Figure 7-4: P-multipliers as a function of Lateral Pile Head Deflection (after Rollins et al. 1998). Other studies have shown that installation methods may also impact the p-multipliers. Driven piles create a densifying effect on the surrounding soil compared to bored piles, which may loosen the surrounding soil. Comparisons of experimental programs on driven versus bored piles indicate that p-multipliers are generally higher for cases of driven piles compared to bored piles (Gandhi and Selvam 1997; Huang et al. 2001). However, inmost projects, the effects of installation are not accounted for because the assumed densification effect would be difficult to estimate and quantify in design, and would have to be verified by in-situ testing or lateral load testing in construction. Most test results have been from static lateral loading tests. However, the limited test data from pile groups loaded at velocities comparable to extreme events such as earthquakes or dynamic impacts indicate that p-multipliers from such dynamic loading are comparable to those from static load tests Brown et al. 2010). 0 10 20 30 40 50 60 Pile Head Deflection (mm) 0 0.2 0.4 0.6 0.8 1 1.2 P -M u lti p li e r Front Row Middle Row Back Row 7.2.2.2 Recommendations for P-multipliers AASHTO (2014) presents p-multipliers for analysis for several example group pile/shaft layouts. These p- multipliers are considered applicable for all subsurface conditions for the design of transportation facilities i.e., these factors are applicable regardless of foundation type, geomaterial, or loading condition. As noted previously, the soil type, strength, and/or density do not have as significant an effect on the p- multiplier as the individual pile size, group size, and group layout. Example group foundation layouts for the application of the P m . values in Table 7-1 are shown in Figure 7-5.
