Geosynthetics February/March 2020 - 14

An innovative erosion control solution using concrete enhanced synthetic turf

Benefits include
the aesthetics of
turf vegetation,
exceptional hydraulic
performance, minimal
maintenance, smaller
carbon footprint,
low-impact, rapid and
scalable installation,
and lower installed
construction cost.

Geosynthetics | February March 2020

gabion structures and roller-compacted
concrete (RCC). Benefits include the
aesthetics of turf vegetation, exceptional
hydraulic performance, minimal maintenance, smaller carbon footprint, lowimpact, rapid and scalable installation,
and lower installed construction cost
(FEMA 2014, Watershed Geosynthetics
2015 and Watershed Geosynthetics
2018). Extensive performance testing has been performed on CEST, and
numerous installations of CEST have
been completed. The remainder of this
article presents the testing and a summary of select installations.

Performance testing
Full-scale hydraulic testing
Full-scale, steady-state overtopping testing was performed at Colorado State
University-Engineering Research Center
(CSU). Testing was performed in accordance with ASTM D7277, Standard
Test Method for Performance Testing
of Articulated Concrete Block (ACB)
Revetment Systems for Hydraulic
Stability in Open Channel Flow. Test
results were analyzed in accordance
with ASTM D7276, Standard Guide
for Analysis and Interpretation of Test
Data for Articulating Concrete Block
(ACB) Revetment Systems in Open
Channel Flow. CEST was installed in
a 2H:1V-sloped flume over a sandyloam-compacted subgrade in general
accordance with the manufacturer's
installation guidelines. The subgrade
was compacted to 90% dry density of
the standard Proctor test (ASTM D698).
A horizontal (cross-flume) seam was
placed in the synthetic turf layer near
the bottom of the flume. The purpose of
the seam was to test seam strength under
high-flow velocity.
The CEST was tested at 1.5-, 3.0-,
5.0- and 5.5-foot (0.46-, 0.91-, 1.52- and
1.68-m) steady-state overtopping depths

for a cumulative total of 24 hours over
two separate tests. One 12-hour test was
performed in April 2013 (Thornton et al.
2013), and the second 12-hour test was
performed in September 2015. After both
tests, the embankment beneath the CEST
system was inspected. The system and
underlying soil were determined to be
intact. Velocity on the system was calculated by CSU using the prescribed methodology in ASTM D7276. CSU reported
stable performance values for velocity of
40.5 feet/second (12.2 m/s) at the 5.5-feet
(1.68-m) overtopping depth. No instability, deformation, loss of intimate contact,
damage to the system or erosion of the
underlying subgrade occurred. The peak
tested velocity of 40.5 feet/second (12.2
m/s) is not the maximum performance
threshold since there was no failure in
the system; the maximum capacity of the
flume under the specific test conditions
was 40.5 feet/second (12.2 m/s). Two
separate, full-scale flume tests have been
performed, demonstrating performance
results are repeatable and CEST provides
embankment protection under high-flow
velocity conditions.
Full-scale simulator for wave
overtopping testing of levee
landward side-slope protection
Tests were performed on CEST at
CSU in the wave overtopping simulator. Wave overtopping testing was performed in accordance with methodology developed by the U.S. Army Corps
of Engineers (Hughes et al. 2012 and
Thornton et al. 2012). The CEST revetment was installed in the flume over
a highly erodible silty sand subgrade
on a 3H:1V slope that transitioned to
a 25H:1V berm at the toe. The CEST
was installed with a downstream seam
following the centerline of the tray to
evaluate seam strength between two
adjacent panels of the synthetic turf
component. The seam was fabricated

Geosynthetics February/March 2020

Table of Contents for the Digital Edition of Geosynthetics February/March 2020