# Bearing Characteristics of Composite Foundation Reinforced by Geosynthetic-Encased Stone Column: Field Tests and Numerical Analyses

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## Abstract

**:**

## 1. Introduction

## 2. Experimental Design for Field Monitoring

#### 2.1. Test Site and Pile Arrangement

#### 2.2. Sensor Layout and Installation

## 3. Results and Analysis of Field Monitoring

#### 3.1. Pile–Soil Stress Ratio

#### 3.2. Excess Pore Water Pressure

#### 3.3. Lateral Displacement of Soil Mass

## 4. Numerical Simulation of the Composite Foundation Reinforced by the GESC

#### 4.1. Establishment of Finite Element Model

_{s}is the shear stress, σ

_{1}and σ

_{3}are the maximum and minimum principal stresses, respectively. The shear stress only depends on the σ

_{1}and σ

_{3}. The second principal stress has no effect on the yield of the material.

_{c}is the shape parameter that controls the yield surface in the π-plane; q is the equivalent shear stress; p is the average principal stress; φ is the internal friction angle; c is the cohesion; r is the third deviator stress invariant; θ is the polar deflection angle.

#### 4.2. Verification of Numerical Model Results

_{e}(Equivalent circle diameter) settlement in field test is 216.6 kPa. The characteristic value of bearing capacity of single pile composite foundation simulated by numerical method is 202.9 kPa, with an error of 6.3%. It can be seen from the above error analysis that the numerical calculation model used in this paper is reasonable and reliable, and further analysis of the GESC composite foundation can be carried out on the basis of this numerical model. In Figure 20, we also compare the results of this study with existing research results. Killeen [24] conducted a static load test of stone column composite foundation. It can be seen that the characteristic value of bearing capacity of stone column composite foundation is significantly smaller than that of GESC composite foundation. Yoo and Lee [15] conducted a static load test of geogrid-encased stone column composite foundation. Their geogrid-encased stone column has larger pile diameter, pile length and wrapping length, so the bearing capacity characteristic value of the geogrid-encased stone column composite foundation are greater.

#### 4.3. Analysis of Influencing Factors

## 5. Conclusions

- (1)
- With the increase of subgrade filling height, the pile–soil stress ratio of the composite foundation with the traditional stone column gradually increases from 1.1 to 1.5 and then tends to be stable. The pile–soil stress ratio of the composite foundation with the GESC reaches 1.5 at the initial filling stage and gradually increases and stabilizes at about 1.7 with the filling construction. This indicates that the restraint effect of geotextile bags can improve the bearing capacity of the pile body so that the GESC can bear more load, which is more obvious at the initial filling stage.
- (2)
- At the intensive filling stage, due to the difference in soil permeability and mechanical loading, the peak value of excess pore water pressure of the composite foundation with the traditional stone column is lower than that of the composite foundation with the GESC. At the interval filling stage and monitoring stage after construction, the dissipation rate of the excess pore water pressure of the composite foundation with the GESC is obviously superior to that of the composite foundation with the traditional stone column.
- (3)
- The lateral displacement of the soil mass at the depths of 3.1 m and 5.1 m of the composite foundation with the GESC is obviously smaller than that of the composite foundation with the traditional stone column. However, due to the impact of surcharge at the slope toe, the lateral displacement of the soil mass at the depth of 1.1 m of the composite foundation with the GESC is greater than that of the composite foundation with the traditional stone column.
- (4)
- The numerical simulations show that increasing the geotextile stiffness, the wrapping length and the internal friction angle of gravel can all improve the bearing performance of the composite foundation with the GESC. However, after the geotextile stiffness and the wrapping length reach a certain value, the influence of its lifting amount on the composite foundation will be reduced. Therefore, it is necessary to determine the different parameters of the GESC based on the site conditions.
- (5)
- Due to the regional characteristics of the test site and the diversities of the construction process and test conditions, more practical applications of the GESC are needed to supplement and improve the existing engineering data. In the future, long-term monitoring of the bearing characteristics of the GESC can be conducted for different construction processes and construction techniques.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

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**Figure 5.**Installation process of test instrument: (

**a**) Inclinometer; (

**b**) Installation of inclinometer; (

**c**) Earth pressure meter; (

**d**) Installation of earth pressure meter; (

**e**) Pore water pressure meter; (

**f**) Installation of pore water pressure meter.

**Figure 6.**Buried sensors in the test area: (

**a**) Plan layout of sensors; (

**b**) Profile layout of sensors.

**Figure 8.**The construction processes of GESC and subgrade filling: (

**a**) Cover the steel pipe with geotextile bags; (

**b**) Pull out the steel pipe to the hole; (

**c**) Calibration of the GESC; (

**d**) Subgrade filling.

**Figure 10.**Time-history curves of excess pore water pressure: (

**a**) Traditional stone column; (

**b**) GESC.

**Figure 11.**The variation of excess pore water pressure at different depths in the different stages: (

**a**) Intensive filling stage; (

**b**) Interval filling stage; (

**c**) Monitoring stage after construction.

**Figure 13.**The variation of lateral displacement at different depths on the 45th day after the completion of subgrade filling.

