# Evaluation of the Pullout Behavior of Pre-Bored Piles Embedded in Rock

^{1}

^{2}

^{3}

^{*}

## Abstract

**:**

## 1. Introduction

#### 1.1. Research Background and Purpose

#### 1.2. Research Trends

## 2. Design-Bearing Capacity of Piles

#### 2.1. Estimation of The Bearing Capacity of Piles

^{2}); ${A}_{s}$ is the major surface area of pile (m

^{2}); ${q}_{p}$ is the unit end-bearing capacity (kN/m

^{2}); and ${A}_{p}$ is the pile cross-sectional area (m

^{2}).

#### 2.2. Skin Friction of Pile

^{2}); and $\mathrm{tan}\mathsf{\delta}$ is the internal friction angle (°).

^{2}); $\mathsf{\alpha}$ is the cohesion force coefficient; and ${c}_{u}$ is the cohesion force in undrained conditions (kN/m

^{2}).

#### 2.3. C.T Cofferdam Method

## 3. Review of Design Data

#### 3.1. Site Overview

#### 3.2. Analysis of Pull-Out Force of Pre-Bored Piles According to Design Criteria

- (1)
- C.T Cofferdam Design Structural Calculation Results

- (2)
- Review of the theoretical equation for calculating the pull-out force of a pre-bored pile according to the design criteria

#### 3.3. Adhesive Force Analysis of Pile and Grout

#### 3.3.1. Adhesive Force Concept of Pile and Grout

#### 3.3.2. Lab Test for Measuring Adhesion Strength

- (1)
- Blending process

- (2)
- Test process

- (3)
- Test results

#### 3.4. Results of Pull-Out Load Test

#### 3.5. C.T Cofferdam Stability Review

## 4. Reviewing the Amount of Pull-Out of Pre-Bored Piles through Numerical Analysis

#### 4.1. Analysis Conditions

#### 4.1.1. Analysis Program

#### 4.1.2. Drilling Section

#### 4.1.3. Calculation of the Material Properties of the Ground

^{2}, which is 40% of the concrete elastic modulus of 2,320,000 kN/m

^{2}, was determined as the elastic modulus of the grout, considering the effects of seawater and slime, and was applied to the numerical analysis. The modulus of elasticity is a factor that greatly affects the amount of elastic settlement and the modulus of elasticity of weathered rocks and soft rocks is not the same. The modulus of elasticity of the grout was applied to both the weathered rock and the soft rock in consideration of the field conditions after the application of the grout.

#### 4.1.4. Modeling

^{2}was applied to the upper leveling concrete upwards.

#### 4.2. Numerical Analysis Review

## 5. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Conflicts of Interest

## References

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**Figure 9.**Numerical analysis result in the P2 direction, (

**a**) Soft rock condition at 1.92 m and the integrated behavior of both the pile foundation and ground; (

**b**) The soft rock insertion condition of 1.92 m and the on-site pull-out load test results are reflective of this.

**Figure 10.**Numerical analysis results in the perpendicular direction of the P2 pier. (

**a**) Soft rock condition at 2.21 m and the integrated behavior of both the pile foundation and ground. (

**b**) Soft rock penetration condition at 2.21 m, reflecting the results of the on-site pull-out load test.

Classification | Equations | Proposers | Applicability |
---|---|---|---|

Skin Friction | ${f}_{s}={a}_{c}+q`Ktan\delta $ | Tomlinson (1972) | Pre-stress and clay soil |

${f}_{s}=K{`}_{q}tan\delta =\beta q`$ | Jennings and Burland (1973) | Effective stress amnd clay soil | |

${f}_{s}=\lambda \left(q`+2{s}_{u}\right)$ | McClelland and Focht (1967) | Mixing method and clay soil | |

${f}_{s}={a}_{cu}$ | Meyerhof (1976) | Clay soil | |

${f}_{s}={K}_{s}\sigma {`}_{v}tan\delta $ | Meyerhof, Colye-Castello, Vesic, API etc | Sandy soil | |

