Earthmoving

How does Earthmoving work, step by step?

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   Step 1: Quantify the earthworks and set the balance

   The starting point is the volume of material to be moved, its condition, where it comes from and where it goes. A cut-and-fill balance that keeps material on site avoids both disposal cost and import cost, and it drives the whole plant selection. The ground investigation says whether the material is suitable for reuse, whether it needs treating and whether it is contaminated. Getting this wrong is expensive in both directions, and it is the single largest commercial variable on an earthworks project.

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   Step 2: Match the fleet so nothing waits

   Plant is selected as a system rather than as individual machines. The excavator size sets the loading rate, the number and size of haulers has to match that rate over the haul distance, and the placing and compaction plant has to keep up with what arrives. A well-matched fleet keeps every machine working; a mismatched one leaves expensive plant idling. Haul distance, gradients, site speed limits and the number of loading points all feed the calculation, and it is revisited when the site layout or the weather changes the cycle times.

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   Step 3: Locate services and clear the ground

   Before anything breaks ground, records are obtained, the area is scanned and traced, and services are marked and proved. Trial holes are dug carefully by hand or by vacuum excavation where a service is expected. Overhead lines are identified and goalposts or exclusions set. Underground structures, tanks, wells, culverts, mine workings and old foundations are all part of the same exercise. Striking a live service with a bucket injures people and stops the project, and the time spent on this step is trivial against the cost of getting it wrong.

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   Step 4: Design the haul routes, platforms and excavation stand-offs

   Haul routes are constructed and drained rather than worn into existence, with gradients, widths, passing places and crossing points set out and maintained. Where plant works close to an excavation, on made ground, on a slope or above a basement or culvert, the platform and the stand-off are designed by the temporary works designer. Excavation support or battering is designed and installed, and nobody enters an unsupported excavation on the basis that the ground looks stable. Routes and platforms are re-inspected as the site changes and after heavy rain.

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   Step 5: Excavate and haul to the design surface

   Material is dug, loaded and hauled in the sequence the earthworks design sets, with the working faces kept safe and the machines positioned so the operator can see what is around them. Machine control makes cutting to a designed surface far more accurate and reduces the setting-out and checking effort, but the survey control it depends on is still established and verified conventionally. Material suitable for reuse is separated from material that is not, and contaminated material is segregated and handled under the arrangements agreed for it.

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   Step 6: Place and compact in controlled layers

   Fill is placed in layers and compacted with the plant and the number of passes the specification requires, at a moisture content the material will actually compact at. Layer thickness, plant type and pass count are proved in a trial area and then held to. Testing during placement confirms the result rather than the intention. Compaction is where earthworks quality is won or lost, because a fill that was placed too thick or too wet will show up later as settlement under a slab, a road or a building, by which time it is somebody else's problem and a very expensive one.

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   Step 7: Trim, drain and protect the formation

   The finished surface is trimmed to level, proof-rolled where the specification requires, and drained so water runs off rather than sits on it. Formations are protected from weather and from site traffic, because an accepted formation left open through a wet week is no longer an accepted formation. Where the earthworks are handing over to another trade, the condition at handover is recorded, and the responsibility for keeping it in that condition is made explicit rather than assumed.