing-thaw cycles
图 4 不同冻融循环次数下花岗岩应力-应变曲线
Fig. 4. Stress-strain curves of granite under different freeze-thaw cycles
a.σ3=3 MPa; b.σ3=6 MPa; c.σ3=9 MPa
图 5 3 MPa围压下不同冻融循环次数下砂岩应力-应变曲线
Fig. 5. Stress-strain curves of sandstone under different freeze-thaw cycles under confining pressure of 3 MPa
图 6 花岗岩弹性模量(a)和泊松比(b)随冻融循环次数变化趋势
Fig. 6. Change trend of elastic modulus (a) and Poisson's ratio (b) of granite with freeze-thaw cycles
图 7 3 MPa围压下花岗岩试样破坏照片
Fig. 7. Failure photos of granite samples under 3 MPa confining pressure
图 8 3 MPa围压下片麻岩试样破坏照片
Fig. 8. Failure photos of gneiss specimens under confining pressure of 3 MPa
图 9 3 MPa围压下砂岩试样破坏照片
Fig. 9. Failure photos of sandstone samples under confining pressure of 3 MPa
图 10 花岗岩1 000倍下不同冻融次数下微观形貌
Fig. 10. Micro morphology of granite under different freeze-thaw cycles at 1 000 times
图 11 片麻岩1 000倍下不同冻融次数下微观形貌
Fig. 11. Micro morphology of gneiss under different freeze-thaw cycles at 1 000 times
图 12 砂岩3 500倍下不同冻融次数下微观形貌
Fig. 12. Micro morphology of sandstone under different freeze-thaw cycles at 3 500 times
图 13 卸围压试验破坏围压
a.花岗岩; b.片麻岩; c.砂岩
Fig. 13. Destruction confining pressure of unloading confining pressure test
图 14 花岗岩卸围压应力-应变曲线
Fig. 14. Stress-strain curves of unloading confining pressure of granite
图 16 花岗岩卸荷过程泊松比随卸荷量变化曲线
Fig. 16. Curves of Poisson's ratio versus unloading amount during unloading process of granite
图 17 砂岩试样卸围压试验破坏照片
Fig. 17. Failure photos of sandstone specimens under unloading confining pressure test
表 1 各岩石主要矿物成分
Table 1. Main mineral components of each rock
岩性 主要矿物 含量(%) 花岗岩 石英 83.2 方解石 3.2 高岭石 11.6 片麻岩 石英 34.6 钠长石 32.6 伊利石 31.5 砂岩 石英 12.1 钠长石 59.0 伊利石 25.8 
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表 2 各岩石含水率参数
Table 2. Water content parameters of each rock
岩性 花岗岩 片麻岩 砂岩 天然含水率（%） 1.6 1.5 2.8 饱和含水率(%) 3.1 3.8 5.1
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表 3 试验分组
Table 3. Test groups
试验方法 冻融循环次数(n) 岩组编号及数量 岩样规格(mm) 三轴压缩 0 A1(3个) 圆柱50×100 30 A2(3个) 60 A3(3个) 90 A4(3个) 卸围压 0 A5(3个) 30 A6(3个) 60 A7(3个) 90 A8(3个) 注：片麻岩、砂岩试验分组以B、C开头，试验分组类似.
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表 4 岩石的粘聚力和内摩擦角参数
Table 4. Parameters of rock cohesion and internal friction angle
岩性 参数 冻融循环次数(n) 0 30 60 90 花岗岩 粘聚力(MPa) 9.29 8.95 8.82 8.77 内摩擦角(°) 51.78 51.60 51.06 50.12 片麻岩 粘聚力(MPa) 11.56 8.73 9.36 9.43 内摩擦角(°) 49.37 51.24 48.86 45.58 砂岩 粘聚力(MPa) 11.41 11.28 10.07 9.88 内摩擦角(°) 57.54 55.39 54.40 51.50
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表 5 冻融后岩石的劣化度情况
Table 5. Degradation of rocks after freezing and thawing
破坏围压(MPa) 岩性 冻融循环n次后的劣化度(%) 30 60 90 3 花岗岩 3.0 6.3 10.9 片麻岩 12.4 15.8 26.0 砂岩 10.3 19.3 32.2 6 花岗岩 2.2 4.5 7.5 片麻岩 8.7 13.8 18.6 砂岩 9.2 17.9 22.5 9 花岗岩 2.3 5.5 10.1 片麻岩 5.0 11.9 23.5 砂岩 11.0 18.8 31.6
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表 6 各岩石卸围压试验破坏围压参数
Table 6. Failure confining pressure parameters of rock unloading confining pressure test
冻融循环次数(n) 0 30 60 90 初始围压(MPa) 3 6 9 3 6 9 3 6 9 3 6 9 破坏围压σd(MPa) 花岗岩 1.61 5.21 7.42 1.75 5.38 7.87 2.01 5.12 7.87 2.08 5.44 8.02 片麻岩 1.22 3.61 6.93 1.42 4.51 7.69 2.12 5.15 8.12 2.62 5.67 8.29 砂岩 1.70 4.21 7.66 2.03 4.51 7.94 2.13 5.23 8.09 2.62 5.64 8.51
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