End-bearing capacity | ${q}_{p}={p}_{0}{N}_{q}\le 5{N}_{q}tan\varphi $ | Meyerhof (1976) | Sandy soil |

${q}_{p}=c{N}_{c}$ | Meyerhof (1976) | Clay soil | |

${q}_{p}=c{N}_{c}+{\sigma}_{0}{N}_{0}$ | Vesic (1977) | Cavity expansion theory | |

${q}_{p}={A}_{k}\gamma B+{B}_{k}{q}_{T}\phantom{\rule{0ex}{0ex}}\left({q}_{T}={a}_{T}\gamma D\right)$ | Berezantzev (1961) |

Classification | Selected Load (kN) | |
---|---|---|

Resistance Load | C.T cofferdam weight | 3665.250 |

Water load inside the tank | 5078.340 | |

Water load inside watertight part | 548.311 | |

Leveling concrete weight | 7591.710 | |

Resistance of piles (600 kN per pile) | 21,600.000 | |

Pile weight (45.2 kN per pile) | 1630.000 | |

Buoyancy | Leveling concrete bottom buoyancy | 29,929.973 |

Fs (Satety rate) | $\mathrm{FS}=\frac{3665.25+5078.34+548.311+7591.71+21,600}{29,929.973}=1.4>1.2$ |

Classification | Allowable Skin Friction of Pile (pull-out, kN) | Remark | |
---|---|---|---|

Existing design data | C.T cofferdam design structure calculation sheet (1.0 m embedded in the rock) | 600 | Depth embedded in the rock 1.92 m Diameter of the pile 0.6 m |

Pull-out force considering the thread-embedded depth of the pile (2.197 m embedded in the rock) | 1209 | ||

Design standard | AASHTO (1996) | 200.5 | |

Canadian Geotechnical Society (1985) | 356.9 | ||

NAVFAC (1982) | 931.8 | ||

FHWA (1988) Horvath and Kenny (1979) | 648.8 | ||

FHWA (1999) Horvath and Kenny (1979) | 770.4 | ||

FHWA (1999) Rowe and Armitage (1984) | 746.8 | ||

Structural Foundation Design Standard (2008) | Wiliams et al. (1980) | 659.6 | |

Rowe and Armitage (1987) | 1774,3 | ||

Horvath and Kenney (1979) | 819.9 | ||

Carter and Kulhawy (1988) | 770.9 | ||

Reynolds and Kaderabek (1987) | 3460.5 | ||

Gupton and Logan (1984) | 2307.8 | ||

Reese and O‘Neil (1987) | 1730.8 | ||

Rosengerg and Journaeaux (1976) | 1489.7 | ||

Anchor method | Putout resistance of anchor | 292.8 | |

Friction of ground and grout | 566.7 | ||

Maximum adhesive force of tensile material and grout | 791.1 |

Classification | Allowable Skin Friction | Test Methods |
---|---|---|

Moon et al. [11] | ${Q}_{u}={f}_{s}\times \pi \times D\times L\phantom{\rule{0ex}{0ex}}{Q}_{u}=920\times \pi \times 0.6\times 1.92\phantom{\rule{0ex}{0ex}}=3327.89\mathrm{kN}\phantom{\rule{0ex}{0ex}}{Q}_{a}=\frac{{Q}_{u}}{FS}=\frac{3327.89}{3}=1109.29kN$ Test conditions: W/C: 50% | |

Moon and Park [13] | ${Q}_{u}={f}_{s}\times \pi \times D\times L\phantom{\rule{0ex}{0ex}}{Q}_{u}=540\times \pi \times 0.6\times 1.92\phantom{\rule{0ex}{0ex}}=1953.33\mathrm{kN}\phantom{\rule{0ex}{0ex}}{Q}_{a}=\frac{{Q}_{u}}{FS}=\frac{1953.33}{3}=651.11kN$ Test conditions: W/C: 60~120% |

Classification | Water (mL) | Cement (g) | Grout Material (g) |
---|---|---|---|

Water curing of concrete: 28 days, 2 EA | 490 | 700 | 70 |

Air curing of concrete: 28 days, 3 EA | 490 | 700 | 70 |

Classification | Allowable Skin Friction | Avgerage Allowable Skin Friction | |
---|---|---|---|

