In any type of construction projects, the temporary works and equipment play vital and significant roles to lead a successful completion. During the construction process, temporary works and equipment represent an area of considerable significance, and also the key cost factor in the contract price. General temporary works design for access, lifting, moving, restraint, and support but it will not be incorporated into the final structure for example access platforms, crossheads, falsework, general temporary works, lifting beams, propping, restraints, trestling, support beams and towers etc. Erection schemes of all types for bridges and special structures includes mobile cranes, floating cranes, jacking, launching, rolling, sliding, strand jacks, wheeled transporters and winches etc. (http://www.chris-booth.com/Temporary_works.htm) The following report is going to demonstrate the role of temporary works and equipment in large scale Tunnel and Bridge construction projects and their impact on the total cost of the project.
Temporary works and equipment of Tunnel
Tunnel is the connection of passage way constructed underground for different purposes such as road or rail transport, subway, canal, sewage and other services. Different purposes of the tunnel will affect the shape and the size of the tunnel. Besides that, there are several factors that would affect the method of construction such as type of tunnel, ground conditions, length of tunnel and the available time for construction.
The tunnel chosen for analysis in the report is Niagara Tunnel under Niagara Falls in Ontario, Canada which is started in 2005 and estimated to be completed in 2013. The purposes of this project are to build aqueduct for hydroelectric station and to supply water for consumption. It diverts the water from Niagara River to Sir Adam Beck Generating Stations at the rate of 500 cubic metres per second. This hydro tunnel project worth $600 million and managed by Austrian General Contractors, Stragbag AG for Ontario Power Generation (OPG).
Figure 1: The tunnel route under the Niagara Falls (Adapted from OPG, 2011)
The main equipment for this project is the world largest hard rock tunnel boring machine, also known as Big Becky to generate a tunnel which has 14.4 metres wide diameter, 10.4 kilometres long and 140 metres deep under the City of Niagara Falls, mostly through solid rock known as Queenston Shale. Big Becky cost more than $ 30 million which is 150 metres in length, 14.4 metres height and weight 4,400 tonnes. This tunnel will allow OPG to provide enough clean water power to generate a further 1.6billion kilowatt-hours of electricity annually which is sufficient to supply electricity for about 160,000 homes.
Figure 2: World largest hard rock TBM, Big Becky
The tunnel will be constructed in two phases. In phase one, the ‘cutting face’ of the tunnel boring machine (TBM) will be bore a hole 14.4m in diameter while the TBM ‘trailing gear’ installs a primary lining around the circumference of the Tunnel.The primary lining, depending on rock conditions, will consist of rock bolts, steel mesh, structural steel ribs and ‘shortcrete’- pre-mixed concrete sprayed on the tunnel walls from a high-pressure hose.The second phase will include the installation of a double waterproof membrane and a cast-in-place concrete lining. The combined linings will form a ring around the circumference about 1.7m thick, reducing the Tunnel’s internal diameter from 14.4m to 12.7m.
Temporary works and equipment in Bridge construction project
There are many types of bridges such as arch bridge, beam Bridge, lifting bridge, swing bridge, suspension bridge and cable stayed bridge. Suspension bridge is built by suspending the roadway from cables attached to a master cable, which runs above the length of the bridge. In addition to being strong and lightweight, suspension bridges are also beautiful, and some of the most famous bridges in the world are also suspension bridges, including New York’s Brooklyn Bridge and San Francisco’s iconic Golden Gate Bridge. The design of a suspension bridge is quite simple and uncomplicated, and takes advantage of several techniques to distribute the weight of the bridge safely and evenly. (http://www.buzzle.com/articles/famous-suspension-bridges.html) The bridge project chosen for analysis in this report is Akashi Kaiyo Suspension Bridge which is the longest suspension bridge in the world. (http://onlinepubs.trb.org/onlinepubs/millennium/00012.pdf)
Akashi Kaikyo Bridge took two million workers ten years to construct the bridge, 181,000 tonnes of steel and 1.4million cubic metres of concrete. The steel cable used would circle the world seven times. It has six lanes and links the island of Awaji and the mainland city of Kobe, a distance of four miles. The concept of building a bridge across the Akashi Straits became urgent after a disaster in 1955. A ferry carrying over one hundred children sank after colliding with another ferry, in the busy shipping lane. One hundred and sixty eight children and adults died in the disaster. Political pressure for a bridge increased and in 1988 construction began.
A suspension bridge starts with building the towers. If possible, the towers are located on dry land and anchored to bedrock. If the towers must be located in the water, structures called caissons are used to force water out of the area of work so that construction can be done in a dry area. Once the towers are built and anchored, the master cables are strung across them and anchored to points on dry land, although some bridges are self suspending, meaning that the master cables are actually anchored to the deck of the bridge itself. Next, suspension cables are strung from the master cables, and then the deck is attached to them. (http://www.wisegeek.com/what-is-a-suspension-bridge.htm)