# Numerical Investigation of a Foundation Pit Supported by a Composite Soil Nailing Structure

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## Abstract

**:**

## 1. Introduction

## 2. Project Overview

#### 2.1. Background

#### 2.2. In Field Monitoring

#### 2.2.1. Horizontal Displacement

#### 2.2.2. Vertical Settlement

## 3. Factors Affecting Stability

#### 3.1. Numerical Model

#### 3.2. Orthogonal Test

#### 3.3. Design of the Orthogonal Test

_{16}(4

^{5}) orthogonal table. It should be noted that 16, 4, and 5 represent the number of tests, levels, and control indicators, respectively. The five control indicators are surface settlement S1, horizontal displacement D of the foundation pit, maximum shear stress T of the soil, axial force N of the soil nail, and uneven settlement S2 of the surrounding foundation pit. The five influencing factors include excavation depth h, horizontal distance H of the building around the foundation pit from its edge, elastic modulus E, cohesive force C, and internal friction angle φ of the soil layer. The five factors of the orthogonal test were selected at four levels for testing. With respect to h, four levels of 4 m, 8 m, 12 m, and 16 m were selected. For H, 3 m, 6 m, 9 m, and 12 m were chosen. In addition, the four levels for the influencing factors E, C, and φ are listed in Table 4. Table 5 shows the values of the orthogonal experiment design, which are based on a combination of levels shown in Table 4.

#### 3.4. Orthogonal Test Results

## 4. Numerical Results

#### 4.1. Vertical Displacement

#### 4.2. Horizontal Displacement

#### 4.3. Axial Force of Soil Nailing

#### 4.4. Foundation Pit Stability

## 5. Deformation Characteristics

#### 5.1. Effect of Soil Nails on Deformation

#### 5.1.1. Inclination Angles of Soil Nails

#### 5.1.2. Prestressing of Soil Nails

#### 5.2. Effect of Mixing Pile on Deformation

#### 5.2.1. Diameter of the Mixing Pile

#### 5.2.2. Embedded Depth of the Mixing Pile

#### 5.2.3. Mixing Pile Position from the Excavation Surface

## 6. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 1.**Location of the Silt-Soil Foundation Pit at Qingdao: (

**a**) Mixing pile composite soil nail support project; (

**b**) Distribution of the monitoring points; (

**c**) Large sample of monitoring points.

**Figure 2.**Foundation pit monitoring results: (

**a**) Monitoring chart for horizontal displacement; (

**b**) Monitoring chart for slope settlement.

**Figure 3.**Calculation model used in this paper: (

**a**) Site pit map; (

**b**) Symmetrical computational model.

**Figure 6.**Settlement of soil inside and outside the foundation pit: (

**a**) Cloud diagram of soil settlement in the foundation pit; (

**b**) Monitoring curve for the foundation pit settlement.

**Figure 7.**Horizontal displacement at different excavation depths: (

**a**) Cloud diagram showing the horizontal displacement of soil in a foundation pit; (

**b**) Monitoring curve showing the horizontal displacement of soil.

**Figure 10.**The effect of soil nail inclination angles on horizontal displacement: (

**a**) The effect of soil nail inclination on horizontal displacement; (

**b**) The effect of soil nail inclination on horizontal displacement of slope top and maximum horizontal displacement.

**Figure 11.**The effect of soil nail prestress on the horizontal displacement: (

**a**) The effect of soil nail prestress on horizontal displacement; (

**b**) The effect of soil nail prestress on horizontal displacement of slope top and maximum horizontal displacement.

**Figure 12.**The effect of diameter of the mixing pile on horizontal displacement of soil: (

**a**) The effect of soil nail diameter on horizontal displacement; (

**b**) The effect of soil nail diameter on horizontal displacement of the slope top and maximum horizontal displacement.

**Figure 13.**The effect of embedded depth of the mixing pile on horizontal displacement: (

**a**) Effect of embedded depth of mixing pile on horizontal displacement; (

**b**) Effect of embedded depth of mixing pile on horizontal displacement of slope top and maximum horizontal displacement.

**Figure 14.**The effect of mixing pile position from the excavation surface on horizontal displacement: (

**a**) Effect of the position of the mixing pile on horizontal displacement; (

**b**) Effect of the position of the mixing pile on the horizontal displacement of the slope top and maximum horizontal displacement.

