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Post Base Support Systems for Flexible Rockfall and Debris Flow Barriers: Design Framework and Performance Criteria

Description:

Flexible Barriers used for protection against geohazards such as rockfalls, debris flows, and avalanches have been used for more than 50 years in Europe and North America. Their effectiveness has been proven both by performance of installed systems, and testing and certification programs from well-established manufacturers and government agencies. Engineers and Geologists have successfully applied these systems to a wide variety of environments and site conditions. The use of such protection measures has saved lives and reduced the economic impact of geohazards on highways, utility corridors, pipelines, hydroelectric projects, mines, and residential developments globally.

With their long history and proven performance, the installation of flexible barriers has become more commonplace to mitigate rockfalls and debris flows. Unfortunately, during the expansion of their use, a thorough understanding of the flexible nature of the systems has not been fully incorporated into post base support designs by some designers. Nor have manufacturers been able to provide guidance on tolerances for post base support systems. An ever increasing trend toward rigid, overly conservative post base anchor designs that implement serviceability requirements for bridge and building foundations has crept into the practice (e.g. use of piles; very large concrete foundations; increased number of anchors). Robust, rigid post base support systems can be detrimental to the functionality of the flexible barriers by decreasing flexibility complicating construction requirements and increasing maintenance needs. In general, this increases installation costs and could cause some systems to no longer be economically feasible.

To better understand the current state of practice for designing and constructing post base support systems, the Association of Geohazard Professionals (AGHP) recently surveyed approximately 50 experienced industry professionals about their opinion of flexible barrier post anchorage. The results suggest that the primary driving force toward rigid post anchorage design is a combination of the absence of design/application guidelines specific to flexible barrier installations and a lack of understanding of the function of the post base support. Both of which can lead to extremely conservative and costly post base support designs.

A review of anchorage designs from recent projects indicates a wide variety of post base support systems are being used for flexible barriers. If a common approach for the design of post base support systems were developed for various levels of serviceability, then designers would have more guidance to prepare less adverse designs for elements of the support systems such as: number and capacity of ground anchors; size and reinforcement of concrete foundations; number of required support systems to meet a desired serviceability; etc. This could improve the function and serviceability of the flexible barriers overall.

Objective:

The primary goal of this proposed research is to establish formal criteria for the design of cost efficient and effective post base support systems. It is anticipated the criteria will be based on flexible barrier functional requirements, serviceability needs, empirical testing, documented project performance, and geotechnical engineering principles. Guidelines for developing designs and use of flexible barriers will help standardize post base support systems. It is important that a design guideline be developed through collaboration between manufacturers, designers, contractors, and owners. It is anticipated that the development of such criteria will result in lower project costs, improved serviceability and life cycle costs of the flexible barrier systems, and increased public safety as more systems are installed.

Benefits:

The current state of the practice implements static designs for post anchorage of dynamic flexible barriers. This will continue to result in expensive and inefficient mitigation of geohazards along highways, utility corridors and other infrastructure. The existing high capital cost of individual projects limits the number of projects that owners (e.g. Departments of Transportation) can carry out and limits their ability to protect assets and lives.

If a standardized approach could be implemented by the creation of design guidelines and criteria as outlined in the research objectives, many benefits would be realized:

  • Designers would have vetted guidelines for designing support systems and consistent design criteria that can be referenced;

  • Designers and owners would be more confident using flexible barriers as a cost efficient mitigation measure;

  • There would be a higher degree of confidence in the level of safety for projects;

  • The cost of preparing designs would be economized;

  • Construction costs would decrease;

  • More projects could be realized and therefore more lives and infrastructure protected with a greater reduction of economic risk;

  • Owners would have a reference document for their asset management and development of maintenance/inspection protocols.
Related Research:

A proposed foundation design concept for flexible barriers was first published by Gerber in 2001. An internal report that describes a safety concept of the foundation loads for the design of rockfall barrier fences was published only in German in Werner in 2008.

There is currently only one public study focused on the function, design, and efficiency of post base supports for flexible barriers, that was conducted by the Colorado Department of Transportation in conjunction with Yeh and Associates. This study looked at low energy dynamic impacts directly to a post and the resulting displacements of a few anchoring systems. Although this research provided valuable information, its focus was on direct impacts, which is not representative of the standard design approach for implementing geohazard barriers. It also did not result in any guidelines for the design of post base support systems.

The proposed research would build on this earlier work and investigate further loading scenarios to build a basis for design guidelines. The data collected also would be used for outlining performance criteria that will help with various research concerns related to the long-term performance and asset management of these mitigation systems. A brief list of known, published, research on the subject of post base support systems is below.

Arndt, B., Arpin, B., Higgins, J.D., Thompson, P. (2016). “Guidelines for Certification and Management of Flexible Rockfall Protection Systems”, NCHRP Report 823, National Cooperative Highway Research Program, 31 pages.

Arndt, B., Arpin, B., Higgins, J.D., Thompson, P. (2015). “Guidelines for Certification and Management of Rockfall Protection Systems: Final Report”, NCHRP Project 24-35, National Cooperative Highway Research Program, 171 pages.

Arndt, B., Ortiz, T., Group, R., (2014). “Full Scale Testing of Rockfall Barrier and Post Foundation Systems”, Geotechnical Practice Publications (GPP) GPP 9, Geo-Influences Proceedings of the 2014 Biennial Rocky Mountain Geo-Conference, Lakewood, CO, edited by: Strickland, J., Wiltshire, R., Goss, C., November 7, 2014.

Arndt, B., Ortiz, T., Group, R., (2013). “Testing of Rockfall Post Foundations in Colorado”, 64th Highway Geology Symposium, September 9-12, 2013.

