Site preparation and soil improvement
Site preparation means getting the land ready. Steps: clear weeds, rubbish and loose stones; mark the plan on the ground with pegs and string; and grade (level or slope) the land.
Cut and fill: cut means digging away high ground; fill means adding soil to low ground. A good design tries to make cut and fill about equal, so no soil must be brought in or taken away. Fill is put in thin layers and pressed down (compacted), or it will sink later.
Soil improvement: poor soil is too hard, too sandy, too clayey or has little food. We loosen it by digging and add compost or manure (food and softness), sand for heavy clay, or clay and compost for very sandy soil. A top layer of 15 to 30 cm of good soil is common for lawns and flower beds.
Concrete work
Concrete work makes hard bases for paths, courts, steps, walls and footings.
- Set out and excavate the area to the right depth.
- Gravel base (about 10 cm), compacted. It gives a firm bed and lets water drain.
- Formwork: wooden or steel side boards that hold the wet concrete in shape.
- Rebar net: steel bars tied in a grid and raised on small blocks so they sit inside the slab.
- Pour and level the concrete, tap out air, and finish the surface.
- Cure: keep it damp for about a week.
Add joints every few metres so that cracks from heat and cold happen in the joints. Give outdoor slabs a very slight slope so water runs off.
Water supply and drainage work
Water supply brings clean water to taps, sprinklers and drip lines. Use pipes of the right size, a main valve to switch it off, and put pipes below the surface (about 30 cm) so spades do not hit them. Test for leaks before covering.
Drainage takes unwanted water away. Water flows only downhill, so every drain needs a slope (gradient). A common minimum for a drain pipe is about 1% (1 cm drop for every 1 m of length). Types: surface drains (the ground slopes to a drain), open channels, and sub-surface pipes in a gravel trench with holes that collect water from soil.
End the drain at a safe outlet: a storm drain, soak pit or pond. No slope means water stays: puddles, rotting roots and mosquitoes.
Try it
In the 3D: in the last step, set the slope to 0 and watch water stay. Raise the slope and watch it flow faster. Then increase rain. Does the pipe still keep up?
At home: pour a cup of water on a tray, then tilt the tray a little. Notice how water runs only when tilted. Measure how much you must lift one end to make it run (a small tilt is enough).
Key formulas and definitions
- Slope (%) = drop ÷ length × 100
- Drop = length × slope (%) ÷ 100
- Volume = length × width × depth (or thickness)
- Cut ≈ Fill is the aim of good grading
- Concrete order: gravel base → formwork → rebar → pour → cure
Worked examples
1. A drain pipe is 20 m long with a slope of 1%. How much lower is the outlet end than the start?
Drop = 20 × 1 ÷ 100 = 0.2 m = 20 cm.
2. A bed 10 m × 5 m needs a 0.15 m layer of improved soil. What volume of soil is needed?
Volume = 10 × 5 × 0.15 = 7.5 m³.
3. A court slab is 6 m × 4 m and 0.1 m thick. A truck carries 3 m³ of concrete. How many truck loads are needed?
Volume = 6 × 4 × 0.1 = 2.4 m³. 2.4 ÷ 3 = 0.8, so 1 truck load is enough (with a little spare).
Common mistakes
- Not compacting fill soil. It sinks and paths crack later.
- Pouring concrete with no gravel base or no formwork.
- Placing rebar on the ground. It must sit inside the slab, held up on small blocks.
- Laying drains flat or with the slope the wrong way. Water will not flow out.