# Behavior Investigation of Necking Pile with Caps Assisted with Transparent Soil Technology

^{1}

^{2}

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## Abstract

**:**

## 1. Introduction

## 2. Experimental Work

#### 2.1. Materials and Model Pile

_{2}, and its purity is 99%. Particles with the sizes of 0.5 mm–1.0 mm and 1.0 mm–2.0 mm were mixed according to the ratio of 2:3. The size distributions of fused quartz sand and standard sand [32] are shown in Figure 1. Pore fluid was prepared by mixing n-dodecane and 90# white oil based on the volume ratio of 1:8.8. The parameters of transparent soil are shown in Table 1, and the transparent soil sample is shown in Figure 2 [31]. The mechanical properties of transparent soil are similar to that of natural sand, and it can be used as a substitute for simulating natural sand [33,34,35].

#### 2.2. Experimental Set-Up

#### 2.3. Experimental Process

#### 2.4. Accuracy Analysis of PIV

_{1}) and (I

_{2}) were taken successively according to a certain loading time sequence, (2) the pixel query window size was set as M × N, and (3) the pictures of I

_{1}and I

_{2}query windows were compared and calculated according to Equation (1).

_{1}and I

_{2}) and becomes a mutual function $R\left(s,t\right)$.

_{1}. The program used in this experiment considers the correlation between images to make the image processing results more accurate.

## 3. Results and Discussion

#### 3.1. Vertical Bearing Capacity Analysis

#### 3.2. Analysis of Soil Displacement around Piles

## 4. Discussion of Bearing Capacity Loss

## 5. Conclusions

- (1)
- The bearing capacity of capped pile is greatly damaged by the existence of necking. When the necking diameter is 4 mm and the necking length is 20 mm, the loss of VUBC is as high as 26.6%. For the pile with the same necking diameter, the vertical bearing capacity will decrease with the increase in necking length. However, when the necking diameter is 16 mm, the VUBC of MLW pile only is increased by 3% compared with that of MMW pile. For the pile with the same necking length, the vertical bearing capacity will increase with the increase in necking diameter.
- (2)
- The necking mainly affects the soil displacement around the pile cap and necking. The soil around the necking develops downward and concentrated displacement, and the pile-shaft resistance at the necking is lost. When the necking size is large, the soils at the necking and around the pile cap are connected. This increases the displacement range of the soil under the pile cap and has a significant impact on the soil displacement direction around the pile cap. In addition, the soil under the pile cap develops more vertically downward displacement, resulting in more loss of pile-shaft resistance.
- (3)
- In this study, the necked pile was placed in the middle of the pile for the first time. At present, there is no relevant study on middle necking pile. This study is compared with the existing studies on necking piles. For example, Xu et al. [31] shows that the necking seriously affects the bearing capacity of piles, the influence of the necking length and different necking diameters on the bearing capacity, which is consistent with the results of this study. The research results in the literature show that shallow shrinkage limits the performance of the pile cap. This study found that the intermediate shrinkage affects the performance of the pile side friction. The research results analyzed the causes of the bearing-capacity loss of necking piles and provided a certain theoretical and technical reference for the rational design and reinforcement of piles.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 3.**Model piles and necking. Note: S represents 100 mm from the necking to pile end; L, M and S represent 20 mm, 10 mm and 5 mm of the necking length, respectively; W, M and T represent 16 mm, 8 mm and 4 mm of necking diameter, respectively.

**Figure 8.**Load-settlement curves of piles: (

**a**–

**c**) represent that the necking lengths are 20 mm,10 mm and 5 mm, respectively.

C_{u} | C_{c} | ρ_{d}/(g·cm^{−3}) | ρ_{dmax}/(g·cm^{−3}) | ρ_{dmin}/(g·cm^{−3}) | γ/(kN·m^{−3}) |
---|---|---|---|---|---|

6 | 1.354 | 1.438 | 1.481 | 1.239 | 2.51 |

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## Share and Cite

**MDPI and ACS Style**

Le, X.; Cui, X.; Zhang, M.; Xu, Z.; Dou, L.
Behavior Investigation of Necking Pile with Caps Assisted with Transparent Soil Technology. *Sustainability* **2022**, *14*, 8681.
https://doi.org/10.3390/su14148681

**AMA Style**

Le X, Cui X, Zhang M, Xu Z, Dou L.
Behavior Investigation of Necking Pile with Caps Assisted with Transparent Soil Technology. *Sustainability*. 2022; 14(14):8681.
https://doi.org/10.3390/su14148681

**Chicago/Turabian Style**

Le, Xudong, Xiuqin Cui, Mengyang Zhang, Zhijun Xu, and Lin Dou.
2022. "Behavior Investigation of Necking Pile with Caps Assisted with Transparent Soil Technology" *Sustainability* 14, no. 14: 8681.
https://doi.org/10.3390/su14148681