## 5 Field Test Results and Discussion
However, the vibration reduction performances vary depending on the directions of the load-induced vibrations and the positions of the accelerometers, as calculated from the maximum spectral magnitudes of different test conditions. The NS direction, perpendicular to the vibration barrier, is the primary direction in which vibrations generated by the hammer impact are effective. Vibration isolation was designed considering the impact in this direction. This design's effectiveness in reducing vibrations is evident when examining the ARR values calculated for the M131 accelerometer positioned directly behind the barrier in the NS direction. Firstly, the vibration reduction performance for all conditions was analyzed in terms of PGA magnitudes. It is well known that an empty trench typically provides better isolation performance than barrier-filled trenches, and this study demonstrated approximately 88% vibration mitigation performance. The vibration reduction performances for the BCCB Trench and the Styrofoam-filled BCCB Trench were calculated to be approximately 88%. Additionally, all three conditions fall within the effective isolation region suggested by [PERSON], with a maximum ARR value of 0.25. These calculations highlight that the BCCB Trench, which contributes to lateral stability in the open trench condition in the NS direction, exhibits both similar behavior and effective vibration performance to that of an open trench, making it a significant finding for practical applications. The infill material placed inside the BCCB neither contributed to  
Figure 24.2 Comparison of normalized amplitude reduction ratio (ARR) in three components of instruments for (**a**) PGA, (**b**) PGV, and (**c**) PGD values [53]. nor negatively affected the vibration mitigation performance of the Empty Trench and the BCCB Trench. Examining the M130 accelerometer positioned in front of the barrier reveals that the PGA\({}_{\text{ARR}}\) values calculated for the BCCB Trench and the Styrofoam-filled BCCB Trench are similar and relatively higher than those for the Empty Trench condition. This can be explained by the BCCB Trench's impact on the reflection of vibration waves recorded by the M130 accelerometer directly in front of the barrier. To express this quantitatively, in the BCCB Trench and Styrofoam-filled BCCB Trench conditions, the vibration amplitudes increased by approximately 30% and 15%, respectively compared to the No Trench condition, due to the combination of reflected and incoming vibration waves. In the Empty Trench condition, the vibration amplitudes decreased by approximately 5% compared to the No Trench condition. The inner filling material placed inside the barrier demonstrated better performance than the BCCB Trench by increasing the vibration amplitudes in front of the barrier less than in the BCCB Trench condition. The PGA\({}_{\text{ARR}}\) values obtained from the M132 and M133 accelerometers, located 2.6 m and 9.6 m behind the barrier, are approximately the same across all test conditions, averaging 0.35 and 0.63, respectively. When the PGAARR values of the accelerometers are analyzed, it is observed that as the distance of the accelerometers behind the barrier to the barrier increases, the effectiveness of the barrier decreases and the vibration mitigation performance also decreases. When analyzing vibration mitigation performances in terms of PGV values, similar behavior to PGA values is observed. For the M131 accelerometer located directly behind the barrier, the PGVAR values for the Empty Trench, BCCB Trench, and Styrofoam-filled BCCB Trench conditions are 0.14, 0.22, and 0.18, respectively. These values are situated within the effective isolation region suggested by [PERSON], as observed with the PGA data. When examined in terms of another metric of Vibration Mitigation Performance (VMP), the vibration reductions in the Empty Trench, BCCB Trench, and Styrofoam-filled BCCB Trench cases are 86%, 78%, and 72%, respectively.