## 4 Field Experiments for Evaluating Vibration Isolation Performance
### Measurement Setup in the Free Field  
To measure the vibration attenuation performance of the developed prototype vertical wave barrier, a series of experiments were conducted at the test site. Initially, the propagation of waves generated by the load source on the ground surface was measured in a free ground environment without a wave barrier. A sledgehammer with a mass of 5 kg served as the load source in the vibration experiments. The choice of this man-made load source is due to its ability to generate surface waves upon impact. The impact energy was transferred directly to the ground environment by a steel rigid plate placed on the surface without loss (Figure 17).  
An AC-3 HDG 32-bit high-resolution, low-noise accelerometer system capable of measuring low-vibration motion using capacitive force micromachined sensors was utilized to measure the vibration energy transmitted from the load source to the free ground surface. The measurement system comprises three basic parts: a GPS antenna, power source, and accelerometer main box. Within the accelerometer main box are three MEMS sensors, an ADC digitizer, and a memory where the accelerations are recorded (Figure 18).  
Figure 17: The dynamic load source and application method.  
Figure 18: The vibration measurement system.  
for surrounding structures. When subjected to impact, soil mediums resist not with their cross-section but with their volume. Therefore, having a volume and form capable of absorbing a large amount of energy is crucial to reducing the spread of vibrations. In line with these definitions, it is among the measures that can be taken to use vibration barriers by opening trenches in the ground, that is, by artificially changing the volume and form of the environment.  
When a wave barrier is placed close to the load source, it is referred to as active isolation, whereas positioning it near the structure or environment to be protected is termed passive isolation. Due to the stability problem on the basis of the load source and the possibility that the waves reflected from the wave barrier may produce undesirable effects on the system generating the vibration, passive isolation is considered more practical. Consequently, this study utilized a passive vertical wave barrier in experimental investigations aimed at reducing the amplitudes of environmental vibrations propagating through the soil under impact load. Based on the information that vibration amplitudes are attenuated by 20% when the excavation depth is 0.2\(\lambda\) in open trench isolation models [49] and considering the groundwater level at the test site, it was determined that the optimal depth for the wave barrier should be 1.5 m.  
Considering the alluvial soil conditions with low shear stiffness at the test site where the experiments were conducted, it was necessary to support the wave barrier from the inner surfaces since the stability problem would arise in the excavated ground to form the wave barrier with a certain depth.  
The most crucial factor here is that the material providing lateral stability and supporting the soil, like a retaining wall, must have low impedance. For this purpose, double-corrugated cardboard panels supported by balsa were developed (see Section 3.2).  
In open trench wave barrier applications, another potential issue is the safety problems that may arise due to the barrier being open. The most effective solution to this problem is to fill the inside of the barrier. It is crucial that the fill material chosen for the open trench wave barrier has low impedance to ensure that the barrier's isolation performance is not significantly affected. Therefore, waste polystyrene foam (Styrofoam) with a very low density of 0.01-0.03 t/m\({}^{3}\) was used as the filling material. The Styrofoam foams used to investigate the effect of these low impedance waste materials on the vibration isolation performance of the wave barrier consist of 42 cm diameter, 2 m long, rolled bundles, each weighing approximately 2 kg, prepared for recycling in a cornice factory (Figure 20).