Experimental Study on Strength and Deformation Characteristics of Red-Bed Soil-Rock Mixture Under Wetting-Drying Cycles
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摘要:
为研究干湿循环下红层土石混合料的劣化规律，以取自四川盆地的红层土石混合料为研究对象，通过静态崩解试验，探讨不同粒径红层软岩块石的崩解特征；对2组红层土石混合路基填料原始级配缩尺，通过叠环式剪切试验，研究干湿循环次数对红层土石混合料黏聚力、内摩擦角、剪胀率和剪切模量等指标的影响. 研究结果表明：红层软岩块石遇水崩解显著，崩解过程可分为剧烈段、过渡段和稳定段，崩解剧烈段块石含量降低近70%；粒径较大时，块石受结构面影响更强，崩解更彻底；随干湿循环次数的增加，抗剪强度在崩解剧烈段明显降低，过渡段基本不变，稳定段略有回升；块石崩解后，其咬合作用显著降低，表观黏聚力急剧减小，静电引力和固化胶结使黏聚力轻微增大，崩解物间的摩擦和重定向排列使内摩擦角轻微增大；最大粒径和含石量显著降低，法向应力下土石混合料更密实，剪胀率明显降低；骨架-密实结构转变为悬浮-密实结构，剪切模量明显降低；干湿循环下黏聚力和剪胀率劣化更明显，内摩擦角的劣化受块石粒径影响最大，剪切模量的劣化受块石粒径影响最小；路堤填筑前，对红层土石混合料进行2次崩解处理，以削弱其受降雨-蒸发循环作用的不利影响.
Abstract:In order to study the deterioration law of the red-bed soil-rock mixture (RB-SRM) under wetting-drying cycles, the RB-SRM in Sichuan Basin was considered as the research object. The disintegration characteristics of red-bed soft rock blocks with different particle sizes were discussed through static disintegration tests. The original gradation scale of two groups of red-bed soil-rock mixed subgrade fillers was studied. The effects of wetting-drying cycle times on the cohesion, internal friction angle, dilation rate, and shear modulus of RB-SRM were studied by the laminated shear test. The results show that the red-bed soft rock block disintegrates significantly in water, and the disintegration process can be divided into the severe stage, transitional stage, and stable stage. The content of the disintegrated rock block in the severe stage is reduced by nearly 70%; for rock block with a larger particle size, it is more affected by the structural plane, and the disintegration is more significant. With the increase in the number of wetting-drying cycles, the shear strength is significantly reduced in the severe stage, while that in the transitional stage is basically unchanged and slightly recovered in the stable stage. After the disintegration of the rock block, the interlocking is significantly reduced; the apparent adhesion is sharply reduced, and the electrostatic attraction and the curing cementation slightly increase the cohesion. The friction and the redirection arrangement among the disintegrated RB-SRM slightly improve the internal friction angle. The maximum particle size and content of rock blocks are significantly reduced so that the RB-SRM is denser, and the dilation rate is significantly reduced under normal stress. Meanwhile, the skeleton-dense structure is transformed into a suspension-dense structure, and the shear modulus is significantly reduced. The degradation of cohesion and dilation rate under wetting-drying cycles is more obvious. The deterioration of the internal friction angle is mostly affected by the particle size of the blocks, and that of the shear modulus is least affected. Before embankment filling, it is suggested to disintegrate the RB-SRM twice to reduce the adverse effect of rainfall-evaporation cycles.
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图 1 红层土石混合料的各粒组土样
Figure 1. Soil samples of each particle group of red-bed soil-rock mixture （RB-SRM）
图 7 干湿循环下崩解物粒组含量变化曲线
Figure 7. Curves of the content of disintegrated RB-SRM with different particle sizes under wetting-drying cycles
图 9 干湿循环下归一化强度劣化曲线
Figure 9. Curves of normalized strength under wetting-drying cycles
图 10 干湿循环下红层土石混合料的强度机理
Figure 10. Strength mechanism of RB-SRM under wetting-drying cycles
图 11 干湿循环下强度指标水平中心梯度分布
Figure 11. Horizontal center gradient distribution of strength parameters under wetting-drying cycles
图 14 干湿循环下归一化力学效应指标分布曲线
Figure 14. Curves of normalized mechanical parameters under wetting-drying cycles
表 1 岩土体基本物理力学指标
Table 1. Basic physical and mechanical parameters of RB-SRM
类型 $\rho $/ （g•cm−3） w/% ${G_{\text{s}}}$ c/kPa φ/（°） ${\sigma _{\text{c}}}$/
MPa黏土 1.78 16.67 2.72 25.32 27.07 粉砂质泥岩 2.56 1.92 560.00 38.40 6.83 
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表 2 干湿循环下红层土石混合料叠环式剪切试验方案
Table 2. Laminated shear test scheme of RB-SRM under wetting-drying cycles
级配 试验组 n/次 法向应力${\sigma _{\text{n}}}$/kPa 级配 Ⅰ 1 0 100，200，400，800 2 1 100，200，400，800 3 2 100，200，400，800 4 4 100，200，400，800 5 6 100，200，400，800 级配 Ⅱ 6 0 100，200，400，800 7 1 100，200，400，800 8 2 100，200，400，800 9 4 100，200，400，800 10 6 100，200，400，800
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表 3 干湿循环下红层土石混合料的力学效应指标
Table 3. Mechanical parameters of RB-SRM under wetting-drying cycles
类型 n/次 c/kPa $\varphi $/（°） $\eta $ ${G_{{\text{0}}{\text{.02}}}}$/MPa 级配Ⅰ 0 94.87 21.24 −0.09 7.78 1 15.17 23.20 −0.15 6.06 2 25.55 20.79 −0.15 5.60 4 26.80 20.97 −0.15 5.29 6 27.17 23.24 −0.15 6.15 级配Ⅱ 0 74.85 30.56 −0.07 9.02 1 63.58 20.04 −0.12 6.75 2 67.53 19.37 −0.09 7.07 4 47.84 22.93 −0.12 6.60 6 51.96 24.01 −0.11 7.13
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