A series of technical presentations at the BTS Conference in London kept the industry up to date with progress and knowledge gained from some of the world's largest mega-projects.
A total of 19 quality lectures were held over two days at the Queen Elizabeth Conference Centre on September 23 and 24, covering developments on some of the UK's and the world's leading tunnelling projects, including: Kuala Lumpur’s Klang Valley MRT project, Crossrail, the Thames Tideway Tunnel, MiamiPort Tunnel, UK High Speed 2, Sparvo and Brisbane’s Airport Link. Additionally, speakers covered more technical aspects pertinent to the underground construction industry, including developments in centrifugal modelling, an updated model for predicting clogging of fines for ERBM drives, and real time fibre optic modelling of ground movement and the relative behaviour of tunnels passing close to one another.
Two special events in the lecture theatre followed the conclusion of each day’s technical sessions. For the first, a special 90-minute update on the host city’s Crossrail project, it was quite literally standing room only. A trio of Andy Alder of design consultant CH2M Hill, and Adrian St John and Stephan Fleischmann of the tunnelling contractor joint venture team Bam/Ferrovial/Kier (BFK), updated delegates on TBM and SCL progress under the UK capital. They also talked in more detail about the procurement methods used and the challenges involved in managing a project that has so many different components, involves so many different contractors, and runs through a crowded underground space underneath some of the world’s most densely packed, and historically valuable, real estate.
Earlier in the day Satpal Bhogal, Project Director of Underground Works for Line 1 of the Klang Valley MRT in Kuala Lumpur, started the technical proceedings with an enlightening presentation about the performance of the world’s first Variable Density TBMs (VD-TBMs). Six of the new type of machines, designed specifically for the Malaysian capital’s significant karstic limestone geology, were procured from Herrenknecht for excavation of nearly half of the project’s 9.5km of twin running tunnels.
Excavation through the numerous voids that are the characteristic, and most challenging, feature of karstic limestone resulted in the appearance of more than 50 sinkholes throughout the city during construction of the SMART tunnel. This was a situation that Klang Valley tunnelling contractor MMC Gamuda could not afford to repeat on an alignment running under the heart of the city, explained Bhogal. The VD-TBM incorporates a design that enables it to alter the density and viscosity of slurry according to geological conditions, reducing the possibility of slurry loss into voids, subsequent loss of face pressure, and, ultimately, surface ground movement and blowouts through fissures. In the event three or four small sinkholes did appear during the north-south alignment in the karstic region in Jalan Bukit Bintang. The more problematic sinkholes that appeared near the launch shaft, and which required some houses to be vacated, were due to the construction of the shaft by drill & blast excavation rather than as a result of VD-TBM tunnelling operations. Successful completion of the karstic alignments without significant damage at ground level, however, represents a good result for variable density TBM technology. This will be of interest to other regions of the world that are characterised by similarly unstable geology, notably Florida in the USA.
“Where ground conditions present problems similar to those encountered in karstic limestone in Kuala Lumpur we believe that VD-TBMs will prove very effective,” concluded Bhogal.
Another feature of the drives has been the enormous amount of grouting required. According to Bhopal this single aspect of the project has accounted for some 4% of its total cost. No news is yet forthcoming about the planned east-west Line 2, but MMC Gamuda must be considered favourite considering its experience on Line 1 and the fact that it already has six very expensive VD-TBMs at its disposal that have been excavated an average of barely 1,500m each.
Next it was the turn of Chris Fesq, Buoygues Deputy Technical Manager for the successful MiamiPort Tunnel project. Delegates heard how 1.5% of total project cost here was taken up by one of the most extensive advance ground investigation programmes ever conducted. Once again a complex limestone-based geology under Biscayne Bay presented a variety of problems, for which a specially designed Herrenknecht dual mode EPB/Water Control Process (WCP) machine was procured.
Excavation through the so-called “Layer 7” (the Key Largo Formation) under extreme pressure presented the project team with a number of challenges. Bouygues elected to mitigate project risk by undertaking, at its own expense, a huge array of geotechnical surveys that included boring 152 additional investigation holes, one for every 10m of tunnel advance, five large diameter shafts, 73 CPT holes and 126 boreholes. Additionally, an extensive formation grouting programme was utilised around the TBM as it advanced to prevent instability at the face and enable the use of WCP excavation mode. Further challenges were presented during the excavation by ground freezing techniques of the tunnel’s five cross passages.
Buoygues, relatively fresh from its success in Miami, maintained a strong presence at the conference, and its large stand in the exhibition hall testified to the company’s desire to gain a foothold in the UK tunnelling market. This market includes construction of the Thames Tideway Tunnel on the immediate horizon, and High Speed Rail 2 and Crossrail 2 somewhat further in the distance.
The company accepts it may not be among the favourites to win the contract for construction of the £500-£800 million East Tunnel section of the Thames Tideway Tunnel (due to be awarded in summer next year along with separate construction contracts for the West Tunnel and Central Tunnel). However, Buoygues is hoping that being the only single company bidder (the other teams are grouped in JVs) will set it apart from the competition.
The French contractor attracted much attention during the conference following last week’s revelation by TunnelTalk that it has procured from Herrenknecht – in joint venture with Dragages – a new world record 17.6m diameter TBM for partial excavation of the 4.2km Tuen Mun-Chek Lap Kok (TM-CLK) undersea highway link in Hong Kong. Speculation as to how the machine fits into the design was rife, especially among delegates present at the well-attended drinks reception on Tuesday evening.
TunnelTalk will continue to update the industry with news of this project as it develops.