Three-dimensional Fracture Network Modeling Of The Rock Mass For Datengxia Water Release Gate Foundation

This paper looks into the engineering geology condition of the rock masses of the water release gate of Datengxia hydropower station.Based on the nearly 1,000 fractures investigated in field,the analyses of the statistical characteristics of the fractures are shown.In addition,3D fracture network modeling of the rock masses of D₁y¹-3 and D₁y¹-2 is done.It can be concluded that:?1?The rock masses where the water release gate lies on are well-bedded,with most bedding surfaces closed tightly and the thickness of 10⁴0 cm between every two surfaces.Soft interlayers are common in the strata of D₁y¹-1 and D₁n₁₃,with the distance of 2⁵m between every two interlayers.The dips of the soft interlayers are facing the lower reaches of the river and parallel to the bedding surfaces.The strata are well-fractured with the average trace length of more than 2 m and the dips of most fractures are facing the upper reaches of the river.It can be concluded that it is likely that deformation and failure can occur in the rock masses of the water release gate under the huge water stress based on the analysis on the bedding surfaces,soft interlayers and fractures within the rock masses.?2?In the strata of D₁y¹-1 and D₁n₁₃,the thickness between soft interlayers is small while fractures are great in size.Therefore it is assumed that fractures are linked up thoroughly.Thus 3D fracture network modeling is unnecessary in the strata of D₁y¹-1and D₁n₁₃.While in the strata of D₁y¹-3 and D₁y¹-2,there is a larger?often more than2³ times of the size of the fractures?distance between every two bedding surfaces.Thus the mechanical property of the rock masses is determined by the characteristics and the link-up of the fractures distributed in the rock masses.Therefore,3D fracture network modeling is necessary in order to make deeper analysis in these strata.?3?A method of 3D fracture network modeling for large-area-collected data is proposed in this paper.The calculation of the diameter of fractures is a critical step in this method.The probability density function of?a?the diameter of fractures intersecting with the exposed rock surface and?b?the diameter of the fractures in the 3D space are deduced.Besides,it can be easy to generate the occurrence of fractures with empirical distribution after the calibration of the probability of fractures with different occurrence.After the intersection of an imaginary exposed rock surface,we can get the number of intersected fractures?i.e.traces?.Therefore,the density of fractures can be determined.?4?After the generation of the 3D fracture network,a plane with the same occurrence as the exposed rock surface is intersected with the 3D fracture network generated.The probability density function of the diameter of fractures that intersect with the plane and the diameter of the fractures in field are almost the same.Therefore,the 3D fracture network modeling method proposed in this paper is rational and can be applied to the analysis of rock engineering.