Water curing | WT-1 | ${Q}_{u}={f}_{s}\times \pi \times D\times L\phantom{\rule{0ex}{0ex}}{Q}_{u}=430\times \pi \times 0.6\times 1.92\phantom{\rule{0ex}{0ex}}=1555.4\mathrm{kN}\phantom{\rule{0ex}{0ex}}{Q}_{a}=\frac{{Q}_{u}}{FS}=\frac{1555.4}{3}=518.4\mathrm{kN}$ | 542.55 kN |

WT-2 | ${Q}_{u}={f}_{s}\times \pi \times D\times L\phantom{\rule{0ex}{0ex}}{Q}_{u}=470\times \pi \times 0.6\times 1.92\phantom{\rule{0ex}{0ex}}=1700.12\mathrm{kN}\phantom{\rule{0ex}{0ex}}{Q}_{a}=\frac{{Q}_{u}}{FS}=\frac{1700.12}{3}=566.7\mathrm{kN}$ | ||

Air Curing | AT-1 | ${Q}_{u}={f}_{s}\times \pi \times D\times L\phantom{\rule{0ex}{0ex}}{Q}_{u}=810\times \pi \times 0.6\times 1.92\phantom{\rule{0ex}{0ex}}=2929.99\mathrm{kN}\phantom{\rule{0ex}{0ex}}{Q}_{a}=\frac{{Q}_{u}}{FS}=\frac{2929.99}{3}=976.66\mathrm{kN}$ | 881.03 kN |

AT-2 | ${Q}_{u}={f}_{s}\times \pi \times D\times L\phantom{\rule{0ex}{0ex}}{Q}_{u}=730\times \pi \times 0.6\times 1.92\phantom{\rule{0ex}{0ex}}=2640.61\mathrm{kN}\phantom{\rule{0ex}{0ex}}{Q}_{a}=\frac{{Q}_{u}}{FS}=\frac{2640.61}{3}=880.2\mathrm{kN}$ | ||

AT-3 | ${Q}_{u}={f}_{s}\times \pi \times D\times L\phantom{\rule{0ex}{0ex}}{Q}_{u}=650\times \pi \times 0.6\times 1.92\phantom{\rule{0ex}{0ex}}=2358.72\mathrm{kN}\phantom{\rule{0ex}{0ex}}{Q}_{a}=\frac{{Q}_{u}}{FS}=\frac{2358.72}{3}=786.24\mathrm{kN}$ |

**Table 7.**Re-examination of allowable pull-out force according to the results of the pull-out load test.

Classification | Re-examination of Allowable Pull-Out Force | Allowable Pull-Out Force | |
---|---|---|---|

On-site pull-out test | P2 | ① ${Q}_{u}=651.1\mathrm{kN}$ (at Offset Point) ${Q}_{u}=651.1\xf70.787=827.3\mathrm{kN}{Q}_{u}=827.3\xf72=413.6\mathrm{kN}$ ② ${Q}_{u}=629.2\mathrm{kN}$ (at 0.25 in) ${Q}_{u}=629.2\xf70.787=799.4\mathrm{kN}\phantom{\rule{0ex}{0ex}}{Q}_{u}=799.4\xf72=399.7\mathrm{kN}$ | 399.7 kN |

**Table 8.**Results of C.T cofferdam stability review according to the recalculation of the pull-out force.

Classification | Pile Pull-Out Force (kN) | Safety Factor (Standard 1.2) | Remark | |||
---|---|---|---|---|---|---|

P2 | Existing design | Original design (1.0 m rock-bottom embedded) | 600 | 1.4 | stable | Estimated value |

Lab experiment | Grout air curing of concrete (1.92 m rock depth) | 881 | 1.7 | stable | Site conditions lacking | |

Grout placed in water (1.92 m rock depth) | 542 | 1.3 | stable | Only the conditions for placing it in water were taken into account | ||

On-site experiment | On-site pull-out test (1.92 m rock depth) | 399 | 1.1 | instable | Test methods have high reliability | |

