Condition Assessment of a 48 PCCP Water Main Within an Abandon Subway Tunnel

Transcription

1 OAWWA 73 rd Annual Conference Condition Assessment of a 48 PCCP Water Main Within an Abandon Subway Tunnel By Jason DeLaet, P.E. Supervising Engineer Greater Cincinnati Water Works & Michael J. Livermore Regional Manager Pure Technologies

2 What are the top 3 things people fear most? 1. Public Speaking 2. Dying 3. Seeing a Doctor

3 Presentation Overview Introduction of GCWW Condition Assessment at GCWW Goals of the Condition Assessment Project History of the Subway Tunnel Current Technologies Available for Condition Assessment of PCCP Water Mains Condition Assessment Testing and Results Recommendations and Actions Taken Questions?

4 Who is GCWW? First publicly owned water utility in the country. Purchased on June 25, 1839 Regional metropolitan utility Supplies approximately 48 billion gallons of water per year Over 240,600 residential and commercial accounts Serving over 1.1 million people

5 GCWW Treatment, Pumping and Storage Facilities Richard Miller Water Treatment Complex (240 MGD capacity) Supplied by Ohio River MGD average finished water production (2010) Charles M. Bolton Water Treatment Plant (40 MGD capacity) Supplied by Great Miami River aquifer 16.2 MGD average finished water production (2010) 23 pumping stations and 32 storage facilities (finished water) Storage capacity of over 300 MG raw water and over 200 MG finished water

6 Water Main Inventory TYPE OF PIPE: DUCTILE IRON MILES STEEL 14.4 MILES CONCRETE MILES TRANSITE 10.1 MILES GRAY IRON MILES HDPE 4.3 MILES PVC 1.0 MILES COPPER 3.8 MILES TOTAL MILES

7 2011 GCWW Budget CIP = $58,600,000 Operating = $100,600,000 Total = $159,200,000 CIP related to aging infrastructure: Water main replacement/upgrade = $26,600,000 Water main replacement/expansion = $7,700,000 Facility maintenance/upgrade = $19,800,000 Total $54,100,000

8 Water Main Replacement Program Goal is to replace 1% of the system annually Approximately 30 miles per year Annual CIP budget of $20 million Extensive planning to develop candidates for replacement and prioritization

9 Condition Assessment Philosophy Condition assessment is a proactive approach to inspect, evaluate, and perform repairs to pipelines before a failure occurs Why is condition assessment important? Identify flaws and enable repairs Prevent future failures before they occur Optimize capital expenditures while reducing risk Extend the life of a pipeline

10 Condition Assessment at GCWW Currently no formal condition assessment program at GCWW Replacement / rehab is based on: Pipe age Pipe capacity Maintenance history Water quality parameters

11 Selection of the Condition Assessment Project Working group established to identify mains for analysis Factors used to identify critical main candidates Pipe age Maintenance history Main location Main usage Level of impact to businesses and customers Cost of main replacement

12 Central Parkway Transit Tunnel Main Cincinnati abandons transit tunnel Partially constructed between 1920 and of the 16 miles were completed $6 million bond issued in 1916 was exhausted in No further money was obtained and construction never resumed

13 Central Parkway Transit Tunnel Main (con t) Water service needs in same corridor Abandoned tunnel in congested area Decision to install main in abandoned tunnel Installed in PCCP LCP Manufactured by Price Brothers Installed within two miles of the abandoned transit tunnel beneath Central Parkway

14 Central Parkway Transit Tunnel Main (con t) Transmission main significance Responsible for conveying water from the Eden Park Reservoir to the Western Hills Pump Station Average daily flow of Western Hills Pump Station is 20 MGD Operating pressure ranges from 65 to 70 psi Responsible for providing water to approximately 170,000 customers

15 Transmission Main Maintenance History One major water break in 1984 Winter of 1988, 21 pipe sections were replaced with new PCCP January 2008 replaced two sections of pipe with new PCCP

16 Condition Assessment Project Goal Evaluate the risk of failure Determine the remaining useful design life Establish a timeline for replacement Develop alignment alternatives and cost analysis for replacement Identify potential funding sources for replacement Determine pipe sections in need of replacement

17 Initiating The Condition Assessment Project Contracted with Pressure Pipe Inspection Company (Pure Technologies)

18 Condition Assessment for PCCP Assessment Options usually dependent upon type of Pipe Material, Application and Accessibility Desktop Study Establish Priorities & Schedule pipelines for inspection Inspection Options: 1. Electromagnetic testing Internal / External 2. Visual and Sounding inspection 3. Structural Analysis - Finite Element Analysis (FEA) 4. Calibration or Validation of testing results 5. Establish repair/replacement priorities implement emergency repairs 6. On-going monitoring

