# A Review of Vertical Shaft Technology and Application in Soft Soil for Urban Underground Space
## 6 Application Cases Overview
A total of four shafts were constructed, with depths ranging from 65 to 83 m. In St. Petersburg, VSM technology demonstrated exceptional efficiency, particularly in meeting time schedules. The first shaft, with a depth of 85 m and a 7.7 m inner diameter, was successfully accomplished in 50 days. The lithology of the underground area consists of soft soils like sand and loam. The upper layer, up to a depth of about 60 m, is groundwater-bearing, while the lower layer consists of hard but dry loam. In the transition zone between these two formations, boulders of up to 2.5 m in length are present, as shown in Figure 10.  
Shaft lining is conducted on the shaft surface simultaneously with the excavation. Four segments, each 1 m in height and designed to withstand pressures of 8.5 bar, are installed as a ring segment. These segments are held by a crane attached to the shaft sinking unit and placed onto the previously installed ring segment [98]. In the Middle East, various microtunneling projects include the construction of deep target or launch shafts with depths ranging from 25 to 45 m. Initially, in 2006, a shaft with an inside diameter of 6.5 m and an outside diameter of 7.3 m was successfully sunk. The construction area consists of heterogeneous ground, including sand, sandy clay, hard coral, and limestone. The high porosity of corals and limestone results in significant groundwater intrusions, posing challenges to shaft construction efforts. Due to the considerable volume of water, drainage is often difficult or impossible, necessitating the deployment of VSM equipment. Through the groundwater-flooded shaft, the excavated material is mucked out, supplemented by a slurry system for soil transport. Due to local regulations, the use of prefabricated segments is prohibited during this project. Shafts are constructed using in situ casting. Every two days, 2 to 4 m are cast using a quick handling formwork and reinforcement system, achieving an average production rate of 1 to 2 m per day. Another sewage shaft was constructed in Jeddah, Saudi Arabia, using VSM technology. The vertical shaft, with an inner diameter of up to 10 m and an outer diameter of 11 m, and a depth of 45 m, was successfully sunk in soft grounds, including loam, sand, and gravel. By utilizing VSM technology, 13 emergency and ventilation shafts with inner diameters ranging from 4.5 to 5.5 m and depths of up to 45 m were constructed for the subway line in Naples, Italy. The project site is located in a densely populated urban area with high traffic levels. The shafts were built on soft ground consisting of silt, clay, and sand gravels. Rapid completion was achieved, with sinking rates reaching up to 5 m per day due to the parallel excavation and lining process using precast concrete segments. In Spain, from 2010 to 2011, four shafts were constructed in Girona using a Herrenknecht VSM as ground stabilization shafts prior to tunneling works, featuring an internal diameter of 5.25 m and a depth of 20 m for the high-speed rail link from Barcelona to the French border. Additionally, in Barcelona, one shaft with an internal diameter of 9.2 m and a depth of 47 m was built for ventilation and as an emergency exit. Extremely restricted working conditions posed significant challenges for construction contractors. For instance, one of the shafts in Girona was situated between rows of houses with only 12 m of spacing. Typical shafts from Naples, Italy and Girona, Spain are illustrated in Figure 11. This project demonstrates the major advantage of VSM's capability to operate under confined space conditions in urban environments [27]. In Singapore, under the Deep Tunnel Sewerage System (DTSS) Phase 2 Contract T11, twenty-one deep circular shafts connecting the tunnels were constructed. Five shafts--K1, K2, K2-DS1, Ki, and L-LS4--were constructed using VSM technology, each with an internal diameter of 10.4 m and depths of 42.2 m, 57.6 m, 55.9 m, 38.6 m, and 41.8 m, respectively.