_{1}

^{*}

In order to analyze the influence of wave scouring on the vertical bearing behavior of the pile foundation, the finite element software ABAQUS was used to simulate the force of the pile foundation under the action of wave scouring. A three-dimensional finite element calculation model of the pile foundation was established according to the actual working conditions, and the calculation results were compared with the field test results to verify the correctness of the built model. Then, the influence of wave scouring depth and pile embedding depth on the vertical bearing behavior of pile foundation was analyzed through calculation examples. The analysis results showed that the greater the depth of wave erosion, the greater the impact on the vertical bearing behavior of the pile foundation. Meanwhile, the smaller the buried depth of the pile body, the greater the impact on the vertical bearing capacity of the pile. Thus, the reduction rate of the vertical bearing capacity under different scouring depths was obtained.

Nowadays, pile foundation is one of the most widely used foundation forms in marine engineering with a long history. In Marine engineering, wave loads cause soil erosion around piles and form local scour pits, which leads to the decrease of bearing capacity or even destruction of pile foundation, thus reducing the safety of the structure. The problem of the piles foundation scouring has attracted the attention of scholars. However, their researches mainly focus on the erosion effect of water flow on the pile foundation [

In this paper, the finite element software numerical method is used to numerically simulate the force of a partially embedded single pile under vertical load by the ABAQUS software, and the numerical simulation calculation results are compared with the field test results to verify the effectiveness and accuracy of the modeling method. Moreover, the influence of the vertical bearing behavior of partially embedded single pile under different wave scouring depth and different embedment depth is analyzed under different working conditions, which provides a certain reference for similar research.

The soil parameters were selected according to references [^{4} MPa, and the Poisson’s ratio is 0.25, which is simulated by a linear elastic model. The soil is simulated by Mohr-Coulomb constitutive model, the model is a three-dimensional solid model, and the size of the numerical model (length × width × depth) is 60 m × 30 m × 50 m.

In this paper, the ABAQUS software uses version 6.14, the pile body adopts the linear elastic body constitutive model and the contact between the side of the pile and the soil around the pile is simulated using the Mohr-Coulomb constitutive

Serial number | Soil layer name | Density/(kg/m^{3}) | Elastic Modulus/(MPa) | Cohesion/(kPa) | Friction Angle/(˚) |
---|---|---|---|---|---|

1 | Silty clay | 1840 | 0.64 | 20 | 18 |

2 | Silt silty clay with sandy silt | 1770 | 0.82 | 10 | 22.5 |

3 | Mucky clay | 1670 | 0.62 | 14 | 11.5 |

4 | clay | 1760 | 0.98 | 16 | 14.0 |

5 | Silty clay | 1840 | 1.34 | 15 | 22.0 |

6 | Silty clay | 1980 | 3.08 | 45 | 17.0 |

7 | Sandy clay with silt | 1870 | 12.33 | 3 | 32.5 |

model. The friction coefficient of tangential contact is 0.3tanφ, where φ is the internal friction angle of the soil layer; the normal contact uses hard contact, which means that slippage or separation can occur after contact. In order to ensure the rationality of the interaction force transfer between pile and soil, the binding constraint (tie) is adopted between pile bottom and soil.

Considering that the main research object and the deformation position is the pile, in order to make full use of computer resources and improve the calculation efficiency, the area near the pile is meshed, while the area far away from the pile is gradually thinning. The mesh is divided by the 8-node three-dimensional reduction unit C3D8R. The scoured soil is simplified into a regular figure, and the meshing of the finite element model is shown in

In the finite element calculation and analysis, the initial ground stress of the soil has a great influence on the calculation results. Thus, after the model is established, the ground stress balance calculation must be performed first. After the ground stress is balanced, a load of 4000 kN is applied to the top of the pile to obtain the displacement-settlement curve of the soil before being affected by wave erosion as shown in

A three-dimensional finite element model of a single pile partially embedded in a single-layer foundation is established. The pile-soil parameters are shown in

Material | Density/ (kg/m^{3}) | Cohesion/ (Pa) | Friction Angle/(˚) | Dilation Angle/(˚) | Elastic Modulus/(Pa) | Poisson’s ratio |
---|---|---|---|---|---|---|

Soil | 1800 | 80,000 | 20 | 0 | 10e6 | 0.2 |

pile | 2400 | - | - | - | 31,500e6 | 0.3 |

pile depth is L = 30 m, L = 20 m, and L = 10 m. The three-pile embedment depth setting conditions analyze the influence of scouring on the vertical bearing capacity of the pile foundation. Because of the complexity of wave scouring process, the impact of scouring is mainly reflected in the contact part between soil and pile foundation. Since it has no significant relationship with the properties of scour pit, the scour pit shape is simplified into regular cuboids in the finite element analysis, while the process of wave scour is simulated by using the function of life and death unit of ABAQUS to remove the soil at the corresponding depth step by step at a unit of 0.5 m depth.

