Twin-tunnelling-induced ground movements in clay

Abstract

This is the published version of the paper.This version of the publication may differ from the final published version. Modern tunnelling methods aim to reduce ground movements arising from the construction process. In clay strata the usual method of construction is by tunnel boring machine, which allows close control of the tunnelling process; however, any movements have the potential to cause damage to existing structures at, and below, the ground surface. The construction of underground rail systems often comprises two tunnels running in opposite directions. Permanent repository linkCommon practice for assessing construction-generated movements around these tunnels is to make predictions based upon individual tunnel construction and utilise superposition to generate a total deformation profile. This approach does not take into account the strain-or stress-dependent effects between tunnel constructions. A delay may result in unanticipated ground movements generated by the construction of the second tunnel. The effect of this delay on the ground movements arising between the first and the second tunnel construction process was investigated in a series of plane strain centrifuge tests. The ground movements at and below the surface were monitored and were assessed against superposition-based predictions for surface settlement with the outcomes highlighting some inconsistencies. A procedure for predicting both surface and subsurface vertical settlement profiles in the plane transverse to the advancing tunnels in clay is suggested.

Twin-tunnelling-induced changes to clay stiffness

“…The relative differences in the Volume Losses have only recently been studied (e.g. Addenbrooke & Potts, 2001;Hunt, 2005 andDivall &Goodey, 2015). These studies offer a means by which the magnitude of the increase in Volume Loss can be ascertained based on the tunnel centre-tocentre spacing.…”

“…These studies offer a means by which the magnitude of the increase in Volume Loss can be ascertained based on the tunnel centre-tocentre spacing. Figure 1 shows the overall trend presented by Divall & Goodey (2015) along with three case studies with some selected field measurements. These case studies (Cooper & Chapman, 1998;Cording & Hansmire, 1975;Nyren, 1998) are consistent with the experimental data supporting the relationship proposed.…”

“…Divall (2013) investigated the relationship between tunnelling-induced settlements and the spacing between sequentially bored twin-tunnels. The results from eight plane strain centrifuge tests were described by Divall & Goodey (2015). The tests consisted of an overconsolidated clay sample with two preformed circular tunnels bored equidistant from the model centreline.…”

“…Previous research (e.g. Addenbrooke & Potts, 2001;Hunt, 2005;Fang et al, 1994;and Divall & Goodey, 2015) have attempted to define the conditions that would ensure there would be no interaction between the tunnels. These studies related relative differences in the tunnelling-induced settlements with the centre-to-centre spacing or pillar width between cavities.…”

Editorial

“…The sixth paper (Divall and Goodey, 2015) is about twin-tunnelinduced ground movements in clay. The authors performed twodimensional plane strain centrifuge tests on twin tunnels at different spacing and found that the second tunnel caused greater volume loss than would be expected by superposition.…”