salt mine
6.Derformation and convergence survey were made on the drift of Qiaohou Salt Mine withthree techniques. It can be concluded from the obtained data that the convergence velocity of the drift hasbeen increasing since 1960′s,with the average convergence rate per day at verical direction increasingfrom about 0.53 mm at early 1960′s to about 0.9~1.1 mm at the present.

