## 5 Field Test Results and Discussion
This means that the best performance in terms of PGV magnitudes is provided by Empty Trench, followed by BCCB Trench and Styrofoam-filled BCCB Trench. The vibration mitigation performance decreases by 8% when BCCB is placed in Empty Trench. However, if Styrofoam material is placed inside the BCCB, the vibration performance is increased by 6% compared to the BCCB Trench case. Hence, the infill material provided additional vibration mitigation performance to the BCCB Trench and made it closer to the performance of the Empty Trench. Examining the PGVAR values obtained from the M130 accelerometer positioned in front of the barrier indicates that, similar to the PGA data, the barrier conditions reflect certain levels of vibration waves, resulting in higher vibrations in front of the barrier compared to the empty trench condition. The PGVAR values obtained from the M132 accelerometer, located behind the barrier, are found to be close to those from the M131 accelerometer positioned immediately behind the barrier. This demonstrates that the barrier's effect is successfully maintained even 2.6 m behind the barrier. The vibration mitigation effect of the barrier decreases with increasing distance. To express these effects in terms of VMP values for the Empty Trench, BCCB Trench, and Styrofoam-filled BCCB Trench: 85%, 75%, and 80% for the M132 accelerometers, and 66%, 53%, and 54% for the M133 accelerometers, respectively. It can be inferred from this information that the Empty Trench case performs better than the other cases even at increasing distances. In addition, the performances of BCCB Trench and Styrofoam-filled BCCB Trench are close to each other. Overall, the vibration performance based on PGV data is better with increasing distance than the PGA data suggests. In quantitative terms, the vibration mitigation performances of the PGV data are about 2%, 11%, and 7% lower than those of the PGA data for the Empty Trench, BCCB Trench, and Styrofoam-filled BCCB Trench cases, respectively. When considering the vibration reduction performance calculated from PGD data, similar behaviors to those observed in the PGV data are noted. These similarities include the reflection of vibration waves by the barrier in front of the accelerometer, the decrease in vibration mitigation performance with increasing distance behind the barrier, and the advantages/weaknesses of the barrier conditions in terms of vibration mitigation performance compared to each other. An important difference is that the ARR coefficients calculated for the position immediately behind the barrier are slightly higher. For the Empty Trench, BCCB Trench, and Styrofoam-filled BCCB Trench conditions, these values are 0.18, 0.37, and 0.31, respectively. In other words, the VMP values are 82%, 63%, and 79%, respectively. Although good vibration performance is achieved in all barrier conditions in UD, the BCCB Trench and Styrofoam-filled BCCB Trench were slightly outside the effective isolation region commonly accepted in the literature. In the EW direction, the best isolation performance was observed for PGD and the lowest for PGA, while the opposite behavior was observed in the NS direction. According to PGA values, the Empty Trench case provides the best isolation performance, while the Styrofoam-filled BCCB Trench case has the worst isolation performance compared to the others. The superiority and weaknesses of the barriers in their performance relative to each other are similar for the EW-NS directions according to the PGA results. According to the PGV and PGD data, the best isolation performance was still achieved in the Empty Trench case, while the infill material used in the BCCB Trench improved the vibration isolation performance compared to the BCCB Trench case. In terms of VMP values of the PGA values, the Empty Trench case provides 12% better performance than the BCCB Trench case, while in terms of PGV and PGD data, this performance is about 6% and 2%, respectively.