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Construction of INA Line-7 Metro Station Over Operational Twin Metro Tunnels of Line-3 of DMRC (Category : Best Practice (Engineering Case Study on Tunnel Safety)) Saurabh Sharma, Ashwani Kumar & Virender Sattawan / Delhi Metro Rail Corporation Limited, Metro Bhawan, Barakhamba Road, New Delhi-110001 E-mail: [email protected] INTRODUCTION GENERAL ARRANGEMENT & METHODOLOGY INSTRUMENTATION Ensuring the safety of a fully operational public utility tunnelling The above construction was critical due to the proximity of soil cover intervention over the existing metro /tunnel and implementation of well Since, the Line-3 tunnels in reference were kept in regular operations system such as a Metro Tunnel has always been a point of immense thought out methodology to ensure the safety of the tunnel at all times during construction was essential. Accordingly, the effected zone throughout without implementing any speed restrictions, it became concern. The same becomes further critical while carrying out ‘Cut & (16m*35m) was divided into 6 compartments for construction purposes (refer plan and L-section of the area below) and the excavation of each of essential to implement a fully automatic Real Time instrumentation Cover’ construction over the tunnel as even the slightest of safety the 6 compartments had to follow a specific sequence so that the safety and alignment of the tunnels underneath was not compromised at any point system to access the health of the tunnel. This was the biggest lapse can be disasterous to the tunnel alignment. of time during removal of soil over burden. The isolation of these compartments was achieved through boring contiguous bored piles upto design concern in view of the fact that passengers trains kept passing through However, DMRC (Delhi Metro Rail Corporation Ltd.) set a landmark depth based on their location. that tunnel every min. of the whole construction cycle. Accordingly, in the field of tunnelling safety by constructing a whole station Further, the whole sequence of execution was strictly carried out using a 24*7 real time instrumentation monitoring plan that ensured that the Beam Sensors (for monitoring deformation in tracks), Strain Gauges platform (INA Metro Station of Line-7) over the existing metro twin serviceability (SLS) of the operational existing tunnels of Line-3 was maintained during the construction of new station platform of Line-7 (for monitoring strain in tunnel lining) and Displacement tunnels (Line-3 of Delhi Metro) and that too without interrupting the Monitoring Points (for monitoring tunnel geometry) were installed operation of the existing tunnel even for a day. It may be noted that in the twin tunnels along with a 24*7 real time monitoring robotic the difference between the platform base slab and tunnel crown of the system existing twin tunnels was only 1.05m. The twin tunnels are circular in shape and had been constructed using Pre cast lining through Shield TBM methodology. To introduce the scenario, it is conveyed that a new INA interchange REAL TIME MONITORING PLAN station of LINE-7 (Pink Line) was to be constructed to integrate proposed LINE-7 with INA station of existing and operational Line-3 The instrumentation monitoring program of tunnels was typically (Yellow Line). However, in order to achieve the same, a part of the designed in order to address 2 critical issues; (a) Monitoring platform of the new station had to cross above the operational twin displacements of the tracks/tunnels in respect to serviceability during tunnels of the existing Line-3, and that too with a available clear train operations and, (b) Monitoring the overall displacements that cover of just 1.05m between the platform slab and tunnel crown. tunnels underwent in respect to the allowable deformation. Accordingly, the robotic arm installed inside the tunnels would Fig. 1 (Location of crossing Area under bubble) continuously record the readings for BS(Beam Sensors), DMP/OT(Optical Targets) and SG (Strain Gauges) as per the schedule (30min./10min.) and the same could be accessed in Real-Time at the DAS (Data Acquisition System) installed at the station area and FIG. 2 & FIG. 3 : PLAN & X-SECTION OF CROSSING AREA WITH SUPPORT ARRANGEMENT remotely connected with the instrumentation system inside the tunnel. The readings were also updated simultaneously over the internet thus enabling the Web-Based-Access. Any violation of the Limiting Values CONSTRUCTION SEQUENCE would automatically trigger alarm at DAS and also in the form of auto-generated SMSs to designated engineering and instrumentation team To begin with, the crossover area was divided into 6 apartments with the help of contiguous bored piled which were of 2 types: Type-1 (Long) & Type-2 (Short) depending upon the location of the piles (refer fig 4). Type-2 piles were done carefully as its founding level had to be only upto 1m above the existing tunnel. Subsequently, the execution was followed in the following stages: Stage-1: Casting of a barrette below permanent stage column was upto soffit of undercroft slab. The minimum horizontal distance between piles Type-1,2 and barrette from existing tunnel was kept more than 1m. TRIGGER VALUES VS. ACTUAL Stage-2: Casting of the whole roof over the crossover area in a single go over Piles type-1 and 2 over the entire tunnel crossover zone and 10m on either side meanwhile, keeping an opening of 1.5 X 1.5m in roof slab over existing tunnels each in compartment 1, 3, 4 and 6 for sand dumping in case any uplift more than desired level was observed during the execution works. Value Stage-3 :Waterproofing & protection layer over roof slab and backfill the area of roof slab over tunnel crossing zone was done up to reinstated level with an aim of neutralising uplift during excavation of base slab level to the Sensor/Gauge Obtained Allowabl Desig Trigger maximum extent since the tunnel confinement would limit the uplift during further excavation. (max.) e n Stage-4: Excavation activity upto 500mm below the strut level in compartment 1 & 4 simultaneously from both side.. Vertical 6.22 7.99 8.88 Stage-5: Installation of waler on Piles Type-1 & Type-2 and fixing of strut between walers. (mm) DMP/OT 2.9 Stage-6: Excavating 100mm below the soffit level of casted undercroft slab and PCC in compartment 1 & 4. Horizontal 3.06 3.96 4.36 Stage-7: Providing the reinforcement (as per drawing) of undercroft slab attached to couplers in D-wall and drilling holes in Pile Type-1 & 2 for rebaring by chemical anchorage. Also reinforcement of retaining wall along both (mm) sides of crossing area was provided. (+/- Strain Gauge (µ) 78 (+/-)84 (+/-)108 Stage-8: Casting of Undercroft slab using crystalline type water proofing system. )120 Stage-9: The compartment 3 & 6 were then taken up for Excavation activity, followed by Stage 5 to Stage-8. Beam Sensor (mm) 0.03 2.8 3.6 4 RESEARCH POSTER PRESENTATION DESIGN © 2015 Stagewww.PosterPresentations.com-10: Finally, the compartment 2 & 5 were then taken up for Excavation activity, followed by Stage 5 to Stage-8..

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