Abstract:The double-line five-step shiplock of the TGP retains a rock mass division pier with 60 m width,which reduces engineering investment greatly. In the course of excavation on shiplock brake-dent,the different extent cracks generate firstly on the concrete surface of the top division pier,then on the shotcrete¢s surface all around valve well. So the stability of division pier rock masses has been noticed highly by all members participating in construction. Therefore,selecting typical sections in construction site,applying various means such as coring bit,water pressure test,rock mechanics test,bore hole elastic modulus test,bore hole total hole wall numerical tape,single sound wave,cross-hole earthquake wave,cross-hole electromagnetic wave CT,numerical caculation,construction geologic survey and construction stage monitoring data analysis,synthetic studying rock masses unloading range and subzone,cracking machine-made,reinforcing effectiveness,and rock masses mechanical condition and stability state of division pier;these outcomes show that the unloading district rock masses can be divided into three belts such as explosion-unloading relaxation belt,unloading relaxation belt,non-unloading relaxation belt,and unloading district rock masses anchored appropriately has still better integration,then the stability of division pier should meet layout requirement.