Study On The Framework Of Tunnel-type Anchorage Design And Its Application

Tunnel-type anchorage (TTA) is one of the two anchorage types used in long suspension bridge. Compared with the other type of anchorage, selfweight-type anchorage (STA), TTA has two obvious advantages: 1) The lower investment, for which half of the normal investment in anchorage can be saved. 2) The less disturbance to the environment, which is of great advantage for environment protection. The only shortcoming is that the hard and soundness rock mass is required in the anchorage zone and its application in plan area is limited. It can be seen form the published literature that there are only 7 TTAs have been established in the world, limited effort has been put in the application and study of TTA. To carry out the policy of developing the west China, the infrastructure for transportation should be constructed firstly. The west China is rich in rocky mountain areas, the geo-condition required for TTA can be satisfied easily. Considered of the advantages and the perspective of the widely using of TTA, It is of great important to study the key problems in TTA design systematically. In this paper, the key problems in designing the TTA have been summarized, and studied theoretically. The resolution schemes for these problems have been given in detail and can be used easily. The application of these schemes has been used in the 1st TTA of long span suspension bridge in China, TTA of the Siduhe Bridge. The theory and the methods have been proved and the 1st full example for TTA design is readily to be referred. Based on the theory and the example, the framework of TTA design has been established primarily. The main results of this investigation are as follows: (1) Based on the analysis of the test data of shaft anchor,the more accurate combined-power model for axial force in anchor shaft is proposed. (2) Based on the combined-power model and the general concept of geo-anchorage, the approximate formula for estimating the length of TTA is proposed. This formula is accurate enough and safer for engineering purpose to determine the length of TTA compared with the result of FE method; (3) By comparing the stress distribution and anchorage length of TTA with different anchorage systems, the reasonable anchorage system for TTA is proposed from the mechanical aspect. (4) For using the input function of initial condition in business FE software conveniently, a method using stress function for simulating the virgin stress state in mountain with complex geometry configuration is proposed. Its special usage for general code ABAQUS has been coded. The output results can be included directly in the input data file of ABAQUS. (5) The sensitive analysis of rock mass parameters using uniform design method(UD) is the 1st time in engineering field and the runs of numerical calculation can be reduced largely. This is a new sensitive analysis method for large civil structures. It is found that the capacity of TTA is sensitive to deformable modulus, E, and cohesion, c, and the displacements are sensitive to the parameter of deformable modulus, E. The suggested values of rock mass parameters of Siduhe TTA are reduced according to the sensitive analysis results. (6) Some key problems about numerical simulation of TTA is discussed, including the elasto-plastic constitutive of sounded rock mass, the simulation of shin weak layer in rock mass, the excavation of anchorage hole, etc. (7) The analysis on the example of TTA of Siduhe Bridge gives the full illustration in solving the key problems in TTA design, from determining the length of TTA, the choice of anchorage system to the verification by numerical analysis. (8) Based on the research of this paper, the frame for designing TTA has been summarized, and the solutions to the key problems are also cited out in the framework. It is useful for unifying the design procedure, and providing references for designers.