Abstract:

Excavation damaged zone (EDZ) is an important factor to the deformation and stability of underground caverns. Taking JinpingⅠHydropower Project for example, the distribution and variation of EDZ for large scale underground powerhouse under the conditions of high geostress and low strength-to-stress ratio are analyzed according to sonic wave measuring and multipoint extensometers monitoring; and the parameters of rockmass are back analyzed by BP network and genetic algorithm. The analytical results indicate that the depth of EDZ obtained by sonic wave measuring is consistent with the main deforming depth obtained by multipoint extensometers; and the depth change of EDZ is corresponding with the surface displacement change of rockmass; therefore the variation of EDZ can be analyzed continuously by the integrated using of sonic wave measuring and multipoint extensometers monitoring. Under the condition of high geostress and low strength-to-stress ratio, the depth of EDZ is much larger than general stress condition; and the unloading relaxation becomes the main factor of surrounding relaxation. The depth of EDZ increases with the stress adjustment of surrounding rock during excavating, in which the horizontal extending of EDZ is obvious. The deformation modulus E and cohesion c of EDZ carried by back analysis is markedly lower than undamaged rockmass, while the reducing of friction angle φ is less. Therefore, the grouting reinforcement of damaged rockmass will be benefit to improve its deformation modulus and cohesion; and the stability of surrounding rockmass will be improved consequently.

Key words: underground powerhouse, excavation damaged zone, high geostress, back analysis, JinpingⅠHydropower Project