## 1 Introduction  
The exposure of embankment infrastructure to natural hazards is unavoidable [1]. This results in the instability of embankment slopes, which has increased in recent times due to human activities [2] and climate variability [3]. On a global scale, this problem poses a serious threat to the management and development of railway infrastructure and similar transportation networks [4]. Recently, the long-term performance of embankment slopes has become a focus of scrutiny [5; 6]. The consequences of climate change have made rail infrastructure more vulnerable to water-related risks, such as floods [7], ponding, and fluctuations in water levels [8]. China has one of the most diversified hydrological systems in the world [9], with a complex network of rivers, such as the Yellow and Yangtze Rivers, as well as enormous lakes, such as Qinghai Lake and Dongting Lake. The area surrounding Dongting Lake (the study area), near the Nanhu railway embankment between Beijing and Guangzhou provinces, has been affected by the lake's fluctuations (and resulting groundwater changes), resulting in multiple failures and constant repair. As a result, these situations not only accelerate embankment deterioration but also drive up rehabilitation and maintenance costs [10]. To address these challenges, several solutions have been used, including the placement of soil reinforcement techniques ranging from fibers and rock mixtures [11] to steel piling [12]. However, the control of traffic loads and the consequences of climate change have made these efforts persistently difficult [13]. Ensuring the long-term stability of embankment slopes under water level fluctuation requires advanced engineering solutions that could capture seasonal and long-term fluctuations while allowing for increased traffic demands at the same time [14; 15]. An attempt to address these difficulties is crucial to ensuring the reliability and resilience of critical transportation systems [16]. Recent studies have stressed the relevance of incorporating soil hydromechanical parameters for evaluating the performance of embankment slope constructions under different geohazard conditions [17; 18; 19; 20]. Using the bibliometric tool VOSviewer 1.6.19 to analyze previous studies from the Scopus database revealed a noticeable trend in slope stability analysis under changing water levels and limited work on sensitivity and optimization of slope stability factors (see Figure 1). In addition to external influences, the physical properties of the material structure are internal elements that play an important role in slope stability, as the changes in saturation states of the soil due to seepage fields impact both local and overall slope stability [17; 21]. Additionally, groundwater table variations could have considerable impact on the slope stability due to its time domain [22; 23]. Another way to improve the performance of railway embankment slopes is to examine the quantitative relationships between parameters regulating safety coefficients [24]. Technically, this requires examining the effect of changes in each hydromechanical parameter on the safety factor and knowledge about their dominating roles in stability analysis [25]. This is critical for developing appropriate mitigation strategies and control guidelines to minimize instability [26]. Unfortunately, water level changes in railway slope stability is a subject that has received little attention [27]. Some  
Figure 1: Map slope stability analysis studies under water level using VOSviewer. studies advise that for long-term performance and a robust railway system, sensitivity assessments for each parameter of the railway slope under bidirectional water levels are critical [28]. [PERSON] [17] investigated the sensitivity of variables such as unit weight, internal friction angle, water level, and cohesiveness on the slope stability factor of safety.