# Effect of Wetting Conditions on the In Situ Density of Soil Using the Sand-Cone Method
## 4 Conclusions  
In this study, the effect of wetting conditions on the determination of the density of compacted soil with the sand-cone method was investigated for a moist ground and moist filling sand. The unit weight of soil was determined in the laboratory by using a small model of the ground. The ground model contained field soil classified as CL and was compacted in a cylindrical container (with a diameter of 41.5 cm and height of 17 cm). The water content of the ground surface varied between 2% and 16%. Furthermore, artificial test holes with cylindrical, conical, and roof shapes, and with depths of 10 and 15 cm, were considered. For these conditions, the test hole volume was determined by the sand-cone method and the dry unit weight was calculated. The results obtained can be summarized as follows:  
1. As the water content of the compacted ground increased from 2% to 16%, the calculated volume of the test hole decreased and the dry unit weight was overestimated by up to 20%. The accumulation of moisture increased the number of voids in the test hole, and, therefore, the calculated volume was lower than the actual volume.
2. For the cylindrical hole, the dry unit weight obtained was similar to the actual dry unit weight. When a sand-cone method is conducted after heavy rainfall at a site, appropriate precautions should be taken since the presence of moisture can lead to the relative compaction of the ground being overestimated. The error in the calculated density can be minimized by considering the wetting condition of the ground. The  
Figure 9: Variation of the error in unit weight with the sand wetness.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \begin{tabular}{c} **Moisture** \\ **Condition of** \\ **The Sand** \\ \end{tabular} & \begin{tabular}{c} **Calculated** \\ **Volume from** \\ **the Filled** \\ **Sand (cm\({}^{3}\))** \\ \end{tabular} & \begin{tabular}{c} **Unit Weight** \\ **with Moist** \\ **Sand,** \\ **Y4**(desperiment) \\ **(kN/m\({}^{3}\))** \\ \end{tabular} & \begin{tabular}{c} **Calibrated Unit** \\ **Weight,** \\ **Error (kN/m\({}^{3}\))** \\ \end{tabular} \\ \hline \
\begin{tabular}{c} 0\% \\ 0.5\% \\ 0.8\% \\ \end{tabular} & 2157.91 & 13.57 & 0.17 \\
\begin{tabular}{c} 0.5\% \\ 0.8\% \\ \end{tabular} & 2094.37 & 13.98 & 0.58 \\ \hline \hline \end{tabular}
\end{table}
Table 5: The results of the effect of moist sand.  
water content measured after heating in a microwave oven for 15 min was similar to that obtained after heating in a dry oven for 24 h.
3. The effect of moist test sand was relatively insignificant. However, the experimental results showed that the calculated volume of the test hole decreased as the water content of the sand increased from 0% to 0.8%.
4. At a moisture content of 1% (and above), the test sand clumped together, rendering the sand calibration difficult. Therefore, sand used for sand-cone tests should be dry. In humid environments, the moisture content of the sand should not exceed 0.8%.  
Conceptualization, S.-S.P. and P.D.O.; methodology, S.-S.P. and P.D.O.; formal analysis, S.-S.P. and S.-W.W.; data curation, S.-W.W.; writing--original draft preparation, S.-S.P. and H.-I.L.; writing--review and editing, S.-S.P., P.D.O., S.-W.W., and D.-E.L.; visualization, P.D.O. and S.-W.W.; supervision, D.-E.L. and S.-S.P.; project administration, D.-E.L.; funding acquisition, D.-E.L. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (No. NRF-2019R1A2C3003890).  
The authors declare no conflict of interest.