Abstract:

       Pi-sandstone, a set of fluvial clastic rock, which is common in the Inner Mongolia, from Dongsheng to Zhungeer. And it is developed in the Triassic, Jurassic and Cretaceous periods. Pi-sandstone area, one of the main sources of coarse sediment of the Yellow River, is an intense erosion center in the middle reach of the Yellow River. This paper analyzes the impact of water on rock weathering and erosion through field investigation, sampling investigation and water-rock interaction modeling. The testing results of water samples collected from the rain water and spring water are simulated using inverse modeling based on PHREEQC software. The simulated results indicate that there are three main influences on Pi-sandstone caused by the water:(1)weaken the cohesion within the rock mass, and expand the porosity, for example, the dissolution of calcite, feldspar, dolomite, gypsum and halite makes rock porosity enlarge；(2)chemical corrosion takes place, causing feldspar and other minerals to be easily weathered into kaolinite and Ca-montmorillonite which expands the fissures of the rock;(3)the precipitation amount of Ca-montmorillonite is much, and its characteristic of expanding when meeting with water can increase the internal pressure. Water-rock interaction influences on the physical and mechanical properties of Pi-sandstone and intensifies the weathering and erosion of Pi-sandstone.

Key words: Pi-sandstone, lithology characteristic, water-rock interaction modeling, weathering and erosion, Inner Mongolia