Tunneling under Dense & Dilapidated Urban Agglomeration-Delhi Gate-Jama Masjid Corridor-Delhi Metro Rail Corporation Limited (DMRC) Kumar Ujwal1, Gupta Sushil Kumar2 1Delhi Metro Rail Corporation, Delhi 2Mega Metro Engineering Pvt. Ltd, Noida Online published on 20 April, 2019. Abstract The construction of mechanized tunnels has witnessed a series of development in the past decades. However, tunneling under urban agglomeration is still a challenge as it has to prevent and predict potential damage to structures on ground. The case is even arduous if the tunneling has to be carried out under the dense cover of dilapidated structures and historical monuments. This case study presents the challenges of TBM tunneling carried out in heterogeneous ground conditions with inadequate geotechnical details and under dense cover of dilapidated structures & historical monuments. The project for extension of DMRC Violet Line from Delhi Gate to Jama Masjid Station presented some unprecedented challenges for the tunneling operation. This Stretch of 2.15 km (twin tunnels) involved three TBMs; Construction of three station end shafts and two intermediate shafts for Launching and Retrieval; and one NATM Launch Chamber for TBM. The tunneling alignment for the aforementioned stretch was revised on two occasions due to factors beyond the control of DMRC. This resulted in the increase of tunneling length and the alignment had now to be shifted beneath the densely populated residential area. Therefore, no geo technical surveys could be carried out. Moreover, on the revised alignment, High Strength Rock (High UCS and Abrasion value) and High water table was encountered. Initially, construction on the stretch was planned to be executed using one TBM. But due to the fore stated factors, the fi rst TBM was completely damaged and stranded. Thus, two TBM's were deployed withal the fi rst TBM, for completion of the tunneling drive. This also demanded construction of additional shaft at Delhi Gate station and midshaft for retrieval of damaged and new TBM in the congested Daryaganj Locality of Old Delhi. The tunnel Construction involved blind but slow tunneling with lowered TBM advance speed & penetration rates. This minimized the volume loss/settlement and helped to achieve reduced construction induced vibration levels. The lowered penetration rates led to more wear and tear of cutter tools & cutter head, and also demanded multiple cutter head interventions (both open & hyperbaric). Also, a total of 41679 meter square of building area was supported by providing prop and jack supports and pre-tunneling retrofi tting of old buildings along the alignment was carried out. Residents also had to be evacuated from these buildings in a phase wise manner as a precautionary measure. A total of 2500 people were evacuated with around 650 people evacuated in a single go. The tunneling operation encountered incidents of formation of sink holes, crack development in old buildings, weak zones in tunneling, fl ooding of shafts etc. which were then and there resolved successfully. The case study provides insights on measures undertaken for safe tunneling under dense & dilapidated urban agglomeration, mitigation procedures for incidents encountered during tunneling; and planning for successful execution of similar tunnel projects worldwide. Top Keywords TBM, Geo-technical, Hard rock, Dilapidated, Volume loss, Sink hole. Top |