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City staff report Stonecrop drainage project mats are failing; contractor asked to submit corrective plan
Summary
City staff told the council that erosion under installed mats in the Stonecrop drainage project caused lifting and indentations; the contractor must submit a corrective plan and engineers will inspect remediation, and the city is evaluating remediation options including rip-rap and curb adjustments.
City staff updated the council on the Stonecrop drainage project, reporting that erosion beneath installed erosion-control mats caused sections to heave and create indentations after water began flowing through the channel.
Public Works staff said installation of mats and related grading were complete but, once water flowed, portions of the mats began to fail because the underside was eroding. Staff said the contractor must submit a written corrective plan of action and that the city’s contract engineer will oversee inspections of the remediation work. The city has engaged mat manufacturer ConTech and the installation contractor to evaluate the problem.
Because the redesign and erosion mean cranes can no longer be used in parts of the channel, staff said some mats may need to be removed and replaced with riprap or other measures, and that slope revisions may affect methods for finishing the work. Staff also said a redesign at a nearby bridge and wing-wall area may require a short curb to direct water into the channel and avoid undermining wing walls, and that field crews are meeting with the contractor to resolve the issues.
Public Works staff said they do not yet have a completion date and that the city is pressing the contractor to provide a remediation schedule; inspections will be frequent and staff will report back to council as the contractor proposes fixes.
