Field-Scale Analysis of a Stormwater Infiltration Trench’s Failure Mechanisms

Abstract

Infiltration trenches are one type of stormwater control measure (SCM) that can help fulfill stormwater management requirements, especially in highly urban areas where open space is limited. Underground infiltration trenches built without pretreatment have a high risk of clogging and subsequent decrease in the rate of stormwater exfiltration from the system. The focus of this study was to assess the cause of failure of an underdesigned infiltration trench without pretreatment that experienced diminished performance after only 1 year of operation. The system was excavated after 11 years of operation and subsequently analyzed for failure using particle size distribution analysis, in-situ infiltration tests, capillary flow analysis to assess geotextile clogging, and soil extractions to quantify metals accumulation. Results indicate that the decrease in infiltration trench performance was caused by a combination of three clogging mechanisms: (1) sediments with a median particle size (D50) of 26.4 μm and a high percentage (52%) of silt-sized particles clogged the perforated inflow pipe, which minimized the amount of stormwater runoff able to enter the trench; (2) stormwater sediments that accumulated in the trench itself created a filter cake on top of the geotextile (i.e., blinding), which minimized exfiltration of stormwater from the trench; and (3) clay-sized particles present in the stormwater sediments migrated through the geotextile and accumulated on the geotextile–subsurface interface, which reduced the permeability of the soil just below the geotextile. These results outlining specific failure mechanisms provide valuable information regarding maintenance requirements for current infiltration trench operation as well as for future infiltration trench SCM design.