ABSTRACT

The underground works of the Rogun dam project in Tadjikistan comprise: machine hall 20m wide, 70m high and 220m long and transformer hall 18m wide, 37m high and 182m long. To assess deformation properties of the rock masses composed of sandstone and aleurolite which surround the underground excavations, a set of methods was applied including dilatometers, seismic and ultrasonic measurements, determination of moduli of deformations by the Hoek and Brown method applying the Bieniawski rock quality classification as well as defining the values of moduli from the measured convergence of the machine hall walls by solving a number of 2-D and 3-D problems to estimate the stress-strain state of the "host rock-underground excavation" system at different phases of construction. Described herein below are the technique and results of conducted investigations as well as comparative evaluation of the moduli of deformation obtained by different methods.

1 INTRODUCTION

Deformability of the rock masses serving as the foundation for the surface structures and as host medium for the underground works is one of the major factors governing behavior and safety of the entire "structure–foundation" system. The criteria of rock deformability – the moduli of elasticity and deformability – are the major parameters used to analyze the rock masses on the computational models (Technical Report 2005, 2006). For the real rock masses featuring their structural heterogeneity and anisotropy as well as certain primary stressed state, estimation of their deformation properties is a complex and critical engineering task. Solution of this problem considering the size of the bearing area and the type of surface structures or volumes of underground excavations is aggravated by the presence of the scale effect i.e. dependence of magnitudes of the moduli of elasticity and deformation on the applied scale of investigations (Savich & Kujundzi'c, 1985). Today's engineering practice uses various direct and indirect methods of determining the moduli of elasticity and deformation, as well as Poisson's ratio for the rock masses in their pristine state including the rating approaches to assess the above parameters by a set of geological features of the rock masses in question (Bieniawski 1979, Bieniawski 1989, Barton et al. 1974). The final results of these determinations can materially vary and therefore there arises necessity of selecting those data which most correspond to the specified design computational model and the real behavior of the "structure–foundation" system. Such a problem arose in construction of a large underground machine hall at the Rogun dam project on the Vakhsh river in Tajikistan.

2 CHARACTERISTIC OF PROJECT AND UNDERGROUNDWORKS LOCATION

The underground works of the Rogun dam project comprise:

  • machine hall 20m wide, 70m high and 220m long;

  • transformer hall 18m wide, 37m high and 182m long located at a distance of 63,5m (within center lines) on downstream from the machine hall, and

  • various underground excavations. Excavation of the machine hall cavern began in 1986 and excavation was carried to the full width of the cavern in 6–11m deep benches. s.

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