Employment of the $P$-Multiplier in Pile-Group Analysis

This paper discusses the variation of the $P$-multiplier ($P_m$) used with the $p\mathrm{\text{-}}y$ curve to assess the response of a pile group under lateral loads, which is a crucial topic for the design of bridge pile foundations. $P_m$ is influenced by the site geotechnical conditions (i.e., soil profile, type and properties), pile front and side spacings, and pile-group deflection. The presented study shows the needs to incorporate these factors with the recommended sets of $P_m$ to avoid any compromise or uncertainty when $P_m$ is treated as a single (unique) value based only on pile spacings. The current study addresses these influential elements using the strain wedge (SW) model technique, suggested $P_m$ values, and data collected from full-scale pile-group load tests. The experimental results show that $P_m$ is not unique and must be assessed based on the site geotechnical conditions along with the pile-row front and side spacings. Because the employed $P_m$ values must be a function of these influential factors, additional full- and model-scale load tests with different pile spacings and soil types might be required. The paper also emphasizes that using other techniques, such as the SW model, in addition to the $P$-multiplier could increase the confidence in the predicted pile-group lateral response.