Construction of a deposit of tunnel muck on soft soil

摘要

The construction of major tunnels in the Alps produces large quantities of non-reusable excavated material or tunnel muck, which often have to be deposited on the remaining, mostly poor ground surfaces. The final deposit of the Ceneri base tunnel in Sigirino will have a final height of 160 m and leans against steep rock slopes and sits on an initial footprint of about 100 by 100 meters on glacial soils 30 to 40 m deep. A layer of 15 to 20 meters of postglacial, normally consolidated clays lies below 12 m of gravel and sands. A deposit for intermediate storage of reusable material has smaller dimensions but undergoes load variations. Comprehensive site investigations with in-situ and laboratory tests served for the design with limit equilibrium and finite element methods. An extensive instrumentation system (horizontal and vertical displacement, pore pressures) was implemented. The prediction of the settlements below the fill with a finite element program was rather accurate. However, while the shapes of the horizontal displacements were predicted accurately, the values were two to three times larger than those measured by inclinometers. Next to the deposit, heave was predicted but settlement was observed. The issues of time dependent (creep or secondary) deformations and the necessity for improved, easily applicable constitutive laws with anisotropic deformations and strength are discussed.