Design data | Designer review (2.197 m rock depth) | 1210 | 2.0 | stable | Cast-in-place pile standards | |

Previous research | Various research standards (1.92 m rock depth) | 680~1160 | 1.4~2.0 | stable | Air curing of concrete | |

Various design standards (1.92 m rock depth) | 220~1700 | 0.8~2.6 | stable~ instable | Cast-in-place pile standards |

Classification | Sedimentary Soil | Weathered Rock | Soft Rock | Leveling Concrete | Rebar Concrete | Steel Pipe Pile | |
---|---|---|---|---|---|---|---|

Wetting unit weight | ${\gamma}_{t}$ (kN/m3) | 17 | 23 | 25 | 25 | 25 | 78 |

Saturation unit weight | ${\gamma}_{sat}$ (kN/m ^{3}) | 18 | 23.5 | 25.5 | 25.5 | 25.5 | 79 |

Cohesion | c (kN/m ^{2}) | 13 | 30 | 50 | - | - | - |

Internal friction angle | $\mathsf{\varphi}$ (°) | 0 | 33 | 35 | - | - | - |

Elastic modulus coefficient | E (kN/m ^{2}) | 4000 | 167,500 | 2,180,000 | 2,320,000 | 2,320,000 | 2.1 × 10^{8} |

Poisson’s ratio | $\mathsf{\nu}$ | 0.38 | 0.3 | 0.26 | 0.2 | 0.19 | 0.3 |

Classification | Weathered Rock (Injection Material) | Soft Rock (Injection Material) | |
---|---|---|---|

Wetting unit weight | ${\gamma}_{t}$ (kN/m ^{3}) | 23 | 25 |

Saturation unit weight | ${\gamma}_{sat}$ (kN/m ^{3}) | 23.5 | 25.5 |

Cohesion | c (kN/m ^{2}) | 30 | 50 |

Internal friction angle | $\mathsf{\varphi}$ (°) | 33 | 35 |

Elastic modulus coefficient | E (kN/m ^{2}) | 928,000 | 928,000 |

Poisson’s ratio | $\mathsf{\nu}$ | 0.3 | 0.3 |

Classification | Displacement (cm) | Stability (Based on 1 inch) | |
---|---|---|---|

P2 lateral direction Soft rock at 1.92 m | Pile tip | 0.22 to 0.29 | 0.29 ≤ 2.54_stable |

Total displacement | 0.70 to 0.77 | 0.77 ≤ 2.54_stable | |

P2 lateral direction Underwater grout Consider material properties | Pile tip | 0.64 to 0.89 | 0.89 ≤ 2.54_stable |

Total displacement | 2.37~2.61 | 2.61 ≥ 2.54_unstable | |

P2 bridge direction Soft rock at 2.21 m | Pile tip | 0.22 to 0.29 | 0.29 ≤ 2.54_stable |

Total displacement | 0.70 to 0.77 | 0.77 ≤ 2.54_stable | |

P2 bridge direction Underwater grout Consider material properties | Pile tip | 0.64 to 0.89 | 0.89 ≤ 2.54_stable |

Total displacement | 2.37~2.61 | 2.61 ≥ 2.54_unstable |

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**MDPI and ACS Style**

Park, K.; Kim, D.; Kim, G.; Lee, W.
Evaluation of the Pullout Behavior of Pre-Bored Piles Embedded in Rock. *Materials* **2021**, *14*, 5593.
https://doi.org/10.3390/ma14195593

**AMA Style**

Park K, Kim D, Kim G, Lee W.
Evaluation of the Pullout Behavior of Pre-Bored Piles Embedded in Rock. *Materials*. 2021; 14(19):5593.
https://doi.org/10.3390/ma14195593

**Chicago/Turabian Style**

Park, Kyungho, Daehyeon Kim, Gyudeok Kim, and Wooyoul Lee.
2021. "Evaluation of the Pullout Behavior of Pre-Bored Piles Embedded in Rock" *Materials* 14, no. 19: 5593.
https://doi.org/10.3390/ma14195593