Foundations

Foundations

1. Types

   • Shallow <3m
     • Raft
       • weak in point loads
       • Expensive
       • Used in mixed soil types
       • Reinforced concrete under entire building
       • Used on compressive soils (clay)
       • Designed to spread entire load
       • Only shallow excavation required
       • Foundation and floor slab combined (saves time and material)
     • Pad
       • Spreads load of columns
       • Low cost (minimal concrete needed)
       • Reduce excavation time
       • Cannot take excess weight
       • Ideal for point loads
     • Short bored pile
       • Used for large loads
       • Transfers loads to deep bearing strata
       • Can be used on tight sites
       • Can be problematic if boulder/debris in ground
       • Noisy construction
       • Expensive
       • Placed - Corners, openings, spaced along walls, high loads ie. chimeys
     • Strip
       • Cheap due to narrow design
       • Limited load carrying
       • Limited depth (2-2.5m due to cost)
       • H & S implications (working at depth)
       • Suited to load bearing walls
       • Traditional design so understood by work force
   • Deep >3m
     • Piles
     • Piers
     • Caissons

2. Strip Design

   • Depth
     • 0.45m Min (prevent frost damage)
     • 1m in clay
     • Increased depth for trees
   • Thickness/Projection
   • Foundation near services
   • Stepped
     • Stages
       • 1. Calculate difference in height (bottom of foundation) ie. 101-99m = 2m
       • 2. Divide difference by block height + 10mm mortar (0.225m) 2m/0.225m = 8.88
       • 3. Round down for steps 8.88 = 8 steps
       • 4. 8 steps x Block (0.225m) = 1.8m (total height gained)
       • 5. Add height gained to lower height for the depth of higher side
       • 6. Draw steps
     • Profile

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