Definition - What does Unconsolidated Deposit mean?
Unconsolidated deposits are the initial result of natural weathering processes that breakdown larger rock into smaller ones.
These deposits consist of loose material like sand, silt, clay and gravel which is neither stratified nor bound together and allow water to flow in between the grain spaces. Encountering unconsolidated deposits during trenchless construction processes such as horizontal directional drilling (HDD), microtunneling and pipe jacking is not uncommon. Dealing with them is important in order to prevent causing soil instability.
Trenchlesspedia explains Unconsolidated Deposit
Sometimes tunnels or pipeline excavation is carried out in the unconsolidated or soft ground. This raises concern about the stability of the excavation face and safety of workers. 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 heaving or collapse of the ground surface.
Controlling this movement during excavation especially in the shallow overburden is very important. For excavating a tunnel with shallow overburden in the soft or unconsolidated soil, the cut and cover method are 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.