ORAL PAPER PROCEEDINGS

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1 ITA - AITES WORLD TUNNEL CONGRESS April 2018 Dubai International Convention & Exhibition Centre, UAE ORAL PAPER PROCEEDINGS

2 Design and Construction of Bored Tunnels for Mumbai Metro Line 3 S.K. Gupta 1, Makarand G. Khare 2, John D. Celentano 3 1 Director Projects, Mumbai Metro Rail Corporation Ltd. (MMRC), India, Subodh.Gupta@mmrcl.com 2 Associate Director, AECOM, makarand.khare@aecom.com 3 Technical Director, AECOM, John.Celentano@aecom.com ABSTRACT This paper discusses the challenges in design and construction of the complete underground Mumbai Metro Line 3 in the city centre of Mumbai, which is the financial capital of India and home to about 22 million people. The Mumbai Metro Line 3, which is a 33.5 kilometre fully underground corridor, is presently under construction. The project scope includes 33.5 kilometre of twin tube tunnelling by tunnel boring machines (TBM). The hydrogeological conditions of Mumbai, challenges posed by tunnelling under existing buildings and its impact on choice of TBM types adopted in the project are described. The design approval process for TBM selection and design features of each TBM type are discussed. Key Words: Mumbai, Hydrogeology, TBM Tunnels, Design, Construction 1. INTRODUCTION India is undergoing rapid urbanization with projected urban population of about 473 million by 2021 and 820 million by The rapid urbanization has led to a high growth in the number of vehicles leading to traffic congestions, higher air pollution, associated health risks, and higher number of road accidents leading to loss of life. Therefore it is necessary to plan the urban transport along a sustainable path to support the desired economic growth, protect the environment and to improve the quality of life. This paper discusses the challenges in design and construction of bored tunnels for fully underground Mumbai Metro Line 3 (MML-3) through the city centre of Mumbai, which is the financial capital of India and home to about 22 million people. The alignment is passing underneath very congested areas including heritage precincts of Mumbai City, therefore safety during tunnel construction and the induced ground movements from tunnelling works have to be strictly monitored and controlled during execution. The choice of tunnel boring machines (TBM) to suit the hydrogeological conditions anticipated along the alignment is critical for the success of the project. Factors governing the choice of TBM such as type, grade and strength of rock, possibilities of mixed ground conditions and water inflows are discussed. 2. PROJECT OVERVIEW The existing public transport of Mumbai is under extreme pressure. The metro master plan has been prepared to provide rail based mass transit facility to people residing in the areas not connected by existing Suburban Rail System and to enable them to reach the stations within the walking distance of 0.5 km to 1 km, with proper interchange

3 facilities. A network of metro corridors of about 150 kilometres is being implemented in a phased manner. Mumbai Metro Rail Corporation (MMRC) is constructing the MML- 3, which is a 33.5 kilometre fully underground corridor. The Figure 1 shows MML-3 alignment plan. The project scope includes 33.5 kilometre of twin tube tunnels by TBM, 19 Cut and Cover Stations, 7 Stations including cross passages and cross overs to be constructed by using NATM. The MML-3 Civil Works is divided into seven packages, keeping in view the size and cost of each package, construction programme, construction methodology, and availability of TBM works sites. The contracts include the installation of station architectural finishes, building services, and station signage. The details of the underground civil works packages are summarized in Table 1. Table 1. Underground stations and tunnels contract description Package No. Limits Length (K.M.) UGC-01 Cuffe Parade to CST 4.20 UGC-02 CST to Mumbai Central 4.05 UGC-03 Mumbai Central to Worli 5.06 UGC-04 Worli to Dharavi 6.08 UGC-05 Dharavi to Santacruz 4.94 UGC-06 Santacruz to CSIA 4.45 UGC-07 CSIA to SEEPZ MUMBAI GEOLOGY Seven islands of Mumbai off the West Coast of India were merged into one landmass by means of multiple land reclamation projects in 19th and 20th century as illustrated in Figure 1. The ground investigations show strata of soft ground (predominantly silty, clayey sand, clay of medium to high plasticity and boulders) followed by Deccan trap formation. The thickness of soft ground varies from about 1m to 14m. The Deccan traps were formed about 65 million years ago as a result of various subaqueous lava flows showing a distinct westerly dips. The major volcanic rocks are basalt, breccia, and tuff. Intertrappean sedimentary rocks such as shale are also found which indicate a long period of quiescence in volcanic activity (Sethna, 1999). The ground water table is shallow and rises close to ground level during monsoon. Although substantial portion of construction is expected in rock strata, geological surprises are expected. In the past various highway, railway, hydropower and water tunnel projects have been completed in and around Mumbai in the Deccan trap rock formation. Table 2 summarizes the anticipated rocks and possible construction issues. Jain et. al (2011) have reported the following issues during the past TBM tunnel projects under hydrogeological conditions of Mumbai:

