The short answer
From June to September, earthwork and granular layers lose most of their working days, a quarry loses some to flooded floors, and a crusher slows on wet feed. Close every open subgrade and GSB front before the rain, build a stockpile of crushed stone for the first weeks of laying afterwards, and use the wet months for liner changes, plant moves and structures.
The monsoon is the one delay on a highway package that arrives on a known date. It still catches programmes every year, mostly because the last dry fortnight gets spent opening new fronts instead of closing the ones already open.
01What rain does to each activity
| Activity | What goes wrong | What still works |
|---|---|---|
| Embankment and subgrade | Soil above optimum moisture cannot be compacted to density | Short windows in sandy soils; drainage and slope protection |
| GSB and WMM laying | Layer goes down on a saturated formation and pumps under the roller | Little, until the formation dries back |
| Bituminous work | Cannot be laid in rain or on a wet surface | Nothing on wet days |
| Quarry face | Water on the pit floor, wet holes, slippery ramps, lightning stoppages | Upper benches, with pumping |
| Crushing | Sticky fines blind the screens; clay carries into the product | Coarse products, at a reduced rate |
| Haulage | Soft haul roads, village roads closed to heavy vehicles | Surfaced routes |
02Before the rain
- Stop opening new earthwork fronts about a month ahead. Everything open should be brought up to a sealed layer and shaped to shed water.
- Cover finished subgrade with GSB, and finished GSB with WMM where the programme allows. An exposed subgrade will be re-done.
- Cut the drains. Side drains, outfalls and temporary cross drains matter more to the next four months than any other item.
- Push the crusher. The dry weeks before the monsoon are the best production of the year, and stone made now is laid in October.
- Move pumps, explosive and spares to the quarry before the approach road softens.
03How much to stockpile
Work out what the laying fronts will take in the first six weeks after the rain stops, when every paver on the package starts on the same Monday. That is the stock to have on the ground. A plant that restarts at the same time as the laying cannot serve it, because it is only then beginning to dry out its own feed.
Stockpiles need a little care to be worth having. Build them on a hard, sloped base so the bottom layer is not lost to mud. Keep sizes apart, with room for a loader between them. Shape the tops to shed water. Do not run tippers over the top of a graded pile, which crushes and segregates it.
04Wet stone weighs more
Stone bought over a weighbridge in the monsoon includes water. Coarse aggregate holds little, about one per cent. Crusher dust and the fine end of GSB can hold several per cent, and that water is paid for at the price of stone. Where the tonnage is large, agree in advance how moisture in the fine products will be handled. It is a small clause that prevents a large reconciliation.
05What the wet months are for
- Changing jaw plates, cone liners and screen decks that would otherwise stop the plant in November.
- Relocating a plant, if one has to move, so that the lost weeks are weeks that were already slow.
- Structures: culverts, minor bridges and retaining walls, which suffer least from rain.
- Stripping overburden for the next benches, which can go on in conditions that stop production drilling.
- Sorting out permits, royalty accounts and weighbridge verification while the dispatch clerk has time.
06Restarting
The first job after the rain is not laying. It is checking what the rain did. Subgrade left exposed needs its density and moisture tested again before anything goes on top. Granular layers that were trafficked wet may have fines pumped to the surface and need scarifying and relaying. Starting a week later on sound layers is quicker than starting on time over a soft one.