A Soil Quake Davisson Offset Method for Drilled Foundations-PPT Presentation

PPT Presentation

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The document presents a modified Davisson Offset Limit (DOL) method for interpreting the ultimate axial capacity of drilled foundations. Load–displacement curves commonly include an initial linear region, a nonlinear transition, and a final near-linear region. Because many failure-load interpretation procedures rely on graphical extrapolation, their results can be uncertain.<br /><br />The original 1972 Davisson method was developed for driven piles. Applied to drilled foundations, its prescribed soil-quake displacement—B/120—often produces an overly conservative capacity estimate, because drilled foundations typically require greater movement to mobilize their capacity. Davisson later suggested increasing the soil-quake term for drilled foundations. The proposed soil-quake method develops revised QDOL and HDOL offsets based on instrumented load-test case studies and comparisons with calculated capacities.<br /><br />The method is intended to provide a practical way to estimate ultimate capacity, including when a load test does not show a clear plunging failure. Its offsets can be tailored to different foundation types, recognizing that installation methods create distinct stress histories and soil disturbance. Using the initial tangent slope of the load–displacement curve also avoids some uncertainty associated with estimating the pile’s elastic modulus.<br /><br />The approach connects ultimate-capacity interpretation with serviceability: under the International Building Code, design loads must account for total and differential settlement, and allowable capacity is limited relative to the interpreted ultimate capacity. The presentation argues that the modified offsets can help establish an ultimate limit state consistent with tolerable settlement at service loads.

Keywords

Davisson Offset Limit

drilled foundations

ultimate axial capacity

load-displacement curves

soil-quake displacement

QDOL

HDOL

load test interpretation

pile capacity

settlement serviceability