Shotcrete, also known as sprayed concrete, is a special cement-based mixture designed to be projected pneumatically at a high velocity towards a target surface. In recent years, the development and application of underground space has made rapid progress, for example, in the subway, tunnel, and mining industries. Shotcrete is one of the important means for maintaining the stability and integrity of underground spaces and structures. Shotcrete has the advantages of simple operation, convenient construction, and high efficiency. Advanced shotcrete technology is increasingly important to ensure the safe and efficient application of underground space engineering.

In the process of underground space development, extreme geological conditions, such as high ground stress and high temperature, can easily cause rock bursts, high temperature heat damage, and harmful gas outbursts. There has been much research into new support technologies and methods for underground space, for example, spraying steel fiber reinforced concrete to prevent concrete cracking, spraying cement-based polymer materials to improve material ductility, and even the emerging development of self-healing shotcrete. There has been much theoretical and technical support for shotcrete supports in underground space, however, with the improvement of occupational safety and health requirements, as well as the complex geological conditions, advanced shotcrete support technology is urgently needed. This can play not only a supporting role, but also be safe, efficient, and environmentally friendly. In particular, in narrow underground spaces, the process of excavation produces high concentrations of dust, which can cause pneumoconiosis in construction workers. Many shotcrete technologies applied on the ground cannot be used in underground spaces due to space constraints. For example, in the process of tunnel excavation or coal mining, the emission of flammable and explosive gas raises new challenges and requirements for underground shotcrete, as the mixing and preparation of the shotcrete must have explosion-proof performance. It is difficult to guarantee the quality of shotcrete mixing on site if there is no reasonable underground mixing equipment. Reasonable shotcrete support technology can reduce the displacement of surrounding rock and reduce dust concentration in working spaces. Therefore, the exchange and discussion of advanced shotcrete support technology for underground spaces is conducive to the safe and efficient development of underground space.

The purpose of the Special Issue is to invite original research and review articles that highlight advances and breakthroughs in shotcrete support technology, both theory and applications, as used for underground space engineering.

Potential topics include but are not limited to the following:

• Failure mechanisms of underground shotcrete under high ground stress
• Advanced cement-based composite materials used for underground space engineering
• Advanced surrounding rock control processes of shotcrete used in underground space engineering
• Advanced dust control technology for shotcrete used in underground space engineering
• Sealing effect of shotcrete on the surrounding rock of roadways
• Deterioration characteristics of shotcrete under high temperature and optimization strategies
• Advanced shotcrete support theory that has been or may be applied in underground space