*2.2. Evaluation Method on Pullout Resistance of Geosynthetic Strip*

For inextensible reinforcement, the pullout resistance design parameters can be easily calculated using the shear strength on the soil-inextensible reinforcement interface because there is little change in the contact area between the reinforcement and soil attributed to tensile deformation during the pullout process. However, extensible reinforcement exhibits tensile deformation in normal stress conditions in soil. In other words, the pullout displacement of the reinforcement decreased as the distance from the front increased during the pullout process. Therefore, the effective area (contact area between the reinforcement and soil) is a very important factor for the calculation of the pullout resistance design parameters of extensible reinforcement.

Ochiai et al. [23] proposed a soil-reinforcement shear strength evaluation method using pullout test results to evaluate the pullout resistance of the extensible reinforcement. This evaluation method comprises a mobilizing process method and an average resistance method. The mobilizing process method evaluates the pullout resistance using the difference in tensile forces between two nodes in arbitrary pullout force conditions and is applicable only to grid-type reinforcement. The average resistance method evaluates the pullout resistance by considering the pullout force distribution along the reinforcement length subject to the maximum pullout force condition and based on the use of the average pullout force. The average resistance method is subclassified in the total area, effective area, and maximum slope methods, depending on the average value calculation method. Their evaluation methods were as follows.

First, the total area method assumes that the pullout resistance applies to the entire area of the reinforcement and is expressed in the form of Equation (3).

$$
\pi\_{\text{av}} = \frac{F\_{T\_{\text{max}}}}{2BL},
\tag{3}
$$

where *B* and *L* are the width and length of the reinforcement, respectively, and *FTmax* is the maximum pullout force.

The effective area method assumes that the pullout resistance applies only to the area wherein the tensile deformation of the reinforcement occurs and is expressed in the form of Equation (4).

$$
\pi\_{\text{av}} = \frac{F\_{T\_{\text{max}}} - F\_r}{2BL\_T},
\tag{4}
$$

where *LT* is the effective length of the reinforcement, and *FTmax*−*Fr* is the effective tensile force corresponding to *LT*.

Finally, the maximum slope method assumes the pullout resistance when the slope of the tangent in the reinforcement-length–tensile-force distribution curve has a maximum value and is expressed according to Equation (5).

$$
\pi\_{\text{d}\upsilon} = \left(\frac{dF}{dL}\right)\_{\text{max}}\tag{5}
$$

The mechanism of each evaluation method can be confirmed in detail through the figures in the previous study [23].

### **3. Pullout Tests**

Large-scale pullout tests were conducted to evaluate the pullout behavior of the geosynthetic strips.

#### *3.1. Apparatus of Large-Scale Pullout Test*

The apparatus for the large-scale pullout test was composed of a rigid (soil) box, a load (normal and pullout) device, and a control box as shown in Figure 1. The rigid box (length: 1600 mm, width: 760 mm, and height: 550 mm) was larger than the minimum recommendations (610 mm length, 460 mm width, and 305 mm height) specified in ASTM D6706-01 [39]. For normal stress, uniformly distributed loading was enabled using an air bag in consideration of the field loading conditions, and up to 500 kN/m<sup>2</sup> could be applied. For pullout loads, up to 200 kN could be applied using the displacement control method (0.5 to 30 mm/min).

**Figure 1.** Schematic of large-scale pullout test apparatus: (**a**) plan view; (**b**) cross-sectional views (dimensions in millimeters).
