20 - The Design and Construction of Underground Hydraulic Structures in Permafrost

Abstract

This chapter describes the design and construction of underground hydraulic structures in permafrost. The character of the permafrost spread and thickness differs from place to place. Design of underground hydraulic structures in permafrost involves certain features, resulting from specific natural conditions. Underground hydraulic structures are generally placed in massive rock, which is predominantly hard, either igneous or sedimentary, and is frozen all the year round. In some cases, particularly at tunnel faces, the underground structures can involve soft Quaternary rocks. The specific composition of the permafrost rock is determined by its natural fracturing and the hydrogeology of the rock mass during freezing. One of the features of permafrost rock is ice inclusions. Permafrost rock also contains ice inclusions in the form of separate clusters or interlayers encountered in bedding planes. In estimating the bearing capacity, stability, and deformability of the rock mass surrounding an excavation, it should be considered as a complex mechanical system composed of rock mineral joints, blocks and beds of different sizes and shapes strengthened by ice or fine ice-saturated formations. Mechanical properties of the permafrost depend greatly on its volume icing and temperature. These properties are not constant and change with temperature fluctuations of the rock mass.