The National Academies

NCHRP 24-09 [Completed]

Static and Dynamic Lateral Loading of Pile Groups

  Project Data
Funds: $499,962
Research Agency: Auburn University
Principal Investigator: Dan A. Brown
Effective Date: 6/15/1997
Completion Date: 12/31/2000

NCHRP Report 461, "Static and Dynamic Loading of Pile Groups," contains the findings of a study to develop and validate an improved design method for pile groups under static and dynamic lateral loads. The report includes recommendations for estimating the distribution of load to piles in a group and provides guidance on analytical methods for predicting dynamic response. The material in this report will be of immediate interest to bridge engineers and geotechnical engineers involved in the design of pile and drilled shaft foundations to resist lateral loads.

The principal force experienced in transportation structures during an earthquake, a hurricane, or a vessel impact is a transient horizontal loading. These loads must be transmitted to the structure's foundation. State-of-the-practice design for lateral loading of pile and drilled shaft foundations uses beam-on-elastic-foundation analysis. In this analysis, load shedding from a pile to the soil is represented by "p-y springs" in which the soil response is modeled as a series of discrete nonlinear springs. The p-y springs currently used in these analyses were developed primarily to determine the load-shedding behavior of single piles subjected to static loads. The use of p-y springs in the analyses of pile groups subjected to static and dynamic lateral loads had not been validated.

The objective of this research was to evaluate and extend current design methods for groups of piles and groups of drilled shafts subjected to lateral loads associated with earthquakes, hurricanes, and vessel impacts. Under NCHRP Project 24-09, Auburn University conducted experimental and analytical studies of pile groups. Through a series of field tests, the researchers determined the distribution of lateral loads to the individual piles in a group and verified that the pile-group response can be predicted analytically using p-y springs. Experimentally determined multipliers were used to adjust the magnitude of load carried by each row of piles in the group. The findings from this research could significantly increase confidence in and reduce the cost of foundations subjected to dynamic loads.

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