Shield Tunnel Construction in Centrifuge

A large number of centrifuge model tests for simulating the shield construction process in dry sand was carried out by using a newly developed 100 mm diameter miniature shield tunnel. Different construction processes were modeled by three series of tests. A “buried tube test” was conducted to measure the lining stress under a centrifugal acceleration, a “tail void test” simulated the process of tail void formation only, and a “shield test” dealt with the complete process of shield construction. Lining stresses, transverse and longitudinal surface settlements, and earth pressures around the tunnel were simultaneously measured during advancement of the shield at a centrifugal acceleration of 25g. The lining stress at the crown elevation was well predicted by Terzaghi's loosening earth pressure. From the comparison with the recent field measurements and the comparative results of three series of tests, it was confirmed that the shield construction process was successfully simulated in a centrifuge. An experimental formula for estimating the surface settlement above the shield was deduced by a function of tail void thickness and cover-to-diameter ratio.