Mitigation of environmental vibrations induced by high-speed trains using a barrier constructed from recyclable materials

The increasing high-speed train (HST) traffic in densely populated urban areas has introduced significant environmental vibration problems, which lead to passenger discomfort, reduction in the service life of structural components, and potential malfunction or damage of precision electronic equipment. This doctoral study aims to design and develop a high-performance, cost-effective, and environmentally sustainable vibration isolation barrier to mitigate these adverse effects. Although open trench systems excavated in firm soils are widely recognized in the literature as effective vibration mitigation solutions, their implementation in weak soil conditions is limited due to lateral stability challenges. Soils with low bearing capacity, such as loose sands, silts, alluvial deposits, and shallow groundwater conditions, require internal trench support, which complicates conventional engineering practices. As an innovative alternative to the open trench method, this research proposes a box-shaped wave barrier (BCCB Trench) constructed from low-impedance, recyclable materials. The barrier features a structural frame made from high-strength balsa wood and sidewalls composed of double-wall corrugated cardboard, which is highly sensitive to vibration transmission. These materials were chosen not only for their environmental advantages but also for their mechanical compatibility with the surrounding soil, ensuring seamless wave propagation without causing abrupt impedance discontinuities. This feature provides a distinct advantage in preserving the natural transmission mechanics of surface and body waves. Designed specifically to reduce ground-borne and airborne vibrations induced by high-speed train passages, the proposed barrier offers a reliable and efficient solution for vibration-sensitive zones such as industrial facilities, residential neighborhoods, and structures housing delicate instrumentation. A series of field and laboratory tests were conducted to evaluate the mechanical strength, water resistance, and vibration attenuation performance of the developed prototype. Among these, full-scale field tests were performed near a high-speed railway line in Pamukova, Turkey, where real dynamic loading scenarios involving the HT65000 train set was utilized to evaluate in-situ vibration and sound reduction effectiveness. Laboratory-based three-point bending tests confirmed the structural adequacy of the barrier under lateral soil loads, verifying its suitability for deeper trench implementations in weak soil environments. To ensure environmental durability, various waterproofing techniques were tested. Among these, the greenhouse nylon coating demonstrated the lowest water absorption rates and was selected as the standard protective layer for field prototypes. The modular design of the barrier, reinforced with an internal orthogonal lattice frame, was also numerically validated using SAP2000 finite element simulations. The numerical model allowed for additional design variations, enabling the adaptation of the system to different soil and load conditions. Moreover, the application of low-density filler material, specifically Styrofoam, inside the BCCB Trench was found to enhance its vibration mitigation performance by decreasing wave reflections and increasing energy absorption. When comparing amplitude increases in front of the barrier due to reflected waves, the Styrofoam-filled version showed only a 15% increase, compared to approximately 30% in the unfilled configuration. These outcomes emphasize the critical role of internal filler material in optimizing isolation efficiency. Another critical aspect of the study was the integration of numerical modeling techniques with experimental observations. The SAP2000-based finite element model developed in this research was used to assess and improve the structural strength of the barrier design. By comparing the simulation results with experimental data, the model served as a valuable tool for validating the barrier's mechanical performance and exploring design optimizations without the need for additional physical testing. Furthermore, the study emphasized the importance of direction-specific vibration analysis, particularly in the horizontal NS and EW directions, where the majority of the train-induced surface wave energy propagates. In contrast to the common assumption that vertical vibrations dominate, this research revealed that the horizontal components were often more critical in evaluating vibration risks. This insight has major implications for the design orientation and positioning of vibration barriers near rail lines. The most distinguishing feature of the developed barrier lies in its ease of manufacturing, transport, and installation. Unlike conventional systems, it requires no heavy machinery or professional engineering labor. Its affordability and use of widely available materials make it particularly attractive for applications in rural or low-budget infrastructure projects. Furthermore, the use of biodegradable and recyclable materials supports broader sustainability goals and promotes eco-conscious engineering practices. Experimental results demonstrated that the BCCB Trench provides significant vibration reduction in soft soil environments, while simultaneously offering lateral support, reducing the need for reinforced trench walls. In particular, time-history acceleration data obtained from accelerometer readings behind the barrier showed substantial decreases in vibration amplitudes, especially in the horizontal (EW, NS) directions. Normalized amplitude and RMS analyses revealed that the foam-filled BCCB Trench achieved amplitude reductions exceeding 40%, with peak ground acceleration values falling within the effective isolation region proposed by Woods. In some cases, the performance of the BCCB Trench matched or surpassed that of traditional empty trench configurations. Comparative analyses of normalized RMS acceleration values revealed that the damping performance of the barrier systems is sensitive to train speed. While the reduction ratios remained limited under slow train passages, especially in the horizontal directions (EW and NS), the presence of the barrier was significantly more effective under high-speed trains, with reductions exceeding 50% in the NS direction. In the vertical (UD) direction, some increases were observed under slow trains, whereas notable reductions occurred during high-speed passages, suggesting a clearer damping effect with increasing wave energy. The higher performance of the foam-filled barrier in certain directions indicates that internal filling enhances energy absorption capacity. In addition to acceleration-based evaluations, sound level measurements under natural train pass-by conditions were also carried out. The presence of the BCCB Trench led to noticeable reductions of up to 20 dBA near the train source and approximately 10 dBA in more remote positions. Frequency-based insertion loss analyses further revealed that the barrier was particularly effective in the 125-500 Hz frequency range, which aligns with the dominant frequencies of ground and structural noise caused by rail systems. These findings indicate that the proposed box barrier not only reduces ground-borne vibration but also offers meaningful sound insulation capabilities. In conclusion, this study demonstrates that the BCCB Trench is an effective and practical alternative to traditional vibration isolation systems. It is capable of attenuating both airborne and ground-borne vibrations across a range of frequencies and soil conditions. Its low impedance structure ensures mechanical compatibility with natural soils, and its modular, sustainable design presents strong potential for widespread implementation in vibration-sensitive areas, including cultural heritage sites, laboratories, and precision manufacturing facilities. Future studies may focus on long-term durability assessments, further optimization of filler materials, and extension of the numerical models to more complex, layered soil environments for broader application scenarios.