**Figure 14.**Schematic diagram of filling at the slope toe of the monitoring section of the traditional stone column.

**Figure 15.**The variation of increment of lateral displacement at different depths on the 125th day after the completion of subgrade filling.

**Figure 17.**Field static load test of single GESC composite foundation: (

**a**) Reference beam and displacement sensor; (

**b**) Field static load test.

**Figure 24.**Bulging deformation of the pile body in the geotextile model with different wrapping lengths.

**Figure 25.**Load-settlement curves of geotextile models with different internal friction angles of gravel.

**Figure 26.**Bulging deformation of the pile body in the geotextile model with different internal friction angles of gravel.

Material Type | Poisson’s Ratio, μ | Unit Weight, γ (kN/m^{3}) | Elastic Modulus, E (MPa) | Cohesion, c (kPa) | Internal Friction Angle, φ (°) | Dilatancy Angle, ψ (°) |
---|---|---|---|---|---|---|

Banket | 0.3 | 18.5 | 25 | 5 | 22 | 0 |

Silty clay | 0.35 | 18.2 | 15 | 32.7 | 12.5 | 0 |

Strongly weathered mudstone | 0.3 | 23.5 | 100 | 450 | 28 | 0 |

Moderately weathered mudstone | 0.3 | 23.8 | 1870 | 1000 | 42.5 | 12.5 |

Gravel | 0.35 | 19 | 50 | 1 | 38 | 8 |

Bearing plate | 0.3 | 78 | 2 × 10^{5} | — | — | — |

Working Condition | Pile Length (m) | Pile Diameter (m) | Wrapping Length (m) | Geotextile Stiffness (kN/m) | Internal Friction Angle of Gravel (°) |
---|---|---|---|---|---|

Model 1 | 4.5 | 0.5 | 3 | 200 | 38 |

Model 2 | 4.5 | 0.5 | 3 | 500 | 38 |

Model 3 | 4.5 | 0.5 | 3 | 800 | 38 |

Model 4 | 4.5 | 0.5 | 3 | 1100 | 38 |

Model 5 | 4.5 | 0.5 | 3 | 1400 | 38 |

Model 6 | 4.5 | 0.5 | 3 | 1700 | 38 |

Working Condition | Pile Length (m) | Pile Diameter (m) | Wrapping Length (m) | Geotextile Stiffness (kN/m) | Internal Friction Angle of Gravel (°) |
---|---|---|---|---|---|

Model 1 | 4.5 | 0.5 | 0.5 | 500 | 38 |

Model 2 | 4.5 | 0.5 | 1 | 500 | 38 |

Model 3 | 4.5 | 0.5 | 1.5 | 500 | 38 |

Model 4 | 4.5 | 0.5 | 2 | 500 | 38 |

Model 5 | 4.5 | 0.5 | 2.5 | 500 | 38 |

Model 6 | 4.5 | 0.5 | 3 | 500 | 38 |

Model 7 | 4.5 | 0.5 | 4.5 | 500 | 38 |

Working Condition | Pile Length (m) | Pile Diameter (m) | Wrapping Length (m) | Geotextile Stiffness (kN/m) | Internal Friction Angle of Gravel (°) |
---|---|---|---|---|---|

Model 1 | 4.5 | 0.5 | 3 | 500 | 32 |

Model 2 | 4.5 | 0.5 | 3 | 500 | 35 |

Model 3 | 4.5 | 0.5 | 3 | 500 | 38 |

Model 4 | 4.5 | 0.5 | 3 | 500 | 41 |

Model 5 | 4.5 | 0.5 | 4.5 | 500 | 44 |

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**MDPI and ACS Style**

Wang, K.; Liu, M.; Cao, J.; Niu, J.; Zhuang, Y. Bearing Characteristics of Composite Foundation Reinforced by Geosynthetic-Encased Stone Column: Field Tests and Numerical Analyses. *Sustainability* **2023**, *15*, 5965.
https://doi.org/10.3390/su15075965

**AMA Style**

Wang K, Liu M, Cao J, Niu J, Zhuang Y. Bearing Characteristics of Composite Foundation Reinforced by Geosynthetic-Encased Stone Column: Field Tests and Numerical Analyses. *Sustainability*. 2023; 15(7):5965.
https://doi.org/10.3390/su15075965

**Chicago/Turabian Style**

Wang, Kaifeng, Mengjie Liu, Jie Cao, Jiayong Niu, and Yunxia Zhuang. 2023. "Bearing Characteristics of Composite Foundation Reinforced by Geosynthetic-Encased Stone Column: Field Tests and Numerical Analyses" *Sustainability* 15, no. 7: 5965.
https://doi.org/10.3390/su15075965