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This study uses a test section of a highway, a study object, to explore the effect of thickness of the gravel base and asphalt layer on the vertical deformation of the road surface. The thickness of the asphalt layer and graded gravel base is changed. The nonlinear description equation of the relationship between the thickness (

Semirigid base asphalt pavement is widely used as the main structure of highway pavements [

In this paper, the numerical simulation methods are used [

A section of a highway is selected for analysis (Figure

Calculation section.

Model size in FLAC3D.

Parameters for the embankment model.

Layer | Height (m) | Elastic modulus | Poisson’s ratio | Constitutive model |
---|---|---|---|---|

Asphalt pavement | H1 = 0.1, 0.15, 0.18, and 0.2 | 1000 MPa | 0.3 | Elastic |

Gravel base | H2 = 0.20, 0.40, and 0.60 | — | — | Mohr–Coulomb |

Embankment fill | H3 = 8 − H1 − H2 | 40 MPa | 0.27 | Elastic |

Foundation | H4 = 10 | 40 MPa | 0.27 | Elastic |

The model range of the embankment is relatively large. The focus of the study is the vertical deformation of the embankment under road load. The action range is not large because the vehicle load force on the road of uniformly distributed load is 167 kPa. The vertical deformation of the pavement is largest in the pavement under load. Therefore, the main part of the study is the road surface. This study selects three kinds of pavement forms with different thicknesses of the asphalt layer and gravel layer. The main contents of analysis and parts of the embankment model are observed. The selection of the pavement and gravel thickness is based on three criteria (Figure

Road surface composition.

Vertical deformation is the vertical deformation of the pavement. The distance between the location and embankment center is given as follows:

his id 1 gp zdis 0.0 0.0 0.0 his id 12 gp zdis 5.7 0.0 0.0

History is divided into two parts, namely, wheel load and unacted part.

His id 1, 2, 7, 12, 17, and 22 are the unapplied load parts located in the middle of the load interval between the two wheels. The other part of his id is the part of the wheel load. Each wheel load has two edges and a total of four points in the center. His id 3, 4, 5, and 6 are the first group. His id 8, 9, 10, and 11 are the second group. His id 13, 14, 15, and 16 are the third group. His id 18, 19, 20, and 21 are the fourth group.

The maximum vertical deformation under load is analyzed in this study. The vertical deformation of different positions is compared, as shown in Figures

The vertical deformation for each history point of 10–20 type.

The vertical deformation for each history point of 18–20 type.

The vertical deformation for each history point of 20–60 type. (a) Thickness of the asphalt layer with 10 cm. (b) Thickness of the asphalt layer with 15 cm. (c) Thickness of the asphalt layer with 18 cm. (d) Thickness of the asphalt layer with 20 cm.

To study the effect of asphalt pavement thickness on the vertical deformation of the embankment, the following data are divided into three categories in accordance with the thickness of the gravel layer, which is 20, 40, and 60 cm, respectively.

As shown in the calculation in Figure

Vertical deformation of the road for 20 cm thickness of the gravel base.

The fitting correlation coefficient of the four groups is higher than 0.99, which indicates high correlation. The vertical deformation of the pavement in the corresponding points is small when the thickness of the asphalt layer is 10 cm. The relative difference of vertical deformation is comparatively small when the thickness sizes of the asphalt layer are 15, 18, and 20 cm. The overall vertical deformation trend of the road is large in the middle and small on both sides. The vertical deformation of the near embankment center is larger than that of the close shoulder. The maximum vertical deformation of the road is at approximately 4.7 m from the embankment center.

Previous analysis shows that vertical deformation of the pavement is the smallest of the four asphalt pavement thickness schemes when the thickness of the gravel layer is certain and the thickness of the asphalt pavement is 10 cm. In addition, the increase of the thickness of the asphalt layer does not significantly decrease the vertical deformation of the road pavement. To better understand the influence of asphalt pavement thickness on the vertical deformation of the pavement, this study analyzes the vertical deformation of the overall difference of the road surface (Figure

Relationship between the asphalt layer and pavement with uneven vertical deformation.

When the thickness of the asphalt pavement is 10 cm (Table

Vertical deformation for the asphalt pavement thickness of 10 cm.

Thickness of the gravel base (cm) | First class | Second class | Third class | Fourth class |
---|---|---|---|---|

20 | 6.679 | 6.921 | 6.673 | 5.683 |

40 | 6.591 | 6.944 | 6.691 | 5.609 |

60 | 6.437 | 6.700 | 6.522 | 5.502 |

When the thickness of the asphalt pavement is 15 cm (Table

Vertical deformation for the asphalt pavement thickness of 15 cm.

Thickness of the gravel base (cm) | First class | Second class | Third class | Fourth class |
---|---|---|---|---|

20 | 6.915 | 7.183 | 6.963 | 5.868 |

40 | 6.812 | 7.204 | 6.995 | 5.85 |

60 | 6.750 | 7.068 | 6.873 | 5.85 |

When the thickness of the asphalt pavement is 18 cm (Table

Vertical deformation for the asphalt pavement thickness of 18 cm.

Thickness of the gravel base (cm) | First class | Second class | Third class | Fourth class |
---|---|---|---|---|

20 | 6.96 | 7.259 | 7.046 | 5.924 |

40 | 6.871 | 7.243 | 7.010 | 5.891 |

60 | 6.778 | 7.110 | 6.900 | 5.884 |

When the thickness of the asphalt pavement is 20 cm (Table

Vertical deformation for the asphalt pavement thickness of 20 cm.

Thickness of the gravel base (cm) | First class | Second class | Third class | Fourth class |
---|---|---|---|---|

20 | 6.977 | 7.263 | 7.051 | 5.924 |

40 | 6.894 | 7.247 | 7.016 | 5.895 |

60 | 6.781 | 7.114 | 6.915 | 5.882 |

Vertical deformation for the asphalt pavement thickness of 20 cm.

The vertical deformation of the pavement increases as the thickness of the asphalt layer increases gradually from 10 cm to 15, 18, and 20 cm, but the slope of the curve gradually decreases.

Asphalt pavement cannot easily facilitate stress coordination when the relative vertical deformation of the pavement is large. Ruts may develop easily, thereby destroying the asphalt pavement. Compared with the vertical deformation of the asphalt pavement with thicknesses of 10 cm, 18 cm, and 20 cm, increasing the thickness of the asphalt pavement can significantly reduce the uneven vertical deformation of the pavement.

When the thickness of the asphalt pavement is certain, the vertical deformation of the pavement decreases with the increase of the thickness of the gravel base from 20 cm, 40 cm, and 60 cm. The vertical deformation of the pavement in each group is smallest when the thickness of the gravel base is 60 cm.

The authors declare no conflicts of interest.