partially embedded single pile. Ds is the scour depth, D is the pile diameter, and L is the depth of the pile. (The erosion is more serious in the direction of incoming wave, so the soil is missing more)

The main research object of this paper is the vertical ultimate bearing capacity, and the load settlement curve of pile foundation (i.e. P-S curve) can directly reflect the stress characteristics of pile. Meanwhile, this curve can directly reflect the pile lateral friction, the load transfer characteristics of pile-soil system and the performance of pile tip resistance. According to the relevant literature, the settlement amount is 3% to 6% of the pile diameter, and the recommended value is 40 mm - 60 mm, referring to the Literature [

In order to explore the influence of scouring depth, the following seven working conditions were set for calculation: the scouring depth was 0 m, 0.5 m, 1 m, 1.5 m, 2 m, 2.5 m, 3 m, respectively; The remaining parameters were D = 1.4 m and L = 30 m. A pile top load of 5000 kN was applied to each working condition.

ultimate bearing capacity of the pile foundation decreases with the increase of the scouring depth, and the trend of bearing capacity gradually slows down with the increase of the scouring depth.

In order to explore the influence of pile embedment depth, the following three working conditions were set for calculation: the pile embedment depth was 30 m, 20 m, and 10 m, respectively; the remaining parameters were: D = 1.4 m. A pile top load of 5000 KN was applied to each working condition.

As shown in

In order to explore the influence of pile embedment depth on vertical bearing capacity under the change of wave scouring depth, the in-depth calculations were carried out according to three different pile embedment depths: the pile embedment depth were 30 m, 20 m, and 10 m; the scour depth were 0 m, 0.5 m, 1 m, 1.5 m, 2 m, 2.5 m, 3 m; the remaining parameters were D = 1.4 m. A 4000 KN pile top load was applied to each working condition.

As shown in

soil around the pile and the decrease of the buried depth of the soil caused by wave erosion, both of which make the contact area between the pile and soil become smaller. As the side friction of the smaller pile decreases, the vertical bearing capacity of the pile also declines. When the pile is buried 10 m and the scour depth is 1.5 m, the bearing capacity of the pile drops sharply. It can be seen that, with the decrease of embedding depth and the increase of scour depth, the vertical bearing capacity has a superimposed effect. Therefore, the scour depth has a greater impact on the pile with a smaller embedding depth.

As shown in

embedded depth scour depth | 30 m | 20 m | 10 m |
---|---|---|---|

0.5 | 0.045% | 0.357% | 0.004% |

1 | 0.037% | 0.082% | 1.045% |

1.5 | 0.036% | 0.681% | 1.112% |

2 | 0.029% | 0.166% | 0.205% |

2.5 | 0.017% | 0.051% | 0.682% |

0.002% | 2.284% | 0.361% |

embedded depth scour depth | 10 m | 20 m |
---|---|---|

0 | 26.57% | 19.57% |

0.5 | 26.80% | 19.28% |

1 | 26.83% | 20.06% |

1.5 | 27.31% | 20.41% |

2 | 27.41% | 20.44% |

2.5 | 27.43% | 20.94% |

3 | 29.09% | 19.39% |

different under divergent scour depth. The effect of scour depth on vertical bearing capacity of pile decreases with the increase of scour depth. Among them, the first scouring has the greatest impact on the vertical ultimate bearing capacity of the pile foundation.

As shown in

In this study, a validated three-dimensional finite element model was used to simulate the load of pile foundation under wave scouring. The results show that the depth of wave erosion has a great effect on the vertical bearing behavior of partially embedded single pile. In practical engineering, the impact of scouring depth needs to be considered. The displacement of partially embedded piles increases rapidly with the increase of scour depth, resulting in a decrease in the vertical bearing capacity. With the increase of pile depth, the displacement of pile top gradually increases, and the vertical bearing capacity decreases accordingly. When the embedded depth of the pile body decreases and the erosion depth increases, the displacement of pile top increases significantly, and the strength of vertical bearing capacity increases. The variation of the vertical ultimate bearing capacity is different at different scouring depths. The effect of scouring depth on vertical bearing capacity of pile decreases with the increase of scour depth. Among them, the first scouring has the greatest effect on the vertical ultimate bearing capacity of pile foundation.

The soil around the pile foundation is prone to scour under the action of waves, which greatly weakens the bearing capacity of the pile foundation. As for pile foundations with relatively shallow initial buried depth, the weakening effect of vertical bearing capacity caused by scouring is particularly significant. Therefore, the depth of the buried pile and the scouring problem should be considered in the project. This article has conducted a deep research on the relationship between the depth of the scouring depth and the vertical bearing capacity, and the obtained the reduction rate can also provide a certain reference for similar research and engineering.

The author declares no conflicts of interest regarding the publication of this paper.

Wang, X.Y. (2021) Research on Vertical Bearing Capacity of Pile Foundation under Wave Scouring. Open Journal of Modelling and Simulation, 9, 124-134. https://doi.org/10.4236/ojmsi.2021.92008