Geotechnical Engineering Circular No. 9 Design, Analysis, and Testing of Laterally Loaded Deep Foundations that Support Transportation Facilities
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- 10.1 DATABASE SUMMARIES
| 10. CASE HISTORY SUMMARY Two types of case histories are described in this section. The first includes published studies summarizing databases of available load test information and performing statistical comparisons of design methods with those load test results. These consist of studies where insights or conclusions are drawn from review and analysis of large data sets. The second type of case history discussed involves research projects performed by DOT agencies using full scale lateral load tests. These case histories were specifically performed to investigate or develop p-y parameters for lateral load analyses to improve the state of the local practice. Additional case histories, are in many cases are either similar to the studies presented herein or are isolated case histories involving design development and/or validation on one particular project. Due to limitations in scope for this literature review, such individual case histories were not reviewed in detail or summarized here. 281 10.1 DATABASE SUMMARIES Paikowsky (2007), Yang, et al. (2007), and the Washington State DOT (1988) published summarized databases related to the accuracy and effectiveness of design methodologies as briefly summarized below. Paikowsky (2007) analyzed over 100 case histories comparing the accuracy of deflection estimates for various methodologies including p-y curves, Broms method, and SWM for open and closed-end pipe piles. The document states that there is good agreement between measured and calculated deflections for both the p-y and SWM methods, with measured values about 10 percent greater than predicted values for most cases, and a coefficient of variation of about 35 percent. Broms method is recommended for initial estimates of lateral force fora given displacement and large diameter piles. Other related statements from the document included For SWM there is a small sensitivity to independent reasonable parameter selection Uncertainty of predictions is greater in sand than in clay Yang et al. (2007) assessed 24 to inch diameter drilled shafts and provided recommendations related to the design of noise wall foundations. Broms and Brinch Hansen estimation methods were compared for assessment of the lateral capacity. The paper concludes that Broms method is preferred because, in about 30 percent of the cases, using the Brinch Hansen method resulted in unsafe estimations, such that the predicted ultimate capacity was lower than the measured ultimate capacity. For comparison, this over-prediction occurred in less than 10 percent of the cases using the Broms method. Additionally, the p- y methodology (using COMP) and NAVFAC DM7 estimation method were compared for estimating shaft head deflection. The paper indicates that at lower loads the NAVFAC method over-predicts deflection while estimates using p-y methodology are in good agreement. At higher loads both methods over-predicted movement. As such, the manual recommends using p-y methodology. In preparation of WSDOT (1988), over 100 lateral load tests were reviewed for assessment of p-y curve development in western Washington. A list of the conclusions and recommendations from that document is included below • P-y methodology should continue to be used. It has improved safety and economy of pile foundations. Clay curves tend to over-predict deflection of large diameter piles. The Integrated Clay Criteria is recommended for modeling clay (due to more supporting data. The Extended Hyperbolic Criteria is recommended for sands (more accurate for tapered piles and H- piles. More research into p-y curves for other soil types (gravel and silt) is needed Download 6.03 Mb. Share with your friends:
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