Question

While pipe jacking or microtunneling, it is usually accepted that cover depths of jacking pipes cannot be also shallow as in less than 2D where D is the diameter of jacking pipes.Give some key reasons?

Answer

For pipe jacking or microtunneling, reasons of large settlement are defeat of face constancy, failure to even out ground around shafts, presence of annular gap around pipes and shield, drag all along pipe joints. Settlement mechanism of low depths of pipe jacking or microtunneling is formation of a settlement trough on top of jacking pipes. Width of trough depends on soil properties; larger is cover depth of jacking pipes, larger is width of settlement trough. For same soil volume beating due to pipe jacking or microtunneling, width of settlement trough for shallow cover depth is lesser and so it results in a larger vertical utmost settlement.