Geotechnical Engineering Circular No. 9 Design, Analysis, and Testing of Laterally Loaded Deep Foundations that Support Transportation Facilities


Figure 6-17: Ground improvement treatment concepts for increasing lateral resistance of pile



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hif18031
Soldier Rev B
Figure 6-17: Ground improvement treatment concepts for increasing lateral resistance of pile
groups in weak soils (modified from Rollins and Brown 2011).
Analysis of ground improvement for improving lateral load resistance requires application of judgment. Two key aspects to be assessed are the coverage of ground improvement and the development of parameters for input in the lateral pile analysis. The coverage of ground improvement must be sufficient to provide a large enough volume of improved soil to provide the required resistance. For example, Figure
6-17 indicates a zone of three to four times the pile width as a minimum. The development of the parameters for input in lateral analysis is also critical to developing an effective design. This include developing appropriate soil parameters and/or p-y curves for the modified ground, as well as considerations for shear or adhesion on the sides of the deep foundation elements, shear, adhesion, and/or passive resistance for the pile cap, etc. Rollins and Brown (2011) present details regarding the results of trial sections and recommendations for design. The study focuses on groups of piles, but the concepts of ground improvement for increasing lateral resistance are applicable to individual deep foundations as well.


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7
LATERAL ANALYSIS OF GROUPS OF DEEP FOUNDATIONS
7.1
INTRODUCTION
The concepts related to the response of a single laterally loaded deep foundation element presented previously can be extended to a group of deep foundation elements. Groups can be analyzed using the p- y method or the strain wedge method discussed in Chapter 6. However, the lateral load resistance of a deep foundation element in a group is less than if the same foundation were an isolated element in the same subsurface conditions. Group efficiency and interaction must be accounted for in a group analysis. Most deep foundation groups involve foundations that are relatively closely spaced and therefore need to account for the interaction and reduction inefficiency within the group.

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