In-situ Model Testing Scheme Research On Tunnel-type Anchorage Of Long-span Railway Suspension Bridge

This essay studies on the in-situ model experimental plan for the rail suspension bridge tunneling anchorage,with the example of Jinsha River Bridge.Research methods including geographical survey,regular experiment for indoor rock mass mechanics and in-situ rock mass mechanics,and on-site scale model experiment are applied to study the geographical condition of the site that the tunnel anchor situated,the physical mechanics properties of the rock mass,deformation and deflection of tunnel anchor and wall rock,rheological behavior,carrying capacity and potential damage of tunnel anchor,and stability of tunnel anchor.In order to get to know the mechanic properties of the wall rock in the area of Shangri-la experimental tunnel anchor,rock mass from this area has been chosen as the subject of the indoor regular physical experiment,and in situ rock mass mechanical experiment has been done in this area.These experiments have been done to obtain the exact physical parameters of the rock mass in this area,and to provide proof for further scale model experiment of the tunnel anchor,as well as the analysis on the stability of the tunnel anchor.The on-site scale model experiment composes the main part of this experimental design plan.Based on the similarity theory,the experiment compares several results of similar on-site experiments,and comes to the conclusions that the alignment of different geometries has great influence on rock mass deformation,and that the different geographic condition and "size effect" also lead to diverse experimental results.To reduce the "size effect" as much as possible,and to truly reflect the deformation and deflection of the tunnel anchor and the surrounding rock mass under the load effect,the ratio of similitude in this scale model is set as 1:10.Based on the confirmed sized of the experimental model,and previous finite element calculating results of Lijiang bridge tunnel anchor,the experiment gets the stress,displacement,variation regulation,and the deformation range of the rock mass under ultimate load of the experimental anchorage and wall rock during the loading procedure,and confirms the site and scope of this experiment.In order to research on the deflection of the anchor and the wall rock under the load effect,the content of this experiment is confirmed as the equivalence of deformation and deflection of the anchor and the wall rock under the load effect.Inductive multi-point displacement meter is adopted to test the interior deformation of the anchorage and the surrounding wall rock;strain gauge is used to test the interior deformation of the anchorage;and the intelligent digital displacement meter is employed to test the surface deformation of the anchorage and the wall rock.To meet the loading requirement of the experiment,multiple load-bearing modes of actual tunnel anchor have been stimulated,and the backstepping loading method has been adopted to install a jack on the back of the anchorage to overcome the disadvantage of the drawing method that the counter force of the cross bean is too heavy.The on-site scale model experiment is systematically designed,with proper experimental site,precise testing instruments,reasonable plan for installment of instruments,and feasible loading equipment and efficient collection equipment.This dissertation will discuss these aspects in the following chapters,and will attempt to formulate a reasonable experimental plan in accordance to the experiment objectives.It will employ methods such as geographical survey,rock mechanics text,and on-site scale model experiment to study the geographical condition of the area that the tunnel anchor is located,the physical mechanics of rock mass,deformation of the tunnel anchor under pressure,rheological behavior,carrying capacity and the potential damage of the tunnel anchor,and the stability of the tunnel anchor.The thesis will also test the feasibility of the design result and calculation method of the tunnel anchor,and will confirm the possibility of the general rule and calculation theory that have been proved by the results that can be applied to actual practice.It will gather experience for similar project in the future,raise the awareness of the influence of various parameters on the performance of the project,provide evidence for establishing systematical theory and methodology of tunnel anchor design and formulating relevant regulations and specifications of tunnel anchor,so as to promote the progress and development of tunnel anchor designing technology.