# A Comparative Study of the Pullout Strength of Geostraps and Geogrids in Reinforced Soil
## 2 Materials and Methods  
This study involved a pullout test conducted on site to evaluate the interaction of geostraps with sandy soil. The test was performed for a geostrap with an M65 strength grade on locally available soil. The soil gradation had 98.39% sand, with \(C_{u}\) and \(C_{c}\) values of 2.47 and 1.07, respectively, and was classified as poorly graded sand (SP). The lab-tested physical properties of the geomaterials used in the study are mentioned in Table 1.  
A specially designed pullout test apparatus was employed, consisting of a soil-geostrap assembly, pullout loading system, and monitoring equipment to measure displacement, as shown in Figure 2. The geostrap was anchored and embedded in the soil with free ends connected to the loading mechanism. The pullout resistance for the M65 grade of geostrap was determined based on the effective area method [33] using the following expression:  
\[\tau_{av}=\frac{F_{max}-F_{T}}{2 BL_{T}} \tag{1}\]  
where  
\(\tau_{av}=\) the average pullout resistance;  
\(F_{max}=\) the maximum pullout force;  
\(B=\) the width of the reinforcement;  
\(L=\) the length of the reinforcement.  
According to the guidelines, a cover of at least 150 mm of soil should be provided above the reinforcement [34]. Therefore, the geostrap was placed 150 mm below the top surface of the subgrade. The tests were conducted with varying normal stresses to simulate field conditions for different vehicular loadings. The pullout force and displacement of the geostrap were noted for each cycle of the pullout test. A pressure gauge utilising strain gauge sensors was used to determine the hydraulic pressure applied by the jack, while an LVDT (Linear Variable Differential Transformer) displacement transducer was used to measure the displacement of the geostrap. After that, the setup was prepared again for a different surcharge value. Once the experimental data for the M65 grade of geostrap  
\begin{table}
\begin{tabular}{c c c c} \hline
**Geomaterial** & **Properties** & **Testing** & **Value** \\ \hline \multirow{6}{*}{Soil} & Classification & IS 2720 (Part 4) a  & SP \\  & OMC (\%) & IS 2720 (Part 8) b  & 11.6 \\  & MDD (g cc\({}^{-1}\)) & IS 2720 (Part 8) b  & 1.853 \\  & CBR (\%) & IS 2720 (Part 16) c  & 16.28 \\  & Angle of internal friction, \(\Phi\) (\({}^{\circ}\)) & IS 2720 (Part 13) d  & 33 \\  & Width (mm) & Vernier Caliper & 91 \\  & Thickness (mm) & Micrometer & 1.8 \\  & Ultimate tensile strength, UTS (kN) & ASTMD-6637 e  & 64.14 \\  & & (Method A) & 64.14 \\  & Elongation at UTS (\%) & ASTMD-6637 e  & 9.45 \\ \end{tabular}
\end{table}
Table 1: Physical properties of geomaterials.  
Figure 2: **(a)** Site images of anchored geostrap, (**b**) pullout test assembly, and (**c**) schematic diagram of the pullout test.  
was obtained, they were reproduced in numerical analysis. After successfully validating the model, the results for different grades (M50, M37.5, and M25) were found numerically. The results were then compared to determine the effectiveness of each grade in providing possible areas of application based on the pullout strength. After that, the M65 grade of geostrap was compared with biaxial geogrids to establish a comparative analysis and their possible areas of applications based on the findings.