Exploring the geochemical mechanism for the saturated permeability change of remolded loess

Abstract

Abstract Loess has been remolded as the foundation for various construction projects with a long period of history. However, the operation of loess construction engineering is affected by the continuous change of loess permeability during the seepage. Physical processes have been found to be responsible for the change of permeability, while neglecting the geochemical processes. In this study, the saturated seepage test was carried out, and the inverse geochemical model based on the PHREEQC software was established for better understanding the change in the saturated permeability of remolded loess and its underlying geochemical mechanism. Results show a negative log correlation of the mean saturated hydraulic conductivity (Ksat) with the dry density of the loess samples. The Ksat of the samples with various dry densities increases with the seepage time as a whole. Taking the loess sample with dry density of 1.45 g·cm−3 as an example, the time dependent change of Ksat can be divided into two stages: relatively stable type in the early stage and significantly increasing type in the later stage. The relatively stable permeability is due to the comprehensive effect of the dissolution of halite, gypsum, and dolomite, the precipitation of calcite, and ion exchange. Dissolution of calcite and dolomite is responsible for the increasing tendency of the permeability of the remolded loess. The cation exchange and the reaction of the clay minerals also need to be considered. In general, the carbonate leaching is the dominant factor for the increase in the saturated permeability of remolded loess. Secondly, the cation exchange and the reaction of the clay minerals lead to the change of the saturated permeability by influencing the enlargement of pore space.