Report. Ministry of Transportation and Infrastructure Henson Culvert Condition Assessment Report. March 2012

Transcription

1 Report Ministry of Transportation and Infrastructure 7862 Henson Culvert Condition Assessment Report March 2012

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3 7862 Henson Culvert Condition Assessment Report Table of Contents SECTION Table of Contents PAGE NO. i 1 Introduction Project Background Project Personnel Construction Existing Information Inspection and Access 3 2 Inspection 4 3 Discussion of Inspection Findings Summary of Needs Regular Monitoring and Maintenance Rotten Floor near the Outlet Scouring Under Floor Rotten Tiebacks Undersized Opening No-post Barriers 7 4 Conclusion 7 5 Closure 7 Appendix A - MOT Condition Inspection Report Appendix B - Inspection Photos Appendix C - Resistograph Output Appendix D - Hydrological Study Report i P:\ \05_3_Scoping_Studies\Engineering\03.00_Conceptual_Feasibility_Design\02_Henson\RPT_ConAssess_15Mar2012(Final)\rpt_mot_7862henson_culvert_ _jj.doc

4 7862 Henson Culvert Condition Assessment Report 1 Introduction 1.1 Project Background Associated Engineering has been retained to provide renewal or replacement strategies for the 7862 Henson Culvert, as part of the General Engineering Services Agreement with the British Columbia Ministry of Transportation and Infrastructure (MoT). To facilitate the development of these strategies, a visual inspection was undertaken. This report summarizes the findings of this inspection and provides a factual baseline for the renewal or replacement options analysis. 1.2 Project Personnel Ryan Veitch, AScT carried out the inspection and condition assessment of the culvert. Jack Jiao, P.Eng., prepared the report and Dale Harrison, P.Eng., reviewed the report. 1.3 Construction The construction date of the 7862 Henson Culvert was unknown, but it was estimated to be between1970 and The culvert carries Pacific Marine Road between Lake Cowichan and Port Renfrew. It is located 24.9 km from Port Renfrew on Vancouver Island (see Figure 1-1). Figure 1-1 Location of 7862 Henson Culvert 1 P:\ \05_3_Scoping_Studies\Engineering\03.00_Conceptual_Feasibility_Design\02_Henson\RPT_ConAssess_15Mar2012(Final)\rpt_mot_7862henson_culvert_ _jj.doc

5 7862 Henson Culvert Condition Assessment Report At this location, the highway pavement is approximately 7.2 m wide. The highway embankment slope appears to be normal on the upstream side but steep on the down-stream side. The culvert measures 1.9 m tall by 4.0 m wide at its inlet. The culvert is approximately 22 m long and has about 3 m top fill. A ditch runs along the upstream side of the road. A plunge pool was formed at the down-stream outlet (see Figure 1-2). Figure 1-2 Plunge pool at the outlet The whole culvert was constructed of cedar logs. At the time of inspection, water runs beneath the timber floor; see Figure 1-3. Hydrological study indicated that the culvert is undersized for today s flows. 2 P:\ \05_3_Scoping_Studies\Engineering\03.00_Conceptual_Feasibility_Design\02_Henson\RPT_ConAssess_15Mar2012(Final)\rpt_mot_7862henson_culvert_ _jj.doc

6 7862 Henson Culvert Condition Assessment Report Figure 1-3 Timber floor at the inlet The channel into the culvert appears to be migrating, causing some undermining of the wingwall. 1.4 Existing Information We reviewed the following information prior to the inspection: British Columbia Ministry of Transportation and Infrastructure Bridge Management Information System Condition Inspection Report, dated March 23, Stantec Consulting Limited Harris Creek Area - Culvert Sizing Review, dated July 15, Inspection and Access We completed a close-proximity inspection of the culvert on September 16, Access to the culvert components was by foot where accessible. 3 P:\ \05_3_Scoping_Studies\Engineering\03.00_Conceptual_Feasibility_Design\02_Henson\RPT_ConAssess_15Mar2012(Final)\rpt_mot_7862henson_culvert_ _jj.doc

