Pile foundations for bridges must often resist lateral loads produced by earthquakes and thermal expansion or contraction. In addition, space constraints are 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 but design codes do not address this issue. In this study, full-scale tests were conducted on three 324 mm pipe piles spaced at 1.25, 2.7, and 6.3 pile diameters behind a 6.78-m high MSE wall. The measured lateral resistance decreased as the spacing decreased. The lateral resistance of the piles spaced at 1.25D and 2.7D was about 40% and 70%, respectively of the pile at 6.3D back from the wall. P-multipliers to account for the reduced capacity were developed by back-analysis and were combined with previous tests to correlate with spacing behind the wall. Measured tensile forces in the reinforcements typically increased from the wall to the pile and decreased behind the pile indicating that the reinforcing was supplying additional resistance to pile movement. Envelopes of the induced tensile stress are proposed based on normalized parameters.
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