Biography
Biography: Honey Mehra
Abstract
Underground Metro station is a very complex structure which involves numerous challenges in design as well as construction. Due to limited space in cities and the problems faced in urban transportation around the world a large no of underground metro stations have been built/ are being constructed .Noteable examples are Liverpool street in London,Chatelet – Les Halles in Paris, Fulton Street in NewYork,Shibuya in Tokyo, Changshu Road in Shanghai and Shalimar Bagh in Delhi. However the construction of underground metro station involves both temporary structures and permanent structures. Various types of temporary structures are adopted depending upon the site conditions, ease of construction and economy. Soldier piles, secant piles and diaphragm walls in combination with Waler beams and struts are the common structural systems adopted worldwide. The design of these systems typically involves the design of the piles/diaphragm walls, the struts and the waler beams. Design also depends on the construction method adopted – Bottom up or Topdown. In bottom up the station is excavated till the bottom and subsequently the permanent components of the station like undercroft ,platform ,concourse and roof slab are constructed. In top down the excavation and construction of the different slabs at various levels go on one after the another. For both topdown and bottom up construction a rigorous construction sequence is followed. The design for the piles is done using geotechnical softwares like Wallap, Deep excavation etc and for the design of waler beams and struts structural analysis softwares like STAADPro are often used. The permanent structure for the station building is a monolithic structure. A typical station can be 225m long,15m deep and 25m wide. This building has floors at different levels, side walls at the periphery and columns in the middle. Generally the size and location of the columns is also governed by architect who sometimes have requirements which the structural engineer finds hard to fulfill. The design of the permanent structure is done by using 2D X- sections at various grids of the station. The loadings include the soil fill on top, water pressure at the sides , train live loads, live loads at concourse and platform. Seismic forces were previously not considered in design since it is a buried structure. However after Kyoto earthquake where several stations in Japan suffered cracks racking force is generally taken for design of the underground stations being constructed nowadays around the world.