|
Embankment Slope Protection
Water Resources Home
> Soil Cement > Embankment Slope Protection
The typical design section used for slope protection depends on
the severity of its intended application. For slopes exposed to
moderate-to-severe wave action the soil-cement is usually placed
in successive horizontal layers 6 ft to 9 ft wide and 6 in. to 9
in. thick adjacent to the slope. This is referred to as "stairstep"
slope protection. The "steps" that are created help to
dissipate the energy in the waves and reduce the height of the wave
runup.
For less severe applications, slope protection may consist of a
6 in. to 12 in. thick layer of soil-cement placed parallel to the
slope face. This method, referred to as "plating," uses
a lot less soil-cement than the stairstep method but cannot be successfully
placed on slopes steeper than 2.5:1 and provides little resistance
to wave runup.
 The
largest soil-cement project worldwide involved 1.2 million cu yd
of soil-cement slope protection for a 7,000 acre cooling water reservoir
at the South Texas Nuclear Power Plant near Houston. Completed in
1979, the 39 ft to 52 ft high embankment was designed to contain
a 15 ft high wave action created by hurricane force winds. The main
embankment was 13 miles long and had another 7 miles of interior
dikes.
Florida Power and Light in South Florida created a cooling reservoir
from an old phosphate pit in 1998. The 30,000 ft long embankment
was designed with riprap slope protection, but the contractor submitted
a value engineering proposal to change the rock riprap to soil-cement.
The contractor placed 80,000 cu yd of soil-cement using the platting
method on slopes that varied from 3:1 to 5:1. The contractor utilized
a paving machine to place all the soil-cement. Serrations were made
in the soil-cement near the top of the embankment to increase the
roughness and reduce wave runup.
 Soil-cement
was used in 2001 to rehabilitate the slope protection at Jackson
Lake Dam east of Denver, Colorado. The fine grain silts and sands
from the reservoir were used to produce the soil-cement. The project
was bid with two options for horizontal width: 6 ft or 8 ft. As
mentioned earlier, an 8 ft width is usually specified because that
is the minimum width on which trucks can operate. Widths narrower
than 8 ft have been found to be uneconomical even through less soil-cement
is used. The contractor was able to develop a delivery system of
trucks and a track excavator to place the soil-cement on the horizontal
lifts. The only equipment operated on the lift were a small dozer
and a smooth drum vibratory roller, which could operate on a 6 ft
wide surface. The contractor placed 130,000 cu yd along the 3,000
ft long dam.
Bank Protection/Levees
 Building
on the success of soil-cement for slope protection for wave action,
engineers transferred this knowledge to protecting streambanks from
lateral erosion during flood events. The success of soil-cement
in this application was demonstrated during two significant flood
events in Tucson, Arizona, in 1983 and 1993. Even though overtopped,
the soil-cement bank protection prevented millions of dollars in
property damage. In Tucson more than 74 miles of streams, rivers,
and washes are now protected with soil-cement.
 A
typical section consists of 8 ft to 9 ft wide horizontal layers
placed in stairstep fashion along 1:1 stream bank slopes. If the
design calls for a "soft" bottom the soil-cement is carried
before the existing channel invert elevation to a depth equal to
the maximum scour depth that could be expected over the life of
the project. At the terminus of the soil-cement reach, the soil-cement
protection is turned perpendicular to the channel into the banks
approximately 50 ft to prevent head-cutting erosion from occurring
behind the soil-cement.
 The
exposed slope facing can be trimmed "smooth," left natural
with loose overbuild soil-cement remaining in place, or rough steps
can be created without any formwork. To withstand the abrasive force
of stormwater flows at velocities up to 20 ft/sec, the soil-cement
is typically designed for a minimum 7-day compressive strength of
750 psi. Some designers who use fly ash in the soil-cement may use
a 28-day requirement for compressive strength.
 In
Albuquerque, New Mexico, soil-cement was used on both the San Antonio
and the Calabacillas arroyos where sensitivity to the environment
was an important consideration. Special artwork was used at Calabacillas.
Colored shotcrete was used above the soil-cement, and precast dinosaur
bones were placed into the shotcrete. The side slopes at Calabacillas
and San Antonio arroyos were stepped to both provide east exit from
the channel and to mimic a layered stone formation.
A soil-cement protected levee was constructed at Camp Pendleton
to protect the airfield. This approximately 2 mile long levee used
over 150,000 cu yd of soil-cement, with the soil coming from the
banks of the Santa Margarita River.
 The
Los Angeles District of the U.S. Army Corps of Engineers designed
soil-cement bank protection along a reach of the Santa Ana River
in Norco, California. The river was encroaching onto a residential
area located on top of a bluff.
|
 |
More on Soil Cement:
Overview
Embankment Slope Protection
Bank Protection/Levees
Drop and Grade Control Structures
Liners
FAQs
Southern California Case Study
Moss Creek Dam Case Study
Rueter-Hess
Dam and Reservoir Case Study
RCC/Soil Cement Contractor Directory
|