The Limit Crack Analysis Of Hydraulic Tunnel Lining Structure

There are many results about the limit crack analysis of hydraulic tunnel lining structure, but the calculation of crack width is based on the pull-out test of the ordinary reinforced concrete,and the truth is neglected that lining and rock are united bearing body.Therefore experimental and theoretical studies are needed about the role of rock on lining.In this paper,the stress and crack of hydraulic tunnel lining structure is studied through a large-scale hydraulic tunnel lining structure model,elasticity theory,fracture mechanics and nonlinear finite element analysis,which could provide a reference for the "design codes of hydraulic tunnel".The main research contents are as follows:1.The rebar stress and lining concrete deformation of the large-scale hydraulic tunnel lining structure model;2.The stress calculation formulae of three typical hydraulic tunnel lining structures,i.e., plain concrete,single-and double-layer reinforced concrete are deduced,and the relationship between inner water pressure and cracking radius is present by elasticity theory.A theoretical calculation is carried out on the large-scale hydraulic tunnel structure model;3.For three typical hydraulic tunnel lining structures,i.e.,plain concrete,single-and double-layer reinforced concrete,the double-K fracture parameters are determined.In addition, a crack width formula is developed based on the fracture mechanics.Then,the crack widths of the single-and double-layer reinforced concrete lining structure under the inner water pressure, which are calculated using new proposed formula,are compared with both experimental results and the results calculated by the equations given in design codes.4.Nonlinear finite element analysis is calculated by ANSYS on three typical hydraulic tunnel lining structures,i.e.,plain concrete structures,single-and double-layer reinforced concrete structures.Then the ANSYS results are compared with both experimental results and the results calculated by elasticity theory.It is found that the inner water pressure is balanced by lining before cracking happens; once cracking happens,cracks will go through the lining very quickly;then,the inner water pressure is mainly borne by rock.The difference of the stress and cracking radius under inner water pressure between single-and double-layer reinforced concrete lining structures is small, which shows the use of rebars mainly ensure the integrity of lining,therefore,it's more economical using single-layer reinforced concrete lining if the crack width can be controlled. The fracture mechanics provides an effective technique for better understanding of mechanical behavior and potential failure mechanism of hydraulic tunnel lining structure.The crack width is in good agreement between fracture mechanics results and experimental results,which implies that the use of fracture mechanics approach will provides better help for modification of the crack width calculation formula used in the existing design codes for hydraulic tunnel lining structure.