IF articles

Although the processes taking place in

the ground around a tunnel in squeezing and in swelling

rock differ from each other fundamentally, there is one

common feature in both cases: with increasing rock deformation

the rock pressure decreases. This fact is

proved both by experience and theoretical investigations

and was clearly recognized as early as at the beginning of

the last century. “With each fraction of a millimetre with

which the rock mass moves, the amount of pressure acting

on the lining decreases” [1]. Based on this recognition

a number of design methods are nowadays at the disposal

of the engineer to control rock pressure even in heavily

squeezing and heavily swelling rock. Both the temporary

and the final lining can be constructed in such a way as

to exert stabilizing pressure on the rock and at the same

time allow the rock mass to deform. In many cases this

combined action, i.e. rock support and letting the rock

deform, not only presents the most economical solution,

in some cases it is the only one that makes tunnel construction

feasible.