The effect of tunnel size, advance rate, and depth of cover on the stand-up time of tunnels in squeezing ground was investigated through a series of 12 physical model tests. The stand-up time, defined as the time elapsed before instability develops, was found to be characterized by increasing deformations and deformation rates rather than a catastrophic collapse of the tunnel. To establish a predictive capability, a constitutive theory describing the time dependent behavior of soft clays has been developed. By generalizing existing empirical rules developed for fixed boundary conditions and then unifying these empirical rules with a tensor framework, a multi-axial constitutive equation describing the stress-strain-time behavior of normally loaded soft clays was formulated.
|Original language||English (US)|
|Title of host publication||US Dep Transp, (Rep) DOT/TST|
|State||Published - Jun 1977|
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