Forepoling is used wherever it is dangerous to expose even small areas of soil or rock for a short time. To be more accurate the time available for support, after excavation (stand-up time) is so little that support must be secured prior to excavation.
Forepoling is used usually in the following cases:
Running ground, such as water-bearing sand or silt Fragmented or squeezing rock.
Bellow are some photos of the drilling project and machine. The holes are drilled with a slight inclination. Then the steel piles are inserted into the hole and are filled with cement. The piles have many holes from which the cement comes out and bonds the pile with the ground. In the picture above you can see the piles before pumping of cement.
The total length of piles is 12m.
Figure 1:The steel piles drilled into the fragmented rock before the first excavation.
T.M. Megaw, J.V. Bartlett, "Tunnels, planning, design, construction",Ellis Horwood International Edition, 1983.