酸性溶液浸泡下原状黄土物理力学特性试验研究

Experimental study on physico-mechanical characteristics of undisturbed loess soaked in acid solution

黄土中存在大量碳酸钙胶结物,该胶结物对黄土力学性状的影响很大。采用浓度为0.1,1和2 mol/L的盐酸溶液,开展了原状黄土试样的浸泡试验,测定了不同时间浸泡溶液中钙离子的浓度,开展了经不同时间浸泡土样的颗粒分析试验、固结试验及剪切试验,分析了酸性溶液浸泡下原状黄土力学特性及其变化规律。试验表明:黄土中胶结物主要是以粒径小于0.01 mm的颗粒存在,在酸性溶液浸泡作用下,土中钙质胶结物逐渐被溶蚀,试样中细小颗粒逐渐减少,尤其是颗粒直径小于0.005 mm的含量明显减少,浸泡液酸性越强,土体中钙质胶结物溶蚀的速度越快并且溶蚀得越充分。胶结物在土体中的作用主要是连接骨架颗粒,因此,胶结物对土体的黏聚力影响较大,而土体内摩擦角受胶结物溶蚀的影响不明显。经盐酸溶液浸泡后,试样的黏聚力随浸泡时间延长持续降低,浸泡60 d后,土体的黏聚力逐步趋于稳定。经0.1,1,2 mol/L盐酸溶液浸泡120 d后,试样的黏聚力分别降低约47%,63%,87%,且呈现出浸泡液酸性越强,黏聚力减少越多的情形。胶结物的溶蚀引起土体孔隙增加,压缩系数增大。随着胶结物的减少,土体的快剪应力–应变关系逐渐由应变硬化型向应变软化型转变。

There are a lot of calcium carbonate cementations in natural loess,and the cementations have significant influence on the mechanical properties of loess.The undisturbed natural loess samples are immersed into the hydrochloric acid solutions with concentrations of 0.1,1 and 2 mol/L,respectively.The concentrations of calcium ions in soaking solution are measured at different time.The particle size analysis tests,oedometer tests and direct shear tests are used to study the mechanical properties and their variations of loess samples soaked in the hydrochloric acid solution for different time.The results show that the particle sizes of the cementations in the loess are mainly smaller than 0.01 mm.Under the action of acid solution,the calcareous cementations are gradually dissolved when soaked in hydrochloric solution.The small particles are gradually reduced,especially the percentage by weight of particles smaller than 0.005 mm is significantly reduced.With the higher acidity of the hydrochloric solution,the viscosity of dissolution is faster and the dissolution is fuller.The cementations in soils play the role of connecting particles in soil skeleton;therefore,the cementations have significant influence on the soil cohesion,while the effect of soil friction angle by the cementations is not obvious.The cohesion of samples decreases with the increase of the soaking time in hydrochloric solution,and it is gradually stabilized after being soaked for 60 d.The cohesion of samples decreases by about 47%,63%,87% after being soaked in hydrochloric acid solution with concentrations of 0.1,1,2 mol/L for 120 d,respectively.It is found that the more decrease of soil cohesion,the higher acidity of the solution.The porosity and the compression coefficient of soils increase with the erosion of calcareous cementations.With the decrease of calcareous cementations,the relationship curves of stress and strain of the loess change gradually from strain hardening type to strain softening one.