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

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.