Dynamic Parameter Inverse Of Ballastless Track Subgrade And Transition Section Optimal Design

Laboratory tests, model tests can not veritably obtain the dynamic shear strain of the roadbed. Furthermore, it is difficult to provide a reasonable roadbed technical conditions and reasonable structural system in the field test. Thus, the aforementioned complex problems have to be solved by numerical simulations. However, "inaccurate parameters" and "inaccurate models" are the two main bottlenecks, which are hard to be broken through using present techniques. It may be the optimum way to breakthrough the bottlenecks by first employing inverse method to obtain the roadbed parameters, and then analyzing roadbed dynamic characteristics and status directly. Nevertheless, it counters conundrum as well. That is, inverse method has its own shortcomings, i.e. ill-posedness, highly nonlinear and involved huge computational cost, which bring great challenge to obtain stable approximate solution.In fact, long-term stability and deformation of roadbed subgrade service depend on its work state; the work state is closely related to the compact, confining pressure, loading frequency, moisture and other factors. However, the structural design parameters, technical conditions and criteria and to maintain long-term dynamic stability of technical parameters, methods and evaluation indicators are lacking currently for transition section roadbed subgrade, especially to meet the requirements of driving comfort.Therefore, this paper aims at solving the above mentioned problems, and at the same time relying on existing test data of high-speed railway roadbed, further laboratory and field tests are conducted to establish numerical simulation models based on formal structure between the bed and the mechanical properties of the under-filled shorted base structures and the transition section design parameters for a more comprehensive study. And then obtain class A stone, group B filled material and packing line service status, roadbed residual deformation prediction, subgrade surface power design parameters, structure-based design of the transitional stage short-circuit parameters of a series of results, as follows:(1) According to the on-site dynamic response test, the state of the high-speed rail service ballastless subgrade is analyzed and evaluated. Later, the dynamic characters of the high-speed railway roadbed after the operation are revealed.(2) Based on the existing geotechnical dynamic strength theory, "strain increment control design method" of ballastless subgrade structure is built using the "critical dynamic plastic strength" as the control indicators. On the basis of laboratory and field test and numerical model analysis, the impact factors of "critical dynamic plastic strength" of high-speed railway roadbed are revealed. It is found that "critical dynamic plastic strength" is affected by the extent of subgrade filling, compact pressure, loading frequency and moisture. The suggested values of "critical dynamic plastic strength" of high-speed railway roadbed under different compaction standard are proposed. Under the allowed vehicle speed range, density, and increase operating a train marshalling, will not adversely affect the status of existing high-speed railway roadbed service, and increase the operating speed will be due to the reduce of the roadbed "critical dynamic plastic strength", resulting in an increase of subgrade defects, line smoothness deteriorates.(3) Based on the dynamic triaxial test of group A and B stone fillers, the curve of shear strain vs. large deformation dynamic load- deformation and the curve of dynamic shear modulus ratio max/ddGG vs. damping ratio D and dynamic shear strain γ are established under the assumption of small deformation. The suitable relationships for both non-ballasted track bed base layer and the accumulated plastic strain vs. dynamic stress and vibration times are completed. Based on the established simulation model of car- rail- road, the service status for various types of high-speed railway roadbed due to the accumulated plastic strain of subgrade layer of soil and road basic body are analyzed and evaluated. Finally, its effectiveness is also verified.(4) Based on the measured irregularity data of the high-speed rail track surface and analysis results of dynamic triaxial test and vehicle-rail-road dynamic finite element, a hybrid model with continuous multi-domain parameters based on mutual influence combinatorial ant colony optimization algorithm is proposed. According to the irregularity inspection data of trail track, the high-speed railway roadbed dynamic calculation parameters are determined to solve the problem that the high-speed railway roadbed service status assessment parameters are hardly determined and to further predict the high-speed railway the service status, and diseases of the roadbed deformation analysis and evaluation. Using a continuous multi-parameter interaction domain combined ant colony optimization algorithm parameters together with Chai and Miura modified index model, the cumulative plastic deformations of the high-speed railway roadbed are calculated. The validity and accuracy of this method is verified by the test data.(5) Based on the "strain increment control design method" of ballastless subgrade structure which chooses the "critical dynamic plastic strength" as the control indicators, and the multi-parameter influenced continuous domain ant colony optimization algorithm and hybrid model, as well as car-rail-road dynamic finite element numerical model of high-speed rail, the intensive transition section roadbed design parameters and control targets are optimized. According to field measurement(roadbed dynamic stress less than or equal to 15.0kPa, dynamic displacement less than or equal to 0.11mm) research and simulation, dynamic stress limit of speed railway ballastless subgrade surface is set as 60.0k Pa. And, the dynamic displacement design limit is set as 0.44 mm. The minimum bearing stiffness of the high-speed railway ballastless subgrade surface should be not less than 200MPa/m.