Distribution Characteristic Research Of Hydraulic Power In The Ballastless Track Crack Under The Train Load

In the area with abundant rainfall and poor drainage system,there will be serious water damage existed in the interlayer of ballastless track.The essence of water damage in the ballastless track is a dynamic evolution process of damage shape under the combined action of train load,water pressure and water velocity.As the main causes of the damage formation in the ballastless track,the fastener pressure is also a direct reason of the hydrodynamic pressure and water velocity existed in the crack.Consequently,the distribution and action characteristics of fastener pressure have become the basis of water damage research in the ballastless track.The hydrodynamic pressure and water velocity are the main causes of water damage formation and the driving force of damage evolution,making the study of hydrodynamic pressure and water velocity become the core of systematic research of water damage in the ballastless track.Aimed at the hydrodynamic pressure and water velocity distributions inside the crack under the action of train load,the preliminary study has been done recently.However these researches not only ignored the distribution and action characteristics of the fastener pressure,but also lacked the corresponding theories of hydrodynamic pressure and water velocity distribution.In this paper,the analytical expressions of hydrodynamic pressure and water velocity in the crack of ballastless track were deduced firstly,the high sensitivity of the hydrodynamic pressure and water velocity to the loading process has also been pointed out,and then the sequential loading method was presented according to the distribution and action characteristics of fastener pressure.Finally,the calculation models of the hydrodynamic pressure and water velocity under the train load were established,and the distributions of hydrodynamic pressure and water velocity in the crack were analyzed systematically.1.Theoretical and experimental researches of hydrodynamic pressure distribution in the interfacial crackIn view of the typical interfacial crack of ballastless track,based on the characteristics of water damage inside the crack,the simplified mechanics model for water and composite slab with interfacial crack was presented in order to obtain the hydrodynamic pressure distribution.Based on the law of mass conservation and momentum theorem,the analytical expressions of water pressure and velocity in the saturated water crack of ballastless track were deduced by using the control volume method.Similarly,the analytical expressions of water pressure and velocity in the unsaturated water crack were deduced by adding the state equation of ideal air.The tests of hydrodynamic pressure in the concrete crack under theaction of dynamic loading were performed to verify the water pressure analytical expression.The results show that,the hydrodynamic pressure is determined synthetically by the fluid viscosity,load characters,crack shape,absolute pressure at the outlet,original volume of air in the crack and so on.And there is a intersecting phenomenon between influence factors.In addition,the hydrodynamic pressure and water velocity in the crack have a direct relationship with the first and second derivatives of the loading functions.In other words,the hydrodynamic pressure is very sensitive to the loading process,which makes the selection of proper loading mode become the key to study the hydrodynamic pressure and water velocity.2.Distribution characteristics research of fastener pressure acting on the ballastless trackIn order to obtain the distribution characteristics of fastener pressure acting on the ballastless track,the analytic expression of fastener pressure was derived on the basis of analytic foundation pressure expression of continuous elastic foundation beam.And the fastener pressure and its first and second derivatives were also analyzed.Aimed at verifying the analytical expression of fastener pressure,the synchronous field tests of the wheel/rail force and vertical fastening force were conducted in an actual operating line.The wheel/rail force was measured by the shear and full-bridge patch method,the tested wheel/rail force was regard as the load boundary condition of fastener pressure calculation.The fastener pressure was measured by a new type of Tekscan thin film sensor in the field,then the tested results were compared with the theoretical results to verify the analytical expressions of fastener pressure distribution.The results show that,under the effect of a single wheel,the curve of vertical fastening load is a harmonic with severe attenuation and a period of 2?L.And the whole loading process can be divided into four stages,i.e.,accelerated loading,decelerated loading,accelerated unloading and decelerated unloading.In the practical application,when the influence of vertical fastening load in the secondary region is neglected,the curve can be replaced by Gaussian distribution approximately.The main influence of wheel group superposition effect on fastener pressure focus on the second derivative of fastener pressure and the tensile fastener force.In view of the high sensitivity the hydrodynamic pressure to the second derivative of loading functions,when the hydrodynamic pressure in the interfacial crack of ballastless track is studied,the basic loading mode should be selected according to the bogie loading,and the adjacent loads should be applied gradually in a sequential way.3.Distribution characteristics research of hydrodynamic pressure in the interfacialcrack of ballastless trackAs for the distribution characteristics of hydrodynamic pressure in the typical interfacial crack of ballastless track,the sequential loading mode of several fastener pressure was adopted,the 2D and 3D models for calculating the hydrodynamic pressure were established in terms of the fluid-structure interaction analysis module of ANSYS Mechanical+CFX in Workbench,respectively.The effects of fluid viscosity,load characters(train speed and axle load),and crack shape(longitudinal length,horizontal depth,vertical aperture)on hydrodynamic pressure were also analyzed,respectively.The results show that,the hydrodynamic pressure is determined by the fluid viscosity,crack shape,and load characters synthetically.When the crack aperture is less than 2mm,there is a phenomenon of cross interaction among the fluid viscosity,crack aperture and loading procedure.The effect of water viscosity on hydrodynamic pressure is negligible when the crack aperture is greater than 2mm,and the value of hydrodynamic pressure is linear with the axle load,proportional to the square of train speed,inversely proportional to the vertical crack aperture,and proportional to the cubic polynomial of horizontal crack depth.But the value of hydrodynamic pressure increases firstly with the increase of longitudinal crack length,then decreases gradually and tends to be stable finally.As the train approaching and departing from the location of a crack,the hydrodynamic pressure changes cyclically under the train load,and both the maximum positive and negative pressure occur at the crack tip.At the same time,there may be a coexistence phenomenon of positive and negative pressure in the crack.And the position of positive and negative pressure zone would change with the running of the train.4.Distribution characteristics research of water velocity in the interfacial crack of ballastless trackIn order to analyze the distribution characteristics of water velocity in the typical interfacial crack of ballastless track,the 3D model for calculating the water velocity was established by adopting the sequential loading mode of several fastener pressure.The effects of water viscosity,load characters(train speed and axle load),and crack shape(longitudinal crack length,horizontal crack depth,vertical crack aperture)on water velocity were also analyzed,respectively.The results show that,the water velocity is determined by the fluid viscosity,crack shape,and load characters synthetically.The value of water velocity is linear with the axle load,proportional to the train speed,inversely proportional to the crack aperture,and proportional to the quadratic polynomial of horizontal crack depth.But thevalue of water velocity increases firstly with the increase of longitudinal crack length,and then tends to be stable.As the train approaching and departing from the location of a crack,the water velocity changes cyclically under the train load,and both the maximum positive and negative velocity occur at the outlet of crack.Simultaneously,there may be a coexistence phenomenon of positive and negative velocity in the crack.And the position of positive and negative velocity zone would change with the running of the train.Through the methods of data collection,theoretical derivation,experimental research and numerical simulation,the distribution characteristics of hydrodynamic pressure and water velocity in the track crack under the action of train load were analyzed systematically,the theoretical system of hydrodynamic pressure and water velocity distribution under the train load was established primarily,which solves the core problems of water damage research in the ballastless track.These research results have important practical value for the further study of water damage in the ballastless track.