Study On Service Performance Of Slab Ballastless Track-subgrade Structure In Severe Cold Region

Based on the viscoelastic theory of CA mortar and the basic principles of thermodynamics,the thermodynamic model of CRTS I slab ballastless track-subgrade structure is established by using the finite element analysis software.By collecting and analyzing the meteorological data of Dalian,Shenyang,Changchun and Harbin from 2011 to 2020,the temperature field distribution of ballastless track structure is analyzed.The prediction formula of the most unfavorable temperature gradient of track slab in Northeast China is sorted out and fitted,and the most unfavorable temperature gradient load used in the inspection of ballastless track structure in Northeast China is summarized;On this basis,the stress,displacement and interlayer damage parameters of each layer of ballastless track structure are calculated under different conditions,such as only temperature gradient,positive temperature gradient and train load coupling,negative temperature gradient and train load coupling,and the whole temperature gradients and train loads coupling.And the development of interlayer damage of the ballastless track structure under the action of long-term complex loads is simulated,and the service performance of the ballastless track structure is evaluated.The main research contents and conclusions are as follows:(1)The temperature in the CRTS I slab ballastless track-subgrade structure shows a nonlinear distribution in the depth direction and a hysteresis,and the track structure bears the alternating action of positive and negative temperature gradients in a day.With the increase of subgrade depth,the influence of external temperature on subgrade is gradually weakened,and the response of subgrade to the change of external temperature is more obvious in the depth range of 0-0.2m.The vertical temperature gradient of the track slab and the subgrade in the range of 0-0.2m is positively correlated with the solar radiation intensity and air temperature,and negatively correlated with the wind speed.According to the three meteorological factors of solar radiation intensity,temperature difference and wind speed,the prediction model of the daily maximum positive and negative temperature gradient of the ballastless track slab in the northeast severe cold region is obtained,and the most unfavorable temperature gradient of the track slab in the northeast region is 120 °C/m for the positive temperature gradient and-40 °C/m for the negative temperature gradient.(2)The stress and deformation values of each layer of CRTS I slab ballastless track structure under the action of temperature gradient load decrease layer by layer,and the attenuation amplitude decreases layer by layer;the position of slab corner is the position where the maximum vertical stress and vertical displacement values appear under the action of negative temperature gradient,and the time of vertical stress peak value appears hysteresis.(3)Under the coupling action of the train at the slab end and the positive temperature gradient load,the vertical compressive stress at the slab end and the slab corner of the track slab and the CA mortar layer is larger;under the coupling action of the train in the slab and the negative temperature gradient load,the vertical tensile stress at the slab corner of the track slab and CA mortar layer is larger;Under the coupling action of the train load and the whole diurnal temperature gradient load,the secondary stress damage at the upper and lower bonding interface slab corner of the CA mortar layer is larger.With the deterioration of CA mortar,the secondary nominal stress damage,the peak value of vertical tensile and compressive stress and the vertical relative displacement of the track structure will increase.(4)Under the long-term action of the simplified temperature and train load,the damage between the track slab and the CA mortar layer of the ballastless track structure first appears at the corner of the slab in the seventh year;with the increase of the load time,the bonding interface expands in the vertical and horizontal directions at a distance of 0.5 m from the corner of the slab,and the damage area is distributed in a ring shape,and gradually expands to the interior of the bonding interface.In the 24 th year,the bonding interface in the range of 0-0.5m of the slab end has been completely debonded.