Geotechnical investigation

Most sites in the Maldives sit on coral sand over porous coral rock, and many are on newly reclaimed land or in a lagoon. We drill, test and log that ground, on land and over water, and turn the results into foundation recommendations a designer can use.

Onshore drilling

Rotary boreholes of about 100 mm diameter. On land we flush with bentonite mud in a closed, recirculating pit, so drilling fluid stays on site. Each hole is backfilled and the location restored when the work is done.

Offshore and lagoon drilling

For lagoons, reef flats and nearshore structures we drill from our jack-up barge. It stands on four spuds with chain blocks, with the deck raised about 1 ft (0.3 m) above the highest high tide, so work carries on through the tidal cycle. Boreholes are advanced by seawater wash boring inside HX or NX casing, and each position is fixed by GPS.

Standard Penetration Tests

• Tests to ASTM D1586 with an automatic trip hammer (63.5 kg, 760 mm drop). The hammer releases from the same height on every blow, which takes operator variation out of the count.
• N is the blow count for the last 300 mm of a 450 mm drive.
• Tests are closely spaced in the upper 3 m, then every 1.5 m.
• Holes typically run to 25 m, or at least 5 m into ground with N above 50, so a cemented layer is not mistaken for rock.
• Groundwater level is read at the end of drilling and again after 24 hours.
• Field N values are corrected to N60 and (N1)60 for hammer energy and overburden before they are used in design.

Sampling and logging

• Disturbed samples from the split spoon for classification and laboratory testing.
• Undisturbed (Shelby tube) samples in soft to stiff clays, with pocket penetrometer readings on cohesive samples.
• Borehole logs prepared to BS 5930.
• Control boreholes taken to 30 m or more where the design calls for it.

See what a SIDCO report contains and the standards we work to.