Combined load bearing mechanism of lining and surrounding rock in hydraulic tunnel during overhauling

External water pressure is one of the main loads acting on hydraulic tunnel,which consists of lining and surrounding rock.A numerical model of a hydropower diversion tunnel is built according to the combined load bearing mechanism of lining and surrounding rock.The deformation modulus of the surrounding rock near to lining is reduced to indicate the influence of surrounding rock.A thin-layer element which has a certain tensile strength is also developed to quantify the limited cooperation between lining and surrounding rock.The results show that the surrounding rock takes an important role.As the deformation modulus of the surrounding rock increasing,the rock bears more external water pressure.And the combined load bearing mechanism is clearer than before when the tensile strength is fixed.The surrounding rock bears more external water pressure before the thin-layer element cracked.The lining bears more pressure after the element cracked.In order to enhance the surrounding rock’s combined load bearing capacity,it’s important to ensure the quality of backfill grouting and consolidation grouting.