Please join us for this month’s lunchtime presentation on Thursday.
Geo-Institute/Seattle Section Geotechnical Group – October Meeting
Thursday, October 21st, 12pm to 1pm
Webinar presentation: An End Bearing Method for Evaluating Instrumented Becker Penetration Test Data
Khaled Chowdhury, PhD, PE, GE
Becker Penetration Tests (BPT) with instrumentation are regularly performed to characterize the density of embankment dams and foundations that consist of sandy gravel, gravelly soils or rockfill, where other methods such as the Standard Penetration Test (SPT) and the Cone Penetration Test (CPT) are difficult to perform. An embankment dam constructed in the 1950s was recently evaluated using instrumented BPT and sonic borings, as well as earlier large diameter in-situ ring density tests and BPTs, original construction records, and observations and in-situ testing as part of a dam modification project. Three commonly used BPT methods for conversion of BPT blow counts to equivalent SPT N60 values were evaluated. Wide differences in the resulting equivalent SPT N60 values between (1) the Harder and Seed (1986) BPT method and the instrumented BPT-based methods of (2) Sy and Campanella (1994) and (3) DeJong et al. (2017) and Ghafghazi et al. (2017) were observed in this project. This finding is consistent with several other projects that were reviewed. These different equivalent SPT N60 blow counts from different methods would result in significantly different estimates of expected seismic performance of an embankment dam or other structures.
Based on an evaluation of the origins and development of the three BPT and instrumented BPT interpretation methods listed above, and further analyses of available data, an alternative “end bearing” method was developed to determine site-specific equivalent SPT N60 values from BPT. This proposed method systematically and transparently analyzes the collected BPT instrumentation data and provides equivalent SPT N60 values considering in-situ soil characteristics; a significant improvement to commonly used procedures. The end bearing method is based on transparently separating the shaft friction and residual force of the BPT piles by using CAPWAP-RSA and CASE methods to accurately determine the end bearing capacity of soil. In addition to site characterization for seismic analyses, this method can be used for deep foundation design and capacity verification.
For more information on the presentation and biographies, visit the Events page at https://seattlegeotech.org/eventlist.
Zoom Link: https://us06web.zoom.us/j/88612944518