DRIVEN PILE, DRILLED SHAFT, AND BACKFILL CONSIDERATIONS

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13.4.1 Pile/Shaft Position and Alignment
Laterally loaded vertical foundation elements, either within a group or spaced at linear intervals, as fora noise wall or top-down wall, are designed inconsideration of overlapping passive influence zones using p-y multipliers determined from the spacing of the foundation elements. It is therefore important that the foundation elements be installed at their design location. To reduce the risk of piles/shafts being installed out of plan location or vertical alignment, care should betaken to clear the foundation locations of potential obstructions, including abandoned foundations, tree roots, and other obstructions. Buried pipes and other utilities that have not been accurately identified or relocated in advance should be field located relative to the planned pile/shaft positions to identify potential conflicts that may require redesign. All field adjustments to planned foundation positions should be approved by the engineer-of-record. Equipment accessories, such as pile leads, pre-bore augers, casing templates, or special tools, e.g., rock chisels, boulder breakers, etc, as needed to maintain piles and drilled shafts plumb during the foundation installation should be considered in advance of construction, consistent with requirements within the project specifications. Any foundation elements installed out of the specified tolerance for location or plumbness, should be promptly communicated to the engineer-of-record for resolution.
13.4.2 Driven Pile Installations
The utility of driven piles for lateral load resistance can be adversely affected by the selected means and methods of installation. Whereas abroad range of construction considerations for driven piles are discussed in detail in Hannigan et al. (2016), the following considerations are specific to laterally loaded pile foundations.
13.4.2.1 Equipment Selection
Wave Equation Analysis (WEA) drivability studies are very useful in assessing the suitability of impact hammers to install piles to at least the minimum tip elevation necessary to achieve the required lateral resistance defined in the foundation design. WEA drivability assessments should be conducted by a knowledgeable foundation specialist, matching the contractor’s proposed driving system with the specific pile type, ground conditions and performance requirements of the design. Additional details regarding the
WEA analysis can be found in Hannigan et al. (2016).
13.4.2.2 Sequence of Driving
When driving piles on slopes, such as a riverbank, the sequence of driving must be considered. Driving the piles sequentially from the bottom to top of the slope typically results in displacement, tilting and possibly bending of previously installed piles. To avoid this situation, pile installation on a slope should progress sequentially from top to bottom. Similar to slope installations, ground displacement during driving favors driving the interior piles within a pile group first to reduce the risk that densification during the driving process will preclude driving following piles in the group to plan depth. Inability to install piles to plan depth may impact the functionality of laterally loaded piles in bending.

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13.4.2.3 Driving Refusal
For various reasons, such as the presence of hard layers, the presence of boulders, an unanticipated higher bedrock elevation, or soil densification from previously installed piles, piles may achieve driving refusal above the plan minimum tip elevation specified for lateral resistance. Whenever such a condition is encountered, the engineer-of-record should be notified to assess the acceptance of the pile in question and to determine if measures need to betaken to achieve the minimum penetration for subsequent piles in the group. Such measures may include predrilling through a hard layer, spudding to breakup obstructions, changing the driving sequence for the remaining piles, or modifying the number or arrangement of the piles in the group.
13.4.2.4 Splicing
Circumstances maybe encountered where piles need to be driven deeper than the original pile order length to meet axial resistance requirements. Splices for steel piles should be full penetration groove welds to develop the full structural capacity of the pile section, and welding should be accomplished by a qualified and experienced certified welder. Mechanical splices with less than full strength in bending should be avoided unless the need for the splice can be anticipated, and thereby located deep within the ground where bending moments are relatively small. Field splices, if required, should be approved by the engineer-of-record. Splices should generally be avoided for precast concrete piles since typical pile splices may not develop the full structural capacity of the pile and maybe damaged by continued driving of the pile.
13.4.2.5 Jetting and Pre-boring
Hard driving or the necessity to control driving vibrations may prompt consideration of jetting or pre-boring from the surface to a limited depth. These techniques are sometimes precluded by the project specifications for reasons such as the unknown reduction inside friction resistance or, more specific to jetting, the potential settlement or undermining of adjacent piles or structures. Where allowed, pre-boring is usually limited by depth and by the hole diameter relative to the pile dimensions, e.g., Hannigan et al.
(2016) recommend limiting the size of the pre-bored hole to not more than 6 inches than the largest dimension of the pile. Both jetting and pre-boring are known to reduce axial pile resistance, as noted in
Hannigan et al. (2016), and may also reduce the available lateral resistance due to loosening of the soils around the pile. Jetting or pre-boring should be avoided, unless specifically allowed by the project documents or approved by the engineer-of-record.

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