## 3 Evaluation of Suitability for Dynamic Compaction in Sabkha Deposit  
The dynamic compaction method has been proven to be applicable to granular soil deposits. However, the dynamic compaction method should be carefully applied in saturated clay soil deposit  
Figure 2: Typical sabkha compaction curve.  
because dynamic compaction may cause reduction of bearing capacity if the excess pore pressure is not appropriately dissipated during compaction.  
[PERSON] [3] proposed the evaluation criteria for applicability of dynamic compaction based on the grain size distribution, plasticity index, and permeability, as shown in Table 2 and Figure 3. The typical grain size distribution curves of sabkha soil are inserted into the evaluation criteria in Figure 3.  
The permeability of sabkha deposit was estimated to be about 1.5-\(2.3\times 10^{-3}\) cm/s from lab permeability tests according to the geotechnical investigation report, and the sabkha deposit in the study area is classified as a pervious soil deposit (zone 1), as shown in Figure 2. However, because the groundwater in this area has high salinity, brine should be used instead of distilled water in permeability tests.  
[PERSON] [5] conducted falling head laboratory permeability tests on sabkha soil obtained in the east coast of Saudi Arabia, as shown in Figure 4. The permeability coefficient was \(1.8\times 10^{-3}\) cm/s, which is similar to the values obtained in the geological investigation for this study. [PERSON] [5] found an increase in permeability as tests were repeated because test repetition is solely attributed to salt dissolution and causes more channels to form.  
On the other hand, the falling head permeability tests with brine showed a permeability of \(1.3\times 10^{-4}\) cm/s, which was reduced to about 1/14 of the permeability obtained from tests using distilled water. Therefore, it is reasonable to classify the sabkha deposit conservatively as semipervious deposit (zone 2) because the grain size distribution of sabkha deposit is close to the boundary of zone 1 and zone 2, and the permeability is in the range for zone 2 (\(10^{-3}\)-\(10^{-6}\) cm/s). Dynamic compaction method can be applied in semipervious deposit, but care must be taken to ensure that sufficient dissipation of excess pore pressure can be achieved during compaction. Because the dissipation of excessive pore  
\begin{table}
\begin{tabular}{c c c c} \hline
**Soil Category** & **Permeability (cm/sec)** & **Plasticity Index** & **Suitability for Deep Compaction** \\ \hline \hline Previous soil deposits & k \(>10^{-3}\) & 0 & Improvements are achievable \\ Intermediate soil deposit & \(10^{-3}\)–\(10^{-6}\) & 0–8 & Dissipation of pore pressure is a necessity \\ Impervious clayey & & & \\ deposits & k \(<10^{-6}\) & PI \(>8\) & Not recommended \\ \hline \hline \end{tabular}
\end{table}
Table 2: Soil suitable for deep compaction [4].  
Figure 3: Range of soil gradation of deposits suitable for deep compaction [4].  
water pressure can take from several minutes to several tens of minutes during dynamic compaction in sabkha deposit, it could be necessary to set a certain period of pause time between tamping in order to improve the effect of the dynamic compaction method.