Orange County Branch Newsletter
ASCE OC Geo-Institute – Determination of P-Y Curves and Pile Lateral Capacity
By: Mr. Clint Isa, P.E., ASCE OC Geo-Institute Chair
The ASCE-Orange County Geo-Institute (GI) hosted a dinner meeting at the Back Bay Conference Center in Irvine on May 24, 2017. The event, which was attended by a mix of more than 75 industry professionals and students, featured a presentation by Dr. Scott Brandenberg, Ph.D., PE (Associate Professor, UCLA) and Dr. Shawn Ariannia, Ph.D., PE, GE (Principal, Geo-Advantec, Inc.).
Drs. Brandenberg and Ariannia presented a new method for developing p-y curves by direct use of CPT measurements, and used method to analyze several load tests of piles where CPT measurements were available. The procedure utilizes a new material model, PySimple3, implemented in the open source finite element platform OpenSees. Inputs to the material model include the capacity, pu, yield value, py, initial stiffness, Ke, and a constant, C, that controls the shape of the curve. These material properties are computed based on: (1) CPT data, (2) pile properties, and (3) any available geophysical data and/or strength measurements. Unlike traditional p-y methods in which a soil profile is divided into discrete layers, the proposed approach computes p-y properties at every depth where a CPT measurement is made, resulting in an essentially continuous profile of p-y properties. These properties are then interpolated at the desired nodal locations along the pile using a weighting scheme that accounts for the fact that softer layers tend to exert more influence on p-y response than stiffer layers.
The calculations have been implemented in a website where users can upload a CPT profile and geophysical information, supply pile properties, and output a TCL script that can be run using OpenSees. The method was used to analyze several case histories of laterally loaded instrumented piles with available CPT data. Soil types included sand, soft saturated clay, and unsaturated clay, and pile types included driven piles, drilled shafts, and torque-down piles. The analyses generally compared well with measurements, though corrections to the stiffness were needed to account for pile installation effects.
On behalf of the ASCE OC GI and our membership, we thank our speakers for having contributed their time and knowledge to this event. We would also like to offer special thanks to our event sponsors: Hayward Baker, Gregg Drilling and Testing, and Farrell Design-Build.