# A Review of Vertical Shaft Technology and Application in Soft Soil for Urban Underground Space
## 4 Technological Advancements in Mechanized Systems
### Blind Shaft Boring
#### 4.2.1 Raise Boring Machine (RBM)  
The raise boring machine (RBM) enhances conventional shaft construction, providing an efficient, mechanized method. This mechanized approach, compared to traditional drill-and-blast methods, significantly reduces the number of operating workers, enhances safety during shaft construction, minimizes worker injuries, and improves overall productivity. Therefore, the advancement and operation of raise boring technology hold promise [42]. Compared to traditional methods, RBMs exhibit improved efficiency, reducing construction time by approximately 20% [43]. In the 1950s and 1960s, the United States and Germany initially developed raise drilling rigs with drill pipes. Since 1968, raise boring has been routinely utilized in the mining industry for mechanically cutting excavations to various diameters and depths, ranging from 0.7 m to 7.1 m in diameter and depths up to 1260 m. In this method, a pilot hole is created by a drilling rig, followed by the use of a specialized cutting head to create a large-diameter hole in an upward direction. In 1971, the first SBM was designed and manufactured in the Federal Republic of Germany, successfully boring a 4.88 m-diameter, 231 m-deep shaft [44]. Since the prototype's initial use in 2010 at the Vianden hydropower plant in Luxembourg, Herrenknecht RBMs have proven their reliability in various projects worldwide [45]. This method significantly enhances drilling speed and addresses the limitations of low productivity and continuous slag removal associated with traditional drilling methods. However, it also imposes constraints on the maximum diameter and length of the hole. In this context, the shaft diameter is limited to 6.0 m, while its depth can reach up to 2 km [46]. Raise drilling rigs are primarily suited for stable rock environments; inadequate self-supporting capabilities may lead to failures during excavation, necessitating careful application or section modification treatment [47]. China began advancing raise drilling rigs and technology in the 1980s, progressing through three stages [48]. From 1980 to 1989, the equipment reproduction stage focused on underground coal mine construction, characterized by small size, explosion-resistant capabilities, and lightweight design suitable for underground transport. The strata typically consisted of soft rock, with diameters ranging from 1.0 to 5 m and drilling depths generally not exceeding 100 m, requiring compressive strength of the broken rock to be less than 60-100 MPa. From 1990 to 2005, the scope of drilling applications expanded from coal engineering to hydropower, mining, and other sectors, leading to increased drilling depth and diameter, with compressive strength requirements rising to approximately 250-300 MPa. The period from 2006 to the present represents the maturation phase for processes and equipment. In the last decade, significant progress has been made in raise boring technology and equipment research [49; 50]. Following the widespread adoption of small raise drilling rigs, China has initiated the research and design of large-scale raise drilling rigs suitable for diverse geological and engineering conditions. These large-diameter rigs are equipped with substantial push-and-pull propulsion systems, multi-cylinder lifting mechanisms, high torque rotation capabilities, and multi-motor driving equipment. The integration of large-diameter reaming drill bits meets the requirements for underground transportation and assembly in confined spaces. Furthermore, advancements in large-diameter raise drilling technology, including measurement while drilling and deviation correction control technology, enhance deflection control precision. This technological progress has led to the successful development of the ZFY5.0/600 RBM, which facilitates large-diameter shaft construction, contrasting with prior RBMs that were limited to small-diameter raises.