Stress Analysis And Safty Evaluation Of Xiaolangdi Pre-stressed Tunnel Lining With Unbounded Circular Anchored Tendons

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, more material can be saved, the excavated volume、the difficulty of theconstruction and the cost of engineering can be also greatly reduced. In view of theadvantage of unbonded prestressed concrete lining, it can be seen that the structurehas a broad application prospect in the hydraulic tunnel in our country. HuangheXiaolangdi sediment tunnels are the first waterway engineering used un-bondedcircumferential pre-stressed lining in China.During the construction perid, the sediment tunnel liner was instrnmented with154meters, such as concrete strainmeters, reinforcement meters, zero stress meters,anchorage load cells, piezometers and joint meters. Xiaolangdi desilting tunnel wasbuilt from1997to1999, and after operationmore than ten years, desilting tunnelundergone various design conditions, and tens of thousands of groups observationaldata was accumulated. In this paper, the data were collected and analysis in order tounderstand the development and changes of stress and strain of Xiaolangdi desiltingtunnel concrete lining during the construction and operation perids, and in order todetermine whether the structure is of reasonable safety.In this paper by using ANSYS the model of Xiaolangdi tunnel is made, and thestress state of the lining during construction and operation stage are respectively analyzed. Through comparsion with the test data, it shows that there is goodconsistency. The results show that the stress state of boxout area is the most complex,both the maximum and minimum stress appear near the boxout area, and tensile stressappears in the axial and radial.In order to solve the problems exposed during construction and operation peridsof Xiaolangdi desilting tunnel, especially the oil leakage of the boxout, the paper triesto optimize the structural design、 the arrangement of tendon and boxout, and also thestress state is analyzed by finite element software. It can be seen from the results thatthe weak area of the structure obviously decreases, the stress distribution of boxoutarea is more uniform and the economic benefit is obvious, then it has certain referencevalue for the future engineering.Based on measured data and simulation results, by using a combination methodof qualitative and quantitative, and mainly through concrete stress state andmonitoring data from anchorage load cells and piezometers, the safety state of theentire unbonded prestressed tunnel is analysed and evaluated. The results show thatthere are no cracking and leakage, the normal use of tunnel can be ensured. Thesecurity warning system created in the construction and operation perids can providethe basis for the designe and optimize of similar projects in the future and the promoteof this new structure.