Development of Tunnel Dismantling Machine (TDM) - ScienceDirect

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ScienceDirect Procedia Engineering 189 (2017) 560 – 568

Transportation Geotechnics and Geoecology, TGG 2017, 17-19 May 2017, Saint Petersburg, Russia

Development of tunnel dismantling machine (TDM) in an underground railway project P.L. Nga*, T.N.D.R. Barrettb, G. Rouxc, S. Polycarped, M. Gonzaleze a

Formerly Dragages-Maeda-BSG Joint Venture, Hong Kong, China b MTR Corporation Limited, Hong Kong, China c CSM Bessac, Saint Jory, France d Dragages Hong Kong Limited, Hong Kong, China e Bouygues Construction, Guyancourt, France

Abstract The MTR West Island Line (WIL) project in Hong Kong involved demolishing and backfilling a 132 m section of the existing Overrun Tunnel (ORT) through complex geology beneath densely populated urban area, in order to enable subsequent excavation of the WIL Down-track (westbound) running tunnel by tunnel boring machine (TBM). To tackle the challenge while minimizing construction risks, a bespoke tunnel dismantling machine (TDM) was innovated. The TDM worked backwards from the operational railway interface inside the ORT to remove each lining segment ring under 2.8 bar compressed air pressure, sprayed shotcrete lining for temporary support, and backfilled the remaining void left underground. The crew behind the demolition chamber of TDM worked under atmospheric pressure. Part of the backfilled tunnel was then re-excavated by slurry TBM to form the re-aligned WIL Down-track running tunnel. The TDM was able to accomplish the works safely and led to the successful opening of WIL. This paper explicates the development of the world-wide unprecedented TDM and the construction process of ORT demolition. © 2017 The Authors. Published by Elsevier Ltd. © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the scientific committee of the International conference on Transportation Geotechnics and (http://creativecommons.org/licenses/by-nc-nd/4.0/). Geoecology. Peer-review under responsibility of the scientific committee of the International conference on Transportation Geotechnics and Geoecology Keywords: Confinement; hyperbaric intervention; lining segment; shotcrete; tunnel dismantling machine; tunnelling

* Corresponding author. Tel.: +852-9587-5310; fax: +852-2559-5337. E-mail address: [email protected]

1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the International conference on Transportation Geotechnics and Geoecology

doi:10.1016/j.proeng.2017.05.089

P.L. Ng et al. / Procedia Engineering 189 (2017) 560 – 568

1. Main text The MTR West Island Line (WIL) in Hong Kong extends the existing Island Line (ISL) from Sheung Wan Station (SHW) to Kennedy Town (KET) via Sai Ying Pun (SYP) and HKU Stations, adding approximately 3.3 km of the railway route length. The SHW to SYP Tunnels belong to the scope of WIL Contract No. 703 (WIL703), which comprises the Up-track (eastbound) and Down-track (westbound) running tunnels excavated by both tunnel boring machine (TBM) and Drill-and-Blast methods [1,2], construction of access tunnels and shafts, artificial ground freezing gallery at existing SHW Crossover Box (COB) to remove pre-existing obstructions prior to TBM excavation [3], construction of SYP Station Entrances A1/A2 structure, and other associated works. Fig. 1 depicts the general layout of WIL703 project. During the construction of ISL in 1980s, the Sheung Wan Overrun Tunnel (ORT), which served as refuge siding for shunting of broken-down train, was designed with planned future extension in mind. The ORT stretched about 500 m from SHW COB to Ko Shing Street ventilation shaft. However, due to changes in land usage, the WIL tunnel alignment was shifted towards the south to better serve the development catchment of the Western District. Thus the end portion of the existing ORT no longer suited the revised alignment and the new westbound tunnel would connect halfway along the existing ORT, as illustrated in Fig. 2. A section of the ORT of 132 m length was in conflict with the Down-track running tunnel and needed to be demolished prior to the new tunnel construction.

Fig. 1. General layout of WIL703 project.

