# Qualitative Prediction Model for Dynamic Behavior of Ballasted Tracks
## 1 Introduction  
The environmental and mechanical conditions to which ballasted railway tracks are exposed to during service causes them to degrade and deteriorate. Because ballasted track structures subject to dynamic loading are usually constructed from various track components made with varying materials, their behavior cannot be easily verified or predicted. Moreover, the low reliability of input variables used in ballasted track analysis can have a potentially large effect on the solution. The dynamic response of ballasted track is affected by several parameters, such as rail pad and ballast stiffness, rail surface roughness, and the condition of track components. Among these, the spring stiffness of the rail pad and ballast has been demonstrated to be most influential to the track support stiffness. The track support stiffness (i.e., track stiffness) influences the bearing capacity of the track, the dynamic interaction force between a vehicle and the track, the quality of the track geometry, and the service life of track components. In general, relatively high track stiffness is beneficial as it provides sufficient track resistance to applied loads and results in decreased track deflection, which reduces track deterioration [1; 2; 3; 4]. However, very high track stiffness leads to increased dynamic forces in the wheel-rail interface and on the sleepers and ballast, which may cause wearing and fatigue of trackcomponents [1; 2; 3; 4; 5; 6; 7; 8]. The track stiffness is also known as a basic parameter that refers to the essential requirement \"technical compatibility\". Hence, further efforts are required to develop a rational approach to the track design and construction to ensure that the track stiffness and its variations are within an acceptable range of values, or ideally, to achieve an optimum track stiffness [2; 8; 9; 10; 11; 12]. Furthermore, the measurement methods for the track stiffness must provide accurate, precise, and reproducible results to evaluate the performance of existing tracks and thus to make appropriate decisions regarding track maintenance. A variety of researchers, including [PERSON], and [PERSON] and [PERSON] conducted research in this area, and this has been reviewed and summarized by [PERSON] [10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23]. [PERSON] et al. presented a review of sensors used for the structural monitoring of railway track infrastructure, as well as their application to sense the performance of different track components during extreme events [24]. [PERSON] et al. presented the dynamic response between vehicle and track considering degradations of rail pads [25]. [PERSON] et al. suggested a rational analysis method for a track ballast wheel interaction that could be further developed to model the interaction in a train-derailment event, based on the discrete-element method (DEM) [26]. [PERSON] analyzed the effects of railway track irregularities on car-body vibrations through railway vehicle travel simulations conducted using the SIMPACK software package [27]. Some researchers analyzed the dynamic behavior of railway through experiments and finite element analysis [28; 29; 30; 31]. In addition, through monitoring of the railway, the condition of safety serviceability was confirmed with the maintenance of the railway due to aging factors [32; 33]. This work, therefore, aims to develop a predictive model relating quantitative and qualitative parameters of a ballasted track to allow for better track design. To do so, theoretical, experimental, analytical, and statistical evaluations were performed to predict and assess a variety of dynamic ballasted track characteristics, including the track support stiffness, track impact factor, dynamic wheel--rail forces, track displacement, and subgrade modulus. In addition, field measurements for evaluating the dynamic characteristics of a ballasted track and its components were performed.