1、外文原文：Determination of the optimal threshold and length measurements for RQD calculationsWen Zhang, Qing Wang, Jian-ping Chen n, Chun Tan, Xiao-qing Yuan, Fu-jun ZhouCollege of Construction Engineering, Jilin University, Changchun 130026, China1 IntroductionThe rock quality designation (RQD) is dened
2、 as the percentage of a scanline consisting of spacing values greater than or equal to 4 in. (100 mm) 1. RQD is widely used around the world as an important parameter for rock mass quality classication.The value of 4 in. (100 mm) has not been proven as the most reasonable threshold. For layered rock
3、 masses, the rock surface spacings are larger than 100mm, but usually not larger than200 mm. The RQD is then 100%, which is incompatible with the actual rock mass quality. The generalized RQD, where the threshold is an arbitrary positive value 2, is introduced in actual engineering practices to obta
4、in a better reection of the inhomogeneous nature of rock masses. To identify the optimal threshold value, Harrison 3 presented equations derived by analyzing fracture frequencies with different distributions, which could expand the range of RQD values. Wang et al. 4 have determined the RQD value in
5、the extension direction of a tunnel by computer modeling in three-dimensional (3-D) space. They have investigated the variations in RQD values with the changes in thresholds.The actual direction of a scanline (core run) is vertical. Given that a rock mass is anisotropic, the RQD value of a single ve
6、rtical scanline could not reect the overall degree of the rock mass quality. Priest and Hudson 2 have studied RQD and proposed a relationship between the fracture frequency and RQD on the assumption that the overall fracture spacing follows a negative exponential distribution. Sen and Kaiz 5,6 have
7、studied the RQD along a scanline with any specic orientation, and established a relationship between the RQD value and fracture frequency along the chosen orientation. Chen 7 has studied RQD values along different scanlines produced automatically by a computer program in all directions in two-dimens
8、ional(2-D) space.An RQD is sometimes expensive to obtain (e.g., in extremely hard rock masses).Therefore, the relationships of the RQD with rock mass parameters, such as fracture frequency, deformation modulus, volumetric joint count, and permeability coefcient, have been established813.Snow12 has p
9、ointed out that the RQD and fracture frequency decreases with increasing depth. Jiang et al.13 have established the relationships of the RQD with the volumetric joint count and permeability coefcient in a granite region.The RQD should be considered as a variable value because it is a function of dis
10、continuity numbers and spacings, which are stochastic1416. In the current study, 3-Dfracture network numerical modeling is applied and scanlines in different directions are set in 3-D space to investigate the homogenous features of a rock mass. RQD values are calculated by a self-written program, an
11、d the statistical features of these RQD values are examined. Given that the threshold and scanline length are essential for RQD calculation, the optimum threshold and mini- mum appropriate scanline length are studied.2 General engineering situation and database2.1Collection of structural dataThe stu
12、died rock mass is located in the dam area of the Baihetan hydropower station in southwest China. The construction of the station project is currently at the feasibility study stage. A double-curvature arch dam will be used for the Baihetan station. The dam is approximately 277m high, with a water su
13、rface elevation of 590m, dam crest of 825m, and storage water level of 820m. The maximum generation capacity of the station is 59.55 billion kWh.The dam area is in the middle of a mountain canyon geomorphology, and the valley in the dam area has an asymmetric V-shape. Cliffs are widely distributed u
14、nderneath at an elevation of 9001100m on the left bank and 10001400m on the right bank. The top of the elevation is predominated by mesas or gentle slopes.The rock mass in the dam area is mainly composed of basalt from the Permian period (P2b), and the overlying rock mass is sandy shale from the Tri
15、assic period (T1f). The riverbed and mesa are composed of alluvium, diluvium, and eluvium deposits from the Quaternary period. Given that the dam will be built upon the basalt area, the characteristic features of basalt play an important role in the engineering stability of the dam.Fig1. Pole and st
16、rike rose diagrams of the fracture sets (the strike satises the right hand rule). (a)Set 1, (b) set 2, (c) set 3 and (d) set 4.Whereas the weathering degree and depth gradually decrease from higher to lower elevations.The occurrence of the rock formation is at N301501E, SE151251. The protogenic columnar joints of the basalt at shallow depths are inhomogeneously developed. The columnar joints could
