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Bank Protection in Los Angeles County
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Background on Soil-Cement Approval for Bank
Protection in Los Angeles County
Mark E. Krebs, P.E., President – Pacific Advanced Civil
Engineering, Inc. (PACE)
LADPW is one of the leading agencies in southern California in the
establishment of flood control criteria and standards. For many
years, concrete and rip-rap have been used per LADPW standards throughout
the county for river and creek bank protection. Based upon improved
environmental sensitivity, public safety and infrastructure cost,
PACE, under the direction of its client, Newhall Land, sought to
apply soil-cement as an alternative bank protection method along
the Santa Clara River, a major regional watershed within LA County.
As a result, a stringent review and analysis process was necessary.
Following the culmination of nearly five years of effort, soil-cement
has finally been approved as a standard bank protection method,
making flood control history in LA County.
County Concerns and Review Process for Alternative Bank
Protection Methods
The LADPW soil-cement review process was fueled to life in early
2000 when Newhall Land sought to place 4,500 linear feet (32,000
cubic yards) of soil-cement as bank protection along a portion of
the San Francisquito Creek for the proposed Westcreek development
project, which is located outside of the City of Santa Clarita and
within LADPW jurisdiction. After reviewing existing soil-cement
project applications and considering the potential far reaching
benefits of soil-cement, LADPW identified Westcreek as a soil-cement
pilot project and established a comprehensive plan to review soil-cement
designs and construction Quality Assurance/Quality Control (QA/QC)
specifications. LADPW, with its desire to apply only the highest
standard of engineering practice, had specific areas of concern
that needed to be addressed in the consideration of soil-cement:
(1) structural integrity, (2) flood protection durability, (3) in-field
testing and quality control, and (4) long-term maintenance requirements.
Technical Demonstration Program
The engineer (PACE) prepared a soil-cement review program that addressed
the agency’s concerns by identifying past successes, other
agency standards, and recommending strict implementation and quality
control standards. The work was closely coordinated with public
agencies such as U.S. Fish and Wildlife, the State Regional Water
Quality Control Board (RWQCB), California Department of Fish and
Game, and the U.S. Army Corp of Engineers (USACE) to ensure the
proposed soil-cement solution would address their concerns regarding
environmental and water quality issues related to bank protection.
The review process began with the engineer providing several presentations
regarding detailed aspects of soil-cement design, construction,
and quality control to numerous departments within LADPW: Building
and Safety, Land Development, Materials Engineering, Flood Maintenance,
Soils and Geology, Stormwater, and Watershed Management. These presentations
addressed the USACE, U.S. Bureau of Reclamation (USBR), Pima County
and other flood control agencies’ experience over the past
50 years with soil-cement applications throughout the southwestern
United States and the design and testing standards that have been
developed along the way.
The Portland Cement Association (PCA) was instrumental in providing
current and historical design and QA/QC data for LADPW review. Additionally,
PCA coordinated with PACE to provide tours of in-place soil-cement
applications in Orange County, California; Pima County, Arizona;
and Maricopa County, Arizona for the Soils and Materials Testing
Division of LADPW. These tours allowed LADPW engineers to view,
first-hand, in place and ongoing soil-cement installations and discuss
with other public agency personnel the past performance and maintenance
requirements of the soil-cement bank protection.
LADPW began to realize the great potential for soil-cement as a
bank protection method. As a result, they established a Soil-Cement
Technical Review Committee (TRC). The TRC was formed to work with
PACE to establish LADPW standards for soil-cement design, construction,
and QA/QC procedures.
Structural Integrity and Durability
A primary soil-cement consideration LADPW wished to address was
structural integrity (durability and life expectancy). In response,
the engineer researched and compiled data from a number of sources
and presented a comparison analysis of soil-cement, rip-rap and
reinforced concrete channels.
