Stress State Analysis In The Boxout Area Of Prestressed Concrete Tunnel Lining

The pre-stressed tunnel lining with unbounded circular anchored tendons is a newstructure applying in hydraulic tunnel. This structure is mainly applied in thehydraulic tunnel which is in the poor geological conditions of surrounding rock, hashigh water pressure, and leads to the slope instability of the surrounding buildingsbecause of the water infiltrating the rock. The pre-stressed tunnel lining withunbounded circular anchored tendons has its special advantages as a new form oflining structure: The steel strand in the unbounded lining is double circle, which canmake the distribution of compressive stress in lining more uniform and can alsoreduce the loss of the stress along the path. Compared with the bounded lining, it haslarger effective press, and it can reduce the thickness of the concrete lining. In thisway, it can save more material and reduce the excavated volume. Above all, it canalso greatly reduce the difficulty of the construction, the cost of engineering, andeffectively speed up the progress of construction. In view of the advantage ofunbonded prestressed concrete lining, it can be seen that the structure has a broadapplication prospect in the hydraulic tunnel in our country. At present, this kind ofconcrete lining is only applied in Xiaolangdi Project and Dahuofang water tunnel. Thestructure also exposes some problems at the point of the operation of the two projects,especially the area of boxout. Through the observation of the Xiaolangdi project, thearea of boxout has the problem of oil leakage, it is the weakest part of the wholestructure.This paper makes the model of NO.2tunnel of Xiaolangdi project using ANSYS,respectively analyzes the stress state of the area of boxout during construction andoperation stage. Through the comparsion with the test data of NO.2tunnel, it showsthat they have good consistency. The results show that the stress state of boxout areais the most complex, both the maximum and minimum stress appear near the boxoutarea, and tensile stress appears in the axial and radial. In order to solve this problem,this paper tries to optimize the position of the boxout and also analyzes the stress stateof the area of boxout during construction and operation in the final chapter. It can beseen from the results that the weak area of the structure obviously decreases and thestress distribution of boxout area is more uniform, then it has certain reference valuefor the future engineering.