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Last edited 04 Sep 2020
Groundworks on construction projects
The term ‘groundworks’ refers to work done to prepare sub-surfaces for the start of construction work. Aside from any demolition or site enabling works that may need to be carried out, groundworks are usually the first stage of a construction project and may include:
- Ground investigation.
- Site clearance.
- Substructure and ground stabilisation works.
- Site services.
As a matter of good practice and a legal requirement of most local authorities, a ground investigation of the site is generally carried out to help identify past land uses, stability and potential problems. These investigations allow data to be accumulated and used for effective design, as well as allowing any potential defects or issues, such as contamination or abandoned mine workings, to be considered.
As part of the initial preparatory works, the site will generally need to be cleared and the topsoil taken up from the footprint of the structure. The depth will depend on the lay of the land, and if it is a sloping site then the ground may need to be levelled. If required, retaining walls may be constructed in order to create level development platforms.
 Substructure and ground stabilisation
Substructure is defined by the RICS as ‘All work below underside of screed or, where no screed exists, to underside of lowest floor finishes including damp-proof membrane, together with relevant excavations and foundations (includes walls to basements designed as retaining walls).’
Retaining walls can be made from stone, brick or blockwork, reinforced concrete or timber. Basement excavations commonly use sheet piling which is a relatively cheap method of retaining wall construction. This involves the use of a large scale hydraulic jack hammer to drive steel sheet piles into the ground and interlocked, forming a continuous wall.
Other methods of ground stabilisation include:
Steel cables with metal wedges on their ends. The metal wedge end is driven pneumatically into the slope face to the desired depth, the cable pulled taut and attached to a finishing plate to maintain tension.
These can be incorporated into retaining walls and embankments and provide reinforcement. Geotextiles are woven and allow the passage of ground water through them. Geomembranes are impermeable and are typically used as liner materials. Geocomposites combine both materials.
Foundations provide support for structures, transferring their load to layers of soil or rock that have sufficient bearing capacity and suitable settlement characteristics. There are a very wide range of foundation types suitable for different applications, depending on considerations such as:
- The nature of the load requiring support.
- Ground conditions.
- The presence of water.
- Sensitivity to noise and vibration.
Very broadly, foundations can be categorised as shallow foundations or deep foundations. Shallow foundations are typically used where the loads imposed by a structure are low relative to the bearing capacity of the surface soils.
Deep foundations are necessary where the bearing capacity of the surface soils is not adequate to support the loads imposed by a structure and so those loads need to be transferred to deeper layers with higher bearing capacity.
Site services may include temporary and permanent drainage and other utilities connections. Complex sites may require specialist tunnelling or shaft sinking solutions to enable service ducts and cabling to the installed. Existing services such as water and electricity cables may also need to be altered.
|D20||Excavating and filling|
|D21||Ground gas collection and venting systems|
|D40||Embedded retaining walls|
|D41||Crib walls, gabions and other gravity retaining walls|
 Related articles on Designing Buildings Wiki
- Building foundations.
- Continuous flight auger piles.
- Diaphragm wall.
- Driven piles.
- External works.
- Ground conditions.
- Ground heave.
- Ground improvement techniques.
- How deep should foundations be?
- Pad foundation.
- Pile foundations.
- Raft foundation.
- Retaining walls.
- Screw pile foundations.
- Sheet piles.
- Temporary works.
- Trial pit.
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