Abstract: Carbon Fibre Reinforced Polymer (CFRP) bears not only the varying external soil and water loads, but also part of the internal water pressure when used in strengthening pressure tunnels. To investigate the joint bearing mechanism of the composite structure containing CFRP, adhesive lining, and concrete under internal water pressure, we established a “solid-spring-solid” 3D finite element model of pressurized water conveyance tunnel strengthened with CFRP, and verified the validity of the model via model test. By using this model, we examined the ratio of bearing internal water pressure between lining concrete and CFRP under varying conditions including elastic modulus of adhesive layer (E_a), thickness of adhesive layer (t_a), elastic modulus of CFRP (E_c), and thickness of CFRP (t_c). Results reveal that t_c and E_c are dominant factors that affect the bearing ratio. In the presence of 1-3 layers of CFRP, with t_c gradually increasing from 0.1 mm to 2 mm, the percentage of internal water pressure borne by lining concrete declined by 34.25%, 47.776%, and 53.931%, respectively; when E_c grew from 100 GPa to 600 GPa, that percentage dropped by 6.482%,11.945%,and 16.509%,respectively. Range analysis also manifest that the percentage of internal water pressure borne by lining concrete is most sensitive to t_c,followed by E_c,E_a,and t_a in descending order. In conclusion, improving the thickness and modulus of CFRP is the key to enhancing the utilization of CFRP and to reducing the percentage of internal water pressure borne by lining concrete.

Key words: pressure tunnel, tunnel strengthened with CFRP, composite structure, bearing ratio of internal water pressure, parameter analysis