# Junction Properties Interpretation of Textile Geogrids Using Multi-Junction Clamp
## 2 Experimental
### Single and Multi-Junction Tests  
A testing apparatus as described in Figure 2a is used mainly for the assessment of only one junction strength of a geogrid, according to GRI GG-2. The test method uses a clamping fixture that grips the transverse ribs of the geogrid immediately adjacent to and on each side of the longitudinal rib. The lower portion of the longitudinal rib is gripped in a standard clamp, and each clamp is mounted in a tensile testing machine, where the test specimen is pulled apart. This method gives single-junction strength, junction efficiency and geogrids junction strength per unit width. The first values of single-junction strength are obtained directly from the test results. In previous research old designed multi-junction clamp was used to test geogrids junction strength (Figure 2b).  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & & & \multicolumn{3}{c}{**Mechanical Properties**} \\ \cline{4-7}
**Geogrid** & **Raw Material** & **Number** & & **Ultimate Strength** & & **Elongationat** \\  & **/Coating Agent** & **of Ribs (/m)** & & **(ton/m)** & & **at Break (\%)** \\ \cline{4-7}  & & & **MD** & **CMD** & **MD** & **CMD** \\ \hline W-GG-1 & PET/PVC & 47 & 6 & 3 & 12 & NA \\ W-GG-2 & PET/PVC & 38 & 10 & 3 & 12 & NA \\ WK-GG-1 & PET/PVC & 42 & 6 & 3 & 12 & NA \\ WK-GG-2 & PET/PVC & 38 & 10 & 3 & 12 & NA \\ \hline \hline \end{tabular} MD is machine direction and CMD is cross machine direction, respectively.  
\end{table}
Table 1: Specifications of geogrids.  
Figure 1: Photographs of geogrid specimens.  
The basic concept for this equipment was to widen the single-junction test clamp and the point-to-point length was determined by the aperture size of test conditions. For the old designed multi-junction test, a point-to-point length was 25 mm and the width of the clamp was 280 mm. The upper clamp has 11 gripping points for junctions and the lower clamp is a kind of flat type which also has 11 gripping points [9; 10]. Using this modified method of determination, the geogrid junction strength should be more reasonable than the single-junction test. However, this kind of clamp is only suitable in testing the geogrids which aperture size was 25 mm. A newly developed multi-clamp was used to test junction strength. Figure 2 shows a composed drawing of multi-junction grip for junction strength testing of geogrid. The clamp is composed of a set of single grips in parallel. The pitch of the clamp grip can be freely adjusted. The total number of the restraining grip is 11. In the lower part, a normal type rib clamp was used. Figure 2c shows the newly designed multi-junction clamps. In order to evaluate the effectiveness of the newly developed multi-junction testing apparatus and test condition (strain rate, specimen length and junction numbers), multi-junction clamp was used for junction strength with 20, 50 and 100 mm/min test speed at ambient condition. One-eight rib specimens were gripped in the clamps and the gage length was 50 mm, 100 mm and 150 mm. Furthermore, single-junction test samples were prepared according to the GRI-GG 2 test method while the test process was according to ASTM D4595 [11] for united test condition. The multi-junction test has been used under the same testing conditions and procedure as ASTM D 4595 except for the clamp devices. The multi-junction clamp proposed in this paper is a clamp that minimizes the error of the test result due to slipping by improving the slippage of the specimen held by the clamp compared to the conventional clamp.  
Figure 2: Overview of junction test clamp: (**a**) single-junction test clamps; (**b**) old designed multi-junction clamp; (**c**) newly designed multi-junction clamp.