INFLUENCE OF MICRO-ENVIRONMENT TO PELITIC SILTSTONE AS SURROUNDING ROCK OF LONGYOU UNDERGROUND CAVERNS

Five complete caverns were un-watered and discovered in Longyou in June 1992. They were manually caved in siltstone at shallow depths more than 2000 years ago. As time goes on,weathering of the surrounding rock of the caverns is increasing severely. The fact that the weathering degree of the surrounding rock nearby the entrance of the No.2 cavern is more serious than that inside the No.2 cavern are explained with the weathering difference of the pelitic siltstone due the difference in the micro-environments. The depths of the chisel marks of the surrounding rock nearby the entrance and inside the cavern No.2 were measured using plasticene. The corresponding curves of chisel mark depths were obtained. According to the measured results,the mean values of the maximum high recession and the maximum fluctuation ratio of the chisel marks inside the cavern is 10.2 mm and 0.43 respectively. The corresponding values of the chisel mark nearby the entrance are smaller. Their mean values are 8.0 mm and 0.35 respectively. The above values indicate that the weathering degree of chisel marks nearby the entrance are larger than that inside the cavern. It is believed that the above difference in the weathering degree is caused by different weathering micro-environments which mainly include rain,temperature,illumination intensity and lichen in the surrounding rock nearby the entrance and inside the cavern.