Development of p- and y- multipliers for design of slope stabilizing piles

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] Slope failures can arise from many factors and such failures can have a big impact on public and private infrastructure. Drilled shafts have been used for the stabilization of slopes for many decades. Micropiling is a relatively new approach in slope stabilization applications that has been adopted by many agencies and used in many problematic sites across the globe. However, limited knowledge regarding load transfer for piles within moving soil may cause design of the piles to be more conservative than is actually needed. The objective of this work is to provide guidance on the effects of pile batter and spacing so designers can reasonably account for these effects when predicting response of piles from lateral loading within moving soils. Load transfer to piles within moving soil masses was analyzed using soil-structure interaction methods. Based on measured soil movements and sliding surface locations, p-y analyses were performed to backcalculate "best fit" p- and y-multipliers that would lead to prediction of the measured bending moments in the micropiles and drilled shafts. The back-calculated p-y parameters were compared with values from literature and with one another to develop recommendations for predicting lateral resistance in deep foundations for slope stabilization applications. As a result of this study, a method was established to obtain p- and y-multipliers for any combination of spacing and batter angle for micropiles with a capping beam. Results of analysis indicate that spacing ratio and batter angle are important factors that influence the resistance. Data suggest that closer spacing increases the resistance, but batter angle was observed to have the greatest effect on resistance. Data show that available resistance increases with batter angle from lower values for piles inclined upslope to greater values for piles inclined downslope. Further, a method was also established to obtain p- and ymultipliers for predicting resistance of piles installed without a capping beam in a continuous row with no batter. Data suggest that closer spacing decreases the resistance.