Improving the structure and mechanical properties of loess by acid solutions – An experimental study

Abstract

The structure of loess is the primary cause of loess-related disasters, such as collapse, seismic subsidence, and liquefaction. To improve the pore structure of loess more effectively, chemical methods are preferred over conventional physical methods. It is found that acidic solutions can readily dissolve the salt crystal cement composed of CaCO3 and other soluble salts in loess, thereby easily and thoroughly destroying the macropores of loess and resulting in a new, superior structure with improved mechanical properties. A series of laboratory tests was performed to investigate and compare the structural and mechanical properties of natural collapsible loess and loess treated with acid (LTA). Scanning electron microscopy (SEM) analysis revealed that the well-spaced granules with point contacts of natural loess were transformed into cemented interlocking amorphous grain modes in LTA. Compression and collapsibility tests proved that the pore structure of the loess was easily destroyed and improved by the addition of an acid solution, and the resulting LTA was more resistant to single and multiple collapse events than the natural loess. Static triaxial tests confirmed that the enhancement of the original cohesion force and curing cohesion force among soil particles improved the shear strength of LTA. Dynamic triaxial tests showed that, because of a lower void ratio (e) than the natural loess, LTA had a better seismic performance as well as a lower likelihood of liquefaction. The new acid-addition presoaking method is shown effective in improving mechanical properties of loess. The implication of this finding is significant for the construction in the loess deposits. The results also provide a valuable reference for studies on construction in loess polluted with acidic wastewater.