4 High ingress of salt and sweet water from jointed basalts and flow contacts due to proximity to Arabian Sea, Creeks and Mithi River, High water inflows especially during monsoon periods, Water inflows can be expected to be saline giving high rate of corrosion to equipment, Probing and pre-excavation (chemical and/or cement) grouting will be necessary to control seepage. MML Present Figure 1. History of Reclamation of Mumbai Table 2. Geological conditions and construction issues Geological Condition Compact Basalt Contact Boundary between Basalt and Breccia Tuff, Tuff Breccia Intertrappean Shale (argillaceous and carbonaceous) Possible Construction Issues Higher degree of jointing, water bearing strata, rockfall, instability Filling of clay at contact plane, weak rock mass at contact zone Clay minerals in these rocks produce sticky muck and may jam cutters affecting progress Unstable due to their inherent softness which may be aggravated by their closely spaced laminations, water seepage along bedding planes, rock fall due to softening in contact with water, swelling behaviour The Tuff Breccia, Tuff and Amygdaloidal Basalt rocks are generally free of joints, stable and impervious and present favourable conditions for construction

5 4. TBM TUNNELS The stations will be connected with twin TBM tunnels of 5.6m internal finished diameter. In conjunction with the TBM tunnelling, precast segmental lining will be used as the main permanent support for tunnels. The choice of TBM to suit the hydrogeological conditions anticipated along the alignment is critical for the success of the project. The type, grade and strength of rock, possibilities of mixed ground conditions and water inflows govern the choice of TBMs. In all 17 TBM are to be deployed to complete the 33.5 km of twin tunnels. Table 3 summarizes the numbers and types of TBMs to be deployed for each contract package. The TBMs proposed for this project can be broadly divided in 3 categories. Dual Mode Earth Pressure Balancing (EPB) Slurry TBM EPB The anticipated average excavation rates range from 8 to 12 m/day. Past experience of TBM tunnels in Deccan trap rocks of Mumbai indicate that cutter abrasion in basalts and breccia may be less due to lower percentage of quartz and silica. However, the clay minerals in tuff and tuff breccia can lead to jamming of cutters and may affect the production cycle due to sticky property of muck (Jain et.al, 2016). Table 3. Summary of TBM deployment Civil Contract Package UGC-01 UGC-02 UGC-03 UGC-04 UGC-05 UGC-06 UGC-07 Type of TBM 2 New Robbins Dual Mode EPB 2 New Terratec Dual Mode EPB 1 New and 1 Remanufactured Robbins NFM Slurry 1 New and 2 Refurbished (New Cutter head and shields) Herrenknecht 3 New and 2 Refurbished Terratec Dual Mode 1 New and 2 Refurbished STEC EPB 5. CHALLENGES IN TBM TUNNELLING Some of the challenges which influenced the choice and design of TBMs are discussed here. 5.1 Dilapidated, heritage and sensitive buildings and structures The alignment is designed to follow the roads as far as possible. The southern parts of city have many existing and under construction high rise buildings (with more than 20 floors above ground) and roads are narrow. This requires site specific studies to evaluate the mutual impact of buildings and metro structures during planning and design phase. The multi-storey buildings over G+2 height founded on shallow foundations and the heritage structures that are within influence zone are considered critical for the design and construction. There are numerous buildings classified in moderate to severe category of damage based on pre-construction

