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

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9.3
DETERMINATION OF EMBEDMENT DEPTH
Once the resultant active earth pressure has been determined above the design grade level (base of lagging or panel fascia, p-y analysis software can be used to assess the embedment requirements for the vertical foundation elements, either by direct application of the factored resultant force on the pile/shaft or, depending upon the limitations of the program, by resolving the factored resultant force to an applied shear and moment at the design grade level. Design grade for passive resistance should betaken at the bottom of the fascia panel (below finish grade in front of the wall) to model the construction condition. A lower level should be considered to account for other potential disturbance during the service life of the wall, such as trenching for installation of utilities. Note that limit equilibrium methods can also be used to assess the embedment requirements for the vertical foundation elements. Following the design process in Chapter 5 of this manual (Section 5.1, Block 9.1), the required embedment can be determined based upon a geotechnical strength limit analysis for individual foundation elements, using the factored strength limit load combinations per AASHTO Section 3.4.1 and a geotechnical resistance factor (Φ) of
0.75 for passive resistance of the embedded vertical piles or drilled shafts, as per AASHTO 11.5.6-1.
9.4
EVALUATION OF DEFORMATION
After the pile or drilled shaft embedment and Structural Strength Limit State (refer to Chapter 11 of this manual) have been satisfied, the service load combinations, per AASHTO 3.4.1 can be used in a p-y analysis to assess deflection. The method of analysis for assessing deflection is discussed in Chapter 5 of this manual (Section 5.1, Block 9.3). If the p-y analysis is performed based upon resolved shear and moment at the design grade elevation, the free-head lateral translation and angular distortion computed result at the design grade level will need to be projected to the top of the wall.

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