## 1 Introduction  
The southwestern and northwestern regions of China have been affected by compression between the Indian and Eurasian plates. As a result, active fault zones are widely distributed. With the rapid development of railway constructions in these areas, the railway network in the southwest and northwest of China has become increasingly dense. More and more railways are facing the challenge of crossing active fault zones [1, 2, 3, 4, 5]. In a seismic recurrence cycle, fault zone deformation can be divided into coseismic, interseismic, and postseismic deformation. Interseismic and postseismic creep and coseismic stick-slip can cause uneven deformation of the railway subgrade, threatening the long-term operational safety and sustainability of the railway [6]. Researchers have mainly studied the influence of fault dislocation on surface deformation and structural sustainability through model tests and numerical simulations. Researchers like [PERSON] [7] and [PERSON] et al. [8] used wet clay and quartz sand as experimental materials to conduct deformation experiments on the overlying layers underneath the strike-slip fault movements. The secondary structures associated with strike-slip faults are primarily categorized into R cracks, R' cracks, P cracks, T cracks, Y cracks, and compressive folds. [PERSON] et al. [9] developed a theoretical formula for the interseismic surface deformation of strike-slip faults. [PERSON] et al. [10] conducted centrifuge model experiments on fault dislocation, analyzing the deformation evolution patterns of interlayer soil fracture induced by normal fault movements in the presence of hidden fractures. [PERSON] et al. [11] used a discrete element numerical simulation to analyze the impact of reverse fault movements on the development of folds in the overlying sedimentary layers. [PERSON] et al. [12] conducted model tests on subgrade deformations induced by reverse fault movements. The damage and fracture characteristics of natural subgrades and subgrades reinforced with various anti-displacement measures were studied. [PERSON] [13] and [PERSON] [14] conducted model tests and a finite element analysis for different angles between the subgrade and the fault zone and the amount of fault displacement to analyze the mechanism of subgrade deformation damage induced by the fault dislocation. [PERSON] [15] developed model test equipment suitable for analyzing the impact of fault dislocations on tunnel deformation. Through numerical simulations and model tests, the deformation and failure mechanisms of tunnel structures under different fault dip angles, fault dislocation speeds, and dislocation amounts were revealed. [PERSON] [16] studied the stress and deformation of a metro viatuct under the action of a fault dislocation. He put forward engineering prevention measures for viaducts crossing a fault zone. To sum up, there is still little research on the impact of fault dislocation on the sustainability of railway subgrades. In current fault dislocation model tests, scholars still rely on the naked eye and ruler measurements to qualitatively analyze the influence range and degree of subgrade deformations in fault dislocation tests. At present, there is a lack of precise monitoring means to analyze the deformation laws of various parts of the subgrade in the process of fault dislocation tests. Regarding numerical simulations, the development law of cracks in subgrades under the dislocation of strike-slip faults has rarely been analyzed in previous finite element calculations. Although discrete element simulations can accurately analyze the deformation and crack development of subgrades, their calculation speed is slow, and they are unable to quickly carry out multi-condition numerical simulation calculations to analyze the propagation and evolution law of deep fracture traces in large-scale subgrades under strike-slip fault dislocations. Therefore, the research on the mechanism of subgrade damage under fault dislocations is still insufficient.