The Study Of Stability For Underground Penstock With Stiffener Ring

Underground penstock is used in water power station of middle or large scale widely, because of its obvious advantages such as being laid out flexibly, sharing internal water pressure with surrounding rock, saving steel, higher safety, performing well and so on. In the process of designing underground penstock, there are two aspects should be taken into account. One is how to determine internal water load proportion between steel lining and surrounding rock, the other is the stability of steel lining under external water pressure action.Steel lining, concrete lining and surrounding rock can work together to share internal water pressure. The analytic method which apply the theory of elastic thin-cylinder and deformation compatibility condition in radial, can't consider plasticity, the influence of surrounding rock's initial stress and secondary stress after excavated on penstock bearing capability, and only apply round tunnel. The Finite element method can solve the problems . existed in analytic method, but simulating the seam which is only 1~2 mm between steel lining and concrete lining will not implement easily. So this paper absorbs advantages of the two methods and combines with the actually loading process of underground penstock. A new method is proposed, that is half analytic method and half finite element method. In order to comparison, another finite element method is put forward by setting contact pair and initial seam value to simulate the initial seam between steel lining and concrete lining. When the seam is closed, it can be good to simulate steel lining, concrete lining and surrounding rock work together.When the steel tube is empty, the steel tube shell is easy buckling due to the underground water acts on steel tube shell directly as external pressure through the concrete fractures. Chinese criterion, American and Japanese all recommend adopting formula Misesof exposed penstock to calculate its critical external compress, regardless of radial restriction of concrete lining to the deformation of steel tube shell, only make this restriction as safety storage and then lower the safety factor. But in generally, initial seam is so small that concrete lining's radial restriction also can increase the critical external compress of penstock, this phenomenon is still not considered in design and anslysis. For take this restriction of concrete lining to steel lining into account, nonlinear buckling analysis technique and contact pair of ANSYS are adopted to analyze the buckling of underground penstock. The affect on critical buckling external compress which caused by radical restriction of concrete lining can react as soon as contact pairs between the steel lining and concrete lining are contact. At last, the results of the critical external compress between ANSYS and Lai huajin formula are contrasted.Even tiny deformation can make concrete and surrounding rock crack under internal water action, and penstock can't make full use of its characteristic to bear more load due to tiny deformation. At the same time, underground water makes thin steel shell buckling easily. In order to make full use of the material based on the stabilization of penstock, this paper combine the fact project to analyze three new type penstocks for more understanding their work capability, which are combined bushing, cushion pipe and interlayer pipe.