Experimental Study On BFRP-grid Reinforced Concrete Lining Of High Hydraulic Pressured Tunnel Under High Geotemperature Condition

This study is supported by National Natural Science Foundation"Research of the load-bearing characteristics for high geothermal gradient and hydraulic pressure tunnel under the action of THM coupling,(Grant NO.51369007.)".During excavation of hydraulic tunnel under high geotemperature and hydraulic pressure,the presence of cracks in the conventional concrete lining structure,that are induced by tensile stress caused by combination of high temperature gradient and hydraulic pressure,may result in serve engineering problem.Aiming at this problem,a basalt fiber reinforced polymer(BFRP:Basalt Fiber Reinforced Polymer)grid reinforced technology,a new lining structure,is developed.A hydraulic structure model test is conducted using this proposed technology.During testing process,acoustic emission and strain are monitored.In addition,contrast test with conventional lining structure is also carried out.The main conclusions are as follows:(1)Elastic mechanical analysis results show that,in the elastic stage,the bearing capacity of tunnel under high geotemperature and high hydraulic pressure is mainly controlled by the tensile stress induced by combination of the temperature load and water pressure.For the same stress,there is a clear linear conversion relationship between temperature gradient load and internal pressure load.Therefore,during the loading procedure of model test of hydraulic tunnel,a simplified loading method that using hydraulic pressure to substitute the effect of tensile stress derived from temperature load is feasible,which is benefit for reducing the technical difficultes of loading in model test.(2)Test results show that compared with the conventional concrete lining structure,the concrete lining structure strengthened with BFRP-grid both on the outer and inner wall of the lining improves the limit bearing capacity of 21%in the elastic stage,the maximum aperture of the main macro crack is reduced by 68%,and that the distribution of macro fractures is more dispersed.(3)Test results show that compared with the conventional concrete lining structure,the circumferential tensile strain on inner wall of BFRP-grid reinforced lining structure increases by 81%,and that the absolute energy of the acoustic emission during the cracking stage is account for 33.78%(the former is 99.38%)of the total cumulative acoustic emission in the whole loading process.It indicates that the main failure mode of conventional concrete lining structure is brittle failure mode,and the main failure mode of BFRP-grid reinforced lining structure is ductile.The reinforcement effect of BFRP-grid comes from its high tensile strength and good tensile deformation properties,which is beneficial to give full play to total loading capacity of lining structures.