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

275 EN 1999: (Eurocode 9) Design of aluminum structures In the UK, the British Standards Institution (BSI) publishes the Eurocodes, and EC is referred to as BS EN and BS EN 1997-2, for parts 1 and 2 respectively. The UK’s national annex was included within the 2013 version of the code, and is titled BS EN 1997-1: A. For ultimate limits states, there are three design approaches with combinations of partial factors on actions (i.e., load factors) and partial factors on resistances (i.e., resistance factors) presented the most applicable design approach is to be determined for the design case being assessed. All factors are 1.0 or greater, however, actions are multiplied by the factor whereas soil parameters and geotechnical resistance are divided by the factors. Lateral loading of piled foundations is addressed in Section 7.7 of EC under the title Transversely Loaded Piles There is a requirement to demonstrate that a pile will support the design transverse load with adequate safety against failure, such that the following inequality is satisfied for all Ultimate Limit State (ULS) load cases and load combinations
F
tr;d
≤ R
tr;d Where
F
tr;d
= Factored transverse design loading.
R
tr;d
= Factored transverse resistance for design. Failure mechanisms that are required to be considered include rotation for short piles acting as a rigid body and bending failure or local yielding/displacement of the soil near the top of the pile for long slender piles. Group effects are to be considered when assessing the resistance of transversely loaded piles, including effects of compression, tension and transverse forces in individual piles within the group. The partial factors are included in the Annex for certain design cases or applications, but the case of transversely loaded piles is not specifically addressed. The standard indicates that if factors are not addressed in the Annex, then the factors in the Annex should be used as a guide. There are multiple design approaches, each with a different combination of partial factors, and therefore it appears that for the case of transversely loaded piles, the designer has some flexibility with regard to which approach and therefore which load factors are used as a guide from the Annex. The specific approach maybe governed by local practice or the type of structure. In general, the design approaches and factors include
1. Design Approach 1: Two combinations a. Combination 1: Load factors of 1.35 and 1.5 for permanent and variable loads (all loads factored up, partial factors for geotechnical parameters and resistances are 1.0. b. Combination 2: Load factors of 1.0 and 1.3 for permanent and variable loads, partial factors for geotechnical strength parameters are 1.25 to 1.40 (i.e., soil strengths are reduced, and factors for geotechnical resistance are 1.0. i. For axially loaded pile design Combination 1: same as above

276 Combination 2: Load factors of 1.0 and 1.3 for permanent and variable loads, partial factors for geotechnical parameters are >1 only if the soil applies an unfavorable action, and factors for geotechnical resistance are 1.3 (resistance is reduced.
2. Design Approach 2: Load factors of 1.35 and 1.5 for permanent and variable loads (all loads factored up, partial factors for geotechnical parameters are 1.0, and partial factors for resistances are 1.1 resistances are reduced.
3. Design Approach 3: Load factors of 1.3.5 to 1.5 for structural actions and 1.0 to 1.3 for geotechnical actions, partial factors for geotechnical strength parameters are 1.25 to 1.40 (i.e., soil strengths are reduced, and factors for geotechnical resistance are 1.0. The British Standard indicates that for the Service Limit State (SLS) case, the partial factors on actions and resistances are normally set equal to 1.0. The standard indicates that limiting values for deformation should beset during the design, but it does not provide actual values for bridge foundation deflections. The determination of transverse displacements is required to take account of nonlinear ground stiffness and its variation with strain level, flexural stiffness of the individual piles, pile head fixity condition with the structure, the pile group effect, and effects of load reversals or cyclic loading. The specific method of lateral analysis is not detailed but references to the subgrade reaction model and p-y methodology are mentioned. Based on this review and the information summarized above, the British Standard follows a similar approach to the AASHTO bridge specifications including load and resistance factors and indicates the same general design procedures as US-based publications, i.e., subgrade reaction model and p-y curves. Strain wedge model is notably not mentioned in the British Standard.

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