中文摘要：

龙游石窟1-5号洞室群几百年来一直处于水下，1992年首次被抽干水用于开发旅游。由于抽水前后环境的强烈改变，以及洞内干湿交替明显，所以洞室围岩风化和破坏都十分严重。其中，本文所讨论的3号洞第3－2号岩柱就是已发生严重开裂，并亟待加固。为对该岩柱的加固提供科学依据，需准确把握变形破坏发展情况和据此研究它的变形破坏机理。为此，作者采用JSYCB-73系列电感式测缝仪和钢尺等手段对岩柱开裂的宽度和长度进行监测。根据监测所取得的大量数据和地质条件，对该岩柱的开裂机理进行了分析，得出了以下结论：（1）用来加固邻区的混凝土喷层的重力部分转移到该岩柱上，从而增加了荷载；（2）由于洞内渗水严重、干湿交替、温差变化较大等使风化作用加大。结果，导致该岩柱的强度降低。（3）该岩柱强度的降低和所施加荷载的增加等两个因素最终导致了岩柱被压裂。根据上述研究结论，并考虑文物保护和旅游的需要，提出了治水、地表卸荷、岩柱加锚、加箍等加固措施。加固后的监测数据表明，开裂已不再发展，岩柱已处于稳定

英文摘要：

The caverns No. 1 to No. 5 of Longyou cavern group had been fully filled with water for many hundreds years. In 1992, the water was pumped out d for tourism. Because of the dramtic changes of the condition and the alternation bettween drying and wetting, the rock mass weathering and the damages have been substantial. Such as, the rock pillar No. 3-2 of the cavern No. 3 has developed many cracks. This pillar has to be reinforced immediately. To provide the basis for the pillar reinforcement, it is needed to fully understand the situation of the deformation development in the pillar. This paper presents the monitoring results of the widths and the lengths of the cracks with the jointmeters of JSYCB-73 series and steel ruler. On the basic of the data obtained from the monitoring and the geology conditions, this paper further analyzes the causes of the cracking. The following findings are obtained： （1） part of the weights of concrete materials that are used to reinforce the other part of the cavern increased the load on the pillar;（2） the leakage of the cavern, the alternation bettween drying and wetting and the changes of the temperature enlarged the weathering, which reduced the pillar strength;（3） the two above factors made the growth of cracks in the pillar. Based on the findings, taking into account the cultural relics and the tourism, this paper suggests the protection measures. They include the water-control, unloading the load, installing rock bolts and hoops. The monitored data after the pillar reinforcments show that the cracks has stopped developping,and the pillar has been stable.