Fig. 2. Geometry of new tunnel connection to ORT.

The ORT was an undrained tunnel with external diameter of 5.8 m and was lined with precast reinforced concrete or spheroidal graphite iron (SGI) segment rings. Each ring of precast concrete lining was 1.0 m wide and 0.25 m thick, whereas each ring of SGI lining was 1.0 m wide and 0.15 m thick. The internal diameter of the ORT was 5.3 m at the precast concrete lining sections and 5.5 m at the SGI lining sections. A photograph of the ORT showing both types of lining is given in Fig. 3. The 132 m section of ORT comprised 125 precast concrete rings and 7 SGI rings. The ORT was curved on plan with a minimum radius of curvature of approximately 600 m, and it sloped down from SHW to Ko Shing Street at 0.5% gradient. The geological condition was variable and complex. Fig. 4 illustrates the geology along the longitudinal section of ORT, which was mainly embedded in completely decomposed granite (CDG) with corestones, and overlain by alluvium and marine deposits. The maximum groundwater head above the tunnel invert level was 27 m. The ORT and the new westbound tunnel were situated underneath dense urban areas with limited clearances to the existing building foundation piles, the closest being circa 400 mm. The above restraints necessitated a promising construction methodology.

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Fig. 3. ORT lining segments.

Fig. 4. Geological section.

2. Principle and details of the TDM As the demolition of ORT constitutes a peculiar challenge to the construction of WIL, a number of construction schemes had been studied throughout the preliminary design stage and tendering stage of the project. With the aim to minimize risks to the construction team and to third parties, the Main Contractor of WIL703, Dragages-Maeda-BSG Joint Venture (DMBJV), proposed to dismantle the existing lining under compressed air pressure and then backfill the ORT by a bespoke tunnel dismantling machine (TDM), before the newly aligned westbound tunnel is re-excavated by a slurry mix-shield TBM. Fig. 5 illustrates the conceptual view of the TDM. Through ingenious combination of inventive thinking and meticulous planning, the first ever TDM in the world was transformed into reality by the joint efforts between MTR Corporation Limited, DMBJV and tunnelling machinery specialist CSM Bessac [4,5]. Prior to demolishing the ORT, the TDM works area was separated from the operational railway by a mass concrete bulkhead. The ground around the ORT was grouted and the ORT segment joints were caulked to minimize water ingress and compressed air leakage. During the tunnel demolition process, the TDM moved backwards from inside the ORT, i.e. from the bulkhead towards Ko Shing Street ventilation shaft. The TDM removed the lining one ring at a time under 2.8 bar air pressure, applied a shotcrete lining as temporary support to the exposed ground of the ORT, and backfilled the remaining void. With the exception of specially-trained personnel for conducting geological inspections and machinery maintenance under hyperbaric condition, the TDM operator and the workforce were remained behind the TDM front shield under atmospheric pressure, and were protected against the hyperbaric environment and exposed geological risks.

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Tailskin shield with brush seals Telescopic stabilizers

Man locks (2) Pilot viewing windows Front shield Protection plates Telescopic arm

Direction of travel

Hydraulic thrust cylinders (8)

Middle shield

Material lock

Fig. 5. Conceptual view of TDM.

Demolition arm

Fig. 6. Anatomic view of TDM.