6 building condition survey. In contract UGC-01 major portion of tunneling is to be carried out near and beneath heritage precinct. The TBM machines and construction methodology are prepared to ensure that serviceability and stability of these buildings is not affected due to tunneling works. At two locations tunnels will pass close proximity to existing flyovers which cater to thousands of commuters. 5.2 Mixed and varying geological conditions Figure 2 illustrates typical cases of varying geological conditions revealed during ground investigations. Figure 2. Illustration of varying geological conditions 5.3 Tunnelling beneath railway lines At two locations the MML-3 tunnels cross existing railway lines. These railway lines are considered as the lifelines of Mumbai and carry millions of passengers every day. Tunnelling below railway tracks requires stringent control on volume loss and ground movement such that maximum permissible total movement shall not be greater than 15 millimetres, angular distortion to rail tracks shall be limited to an absolute maximum of 1:2000 longitudinally, and 1 in 2500 transversely as measured across any one single track set.

7 5.4 Tunnelling below river Tunnels are also required to be bored through poor geological conditions below Mithi river. The geological conditions are illustrated in Figure 3 below indicates tunnels are likely to be constructed in Grade V breccia rock with high risk of water ingress. 12.6m Clay Breccia Grade III Breccia Grade IV/V Figure 3. Geological conditions for tunneling under Mithi river 6. TBM DESIGN APPROVAL PROCESS Due to the diversity and complexity of the hydrogeological conditions and the sensitive nature of tunnelling under heavily congested Mumbai city which included a number of areas comprising of high rise buildings, heritage and religious sites, dilapidated buildings the TBM design approval process was established shortly after contract award. This was paramount and subsequently was the key in ensuring the correct choice of TBM along the full alignment and obviously critical for the successful delivery of the tunnels The seven contractors adopted this approach and resulted in five different TBM manufacturers supplying 17 TBMs as described in Table 3. The final choice of TBMs adopted 3 different excavation methods including Slurry TBM, EPB TBM and Dual Mode or Crossover TBMs. 6.1 Initial review of TBM design Following initial geotechnical and hydrogeological investigations which formed part of the tender documents, the chosen alignment and the envisaged difficulties of TBM mining beneath Mumbai, it was considered prudent and beneficial to engage in early discussions with contractors and their chosen TBM suppliers. These early discussions were found beneficial and brought an integrated approach and collaboration to the TBM design development processes. The following basic requirements of TBM design were established and adopted across all contractors and TBM suppliers, namely

8 Geometric parameters including alignment, excavation diameter, segmental lining preliminary design including ring width, minimum radius of curvature along the alignment. Geotechnical and hydrogeological parameters including height of water table, rock types, specific gravity, cohesion, angle of friction, elasticity and permeability of the materials to be mined. At this early stage design only Tender Geotechnical Reports were available but these were deemed sufficient in detail to commence the TBM design process. Furthermore it was agreed by all parties, namely Contractors and TBM suppliers that a reality check during each stage of design development would be performed following the availability of Contractor s own additional geotechnical investigation reports including both Geotechnical Factual and Interpretive reports. This led to the development of the outline design and choice of excavation method. Assessment of key mechanical requirements of the TBM such as total thrust pressure, torque requirements, cutter head design layout, number and size of disks cutters, scrapers buckets and their respective spacing, geometrical configuration of thrust pads, annular grouting pressures and the like. Critical natural obstructions such as rivers, railway lines, high rise buildings, critical and religious structures, overburden and availability of land at each launching shaft. Other design loads such as geostatical, gantry thrust and main bearing loads, dead loads, storage and erection loads and the like Geometrical and spatial requirements for TBM transportation through congested and constrained roads in Mumbai. These fundamental TBM design requirements were discussed during initial design meetings with each contractor and manufacturer and were universally adopted for each tunnel section along the whole 33.4Km of the tunnel alignment. These meetings resulted in the outline or preferred choice of TBM whereby allowing consultants, contractors and manufacturers to proceed in developing the outline design for the TBM of choice. Cutterhead design, thrust and torque requirement are fundamental and critical requirement for the successful operation of the TBMs. The design layout of the cutterheads varied considerably between manufacturers and TBM types. Following the initial design meetings, outline design for cutterhead was developed for each TBM type, however this was based on the limited geotechnical data available at the time. Once the outline cutterhead design was completed, manufacturers used additional geotechnical data obtained from contractor s own additional investigations to validate the cutterhead design and develop thrust and torque requirements. These were submitted and subsequently approved in principle by the consultant. This approval in principle triggered the next process to develop the detailed design for the TBMs. In all, 9 different cutterhead designs, with varied excavation methodology, thrust and torque requirements were put forward by the 5 manufacturers. These included cutter head designs for mixed ground and hard rock conditions. The three types of TBMs and its design features are discussed in the next section.

