Performance of Large-Diameter Bored Pile Socketed in Sandstone and Siltstone in Thailand-Paper

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The paper evaluates the load-transfer and settlement behavior of large-diameter bored piles constructed in aeolian soils and socketed into sandstone or siltstone in northeastern Thailand. The analysis uses seven instrumented static compression tests on 1.2- and 1.5-m-diameter piles, with socket lengths of 1–3 pile diameters, tested to 2.5 times their safe working loads. Conventional analytical methods were used to estimate settlement and back-analyze shaft friction and end bearing.<br /><br />At the safe working load, pile-head settlements were approximately 2–3 mm. Even at maximum test load, settlement remained below 1% of pile diameter, indicating that shaft resistance and end bearing were not fully mobilized. Pile settlement estimates were generally consistent with measurements for piles founded in soil, but less accurate for siltstone, likely because rock quality and weathering varied. Shaft shortening accounted for about 70–80% of total head settlement.<br /><br />For siltstone, measured mobilized unit shaft friction was reasonably represented by 0.1–0.3 times the square root of unconfined compressive strength, lower than values reported for fully mobilized resistance. The limited shaft movement during testing may explain the difference. Mobilized end bearing in siltstone exceeded that in soil but also remained below design estimates. For sand, accounting for high overconsolidation improved estimates of shaft friction, while conventional methods generally provided reasonable estimates for clay.<br /><br />The authors conclude that pile response depends on founding material, socket conditions, and stress history. More extensive testing, particularly at greater settlements, is needed to establish fully mobilized resistance in these sedimentary rocks.

Keywords

bored piles

load-transfer behavior

settlement analysis

aeolian soils

sandstone sockets

siltstone

static compression tests

shaft friction

end bearing

northeastern Thailand