Study on the Influence of Mineral Evolution on Structural Strength of Loess During Collapsibility

With the implementation of the western development strategy, the continuous promotion of the transportation strategy, the construction and operation of a series of high-speed railroad projects, such as the Yinxi High-speed Railway and the Yinlan Railway, higher requirements have been put forward for the engineering and construction technology in loess areas. To study the variation rule of the mineral composition evolution on the structural strength influence situation with time in the process of loess wet subsidence. The test results show that the structural strength of loess will be obviously reduced after being exposed to water, which can be divided into three stages of steep decline, slow decline and slow rise in different time. The change of mineral composition of loess from the beginning of water immersion to 24 h is mainly the dissolution of easily soluble salts, and the structural strength decreases rapidly; from 24 h to 336 h, the dissolved encapsulated colloidal particles slip and fill in between the skeleton particles, and the structural strength decreases slowly. From 336 h to 672 h within the influence of feldspar hydration, the structural strength rises slowly and the microstructure is gradually stabilized. The structural strength was power function correlated with the change of calcite content from the beginning to 168 h. The microstructural observation shows that the pore structure shows a change process from destabilization to stabilization. It can be seen that the evolution of loess mineral composition and loess structural strength show consistency, and the microstructure shows salt dissolution and regular changes in particle size and pore space, and mineral hydration and dissolution is an important reason for the change of loess structural strength.