# A Practical Group Symbol and Group Name Approach (PSNA) according to EN ISO 14688-2:2018
## 2 Standards
### EN ISO 14688-2:2018  
Technical Committee ISO/TC 182, known as \"Geotechnics\" in collaboration with Technical Committee CEN/TC 341, dubbed the \"Geotechnical Investigation and Testing\", prepared EN ISO 14688-1:2018 [20] and EN ISO 14688-2:2018 [21]. There are 34 members of CEN and the texts of ISO 14688-1:2017 [26] and ISO 14688-2:2017 [27] were approved by CEN as EN ISO 14688-1:2018 [20] and EN ISO 14688-2:2018 [21] without any modification. EN ISO 14688-2:2018 [21] was given the status of a national standard in all CEN countries, either via publication of an identical text or by endorsement, by August 2018 at the latest. In the event of a conflict arising between EN ISO 14688-2:2018 [21] and the national standard, the national standard of that country was withdrawn (e.g., TS 1500 [24]).  
EN ISO 14688-2:2018 [21] is a general standard that uses particle sizes from EN ISO 14688-1:2018 [20] in engineering descriptions (Table 1). The particle sizes are divided into three parts such as very coarse, coarse, and fine material. If the particle size is >63 mm, it is defined as very coarse material. The particle size of coarse material changes from >0.063 mm to \(\leq\)63 mm. The particle sizes of fine material are \(\leq\)0.063 mm.  
EN ISO 14688-2:2018 gives symbols for the particles, such as Cl for clay, Si for salt, Sa for sand, and Gr for gravel. According to EN ISO 14688-2:2018, the boundary of sand and gravel is 2.00 mm, the boundary of coarse material and fine particle size is 0.063 mm, and the boundary of clay and silt is 0.002 mm.  
EN ISO 14688-2:2018 [21] also includes the uniformity coefficient (C\({}_{\rm u}\)), and the coefficient of curvature (C\({}_{\rm c}\)) for the shape of grading (Table 2) and the plasticity chart (Figure 1, Table 3).  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Soil Group** & **Particle Size Fractions** & **Range of Particle Sizes (mm)** \\  & **(Symbol)** & **Range of Particle Sizes (mm)** \\ \hline \multirow{3}{*}{Very coarse soil} & Large boulder (IBo) & \textgreater{}630 \\  & Boulder (Bo) & \textgreater{}200 to \(\leq\)630 \\  & Cobble (Co) & \textgreater{}63 to \(\leq\)200 \\ \hline \multirow{8}{*}{Coarse Soil} & Gravel (Gr) & \textgreater{}2.0 to \(\leq\)63 \\  & Coarse gravel (cGr) & \textgreater{}20 to \(\leq\)63 \\  & Medium gravel (mGr) & \textgreater{}6.3 to \(\leq\)20 \\  & Fine gravel (fGr) & \textgreater{}2.0 to \(\leq\)6.3 \\  & Sand (Sa) & \textgreater{}0.063 to \(\leq\)2.0 \\  & Coarse sand (cSa) & \textgreater{}0.63 to \(\leq\)2.0 \\  & Medium sand (mSa) & \textgreater{}0.20 to \(\leq\)0.63 \\  & Fine sand (fSa) & \textgreater{}0.063 to \(\leq\)0.20 \\ \hline \multirow{8}{*}{Fine soil} & Silt (Si) & \textgreater{}0.002 to \(\leq\)0.063 \\  & Coarse silt (cSi) & \textgreater{}0.02 to \(\leq\)0.063 \\ \cline{1-1}  & Medium silt (mSi) & \textgreater{}0.0063 to \(\leq\)0.02 \\ \cline{1-1}  & Fine silt (fSi) & \textgreater{}0.002 to \(\leq\)0.0063 \\ \cline{1-1}  & Clay (Cl) & \textgreater{}0.002 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Particle sizes [20].  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Term** & **C\({}_{\bf u}\)** & **C\({}_{\bf c}\)** \\ \hline Uniformly graded & \textless{}3 & \textless{}1 \\ Poorly graded & 3 to 6 & \textless{}1 \\ Medium graded & 6 to 15 & \textless{}1 \\ Well graded & \textgreater{}15 & 1 to 3 \\ Gap graded & \textgreater{}15 & \textless{}0.5 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Shape of grading curve [21].  
\(\rm C_{u}\) and \(\rm C_{c}\) are defined as  
\[C_{u}=\frac{D_{60}}{D_{10}} \tag{1}\]  
\[C_{c}=\frac{{D_{30}}^{2}}{D_{10}\times D_{60}} \tag{2}\]  
where \(\rm D_{10}\), \(\rm D_{30}\) and \(\rm D_{60}\) are the particle sizes corresponding to 10%, 30% and 60% finer materials on the particle size distribution graph, respectively.