Image Number 2 for United States Patent #5678957.
A method for underground excavation below an area, without opening the area above the excavation, the method comprising constructing at least a pair of diaphragm walls, the walls being at two opposite sides of the area and extend substantially from the surface area to beneath the lowest level of the excavation. Either prior or after constructing the walls, a plurality of tunnels are bored under the surface area, with the tunnels extending from one diaphragm wall of a pair to another and having a diameter allowing them to accommodate one or more cables. Then, the one or more cables are inserted through the tunnels, and tensioned with their ends anchored to two diaphragm walls of a pair and excavating is performed between said diaphragm walls and beneath the cables.
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