Flagstaff railway station

Flagstaff railway station is an underground station on the metro network in Melbourne, Australia. It is one of five stations (and one of three underground) on the City Loop, which encircles the Melbourne CBD. The station takes its name from the nearby Flagstaff Hill, a significant site in Melbourne's early history, and services Melbourne's legal district. It runs under La Trobe and William Streets, near the north western corner of the CBD.In 2013/14 it was the fifth busiest station on Melbourne's metropolitan network, with 4.5 million passenger movements. Flagstaff station commenced opening on weekends and public holidays from 1 January 2016 – it was previously the only station in Melbourne to be closed on weekends and public holidays due to its proximity to business-related buildings such as the Commonwealth Law Complex, banks and major office buildings.HistoryThe station was constructed by mining methods, and has four levels to a maximum depth of 32 metres. The site was a geological "sandwich" of basalt in the arch area, Silurian mudstone bedrock in the lower half, and silt in the middle, which precluded the construction of lower and upper platforms as separately driven tunnels.Instead, the station platforms consist of two chambers linked by cross tunnels, each having two platforms on top of each other. The side of each chamber was made up of two drift tunnels, one at the top and one at the bottom. These were then linked together by 228 vertically raise bored shafts, 1 metre in diameter and 3 metres apart. The shafts and drifts were then filled with concrete, and formed the side skeleton of the station chambers. The arch of each chamber was then constructed underground across the top of the two side walls, the material below the arch excavated down to the bottom of the side walls, and temporary cross struts added between the raise bored columns until the permanent elements were added. This innovative method resulted in a $1 million saving in construction costs (in 1975 dollars).