What system is utilized for restraining a vertical wall of soil in densely populated areas?

The system utilized for restraining a vertical wall of soil in densely populated areas is indeed cribbing and tie-backs. This method is particularly effective in urban settings where space is limited and there is a high density of surrounding structures.

Cribbing refers to the use of a framework, often made of timber or other durable materials, that provides support to the soil or other materials being retained. This framework helps distribute loads and prevents soil from collapsing. Tie-backs are additional supports that anchor the cribbing to more stable ground, which stabilizes the vertical wall and resists lateral soil pressure.

Using cribbing and tie-backs allows for a more secure and effective means of managing earth retention without the extensive excavation or space that other methods might require. This makes it ideal for projects in crowded environments where existing buildings and infrastructure limit the alternatives available.

In contrast, mobilization pertains to preparing and moving construction equipment to site locations and isn't related to soil restraint. Underpinning is a technique used when existing foundations need reinforcement, but it doesn't focus directly on restraining vertical soil walls. Cofferdams are temporary enclosures used to keep water out of a construction site, primarily in aquatic environments, rather than for soil restraint in urban areas.