Pile Lateral Load Evaluation
The stability analysis was performed using the computer program FB-MULTIPIER . The FB-MULTIPIER program considers both axial and lateral pile-soil interaction . The soil is characterized by user-defined parameters . Group effects are considered through P-Y multipliers that are assigned for each row within the pile group . The recommended FB-MULTIPIER soil parameters are shown in Attachment C .
4.0 STRUCTURAL ASSESSMENT
The foundation stability of Bascule Pier No . 17 at the 100-year scour elevation was evaluated in accordance with the Department ' s directives . The remaining pile embedment and unsupported length for the intermediate bents were determined at the existing conditions ( using the 2011 Bridge Survey and the 6 / 14 / 2011 Field Visit Channel Profiles ) and at the calculated 100-year scour event . Bascule Pier No . 17 ( 1-W per plans ) was chosen for the analysis because its piles have the least amount of remaining embedment and the longest unsupported length . At the 100-year scour event , the piles at Bascule Pier No . 17 would have scour up to 18.6 ft . and have 69.7 ft . of reamining embedment . A stability analysis , using FB-MULTIPIER , showed Bascule Pier No . 17 to be unstable for the modified Group 1 loads at the calculated 100-year scour elevation , however , it is stable at its existing conditions . The bridge is therefore rated scour critical .
The vertical and lateral loads for Bascule Pier No . 17 were estimated in accordance with the 17th edition of the " Standard Specifications for Highway Bridges " ( AASHTO ). The Load Factor Design method was used to evaluate the foundation stability . The Department directive states that load factors ( gamma and beta ) of 1.0 are to be used for Group 1 loading combination as specified in Table 3.22.1A of AASHTO . Serviceability requirements were not considered . Construction tolerances were also not included in this analysis . The stream pressure was calculated in accordance with Article 3.18.1 of AASHTO and applied only to the exposed pile surfaces . Debris accumulation and ship impact were not considered .
The axial forces in all the piles were lower than the soil ' s ultimate ( theoretical ) compression capacity . The applied moments were insignificant . Pile axial and lateral displacements are within tolerable limits . These results indicate that Bascule Pier No . 17 is stable under the applied loads at the 100-year scour elevation , and the bridge was therefore rated low risk .
For further information , refer to Attachment D . See Page 1 of 3 for recommendations .
5.0 MATERIALS AND DOCUMENTATION
· 1957 Bridge Design Plans
· 2004 Bridge Rehabilitation Plans
· 2010 Bridge Inspection Report
· Scour Evaluation Report , Phase 1 , Phase 2 , Phase 3 , & Phase 4 ( Ayres Associates , Inc .)
· Attachments A . FDOT Memorandums regarding Phase 3 Scour Evaluation Criteria B . Nondestructive Parallel Seismic Testing Evaluation Report C . Geotechnical Evaluation D . Structural Evaluation
4 / 25 / 2013 FINAL Page 4 of 12 62-0144.00 BRIDGE NO 794004
Supplementary Report Page SR-34