# Study on Interface Interaction between Uniaxial Geogrid Reinforcement and Soil Based on Tensile and Pull-Out Tests

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## Abstract

**:**

## 1. Introduction

## 2. Experimental Preparation

#### 2.1. Testing Apparatus

#### 2.2. Material Used

#### 2.2.1. Sand

#### 2.2.2. Geogrid

#### 2.3. Testing Program

_{v}= 40 kPa (TG2), σ

_{v}= 40 kPa (TG3), and σ

_{v}= 60 kPa (TG4), was used to study the influence of the tension–strain of the G1 reinforcement under confined conditions. Under the σ

_{v}= 40 kPa condition, we changed the tensile rate to 200 mm/min (TG5), 150 mm/min (TG6), and 1 mm/min (TG7) in order to study the effect of the strain rate on the tension–strain of the G1 geogrid under confined conditions. The tensile test conditions are shown in Table 3.

## 3. Results

#### 3.1. Tensile Test

#### 3.1.1. Effect of Normal Stress

_{ε}(kN/m), of reinforcement is calculated by the following formula:

_{ε})

_{c}is the value of the secant tensile stiffness tested under confined conditions and (J

_{ε})

_{un−c}is the value of the secant tensile stiffness tested under unconfined conditions. Table 5 summarizes the influence of normal stress on the stiffness coefficient under conditions of 2% strain, 5% strain, and peak strain,.

_{v}= 20 kPa, 40 kPa, and 60 kPa were applied, the stiffness coefficients δ were 1.68, 1.73, and 1.73 at 2% strain and 1.55, 1.69, and 1.76 at 5% strain, respectively. It can be observed that the stiffness coefficient δ increased with the increase in normal stress. At 20 kPa and 40 kPa, the stiffness coefficient δ corresponding to the 2% strain of the geogrid increased, which may be due to the fact that, during the tensile process of reinforcement in sand, tension is provided by the relative displacement of the geogrid transverse ribs and the sand. With the increase in normal stress, the shear strength of sand increases while the secant tensile stiffness of reinforcement changes little. The stiffness of the reinforcement is mainly affected by the mutual displacement of the geogrid transverse ribs and the sand.

#### 3.1.2. Effect of Loading Rate

#### 3.2. Pull-Out Test

#### 3.2.1. Effect of Normal Stress

_{r}) of three types of geogrids was evaluated. The friction and passive resistance provided by the transverse ribs of the G1, G2, and G3 geogrids were considered to be the same, and the difference between them was that the friction provided by the longitudinal ribs was different. The end bearing resistance and friction (P

_{rT}) of the transverse ribs were calculated by the following formula:

_{rT}= P

_{r(G2)}+ P

_{r(G3)}− P

_{r(G1)}

_{rL}) is

_{rL}= P

_{r(G1)}− P

_{rT}

#### 3.2.2. Apparent Friction Coefficient

_{R}is the pull-out force per unit width, L is the anchorage zone length of the reinforcement, σ

_{v}′ is the effective normal stress, φ is the internal friction angle of the sand, f

_{b}is the interaction coefficient of the reinforcement and the soil, f* is the apparent friction coefficient, F* is the pull-out force coefficient, and α is the scale effect correction factor considering the nonlinear stress reduction of extensible material in the embedded length.

_{b}is not explicitly expressed to be used for calculation, and in order to avoid numerical analysis that is too complex, the apparent friction coefficient can be used for calculation, which depends on the normal stress. The formula is as follows:

_{a}is the average soil depth considered in the calculation, h

_{0}= 6 m, and f

_{0}* is the apparent friction coefficient at the top. The calculation formula is as follows: ${f}_{0}^{*}=1.1\left(\frac{\mathrm{tan}\phi}{\mathrm{tan}{36}^{\circ}}\right)$, where f

_{1}* is the apparent friction coefficient at depths of 6 m or below and the calculation formula is ${f}_{1}^{*}=0.8\mathrm{tan}\phi $.

## 4. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## Appendix A

_{v}) along the soil column, assuming that the stress is proportional to the arch formed in the soil [37]:

**Figure A1.**Terzaghi arching effect theory [38].

Parameter | Definition | Figure |
---|---|---|

K_{a} | Coefficient of active earth pressure, in this case K_{a} = K_{0} | 0.34 |

B_{C} (m) | Width of soil column | 0.7 |

H_{R} (m) | Soil height | 0.4 |

H_{e} (m) | Equivalent soil settlement height | 0.4 |

σ_{v} (kPa) | Normal stress along soil column | - |

σ_{v1} (kPa) | Normal stress at the bottom of soil column | - |

σ_{0} (kPa) | Load | 0 |

φ_{R} (°) | Internal friction angle of soil | 41 |

_{e}= H

_{R}[39], the normal stress applied to the bottom of the soil column can be calculated as follows:

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**Figure 1.**Internal mechanism of reinforced soil retaining wall [13].

