Geotechnical Engineering Circular No. 9 Design, Analysis, and Testing of Laterally Loaded Deep Foundations that Support Transportation Facilities
FHWA-NHI-11-032: LRFD SEISMIC ANALYSIS AND DESIGN OF TRANSPORTATION
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Soldier Rev B
| 6.7 FHWA-NHI-11-032: LRFD SEISMIC ANALYSIS AND DESIGN OF TRANSPORTATION GEOTECHNICAL FEATURES AND STRUCTURAL FOUNDATIONS (2011) The manual presents the state of the practice for seismic analysis and design at the issue date in 2011. It recognizes that the there is no clear consensus on some subjects, such as the p-y curve selection for liquefied soils, and that the evaluation methods and estimated magnitudes are uncertain. Therefore, design professionals should be conscience of ongoing research. The suggested procedure for analysis of flow failures and lateral spreading or lateral flow are summarized below 1. Slope stability analyses are performed for the liquefied condition, using the residual shear strength parameters for the affected layers, to determine the post-liquefaction yield acceleration and the associated failure surface. 2. Newmark sliding block analysis is conducted using the post-liquefaction yield acceleration from Step 1 to estimate displacements of the soil-pile system. 3. Based on Step 2, the forces on the structure and foundation due to lateral spreading or lateral flow movements are calculated. 4. Determination of plastic hinge mechanisms that are likely to develop in the deep foundation elements. This can be assessing moment and shear induced in the foundation using a soil-pile interaction analysis. The reference describes two main methodologies for p-y curve representation of liquefied soils 1) Soft cohesive soil using the undrained residual shear strength as the cohesion, 2) Liquefied sand curves by Liu and Dobry (1995). 6.8 LPILE TECHNICAL MANUAL (2012) The manual interprets load and resistance factors by using lowerbound and upperbound values for important soil parameters. It employs a procedure similar to that presented in Reese (1984, 1985), which iterates analyses until failure moment/shear occur and then uses a safety factor to determine working loads. The element is then analyzed for behavior under working stresses for acceptability. The concept of critical length is included, stating that the designer will normally select a pile fora particular application whose length is somewhat greater than L crit .” A chapter for using vertical piles to stabilize slopes is presented, but no specific guidance is given on the applied load above the failure surface. Download 6.03 Mb. Share with your friends:
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