# Protection of Buried Pipelines from High-Speed Train Vibrations with Expanded Polystyrene Geofoam
## 1 Introduction  
In recent years, train-induced vibrations and associated detrimental effects have become even more pronounced. The higher living standards of the population have increased the need for fast, safe, economical, and comfortable traveling. This fact has led to the development of new high-speed railway (HSR) lines and/or the upgrading of existing railways to become suitable for high-speed trains (HST) [1]. Hence, the impact of developed vibrations on the structural safety [2, 3] and primarily the discomfort/disruption of residents' activities in adjacent buildings has become a crucial issue [4]. Train-induced vibrations are mainly propagated on the surface of the underlying soil in the form of surface Rayleigh waves. This complex phenomenon has drawn the attention of several researchers and engineers [5, 6]. The growth of researchers' knowledge on numerical and analytical methodologies in recent years has contributed to the accurate prediction of the response of railway tracks and the subsoil's surface when subjected to HST-induced vibrations. Relevant investigations focus on wave propagation and surface vibrations [7] as well as on mitigation measures [8, 9]. Vibrations due to HST passage can disturb the residents of adjacent buildings, affecting the railway lines and the safe operation of nearby infrastructure. In recent years, severalstudies have been performed to investigate these potential problems, including numerical approaches and field tests. In order to study this complex phenomenon, 2D, 2.5D, or 3D numerical boundary element--[8; 10] or finite element [11; 12]--based approaches have been used. The majority of the relevant studies have examined quite accurately the propagation of vibrations on the soil surface. Nonetheless, only a few studies have investigated the effects of developing vibrations induced by the passage of HSTs on the subsoil [13] and underground infrastructure [14]. Hence, in the present study, a first attempt is made to investigate the dynamic response of buried pipelines crossing an HSR line vertically, aiming to protect them using expanded polystyrene (EPS) blocks. EPS geofoam is a lightweight material widely used in various geotechnical applications [15; 16]. The Norwegian Public Roads Administration (NPRA) introduced this low-cost, high-performance material as base layer in road construction in 1972 [17]. More specifically, the implementation of two layers of EPS blocks with a total height equal to 0.5 m resulted in a 5 kPa decrease in the weight surcharge. Since the first applications in transportation infrastructure, EPS has been widely used in many engineering projects worldwide to resolve various construction issues, including highways passing through sites of poor soils, road widening, lightweight rail embankments, bridge abutments fill, the protection of underground structures, and slope stabilization. For instance, [PERSON] et al. [18] examined several techniques for protecting underground pipelines and culverts in transportation infrastructure by implementing EPS blocks. In a recent work, [PERSON] et al. [19] presented a series of full-scale tests on underground pipelines subjected to traffic-induced loading and examined the reinforcement of these pipelines by implementing EPS geofoam and geocell as backfill layers. According to this study, the use of EPS blocks with a height equal to 0.3D and width 1.5D (where D is the pipe diameter) above the pipeline is proposed as a very practical and efficient mitigation measure. The beneficial role of the implementation of EPS backfills for the protection of buried pipelines subjected to other types of loading has also been investigated. [PERSON] et al. [20] studied the beneficial role of EPS geofoam backfill for the protection of buried pipelines subjected to permanent ground displacements (e.g., surface faulting, land sliding, seismic settlement, and lateral spreading due to soil liquefaction).