## 2 Materials and Methods
### Downhole Seismic Method
#### 2.5.4 Data Acquisitions  
For the purpose of the present research, data acquisition is classified into two different types, namely geotechnical data acquisition (core drilling, soil boring, and laboratory testing) and geophysical data acquisition (the seismic down-hole logging method). The seismic downhole logging was conducted with the help of 24 channel ABEM Terraloc MK8 seismograph well attached to downhole seismic cables. A six-Hz detector containing three geophone components was attached to the end of the seismic cable; two horizontal geophones were also utilized for the purpose of recording S-waves and a single vertical geophone was utilized for recording P-waves (Figure 8). Then, 3 inches of (77 mm) PVC pipe was implemented in the borehole. The bottom end of the PVC pipe was positioned very close to the PVC cap; this was because of the fact that where steel casing is utilized, the impacts will be of a higher importance. Right at the PVC cap center, a hole of the  
Figure 6: The behavior of particle elliptical motion in Rayleigh waves. Figure 7: Particle motion of Love waves in horizontal plane. size 17 mm was drilled for the aim of grouting. In addition, to make sure the hole would remain intact with rock mass or soil, cement-bentonite was used for grouting the space between the PVC casing and borehole wall with a mixture ratio of 1:1; the procedure started from the borehole bottom in a way to avoid cavities that may appear in the course of grouting. The seismic downhole method performs direct measurement of Compression (P) or Shear (S) wave velocities or both in a PVC cased borehole which advanced through soil to require depth. The annulus between the borehole surface and the PVC casing is carefully cement-grouted to ensure the hole remains intact with the soil. Water was filled inside the cased borehole before starting the measurements to improve or enhance the grounding of the soil. The test was carried out using a 24 channel ABEM Terraloc MK8 seismograph by lowering a geophone to a full depth in the cased borehole. A seismic source is triggered by a 12 lb sledgehammer by striking vertically onto a steel plate placed on the ground near the borehole to create the compression or P-wave. Alternatively, the sledgehammer strikes horizontally to either ends of the concrete/wooden block to generate the shear or S-wave. The travel time is recorded from the moment of seismic source initiation until reception at the geophone. The geophone is raised to a new depth at every 1 m depth interval. The same process is repeated from the bottom of the borehole until to the top of the PVC casing (Figure 9). After that, the detector was cautiously lowered down to the end of the grouted borehole; then, it was fastened firmly to the borehole wall for the purpose of achieving better grounding, hence producing finally results of a higher quality and reliability. In the interval of 0.5-1 m, data regarding the P- and S-waves were attained with considering the borehole situation to seismic source distance (P- or S-waves). It was necessary because with an increase in the distance, it could result in velocity error calculation. With an assumption indicating that the distance between the borehole and seismic source is getting close to zero, it was recognized that wave might travel not through the soil layer, but through the borehole casing, where an incorrect arrival time could be detected [76]. It is somewhat different to acquire downhole-related data in the cases of the P-wave and S-wave. The data related to the downhole P-wave seismic are obtained from the P-wave seismic source. Such data are generated through vertically striking a steel plate situated at 1-1.84 m from borehole with the use of a 6 kg sledgehammer (Figure 9a). The downhole S-wave seismic data are obtained from an S-wave seismic source, which is generated through horizontally striking on the opposite direction of a weighted wooden plank (on top of it by car/lorry) using a 6 kg sledgehammer (see Figure 9b).