Arndt, B., Ortiz, T., Turner, K., (2009). “Colorado’s Full-Scale Field Testing of Rockfall Attenuator Systems”, Transportation Research Circular E-C141, October 2009.

Gerber, W., (2001). Guideline for the Approval of Rockfall Protection Kits. Swiss Agency for the Environment, Forests and Landscapes (SAEFL), and the Swiss Federal Institute (WSL), Berne, Switzerland, 2001. www.environment-switzerland.ch/publications.

Gerber W. (2008). “Verankerung und Fundation von Schutznetzen gegen Steinschlag“, Entwurf 2008 zu Kapitel 7 der Schweizer Steinschlagrichtlinie, WSL Switzerland.

Giacchetti, G., Brunet, G., Grimod, A., (2014). “Case Histories on Light Anchor Post System for Flexible Barriers”, 65th Highway Geology Symposium, July 7-10, 2014.

Ingraham, P. and Telesnicki, M., (2014). “Ground Anchor Selection and Testing – Matching Ground Anchors to Their Desired Function and Testing Their Serviceability”, 65th Highway Geology Symposium, July 7-10, 2014.

Scarpato, D. (2016)). “Rockfall Barrier Foundations and Challenges Associated with Estimating Design Basis Loads”, 67th Highway Geology Symposium, July 2016.

Stelzer, G., Bichler, A. (2013)). “ONR 24810 – A Comprehensive Guideline for Building Better Rockfall Protection Structures”, 64th Highway Geology Symposium, September 2016.

Platzer K. (2013). “_Kraftmessung entlang von Ankern einer flexiblen Lawinenverbauung unter dynamischen Einwirkungen, _Geotechnik Schweiz.

Turner, R., Duffy, J., Turner, J., (2009). “Post Foundations for Flexible Rockfall Fences”, 60th Highway Geology Symposium, September 29-October 2, 2009.

Volkwein A., Krummenacher B., Wendeler C., (2016). “Load on post foundations of flexible rockfall barriers“, Interpraevent Luzern Switzerland, 2016.

William F. Kane, W. and Shevlin, T., (2012). “Rockfall and Debris Flow Barrier Post Foundation Design”, 63rd Highway Geology Symposium, May 7-10, 2012.

Tasks:

The direct products of this research will be:

  1. Database of current and historic post base support designs: Case studies from around the world will be collected and cataloged with particular focus on designs that have been impacted by events that tested the capacities of the systems
  2. Empirical testing data of loading and reaction of post base support designs: Selected post base support designs will be investigated, including full scale testing, in order to obtain relevant parameters useful for the development of a design method
  3. Circular summarizing database and test data: A summary of the findings from the first two tasks that will be published for peer review
  4. Design guideline for post base supports: The primary publication will be a guideline for a standardized approach to post base support design.
  5. Circular regarding the application of the design guideline and best practices for construction and maintenance of post base supports: A secondary publication will be a circular that explains the development process of the guideline and its proper application. It will also cover best practices for the construction of post base supports as well as their inspection and maintenance.
  6. Professional education: A series of workshops/webinars will be developed to help disseminate the information to engineers, contractors and owners
Implementation:

(a) Appropriate target audience: Design Professionals (Geotechnical/Geological Engineers, Engineering Geologists, and Geologists) in the geohazard mitigation industry, as well as owners of mitigation structures (e.g. DOT’s).

(b) Key-decision-makers: Doug Anderson, Western Federal Lands; Scott Anderson, BGC Engineers; Ryan Turner, CALTRANS; Bob Group, Ty Ortiz, CDOT; Ben Arndt, John Duffy, Yeh and Associates; Brent Black, Landslide Technology; Marilyn Dodson Central Federal Lands

(c) AASHTO committees and other organizations: Engineering Geology and Rockfall Management Subcommittee, Geotechnical Asset Management; Association of Geohazard Professionals

(d) “Early Adopters”: Colorado DOT, Washington DOT, California Department of Transportation, Association of Geohazard Professionals.

A possible impediment will be practitioners within the broader civil engineering community who are inexperienced with geologic hazard mitigation design and might be tempted to follow “standard” engineering procedures for building or bridge foundation design or established national and local building codes. Many of which have been adopted or referenced due to a lack of more appropriate barrier foundation design criteria.

Relevance:

Given the common usage of these systems, it is important that a design guideline be developed through collaboration between manufacturers, designers, contractors, and owners. Multiple state, federal, and local transportation agencies have, or potentially install, these systems. States that have expressed interest include: Colorado, Washington, and Californian.

Sponsoring Committee:AFP10, Engineering Geology
Research Period:24 - 36 months
Research Priority:High
RNS Developer:Tim Shevlin, R.G. Geobrugg North America, LLC 22 Centro Algodones, NM 87001 Ahren Bichler Trumer North America Inc., 14900 Interurban Ave S., Suite 271 #19, Seattle, Washington, 98168
Source Info:Doug Anderson, Western Federal Lands; Scott Anderson, BGC Engineers; Ryan Turner, CALTRANS; Bob Group, Ty Ortiz, CDOT; Ben Arndt, John Duffy, Yeh and Associates; Brent Black, Landslide Technology; Marilyn Dodson Central Federal Lands
Date Posted:05/08/2017
Date Modified:05/22/2017
Index Terms:Geotechnical engineering, Rockfalls, Anchorages, Avalanches, State of the practice, Bridge foundations, Debris flows, Piles (Supports),
Cosponsoring Committees: 
Subjects    
Highways
Design
Maintenance and Preservation
Geotechnology

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