# Experimental Study on Cavity Formation and Ground Subsidence Behavior Based on Ground Conditions
## 3 Experimental Results
### Experimental Results with Respect to Fines Content  
After preparing samples under experimental conditions by mixing the standard sand and marine clay, the ground was simulated in the soil box. Fines were obtained by sifting dried clay using a #200 sieve, and they were mixed with the standard sand by calculating the weight based on the conditions. Table 6 presents the results of the time until cavity formation and ground subsidence with respect to the fines content. The sample with a fines content of 5% under a groundwater level of 10 cm exhibited cavity formation on the walls of the soil box in 8 min after the start of the experiment. No ground subsidence, however, occurred, and the experiment was stopped in 14 min and 30 s given the lack of soil loss. When the groundwater level was increased to 20 cm, the time until cavity formation sharply decreased to 1 min and 23 s, and ground subsidence occurred in 3 min and 43 s. Under a groundwater level of 30 cm, the cavity occurred in 42 s, and the shortest time until ground subsidence (2 min and 15 s) was observed. The model ground with a fines content of 7.5% under a groundwater level of 10 cm required 5 min and 40 s for cavity formation and 11 min and 6 s for ground subsidence. When the groundwater level was increased to 20 cm, the cavity occurred in 10 min and 42 s and ground subsidence in 22 min. Under a groundwater level of 30 cm, the time until cavity formation sharply decreased to 18 s, and ground subsidence also rapidly occurred in 50 s.  
For the sample with a fines content of 10% under a groundwater level of 10 cm, cavity formation could not be observed through the walls of the soil box. Soil was continuously \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Fines (\%)**} & **Groundwater Level** & **Cavity Formation** & **Ground Subsidence** \\  & **(cm)** & **(min)** & **(min)** \\ \hline \multirow{4}{*}{5} & 10 & 8.00 & 14.50 (none) \\  & 20 & 1.38 & 3.77 \\  & 30 & 0.70 & 2.25 \\  & 10 & 5.67 & 11.10 \\ \multirow{4}{*}{7.5} & 20 & 10.70 & 22.00 \\  & 30 & 0.30 & 0.83 \\  & 10 & - & 30.00 (none) \\
10 & 20 & 2.25 & 3.15 (none) \\  & 30 & 0.22 & 1.15 \\ \multirow{4}{*}{12.5} & 10 & 13.80 & 14.72 (none) \\  & 20 & 2.75 & 6.75 (none) \\  & 30 & 7.83 & 11.50 \\ \multirow{4}{*}{15} & 10 & - & 18.00 (none) \\  & 20 & 24.57 & 33.00 (none) \\  & 30 & 4.00 & 22.00 (none) \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Experimental results with respect to the fines content. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Relative Density (\%)**} & **Groundwater Level** & **Soil Discharge** & **Cavity Volume** \\  & **(cm)** & **(kg)** & **(cm3)** \\ \hline \multirow{4}{*}{60} & 10 & 9.77 & 6560 \\  & 20 & 17.13 & 11500 \\ \multirow{4}{*}{75} & 30 & 14.35 & 9640 \\  & 10 & 13.86 & 9080 \\ \multirow{4}{*}{75} & 20 & 24.05 & 15750 \\  & 30 & 12.51 & 8190 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Amount of soil discharged and cavity volume with respect to the relative density and groundwater level. discharged during the experiment; however, the experiment was stopped in 30 min because no soil loss occurred. When the groundwater level was increased to 20 cm, the cavity occurred in 2 min and 15 s and ground subsidence in 22 min. When it was increased to 30 cm, the cavity occurred in 13 s after the start of the experiment and ground subsidence in 1 min and 9 min. For the model ground with a fines content of 12.5% under a groundwater level of 10 cm, the cavity occurred in 13 min and 48 s, and the experiment was stopped in 14 min and 43 s after the start of the experiment due to the lack of soil discharge. Under a groundwater level of 20 cm, there was no ground subsidence, and the cavity occurred in 2 min and 45 s. When the groundwater level was increased to 30 cm, the cavity was observed in 7 min and 50 s and ground subsidence in 11 min and 30 s. The model ground with a fines content of 15% showed no ground subsidence under any of the groundwater level conditions.