A tunnel built in soft ground – such as clay, silt, sand, gravel, or mud – requires specialized techniques compared to hard rock, to support the unstable nature of the soil. At WSP, we have extensive experience with soft ground tunnels on every continent and we pride ourselves on developing innovative strategies to deal with even the most complicated soil characteristics while preserving stability. There is a wide variety of techniques for soft ground tunnelling, and the best fit is ultimately determined by ground type, program, budget, and surrounding structures.

Putting our soft ground tunnelling to work for you

To select the most appropriate method for a particular tunnel, several factors need to be considered, including but not limited to ground conditions, length, depth, diameter, alignment geometry, and budget. Another important consideration is the risk and sensitivity of nearby infrastructure and buildings to ground movement.

At WSP we know that an important aspect of soft ground tunnelling is the protection of existing structures and utilities, as many soft ground tunnels are located in sensitive urban environments where settlement caused by tunnelling is a major concern. Protective measures such as ground improvement, compensation grouting, and positive pre-support can be used to tunnelling in soft ground successfully.

Shaft design and construction

We recognize that shafts are critical to the construction and operation of tunnels structures. They enable access from the surface to the tunnel level, including passenger access to underground mass transit and rail tunnels. They act as drop shafts for wastewater tunnels and down take and uptake shafts for water supply tunnels, as well as inlet and outlet structures for flood control tunnels and dams. Shafts also provide ventilation for highways, mass transit, and rail tunnels.