SOFT GROUND - BTS LECTURE | TECHNICAL


The project built 46 cross passages by this method,


using 3.66m-diameter mini-TBMs that were jacked from one main tunnel through to the other, and using both temporary and permanent sealing systems under the high water pressure conditions. The concrete pipes were the permanent lining for the cross passage structures. Construction time per cross passage with this method was targeted as 20 days.


Standardisation and Structure The industrialised approach for cross passage construction needed standardisation of the element and methods. The initial plan for two types of cross passages was changed to one type, and none would hold M&E equipment. The proposal had been for pedestrian-only cross


passages (boring diameter 4m, spaced at 200m intervals; and, pedestrian tunnels that were larger to house M&E equipment (boring diameter 5.6m, also at 200m intervals). The effect was a cross passage every 100m and alternating in size. Discussions with the client led to the bottom space of


the large main tunnels, below the road deck, to become a service gallery holding all the M&E equipment. The change enabled all cross passages to be pedestrian only and smaller (about 3.665m, boring diameter), still spaced at 100m intervals. Standardisation for construction would use mini-


TBMs along with pipejacking. For this approach, the tunnel wall had be able to


take load transfer from the jacking operation. This was achieved structurally by adding a ‘tympanum’ to each opening. The tympanum is a wide and tall reinforced concrete wall, able to cover the portions of the main tunnel rings immediately around opening to be bored. Preparations for cross passage construction start


early, during construction of the main tunnels. Special segments were erected in the main tunnel rings, at the future cross passage locations, and had connecting couplers installed for casting the tympanum, and glass fibre reinforced plastic (GFRP) where the mini-TBM would break-in.


Mini-TBM: Launching Side Pipejacking Equipment A lot of time was spent developing the technical solution for this mechanised cross passage construction solution with Herrenknecht. The system uses a mini- TBM and then some large diameter pipes. The shield is launched from one main tunnel and excavates through to, and emerges from, the other parallel main tunnel. In the launching side, a ‘jacking trailer’ system


attaches the thrust assembly to the tympanum. An open frame with a gantry crane is rolled into position to move the mini-TBM and then pipes into position for the thrust ring to push each forward in turn. The entire equipment arrangement is compact and linear, enabling construction traffic to pass by in the main tunnel. The permanent lining pipes are prepared with seals and waterproofing before arrival in the tunnel. At any


Tunnel special segments ML03 (Phase 1)


4 Nos. ∅150 PVC duct sleeves for E&M cables


Cross passage tunnel jacking pipes GFRP area ML03 (Phase 1)


Tunnel special segments ML02 (Phase 1)


4 Nos. ∅150 PVC duct sleeves for E&M cables


In-situ concrete (Phase 5) Corbel


In-situ concrete (Phase 5) Tympanium ML02 (Phase 2)


Corbel


In-situ concrete ML03 (Phase 5) Tympanium ML03 (Phase 2)


In-situ concrete (Phase 5)


and all stages of the process the watertightness of the works and ground stability are maintained.


Mini-TBM: Receiving Side ‘Steel Bell’ and Final Works In the parallel main tunnel, the mini-TBM needs to be retrieved safely and systematically for stability of the tunnels and reuse of the shield at the next cross passage. The receiving equipment is a pressurised steel vessel,


bolted to a flange in the tympanum, and it also has emergency seal support. The vessel has a domed end, or ‘steel bell’ like a cap which is eventually removed to extract the mini-TBM. Before then, after completion of the excavation, the


pressurised vessel continues to hold the mini-TBM while grouting is done to ensure temporary water tightness at the interface of the cross passage and main tunnel. Then, the pressure in the vessel is lowered, the bell opened and the mini-TBM retrieved.


Top:


Schematic of standardised system for cross passage construction used an industrialised approach, employing a combination of mini-TBM and pipejacking


Above:


Photo of mini-TBM after completing a cross passage construction and arriving at the ‘steel bell’, which then has been depressurised and opened


November 2025


| 15


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