Design of Drilled Shafts Supporting Sound Walls-Article

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The study evaluates design methods for drilled-shaft foundations supporting highway sound walls, where inconsistent analysis methods, safety factors, and deflection limits have led to conservative and costly designs.<br /><br />Researchers compared existing methods against full-scale lateral-load tests: seven tests in clay and five in sand from previous studies, plus two instrumented tests in Colorado. They assessed methods for predicting ultimate capacity and load–deflection behavior, and examined how soil parameters derived from SPT, laboratory tests, and pressuremeter tests affected results.<br /><br />The authors recommend a combined strength-and-serviceability approach. Use Broms’ method to determine shaft length for ultimate capacity, with a factor of safety of 2, for shafts in both cohesive and cohesionless soils. Then use COM624P or LPILE to check shaft-head deflection under design loading. A permissible deflection of 1 inch (25.4 mm), or a limit set by the structural engineer, is recommended. If the deflection limit is exceeded, use COM624P or LPILE to determine the required shaft length.<br /><br />For soil characterization, laboratory testing is preferred for clay, while SPT values interpreted using Liang’s correlations are recommended for sand; pressuremeter testing also provides reasonable estimates. The proposed approach aims to make designs more consistent and cost-effective. In the cited Colorado project, it reduced required shaft length by 25% compared with the original design approach.

Keywords

drilled-shaft foundations

highway sound walls

lateral-load tests

ultimate capacity

load-deflection behavior

Broms method

COM624P

LPILE

SPT correlations

pressuremeter testing