The TDM was composed of different functional components. An anatomic view is presented in Fig. 6 for ease of visualization. The demolition arm performed multiple functions in the demolition chamber. It was made up of a retractable hydraulic breaker for demolishing ORT segments, grabbing claws for transferring segments from their original position to the material lock, a scraper plate for cleaning the invert, a shotcrete nozzle for concrete spraying, and a device for checking the thickness of freshly sprayed shotcrete lining. Being capable of operating radially through 360 degrees, the demolition arm was comprised of two articulated modules on a horizontal turret. The design of this heavy duty and sophisticated demolition arm with many movable parts presented enormous engineering challenges in its own right. Robust protection systems for the arm without interfering its functionality and movability were required. The TDM was equipped with two man locks and a material lock. The man locks were provided to compress and decompress the workers undergoing hyperbaric interventions in the demolition chamber. The durations of compression before hyperbaric work and decompression after hyperbaric work were determined according to the project decompression tables approved by the Labour Department of Hong Kong for compressed air work. The tables were based on the French Ministry of Labour Tables [6] which are commonly referred to as French Decompression Tables. The material lock allowed transferral of demolished segments and debris to the free air for removal. Due to limited width of the material lock, the demolished segments needed to be rotated 90 degrees by the demolition arm for entering into the material lock with its short side (i.e. 1.0 m width of segment). The ring being demolished was temporarily propped at the crown by six telescopic arms which supported the upper half of ring in place to avoid uncontrolled dislocation once the key was removed. The upper part of the front shield was fitted with telescopic crown protection plates to protect workers from falling material. Hence, safe access to the demolition arm for mechanical repairing and for cleaning the spraying nozzle after shotcreting was maintained. The shields of TDM comprised the front shield, central shield, and rear shield. The shields had an external diameter of 5.1 m and a total length in the longitudinal direction of approximately 6.8 m. The shields protected the TDM components, contained the compressed air, and provided articulations (between the front and central shields and between the central and rear shields) so as to cater for the curvature of ORT. For optimal centering of the TDM, the tail skin of rear shield was designed to allow for an all-round radial movement of 20 mm to accommodate the curvature of ORT and initial deviations of the ORT segment ring from a perfect circle. At the same time, the tail skin had to be air-tight to maintain the compressed air in the demolition chamber from atmosphere pressure in the operating area. To achieve effective sealing while allowing the radial movement, the tail skin seal was formed by three sets of wire brushes with grease injection forming two sealant chambers against the segment intrados. This is in contrast to the provision of rows of brushes for sealing a TBM, where the brushes are sealed against the segment extrados. In order to validate the proper functionality of various elements of the TDM, a series of tests were conducted. The demolition arm was thoroughly tested with purposely-built precast lining segments replicating the existing ORT segments as depicted in Fig. 7. The segment concrete breaking, removal of segment from its constructed position, and handling of segment including moving and rotating by grabbing were fully validated in the testing regime. The tail skin was tested by placing concentrically as well as eccentrically into a prefabricated steel ring corresponding to the

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worst-case geometry of the ORT. Compressed air was applied to the annular space between the ring and tail skin, and the pressure drop after switching off the compressed air supply was measured to testify the air-tightness of the tail skin seal.

Fig. 7. Testing of demolition arm.

Fig. 8. Pressure chamber for shotcrete trials.

A 3 m diameter pressure chamber was fabricated as shown in Fig. 8 for conducting shotcrete trials in compressed air. The pressure chamber conformed to statutory requirements of the Boilers and Pressure Vessels Ordinance of the Laws of Hong Kong. The trials provided useful data for adjusting the shotcrete mix designs to fulfill the requirements on workability for spraying, rate of strength development in compressed air environment, and robustness of performance against variations in operation parameters. The shotcrete strength at different ages was measured with core samples taken from trial shotcrete panels, and this was a key performance attribute determining the thickness of temporary shotcrete lining required and the time to permit loading in the detailed design. Trial operation of the TDM was performed inside a 15 m long full-scale mock-up tunnel, which helped fine-tuning the machinery and eliminating potential problems in every element of work. 3. Analysis and design The ORT demolition was analysed by 3-dimensional finite element (FE) software Plaxis 3D. Fig. 9 depicts the FE model. The soil and rock properties were established from the ground investigation results. The earth pressure, building loads, surcharges and hydrostatic pressure were considered. At the time of carrying out the tunnel demolition work, the new WIL Up-track running tunnel was already excavated. Therefore, both the effects of Up-track running tunnel on ORT demolition as well as the effects of ORT demolition on the Up-track running tunnel needed to be analysed and assessed. In the FE modelling, the presence of ORT, Up-track running tunnel, as well as the construction sequence were simulated. The analysis had verified the adequacy of the proposed 2.8 bar compressed air pressure to ensure the face and sides stabilities of the unsupported excavation. The computation results revealed that the maximum ground settlement was 2.4 mm and the maximum face loss was 0.4%. These movements would cause no significant adverse effect on the existing buildings and structures. The minimum thickness of temporary shotcrete lining was also established by the FE analysis. Structural actions of the temporary shotcrete lining were evaluated from the computation results. Early-age strengths of shotcrete were obtained from the shotcreting trials for deriving the shotcrete strength development curve. The axial, flexural and shear capacities of the shotcrete lining were checked based on the M-N (bending moment-axial force) interaction envelopes at different ages. The design checking confirmed that a 300 mm thick shotcrete lining would suffice. In conjunction with the given thickness, the time to permit loading onto the shotcrete lining was determined based on the shotcrete strength attained, which was a key design criterion requiring verification during construction.

