Phase 3: Build

Preparing the ground

These activities help students to establish what work takes place to prepare the ground before building can begin. They explore some common foundation types and get students to consider when each might be used.

  • You could link this topic to a survey of your area to find out the state of brownfield sites (do not enter!). You could also find out, for example from your County Surveyor or local library, what soil types exist in your area.
  • This can also link to Infrastructure and utilities in Phase 2, and Site safety, when identifying hazards on an old brownfield site.

Groundworks and foundations

Introduction

  • Establish what a brownfield site is, using local examples. What might be left from the previous buildings and their infrastructure? What hazards?
  • Discuss why the ground needs to be prepared – what might happen if a building is constructed on ground that is not firm and level?

Main activity

  • Use Groundworks with the group. First, put the stages in order. Then, match the right explanation.
  • Consider flat and sloping sites, and the work required to cut and fill.
  • Briefly discuss the benefits of rubble recycling, and construction plant, as time permits.
  • Use Foundations to explore each type and match to the building.>

Plenary

  • Use a few more building ideas to review what students have learned.

Differentiation

Easier/Level 1:
Prepare a template table, adding stages in order if you think appropriate. Omit discussions of bearing capacity – talk in terms of hard and soft ground. Use shoe heels as an analogy – compare a flat heel with a stiletto. Remind students that foundations also depend on the type and height of the building.

Harder:
Get students to research subsoil types: gravel, sand, clay etc. and group them into ‘high load-bearing’ and ‘low load bearing’. Add other building examples to the list.

Notes

Add functional maths activities by getting students to work out the volume of concrete needed for each type of foundation. Give them dimensions for a strip, deep strip, raft and pile. Provide formulae if necessary.

Answers: Groundworks

Brownfield sites require preparation for a range of reasons that depend on the site’s prior use. They include removal of old structures, stabilising loose ground, creating a new ground level, importing suitable topsoil, removal of hazardous materials and decontamination.

Correct order for the work:

Site survey and tests – Establishing the work to be done and the bearing capacity of the subsoil.
Clearance – Removal of waste, hazards and the remains of old buildings.
Excavation and filling - Stripping away the ground or adding hardcore to create a level surface at the right level.
Compacting – Compressing and flattening to create a final surface.
Stabilisation – Adding concrete or hardcore to areas that are less stable.

Using non-hazardous rubble for filling and stabilising minimises the need to quarry for new aggregates, keeps these materials out of the waste stream, and reduces the carbon emissions from quarrying and transportation.

Answers: Foundations

Bearing capacity is the amount of pressure that the supporting soil can take without causing movement in the soil. Engineers must know the load per unit area that the building will exert on the soil. Bearing capacity is measured in kN/m2.

15 storey office building – Combination of piles/pads, connected by deep strip or concrete beams (to support large downwards pressure).
Single storey visitor centre on sandy ground – Raft (provides uniform stability).
Timber framed sustainable house – Pads (minimises concrete used).
3-bedroom house – Strip (standard approach).

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