Rehabilitation or Replacement? That Is The Question

Transcription

1 Rehabilitation or Replacement? That Is The Question Chris L. Windley PE Greg Anderson, PE 94th Annual Conference November 18, 2014

2 Overview Project Background Existing Sewer Condition Flow Projections and Impact Replacement/Rehabilitation Alternatives Evaluation of Rehabilitation Technologies Summary/Conclusions

3 Project Background Existing Lower Walnut Creek Interceptor Approximately 16,000 LF of 48-inch and 54-inch gravity sewer Reinforced concrete pipe installed around 1975 Located in existing 100 wide utility easement Thirty-two (32) manholes primarily brick construction Discharges to concrete octagon shaped junction box Siphon across Walnut Creek to COR Walnut Creek Pump Station

4 Project Background

5 Existing Sewer Condition 2012 CCTV and limited manhole inspections indicated significant corrosion in the majority of the pipe sections. Corrosion pipe defect scoring ranged from 3 to 5

6 Existing Sewer Condition Limited inspections on 4 manholes Moderate hydrogen sulfide corrosion in the concrete manholes Missing mortar in the brick manholes

7 Existing Sewer Condition Limited structural analysis for greenway trail construction: Indicated pipe sections could fail under certain loading conditions The results of this analysis highlighted the need for a rehabilitation technology that provides structural integrity independent of the existing host pipe

8 Flow Projections and Future Pipe Sizing 2040 planning horizon Average daily flow of 16.4 mgd Peak flow of 69.6 mgd Anticipated single replacement in 66-to 72-inch range. If rehabilitation was selected, parallel pipe in 54-inch to 60-inch range

9 Replacement/Rehabilitation Alternatives CORPUD initiated an evaluation of multiple rehabilitation technologies and replacement methods for largediameter gravity sewer. The evaluation included four alternatives: 1. A single replacement interceptor 2. A single parallel interceptor replacement 3. Rehabilitation of the existing 48-inch and 54-inch interceptor and construction of a parallel interceptor 4. A combination of Alternative 2 and Alternative 3

10 Rehabilitation Technology Evaluation Rehabilitation technology for the LWC should provide the following: Applicable to the LWC pipe sizes and materials Corrosion resistance inherent to the rehabilitation technology materials without additives or field-applied coatings or sealants Stand-alone structural characteristics Reduced requirements for manned entry during installation

11 Rehabilitation Technology Evaluation 12 technologies reviewed 3 selected for further investigation: Segmented sliplining Geopolymer spray-in-place pipe Cured-in-place pipe (CIPP) 7 criteria to assess the pipe renewal methods: Flow capacity and diameter range Structural integrity Corrosion resistance Expected useful life Construction factors Social costs Previous experience with the City

12 Rehabilitation Technology Evaluation The Environmental Protection Agency (EPA) characterizes renewal of gravity sewer mainlines as repair, replacement, or rehabilitation Repair techniques are generally referred to spot or point repairs and not applicable to this project Replacement techniques make no use of the existing pipe structure and a new stand-alone pipe is provided, such as sliplining Rehabilitation techniques are defined as those that utilize the existing pipe structure, such as CIPP or sprayin-place pipe

13 Replacement - Segmented Sliplining One of the earliest forms of pipeline rehabilitation recorded, with installations dating back to the 1940s The process involves installing a smaller diameter carrier pipe within the existing host pipe by pushing or pulling the carrier pipe into place and filling the annular space between the two pipes with grout The final product provides a new pipe with adequate structural stability and a projected life expectancy of between years

14 Replacement - Segmented Sliplining There are many different types of piping materials that have been successfully used for sliplining applications The three generally utilized pipe materials for segmented sliplining are: Glass-reinforced plastic (GRP)/fiberglass reinforced plastic (FRP) Polypropylene (PP) PVC (closed profile) Will require a reduction in the capacity of the pipe

15 Replacement - Segmented Sliplining Pipe pushing force and push lengths for each type of sliplining pipe material are project dependent Grouting is required to seal the annular space between the new, slipline pipe and host pipe. A benefit of a segmented installation approach involves the potential to install the carrier pipe without having to bypass the flow during the sliplining installation

16 Replacement - Segmented Sliplining Evaluation Criteria Sliplining - Segmented Flow Capacity/Diameter Range Reduction of pipe capacity of approximately 20-25% based on LWC slope. Diameter reduction of approximately 10% depending on pipe material selected. Structural Integrity Corrosion Resistance Expected Useful Life Construction Factors Social Costs Previous Experience with City Excellent. Structural strength of the slipline pipe is independent of the host pipe. High years May not require bypass pumping. Requires excavation of installation pits depending on material/length of push. Residents could be impacted by noise and limited access due to staging of equipment. Yes