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Sensitivity analysis was conducted with variations of the compressed air pressure, shotcrete strength, shotcrete thickness and length of unlined section. Optimization of production cycle was carried out based on the sensitivity analysis results. By checking the loading on the temporary shotcrete lining for different lengths of unlined section, the viability of 1-ring cycle (dismantling 1 segment ring followed by shotcreting) and 2-ring cycle (dismantling 2 segment rings followed by shotcreting) was established.

(a)

(b)

Fig. 9. FE analysis of tunnel dismantling: (a) 3-dimensional FE model, (b) Deformed shape.

For the first four rings where the new Down-track running tunnel connects with the existing ORT, an overexcavation of 600 to 900 mm was required for the TBM arrival. This enlargement was constructed to allow room for dismantling the TBM cutter-head as well as for constructing the in-situ permanent reinforced concrete tunnel lining at the TBM tunnel to ORT connection under atmospheric pressure. The thickness of shotcrete lining of the overexcavated portion was increased to 400 mm minimum and was verified by FE analysis to be adequate. As part of the WIL703 project instrumentation and monitoring (I&M) plan, a comprehensive I&M plan in the vicinity of tunnel demolition works area was included in the design. At ground surface, within the monitoring zone, the ground settlement and groundwater drawdown were respectively measured by ground settlement markers and piezometers, and recorded systematically as per the I&M plan. Movements of buildings and operational railway tunnels were monitored and recorded by the Automatic Deformation Monitoring System (ADMS), whereas the newly constructed eastbound tunnel and the section of ORT to be demolished were manually surveyed using prism convergence arrays along the tunnels. Alert-action-alarm (AAA) values were defined in the I&M plan with corresponding contingency measures to be undertaken should the AAA levels be reached. 4. Tunnel dismantling operations 4.1. Site installations At ground surface, the site area occupied the Ko Shing Street junction, a section of westbound traffic lane in Des Voeux Road West, and the existing disused ISL ventilation building (Fig. 10). The site installations at surface included a 10 ton lifting capacity monorail crane, a water treatment plant, an electric switch container, an 1000 kVA mini substation, an emergency generator with cooling tower situated above, a concrete pump with emergency compressor situated above, and ventilation fans with silencers inside the ventilation building. The Ko Shing Street ventilation shaft and building openings were covered with noise attenuating panels/doors to abate the noise. The ventilation shaft was 30 m deep with diameter between 7.4 m and 6.4 m. The site installations in the shaft included a man-lift, exhaust fans with ducts, two breathable air compressors (one active and one stand-by connected

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to the emergency generator) for providing confinement for the TDM, two 10 bar industrial air compressors for shotcreting, compressed air receivers, and a power pack located at the shaft base. Along the ORT, rails were installed for running a 10 ton Clayton locomotive and flat car fixed with a 10 ton capacity Fassi crane to facilitate transportation of materials. Besides, temporary services including ventilation duct, water supply and wastewater discharge pipes, compressed air pipes, concrete supply pipes, main power, task and emergency lighting cables, data cables and pedestrian walkway were installed. Near the end of ORT, the site installations included a 3.2 ton capacity stationary jib crane mounted at the invert, two concrete agitating tanks, concrete pump and storage platforms.

