# A Review of Vertical Shaft Technology and Application in Soft Soil for Urban Underground Space
## 4 Technological Advancements in Mechanized Systems
### Shaft Boring System  
The shaft boring system, a development for the mechanized excavation of deep vertical blind shafts in hard rock conditions, represents a large, complex shaft excavation equipment. Its main functions include rock cutting, muck removal, and shaft support. Due to its high excavation efficiency, geological adaptability, and quality of completion [32], it can be widely applied in the construction of shafts in UUS and mineral resources development, such as underground parking lots, water storage tanks, and mine shafts. With the increasing utilization of underground space, mechanized excavation has become a prevailing trend to replace traditional methods [33]. This system employs a rotating cutting wheel to excavate the full shaft diameter in a two-stage semi-full-face sequential excavation process. The two-step excavation process includes trench excavation, where the cutting wheel rotates around its horizontal axis to a depth of one stroke, followed by downward pushing in the shaft direction. In the second step, the entire bench area is excavated by slewing the rotating cutting wheel 180\({}^{\circ}\) around the shaft's vertical axis. The SBS machinery consists of three key operations and components: the shaft boring machine (SBM), which manages excavation, much transportation, and gripping systems; equipment for primary rock support and probe drilling; a primary platform deck for SBS infrastructure and power packs; and a secondary platform deck for final lining installation, muck handling, and service extension. Power packs supply energy to the systems used in shaft boring, enabling cutting tools and other operational systems to function efficiently. The machinery also includes hydraulic systems, control systems, and other equipment vital for the progression of shaft boring. The infrastructure on the primary platform deck is designed to facilitate the efficient and safe operation of the boring equipment. After excavation is complete, the secondary platform of the SBS aids in the installation of the final shaft lining, essential for maintaining structural integrity and preventing failures, as well as protecting the excavation from groundwater and geological pressures. In addition to lining installation, it supports efficient muck handling, ensuring the timely removal of excavated material to maintain a clear working area and smooth operations. The platform also allows for the extension of essential utilities required for the safe and effective management of the shaft environment, such as water supply, ventilation, and drainage.  
The application of the SBS in soft UUS faces numerous limitations, primarily due to unstable soils and high groundwater tables. In such circumstances, soft ground necessitates additional support measures, such as soil stabilization or grouting. The presence of a high groundwater table in soft grounds complicates operations further, necessitating dewatering systems and increasing the risk of land subsidence. Additionally, the SBS typically employs rotating cutters or drills for shaft advancement, which are not effective in soft soil, making cutting and aligning the shaft face more challenging, reducing productivity and potentially increasing costs and delays. Furthermore, urban environments complicate SBS implementation due to confined spaces, existing infrastructure and utilities, vibrations, and the potential for differential settlement in densely populated areas. Alternative shaft construction technologies are necessary, as SBSs often require more complex and expensive solutions, increasing safety and environmental risks in soft UUS.