黑洞大型古地下洞室群工程地质条件及岩体稳定性分析

位于浙江天台县蟹山山体内的黑洞洞室群, 以其优越的工程地质条件和完整的岩体结构, 自隋朝以来成为大型古地下采石场。洞室群包括总面积达24 000 m²的21个洞室, 其长轴方向基本沿两组主要地质结构面走向展布。研究显示:总体采石层系上白垩统塘上组(K₂t)第6层灰白色含玻屑熔结凝灰岩;岩体质量指标Q值计算结果为53(I级)。按现代地下洞室设计理念, 其长期稳定最大跨度应不大于50 m, 但实际上5号洞最大跨度达81 m, 可望成为地下人工岩石单洞跨度之最。现场调查发现, 古人在蟹山山脚残留多处地质探洞。古代工匠在洞室开挖过程中遇到断层破碎带时, 采用了近垂直、小断面、高台阶穿越技术方法, 有效保证了不良地质体中无支护开采的安全性和长期稳定性, 这对现代地下工程具有借鉴和工程类比意义。

Study of the Engineering Geological Conditions and Rock Mass Stability of Heidong Large Ancient Underground Caverns

The favorable engineering geological conditions and the structural integrity of rock mass make the Heidong ancient man-made underground caverns in Tiantai County,Zhejiang Province a large scale subterraneous quarry ever since the Sui Dynasty.Consisting of 21 single caverns,the group caverns situated in Xieshan cover an area of 24 000 m2 ,and the long axis of the caverns tend towards the same direction of the strike of the major two sets of geological structural planes.The lithology of the overall quarrying area is composed of the Upper Cretaceous Tangshang Formation layer No.6 off-white vitric ignimbrite.The value of the rock mass quality index Q is 53 (class I).If the concept of modern underground caverns’architectural design is held,the maximum allowable span for the caverns’secular stability should not be greater than 50 m,and the maximum span of cavern No.5 actually reaches 81 m-promises to be perhaps the greatest span of single cavern.The several geological exploratory holes excavated by the ancients in the foot of Xieshan and the large angle small section high bench passing technique adopted in regional fault fracture zone effectively ensure the safety and secular stability of unsupported mining in unfavorable geological bodies.By piling massive quarrying waste in the cavern, the stability of the side walls is enhanced to some extent,and besides,the disposal method is also beneficial to the environment.