Lateral Load Testing Micropiles to Evaluate the Impact of Threaded Joints and Casing Embedment on Short Micropiles in Shallow Rock-Article

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The study evaluated how threaded casing joints and rock-socket embedment affect the lateral behavior of micropiles used for bridge foundations in shallow rock. Researchers tested ten 273-mm-diameter steel-cased micropiles, installed in pairs and pulled laterally. The piles had 0.3, 0.6, 1.5, or 3.0 m of rock embedment. Loads and pile-head displacements were measured, while inclinometers tracked deflection with depth. Vibrating-wire strain meters in two piles recorded bending strains.<br /><br />Piles embedded 0.6, 1.5, and 3.0 m carried lateral loads exceeding 180 kN. By contrast, the 0.3-m embedment piles rotated in the socket and could not sustain load. In tests taken to failure, piles generally showed little deflection before a sudden failure at a threaded joint; excavation confirmed joint separation, thread damage, and crushed grout. One pile with 3.0-m embedment failed at a lower load than expected, possibly because of construction damage. Strain measurements showed that bending moment was transferred across the joint and reduced within the rock socket.<br /><br />Initial numerical predictions were generally less stiff and strong than the field results. The researchers calibrated the FB-Multipier model using measured bending moments and load–deflection data, adjusting the assumed casing yield strength and soil parameters. The calibrated model reasonably reproduced most test responses, although one test showed some mismatch.<br /><br />The findings indicate that modest rock embedment can provide adequate lateral resistance when joint capacity governs, while very shallow embedment is inadequate. They also demonstrate that strain meters embedded in grout can capture useful bending-moment profiles. The authors caution that the tests involved specific pile dimensions, materials, and site conditions, so project-specific design and assessment of casing joints remain important.

Keywords

micropiles

lateral behavior

threaded casing joints

rock-socket embedment

bridge foundations

load-displacement response

bending moment

inclinometer measurements

grout strain meters

FB-Multipier model