New designs of supports for large chamber workings

Abstract

Among the current trends determining progress in the area of designing supports of chamber working, we can distinguish two main ones: the maximum use of the load-bearing capacity of the earth mass and the creation of designs having an increased deformability (yielding), satisfying at the same time the requirements of the calculated limit state imposed on them.Among the most complicated with respect to designing reliable supports are the workings of the machine halls and transformer rooms of the powerhouses of hydroelectric and pumped-storage stations. As a consequence of the construction, technological, and operating advantages, the workings of such structures, as a rule, are designed with an inverted U-shape. In such workings two main elements of the supports --support of the arch and bolting scheme of supporting the walls --are clearly distinguished in the design and construction plans.Considerable experience in solving the problems in question with consideration of the above-indicated trend was gained during the design and construction of the unique Rogun hydroelectric station. The need to make economical and reliable decisions required the conduction of considerable surveys, design studies, and scientific investigations, effected in many cases by the occurrence of new problems owing to the impossibility of realizing traditional approaches. An analysis of the experience of the Rogun hydrostation unconditionally will be useful in the design of other future hydraulic structures.1. In addition to the large dimensions of the workings of the powerhouse complex (PHC) of the Rogun hydrostation, to a considerable extent the complexity of the problems of designing their support was determined by the characteristics of the engineering-geological situation. The PHC is located in the upper pool of the hydro development at a depth of about 40 m in a stratum of hard siltstones and sandstones, the uniaxial compressive strength (Rco) of which is respectively 80 and 100 MPa. One of the most essential factors which predetermined the need to find unconventional solutions was the pronounced prevalence of contemporary tectonic processes in the formation of the field of natural stresses of the mass. As a result, the components of the tensor of the principal natural stresses were substantially different from the values caused just by gravitational forces. Directly in the stretch of the powerhouse workings the vertical stresses exceed the weight of the overlying rocks by almost 1.5 times and are equal to 14 MPa and the horizontal stresses are equal to 17 MPa. With consideration of the relationship of the values of the natural stresses and strength of the rocks Rco the latter should be classified as strong [1]. Thus fracture of the mass in the vicinity of the workings is possible only along natural joint systems.Sandstones and Siltstones Are Bedded Rocks. The thickness of the beds is 0.5-0.7 m, they occur monoclinally and dip toward the lower pool at an angle of 65-70 ~ The long axis of the powerhouse workings is oriented almost acros...