The Jinping Hydropower Station is a large-scale national key project, of which the diversion tunnels are deep-buried. Especially the tunnels are located in a high geostress area; so it is of significance to study the variation laws of unloading mechanical properties under high geostress conditions. To simulate the tunnel excavation unloading effect, a series of triaxial unloading tests and a special designed multiple failure state unloading tests are carried out. The results show that under high geostress conditions, the unloading properties of marble specimens are as follows. (1) Under same initial stress conditions, stress needed in axial compression failure is more than that in confined unloading failure. Confining pressure reduction is prone to cause rock failure. (2) From the very beginning of unloading, the lateral deformation increases remarkably; and dilatancy presents prominently. Moreover, if the deformation caused by initial axial compression is disregarded, the volumetric deformation increasing is dominated by lateral deformation. (3) During the unloading stage, the relationship between Poisson's ratio rises up; and the confining pressure could be well described by biquadrate. The deformation modulus declines indistinctly at first, while as failure approaching, even little confining declination would cause large decreases. (4) Shear strength parameter c under unloading conditions is 14%lower than that under conventional compression conditions; while ψ is greater than that about 23%. These conclusions reveal the unloading properties of marble under high geostress conditions and offer important references for stability analysis of deep-buried tunnels.
Chinese Journal of Rock Mechanics and Engineering
Hydroelectric power plants