## 4 Research on the Influence of Track Structure Stiffness Change on Track Deformation
### Analysis of Sensitivity Indexes of Vehicle-Track System Dynamics Response
According to Table 12, it can be seen that there is different relationship between the dynamic response coefficient and the stiffness of the track structure:When the vertical stiffness under rail changes, except for the vehicle body vertical acceleration sensitivity index which is positive, the other dynamic response parameter sensitivity indexes are all negative values, indicating that the vertical stiffness under rail increases, which is beneficial to reduce the rail system dynamic response level. In terms of the sensitivity to changes in the dynamic response parameters, the lateral acceleration of the vehicle body is the most obvious, while the vertical wheel-rail force, gauge expansion, and vertical acceleration of the vehicle body are not sensitive to changes in the vertical stiffness under rail, the wheel load shedding rate is the second, and the wear coefficient is, again, indicating that the vertical stiffness under rail is increased, which is beneficial to improve the dynamic stability of the vehicle body and reduce the wear between the wheel and the rail. 2. When the lateral stiffness under rail changes, the wear coefficient, the lateral displacement of the rail, the gauge expansion, and the lateral and vertical acceleration sensitivity indexes of the vehicle body are negative values, and the rest are positive values, indicating that the increase in the lateral stiffness under rail is beneficial to improve the lateral and vertical dynamic stability of rail system. In terms of the sensitivity of the changes in the dynamic response parameters of the rail system, the lateral acceleration of the vehicle body is the most obvious, followed by the vertical acceleration of the vehicle body, and the vertical displacement of the steel rail getting large, the wheel-rail vertical force and wheel load reduction rate are less affected by it. 3. When the vertical stiffness under block changes, except for the negative value of the wheel-rail vertical force and wheel load reduction rate, the sensitivity indexes of the other coefficients are all positive values, indicating that the increase in the vertical stiffness under block is not conducive to the overall rail system dynamic stability; in terms of sensitivity to changes in dynamic response parameters, the rail vertical displacement sensitivity is the highest, followed by the lateral acceleration of the vehicle body, and the wheel load reduction rate again, the vertical force of the wheel and rail, and the vertical acceleration of the vehicle body. The change of wheel-rail lateral force is less affected by the change of vertical stiffness under block, indicating that the dynamic response of the track system is highly sensitive to the influence of the vertical stiffness under block, and the vertical dynamic performance of the vehicle body is slightly affected by the vertical stiffness under block. The increase in vertical stiffness under block will intensify the lateral dynamic response level of the rail system. 4. When the lateral stiffness under block changes, the wheel-rail lateral force, wheel load reduction rate, and vehicle body lateral and vertical acceleration sensitivity indexes are positive values, and the other coefficients are negative values, indicating that the increase in lateral stiffness under block is beneficial to the track system. Improved dynamic performance will reduce the stability of train operation performance; in terms of sensitivity to changes in various dynamic response parameters, the lateral acceleration of the vehicle body is the most significant, followed by the vertical displacement of the rail, the gauge expansion again, and the sensitivity of other coefficients lower, indicating that although the increase in lateral stiffness under block is not conducive to the lateral dynamic stability of the vehicle body, it is conducive to maintaining the lateral stability of the track.