19 Electromagnetic PCCP Inspection Technology

20 Prestressed Concrete Cylinder Pipe Background Lined Cylinder Pipe (SP5) 48 PCCP LCP Installed in 1957 Manufactured by Price Brothers Embedded Cylinder Pipe (SP12)

21 Electromagnetic Basics Function like a radio transmitter and receiver Transmitter produces electromagnetic field which is amplified by prestressing wires Receiver captures the signal and: - Detects and quantifies wire break damage - Provides estimate of wire breaks in each pipe section - Provides location of wire breaks

22 PCCP Deterioration Cracking of Outer Mortar Corrosion or Embrittlement of Wires Wires Break Mortar Coating Delaminates Concrete Core Delaminates Core Cracks Failure

23 Typical Evaluation Findings 4 to 7% of pipe sections have wire break damage <1% of pipe requires immediate repair Low number of leaks is likely (given the length of pipe) Minor joint repairs

24 Electromagnetic tools used in the Inspections Phase 1 Sta to Sta Phase 2 Sta to Sta Pipe Rider Line Preparation: Dewatered Manned Internal Inspection Visual Inspection of the Pipe Interior Pipe Scanner Line Preparation: Live Manned External Inspection Visual Inspection of the Exterior

25 Condition Assessment Project Photos

26 Condition Assessment Project Photos (con t)

27 Condition Assessment Project Testing Results Phase 1 Sta to Sta March 2008 (.97 miles) Manned Inspection utilizing the Pipe Rider Results 94% of the pipes showed no signs of distress 21 pipes displayed evidence of wire breaks (5.92%) 18 of the 21 pipe sections had < 25 wire breaks (5.07%) 2 of the 21 pipe sections had between 25 and 50 wire breaks (0.56%) 1 of the 21 pipe sections had > 50 wire breaks (0.28%) Interior Joints were not mortared

28 Condition Assessment Project Testing Results (con t) Phase 2 Sta to Sta March 2009 (.85 miles) Exterior Pipe Wall Inspection utilizing the PipeScanner Results 94% of the pipes showed no signs of distress 21 pipes displayed evidence of wire breaks (7.19%) 5 of the 21 pipe sections had < 10 wire breaks (1.71%) 13 of the 21 pipe sections had between 10 and 15 wire breaks (4.45%) 3 of the 21 pipe sections had > 15wire breaks (1.03%) One section of pipe was found to have longitudinal cracking and hollows on the exterior

29 Condition Assessment Project Testing Results (con t) FAILURE RISK ANALYSIS (Performed by SGH) The risk of failure of distressed pipes is evaluated using risk curves. A risk curve defines the relationship between the maximum pressures in the pipe and the effective number of broken wires that results in different limit states. The limit states quantify the level of damage in the pipe and are used to assign repair priorities.

30 Condition Assessment Project Testing Results (con t)

31 Condition Assessment Project Testing Results (con t) Repair Priorities The limit states divide the plots of pressure versus number of broken wires into different zones as shown in the risk curves. Each zone is assigned an alphanumeric order, depending on the risk of pipe failure and the need for repair. Priority 1: The maximum pressure in the line exceeds the pressure that produces the ultimate strength (note: there is no contribution of soil resistance since there is no earth load). The failure can occur at any time. Priority 2: The maximum pressure exceeds the minimum pressure that produces damage limit states. The failure occurs with time as the number of broken wires increases, or when the steel cylinder corrodes.

32 Condition Assessment Project Testing Results (con t) Priority 3: The maximum pressure in the line exceeds the pressure that produces serviceability limit states, but not the damage limit states. The failure of the pipe, if it occurs at all, is after a much longer time period than in Priority 2. Priority 4: The maximum pressure in the line is less than the pressure that produces serviceability limit states. The failure of the pipe, if it occurs at all, is after a much longer time period than in Priority 3.

33 Condition Assessment Project Recommendations Out of 42 total distressed pipes, 2 were in Repair Priority 1, 23 were in Repair Priority 2, 17 were in Repair Priority 3, and none is in Repair Priority 4, at a working-plus-transient pressure of 110 psi. Recommendations as a result of Inspection: Complete replacement not necessary, 94% of the pipe showed no signs of distress Monitor, repair, or replace

34 Post Condition Assessment Repairs Replaced 10 pipe sections, 2 with concrete and 8 with ductile iron. Repaired 5 pipe sections with pipe clamps.

35 Post Condition Assessment Evaluations Visual inspection once a year Focus visual inspections on the remaining 42 sections of pipe that showed signs of distress

36 Questions??? Jason DeLaet, P.E. Greater Cincinnati Water Works Supervising Engineer Office #: jason.delaet@gcww.cincinnati-oh.gov Michael J. Livermore Pure Technologies Regional Manager Cell #: michael.livermore@soundprint.com