Serviceability Limit State Design: Base Response of Screw Injection Piles-Paper

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The study evaluates methods for predicting the serviceability-limit-state (SLS) load–displacement response of screw injection piles in sand. These piles are installed using rotation, downward force and grout injection, but design standards offer limited guidance on their settlement behavior.<br /><br />Researchers compared instrumented static load tests on three screw injection piles at two Dutch sites—Amaliahaven and Delft—with a driven closed-ended pile. They assessed the Dutch NEN 9997-1 type-curves and a stiffness-based prediction method that uses the in-situ stiffness of the soil beneath the pile base.<br /><br />The screw injection piles mobilised base resistance more gradually than the driven pile at Amaliahaven. Their initial stiffnesses broadly matched the soil’s pre-installation stiffness, indicating little or no prestressing around the pile base. The driven pile was initially much stiffer, likely because driving prestressed the surrounding soil. At a base displacement of 10% of pile diameter, the screw injection piles reached a normalised base resistance of about 0.28, roughly half that of the driven pile.<br /><br />The stiffness-based method predicted the measured base response well at both sites, particularly at Amaliahaven, where the standard type-curve substantially overestimated initial stiffness. At Delft, both approaches performed similarly.<br /><br />The findings indicate that in-situ soil stiffness is a useful basis for predicting screw injection pile settlement in sand and may provide a more adaptable SLS design method than fixed type-curves. The approach could also improve the interpretation of proof-load tests and help verify pile capacity after installation. The authors recommend direct geophysical measurements of soil stiffness where possible, while noting that further work is needed on CPT-based stiffness correlations.

Keywords

screw injection piles

serviceability limit state

load-displacement response

sand settlement

Dutch NEN 9997-1

stiffness-based prediction

in-situ soil stiffness

base resistance

instrumented static load tests

pile settlement behavior