7 7862 Henson Culvert Condition Assessment Report 2 Inspection At the time of the inspection, there was no water flowing on the surface of the culvert floor. Water appears to be flowing under the timber floor. Minor debris build-up was observed near the culvert inlet at the upstream end. In general, the culvert is in fair condition. The roof consists of 36 log stringers, approximately mm in diameter. Each sidewall consists of three log stringers, approximately mm in diameter with tiebacks between stringers. Each wingwall consists of two or three logs, with the diameter varying from mm. The whole culvert floor is covered with 38 mm by 191 mm cedar boards. We preformed microdrill testing on selected stringers, cribs and tiebacks using IML Resistograph F500. With this Resistograph, a very fine drill is fed into the wood at a predetermined rate. As the drill enters and passes through the wood, it encounters variable amounts of resistance. The variation in resistance results in increase or decrease in the amount of torque applied to the drill shaft. By means of mechanical and electrical sensors, the variations in torque are translated into graphic output which depicts the conditions encountered by the drill at the specific point of drilling. The outputs of the testing are shown in Appendix C, in which the horizontal baseline of the charts is the depth of drilling and the vertical axis is unitless measurement of the relative density of wood. The charts indicate that the stringers and cribs have about 10 mm sap rot in general and one tieback is in poor condition. We hammer sounded stringers, sidewalls and tiebacks randomly. Roof stringers appear to be sound but have surface sap rot. Sap rot was also observed in the sidewalls and some tiebacks are also rotten. Inspection of the sidewall below the timber flooring is not possible due to access issues. The roof and the sidewalls appear to have settled near the centre of the road, under combined dead and live load, resulting in reduced clearance of 1.55 m as opposed to 1.9 m at the inlet. About 1/3 length of the floor was rotten near the culvert outlet. This is a continuing potential liability for the Ministry, should someone fall through the floor into the plunge pool. The wood flooring appears to provide scour protection for the gravel bedding through most of the culvert length, but is not water-tight, therefore water will flow through the flooring and continue to scour and erode the bedding of the culvert. A previous inspection report noted that the downstream outlet wingwalls were in poor condition. We did not observe that but found that some of the tiebacks are rotten. 4 P:\ \05_3_Scoping_Studies\Engineering\03.00_Conceptual_Feasibility_Design\02_Henson\RPT_ConAssess_15Mar2012(Final)\rpt_mot_7862henson_culvert_ _jj.doc

8 7862 Henson Culvert Condition Assessment Report A copy of the MoT Bridge Inspection Report, dated March 23, 2011, is included in Appendix A. Selected inspection photographs are included in Appendix B. 3 Discussion of Inspection Findings 3.1 Summary of Needs The needs have been classified into Maintenance Needs and Capital Renewal Needs and are listed in the appropriate tables below. The Maintenance Needs refer to needs with dollar values less than $30,000 and Capital Renewal Needs with dollar values greater than $30,000. In addition, Functional Upgrade Needs to address various functional deficiencies noted on the bridge have also been identified and listed in another table. Table Henson Culvert Maintenance Needs Component Maintenance Need Year to Repair Unit No. Condition Code Description Complete Quantity N/A Rotten culvert base board. N/A Maintenance and replacement LS 1 N/A Scouring under floor N/A Fill repair 2012 LS 1 N/A Aging culvert. N/A Regular maintenance and monitoring. On going LS 1 Table Henson Culvert Capital Renewal Needs Component Capital Renewal Need Year to No. Condition Code Description Complete Unit Repair Quantity N/A NA N/A NA NA NA NA 5 P:\ \05_3_Scoping_Studies\Engineering\03.00_Conceptual_Feasibility_Design\02_Henson\RPT_ConAssess_15Mar2012(Final)\rpt_mot_7862henson_culvert_ _jj.doc

