Pile Design Using CPT Results: The "LPC Method"-Paper

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The LPC method estimates the axial capacity of piles from cone penetration test (CPT) cone resistance, calculating ultimate base pressure and shaft friction. Developed in France in the early 1980s, it was revised in 1993 and substantially updated in the current French piling code, AFNOR 2012.<br /><br />The 1982 method correlated base pressure and shaft friction linearly with CPT resistance. Soil and pile-type factors, along with maximum shaft-friction limits, were provided in tables. The 1993 revision retained this approach but simplified and adjusted the tabulated factors and limits.<br /><br />The 2012 method uses a larger body of pile-test data and provides factors for a wider range of pile types and ground conditions. Base pressure is calculated from a representative CPT resistance near the pile toe multiplied by a bearing factor. Shaft friction is determined from a reference friction related to CPT resistance and soil type, adjusted for pile and soil conditions, and subject to tabulated maximum values.<br /><br />To estimate representative resistance at the pile toe, the method averages CPT results over a specified zone around the toe, considering only the bearing layer and excluding unusually high values. It also reduces the bearing factor where a pile has limited embedment in a strong layer over weaker soils. Full bearing resistance is generally used when embedment is at least five pile diameters; shallower embedment may require a calculated reduction.<br /><br />The paper traces the method’s development and explains the 2012 procedure for English-speaking practitioners. It notes that the LPC method is widely used in France and forms part of the current national code.

Keywords

LPC method

pile axial capacity

cone penetration test

CPT cone resistance

ultimate base pressure

shaft friction

French piling code

AFNOR 2012

pile toe resistance

bearing factor