Abstract
Mechanically Stabilized Earth (MSE) walls may intersect utilities such as pipes and culverts, which may be located within the reinforced backfill or foundation soil. Evidence from previous failures has shown that leakage or collapse of these utilities can lead to severe deformation or loss of wall integrity. Despite the critical implications of pipe failure, there are no standardized guidelines in the U.S. regarding the placement of utilities within or beneath MSE walls, and current practices vary widely among state DOTs. This report describes the mechanical interaction between MSE walls and buried utility pipes and explores configurations where pipes are placed parallel, perpendicular, or at an angle to the wall, either in the reinforced zone or in the foundation soil. In addition, the report also includes an investigation of the minimum depth at which a pipe should be placed under the MSE wall such that failure of the pipe does not affect the MSE wall or its performance. The work consists of an extensive series of finite element analysis using PLAXIS 2D and 3D, where the wall system and pipe are explicitly considered. The results of the numerical experiments indicate that pipes significantly influence the axial force and displacement of reinforcements located immediately adjacent to the pipe. More precisely: (a) pipes placed parallel to the wall face may increase the axial force in the reinforcement by up to 60% compared to the case where there is no pipe; (b) the internal stability of the wall remains unaffected (provided reinforcement safety factors are met), but the stresses within the reinforced zone change noticeably with the pipe; (c) pipes perpendicular or skewed to the wall may reduce reinforcement demand by acting as large frictional surfaces; (d) the zone of influence of those perpendicular or skewed pipes extends over a distance of 2-2.5 times the diameter of the pipe; (e) when a pipe with diameter 36” or larger is placed at a depth of ten times the radius of the pipe underneath the wall, collapse of the pipe does have a negligible effect on the stability or performance of the wall (this finding applies to MSE walls with height up to 25 ft). The report also offers recommendations for monitoring and strengthening the pipe to detect and mitigate the consequences of damage to the pipe. The research highlights the intricate and interdependent behavior of the reinforced soil, reinforcement and pipe. While the general trends obtained from the research can be generalized, they may not be applicable to situations that fall outside the cases investigated. Case-specific analyses should be conducted to ensure that the presence of the pipe and its possible collapse do not compromise the integrity of the wall, nor its performance.
Keywords
depth, earth walls, location, mechanically stabilized earth, public utilities
Report Number
FHWA/IN/JTRP-2025/25
SPR Number
4715
Sponsoring Organization
Indiana Department of Transportation
Performing Organization
Joint Transportation Research Program
Publisher Place
West Lafayette, Indiana
Date of Version
2025
DOI
10.5703/1288284318546
Recommended Citation
Ahmad, M. A., & Bobet, A. (2025). Study on the permissible depth of utilities under the MSE walls and means and methods of protecting the MSE walls when the permissible depth cannot be provided (Joint Transportation Research Program Publication No. FHWA/IN/JTRP-2025/25). West Lafayette, IN: Purdue University. https://doi.org/10.5703/1288284318546
SPR-4715 Technical Summary