Final breakthrough ends KVMRT TBM tunnelling 16 Apr 2015

All running tunnel TBM excavation for the Klang Valley metro Line 1 project in Kuala Lumpur, Malaysia, is complete. The last TBM breakthrough on Saturday 11 April completes 9.5km of 5.8m i.d. twin-tube TBM running tunnel alignment for the project from the Semantan North Portal to the Maluri South Portal. Final breakthrough at the Pasar Seni underground station completes the central underground section of the city’s first 51km high-capacity heavy rail metro line and draws to a close TBM operations that started when the first TBM was launched in May 2013.

The last breakthrough is in fact achieved by the first TBM launched on the project and after completing a drive of 4.4km of excavation through a mix of karstic limestone and Kenny Hill sedimentary deposits. It completes the longest drive of any TBM on the project and is a breakthrough for a Herrenknecht multi-mode TBM. The machine started in the VD (variable density) slurry mode from the Cochrane open cut station box at the end of May 2013 and passed through three station zones and two intermediate shaft locations before ending its drive on Saturday 11 April at the Pasar Seni open cut station excavation.

Ten TBMs were procured for the underground central section of the first MRT line for the Malaysian capital city and eight were launched and operated (Fig 1). By completing the 4.4km running tunnel from Cochrane to Pasar Seni, the last machine to breakthrough spared the launch of one VD machine and also a Herrenknecht EPBM. The change in strategy was adopted to mitigate various programme conflicts together with the possibilities available to the contractor that was engaged to complete the total underground section as one contract.

MMC-Gamuda, the Malaysian construction JV engaged to complete the 9.5km underground section of the 51km long MRT Line and its seven underground stations, procured six specialist variable density TBMs (VDMs) from Herrenknecht AG to work through Kuala Lumpur’s karst limestone; and four EPBMs, two from Herrenknecht and two from CREG of China, to excavate the sedimentary clays and silts of the Kenny Hill Formation (Fig 1).

Fig 1. Original strategy for the 10 TBMs procured for the project with the continuous drive of one machine from Cochrane to Pasar Seni saving launch of two machines

The two CREG EPBMs launched from the Semantan North Portal in June 2013 and completed their programmed drives at Pasar Seni station (Fig 1). Four VDM machines launched in opposite directions from the Cochrane open cut station box with the two heading south completing their drives at Maluri South Portal in April 2014. Another Herrenknecht VDM machine launched from the Inai intermediate working shaft in December 2013, completing its planned drive at the Pudu shaft; and a Herrenknecht EPBM launched in May 2014 from the Pudu shaft, completing its planned drive through Merdeka station to finish at Pasar Seni station in January 2015.

But it was the Herrenknecht VDM launched by the Prime Minister of Malaysia Datuk Seri Najib Tun Razak in May 2013 from the Cochrane station box heading north that is the star of the project. Instead of completing its work at Pasar Rakyat station box, as planned, it was running ahead of station excavation and the plan changed to allow the machine to mine through the Pasar Rakyat station zone as well as the Inai shaft location, where there were ground condition and water inflow problems, before proceeding through the Bukit Bintang and the delayed Pudu shaft excavation locations for a breakthrough and pull through at Merdeka station and relaunch on the last drive to the Paras Seni station in January 2015.

Prime Minister Datuk Seri Najib Tun Razak powered up the first VDM and the first machine on the project in May 2013

As the trail blazer, the TBM arrived ahead of programme at Pasar Rakyat station box and mined on through while its partner and following VDM from Cochrane broke through and was withdrawn from Pasar Rakyat station as planned. Problems with groundwater control at the Inai shafts saw launch of only one of two planned VDMs at the intermediate working shaft with the machine from Cochrane mining through. Both machines progressed through the narrow Bukit Bintang station corridor on a stacked configuration and while the leading machine launched from Inai shaft was retrieved from Pudu Shaft as planned, and an EPB machine introduced at Pudu for the drive to Merdeka station, the same machine from Cochrane was again pressed into further duty, mining through the bottom of the delayed Pudu shaft, after starting the upper machine of the stacked configuration first. Both machines then broke through at Merdeka station to be pulled through and relaunched at the far end wall to complete the last drives in Pasar Seni station; the TBM from Pudu Shaft finishing in early January 2015 and the TBM from Cochrane breaking through on 11 April after completing 4.4km of continuous operation.

Further to its long drive performance, the last TBM to break through functioned successfully in its different modes. After starting in the variable density slurry mode to work through highly karstic limestone from Cochrane station, it finished its 4.4km long drive in full EPB mode, making the changeover soon after driving through the Inai shaft location for the final drive through Bukit Bintang, Pudu shaft and Merdeka station and on to final breakthrough in Pasar Seni station.

“The performance of the machine was excellent in both modes,” said Gus Klados, Project Manager for the MMC-Gamuda JV tunnelling team. “It proved its ability through the karstic limestone strata and also in the converted EPBM mode through the Kenny Hill sedimentary deposits in which a second EPBM from Herrenknecht had been planned to operate from the Inai shaft location to final breakthrough at Pasar Seni station.”

Water inrush through the end wall of the Pasar Rakyat station box from a network of karst features

The effectiveness of the variable density concept through the highly karstic nature of the Kuala Lumpur limestone was illustrated clearly at the excavated Pasar Rakyat station and ahead of approach of the two VD machines from Cochrane station box. Control of groundwater in the karstic limestone caused delay during excavation of the station box with major inrushes of water through interconnected karstic features being recorded.

Water-filled karst voids caused excavation problems also in the adjacent Inai TBM working shafts. Excavation of one of the shafts ahead of planned drill+blast excavation of a TBM launch gallery had to be abandoned and backfilled when excessive water inflow from a karst feature became too much. “While drill+blast of the starter tunnel was successful for launch of the upper VDM, the deeper shaft for launch of the lower one had to be abandoned and backfilled. The change of strategy was to have the VDM from Cochrane mine on through the troubled zone, which it did without any problem whatsoever,” reported Klados.

The two TBMs not launched on the project – a Herrenknecht EPBM and a Herrenknecht VDM – are both held in storage by MMC-Gamuda, along with the other six machine supplied by Herrenknecht, ahead of potential use on the 10.2km underground section of the planned MRT Line 2. The project has been approved by the Government of Malaysia and the contract procurement phase is expected to begin during 2015 for a potential start of construction in 2016 or early 2017. Services on the completed Line 1 project are scheduled to start by end of 2016 for Phase 1 and by mid-2017 for Phase 2, which includes the 9.5km section beneath the streets of the city centre.