| A geomechanical model, which simulated shield tunneling through soft ground, was developed and tested in dry sand. The test program was divided into four series of tests. In the O-, M-, and T-series, two concentrically placed circular tubes were used representing the model shield and model liner, respectively. The model shield was pulled out of the test bin in several steps and an annular gap between the two tubes simulated the tail void in an advancing shield. Three-dimensional development of ground movements was observed. In the L-series a movable roof section was lowered progressively to simulate yield of the tunnel roof and two-dimensional ground movements were observed. Single tunnels were tested in the O-, M- and L-series, while two parallel tunnels were excavated one after the other in the T-series tests to investigate interaction effect of the two tunnels on the ground movements.;Effects of the amount and distribution of ground loss into the tunnel on the ground movements were studied. In addition, tunnel depth, sand density and pillar width between two parallel tunnels were varied and their effects on the ground movements were also studied.;Case histories of tunnels in a variety of soil conditions and construction details were compiled and compared with the experimental results.;It was possible to establish the mechanism of ground movements and volume changes in the ground due to tunneling. The test results agreed well qualitatively and quantitatively with the observed ground behavior in real tunnels driven through granular soils. A procedure for the first approximation of ground movements at surface and at subsurface level was suggested. The results of the model tests should be helpful to the designers in estimating ground movements, in assessing potential damage to nearby structures, in designing an instrumentation program, and in planning measures to control the ground movements.;A combination of stereo-photogrammetry, dial gages, embedded electromagnetic and mechanical gages was used to observe settlements and lateral displacements at surface as well as at subsurface level. |
