**Preface to "Advanced Support Technologies in Roadway"**

In the continuous development and application of underground spaces (such as roads, tunnels and underground caverns), safe and efficient support technology is an important means to maintain the stability and integrity of roadways. With the improvement in occupational health requirements and complex and changeable geological conditions, the application of advanced support technology is particularly important for underground work. Exchange and discussion of advanced tunnel support technology is conducive to the safe and efficient development of underground spaces.

The theme of the book is "Advanced Roadway Support Technology", and it aims to collect and display breakthroughs and high-level research progress of advanced support technology, including advanced cement-based materials for tunnel support, advanced surrounding rock control technology, road dust control methods, advanced tunnel support equipment, and advanced road disaster control theory.

This book contains nine papers (eight research papers and one review paper) covering many fields of advanced support technology, including support materials, disaster prevention of surrounding rock damage, deterioration of support structure, pipeline pumping, and road traffic. Xie et al. reported the influence of different additives on the fresh performance of wet shotcrete. Lapian et al. determined the optimum proportion for the asphalt mixture of modified asbuton with PET plastic waste by response surface methodology. Zhang et al. identified damage evolution law and frequency domain distribution characteristics of the acoustic emission signal of deep granite under triaxial loading. Liu et al. summarized the evolution law of mechanical properties and morphological characteristics of shotcrete microstructures at high temperatures. Useche et al. evaluated the effect of a driver's gender on their intention to use an automatic car through robust testing and bias-correction multi-group structural equation modeling. Ma et al. established a prediction model of the compressive strength of artificial sand concrete by response surface methodology. Ma et al. investigated the two-phase flow characteristics of shotcrete in the pipeline based on the CFD-DEM coupling model and on-site measurement. Alonso et al. assessed the development of intelligent transportation systems and other technologies regarding the promotion of population mobility by investigating 1414 Dominicans aged between 18 and 40. Zhu et al. revealed the internal load transfer behavior and failure mechanism of the bird's nest anchor cable anchored structure.

While advanced support technology provides a guarantee for the development of underground spaces, it still faces many challenges. This book is for scholars whose area of research is roadway support, and other scholars are also welcome to read and discuss.

> **Guoming Liu and Xiangming Hu** *Editors*

### *Editorial* **Advanced Support Technologies in Roadway**

**Jiahao Sun 1, Guoming Liu 1,2,\* and Xiangming Hu 1,2**


**\*** Correspondence: skd995978@sdust.edu.cn

In the continuous development and application of underground spaces (such as roads, tunnels and underground caverns), safe and efficient support technology is an important means to maintain the stability and integrity of roadways. Advanced support technology includes the development of support materials with superior performance, the improvement and innovation of existing support theory, and the development of mechanical equipment with comprehensive functions. For example, the mechanical strength of shotcrete can be enhanced by adding fibers [1,2], improving work efficiency and reducing safety risks through intelligent mechanical equipment [3,4], analyzing the movement characteristics of materials and the control of pipe jam during long distance pumping [5,6], and studying the support structure under complex geological conditions such as high in situ stress [7,8]. Therefore, with the improvement of occupational health requirements and complex and changeable geological conditions, the application of advanced support technology is particularly important for underground work. Exchange and discussion of advanced tunnel support technology is conducive to the safe and efficient development of underground spaces.

This Special Issue aims at collecting and displaying breakthroughs and high-level research progress of advanced support technology, including advanced cement-based materials for tunnel support, advanced surrounding rock control technology, road dust control method, advanced tunnel support equipment, and advanced road disaster control theory.