Fig. 10. Site installations at ground surface.

Fig. 11. Thrust reaction structure system.

4.2. Thrust reaction structure The 2.8 bar compressed air pressure created a thrust that pushed the TDM backwards. This force was counteracted by a thrust reaction structure system which consisted of three reinforced concrete thrust reaction rings and a steel thrust reaction frame as shown in Fig. 11. The 132 m long section of ORT was equally divided into 3 sub-sections of 44 m and a reinforced concrete thrust ring was constructed at the end of each sub-section. Between the concrete thrust ring and the TDM, a steel thrust frame was installed along the sub-section to transmit the backward force from the TDM via the concrete thrust ring to the surrounding grouted ground. The steel thrust frame consists of steel struts coaxial with the 8 nos. perimeter hydraulic thrust cylinders of the TDM, and steel arches restraining the struts at every 3 m interval. The struts were approximately 3 m in length, and were supplied in two sets (2.99 m painted in blue and 3.01 m painted in red, Fig. 11 refers) with difference of 20 mm to accommodate the curvature of ORT. To economise the fabrication quantities of steel thrust frame members, the steel arches and struts were re-used in each sub-section. The alignment of the steel thrust frame was subjected to close inspection against buckling and instability. 4.3. TDM assembly The TDM was delivered on site in parts each not exceeding 10 ton and lifted down by the monorail crane to the ORT. Some TDM parts could only fit through the lifting window of the shaft tightly with very small clearance. With the experience gained in the trial assembly, the TDM was assembled using the Fassi crane mounted on flat car in the ORT efficiently in 55 days. The completion of TDM assembly was followed by testing and commissioning of the control system, initial checking of thrust reaction structure, staged hydrostatic pressure testing (hydrostatic instead of


compressed air pressure was exerted for more stable pressure increment and decrement), as well as re-checking of thrust reaction structure upon pressure increments and after unloading. 4.4. Work cycling The initially planned work cycle involved shotcreting the exposed ground in compressed air after dismantling each ring and weekly backfilling of the tunnel void at atmospheric condition. It was thought that such weekly cycle would best utilize the capacity of concrete pump and lead to better production rate. However, upon reviewing the potential risks associated with the erection of formwork outside the reach of the crown protection plates and the prolonged standing time of the temporary shotcrete lining, an alternative work cycle was developed. To maintain the confinement by compressed air and to minimize hyperbaric works as much as possible, the tunnel was backfilled with shotcrete on a daily basis under compressed air. The shortened standing time of tunnel void before backfilling reduced the risk of ground settlement. The weekly cycle was revised such that scheduled maintenance works would be carried out in the demolition chamber in weekends at atmospheric pressure. Before depressurising, all shotcrete sprayed during the cycle must be confirmed by tests to have compressive strength of no less than 15 MPa and minimum 300 mm thickness. Design checking was performed to validate both sequences of dismantling one ring followed by shotcreting and backfilling (1-ring cycle) and dismantling two consecutive rings followed by shotcreting and backfilling (2-ring cycle). The latter sequence was achievable on site in 24-hour cycle (dismantling in night shift and completing the backfilling within the following day shift), and thus it was adopted. Fig. 12 depicts the segment dismantling operation. The backfill material was a fly ash-cement mix with 28-day compressive strength of no less than 1.5 MPa (such that it is not too weak to cause additional ground settlement after backfilling). The mix contained high fly ash content to reduce heat generation during curing. The low cement content helped mitigating the degradation of bentonite slurry used to support the subsequent TBM excavation and enhancing the sustainable performance. Trial mixing was conducted to establish the mix proportions of the backfill material prior to launching the TDM.

Fig. 12. Segment dismantling operation.

Fig. 13. Demolition chamber during an atmospheric stop.

