Methods for evaluation of fractures in granitic rock mass as a safety assessment technique for nuclear waste disposal

1. 基于野外观测的花岗质岩体裂缝表征通过对中部良带分布的花岗质岩体的野外地质调查，分析了宏观（露头尺度）裂缝的走向和产状，以表征研究区各向异性裂缝网络系统。测量了纵波速度的变化，以确定花岗岩中发育的弱平面的优选方向。稻川花岗岩东北部发育由3个优选方向裂缝组成的平行六面体块体构造。推断该构造来源于花岗岩体中的拉应力场。相反，稻川花岗岩体和老良约克花岗岩体西南部以复杂剪切裂缝为主。这些宏观裂缝的优势取向接近中部构造中线（NE -SW走向）和阿特拉断裂（NW-SE走向）等中部地区具有代表性的主要活动断裂系统的方向。纵波速度测量结果表明，纵波速度的各向异性与平行六面体裂缝的分布密切相关，而剪切裂缝与纵波速度的变化关系不明显。结果表明，在高应力岩体中，考虑主要断裂的产状和该区域分布的构造应力状态，可以较好地逼近裂缝的优选方向。裂缝孔径分布和流动路径的表征我们试图通过结合实验室实验和流动模拟来揭示裂缝孔径与拉伸裂缝中流体流动之间的关系，以研究高达100mpa的拉伸裂缝中的流动特性以及与施加到裂缝上的剪切偏移相关的流动特性的变化。结果表明：(1)张性裂缝的渗透率随着法向应力的增加而迅速下降；(2)当法向应力大于40-50 MPa时，裂缝渗透率基本保持恒定值；(3)在流动路径上产生通道，这意味着裂缝的特定区域表现为主流道；(4)在更高的法向应力条件下，通道得到了阐明。我们还提出了一种结合流动实验和流动模拟来评估裂缝流动特性的技术，该技术考虑了表明微观流动特性的流道分布以及表明宏观流动特性的裂缝渗透率。少

1. Characterization of fractures in granitic rock mass on the basis of field observationBased on geological field survey on granitoids distributed in the Chubu Ryoke Belt, orientation and occurrence of macroscopic (outcrop scale) fractures were analyzed to characterize the anisotropic fracture network system in the study area. Variation of P-wave velocity was measured to identify preferred orientation of weak planes developed in the granitic rocks. In northeast part of the Inagawa granite, parallelepiped block structure composed from fractures with three preferred orientation was observed. The structure is inferred to be derived from tensile stress field in the granitic body. On the contrary, in southwest part of the Inagawa granite and the old Ryoke granitic rocks, complex sheared fractures were dominant. Predominant orientations of those macroscopic fractures were close to the directions of major and representative active fault systems of the Chubu Ryoke area such as the Median Tecto … More nic Line (NE -SW strike) and the Atera fault (NW-SE strike). P-wave velocity measurement revealed that anisotropy of the P-wave velocity was closely related to the distribution of parallelepiped fractures, however, shear fractures had no clear relation to variation of the P-wave velocity. We showed, in the case of highly stressed rock mass, better approximation on preferred orientations of fractures is likely to be achieved with consideration for occurrence of major faults and tectonic stress regime distributed in the area.2. Characterization of aperture distribution and flow paths of fracturesWe attempted to reveal a relationship between fracture aperture and fluid flow in a tensile fracture by combining laboratory experiments and flow simulations in order to investigate flow properties in a tensile fracture up to 100 MPa and a variation of the flow properties associated with shear offset applied to the fracture. Our results showed 1) permeability in a tensile fracture rapidly decreased with an increase in normal stress, 2) the fracture permeability showed almost constant value at normal stress more than 40-50 MPa, 3) channeling in flow paths, which means specific area of the fracture behaves as major flow paths, is yielded, 4) the channeling was elucidated at higher normal stress conditions. We also proposed a technique for evaluating flow properties of a fracture in combination with the flow experiments and the flow simulation with considering flow path distribution indicating a microscopic flow property in addition to fracture permeability indicating a macroscopic flow property. Less