Applying supports like buttresses or boughs in underground structures such as tunnels and mines cause indentation of the support into the bearing floor due to the creep, which is caused by constant load from the support. Since creep behavior is a time dependent characteristic of rocks, it is hard in practice to investigate the indentation depth of the support, the changes in profile of the floor due to the indentation creep, and the best support tip shape. It seems that for this kind of investigation impression creep test is a suitable one to obtain the creep behavior of the material of the floor in small scale and in short periods of time. In this study, the effects of different kinds of punch tip are compared experimentally and numerically. For this purpose, four different shapes of punch tip (cylindrical with flat end, two conical shapes and cubic) are used to perform impression creep tests under different loading levels. These tests are carried out on rock salt because of its softness and creep behavior. Furthermore, all of these experiments were investigated numerically using commercial finite element analysis (FEA) software, ANSYSTM, to acquire the profile of material beneath the punch during the experiment.
Many sedimentary and metamorphic rocks exhibit significant creep behavior over time. Many studies have been carried out on deformation of underground structures due to static and dynamic loading, but there are not enough studies involve the deformation and failure modes of floor rock beneath the local supports like buttresses and boughs or pillars in pillar supported mining methods [2, 3]. In this study the profile of creep deformation of floor rock using different tip shapes of supports has been investigated using both empirical and numerical methods.