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Guidelines for Certification and Management of Flexible Rockfall Protection Systems (2016)

Chapter: Chapter 4 - Proposed Inventory and Condition Assessment of Rockfall Fence Systems for Agencies

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Suggested Citation:"Chapter 4 - Proposed Inventory and Condition Assessment of Rockfall Fence Systems for Agencies." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for Certification and Management of Flexible Rockfall Protection Systems. Washington, DC: The National Academies Press. doi: 10.17226/23519.
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Suggested Citation:"Chapter 4 - Proposed Inventory and Condition Assessment of Rockfall Fence Systems for Agencies." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for Certification and Management of Flexible Rockfall Protection Systems. Washington, DC: The National Academies Press. doi: 10.17226/23519.
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Suggested Citation:"Chapter 4 - Proposed Inventory and Condition Assessment of Rockfall Fence Systems for Agencies." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for Certification and Management of Flexible Rockfall Protection Systems. Washington, DC: The National Academies Press. doi: 10.17226/23519.
×
Page 12
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Suggested Citation:"Chapter 4 - Proposed Inventory and Condition Assessment of Rockfall Fence Systems for Agencies." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for Certification and Management of Flexible Rockfall Protection Systems. Washington, DC: The National Academies Press. doi: 10.17226/23519.
×
Page 13
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Suggested Citation:"Chapter 4 - Proposed Inventory and Condition Assessment of Rockfall Fence Systems for Agencies." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for Certification and Management of Flexible Rockfall Protection Systems. Washington, DC: The National Academies Press. doi: 10.17226/23519.
×
Page 14
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Suggested Citation:"Chapter 4 - Proposed Inventory and Condition Assessment of Rockfall Fence Systems for Agencies." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for Certification and Management of Flexible Rockfall Protection Systems. Washington, DC: The National Academies Press. doi: 10.17226/23519.
×
Page 15

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10 C H A P T E R 4 The following forms are proposed for use in inspecting, inventorying, and assessing flexible rockfall fence systems. Examples of completed forms can be found in the case his- tory presented in the Final Report, which is available on the NCHRP Project 24-35 web page at www.trb.org. 4.1 Condition Rating of Rockfall System Elements Rockfall systems are composed of elements that contribute to the function and performance of the system. These ele- ments have been divided into primary and secondary ele- ments based on the importance of the element in the system’s ability to function as designed. Primary elements are compo- nents of the system that, if damaged, significantly reduce the functionality of the system. Secondary elements are compo- nents that are important in the functionality of the system to perform as designed, but the system would likely still provide protection from an impact near the design energy level even if the secondary element is damaged. Condition ratings of primary elements and secondary ele- ments range from 10 (excellent) to 1 (critical). Table 4-1 and Table 4-2 describe the condition state of primary and sec- ondary elements, respectively, and the associated condition rating that would be assigned based on observation during the field inspection. Condition ratings are recorded on the Rockfall System Inventory Form described in Section 4.7. 4.2 Rockfall System Performance Rating In addition to primary and secondary condition ratings, the overall performance of the system is evaluated. The per- formance rating is intended to capture the condition of the system related to items and elements that are not captured by the primary and secondary element condition ratings. As with the condition element ratings, performance ratings vary from 10 (excellent) to 1 (critical). Table 4-3 describes the condition state and the associated condition rating for performance. 4.3 Rockfall System Condition and Performance Weighting Factors Weighting factors are used to account for various levels of element importance in the overall system rating. Proposed weighting factors presented in Table 4-4 are based on expe- rience and calibration using this system to evaluate various rockfall protection measures that are discussed in a case history in the Final Report. Proposed weighting factors for primary elements range from 3 to 10 to reflect the overall importance of the element in the ability of the system to func- tion as designed. A weighting factor of 10 is proposed for elements that are essential to the performance of the system such as panels, posts, bearing ropes, and lateral anchors. A weighting factor of 1 is proposed for secondary elements because these elements are typically not essential to the func- tion of the system. A weighting factor of 10 is proposed for the performance rating of the system because the overall per- formance of the system is essential to its function as designed. The proposed weighting factors may need to be adjusted as the system is implemented and more experience is gained in using the system. Additionally, weighting factors will need to be adjusted to calibrate the system to the practices of specific agencies to account for the varying use of elements and the importance of the elements in the system performance. 4.4 Rockfall System Inventory and Assessment Data Reliability Rating Data reliability ratings are also included in the Condition Assessment Forms to capture the level of confidence in the data that is used to evaluate the overall system condition. Table 4-5 summarizes data reliability rating guidance. Proposed Inventory and Condition Assessment of Rockfall Fence Systems for Agencies