9 7. CROSS OVER OR DUAL MODE TBM Cross over or dual mode TBMs, 7 in number will excavate approximately 15Km of the 33.4 km dual running tunnels and will be supplied by manufacturers Robbins and Terratec (2 numbers) and (5 numbers) respectively. Photograph of dual mode TBM is shown in Figure 4. Figure 4. Terratec dual mode TBM Cross over or dual mode TBMs were the machine of choice along this section of the alignment primarily because of the enhanced and more favourable geological conditions allowing greater excavation rates to be obtained in open mode operation with the use of belt conveyors instead of screw conveyor, the reduced risk associated with less congested areas and the effectiveness of operations compared to other TBM types. Typical geology along the tunnel alignment is simplified and summarised in Table 4below.

10 Table 4. Dual mode TBM Summary of geological conditions Geological Description Unconfined Compressive Strength (MPa) Fresh Basalt with volcanic rock in whole face of the 85 tunnel. Basalt comprises infillings of silica and zeolites Fresh Basalt and Volcanic Tuff Mixed face with Volcanic Tuff, Fresh Basalt and Up to 125 Moderately weathered Breccia Fresh greyish Basalt Design features of the cross-over or dual mode TBM With enhanced ground conditions over a greater distance along the alignment, the design of the TBM still had to cater for the possibility of the following geological conditions, Variations in ground type Possibility of running ground and/or face collapse Flowing and faulted ground Possible water inflow Based on these, and other mechanical properties obtained from the ground investigations, Dual mode or Crossover Single Shield machine with special features were considered appropriate as shown in Figure 4. These special features included heavy duty main bearing and modified cutterhead structure to cater for hard rock conditions, quick change over from open to close mode by changing from belt conveyor to screw conveyors to cater for unexpected water conditions, inclusion of high capacity heavy duty 17 disc cutters with an efficient method of cutter disc change in-case of interventions during closed mode operation which would result in the least amount of downtime. Other special feature attributed to this type of TBM is the ability to close off the machine should soft flowing ground, faulted ground or high water inflows be encountered. The Dual mode or Cross over TBM is equipped with a screw conveyor. This screw conveyor can be activated and prevent any material or water from exiting the cutter chamber and entering into the machine. The system can also operate in a semi-epb mode, in which as the pressure in the cutterhead chamber increases, the screw conveyor discharge gate is opened and material is discharged on the conveyor belt located on TBM backup system. Additionally and in extreme conditions, once the muck chamber is sealed against material or water inflows the probe/grout drill can be utilized to forward drill and grout, for ground consolidation and to seal off the inflow of water or poor ground. 8. SLURRY TBM Slurry machines will excavate approximately 3.6 Km of the twin bore running tunnels and being supplied by NFM/Robbins Limited as shown in Figure 5. In total 2 slurry TBMs will be used to excavate the twin bore running tunnels.

11 Figure 5. NFM Slurry TBM Slurry machines were the machine of choice along this section of the alignment primarily because of varied geological conditions, close proximity of the tunnel alignment to heavily the congested areas and sensitive structures, condition of the buildings and the abundant availability of land for the use of desilting plant adjacent to the launching shaft. Typical geology along the tunnel alignment is summarized in Table 5 below. Table 5. Slurry TBM - summary of Geological Conditions Geological Description Unconfined Compressive Strength (MPa) Fresh Basalt with infillings of silica and zeolites 100 Mixed face conditions with Volcanic Breccia near the crown while greyish Basalt in invert zone Weathered Tuffaceous Breccia Up to 20 Fresh Amygdloidal Basalt with Breccia Up to 60 Mixed face with Basalt and Breccia 80 Slightly weathered to Fresh Basalt Design features of the slurry TBM With poorer ground conditions along the alignment, the design of the TBM had to cater for the following geological conditions, Large variations in ground type over shorter distances which varied from hard rock to soft soils Possibility of running ground and/or face collapse under sensitive and congested areas Flowing and faulted ground along most of the alignment Possible water inflow

