What Does Excessive Vertical Ground Movement Mean?
Excessive vertical ground movement can occur because of soil settlement during trenchless construction projects.
It can result in the distortion of nearby structures, eventually leading to the development of cracks and, in some cases, total failure or collapse of the structure. It can also cause damage to structures standing over the area where the movement occurs.
During trenchless construction operations, the strength and stability of the soil matrix are affected causing vertical ground movement, sometimes excessive.
Trenchlesspedia Explains Excessive Vertical Ground Movement
Ground loosened by the excavation has a tendency to expand into the surrounding soil and can also affect the overburden above the excavation, leading to the heaving or collapse of the ground surface.
Controlling this movement during excavation, especially in shallow overburden, is very important. For excavating tunnels with shallow overburden in soft or unconsolidated soil, the cut and cover method is popular, and the New Austrian Tunneling Method (NATM) is now gaining popularity. NATM is used after using vertical pre-reinforcement or pipe forepiling at the construction site and conducting crown stabilization and prevention of ground settlement.
Another method to control excessive vertical ground movement is the sequential excavation method (SEM) that is employed during tunneling. The proposed tunnel location is first divided into segments, which are then mined using an excavator and road header in a sequential manner by providing supports. As soil from each section is removed, pressurized concrete known as shotcrete is sprayed on the ceiling, walls, and sides. Additional structural support is provided by installing lattice girders.