信阳牢山寨花岗岩岩体节理发育特征及构造应力分析

信阳牢山寨花岗岩岩体位于大别造山带北麓，北淮阳构造带内，属燕山晚期第一次岩浆侵入的产物，主要岩性为中粒二长花岗岩。研究区规划为五岳抽水蓄能电站上水库，明确花岗岩的节理特征及构造应力场对水库的防渗处理和设计施工具有重要的指导意义。本次研究统计分析了库区范围内的351条节理，查明节理的优势方位为NNW-SSE向，倾角均为大倾角，节理面在浅部风化较为强烈，风化程度随深度增加而降低；节理张开度主要是微张—闭合，充填物主要为石英脉、岩屑和泥质，透水性较差。利用共轭剪节理的配套和分期，反演得出研究区构造应力演化史：燕山晚期主应力方向为NEE—SWW，至喜山期主应力方向转变为近E—W向；此两期构造应力与大别山地区构造运动应力方向一致。在喜山期之后，研究区主应力方向转变为NNE—SSW，此为该地区小范围的构造应力场特征。水压致裂法试验测试得出研究区构造应力略大于自重应力，属于低应力场区域。压水试验结果显示，随着深度的增加，岩体透水率降低，但在节理密集段其透水率伴随节理的发育而增大。这表明，研究区近地表中—强风化花岗岩岩体，风化程度高、卸荷严重、节理裂隙发育，岩体较破碎，透水率较大；随着深度的增加，岩体的风化程度降低，卸荷减弱；同时，自重应力和围压的增加迫使岩体节理张开度减小，NNW和近NWW向、填充度小的节理成为深部岩体的主要透水通道。因此，水库设计中应针对该类型节理进行防渗处理。

Analysis of Joint Development Characteristics and Tectonic Stress of Granite Rockmass in Xinyang Laoshanzhai

The Laoshanzhai granite body is located in the North Huaiyang tectonic belt, north part of the Dabie orogenic belt. This granite is generated from the first magma event of the late Yanshan movement. The Laoshanzhai granite is mainly composed of medium-grained monzonitic granite. The study area is designed to be the upper reservoir of Wuyue Pumped Storage Power Station. It is important to clarify the characteristics of joints and tectonic stress field of granite for the impermeability treatment and construction of the reservoir. In this study, 351 joints were investigated within the reservoir area. The dominant orientation of the joints was identified as NNW-SSE, and the dip angles were steep.The joint surface was more strongly weathered in the shallow part, and the weathering degree decreased with increasing depth. The aperture of joints was mainly micro-tensioned-closed. The fillings of joints were quartz veins, rock particles and mud, which have poor permeability. Using the matching and staging of conjugate shear joints, the evolution of tectonic stresses was indicated in the study area. The main stress direction in the late Yanshan period is NEE-SWW, while that was transferred to near E-W during the Xishan period. The tectonic stresses in these two periods are consistent with the stress direction of tectonic movements in the Dabie Mountain area. After the Xishan period, the main stress direction in the study area was NNE-SSW, which is the characteristic of the tectonic stress field in the local area. The hydraulic fracturing test show that the tectonic stress in the study area is slightly higher than the self-gravity stress, which means that the study area is a low stress field area. The hydraulic test results show that the permeability of the rock decreases with increasing depth, but the permeability increases with the development of joints in the dense section of joints. It indicates that the near-surface medium-strongly weathered granite in the study area were characterized as severe unloading, developed joints and high permeability. with the increase of depth, the degree of weathering decreases and the unloading is weakened. Meanwhile, the increase of self-weight stress and surrounding pressure compressed the joints, reducing the aperture. The NNW and near-NWW-oriented joints without fillings were defined as the main permeable conducts at the deep area. Therefore, impermeability treatment should be carried out for this type of joints during the design and construction of the reservoir.