Pore characteristics and micro-structure change of undisturbed loess induced by acid corrosion

Abstract

With the rapid development of coal chemical base and urbanization construction in China's Loess Plateau, the phenomenon of acid corrosion induced loess geological disasters tends to occur frequently in this region. Loess is characterized by high water sensitivity, dense vertical joint surface, and rich in carbonate minerals, which providing a good precondition for acid solution corrosion. Due to the occurrence of chemical erosion, the changes of loess structure and strength become more complex, and there is a significant difference from the conventional water infiltration-induced loess disasters. In order to clearly grasp the internal mineral and structural damage characteristics of loess under acid dissolution conditions, this work studies the pore characteristics and micro-structure change of undisturbed loess under acid corrosion conditions with different pH values (7, 5 and 3) and dissolution times (5,10 and 15 days). It is found that the content of carbonate minerals in the undisturbed loess,and the combined structure characteristics are the two main factors affecting its acid corrosion effect. Specific findings include as: (1) With the decrease of pH, the dissolution of carbonate minerals such as calcite and dolomite intensifies (the element content of the precipitate: Ca96.58%, Mg1.26%), and the selective dissolution of silicate minerals (albite and chlorite) are obvious, which provides expansion space for pores. As a result, the change of the pore structure of undisturbed loess by acid leaching is as follows: Expansion of initial joints→Connectivity and enlargement of internal pores→The increase of new shallow pores. Meanwhile, under the action of acid dissolution, the cohesive substances were rearranged due to the dissolution, disintegration and rotation of the skeleton particles during the collapse, resulting in an increasing in the content of fine particles in the soil. (2) With the increase of corrosion time, the roundness increased from 7.19 to 25.98 which proves that the contact between the acid solution and mineral particles is more complete, and the effect of corrosion and particle aggregation is more significant. This results in a reciprocating unidirectional development of the pore structure. Flocculated particles with clay properties appear alternately in the soil structure. (3)The occurrence of acid-sensitive geological disasters in loess is mainly divided into three stages: The filling of the structural surface is eroded by acid→The horizontal and vertical erosion is intensify→The soil is broken down into particles that are washed away. This study has a certain reference for understanding the damage mechanism and early warning of loess eroded by acid solution in China's Loess Plateau.