# Assessment of the Shear Strength of Pile-to-Soil Interfaces Based on Pile Surface Topography Using Laser Scanning

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## Abstract

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## 1. Introduction

- Drilling a full-length auger with a hollow stem (temporarily plugged) into the soil using a constant penetration rate;
- After reaching the design toe, concrete is pumped through the hollow stem of the auger while the rotating auger is extracted at the same time. It is important that the auger always remains embedded in the concrete and that a positive concrete pressure is maintained throughout the placement of the concrete;
- After completion of the concrete placement process, the reinforcement cage (Figure 1, detail 2) is thrown into fluid concrete.

## 2. Materials and Methods

#### 2.1. Terrestrial Laser Scanning

- Pulse scanners, in which the time of passage of the laser beam from the scanner to the object is measured (the so-called time-of-flight measurement);
- Phase scanners, in which the phase difference between the sent signal and the returned signal is measured (the so-called phase measurement technique); and
- Triangulation scanners, whose operation consists of detecting the position of a single laser beam reflected from the object and determining the distance to the measured object using trigonometric relations in a triangle.

#### 2.2. Principles of Roughness Parameters

- Height parameters;
- Spatial parameters;
- Hybrid parameters;
- Functional parameters;
- Feature parameters; and
- Other 3D parameters.

#### 2.3. Assessment of Shear Strength Parameters

- Cohesion, due to mechanical interlocking between particles;
- Friction, due to the existence of compression stresses at the interface and to the relative displacement between concrete parts; and
- Dowel action, due to the deformation of the reinforcement bars crossing the interface.

- Pile characteristics, such as pile length, cross section, and shape;
- Soil configuration and short- and long-term soil properties; and
- Pile installation method.

- α—a method used to calculate the short-term load capacity (total stress) of piles in cohesive soils; and
- β—a method used to calculate the long-term load capacity (effective stress) of piles in both cohesive and non-cohesive soils.

#### 2.4. Research Study Site

#### 2.4.1. General Description of Study Site

_{D}is density index.

#### 2.4.2. Acquisition and Processing of Data

## 3. Results

#### Determination of Roughness Parameters

## 4. Discussion

_{z}on the concrete surface in the cavities is less than the effective stress σ

_{z}resulting from the soil rest pressure on the basic vertical surface of the pile. The obtained values of Vmp and Vvv explain the expected higher pile shaft resistance in the medium sand layer. Practical engineering application may take into account the influence of skewness and kurtosis on the static coefficient of friction. In [43], the effects of kurtosis and skewness on different levels of surface roughness were investigated independently. It was found that positive skewness values were associated with larger contact force, real area of contact, and tangential and adhesion forces than the Gaussian case, while negative skewness values predicted lower values tangential and adhesion forces and larger deviations from the Gaussian case. It was also found that distributions with kurtosis higher than 3 predict higher friction parameters compared with the Gaussian case, while distributions with kurtosis lower than 3 predict lower values than the Gaussian case [43]. In the case of the studied surface areas, lower shear strength can be expected for areas 2 and 3 than for areas 4 and 5.

## 5. Conclusions

- There are visible differences in the topography of the pile’s surface within various geotechnical layers;
- The method of performing geotechnical works and earthworks significantly affects the topography of the pile’s surface;
- The actual diameter of the pile in the layer of embankments and medium sand is greater than the nominal diameter of the casing;
- The obtained values of the roughness parameters of the CFA pile surface are greater than the analogical parameters for the surface of the sand-blasted concrete and shot-blasted concrete (i.e., after laboratory artificial treatment).

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**Protection of deep excavation by means of continuous flight auger (CFA) palisade: (

**1**) the wall of the nearest existing building; (

**2**) reinforcement cage; (

**3**) special target used as the tie point for combining scanner positions; (

**4**) palisade made of CFA piles; (

**5**) steel strut; and (

**6**) position of the laser scanner.

**Figure 3.**Geotechnical profile cross-section of the excavation site (from Cone Penetration Testing) with the location of the point cloud subsets.

**Figure 4.**View of a combined point cloud colored on the basis of photos from the scanner with marked tie points (T1–T5) and scanner central points (Stat. 1–Stat. 3).

**Figure 8.**Isometric views of the surfaces of the samples #1, #2, and #3 before and after removing the multi-plane form.

**Figure 9.**Isometric views of the surfaces of the samples #4, #5, and #6 before and after the removing multi-plane form.

**Table 1.**Examples of surface parameters and their definitions according to [13].

Name of Parameter | Definition |
---|---|

Height Parameters | |

Root-mean-square height | $Sq=\sqrt{\frac{1}{A}{{\displaystyle \iint}}_{A}^{}{\left(Z\left(x,y\right)\right)}^{2}dxdy}$ |

Skewness | $Ssk=\frac{1}{S{q}^{3}}\left[\frac{1}{A}{{\displaystyle \iint}}_{A}^{}{\left(Z\left(x,y\right)\right)}^{3}dxdy\right]$ |

Kurtosis | $Sku=1/{S}_{q}{}^{4}/A{{\displaystyle \iint}}_{A}^{}Z{\left(x,y\right)}^{4}dxdy$ |

Maximum peak height | $Sp=sup\left\{Z\left({x}_{i},{y}_{i}\right)\right\}$ |

Maximum pit height | $Sv=\left|inf\left\{Z\left({x}_{i},{y}_{i}\right)\right\}\right|$ |

Maximum height | $Sz=Sp+Sv$ |

Arithmetic mean height | $Sa=1/A{{\displaystyle \iint}}_{A}^{}\left|Z\left(x,y\right)\right|dxdy$ |

