Hong Kong - We are the Contractor’s Designer for Express Rail Link (XRL) Contract 825, which forms part of the Hong Kong section of Guangzhou-Shenzhen-Hong Kong cross boundary Express Rail Link project.
The contract comprises construction of a section of 2.35km twin bore single track TBM tunnels with 8.15m internal diameter running between Mai Po and Ngau Tam Mei, cross passages at 250m spacing along the tunnel alignment and a 110m long x 36m wide x 35m deep launching shaft at Mai Po area.
Design and approval of the tunnels and launching shaft were required to be completed within a very tight time frame to meet the contract programme. The tunnels come across a full range of ground conditions from fill and alluvium sand to Completed Decomposed Granite/Tuff and eventually encountering full face of rock at retrieval shaft.
The tunnel alignment ran underneath some sensitive structures, including a footbridge across Castle Peak Road, where ground treatment for underpinning the footbridge foundations was anticipated.
We contributed to success of the tender by adopting limit state design approach to CIRIA C580 to optimize the depth of diaphragm wall panels and value-engineering the segmental lining thickness from that of the reference design in tender stage. The lining thickness was further reduced in detailed design stage to achieve further cost saving.
We used 3D numerical modelling to evaluate the face pressure required when the TBM passed under the footbridge at Castle Peak Road, thus eliminating the originally perceived grouting works for underpinning the footbridge.
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