Abstract：An ancient relics near ground surface rock cavern group was found in Longyou County，Zhejiang Province. The 24 large caverns were excavated 2 000 years ago. The finding of the Longyou Grottoes attracts the attentions of the scholars in the world. Researches have been done to find out the characters and the structures of the mineral in sandstone clay，i.e. montmorillonite in the Longyou Grottoes，to learn the different solubilities of different minerals，to measure the surface area of the rock meeting the water(namely，the porosity ratio)，and to find out the chemical character of the water which has the action on the rock so as to prove the caves under the water to be comparatively stable. Based on the analysis of the mineral composition，the clay minerals in bonded clay，the surface water and the seepage at Longyou Grottoes in Zhejiang Province，the researches on weathering rate of sandstone immersed by different salting liquids in sequence are carried out. The saturated solutions of sodium chloride and sodium sulfate are prepared as contrasts to the distilled water to immerse the sandstone samples that are subjected to certain cycles of immersion and drying. The elastic wave velocity is obtained each time when the sandstone is dried. The weathering rate is proved to be in good correlation with the decrease of elastic wave velocity.