Functional Volume Parameters | |

Peak material volume | $Vmp=Vm\left(p\right)$ |

Core material volume | $Vmc=Vm\left(q\right)-Vm\left(p\right)$ |

Core void volume | $Vvc=Vv\left(p\right)-Vv\left(q\right)$ |

Dale void volume | $Vvv=Vv\left(q\right)$ |

Subsets of Point Cloud | Soil Layer Description | Remarks |
---|---|---|

#1, #4, #5 | MSa/siSa, I_{D} = 0.45 | |

#3, #6 | Earthwork/MSa/siSa, I_{D} = 0.45 | Transition from earthwork to MSa/siSa |

#2 | Earthwork (fill ground) |

Subset of Point Cloud No. | #1 | #2 | #3 | #4 | #5 | #6 |
---|---|---|---|---|---|---|

Radius of fitted cylinder [m] | 0.2842 | 0.2681 | 0.2709 | 0.2667 | 0.2650 | 0.2745 |

Number of points in subset | 15,407 | 569,325 | 519,299 | 147,433 | 106,513 | 134,489 |

Density of points [pt/mm^{2}] | 0.13 | 4.65 | 4.24 | 3.69 | 2.66 | 3.36 |

**Table 4.**Results of the measurement of the three-dimensional (3D) roughness parameters for each sample before removing the multi-plane form.

Description | Name | Unit | Before Removing Multi-Plane Form—Sample No. | |||||
---|---|---|---|---|---|---|---|---|

#1 | #2 | #3 | #4 | #5 | #6 | |||

Root-mean-square height | Sq | mm | 3.3 | 2.8 | 2.4 | 1.7 | 1.6 | 2.7 |

Skewness | Ssk | - | 0.1 | −0.4 | −0.1 | 0.1 | 0.1 | 0.1 |

Kurtosis | Sku | - | 2.7 | 3.0 | 2.6 | 3.0 | 3.0 | 3.0 |

Maximum peak height | Sp | mm | 10.4 | 11.6 | 11.1 | 7.1 | 6.9 | 10.1 |

Maximum pit height | Sv | mm | 9.6 | 15.1 | 11.1 | 7.0 | 6.3 | 11.2 |

Maximum height | Sz | mm | 20.0 | 26.7 | 22.2 | 14.0 | 13.2 | 21.3 |

Arithmetic mean height | Sa | mm | 2.7 | 2.3 | 1.9 | 1.3 | 1.3 | 2.1 |

**Table 5.**Results of the measurement of the 3D roughness parameters for each sample after removing multi-plane form.

Description | Name | Unit | After Removing Multi-Plane Form—Sample No. | |||||
---|---|---|---|---|---|---|---|---|

#1 | #2 | #3 | #4 | #5 | #6 | |||

Root-mean-square height | Sq | mm | 1.2 | 1.3 | 1.0 | 0.8 | 0.9 | 0.9 |

Skewness | Ssk | - | −0.4 | −0.2 | −0.4 | −0.1 | −0.2 | −0.1 |

Kurtosis | Sku | - | 3.9 | 4.9 | 4.1 | 3.7 | 3.8 | 3.6 |

Maximum peak height | Sp | mm | 4.5 | 10.3 | 6.4 | 4.8 | 5.3 | 5.0 |

Maximum pit height | Sv | mm | 6.9 | 13.1 | 8.4 | 5.2 | 5.9 | 7.3 |

Maximum height | Sz | mm | 11.4 | 23.3 | 14.8 | 9.9 | 11.2 | 12.3 |

Arithmetic mean height | Sa | mm | 1.0 | 1.0 | 0.8 | 0.6 | 0.7 | 0.7 |

Peak material volume | Vmp | ml/m^{2} | 53.7 | 71.6 | 48.2 | 40.5 | 42.0 | 45.8 |

Core material volume | Vmc | ml/m^{2} | 1064 | 1046 | 888 | 704 | 752 | 788 |

Core void volume | Vvc | ml/m^{2} | 1388 | 1429 | 1165 | 949 | 1003 | 1061 |

Dale void volume | Vvv | ml/m^{2} | 166 | 176 | 143 | 101 | 110 | 112 |

**Table 6.**Coefficient of friction according the Eurocode 2 standard [3].

Type of Surface | Coefficient of Cohesion c | Coefficient of Friction μ |
---|---|---|

Very smooth | 0.025–0.10 | 0.50 |

Smooth | 0.20 | 0.60 |

Rough | 0.40 | 0.70 |

Indented | 0.50 | 0.90 |

Soil–Structure Interaction | Strength Reduction Factor ${\mathit{R}}_{\mathit{i}\mathit{n}\mathit{t}\mathit{e}\mathit{r}}$ |
---|---|

Sand/steel | 0.6–0.7 |

Clay/steel | 0.5 |

Sand/concrete | 1.0–0.8 |

Clay/concrete | 1.0–0.7 |

Soil/geogrid (grouted body) | 1.0 |

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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**MDPI and ACS Style**

Muszyński, Z.; Wyjadłowski, M. Assessment of the Shear Strength of Pile-to-Soil Interfaces Based on Pile Surface Topography Using Laser Scanning. *Sensors* **2019**, *19*, 1012.
https://doi.org/10.3390/s19051012

**AMA Style**

Muszyński Z, Wyjadłowski M. Assessment of the Shear Strength of Pile-to-Soil Interfaces Based on Pile Surface Topography Using Laser Scanning. *Sensors*. 2019; 19(5):1012.
https://doi.org/10.3390/s19051012

**Chicago/Turabian Style**

Muszyński, Zbigniew, and Marek Wyjadłowski. 2019. "Assessment of the Shear Strength of Pile-to-Soil Interfaces Based on Pile Surface Topography Using Laser Scanning" *Sensors* 19, no. 5: 1012.
https://doi.org/10.3390/s19051012