土中结合水对红黏土抗剪强度特性的影响机制

通过室内红黏土试样的直剪试验和等温吸附试验,探讨了含水量对红黏土抗剪强度的影响,并对红黏土中吸附结合水含量和类型进行了测定和划分,阐释了结合水影响红黏土强度特性的微观机制。结果表明:(1)红黏土吸附曲线可分为稳定吸附阶段(RH<0.908,此阶段主要吸附强结合水),强吸附阶段(RH=(0.908, 0.976),这一阶段主要吸附弱结合水),吸附平衡阶段(RH>0.976);(2)红黏土的抗剪强度值与黏聚力均随含水量增加呈先增后减的趋势,且均存在临界含水量,R1和R2分别约为23.0%和12.0%(与各自的土中结合水总含量接近),内摩擦角则随含水量增加不断减小,呈一阶线性负相关;(3)红黏土强度的改变是土中各种微观作用力共同作用的结果,当土中吸附水主要为强结合水时,颗粒间的水膜连结力和胶结作用力增大,宏观表现为黏聚力增大,抗剪强度增大;(4)随着土中自由水的出现,结合水膜变厚,水膜连结力减弱,同时胶结作用也被破坏,黏聚力下降,抗剪强度减小。

Influence Mechanism of Bound Water on Shear Strength Characteristics of Lateritic Clay

To explore the effect of bound water on shear strength of lateritic clay, direct shear tests and isothermal adsorption of lateritic clay are conducted. The content and types of adsorbed bound water in lateritic clay are determined and classified, and the microscopic mechanism of the influence of bound water on the strength characteristics of lateritic clay is explained. The test results show that: (1) The isothermal adsorption curve of lateritic clay can be divided into three stages: the first stage (RH<0.908), the lateritic clay mainly absorbs strong bound water; the second stage (RH=(0.908,0.976)), it mainly absorbs loose bound water; the third stage (RH>0.976) is adsorption equilibrium stage. (2) The shear strength and cohesion of lateritic clay increase firstly and then decreased with the increase of water content, and the critical water content of R1 and R2 is about 23.0% and 12.0% (the "critical water content" is very close to the total content of adsorptive bound water in lateritic clay). The internal friction angle decreases with the increase of water content, showing a first-order linear negative correlation. (3) The change of lateritic clay strength is the result of various micro forces in the soil. When the adsorbed water in lateritic clay is the strong bound water, the water film connecting force and the cementing force between the particles both increase, which is manifested as the increase of cohesion and shear strength in macro aspect. (4)With the emergence of free water in the soil, the bound water film becomes thicker, and the water film connection force is weakened. Meanwhile, the cementation is destroyed, resulting in a decrease in cohesion and shear strength.