Effect of Coupling on A-Walls for Slope Stabilization

Project Details









Deep Foundations Institute
Midwest Transportation Center
University of Missouri - Columbia

Principal Investigator
Andrew Boeckmann
Co-Principal Investigator
J. Erik Loehr

About the research

A-walls are retaining structures composed of regularly spaced deep foundation elements battered in opposing directions and connected through a grade beam to mitigate movements of a slope or embankment. Analysis of A-walls for slope stabilization applications is challenging because of complex interactions between deep foundation elements and moving soils. A previous method was successful in modeling A-walls with consideration of both lateral and axial load transfer, but interaction between upslope and downslope A-wall elements through the capping beam is neglected in the “uncoupled” analysis. To evaluate the effect of coupling, the research team analyzed slopes stabilized with A-walls using finite element models with upslope and downslope piles connected at the pile heads. Results of the analyses were compared to those of uncoupled lateral and axial analyses utilizing the p-y and t-z methods. Load transfer parameters for the analyses were calibrated to field measurements of load transfer in A-walls to demonstrate viability of the revised methodology. Results of the coupled analyses were then compared to results from uncoupled analyses to evaluate the effect of interaction between upslope and downslope piles.

Coupled analyses produced bending moment and axial force profiles in reasonable agreement with measured values. Calibration of p-y and t-z curves to achieve predictions consistent with field measurements required significant softening of ultimate lateral and axial resistance values, but the softening was less than that required for calibration of uncoupled analyses. Modeling of interaction through the capping beam resulted in more reasonable calibrated values of lateral and axial soil resistance, better agreement with measured axial force profiles, and better agreement with measured bending moments and axial forces at shallow depths. The results indicate that interaction facilitated by the capping beam has a significant effect on development of forces within the A-wall elements. For deep sliding, reasonable predictions of pile resistance can be achieved using uncoupled models. However, for shallower sliding, the capping beam is likely more consequential and a coupled analysis is prudent. Coupled analysis is also beneficial for structural design of the capping beam.

Both calibration case histories involved relatively deep sliding and relatively small values of total soil movement. Additional analyses with new datasets from A-wall applications for shallower slides and greater movement are recommended.

Funding Sources:
Deep Foundations Institute ($18,700.00)
Midwest Transportation Center
University of Missouri – Columbia ($6,100.00)
USDOT/OST-R ($20,000.00)
Total: $44,800.00

Contract Number: DTRT13-G-UTC37