TECHNICAL | SOFT GROUND - BTS LECTURE


A similar principle was used for the overhead


ventilation ceiling slab, using a gantry crane also developed with VSL. The prestressed slabs were transported into the tunnel and lifted by crane to be positioned automatically, using ISSG equipment, onto supporting cast in-situ corbels. Only the final fine-tuning and positioning was done manually. The process could erect 60m in a day. The systems were also used on Tunk Road T2, which


has similar internal structures. For its cast in-situ corbels, another robotic arm was developed - and mounted on a backup gantry - to etch and drill into tunnel lining, preparing for later casting of the corbel. The TBM environment, and difficulty of doing a proper survey of the lining, led to specific software being developed to give sufficient accuracy to the automatic robotic process.


TMCLK - SOUTHERN LANDFALL As the TBMs completed the subsea tunnel they would pass through stone columns, supporting sea walls, on approach to the Southern Landfall. But the columns had not been treated, meaning it was effectively a permeable zone and a major risk for slurry tunnelling. Loss of confinement pressure could lead to ground collapse. It was proposed to avoid the problem by boring about 9m below the columns, on a deeper alignment. Other difficulties arose from the ground condition of


the area, where the natural ground was very clayey, with a thick layer of marine deposits over a thick layer of clay alluvium. The reclamation contractor had been relying on consolidation for proper settlement, but during surcharging at the tip of Southern Landfall the sea walls moved. Ground treatment would be needed. Just inland there was to be large, rectangular


Top:


Placement of overhead precast slabs for ventilation duct


Above:


Installation of precast section for road deck and service gallery below


PRECAST INTERNAL STRUCTURES


The construction programme was tight for the main tunnel internal structures, which stretched over 10km of main tunnels. Access to the TBM had to be maintained while the internal structures were built. Principal internal structures were the road deck,


the service gallery below, and the ventilation duct above (TMCLK does not have jet fans). Again an industrialisation approach was adopted. Precast solutions were use as much as possible, delivery logistics helped by the project site being next to the sea. Specific tools were developed for each type of


internal structure, and manufacturing made to suit - which is the principle of Design for Manufacture and Assembly (DfMA). The service gallery was cast in whole sections,


topped by the road deck. Construction traffic could pass via a mobile ramp, extending from the deck to the tunnel floor. To install a concrete section, using ISIG equipment, the rear of the ramp was folded up to reveal the slot for placement. After installation, the ramp was lowered and grouting done.


16 | November 2025


ventilation shaft that would also function as a retrieval shaft for the TBMs. From there, along much of the rest of the Southern Landfall there was to be Cut & Cover construction. However, the proposed deeper tunnel alignment required changes to the plans, also given ground conditions. But, first, the focus was to be able to retrieve the


TBMs. Eventually, the solution developed was for a modified


hybrid scheme from among the different options being considered. As a result, TBM retrieval would not be at the shaft - in fact, the plan for the shaft was also changed. The TBMs would pass the location - after some complex engineering work - and drive beyond. The TBMs could go as far as their crowns reaching the marine deposit layer, which is subject to lateral movement. This helped to determine to start of the Cut & Cover tunnel, where they would break into. This modified hybrid was helped by a major


complication being removed: the client had obtained a waiver on the third lane for slower traffic for this end of the TMCLK road link, meaning there was no longer a need to switch over to larger TBM, for a short drive. Both of the 14m-diameter TBMs could pass the shaft area and keep going.


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