Research On Stability And Dynamic Characteristic Of Tunnel-Tunnel Transition Section Filled By Improved Completely Weathered Granite For Passenger Dedicated Railway

There are many problems and difficulties confronted geotechnical engineers at present, as the construction of dedicated passenger railway with high operation speed is at the developing phase. In a newly-built dedicated passenger railway where fillings of A or B groups is not enough, the problem that whether cutting spoil or improved soils could be instead of the fillings of A or B groups is a key technology related to operation quality, construction cost and environmental protection. Aim at main characteristics of the newly constructed Wuhan-Guangzhou dedicated passenger railway, namely, a quite section of line through completely weathered granite region, filling of A or B groups is deficient, various transitions arranged with big density, a series of research was performed in this thesis based on the research project from nation and ministry of railway, focusing on dynamic characteristics and stability behaviors of the tunnel-tunnel transition section built by improved completely weathered granite under vehicles' dynamic loads. Basing on present domestic and international research and by means of combining the research with laboratory tests, in-situ tests, theoretical analysis and numerical simulation, this dissertation contributes many efforts to systematically and deep analyze some difficult problems in theory and engineering practices such as the 3-D dynamic intercoupling analysis for vehicle-track-subgrade and road performance of the completely weathered granite, etc. The research work has been accomplished with the following achievements:(1) Based on multi-rigid-body dynamics and distribution parameter method, a vehicle-track spatial coupling time-varying model has been established; based on modified total potential energy function theory, a 3-D dynamic FEM model for track-foundation under the track has been built; considering vertical loads as a connection coupling condition of both model, a 3-D dynamic intercoupling model for vehicle-track-subgrade has been set up.(2) In view of track's technical indexes in our country's dedicated passenger railway, and on the basis of the concept of reasonable rigidity of railway track, the comparative analysis to the track general rigidities was carried out by means of three methods respectively, namely, allowable rail bending stress method, allowable track deformation method and critical speed method. An appropriate method to calculate the track rigidity of the dedicated passenger railway was determined.(3) Based on the designing style and structure size of the ballastless track at tunnel-tunnel transitions along the Wuhan-Guangzhou dedicated passenger railway, a formulation of calculating component's rigidness of ballastless track has been established by Eisenmann's multiple-beam theory, and then the rigidities of each structure layer of the ballastless track were obtained.(4) By means of mechanics of vibration, the rail structure with low joint has been analyzed. Meanwhile, mechanics analysis has been carried out on the twin-block ballastless track by composite beam theory and Eisenmann's multiple-beam theory. Dynamic and static mechanics characteristics were obtained. The reliability of the design was proved by comparing the calculating dynamic stress with allowable dynamic stress at the structure layers under the track.(5) A comprehensive laboratory test plan for natural, remolded or improved completely weathered granite has been worked out to accomplish this task of this thesis. A series of experiment results shows that the completely weathered granite could not satisfy the requirements of ballastless-track dedicated passenger railway in terms of dynamic and static strength, rigidity and water stability in long-term for the subgrade. So it is not suitable to be directly used as the filling of embankment and chemical improvement must be adopted. With some amount of cement, the improved soils could be as the filling of the bed bottom and subgrade body. Furthermore, the effect of content of cement, degree of compaction, water content, age on unconfined compression strength and coefficient of water stability of improved completely weathered granite has been obtained, which can be used guidance to construction of practical engineering.(6) Numerically simulation for practical engineering has been carried out by the suggested vehicle-track intercoupling dynamic analysis, and a point of view was proposed that the subgrade should be regarded as flexible structure when using the vehicle-track spatial coupling time-varying model. Besides, the phenomenon was observed that irregularity derive from the deflection angle and rigidity difference will affect badly the quality of track and subgrade. When the deflection angleθ≥3‰and other conditions were ideal, relative lateral displacement, derailment coefficient Q/P, lateral and vertical loads all exceeds the allowable values from 'Study on parameter selection for road -bridge-tunnel design of high-speed railway'.(7) Based on dynamic FEM analysis of the track-foundation under the track, the conclusions that improved completely weathered granite with 5% cement additives could be used as filling of bed bottom and subgrade body at the tunnel-tunnel transitions was obtained. Compared with ballasted track, the effective vibration acceleration and dynamic stress decrease sharply at the roadbed by applying the ballastless track.