3.2 Foundations

• The functions and functional requirements of a foundation
• Types of foundations: strip, pad and raft (shallow foundations)
• Setting out and preparing trenches for a strip foundation
• Laying a strip foundation, and safety measures

• describe the types of foundations used in building construction
• set out a strip foundation from working drawings
• prepare trenches for the construction of a strip foundation
• lay a strip foundation for a building
• acknowledge the importance of foundations in a building

“Why is a foundation important to a building?”

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1. What a foundation does
   40 min · 1 practice tasks · quiz
   The purpose of a foundation: spreading the building load over enough ground to carry it, and anchoring the building.
2. The functional requirements of a foundation
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   The six things a foundation must achieve, and the failure that follows from ignoring each one.
3. What the ground is made of
   40 min · 1 practice tasks · quiz
   Topsoil, subsoil and the firm bearing stratum, and the four soils a builder in Kenya will meet.
4. Bearing capacity: pressure, not weight
   40 min · 1 practice tasks · quiz
   How pressure is calculated from load and area, and how the width of a foundation is worked out from the soil.
5. Settlement and differential settlement
   40 min · 1 practice tasks · quiz
   Why all buildings settle a little, why uneven settlement is what cracks them, and how to read the cracks.
6. The strip foundation
   40 min · 1 practice tasks · quiz
   The commonest foundation type: its parts, its proportions, and why the projection is limited.
7. The pad foundation
   40 min · 1 practice tasks · quiz
   The foundation for a point load: what a pad is, where it is used, and how its size is worked out.
8. The raft foundation
   40 min · 1 practice tasks · quiz
   A slab under the whole building: when a raft is used, and why it deals with poor ground so well.
9. Sketching shallow foundations
   40 min · 1 practice tasks · quiz
   The drawing conventions for a foundation section, and what must appear on every foundation sketch.
10. Choosing the foundation type
    40 min · 1 practice tasks · quiz
    Two questions that settle most foundation choices, and knowing when to say the job needs an engineer.
11. Reading a foundation plan
    40 min · 1 practice tasks · quiz
    Finding the information on a foundation plan, and the one question to ask of every dimension.
12. Datum, levels and the building line
    40 min · 1 practice tasks · quiz
    Setting a permanent datum, carrying levels across a site, and the legal building line.
13. Setting out a right angle
    40 min · 1 practice tasks · quiz
    The 3-4-5 method for forming a true right angle with a tape, and why bigger multiples are more accurate.
14. Profile boards and lines
    40 min · 1 practice tasks · quiz
    Why setting-out marks are transferred to profile boards clear of the trench, and how the boards are made and set.
15. Setting out a building, step by step
    40 min · 1 practice tasks · quiz
    The fixed sequence for setting out a rectangular building, and why the order matters.
16. Checking squareness with the diagonals
    40 min · 1 practice tasks · quiz
    Why equal sides prove nothing and only equal diagonals prove a shape is square.
17. Excavating the trench
    40 min · 1 practice tasks · quiz
    Digging to line and level, keeping the sides vertical and the bottom undisturbed, and never backfilling an over-dig.
18. Trench safety
    40 min · 1 practice tasks · quiz
    Why trenches collapse, how quickly they kill, and the measures that prevent it.
19. Water in the trench
    40 min · 1 practice tasks · quiz
    How groundwater and surface water affect a trench, and how they are dealt with before concreting.
20. Levelling the trench bottom
    40 min · 1 practice tasks · quiz
    Setting pegs to the concrete level, and why foundations on sloping ground are stepped and never sloped.
21. Concrete for foundations
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    Batching a foundation mix by gauge box, and why extra water is the commonest and costliest site mistake.
22. Placing and compacting the concrete
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    Placing in layers, compacting properly, avoiding segregation, and finishing to the peg tops.
23. Curing the concrete
    40 min · 1 practice tasks · quiz
    Why concrete gains strength by reacting with water rather than drying, and how to cure in a hot climate.
24. Foundation defects and their causes
    40 min · 1 practice tasks · quiz
    The common defects, the decisions that caused each, and why almost none of them are bad luck.
25. The whole foundation process
    40 min · 1 practice tasks · quiz
    The ten stages from soil investigation to curing, the check at each, and the answer to the inquiry question.