International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 10 Issue: 07 | Jul 2023
p-ISSN: 2395-0072
www.irjet.net
Analysis of stability of rock column between cut & cover Metro Station and NATM Tunnels Swarup Maiti1, Prof. Dr. Sandeep Potnis2 1PG student, MIT World Peace University, Pune, India
2Head, School of Tunnel Engineering, MIT world Peace University, Pune
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Abstract: Planning and accommodation of underground metro stations in available land areas is an important aspect of any metro project. Designer has to adopt the innovative solution for station design due to limited space. To accommodate the station box within the available area, station may have to be constructed with the combined construction approach of NATM and cut and cover. In this approach main station box is constructed with a cut and cover method and platform tunnel is constructed with a NATM method. The sequence of construction can be simultaneous or opening of tunnel is carried out from the cut & cover shaft or TBM tunnel excavation is done before station excavation. Any underground excavation has a major influence on the nearby existing structures. This paper covers the various aspects of ground response to the interaction between strutted excavation and NATM tunnel excavation. Study of integrated excavation is carried out with varying the width of rock column between station excavation and NATM platform tunnel. The variations in the geological stratification and impact of different construction sequences are investigated. Key words- Earth Retaining System (ERS), secant pile, Platform NATM tunnel, Surface settlement, Underground metro, Rock column, cut and cover structures, deep excavations.
1. INTRODUCTION India has seen a huge development in the metro rail projects in the last 3 decades. Several Underground Metro projects have been constructed and many are in the under-construction and planning phase. Planning and design of the underground metro station is a challenging job. As most of the underground stations are planned in a densely populated area to gain more public ridership. Underground metro stations are usually planned under roads, empty ground. Planning of underground station under existing road has major issue i.e., protection of buildings adjacent to the metro station. One of the underground metro stations were planned in a densely populated area in Mumbai, on narrow roads, and in the station vicinity, several dilapidated buildings were present. Hence few stations were planned to construct with a mixed method of cut and cover for station box and NATM method for Platform tunnel. Owing to the presence of buildings in the vicinity of the station footprint the possibility of a complete cut and cover station was not feasible. Hence the innovative idea of integrated NATM platform tunnel and cut & cover station excavation is adopted in many stations. This study inspires by the same case where the station box is being executed by adopting the methodology of cut and cover method and the platform is being constructed by the NATM tunneling method [1]. Connection with station box and NATM platform is made with the intermediate cross passages at regular intervals. Research study emphasis on the behavior of integrated cut and cover excavation and excavation of NATM tunnel using predictable element of soil-structure interaction analysis. The results response of ground under different parameters are presented in this paper. Alignment of the underground metro is generally planned through a heavily built-up urban area. Many times, important Landmarks and Heritage structures are located nearby or directly above the tunnel alignment. Owing to land availability constraints, cost of private properties, inadequate available road width, and the very important presence of Heritage buildings planning, and design of metro alignment is important part of any underground metro project. The alignment of an underground metro project is constructed with twin tunnels by Tunnel Boring Machine (TBM) connecting two stations. The underground stations or shaft are generally proposed to be constructed by adopting the cut & cover construction methodology, and NATM method of construction and ground settlements are to be limited to protect existing buildings. Due presence of a high-water table, high rise building imposes a higher surcharge load which leads to higher settlements; however, the designer has to control it well within the acceptable limit. In high water table areas generally, excavation is done with a water-tight retaining system to prevent ground settlements due to seepage during excavations. To maintain the water table in the non-excavated area proposal of the recharge well may be required.
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