干湿循环下红砂岩改良土抗剪强度特性试验研究

Research on the Shear Strength Characteristics of Red Sandstone Improved Soil under Drying and Wetting Cycles

红砂岩路基在压实致密时具有良好的路用性能,但受干湿循环效应影响,路基强度劣化特性显著。以红砂岩改良土为研究对象,开展了1~7次干湿循环试验,通过直接剪切试验,分析了干湿循环条件下增湿过程中红砂岩改良土剪切强度的劣化特性。(1)红砂岩改良土的峰值强度、抗剪强度损失随着含水率增大而减小。(2)随着干湿循环次数的增加,红砂岩改良土呈现出脆性破坏向塑性破坏发展的趋势。增湿过程中试件的破坏类型也逐渐由脆性破坏过渡到塑性破坏;而且随着正应力增大,试样应变硬化的趋势愈发显著。(3)低压实度条件下,试样的脆性破坏特征比高压实度时更明显。(4)剪切试验表明,试件的剪切破坏面形状与增湿和脱湿过程中水分迁移路径紧密相关。(5)SEM图像表明红砂岩改良土内部结构为复杂的“骨架-空隙”结构,是典型的非饱和土。随着干湿循环次数的增加,孔隙率和圆形度增大,导致土体抗剪强度和抗剪强度参数(黏聚力c和内摩擦角φ)劣化。

Red sandstone subgrade has good road performance when being compacted,but the strength deterioration of subgrade is remarkable due to the influence of drying and wetting cycle effect.In this paper,1-7 drying and wetting cycle tests are carried out by taking red sandstone improved soil as the research object.Through direct shear tests,the deterioration characteristics of the shear strength of the red sandstone improved soil during the humidification process under the condition of drying and wetting cycle are analyzed.The results are as follows:(1)the peak strength and shear strength loss of the red sandstone improved soil decrease with the increase of water content.(2)With the increase of the number of drying and wetting cycles,the red sandstone improved soil presents a development trend from brittle failure to plastic failure.In the process of humidification,the failure type of the specimen gradually transits from brittle failure to plastic failure.Moreover,with the increase of normal stress,the trend of strain hardening of samples becomes more obvious.(3)The brittle failure characteristics of the specimen under low pressure compactness are more obvious than those under high pressure compactness.(4)The shear test shows that the shape of the shear failure surface of the specimen is closely related to the water migration path during humidification and dehumidification.(5)SEM images show that the internal structure of red sandstone improved soil is a complex"skeleton-void"structure,which is a typical unsaturated soil.With the increase of drying and wetting cycles,porosity and roundness are increased,which leads to the deterioration of soil shear strength and shear strength parameter(cohesion c and internal friction angleφ).