Abstract: Geothermal energy is the development trend of green building. However, it is not clear about the relationship between the problems of building foundation impairment and the geothermal system in red-layer soft rock areas. Based on an accident investigation project of building clusters in Chengdu, the engineering characteristics of mudstone and gypsum rock with or without geothermal system were studied, and the macro-mechanical and micro-structural characteristics of rock under different heating methods, different temperatures and different soaking times were studied as well. The results show that: 1) At the same site, there is little influence of geothermal system on rock mechanical properties, but when geothermal system is in place, the number of fissures and the cumulative opening has an obvious increase. 2) With the increase of soaking time, the maximum water content of mudstone can reach more than 30%, the water content of gypsum can not exceed 15%, the water softening effect of mudstone is more obvious than that of gypsum, and the mechanical index of mudstone decreases with the increase of water content. 3) In the natural state, the gypsum rock is brittle and the mudstone is ductile; the water-rock interface of the gypsum rock has a significant effect of dissolution, and the dissolution of the gypsum rock is intensified from the surface to the interior. 4) In the temperature ranges from 20 °C to 50 °C, the compressive strength of gypsum rock parabolically changes with temperature, while that of mudstone monotonously increases. 5) The loose filling between geothermal pipe and rock mass is easy to form seepage pathway and change the hydrodynamic condition. Under the action of flowing water, the rock mass at the crack of gypsum rock and the weak interlayer dissolves, forming big cavity and inducing building subsidence.

Key words: mud-stone, gypsum rock, geothermal system, experimental study, building subsidence