Concrete Cloth Erosion Control
Concrete Cloth Erosion Control
Concrete Cloth Erosion Control

Seattle, WA
Concrete Cloth™: Erosion Control

Project Overview

In late 2014, a new gas line lateral installed on a steep 2:1 slope faced severe erosion issues due to the effects of heavy Pacific Northwest rainfall. Within weeks of installing a conventional rip-rap drainage channel, excess runoff water bypassing the faulty channel began eroding the soil near the gas line and potentially destabilizing the bedding material around the pipe.

The design goal was to direct the water down the slope and eliminate the erosion caused by shear forces from the water flow (more than 14 lbs/ft2). Per Federal Energy Regulatory Commission (FERC) requirements, the ground surface also had to remain at the same elevation during preconstruction.

Rip-rap typically requires maintenance when used in drainage channels, riverbanks and slopes. While the solution usually creates an acceptable drainage structure, it degrades easily on slopes greater than 3:1. Rip-rap also moves over time, creating instability issues and excessive vegetation growth that can lead to flow restrictions, hydraulic capacity reductions and additional limitations. These were the major causes of the problem at this site.

Possible repair solutions included:
Poured concrete. This solution caused concerns for the asset owner, since FERC codes require the slope, with its 80-foot elevation change, be returned to its normal state after construction. The steep grade made direct cement truck access practically impossible; a large pumper truck would not have had a direct laydown area to set up.
Turf Reinforcement Mats (TRMs). TRMs require constant maintenance to ensure vegetation is healthy and meets expected hydraulic performance values. This solution was immediately eliminated because vegetation could not be established in the drainage channel to meet the acceptable shear values prior to the next storm (which could have occurred within days or weeks after repairs were completed). There were also concerns about wildlife entanglement and mowing issues that affect TRMs when they are not soil-filled.
Articulate Concrete Blocks (ACBs). Potential issues transporting ACBs up the steep slope without causing a major disturbance around the pipe – as well as the time and expense to remove and dispose of soil off site – made this option unviable.
Geosynthetic Concrete Composite Mats (GCCMs). GCCMs offered quick installation with limited disturbances to the area, advanced hydraulic performance capabilities, and natural blending with the surrounding vegetation.

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