Last edited 25 Mar 2021

Bedrock

Bedrock is rock that underlies loose deposits such as soil or alluvium. Ref The HS2 London-West Midlands Environmental Statement, published by the Department for Transport in November 2013.

The National Geographic Society suggests that ‘Bedrock' is the hard, solid rock beneath surface materials such as soil and gravel. Bedrock also underlies sand and other sediments on the ocean floor. Bedrock is consolidated rock, meaning it is solid and tightly bound. Overlying material is often unconsolidated rock, which is made up of loose particles.’ Ref https://www.nationalgeographic.org/encyclopedia/bedrock/

Identifying bedrock is an important part of civil engineering, as it can be used to help support built assets such as buildings, bridges and other structures. Foundations may be built onto the rockhead, that is the upper boundary of the bedrock. This can involve excavating through surface soils.

The depth of bedrock can be determined by desk studies, digging, drilling and other geophysical methods. It varies significantly at different locations, and necessitates different types of foundations or other structural supports.

Shallow foundations are typically used where the loads imposed by a structure are low relative to the bearing capacity of the surface soils. This might include; strip foundations, pad foundations or raft foundations. Raft foundations are slabs that cover a wide area, often the entire footprint of a building, and are suitable where ground conditions are poor, effectively floating on poor ground like a raft.

Deep foundations are necessary where the bearing capacity of the surface soils is insufficient to support loads imposed and so they are transferred to deeper layers with higher bearing capacity. Deep foundations are typically formed by piles, which are long, slender, columns typically made from steel or reinforced concrete, or sometimes timber.