Page 49 - CO April 2017 Full Issue

Powered by COVER STORY piles are built frst to stabilise the ground, drilled between these two pillars to make then the excavation starts followed by the the muddy ground hard for tunnelling. intermediate construction sequence. Afer consolidation of the ground a sample piece was tested for the required strength CASE STUDY Challenges encountered and then tunnelling process began under While tunnelling in an urban environment, the viaduct. While tunnelling the vibrations utmost care is taken so that the underground caused by the TBM drive were measured. construction activities do not disturb Te vibrations during tunnel driving was the buildings on the ground. Along the less than the one caused by the movement alignment of the CC30 tunnel, there are of the train on the viaduct. various new and old buildings. A detailed Te next challenge was tunnelling under an study was undertaken to find out the existing canal. Te tunnel was passing under status of various structures, their building the canal at a depth of 14 meters. Tough the foundations and adequate steps were taken canal had very less amount of water in that including stabilisation of ground and season, the lining of the canal was weathered. continuous monitoring during the TBM Due to seepage of water, the ground under drive so that these structures were not the canal was muddy. A similar exercise was disturbed. For instance, adjacent to the carried our while tunnelling under the canal Shalimar Bagh station there is a shopping by putting various instrumentation and centre where the distance between the regular monitoring of the soil conditions two is bare minimum. A rigorous scheme during tunnelling. Tus the TBM could CC30 package, was the second area handed of instrumentation was set-up on this successfully be used without disturbing the over to HCC for construction. Te shaf structure to measure deflections if any. canal. is of 20 m in length, 17 mtr in width and Instruments like 3D tilt meters, Ground Rajesh Kumar, HCC’s Project Manager is 12 mtr deep. Soldier piles are drawn at Settlement Markers (GSM), inclinometer... for CC30 project explains, “All along the the periphery of the shaf to stabilize the etc were set-up to measure the slightest tunnel alignment we installed intensive ground. Between the shaf and Subhash variations as minute as few millimetres. ground instrumentation and monitoring Place station area is a 75 mtr long tunnel Tese were monitored continuously during schemes such as ground settlement monitor done by the Cut and Cover method. Te the construction phase. and settlement markers in order to study entire length of shaf plus the cut and cover Te frst major challenge encountered afer the impact of TBM on above ground tunnel area was utilized for installation of commencing the TBM operations was structures. TBM. Afer lowering the TBM part by crossing the via-duct. Around 138 meters The tunnel passed under some of the part and assembling it in the Shaf and Cut from the TBM entry point the tunnel was landmark structures such as Kasturba and Cover area, it started its drive towards crossing between the piers of the via-duct of Polytechnic building, Kendriya Vidyalaya Shalimar Bagh Station. Te Cut and Cover an existing metro line. Te depth of tunnel and even the slum area where the building area was an added advantage to assemble below the ground level under the viaduct conditions are very poor. In addition, while the TBM in one-go before the start of the was only 10 meters. While planning the carrying out the tunnelling work, proper Initial Drive. Te Subhash Place station was project, DMRC had taken care to draw the care was taken while fnalising the alignment the next area handed over to HCC to begin tunnel alignment between the two pillars. of the tunnel that it did not infringe the Pile work. Tis station is semi-underground as Te challenge was tunnelling between these area of the ‘Azadpur to Prem Bari fy over’. only 12 mtr of this station is below the pillars without disturbing the pillars in any TBM steering was difcult in the last 500 ground level and the balance is above. way. HCC did a three dimensional analysis mtr excavation as the strata encountered in In the Cut and Cover area there were of the area using “Plaxis” sofware suggested this stretch was clayey wherein driving of three PSC pipe lines of 800mm, 900mm by its Drawing Design Consultant (DDC). TBM was difcult. Despite these challenges and 1100mm diameters which were to be Te instrumentation was in place to measure we managed to complete construction of diverted before the start of the excavation for the volume loss during tunnelling and it was Tunnel 1 without causing any damage to which the approval from the owner agency not allowed to cross 0.3 per cent. Te soil the structures on ground and also without was to be obtained. HCC initiated the condition was clayey with signifcant water afecting the movement of the Trafc which documentation to seek approval. However, presence. Hence the ground between the runs over Ring road.” the permission formalities for shifting pillars was strengthened by TAM Grouting. Te tunnel boring began in October 2013 these utilities was taking considerable time. TAM grouting is done by drilling boreholes and completed the 1,247 meter long tunnel Hence, in consultation with DMRC, it was in the soil and injecting cement slurry from Netaji Subhash Place to Shalimar Bagh decided to hang these pipelines with the under pressure so that all cracks or fssures consisting of 1,037 rings with a fnished help of a temporary bridge to proceed with gets filled with the slurry. This process diameter of 5.7 meter in 111 days. The the work on the station and the excavation consolidates the ground so that there is average monthly boring progress achieved was completed. Te station was built with no lateral defection on the piles during during the construction was 337 meters the bottom-up approach where soldier tunnelling. Around 90 boreholes were with installation of over 9 rings per day. u aPrIL 2017 |construction opportunities 51