TECHNICAL | SOFT GROUND TUNNELLING


Above: East portal during construction (left) and completed (right) The chosen excavation and support sequence was a


short ring closure method with top-heading/ combined bench/invert sequence, changed later to a top heading sequence with a temporary invert. Both methods worked equally well and did not show significantly different deformation patterns. Tunnel excavation was managed by the RES (required excavation and support) process, where a daily meeting between construction team, designer and client assessed the performance of the tunnel construction, surface settlement and changes to the excavation process were discussed. Also, two cross passages were constructed along the tunnel alignment. Due to the close proximity of the


14 | November 2024


two new tunnels the cross passage construction was more similar to a ‘punching-through’ exercise rather than tunnel excavation. As high waterflows during rain events were expected to occur within the highway embankment, a compartmentalised PVC waterproofing system was installed in both tunnels. The tunnel final lining was constructed using fibre-


reinforced concrete, with additional reinforcement provided only at the portal areas where structural loads were higher. The lining design was informed by the results of the numerical modelling, which allowed the team to optimise the reinforcement while maintaining the required safety factors.


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49