TITLE:
Methodology for Obtaining Optimal Sleeve Friction and Friction Ratio Estimates from CPT Data
AUTHORS:
Erick Baziw
KEYWORDS:
Cone Penetration Testing (CPT), Optimal Estimation, Geotechnical Site Characterization, Sleeve Friction, Cone Bearing, Friction Ratio, Iterative Forward Modelling (IFM), Soil Behavior Type (SBT)
JOURNAL NAME:
International Journal of Geosciences,
Vol.14 No.3,
March
27,
2023
ABSTRACT: Cone penetration testing
(CPT) is a cost effective and popular tool for geotechnical site
characterization. CPT consists of pushing at a constant rate an electronic
penetrometer into penetrable soils and recording cone bearing (qc),
sleeve friction (fc) and dynamic pore pressure (u)
with depth. The measured qc, fs and u values are utilized to estimate soil type and associated soil properties. A
popular method to estimate soil type from CPT measurements is the Soil Behavior
Type (SBT) chart. The SBT plots cone resistance vs friction ratio, Rf [where: Rf = (fs/qc)100%].
There are distortions in the CPT measurements which can result in erroneous SBT
plots. Cone bearing measurements at a specific depth are blurred or averaged
due to qc values being strongly influenced by soils within 10
to 30 cone diameters from the cone tip. The qcHMM algorithm
was developed to address the qc blurring/averaging limitation. This paper describes the
distortions which occur when obtaining sleeve friction measurements which can
in association with qc blurring result in significant errors
in the calculated Rf values. This paper outlines a novel and
highly effective algorithm for obtaining accurate sleeve friction and friction
ratio estimates. The fc optimal filter estimation technique
is referred to as the OSFE-IFM algorithm. The mathematical details of
the OSFE-IFM algorithm
are outlined in this paper along with the results from a challenging test bed
simulation. The test bed simulation demonstrates that the OSFE-IFM algorithm derives accurate estimates of sleeve friction from measured values.
Optimal estimates of cone bearing and sleeve friction result in accurate Rf values and subsequent accurate estimates of soil behavior type.