Investigating allowable distance between powerhouse and transformer caverns to prevent buckling phenomenon using numerical and analytical methods (case study: Bakhtiary dam and HPP)

 B Dehghani^1,*, L Faramarzi¹, A Azhari¹, M Sanei²

¹ Department of Mining Engineering, Isfahan University of Technology, Isfahan, Iran

² Department of Petroleum Engineering, University of Campinas, Brazil

Doi:10.1088/1742-2140/aac18d

Abstract

One of the most significant challenges of constructing large underground spaces is to determine the allowable distance between these structures. For instance, a large distance between the caverns at a hydroelectric power plant incurs a higher cost due to the transfer of electricity from the powerhouse cavern to the transformer cavern via underground openings called bus tunnels and bus shafts. However, reducing the distance between the caverns would result in the undamaged rock pillar between the caverns being narrow. Thus, with regard to the interaction between the caverns and the induced stresses in the rock pillar, buckling may potentially occur. Based on the results of laboratory and in situ rock mechanics tests performed in the Bakhtiary dam and the HPP project, this paper includes reports on (but is not limited to): (A) laboratory tests such as 162 unconfined compression tests, 125 triaxial compression tests, 94 direct shear tests on rock discontinuities, 47 indirect tensile strength (Brazilian) tests; and (B) in situ tests such as 91 dilatometer tests, 12 large flat jack tests, 48 plate load tests, 58 borehole slotter tests and 62 hydraulic fracturing tests. The geomechanical parameters of the rock masses surrounding the caverns are estimated. Then, the allowable distance between the powerhouse and transformer caverns is determined using analytical relations of buckling in thin pillars and numerical simulations based on the distinct element method.

Keywords: undamaged rock pillar, buckling, induced stress, allowable distance, caverns