This Special Issue has published nine papers (eight research papers and one review paper) covering many fields of advanced support technology, including support materials, disaster prevention of surrounding rock damage, deterioration of support structure, pipeline pumping, and road traffic. Xie et al. [9] reported the influence of different additives on the fresh performance of wet-shotcrete, finding that free grout effect and ball effect would significantly affect the performance of wet-shotcrete. The authors discussed the relationship between rheological characteristics and pumpability and spraying ability, and finally put forward suggestions for a mixing ratio meeting the requirements of various shotcrete. Lapian et al. [10] determined the optimum proportion for the asphalt mixture of the modified asbuton with PET plastic waste by response surface methodology, and the final properties of the mixture (stability, Marshall quotient, void in MIX, void mineral aggregate and density) met the specifications of the local engineering department. Zhang et al. [11] identified damage evolution law and frequency domain distribution characteristics of acoustic emission signal of deep granite under triaxial loading. The structure defined signals with amplitude greater than 85 dB, peak frequency greater than 350 kHz and frequency center of gravity greater than 275 kHz as early warning signals of rock failure. Liu et al. [12] summarized the evolution law of mechanical properties and morphological characteristics of microstructures of shotcrete at high temperature, introducing a multi-dimensional morphological formula in the process of heat conduction. The authors established a heat transfer model with spiral shape, and finally put forward opinions regarding the challenges faced by high temperature shotcrete. From the perspective of human factors, Useche et al. [13] evaluated the effect of a driver's gender on their intention to use an automatic car

**Citation:** Sun, J.; Liu, G.; Hu, X. Advanced Support Technologies in Roadway. *Appl. Sci.* **2022**, *12*, 10233. https://doi.org/10.3390/ app122010233

Received: 14 September 2022 Accepted: 8 October 2022 Published: 11 October 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 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 (https:// creativecommons.org/licenses/by/ 4.0/).

through robust testing and bias-correction multi-group structural equation modeling. They found that the driver's intention to use an automatic car could be explained differently according to their gender, which provided a guiding result for the people those studying traffic planning and road safety. Ma et al. [14] established a prediction model of the compressive strength of artificial sand concrete by response surface methodology, and studied the influence of stone powder, fly ash, and silica powder on the compressive strength of artificial sand concrete. The research found that the content of stone powder has the greatest influence on the compressive strength, while the content of silicon powder has the least effect on the compressive strength. Ma et al. [15] investigated the two-phase flow characteristics of shotcrete in the pipeline based on the CFD-DEM coupling model and on-site measurement, determining the velocity of shotcrete materials and the pressure distribution in the pipeline. The authors found that turbulence and secondary flow prevented the pipeline from blocking, and revealed that the energy loss of aggregate particles in the elbow of the pipeline was about 30 times that in the horizontal straight pipe. Alonso et al. [16] assessed the development of intelligent transportation systems and other technologies regarding the promotion of population mobility by investigating 1414 Dominicans aged between 18 and 40, and proposed the need to strengthen the information and communication flow of emerging transportation-related technologies. Zhu et al. [17] revealed the internal load transfer behavior and failure mechanism of the bird's nest anchor cable anchored structure through theoretical analysis, bird's nest anchor cable pull-out test, and particle flow program numerical simulation test. The authors proposed that the failure mode was the combination of the interface debonding and sliding and rock shear failure.

The submission period of this Special Issue has ended. While advanced support technology provides a guarantee for the development of underground spaces, it still faces many challenges, such as the deterioration of support structure under extreme environment, the impact of complex in situ stress, and the implementation of carbon peak policy. Regarding advanced support technology, the future research directions may face the following aspects. The first aspect is the intellectualization and integration of support technology to realize the integration of spraying technology and the intellectualization of spraying equipment, such as the research and application of shotcrete manipulator and shotcrete robot, which can greatly improve work efficiency and ensure the personal safety of construction workers. The second aspect is the development and application of long-distance pumping in underground spaces. When long-distance pumping is carried out, it is extremely important to ensure the fluidity of materials in the pumping pipeline and prevent pipe plugging. For example, the addition of an air entraining agent can significantly improve the fluidity and workability of concrete, but the migration law and time-varying effect of bubbles in fresh concrete still need to be solved. The third aspect is the development of low-carbon concrete. The implementation of carbon neutralization and carbon peak policies has made cement and related industries face tremendous reforms, such as developing and promoting low-carbon cement materials and improving carbon capture, utilization, and storage technologies.

**Author Contributions:** Writing—original draft preparation, J.S.; investigation, writing—review and editing, G.L.; supervision, methodology, X.H. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** Thanks to all the authors and peer reviewers for their valuable contributions to this Special Issue 'Advanced Support Technologies in Roadway'. I would also like to express my gratitude to all the staff and people involved in this Special Issue.

**Conflicts of Interest:** The authors declare that they have no known competing financial interest or personal relationships that could have appeared to influence the work reported in this paper.

#### **References**