11 ROCKFALL SYSTEM CONDITION RATING PRIMARY ELEMENTS Element Condition Ratings 10 to 8 7 to 6 5 to 1 GOOD TO EXCELLENT (A to B) FAIR (C to D) POOR TO CRITICAL (F) Primary System Elements Panel Panel elements are as constructed and show no signs of rockfall impacts that resulted in significant damage. Panel elements show signs of rockfall impacts that resulted in moderate damage, but can still contain a rockfall event. Panel elements show signs of rockfall impacts that resulted in severe damage and likely cannot contain a rockfall event. Post Posts are as constructed and show no signs of rockfall impacts that resulted in significant damage. Posts show signs of rockfall impacts that resulted in moderate damage, but are still functional. Posts show signs of rockfall impacts that resulted in significant damage and are not fully functional. Bearing/ Retaining Ropes and Anchors Wire ropes and anchors are as constructed and show no signs of rockfall impacts that resulted in significant damage. Wire ropes and anchors show signs of rockfall impacts that resulted in moderate damage but are still functional. Wire ropes and anchors show signs of rockfall impacts that resulted in severe damage and are not fully functional. Post Foundation Foundations are as constructed and show no signs of rockfall impacts that resulted in significant damage. Foundations show signs of rockfall impacts that resulted in moderate damage, but are still functional. Foundations show signs of rockfall impacts that resulted in severe damage and are not fully functional. Braking Elements Braking elements are as constructed and show no signs of rockfall impacts that resulted in significant damage. Braking elements show signs of rockfall impacts that resulted in engagement, but are still functional. Braking elements show signs of rockfall impacts that resulted in engagement and are not functional. Table 4-1. Proposed rockfall system condition rating—primary elements. ROCKFALL SYSTEM CONDITION RATING SECONDARY ELEMENTS Element Condition Ratings 10 to 8 7 to 6 5 to 1 GOOD TO EXCELLENT (A to B) FAIR (C to D) POOR TO CRITICAL (F) Secondary System Elements Panel Secondary Mesh Panel elements are as constructed and show no signs of rockfall impacts that resulted in significant damage. Panel elements show signs of rockfall impacts that resulted in moderate damage, but can still contain a rockfall event. Panel elements show signs of rockfall impacts that resulted in severe damage and likely cannot contain a rockfall event. Shackles, Clips, Connections Elements are as constructed, and no elements are missing. Elements show signs of moderate damage, but are still functional. Minor elements are missing creating gaps < 3 inches wide. Elements show signs of severe damage and are not functional. Major elements are missing creating gaps ≥ 6 inches wide. Corrosion No evidence of corrosion, staining, contamination, or crack/spalling due to weathering or chemical attack. Minor evidence of corrosion, staining, contamination, or cracking/spalling due to weathering or chemical attack. System is compromised by corrosion, staining, contamination, or cracking/spalling due to weathering or chemical attack. Foundation Protection Systems Systems are as constructed and show no signs of rockfall impacts that resulted in significant damage. Systems show signs of rockfall impacts that resulted in moderate damage, but are still functional. Systems show signs of rockfall impacts that resulted in severe damage and are not functional. Other As constructed. Moderate damage, but still functional. Severe damage, not functional. Table 4-2. Proposed rockfall system condition rating—secondary elements.

12 ROCKFALL SYSTEM CONDITION RATING PERFORMANCE ELEMENTS Element Condition Ratings 10 to 8 7 to 6 5 to 1 GOOD TO EXCELLENT (A to B) FAIR (C to D) POOR TO CRITICAL (F) System Performance Performance No combinations of element distresses that indicate unseen problems or create significant performance problems are observed. No history of remediation or repair to adjacent elements is observed. No impacts from rockfall accumulation or vegetation noted within the system or within adjacent elements. Some observed distresses to specific elements. Some element distress combinations are observed that indicate fence component problems. Minor work on primary elements or major work on secondary elements has occurred improving overall system function. Minor impacts from rockfall accumulation or vegetation noted within the system or within adjacent elements. System elements that have failed are apparent, rockfall impacts significantly damaged system. Distresses clearly indicate serious stability problems with components. Major repairs have occurred to structural elements, though functionality has not improved. Adverse impacts from rockfall accumulation or vegetation noted within the system or within adjacent elements interfering with system. Table 4-3. Proposed rockfall system performance rating. ROCKFALL SYSTEM WEIGHTING FACTOR GUIDANCE Suggested Weighting Factor Weighting Factor Definition 3 to 10 Primary Elements (Panel, Posts, Top Bearing Rope, Lateral Anchors) 1 Secondary Elements (Other Elements) 10 Performance Table 4-4. Proposed rockfall system weighting factor. ROCKFALL SYSTEM DATA RELIABILITY RATING GUIDANCE Data Reliability Factor Data Reliability Factor Definition 1 Very Good Observed conditions clearly describe system performance. Additional investigations are not needed. 2 Good Observed conditions are sufficient to rate the condition of element(s); however, additional investigations would be useful to better understand element performance. 3 Poor Conditions cannot be sufficiently observed to rate element(s), warranting additional investigation to better define element performance and/or to determine the cause(s) of poor performance. Table 4-5. Proposed rockfall system data reliability rating.

