In: Civil Engineering
Tunnel Problem
You are going to build a tunnel 10 miles long with a shaft at one end and a portal at the other. It is part of the first phase of the gateway tunnel to New York.
* The shaft is 185 ft. deep to the invert of the tunnel and 22 ft. excavated diameter.
* The tunnel is 26 ft. excavated diameter in competent sandstone and limestone.
* The profile of the shaft is as follows: From the surface down- 15 feet of fill; 30 feet of sand and clay; 20 feet of silty gravel; 40 feet of limestone and 80 feet of sandstone.
* Groundwater is 35 feet down.
* The tunnel runs for 5 miles in sandstone and 5 miles in limestone.
Determine the following:
1. Using a TBM, how long will it take to excavate the tunnel?
2. Will blasting need to be done anywhere? If so, where?
Commencement of Shaft access will be done by the excvating the top 15 feet fill soil, Sheet piles are required below 15 ft depth to support the sandy clay profile. At depth of 35 ft where ground water is encountered need to be removed using open pump system or deep well. Pneumatic or dredge cassion may be installed for which dredging and sinking operation may be carried out simultaneously.
1. Depending upon overall geological profile, tunnel alignment and design requirements the minimum is 450 to 500 meters/ month for sandstone and limestone rock. Hence for working with 10 miles of sandstone and limestone strata 32 to 36 month would be required. However, other influencing parameters are muck disposal, linings works etc.
It is to be noted that EPB type TBM should be used for these type of rock condition and wet strata.
2. Yes, Drill and Blasting would be required after pumping out water and excavating after drill blast from depth of reaching converging limestone to sandstone strata.