高温作用对黏土抗剪性能影响及其机理分析

Effect of high temperature on clay shear strength and mechanism analysis

为了研究高温作用对黏土抗剪性能的影响,采用高温炉对土体加热至105℃、200℃、300℃、400℃、500℃和600℃,待冷却后重塑制样,通过三轴剪切试验、成分分析测试、粒度分布测试和扫描电镜观察等手段获得抗剪性能指标及其影响机理。研究表明:105℃与200℃处理土体抗剪性能指标基本不变。200℃后处理的黏土重塑样初始切线模量随着温度增大始终增大。当温度由400℃升高至500℃时,应力-应变关系由硬化型转变为软化型。土体黏聚力c值随温度升高先减小后增大,400℃是黏聚力最低值温度。c值降低阶段是由高温作用下土中有机质降解、矿物成分脱水所致,增大阶段是由于高温作用后土粒咬合作用加剧形成表观黏聚力。土体内摩擦角φ值随温度升高而增大(>200℃),分析认为是与高温作用后土粒表面的粗糙程度和土粒咬合作用加剧相关。微观试验表明:105℃土体中具有絮凝结构。400℃土体粒间胶结作用不明显,土粒连接方式由面-面形式过渡到边-边与边-面形式。500℃与600℃土体孔隙减少,土粒间结合更为紧密。

To explore the effects of high temperature on properties and shear strength index of clay,triaxial samples are remolded by clay after being heated at 105℃,200℃,300℃,400℃,500℃and 600℃.Then a series of experiments are carried out to investigate the variation of shear strength index of samples,including triaxial test,component analysis test,particle size distribution analysis and SEM test.The results show that,the shear indexes are basically unchanged at 105℃and 200℃,and the initial tangent modulus always increases after 200℃.The stress-strain relation changes from hardening to softening as the temperature increases from 400℃to 500℃;c value decreases from 200℃to 400℃and increases from 400℃to 600℃.The decrease of c value is mainly caused by the degradation of hydrophilic organic matter and mineral dehydration.The increase of c value is related to the intensification of intergranular bite due to the increase of expected particle size after high temperature.φvalue always increases with the temperature(>200℃)due to the increase of expected particle size caused by the effect of temperature and enhancement of roughness on the surface.SEM test shows that the soil at 105℃has a flocculating structure,and the cementation between the grains is not obvious after 400℃.The connection mode between the grains is transferred from the face-surface to the edge-to-edge form.The soil porosity decreases and the soil particles are more compact at 500℃and 600℃.