Lateral Load Capacity of Cast-in-Place Shafts behind an MSE Wall

Abstract

Current practice for designing laterally loaded cast-in-place shafts that pass through an MSE Wall involves isolating the shafts from the MSE mass and anchoring the shafts into the underlying foundation material. Sizeable cost and time savings could be realized, while still maintaining stability and reliability, if a method were available to evaluate the lateral load capacity of a shaft that is supported by the MSE mass alone with no rock socket.Construction, instrumentation, and testing of multiple 0.9m (36in.) diameter shafts solely supported by a 6m (20 ft) MSE block wall was conducted for the Kansas Department of Transportation (KDOT). This paper describes the design and construction of the wall and shafts, and the results from the lateral load tests of two of the shafts. These shafts had lengths that were equal to the full height of the wall and 75 percent of the full height of the wall to evaluate the reduction in capacity if shorter foundation elements suspended in the MSE mass were used. Results for both load and deflection of the shafts and the relative deflections of the shafts and wall facing during loading are presented.

Analysis of Laterally-Loaded Piles in MSE Embankments

“…Two sets of full scale tests were described in the introduction (Parsons et al 2009 andRollins et al 2013 Rollins et al (2013) developed tentative p-multipliers for reducing conventional p-y curves to model piles in MSE based on their experiments. The p-multipliers were presented as a function of the normalized distance from the wall facing and L/H ratios (L is the length of the MSE reinforcement and H is the wall height) as shown in Figure 12.…”

“…There is currently little guidance available for assessing the performance of these complex systems under lateral loads, such as during an earthquake. Simple design approaches such as isolating the piles from the MSE mass, neglecting any lateral resistance from the MSE backfill, or locating abutment piles farther back from the wall face can lead to increased bridge cost (Parsons et al 2009, Rollins et al 2013. The level of added conservatism and increased cost could potentially be reduced by an improved understanding of the lateral behavior of pile-supported MSE abutments.…”

“…The tested shafts ofParsons et al (2009) shared the same diameter (3 feet) as those of the 3D FE model investigation presented in the current study. However there are significant differences in the Parsons et al (2009) configuration including: shorter shaft lengths that do not extend into the native subgrade, a single pile configuration with the shaft centered in a 4.6 m (15 feet) test section, a different MSE reinforcement configuration, a center of the shaft to wall distance of 1.8 m (6 feet), and a shorter wall height of 6 m (19.7 feet) as well as other factors.…”