Findings concluded that soil-cement has very low maintenance requirements
and outstanding long-term flood control/erosion resistance effectiveness
compared to the alternatives. Pima County, AZ, was able to compare
the durability of soil-cement in a before and after-installation
comparison during 100-year storm events. Subsequently, Pima County
will only allow the use of soil-cement for major bank protection
projects, and over the past 30 years has placed more than 75 miles
of soil-cement.
In-field Testing and Quality Control
To address the LADPW TRC’s concerns regarding in-field testing
and quality control, the engineer developed numerous control systems
and delivered presentations identifying design, construction testing
and process overviews and standards including those applied by other
agencies throughout the southwest. These presentations also stressed
the importance of QA/QC through proper construction monitoring,
review, and testing processes.
Maintenance Requirements
The best way to determine true maintenance requirements of soil-cement
bank protection was to obtain accounts from flood control agency
maintenance personnel in areas where soil-cement has been in place
for many years. The engineer and LADPW found through interviews
with the USACE, Orange County, Pima County, and Maricopa County
personnel that soil-cement has minimal maintenance requirements
and has proven to be exceptionally durable over long periods of
time.
Implementing Soil-Cement as a Standard in LA County
After some additional tours of soil-cement applications and numerous
technical meetings with the TRC, LADPW was ready to finalize standards
for soil-cement implementation. As part of this final phase, the
engineer prepared design, construction and QA/QC guidelines that
included specific guidelines for feasibility, design specifications,
construction and QA/QC standards. In particular, specifications
were provided for mixing and placement of soil cement based on a
combination of existing specifications used by the USACE, Orange
County, and Pima County. These guidelines provide a detailed plan
for the developer, contractor, review agency, project engineer and
geotechnical engineer for implementing a highly controlled and successful
soil-cement project.
LADPW Staff Training
The final step in getting a soil-cement standard approved by TRC,
was to provide training for the LADPW Materials Testing and Construction
personnel. PACE, along with other recognized experts in the field
of soil-cement from the USACE and PCA, sponsored a two-day, hands-on
training program in November, 2002, in conjunction with the construction
of the Westcreek soil-cement project. The program was designed to
train LADPW personnel in soil-cement field and laboratory testing
standards, and construction QA/QC methods. The training included
hands-on soil-cement testing in a laboratory and quality control
field testing at the Westcreek project site.
LADPW approved soil cement as a standard approved bank protection
method soon after the training workshop and completion of the Westcreek
soil cement project.
First LADPW Approved Soil-Cement Application
Following LADPW’s change in classification from “pilot”
to “approved project,” Westcreek became the first approved
application of soil-cement as bank protection in LADPW’s history
and the first new bank protection standard for LADPW in over 50
years. The project includes over 4,500 linear feet (32,000 cubic
yards) of soil-cement bank protection. It embodies all that is right
with the engineering profession:
1. Engineers’ desire to improve the methods and procedures
used in the flood control industry.
2. Government agencies willing to accept new and innovative solutions
after careful and thorough scrutiny.
3. Developers’ willingness to improve upon environmental sustainability
of projects and perseverance to implement new and better standards.
The Westcreek soil-cement project has both buried-revegetated and
exposed conditions. The buried-revegetated areas appear undisturbed
and the exposed soil-cement bank protection appears as native hardened
soil providing a natural appearance along the creek edge.
Since the approval of Westcreek, over 37,500 linear feet (290,000
cubic yards) of soil-cement bank protection has been constructed
in LA County, and there are plans for future construction of more
than 75,000 linear feet.
Implications for Future Flood Control Practice in Los Angeles
County
Soil-cement is the first bank protection alternative to be approved
within LADPW for nearly a half-century. It has made a significant
improvement to the environmental and aesthetic aspects of bank protection,
while maintaining a high level of flood protection for LADPW and
the public. Through the efforts of PACE, Newhall Land, and LADPW,
an innovative and improved bank protection method that is hydraulically
sound, environmentally responsible and aesthetically superior can
now be applied.
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