Soil Bridging Effects within Permafrost-Supported Embankment Infrastructure

Abstract

Accidents, infrastructure closures and reductions in capacity, and delays have occurred and are documented in the literature due to bridge formation, sinkholes, or rapid collapses within embankment infrastructure on permafrost. However, the failure mechanics are not well understood or studied. This paper investigates soil particle position, negative pore-pressure generation, and frozen soil flexure as possible mechanisms for bridging. Published literature and laboratory testing confirmed that soil particle position is a possible mechanism for bridging voids within embankments. Factor of safety equations were developed for (1) tensile stress conditions within a loaded frozen soil beam and (2) tensile stress from matric suction conditions within unfrozen soils over a void. Using published data for common embankment materials, example calculations for bridging via matric suction and frozen soil flexure are presented. All of the presented mechanisms for creating and maintaining bridges are possible, depending on site conditions; however, the probability and consequences of bridge collapse after formation vary widely depending on the mechanism.