9 7862 Henson Culvert Condition Assessment Report Table Henson Culvert Functional Upgrade Needs Component Functional Upgrade Need Year to Repair Unit No. Condition Code Description Complete Quantity N/A No roadside barrier* N/A Install no-post barriers 2012 LS 1 Note: * subject to barrier warrant assessment. 3.2 Regular Monitoring and Maintenance This includes regular monitoring and maintenance of the cribs, wingwalls and roof stringers for any signs of distress. 3.3 Rotten Floor near the Outlet We recommend replacing rotten/deteriorated boards as required. 3.4 Scouring Under Floor We recommend that the scour below the timber floor be investigated by removing the flooring adjacent to the sidewalls. Any loss of material from behind the crib wall (sidewall) or from the bedding supporting the crib base lag should be noted and if necessary sand-cement bags installed in the gaps to prevent further erosion occurring. The removed flooring should be re-installed (and replaced if rotten). 3.5 Rotten Tiebacks Some tiebacks are in poor condition. But we consider the sidewalls to be stable as a result of the inherent stability of three-log high cribs. The wingwalls are currently stable but should be monitored for movement, given the condition of the tiebacks. 3.6 Undersized Opening A hydrological study of the culvert was carried out by Stantec Consulting Limited. The study shows that the culvert does not have enough capacity to convey the 36 m 3 /s 100-year peak flow and one of the replacement options would be a 3.05 m x 3.05 concrete box culvert. See Appendix D for details of the report. 6 P:\ \05_3_Scoping_Studies\Engineering\03.00_Conceptual_Feasibility_Design\02_Henson\RPT_ConAssess_15Mar2012(Final)\rpt_mot_7862henson_culvert_ _jj.doc

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11 7862 Henson Culvert Condition Assessment Report Appendix A - MOT Condition Inspection Report A-1 P:\ \05_3_Scoping_Studies\Engineering\03.00_Conceptual_Feasibility_Design\02_Henson\RPT_ConAssess_15Mar2012(Final)\rpt_mot_7862henson_culvert_ _jj.doc

12 BISR7000 BRITISH COLUMBIA MINISTRY OF TRANSPORTATION PAGE 1 OF BRIDGE MANAGEMENT INFORMATION SYSTEM Condition Inspection Report 09 Sep 2011 BRS Criteria: Structure No = Include Inspection Condition Photos = N - Include Additional Blank Lines for Notes = N - Show Not Applicable (N/A) Components = N 2 Structure No: HENSON CULV Status: Open/In Use Inspection Type: Detailed Condition Region: 1 - South Coast Region RFI: D-D PACIFIC MARINE ROAD - OVER Component Group/Component HYDROTECHNICAL : Debris Risk Channel Substructure Scour Flow Capacity STRUCTURE : Roadway Over Culvert Wing Walls Inlet Outlet Roof/Crown Sidewalls Floor District: 2 - Vancouver Island District Inspector/Inspected By: ANDY FLYNN On 2011/03/23 Urgency Notes: Urgency Rating Note: Item Notes: 1. Debris Risk Urgency: Features Crossed: Contract Area: 1 - South Island CA E G F P V X N/A Year Built: 1970 Estimated? Length (m): Culvert Type: Timber Culvert Shape: Box (Single or Twin- Cell) BCI Rating: 2.72 Adjusted BCI Rating: 2.8 Amendment/Partial Inspection? urgency set at 3 due to age and outward appearance of logs and the scour at outlet, no drilling done this inspection. Will be drilled in 2011 and urgency may rise Detail inspection completed. Tiebacks & crushed sil logs are the weak link of this structure. Stringers are sound, but starting to turn soft Minor debris upstream. No cercerns N N N N N N N N N N N 2. Channel Channel is migrated into the east abument, causing undermining of the crib. Structure is undersized. Monitor 4. Substructure Scour On the west abutment at approximately 12m in from the inlet, the stream has scoured under the bottom sillog & floor boards. Extent of scour has not been determined due to access. Also at the inlet on the east abutment, water has migrated east and is scouring under the cribwork. Monitor 5. Flow Capacity Structure is undersized for todays flows 8. Wing Walls Varying degree of rot. Tiebacks are rotten. 11. Inlet Minor aggradion. Culvert undersized for channel. 12. Outlet A false wooden floor is constructed for the last 3m of the outlet. Water is flowing under the south sillog causing scouring. Caution when inspecting this area as to not fall through the rotten floor Scour occuring as a result of plunge pool 13. Roof/Crown Roof consist of 37 cedar log stringers ranging from 300 to 500mm. Varying degree of rot is present. Detail inspection on next visit Roof consist of 36 cedar log stringers varing in size from 400 to 600mm. Stringers where drilled. Most are sound, but starting to go soft. A couple have 50mm of center rot. Monitor

