Disintegration and strength weakening characteristics of red-bed soft rock in the Shengzhou-Xinchang area under dry-wet cycles
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摘要:
红层软岩遇水易崩解并造成其强度弱化，在边坡工程建设中易造成其稳定性弱，导致经济损失，甚至人员伤亡。揭示红层软岩干湿循环作用下黏聚力与内摩擦角的变化特征对于针对性设计边坡处理措施具有重要意义。以浙江嵊州-新昌地区下白垩统朝川组3组红层软岩为研究对象，通过干湿循环试验、崩解岩块点荷载强度试验和崩解颗粒直剪试验研究了红层软岩崩解及强度弱化特性。结果表明：试样在干湿循环作用下呈碎块状-粒渣状-泥糊状依次崩解的形态，其主要崩解过程可分为初始崩解、快速崩解、细微再崩解和崩解稳定4个阶段；试样的点荷载强度
I s(50)随干湿循环次数的增加而降低，耐崩解指数I dn 与点荷载强度I s(50)呈正指数关系，试样的点荷载强度I s(50)在耐崩解指数I dn 为80%~100%之间急速弱化，在耐崩解指数I dn 为50%~80%之间表现缓慢弱化特性；试样的峰值抗剪强度介于0.567~1.219 MPa之间，其多发生在剪切位移3 mm前后，同组试样在相同轴压下，峰值抗剪强度随循环次数的增加而减小，试样崩解颗粒内摩擦角在22.28°~33.03°之间，黏聚力在0.46~0.74 MPa之间。试样的摩擦角和黏聚力随着干湿循环次数增加，都呈负指数关系。试验结果表明砂质比泥质胶结的耐崩解性更好，黏土矿物高的岩石更容易崩解，而"白色矿物"钠长石的吸水膨胀能力远不及黏土矿物，其含量差异对耐崩解性的影响不及黏土矿物。Abstract:Objective The red-bed soft rocks is easy to disintegrate and weaken its strength when it encounters water, which is easy to cause poor stability and economic loss or even casualties in slope construction. It is of great significance to reveal the variation characteristics of cohesion and internal friction angle of red-bed soft rocks under the action of dry and wet cycling for the design of slope treatment measures.
Methods Investigating the three groups of red-bed soft rock formations within the Lower Cretaceous Chaochuan Formation situated in the Shengzhou-Xinchang region of Zhejiang Province, this study delves into the disintegration and strength attention tendencies inherent in these formations. This exploration unfolds through a comprehensive suite of method ologies, including dry-wet cycle tests, point load strength tests of disintegrated rock blocks and direct shear tests of disintegrated particles.
Results The results reveal that the sample undergoes disintegrates, in the form of fragments, particle slag, and mud paste due to successive dry-wet cycles. The main disintegration process can be divided into four distinct stages: Initial disintegration, rapid disintegration, fine reconfiguration, and eventual stabilization. The point load strength of the sample decreases with the increase as the number of dry-wet cycles increases, while the disintegration resistance index
I dn shows a positive exponential relationship with the point load strengthI s(50). Notably, the point load strengthI s(50) of the sample experiences rapid weakening between 80% to 100% and 50% to 80% of the disintegration resistance indexI dn, demonstrating gradual attenuation characteristics. The peak shear strength of the sample ranges between 1.219 MPa and 0.567 MPa, which mostly occurs before and after the shear displacement of 3 mm. Under the consistent axial pressure, the peak shear strength of the same group decreases with an increasing number of cycles. Additionally, the internal friction angle of disintegrated particles of the sample ranges from 22.28° to 33.03°, while the cohesion is between 0.46 MPa and 0.74 MPa. Both the friction angle and cohesion of the sample show a negative exponential relationship with the number of dry-wet cycles.Conclusion The test results indicate that siliceous cementation exhibits better disintegration resistance compared to argillaceous cementation, and the rock with high clay minerals more easily disintegrates. Additionally, the water absorption and expansion capacity of "white mineral" albite significantly lag behind that of clay minerals, with a lesser variance in its content compared to clay minerals.
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图 3 3组崩解物各粒径百分比随干湿循环次数的变化曲线
Figure 3. Variation curve of the percentage content of each particle size of disintegration with the number of dry-wet cycles
图 4 耐崩解指数随干湿循环次数的变化曲线
Figure 4. Variation curve of disintegration resistance index with the number of dry-wet cycles
图 5 点荷载强度指数随干湿循环次数的变化曲线
Figure 5. Change curve of the modified point load strength index with the number of dry-wet cycles
图 6 点荷载强度指数与耐崩解指数的关系曲线
Figure 6. Relation curve between point load strength and disintegration resistance index
图 7 试样在不同轴压下第8，12，16，20次干湿循环后试样剪切应力-位移曲线
Figure 7. Shear stress displacement curves of the sample after the 8, 12, 16, 20 th dry-wet cycles under different axial pressures
图 8 试样在不同干湿循环条件下试样抗剪强度随轴向压力变化的关系曲线
Figure 8. Relationship curves of shear strength with axial pressure under different dry-wet cycles
图 9 试样内摩擦角(a)和黏聚力(b)随干湿循环次数的变化曲线
Figure 9. Variation curve of the internal friction angle (a) and cohesion (b) of the sample with the number of dry-wet cycles
表 1 岩样矿物成分
Table 1. Mineral composition of the rock samples
岩样编号 蒙脱石 伊利石 石英 钠长石 方解石 微斜长石 赤铁矿 绿泥石 胶结物 φB/% A组 21.98 22.05 21.73 10.7 14.08 8.5 0.96 — 泥质为主，少量砂质 B组 18.52 15.81 22.32 24.31 8.71 10.33 — — 泥质为主，少量砂质 C组 9.98 14.4 51.28 10.57 11.58 — 2.2 砂质为主，泥质次之 
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表 2 拟合曲线参数
Table 2. Fitting curve parameters
回归方程 $ y=y_0+A\left[\frac{p}{1+e^{\left(x-x_{01}\right) / k_1}}+\frac{1-p}{1+e^{\left(x-x_{02}\right) / k_2}}\right]$ 岩样分组 A B C y0 0.111 4 6.521 7 10.439 6 A 107.652 1 94.419 0 92.480 3 P 0.631 5 0.908 5 0.792 1 x01 7.006 1 8.221 1 8.588 4 x02 5.644 9 2.506 3 9.185 1 k1 1.023 5 1.400 8 2.641 2 k2 3.920 7 1.022 8 0.930 1 R2 0.999 9 0.999 5 0.999 9
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