# Compaction Quality Inspection and Uniformity Analysis of Soil-Rock Mixed Subgrade

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## Abstract

**:**

## 1. Introduction

## 2. Compaction Quality Test Method

#### 2.1. GeoGauge Detection Principle

#### 2.2. Differential Settlement Detection Principle

_{i}

_{1}, H

_{i}

_{2}…H

_{ij}point by point, accurate to 0.1 mm. The above rolling and measurement process is repeated until the settlement data meet the requirements.

## 3. Indoor Model Test

#### 3.1. Indoor Model Test Scheme

#### 3.2. Test Result Analysis

#### 3.2.1. Influence of Water Content on Test Results

- (1)
- When the degree of compaction is constant, the stiffness value of soil-rock mixture increases first and then decreases with the increase of water content. When the water content is lower than 8%, the stiffness curve under the influence of water content changes slightly, which indicates that the water content has little influence on the rigidity of compacted soil-rock mixture within this range. When the water content is higher than 8%, the variation amplitude of the stiffness curve increases, which indicates that when the water content is higher, the stiffness of the compacted soil-rock mixture is greatly affected.
- (2)
- The quadratic polynomial was used to fit the test results. When the compactness is 93%, the moisture content corresponding to the maximum rigidity of the soil-rock mixture is 8.0%. When the compactness is 94%, the water content corresponding to the maximum rigidity is 7.7%. When the compactness is 96%, the water content corresponding to the maximum rigidity is 8.0%. The above results show that the maximum stiffness of the soil-rock mixture is near the optimum moisture content.
- (3)
- When the water content of the soil is fixed, the stiffness value of the soil increases with the increase of the compactness. Under the optimum moisture content, the stiffness of the soil with a compactness of 94% is 3.6% higher than that with a compactness of 93%. The rigidity of soil with compactness of 96% is 9.9% higher than that with compactness of 93%.

#### 3.2.2. Influence of Compactness on Test Results

## 4. Field Test

#### 4.1. Field Test General Introduction

#### 4.2. Analysis of Test Results

#### 4.2.1. Relationship between Settlement Difference and Rolling Repetitions

#### 4.2.2. Relationship between Stiffness and Rolling Times

#### 4.2.3. Relationship between Stiffness and Settlement Difference

## 5. Analysis of Subgrade Compaction Uniformity Based on Ordinary Kriging Method

#### 5.1. Ordinary Kriging Interpolation

#### 5.2. Analysis of Interpolation Prediction Results

## 6. Conclusions

- (1)
- When the degree of compaction is constant, the stiffness value of soil-rock mixture increases first and then decreases with the increase of water content. The compaction stiffness is the largest near the optimal water content. When the water content of soil is lower than the optimum water content, the change of water content has a relatively small impact on the stiffness of the filler. When the soil moisture content is greater than the optimum moisture content, the change of moisture content has a relatively large impact on the stiffness of the filler.
- (2)
- The GeoGauge detection stiffness value increases with the increase of the compactness of the soil-rock mixture, and there is a good exponential relationship between the compactness of the soil-rock mixture and the GeoGauge detection stiffness value. The correlation coefficient is 0.96855. It can be seen that the regression equation has a high degree of fitting, indicating that the GeoGauge test results have high stability and small dispersion.
- (3)
- In the field test, with the increase of the number of rolling passes, the settlement difference of the foundation decreases gradually, and the compaction stiffness value increases gradually. At the same time, the compaction uniformity of the subgrade has also been improved.
- (4)
- There is a good exponential relationship between the GeoGauge detection stiffness value and the settlement difference, which indicates that the GeoGauge detection method is feasible for the compaction quality detection of soil-rock mixed subgrade. According to the regression equation, the specific index of subgrade stiffness when the compactness meets the design conditions is calculated, which provides a reference for the practical engineering.
- (5)
- The subgrade compaction uniformity is evaluated according to the measured data of the detection indicators in the study area and the predicted value obtained by the ordinary Kriging interpolation method. The results show that Kriging interpolation prediction has good accuracy and can better evaluate the compaction uniformity of subgrade.

## Author Contributions

## Funding

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 2.**Basic mechanical properties of test materials: (

**a**) gradation curve of soil-rock mixture; (

**b**) compaction curve of soil-rock mixture.

**Figure 8.**Relationship between rolling repetitions and compactness of soil-rock mixture: (

**a**) variation trend of compaction degree; (

**b**) relationship between rolling times and settlement difference of each inspection point.

**Figure 10.**Relationship between rolling repetitions and stiffness: (

**a**) variation trend of compaction degree; (

**b**) relationship between rolling repetitions and compaction degree of each detection point.

**Figure 12.**Kriging interpolation results of detection indicators in different subgrade sections: (

**a**) top of embankment of general subgrade section; (

**b**) top of roadbed section of general roadbed; (

**c**) top of roadbed of platform back.

Coefficient of Uniformity ${\mathit{C}}_{\mathit{u}}$ | Coefficient of Curvature ${\mathit{C}}_{\mathit{c}}$ | Optimum Moisture Content ${\mathit{\omega}}_{\mathit{o}\mathit{p}\mathit{t}}$ [%] | Maximum Dry Density ${\mathit{\rho}}_{\mathit{d}\mathbf{max}}$ [g/cm^{3}] | Uniaxial Saturated Compressive Strength [MPa] | |
---|---|---|---|---|---|

soil-rock mixture | 14.83 | 1.46 | 8.0% | 2.28 | 62.9 |

**Table 2.**Corresponding relationship between settlement difference and stiffness value after fitting.

Differential settlement (mm) | 2 | 3 | 4 | 5 |

Stiffness (MN/m) | 17.57 | 16.23 | 15.00 | 13.86 |

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## Share and Cite

**MDPI and ACS Style**

Zhang, X.; Yang, G.; Wang, X.; Cao, H. Compaction Quality Inspection and Uniformity Analysis of Soil-Rock Mixed Subgrade. *Sustainability* **2023**, *15*, 5809.
https://doi.org/10.3390/su15075809

**AMA Style**

Zhang X, Yang G, Wang X, Cao H. Compaction Quality Inspection and Uniformity Analysis of Soil-Rock Mixed Subgrade. *Sustainability*. 2023; 15(7):5809.
https://doi.org/10.3390/su15075809

**Chicago/Turabian Style**

Zhang, Xinyu, Guangqing Yang, Xin Wang, and Haisheng Cao. 2023. "Compaction Quality Inspection and Uniformity Analysis of Soil-Rock Mixed Subgrade" *Sustainability* 15, no. 7: 5809.
https://doi.org/10.3390/su15075809