13 BISR7000 BRITISH COLUMBIA MINISTRY OF TRANSPORTATION PAGE 2 OF BRIDGE MANAGEMENT INFORMATION SYSTEM Condition Inspection Report 09 Sep 2011 BRS Criteria: Structure No = Include Inspection Condition Photos = N - Include Additional Blank Lines for Notes = N - Show Not Applicable (N/A) Components = N 2 Structure No: HENSON CULV Status: Open/In Use Inspection Type: Detailed Condition Region: 1 - South Coast Region District: 2 - Vancouver Island District Contract Area: 1 - South Island CA Item Notes: 14. Sidewalls Sidewalls consist of 3 cedar log stringers with log tiebacks ranging from750 to 1200mm. Varying degree of rot is present. Detail inspection on next visit Crib consist of 3 cedar log on the west and 2 cedar logs on the east, varing in size from 600 to 750mm. Sills are complemented with tieback which are rotten. This is the weak link of the structure. Sills are showing signs of being crushed/split. Sills where ramdomly drilled. Most are sound, but starting to go soft. A couple have 50mm of center rot. Monitor 15. Floor Inspection Notes: General Inspection Notes Inspection completed by A Flynn. Detail inspection to be completed to on next visit Detail completed by Andy Flynn / Kevin Carter. Tiebacks are the weak link of the structure. On the west abutment at approximately 12m in from the inlet, the stream has scoured under the bottom sillog & floor boards. Extent of scour has not been determined due to access. Also, the channel has migrated to the east underming the east abutment. Monitor Floor consist of 2 x 8 lumber. Varying degree of rot is present. Detail inspection on next visit Detail completed. Varying degree of rot is present. Floor is supended at the last 3m from outlet.

14 7862 Henson Culvert Condition Assessment Report Appendix B - Inspection Photos Culvert Inlet Timber Floor B-1 P:\ \05_3_Scoping_Studies\Engineering\03.00_Conceptual_Feasibility_Design\02_Henson\RPT_ConAssess_15Mar2012(Final)\rpt_mot_7862henson_culvert_ _jj.doc

15 Ministry of Transportation and Infrastructure Inlet Close-Up Steep Side Slope B-2 P:\ \05_3_Scoping_Studies\Engineering\03.00_Conceptual_Feasibility_Design\02_Henson\RPT_ConAssess_15Mar2012(Final)\rpt_mot_7862henson_culvert_ _jj.doc

16 Report 7862 Henson Culvert Condition Assessment Report Side Wall Plunge Pool Close-Up B-3 P:\ \05_3_Scoping_Studies\Engineering\03.00_Conceptual_Feasibility_Design\02_Henson\RPT_ConAssess_15Mar2012(Final)\rpt_mot_7862henson_culvert_ _jj.doc

17 7862 Henson Culvert Condition Assessment Report Appendix C - Resistograph Output C-1 P:\ \05_3_Scoping_Studies\Engineering\03.00_Conceptual_Feasibility_Design\02_Henson\RPT_ConAssess_15Mar2012(Final)\rpt_mot_7862henson_culvert_ _jj.doc

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37 REPORT Appendix D - Hydrological Study Report D-1 P:\ \05_3_Scoping_Studies\Engineering\03.00_Conceptual_Feasibility_Design\02_Henson\RPT_ConAssess_15Mar2012(Final)\rpt_mot_7862henson_culvert_ _jj.doc

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