The Impact of end bearing plate on Micropile capacity casted in cohesive soil-Paper

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The study examines whether an end-bearing plate increases the axial capacity of micropiles installed in cohesive soil. Field tests were conducted at the University of Khartoum’s site in Soba, Sudan, where the soil profile included low-plasticity silty clay near the surface, underlain by clayey sand and deeper high-plasticity silty clay.<br /><br />Eight tested micropiles are reported in the results table: four without end-bearing plates and four with plates. They had the same diameter and 4 m length and were pressure-grouted at 1 MPa. Compression load tests were carried out using a quick maintained-load procedure, loading the piles up to three times the design working load.<br /><br />Failure loads for piles without plates ranged from about 160 to 202 kN, averaging approximately 189 kN. Those with plates ranged from about 154 to 195 kN, averaging approximately 178 kN. Thus, the plated piles did not show higher capacity; their average failure load was roughly 6% lower.<br /><br />The authors explain that micropile resistance is primarily provided by shaft friction, while the small pile-tip area makes end bearing relatively insignificant. They also suggest that a plate may restrict downward movement at the pile tip and increase the likelihood of grout crushing under compression. The study concludes that an end-bearing plate provided no positive capacity benefit under the tested conditions. These findings are specific to the materials, installation method, and limited field-test program described.

Keywords

micropiles

end-bearing plate

axial capacity

cohesive soil

field tests

compression load test

shaft friction

grout crushing

pressure grouting

Sudan