Abstract
Bakhtiari dam is located on the Bakhtiari river, 120 km away from the north of the Andimeshk city. Upper diversion tunnel of this dam with large cross section (13.7 m excavation diameter) and more than 1 km length is a huge construction. The tunnel is placed in the Sarvak formation carbonate rocks of Bangestan group which passes through seven different geological zones with various specifications (SV1, SV2, SV3, SV4, SV5, SV6, and SV7). Joint studies show two main discontinuit including bedding and a main group of joint (J1) together with random joints (faults and fractures). Most of discontinuities have been filled mainly by calcite or calcite and clay. Data deduced from testing and analysis shows good-to-excellent RQD classes with 75 to 90 values. Based on RMR and Q methods, generally rock masses have good to very good quality with 61 to 95 values for RMR and 10 to 35 values for Q. Based on conducted stability analysis, suitable supports were suggested for tunnel by RMR and Q methods. As a result, it can be concluded that all units have a good stability. Therefore, systematic rock bolting with 40–50 mm unreinforced shotcrete has been proposed for some special place. For rock support, according to RMR method, 3 m rock bolts in crown, 2.5 m spacing and with 50 mm shotcrete in crown has been proposed also 3 m rock bolts, based on Q method, 2.3-2.4 m spacing with systematic Bolting without shotcrete or 40 mm unreinforced shotcrete in some units, has been proposed. According to RMR method, for SV5 zone with very good and excellent quality, local 33 bolting without shotcrete and 3m rock bolts, 3 m spacing and spot bolting according to Q method has been proposed.
Highlights
In recent years, following the increasing need to create spaces underground with larger scale and in greater depth in poor areas, identifying more and more of the earth is evident
This paper presents the results of rock mechanics studies of the upper diversion tunnels at Bakhtiari dam
According to the interpretation of surface geology and data from drilling and exploration boreholes, damsite and its surrounding consists of folded carbonate sedimentary rocks which belong to Sarvak formation from Bangestan group
Summary
In recent years, following the increasing need to create spaces underground with larger scale and in greater depth in poor areas (such as underwater), identifying more and more of the earth is evident. In relation to construction of dams, geological survey is the most important parts of studies which can be useful and valuable information about the design of underground spaces offer [2]. Feasibility of these constructions in natural materials, such as rock and soil, causes the geological conditions to play a major role in their stability [3]. In order to design dam and its appurtenant structures and assure about their stability, it is required to evaluate the engineering behavior of their surrounding rock masses In this regard, physical and mechanical properties of the rock masses should be estimated based on engineering geological and rock mechanics field and laboratory investigations
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