PERFORMANCE OF SOCKETED MICROPILES IN WEAK SOILS-Paper

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The study evaluates gravity-grouted Type A micropiles as a foundation rehabilitation method for Tikrit University’s Building No. 12, which developed severe cracking and settlement. Site investigations identified poorly compacted, weak gypseous silty sand extending more than 6 m; the soil is prone to collapse when wetted.<br /><br />The researchers used ABAQUS finite-element modeling to analyze axially loaded micropiles embedded in weak soil and either resting on or socketed into a dense layer. Models covered pile lengths of 5–20 m, diameters of 0.1–0.3 m, and socket lengths equal to 5–20% of total pile length. Soil behavior was represented using the Mohr–Coulomb model.<br /><br />Results showed that increasing the socket length generally increases ultimate capacity. The capacity ratio of socketed piles to piles resting on the dense layer ranged from 1.029 to 1.487. Longer piles tended to achieve greater gains, while pile diameter had little influence on the capacity ratio. Increasing the soil’s friction angle reduced the additional benefit of socketing, because the surrounding soil properties became more similar. Most load was transferred through shaft friction; end bearing was not fully mobilized. For long piles, load–settlement curves did not show a clear failure point.<br /><br />For rehabilitation, the authors recommend 0.2 m diameter micropiles socketed 20% of their length into dense soil, installed at 2 m center-to-center spacing. This arrangement is expected to transfer building loads to stronger ground and may also densify the surrounding soil. The findings are based on numerical modeling and address the specific soil and foundation conditions examined.

Keywords

gravity-grouted micropiles

foundation rehabilitation

Tikrit University Building No. 12

gypseous silty sand

severe cracking and settlement

ABAQUS finite-element modeling

socketed micropiles

Mohr-Coulomb soil model

shaft friction

load settlement behavior