Substructure Build Sequence
Before Substructure Starts
1. Site Clearance: Removal of any existing structures, debris, vegetation, or obstacles from the footprint of the building.
2. Soil Investigation: Conduct soil and geotechnical tests to assess the soil conditions and determine the appropriate foundation design.
3. Design and Engineering: Structural Engineers develop detailed engineering plans and designs for the substructure, including foundation types, dimensions, and load bearing capacity.
4. Licences and Approvals: Obtain all necessary permits and approvals from local authorities and regulatory bodies. For example, if there are any foundation works that need to happen on a public highway a local authority license may be required.
5. Utility Marking: Identify and mark the locations of underground utilities (water, gas, electricity, sewer) to prevent accidental damage during excavation. Could be done using pegs in the ground or spray paint.
6. Surveying: Conduct a topographic survey to establish existing levels on site and approximate ground to be removed.
7. Environmental Considerations: Address any environmental concerns or regulations related to the construction site, such as water courses, protected species or archaeological sites.
8. Access and Logistics: Plan for site access, temporary roads, and logistics for plant, materials and equipment delivery.
10. Site Establishment: Implement security measures to protect the site from unauthorised access and theft through fencing/hoarding. Also, provide adequate welfare facilities for operatives.
Constructing Substructure
1. Set out Substructure Plan: Mark out physically on site where elements of the substructure will be formed. Usually done by the Groundworker subcontractors engineer but Main contractors provide them with control points.
Total station - used by engineers to set out
2. Excavation: Dig trenches or excavate the area where the elements of the substructure will be cast.
It is important to ensure the excavation is done to the required depth and dimensions specified in the structural engineers drawing.
An excavator breaking ground
2.5 Pile Cropping: If the substructure requires pile caps the top part of the steel reinforcement in the exposed piles will need to be tied into the pile cap reinforcement.
To allow this a section of concrete will be broken out from the top of the pile.
3. Soil Compaction: Compact the soil at the base of the excavation to achieve the desired density and load-bearing capacity.
Roller used to compact ground
4. Formwork: Install timber or cordek shuttering in the shape of the foundations. Think of this as a mould for the concrete to be poured into.
Example of formwork shuttering for ground beams
5. Steel-fixing: Steel reinforcement is placed where it's required and tied with steel wire.
Steel reinforcement bars pre-fixing
6. Pre-pour check: This is an important Quality hold point. A main contractor representative should inspect the substructure element before concrete is cast.
They should check if it's in the correct place, is the correct size, if the concrete has enough cover and whether all required cast-ins are in place.
6. Pour Concrete: Concrete is delivered to site and can be pumped into the substructure element. An excavator bucket or dumper could also be used.
Concrete being poured
7. Concrete Curing: Process of maintaining adequate moisture and temperature conditions for enough time to allow newly poured concrete to hydrate and achieve its desired strength and durability. This curing process is critical for the long-term performance of concrete structures.
In most cases, there is no requirement for any additional measures when waiting for concrete to cure. If the weather is very hot additional water may need to be poured onto substructure element to aid curing.
After Substructure complete
Documentation and Record-Keeping: Groundwork subcontractors are usually responsible for maintaining accurate records of substructure construction, including inspection reports, as-built drawings, and concrete curing results.
This information should be kept on file by the Main contractor.
Handover to Superstructure Construction: Once the substructure is complete and has passed all inspections, hand over can be done through a form to the Main contractor ready for the superstructure to begin.
Definitions
Load Bearing Capacity - maximum weight/loading that a soil can support without excessive settlement or failure
Topographic Survey – often shortened to Topo survey, maps land features, elevations, and contours, helping with site planning and engineering Control Points - physical stickers or pins in the ground for which geographical co-ordinates are known
Concrete Cover - distance between the end steel reinforcement and the shutter in which concrete will be placed. If the cover is less than required the element will not operate as specified and this can cause issues
Cast-Ins - refers to objects or items that are embedded or cast into concrete during its pouring and curing process. For example, a post bracket to screw the bottom of a post into
Posts to Follow
We plan to go into more details on Substructure and add sections on:
· Health, Safety & Environment
· Quality
· Programme
· Commercial
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