Parameters | Value |
---|---|

Elastic Modulus/(MPa) | 18 |

Poisson’s ratio | 0.3 |

Cohesion/(kPa) | 18 |

Internal friction angle/(°) | 20 |

Natural severe (kN/m^{3}) | 18.5 |

Parameters | Value |
---|---|

Unconfined compressive strength/(MPa) | 1 |

Cohesion/(kPa) | 200 |

Deformation modulus/(MPa) | 120 |

Internal friction angle/(°) | 20 |

Poisson’s ratio | 0.3 |

Bulk modulus/(MPa) | 100 |

Shear modulus/(MPa) | 46.15 |

Parameters | Value |
---|---|

Elastic modulus/(MPa) | 2.4 × 10^{4} |

Tensile strength/(MPa) | 30 |

Poisson’s ratio | 0.25 |

Cross-sectional area (mm^{2}) | 314.2 |

Thermal expansion coefficient | 0 |

Level | h (m) | H (m) | E (MPa) | C (kPa) | φ (°) |
---|---|---|---|---|---|

1 | 4 | 3 | 6 | 5 | 10 |

2 | 8 | 6 | 9 | 15 | 15 |

3 | 12 | 9 | 12 | 35 | 27 |

4 | 16 | 12 | 15 | 55 | 45 |

Number | h (m) | H (m) | E (MPa) | C (kPa) | φ (°) |
---|---|---|---|---|---|

1 | (1)4 | (1)3 | (1)6 | (1)5 | (1)10 |

2 | (1)4 | (2)6 | (2)9 | (2)15 | (2)15 |

3 | (1)4 | (3)9 | (3)12 | (3)35 | (3)27 |

4 | (1)4 | (4)12 | (4)15 | (4)55 | (4)45 |

5 | (2)8 | (1)3 | (2)9 | (2)15 | (4)45 |

6 | (2)8 | (2)6 | (1)6 | (4)55 | (3)27 |

7 | (2)8 | (3)9 | (4)15 | (1)5 | (2)15 |

8 | (2)8 | (4)12 | (3)12 | (3)35 | (1)10 |

9 | (3)12 | (1)3 | (3)12 | (4)55 | (2)15 |

10 | (3)12 | (2)6 | (4)15 | (3)35 | (1)10 |

11 | (3)12 | (3)9 | (1)6 | (2)15 | (4)45 |

12 | (3)12 | (4)12 | (2)9 | (1)5 | (3)27 |

13 | (4)16 | (1)3 | (4)15 | (2)15 | (3)27 |

14 | (4)16 | (2)6 | (3)12 | (1)5 | (4)45 |

15 | (4)16 | (3)9 | (2)9 | (4)55 | (1)10 |

16 | (4)16 | (4)12 | (1)6 | (3)35 | (2)15 |

$\overline{{T}_{ij}}$ | T_{ij} is the sum of the test indicator values for all factor i and level j | ||||

$\overline{{T}_{ij}}$ | $\overline{{T}_{ij}}={T}_{ij}/4$ | ||||

$R$ | $R=\mathrm{max}(\overline{{T}_{\mathrm{ij}}})-\mathrm{min}(\overline{{T}_{\mathrm{ij}}})$ |

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**MDPI and ACS Style**

Han, W.; Li, G.; Sun, Z.; Luan, H.; Liu, C.; Wu, X.
Numerical Investigation of a Foundation Pit Supported by a Composite Soil Nailing Structure. *Symmetry* **2020**, *12*, 252.
https://doi.org/10.3390/sym12020252

**AMA Style**

Han W, Li G, Sun Z, Luan H, Liu C, Wu X.
Numerical Investigation of a Foundation Pit Supported by a Composite Soil Nailing Structure. *Symmetry*. 2020; 12(2):252.
https://doi.org/10.3390/sym12020252

**Chicago/Turabian Style**

Han, Wei, Genxiao Li, Zhaohui Sun, Hengjie Luan, Chuanzheng Liu, and Xianlong Wu.
2020. "Numerical Investigation of a Foundation Pit Supported by a Composite Soil Nailing Structure" *Symmetry* 12, no. 2: 252.
https://doi.org/10.3390/sym12020252