Reduced lateral resistance of abutment piles near MSE walls based on full-scale tests

Abstract

Pile foundations for bridges must often resist lateral loads produced by earthquakes and thermal expansion or contraction. In addition, space constraints are also leading to vertical mechanically stabilized earth (MSE) walls at abutment faces. Available test results indicate that lateral pile resistance can decrease significantly as piles are placed closer to MSE walls. However, no design procedure is available for assessing the decrease in resistance or the effect of the reinforcement on lateral resistance. In this study, full-scale tests were conducted on three 400 mm pipe piles spaced at 1.6, 2.9 and 5.2 pile diameters behind a 10.5-m high MSE wall. The piles were double wrapped with a 0.25 mm thick sheet of low-density polyethylene (LDPE) to reduce down drag. The measured lateral resistance decreased as the spacing behind the wall decreased. The lateral resistance of the pile at 1.6 diameters from the wall was less than one-half of that for the pile at 5.2 pile diameters. Measured tensile forces were higher in the reinforcements adjacent to the pile closest to the wall indicating that the reinforcing grid was supplying additional resistance to pile movement. Back-analyses using a <i>p-y</i> curve approach found the friction angle and <i>k</i> value to be 28° and 41 MN/m³, respectively for the pile located 5.2 diameters away from the wall. These values are significantly lower than other lateral load tests in similar gravels on piles without LDPE sheets. P-multipliers to account for the reduced capacity were developed and provided reasonable agreement with measured response.