**Figure 5.**The three kinds of uniaxial geogrid specimens used in the tests: (

**a**) G1 uniaxial geogrid (no rib removal treatment), (

**b**) photo of G1 uniaxial geogrid, (

**c**) G2 uniaxial geogrid (60% of longitudinal ribs remaining after rib removal), (

**d**) photo of G2 uniaxial geogrid, (

**e**) G3 uniaxial geogrid (40% of longitudinal ribs after rib removal), and (

**f**) photo of G3 uniaxial geogrid.

**Figure 14.**Effect of tensile rate on tensile properties of uniaxial geogrid; (

**a**) tensile–strain curve, (

**b**) stiffness–strain curve.

**Figure 15.**Relationship between pull-out force and displacement of three uniaxial geogrid specimens under different normal stresses.

Relative Compaction (%) | Density ρ (g·cm^{−3}) | Specific Gravity Gs | Angle of Internal Friction φ (°) | Characteristic Particle Size (mm) | ||
---|---|---|---|---|---|---|

d_{10} | d_{30} | d_{60} | ||||

70 | 1.82 | 2.86 | 41 | 0.18 | 0.29 | 0.37 |

Type | Thickness (mm) | Rib Spacing (mm) | Length of Tensile Unit (mm) | Raw Material |
---|---|---|---|---|

Uniaxial geogrid | 1 | 22.2 | 225 | Polyethylene |

Test Number | Grid Type | Length (mm) | Width (mm) | Normal Stress (kPa) | Rate (mm/min) |
---|---|---|---|---|---|

TG1 | G1 | 1400 | 240 | 0 | 247 |

TG2 | G1 | 1400 | 240 | 20 | 247 |

TG3 | G1 | 1400 | 240 | 40 | 247 |

TG4 | G1 | 1400 | 240 | 60 | 247 |

TG5 | G1 | 1400 | 240 | 40 | 200 |

TG6 | G1 | 1400 | 240 | 40 | 150 |

TG7 | G1 | 1400 | 240 | 40 | 1 |

Test Number | Grid Type | Length (mm) | Width (mm) | Normal Stress (kPa) | Rate (mm/min) |
---|---|---|---|---|---|

PG1 | G1 | 1400 | 550 | 20 | 1 |

PG2 | G2 | 1400 | 550 | 20 | 1 |

PG3 | G3 | 1400 | 550 | 20 | 1 |

PG4 | G1 | 1400 | 550 | 40 | 1 |

PG5 | G2 | 1400 | 550 | 40 | 1 |

PG6 | G3 | 1400 | 550 | 40 | 1 |

PG7 | G1 | 1400 | 550 | 60 | 1 |

PG8 | G2 | 1400 | 550 | 60 | 1 |

PG9 | G3 | 1400 | 550 | 60 | 1 |

Test Number | σ_{v} (kPa) | J_{0.02} | J_{0.05} | J_{peak} | δ_{0.02} | δ_{0.05} | δ_{peak} |
---|---|---|---|---|---|---|---|

TG1 | 0 | 847.62 | 616.75 | 503.15 | - | - | - |

TG2 | 20 | 1423.03 | 955.20 | 867.44 | 1.68 | 1.55 | 1.72 |

TG3 | 40 | 1468.42 | 1041.92 | 955.00 | 1.73 | 1.69 | 1.90 |

TG4 | 60 | 1465.51 | 1082.78 | 1024.64 | 1.73 | 1.76 | 2.04 |

σ_{v}(kPa) | P_{r(G1)}(kN/m) | P_{r(G2)}(kN/m) | P_{r(G3)}(kN/m) | P_{rT}(kN/m) | P_{rT}/P_{r(G1)}(%) | P_{rL}(kN/m) | P_{rL}/P_{r(G1)}(%) |
---|---|---|---|---|---|---|---|

20 | 37.70 | 27.11 | 18.36 | 7.77 | 20.61 | 29.93 | 79.39 |

40 | 41.77 | 27.45 | 18.46 | 4.14 | 9.91 | 37.63 | 90.09 |

60 | 39.46 | 25.89 | 17.48 | 3.91 | 9.91 | 35.55 | 90.09 |

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**MDPI and ACS Style**

Cai, X.; Feng, J.; Li, S.; Xu, H.; Liu, W.; Huang, X.
Study on Interface Interaction between Uniaxial Geogrid Reinforcement and Soil Based on Tensile and Pull-Out Tests. *Sustainability* **2022**, *14*, 10386.
https://doi.org/10.3390/su141610386

**AMA Style**

Cai X, Feng J, Li S, Xu H, Liu W, Huang X.
Study on Interface Interaction between Uniaxial Geogrid Reinforcement and Soil Based on Tensile and Pull-Out Tests. *Sustainability*. 2022; 14(16):10386.
https://doi.org/10.3390/su141610386

**Chicago/Turabian Style**

Cai, Xiaoguang, Jiayu Feng, Sihan Li, Honglu Xu, Weiwei Liu, and Xin Huang.
2022. "Study on Interface Interaction between Uniaxial Geogrid Reinforcement and Soil Based on Tensile and Pull-Out Tests" *Sustainability* 14, no. 16: 10386.
https://doi.org/10.3390/su141610386