13 Table 4-6. Proposed rockfall system failure consequence rating. ROCKFALL SYSTEM FAILURE CONSEQUENCE RATING GUIDANCE Definitions Consequence of Failure Low: No loss of roadway, no-to-low public risk, no impact to traffic during construction Moderate: Hourly to short-term closure, low-to-moderate public risk, multiple alternative routes High: Seasonal to long-term loss of roadway, substantial loss or public risk, no alternative routes 4.5 Rockfall System Failure Consequence Rating The Rockfall System Failure Consequence Rating (Table 4-6) is based on the impact to roadway users, public safety, and availability of alternate routes. 4.6 Rockfall System Condition Rating The overall system condition rating is evaluated using the total of the condition scores and the total of the weighting factors and is assigned a letter grade based on the criteria out- lined in Table 4-7. As with the weighting factors, the criteria used to assign grades are based on experience and should be reevaluated as additional data becomes available and to suit specific agencies. 4.7 Proposed Rockfall System Inventory Form The Rockfall System Inventory Form (Table 4-8) gathers information about the system identification, location, type of components, dimensions, and a summary of the overall system condition based on the detailed condition assessment. 4.8 Proposed Rockfall System Condition Assessment Form The Rockfall Fence Condition Assessment Form (Table 4-9) is used to guide detailed inspection and documentation of the condition of individual elements of the system. A descrip- tion of the condition of the elements is recorded and a condi- tion rating and data reliability score are assigned. The condition score is calculated as the condition rating multiplied by the weighting factor. Table 4-7. Proposed rockfall fence system rating criteria. ROCKFALL FENCE SYSTEM CONDITION RATING CRITERIA Grade Criteria A Fence condition ≥ 9 B Fence condition rating between 8 and < 9 C Fence condition rating between 7 and < 8 D Fence condition between 6 and < 7 F Fence condition < 6

14 ROCKFALL SYSTEM INVENTORY FORM Rockfall System ID Chute orPathway Location Roadway and MM Start (Approx) Manufacturer Station Roadway and MM End (Approx) Inspected By Distance Centerline Latitude Inspected Date Left or Right of Centerline Longitude Approx. Year Built Project Code for System Elevation SYSTEM FUNCTION, DIMENSIONS, and DESCRIPTION Rockfall Mitigation Type Panel Lacing Rope Dia. Post to Foundation (Fixed/Pinned/Hinged) Panel Type Ring Net Designation Uphill Retaining Anchor Dia. Panel Aperture Opening Post Flange Dimension (bf) Lateral Retaining Anchor Dia. Panel Wire Thickness Post Depth Dimension (d) Type and Dia of Anchors Secondary Mesh Clip Spacing (ft) Post Thickness (ft) Secondary Panel Cover Type Rockfall Accumulation (cy) Post Foundation Diameter, Size and No. bars Painting/Powder Coating Fence General Description Notes (draw in Post/Foundation/Anchors if necessary): System Length (ft) System Panel Face Area (sf) System Height (ft) Vertical Offset (+/- ft) Photo Description/No. Post Batter Down Slope (deg) REPAIR/REPLACE RECOMMENDATIONS AND WORK ORDER Further Investigation? Failure Consequence System Condition Rating (Insert from Inspection Form) Action Maintenance/Repair/Replace Recommendations: Table 4-8. Proposed rockfall system inventory form.

15 ROCKFALL SYSTEM CONDITION ASSESSMENT Element Photo Number Condition Narrative Condition Rating Weighting Factor Condition Score Data Reliability Primary System Elements Panel 10 0 Post 10 0 Top Bearing Rope and Anchors 10 0 Lateral Retaining Rope and Anchors 10 0 Uphill Retaining Rope and Anchors 7 0 Post Foundation 3 0 Braking Elements 3 0 Secondary System Elements Panel Secondary Mesh 1 0 Shackles, Clips, Connections 1 0 Corrosion 1 0 Foundation Protection Systems 1 0 Other 1 0 System Performance Performance 10 0 System Rating Weighting Factor (X 10) and Condition Score Totals 0.0 0 0.0 Fence Condition Rating ( = [Condition Score Total/Weighting Factor Total = ] (X 10) X 100) 0.0 System Grade Data Reliability Table 4-9. Proposed rockfall system condition assessment form.

Next: Chapter 5 - Discussion of Management of Rockfall Fence Systems After Inventory and Condition Assessment »
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TRB's National Cooperative Highway Research Program (NCHRP) Report 823: Guidelines for Certification and Management of Flexible Rockfall Protection Systems provides advice on rockfall fence systems for transportation agencies. It also outlines data that are needed to evaluate the results of rockfall fence systems tested using the procedure recommended for acceptance. Finally, the report presents guidelines for asset management for rockfall fence systems to assist transportation agencies in incorporating these systems into existing transportation asset management plans.

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