When the ORT dismantling for one sub-section was completed, the concrete thrust ring needed to be removed for the TDM to move backward. At this juncture, the TDM was stopped and depressurised for one week during the concrete thrust ring demolition. Fig. 13 shows a photograph of demolition chamber during an atmospheric stop. The depressurisation of TDM must strictly follow a detailed staged decompression plan to ensure no undue ground deformation and surface settlement. For the last 7 rings of SGI segments, they were demolished with the hydraulic breaker of the demolition arm in view of their brittle nature. The last few rings only encroached partially into the TBM

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alignment and hence they were partially demolished. Overall the tunnel dismantling was completed safely and on time. 5. Conclusions To overcome the immense challenge in the MTR West Island Line (WIL) project of demolishing and backfilling an existing segment-lined railway tunnel to allow for constructing a new re-aligned railway tunnel connecting to it, the tunnel dismantling machine (TDM) was developed as an innovative and unique solution. Being able to remove tunnel segments, spray temporary shotcrete lining in compressed air, and backfill the tunnel void, the TDM was designed to minimize the construction risks due to variable geology, constrained space, and dense urban environment. It reduced to the largest extent the exposure of workers to hyperbaric condition by localising the compressed air in the demolition chamber, thus constituting a major health and safety improvement. The TBM confinement concept was re-engineered for application to the TDM to ensure the tunnel face stability. The adequacy of the compressed air pressure and temporary shotcrete lining was verified by finite element analysis, and the performance and strength development of shotcrete under hyperbaric condition were established by extensive trials and mix optimizations. The TDM works were completed safely with minimal impact to third parties. The success of TDM works was the result of dedicated teamwork, non-conventional design, thorough testing and trials, detailed construction planning, advertent site inspections, optimized work cycling, extensive monitoring and comprehensive contingency planning. The accomplishment of TDM enabled the opening of WIL, and once again provided a remarkable paradigm of engineering excellence in Hong Kong. Acknowledgements The authors would like to thank MTR Corporation Limited for permission to publish this paper. References [1] M. Baribault, M. Knight, W.S. Chow, Risk management and construction of drill and blast tunnel in shallow rock cover, in: Geotechnical Aspects of Tunnelling for Infrastructure Development, Proceedings of the 32nd Annual Seminar, Geotechnical Division, The Hong Kong Institution of Engineers, Hong Kong, 2012, pp. 159–167. [2] A.C.M. Tsang, C.D. Salisbury, S.S.M. Yeung, Confinement pressure for face stability of tunnel boring machine (TBM) tunnel excavation under Hong Kong’s Western District, in: Geotechnical Aspects of Tunnelling for Infrastructure Development, Proceedings of the 32nd Annual Seminar, Geotechnical Division, The Hong Kong Institution of Engineers, Hong Kong, 2012, pp. 147–158. [3] S. Polycarpe, P.L. Ng, T.N.D.R. Barrett, Construction risk mitigation of the tunnel to station connection using artificial ground freezing in the MTRCL West Island Line Contract 703, in: Geotechnical Aspects of Tunnelling for Infrastructure Development, Proceedings of the 32nd Annual Seminar, Geotechnical Division, The Hong Kong Institution of Engineers, Hong Kong, 2012, pp. 137–146. [4] F. Vallon, J.M. Sabatié, E. Baranger, Machine à démonter un tunnel, in: Proceedings, 13th AFTES International Congress, Association Française des Tunnels et de l’Espace Souterrain, Lyon, France, 2011 (in French). [5] F. Vallon, C.D. Salisbury, G. Roux, M. Gonzalez, Tunnel dismantling machine - from innovation to completion, in: G. Anagnostou, H. Ehrbar (Eds.), Underground – The Way to the Future, Proceedings of The World Tunnel Congress, Geneva, Switzerland, 2013, pp. 1281–1288. [6] Direction des Journaux Officiels, Travaux en Milieu Hyperbare: Mesures Particulières de Prévention, Brochure No. 1636, Imprimerie du Journal Officiel, Paris, France, 1992 (in French).