# Experimental and Numerical Studies on Ground Shock Generated by Large Equivalent Surface Explosions
## 3 Experimental Results and Analysis  
The detonation of the above explosive charges placed either above or below the ground surface resulted in the generation of a ground shock that had the potential to cause severe structural damage [3]. Structural damage by ground shocks was recorded at an observation station that was set up in a pit 100 m away from the site of the explosion. A \"damping\" ditch with a width of 0.5 m was dug in front of the station, and the top of the station was covered by a polyurethane-sandwiched steel panel (PSSP) and plastic sheet. The interior of the station was lined with another pair of PSSPs, and a foam board was placed on top. Photographs of the inside and outside of the station are shown in Figure 4a,b. The inside and outside of the station remained unaffected after the 1 t TNT test, but the ground shock caused by the 10 t TNT test led to the collapse of the PSSP on top of the station, and large amounts of sand entered the station. The photographs shown in Figure 4c,d show the outside and inside of the station after the 10 t TNT test. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Type** & **Model** & \begin{tabular}{c} **Sensitivity** \\ **(mV/m\(\cdot\)s\({}^{-2}\))** \\ \end{tabular} & **Range** & \
\begin{tabular}{c} **Frequency** \\ **Range (Hz)** \\ \end{tabular} \\ \hline Acceleration sensors & 1B314E & \(\sim\)10 & 0–500 &
\begin{tabular}{c} Y/Z 0.5–7000; \\ X 0.5–5000 \\ 2-6000 \\ \end{tabular} \\ Velocity sensor & 2A101E & \(\sim\)4 & 1270 & 2–6000 \\ \hline \hline \end{tabular} Note: The units of the acceleration sensor range and velocity sensor range are m\(\cdot\)s\({}^{-2}\) and mm\(\cdot\)s, respectively.  
\end{table} 
Table 1: Sensor specifications. Figure 3: Sensor layout and photographs of the sensors, (**a**) layout of the sensors, (**b**) photograph of the sensors, (**c**,**d**) the pits. No test data could be acquired on the 10 t TNT test, because all the wires leading to the acceleration sensors and velocity sensors were snapped during the explosion. However, during the 1 t TNT test, data were acquired from the acceleration sensors at the 21 and 42 m points and from the velocity sensor at the 21 m point. The data cables of the velocity sensor at 42 m were snapped during the explosion. Figures 5a and 6a present the acceleration sensor data that were acquired at the 21 and 42 m points. It can be observed that the accelerations in the X and Y directions were higher, whereas that in the Z direction was comparatively lower. Parameters \(\alpha_{X}\), \(\alpha_{Y}\), and \(\alpha_{Z}\) are the accelerations that were measured in the X, Y, and Z directions, respectively, and \(\alpha\) is the resultant acceleration (\(\alpha=\sqrt{\alpha_{X}^{2}+\alpha_{Y}^{2}+\alpha_{Z}^{2}}\)). It can be observed that the maximum acceleration due to the 1 t TNT explosion at the 21 m point was 16.5 m/s\({}^{2}\) (shown in Figure 5b), while that at the 42 m point was 1.3 m/s\({}^{2}\) (shown in Figure 6b). Figure 4: Photographs of the measurement station before and after the 10 t TNT test, (**a**,**b**) photographs of the inside and outside of the station before test, (**c**) photograph of the outside of the station after the 10 t TNT test, (**d**) photograph of the inside of the station after the 10 t TNT test. Figure 5: Acceleration data measured at 21 m in the one-ton TNT ground explosion test. It may be observed from Figures 5a and 6a that the maximum positive and negative acceleration in the X direction decreased by 88 and 91.9%, respectively, in correspondence with the increase in distance from the blast site from 21 to 42 m. The corresponding decreases were 94 and 96.8% in the Y direction and 84.1 and 90% in the Z direction, respectively. Thus, it is evident that consequent to an explosion, the accelerations induced by the ground shock in the X, Y, and Z directions decreased very significantly with the increase in distance from the blast site. At 21 m, the maximum positive accelerations in the X and Y directions were 6.65 and 8.15 times that in the Z direction.