基于微震监测的大岗山水电站高拱坝廊道裂缝形成原因研究

Study on formation causes of gallery cracks in Dagangshan high arch dam based on microseismic monitoring

针对大岗山水电站高拱坝廊道顶拱在蓄水前出现了多条深层裂缝的现象,通过构建的高拱坝微震监测系统,对蓄水前后979 m高程交通廊道、940 m高程基础廊道和937 m高程排水廊道产生的微破裂信息进行分析,再现混凝土拱坝廊道裂缝产生的演化过程,研究廊道裂缝形成的真正原因。结果表明:大岗山高拱坝廊道微震活动性与坝前库水位具有明显的相关性。蓄水前,大岗山高拱坝坝踵区廊道顶拱微震活动性较强,超过廊道顶拱开裂阈值,诱发顶拱产生横河向裂缝。蓄水后,随着库水位的升高,坝踵区廊道裂缝趋于稳定,而坝趾区廊道呈现开裂的趋势。揭示大岗山水电站蓄水过程中,拱坝廊道开裂有由坝踵向坝趾转移的趋势。建议蓄水期阶段应密切关注拱坝坝趾区混凝土的损伤情况。

Multiple deep cracks appeared at the top arch of galleries in Dagangshan high arch dam before the impoundment. Cracking characteristic around the access gallery at E.L. 979 m,foundation gallery at E.L. 940 m and drainage gallery at E.L. 937 m before and after the impoundment was analyzed using the installed microseismic monitoring system in the high arch dam. The process of crack inducement was reproduced and the real cause of cracking in galleries was studied. The results show that the microseismic activities in galleries are significantly coherent to the water level. Before the impoundment,the microseismicity of the gallery top arch of dam heel area was strong which exceeds its cracking limit,thus inducing gallery cracks in the cross sections of river. After the impoundment,with the rising of water level,the gallery cracks in the area of arch dam heel tends to be stable while galleries in arch dam toe area tend to crack. The trend of the cracking which transferrs from the dam heel area to the dam toe aera during the impoundment process was revealed. It is recommended to keep a close eye on the damage conditions of concrete in arch dam toe area during the impoundment period.