Piling and ground engineering

How does Piling and ground engineering work, step by step?

1. 1

   Step 1: Let the ground choose the technique

   The ground investigation, the loads and the constraints between them narrow the technique long before any rig is priced. Soil and rock profile, water table, obstructions, contamination, the proximity of neighbours and the sensitivity to noise and vibration all bear on it. A technique that is efficient in one ground condition is unusable in another, and the specialist contractor and the geotechnical designer settle this together. Selecting on rate alone, before the ground is understood, is how projects find themselves with a rig that cannot get through the made ground it has been sent to drill.

2. 2

   Step 2: Design, build and certify the working platform

   The platform is the single most important temporary works item on a piling project. The temporary works designer specifies the formation, the build-up, any geogrid or reinforcement, the gradients, the drainage and the stand-off from every excavation, basement, culvert and service. It is constructed, tested and certified in writing before a rig arrives, and the certificate is a live document: the platform is inspected on a set frequency, after heavy rain and after any excavation nearby changes the geometry, and it is repaired and re-certified when it deteriorates. This is not paperwork; it is the control that keeps the rig upright.

3. 3

   Step 3: Locate services, obstructions and the things nobody drew

   Before any rig position is used, buried services, old foundations, basements, tanks, wells, culverts, mine workings and archaeology are researched, scanned and where necessary proved with trial pits or probes. Overhead lines are identified and the mast height considered against them, because a piling mast is tall enough to reach lines that other plant passes safely beneath. Obstructions found during the works are reported and dealt with by the designer rather than drilled through on the assumption that they are unimportant.

4. 4

   Step 4: Mobilise the spread and lay it out

   The rig arrives with a supporting spread: service crane, concrete or grout supply, spoil handling, bentonite mixing and recycling where the technique needs it, testing equipment, welfare and storage. Laying that out is a real planning exercise, because the support plant needs to reach the rig throughout the campaign as the rig works across the site. Access for concrete trucks, spoil removal and reinforcement delivery is planned along the same lines. A well-laid-out piling spread keeps the rig drilling; a poorly laid-out one leaves an expensive machine waiting for concrete.

5. 5

   Step 5: Erect the mast and set up under specialist control

   Rigs are delivered in parts and assembled on site by the supplier's or specialist contractor's competent crews, with mast erection carried out under a lifting plan using a service crane. This is a hazardous operation with a clear exclusion, and it is not something the project's own people take part in. Once erected the machine is checked, its monitoring and recording systems are commissioned, and it is handed over for work. Moving the rig between working areas, and any change to the mast or tooling, is planned in the same way.

6. 6

   Step 6: Install the works and record what the rig did

   Piles and ground treatment are installed to the design layout, with the rig recording depth, torque or energy, concrete or grout volumes and the other parameters the technique produces. Those records are the first quality document on the job and they are reviewed daily, not filed. A pile that took markedly more or less concrete than its neighbours, or refused short of design depth, is investigated at the time. Spoil, water, grout and bentonite returns are contained, treated and disposed of under the arrangements agreed for the site.

7. 7

   Step 7: Test, trim and hand over

   Verification follows the specification: integrity testing, static or dynamic load testing, and testing of treated ground where ground improvement has been used, at the frequencies set before mobilisation rather than negotiated after a poor result. Piles are trimmed down to cut-off, which is a separate operation with its own dust, noise and hand-arm vibration issues, and the heads are prepared for the pile caps. Records, test results and as-built positions are handed over as a set, and any pile outside tolerance is referred to the designer rather than adjusted on site.