The key equipment of thickening process in the action of cemented paste backfill (CPB) is deep cone thickener (DCT). The underflow mass fraction of DCT is significant related to the slurry pressure. And the void ratio is an important representation parameter of the underflow mass fraction. However

the change rule between the void ratio and the slurry pressure is not clear. For the interpretation of the problem aforementioned

a new concept for the tailings thickening degree is proposed and named as effective void ratio (EVR). The EVR is referred to void ratio minus saturated void ratio. A total tailings dynamic thickening experiment is conducted. The results show that the slurry pressure is between 2 477-4 410 Pa as the slurry height is between 31-200 mm. The underflow mass fraction is calculated as 73.26%-78.30%

which corresponding the EVR is 0.433-0.191. The regression result indicates that EVR and slurry pressure follow the power function. Moreover

the paste dynamic thickening model is proposed. According to this proposed model

the paste dynamic thickening behaviour is divided into three processes: (1) linear thickening zone

with the increasing of slurry pressure

the void ratio decreases quickly almost as linear

(2) attenuation compression zone

with the slurry pressure increasing continues

the void ratio decreases gradually and the paste tends to be saturated

(3) constant thickening zone

the tailings achieve saturated state and the void ratio become constant. This study reveals the change rule between the void ratio and slurry pressure in the process of thickening and provides the theoretical foundation for the thickener design and operation.