12 Based on foregoing and the geological data provided by the contractors additional geotechnical investigations the following special features were considered appropriate. Heavy duty main bearing and mixed ground cutterhead structure to cater for soft and hard rock conditions. Special design of the chamber allowing easy access during hyperbaric interventions for quick change over of cutting tools especially when changeovers are required beneath congested areas. Inclusion of high capacity heavy duty 17 disc cutters and scrapers. Prevention of occurrence of sink holes beneath or adjacent to buildings by inclusion of full peripheral grouting. Inclusion of a rock crusher Some of the advantages that slurry methods include: Reduced wear from the abrasivity while mining in hard rock of the excavated material due to the beneficial effects of the cutters being permanently immersed in a slurry and its associated lubricating effects. Reduced possibility of ground settlement due to the positive face support provided by slurry pressure independent of the machine advance especially in congested areas with sensitive buildings Better control of the ground and ground water pressures when excavating through soft ground/rock interface zones 9. EPB TBM EPB machines will excavate approximately 14.8 Km of the twin bore running tunnels. In total 7 EPB TBMs will be used to excavate the twin bore running tunnels. Three TBMs being supplied by Herrenknecht and shown in Figure 6, two from Terratec and two from Shanghai Tunnelling Engineering company. EPB machines were chosen along these sections of the alignment primarily because of largely varying geological conditions, surface features such as rivers and railway tracks and the reduced cover to sensitive structures. The contractors and TBM manufacturer concluded that the following geological risk existed at various sections along the alignment, Unstable face weak rock mass (soil like) and water Material erosion at the face weak material which can be washed out by water flow or disintegrates in contact with water Weak joint fillings which can be washed out by water flow leading to blocky failure Localized / Concentrated water inflow which may erode material in the weak layers above resulting in sinkholes and volume loss Small block fall at the face resulting in local instability

13 9.1 Design features of the EPB TBM Based on the geological data provided by the contractors additional geotechnical investigations the following special features were considered appropriate. Large opening ratio of between 28 and 35% Additional injection ports in the cutter head to enhance soil conditioning Closer spacing than normal for forward probing and ground enhancements Bespoke cutter head design with closer spaced disk cutters, scrapers and peripheral cutters to accommodate the large opening ratio. Figure 6. Herrenknecht EPB TBM

14 10. CONCLUSIONS Due to the fast track approach in construction of Mumbai Metro line 3 project a clearly defined and systematic approach was taken in the design development and choice of the TBM to be used during tunnel excavation. Outline design of the TBM were developed in parallel with other designs such as segmental lining, appropriation of additional geotechnical information, construction methodology and building condition surveys. Additionally, close collaboration between Client, Contractor TBM Manufacturer and General Consultant combined with the iterative design process contributed immensely to the successful delivery and launch of the TBMs. A unique approach but one which has proved successful. Other factors such as development of detailed Factory and Site acceptance test methodology ensured that all TBMs were tested before delivery and launch respectively. Tunnelling operations has commenced and all initial indications seem to suggest that they are performing satisfactorily with average excavation rates predicted to be in the order of 20 to 25m per day for each TBM in varied and difficult ground and operational conditions. 11. REFERENCES Jain, P., Naithani, A. K. and Singh, T. N. (2011). Application of Tunnel Boring Machine for the construction of Maroshi-Ruparel College Tunnel Mumbai, India. Journal of Engineering Geology, 37 (1-4), Jain, P., Naithani, A. K. and Singh, T. N. (2016). Estimation of the Performance of the Tunnel Boring Machine (TBM) Using Uniaxial Compressive Strength and Rock Mass Rating Classification (RMR) A Case Study from the Deccan Traps, India. J. Geol. Soc. India, 87, Sethna, S.F. (1999). Geology of Mumbai and surrounding areas and its position in the Deccan volcanic stratigraphy, India. J. Geol. Soc. India, vol. 53,

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