叶巴滩水电站坝址区挤压破裂带发育分布特征

DEVELOPMENT AND DISTRIBUTION CHARACTERISTICS OF COMPRESSIONAL FRACTURE ZONE IN DAM SITE AREA OF YEBATAN HYDROPOWER STATION

勘探表明,在叶巴滩水电站坝址区岸坡石英闪长岩内广泛发育具有一定厚度和延伸长度的碎粒状岩屑条带——“挤压破裂带”,不仅使岩体完整性降低,而且劣化建基岩体质量。为了研究其发育特征、分布规律,基于野外调查、精细测量等方法,对施工期新揭露的典型挤压破裂带进行详细描述,揭示其发育特征、分布规律等。研究表明:叶巴滩水电站坝址区挤压破裂带在强弱卸荷带及以里均有发育,且空间分布不均匀,主要集中在左岸中高程;表现为有明显边界且具有一定厚度和延伸长度的碎粒状岩屑条带,一般发育在新鲜、完整的坚硬岩体内;可能为构造成因常依附于断层(或长度较大的结构面),范围有限,产状不稳定;带内大多劈理岩化,部分可见颗粒定向排列,具有分带性,无明显错距,表现出高地应力下的挤压变形特征;易受后期改造影响,局部可见风化加剧、锈染和泥质条带;主要分布于断层(长大结构面)夹持或围限区、断层(长大结构面)的端部、长大结构面的一侧。

The exploration shows that the grained cutting band with certain thickness and extension length is widely developed in the quartz diorite on both sides of the dam site of Ye Batan Hydropower Station.This kind of cutting band not only reduces the integrity of rock mass,but also deteriorates the quality of foundation rock mass.According to its manifestation and developmental characteristics,it is called“compressional fracture zone”.Based on the field investigation,this paper describes in detail the typical compression fracture zone newly revealed during the construction period.The development and distribution characteristics of the compression fracture zone are revealed.The study shows that the compression fracture zone develops in both strong and weak unloading zones and deeper areas.It is mainly distributed in the medium elevation of the left bank.The compressional fracture zone in the dam site of Ye Batan Hydropower Station is formed by tectonics.It appears as a clastic debris strip with a clear boundary and a certain thickness and extension,which is developed in fresh,complete and hard rock mass with obvious boundary.It may be formed by tectonic forces and generally attached to faults or structural planes of larger length.Its extent is limited and its occurrence is unstable.Most of the cleavage lithification in the zone,and part of the grains can be observed in directional arrangement,with zonal characteristics,no obvious dislocation distance.All these belong to the characteristics of rock mass extrusion deformation under the condition of high ground stress.At the same time,the compressional fracture zone is easily affected by the later transformation,and weathering,rust dyeing and muddy bands can be observed in some extrusion fracture zones.They are mainly distributed in the clamping or confining area of faults(long structural planes),the end of the fault(long structural planes),or the side of the long structural planes.