17 Rehabilitation - Geopolymer Centrifugally Sprayed-In-Place Pipe The most utilized material for rehabilitating large-diameter concrete pipes and concrete structures is a Portland cement-based cementitious mortar Recent advancements in the development of geopolymer-based materials with anti-microbial systems now provide a renewal system applicable for large-diameter piping systems and structures that are subjected to corrosive environments

18 Rehabilitation - Geopolymer Centrifugally Sprayed-In-Place Pipe Evaluation of the geopolymer technology indicated that, to accurately identify the associated cost for completing rehabilitation of the 48-inch and 54-inch gravity sewers, several key items would need to be evaluated, including: Bypassing of wastewater flows if necessary, based on the size of the parallel line Equipment setup for centrifugal casting Application thickness

19 Rehabilitation - Geopolymer Centrifugally Sprayed-In-Place Pipe Evaluation Criteria Flow Capacity/Diameter Range Structural Integrity Corrosion Resistance Expected Useful Life Construction Factors Social Costs Previous Experience with City Geopolymer Coating Negligible. Geopolymer application will only be ½-inch thicker than original deteriorated thickness of concrete pipe Excellent High, but limited age on existing applications in sanitary sewer years May require bypass pumping of a minimum of two sections of interceptor at a time if parallel line is not available to convey flow. Receiving surface must be cleaned and all loose material removed Does not require excavation pits on both sides. Residents could be impacted by noise and limited access due to staging of equipment. None

20 Rehabilitation - Cured-In-Place Pipe (CIPP) CIPP was the initial product utilized for rehabilitating deteriorating utility piping, with the first known installation dating back to It is estimated that approximately 40,000 miles of CIPP liners have been installed worldwide to date. Basic CIPP concept involves resin impregnation of a felt/ fiberglass tube by use of a pinch roller type assembly, with needle felt tubing being saturated at a controlled volume per length of proposed installation. Following resin impregnation, the tubing is inserted within a host pipe using water or air pressure and cured by the introduction of heat, UV light or ambient temperature

21 Rehabilitation - Cured-In-Place Pipe (CIPP) Currently there are many variations in method of installation, tube construction, resin systems and curing methods. Structural enhancements in CIPP lining are more related to resin and tube material changes than installation and cure methods. Improvements/changes in installation method generally dictate the cure method and are generally driven by a cost saving advantage.

22 Rehabilitation - Cured-In-Place Pipe (CIPP) Evaluation Criteria Flow Capacity/Diameter Range Structural Integrity Corrosion Resistance Expected Useful Life Construction Factors Social Costs Previous Experience with City Cured-In-Place Pipe Negligible. CIPP liner will generally replace original deteriorated thickness of concrete pipe and flow characteristics of the pipe will be enhanced with reduced roughness and elimination of joints Excellent High years Required onsite resin impregnation will significantly affect the cost of installation. May require bypass pumping if parallel line is not available to convey flow. Does not require excavation pits, however due to the size of the CIPP liner tops of manholes will need to be removed. Yes (smaller diameter applications)

23 Discussion The analysis revealed that each of the three types of products/installation processes evaluated could be successfully employed on the LWC project. All of the products provide corrosion resistance When evaluating the soft costs associated with each option, the commonality that exists is the need for accessing the piping to install any of the products. Sliplining approach requires the most excavation Both the geopolymer and CIPP liner installation processes also require limited excavation.

24 Discussion The geopolymer and CIPP liner approaches offer the best solution from a hydraulic standpoint Geopolymer products have limited long-term data available on corrosion resistance in sanitary sewer environments The City has limited experience with geopolymer products and there are limited applications of the relatively new product in North Carolina.

25 Conclusions Based on presentation of the results and discussions with CORPUD, the client selected CIPP and segmental sliplining with fiber reinforced plastic/glass reinforced plastic (FRP/GRP) pipe to be further evaluated for applicability and cost in this particular situation

26 Conclusions Alternative Description Opinion of Probable Construction Cost 1 A single, replacement interceptor located in the same alignment as the existing interceptor and sized to carry the entire future flow. $29,704,000 2 A single, parallel interceptor replacement sized to carry the entire future flow and abandonment of the existing 48- inch and 54- inch interceptor. $27,053,000 3 Rehabilitation of the existing 48- inch and 54- inch interceptor and construction of a parallel interceptor sized to carry the remainder of the future flow. ~$31,000,000 to $33,000,000 depending on rehabilitation method 4 A combination of Alternative 2 (single, larger parallel interceptor) and Alternative 3 (rehabilitation/smaller parallel interceptor) to address areas with potential constructability issues. ~$28,250,000 to $28,550,000 depending on rehabilitation method

27 Conclusions Alternative 2 a single parallel interceptor replacement sized to carry the entire future flow and abandonment of the existing 48-inch and 54-inch interceptor offers the most viable and economical solution for the CORPUD. the parallel line sizes required for rehabilitation of the existing interceptors were only one to two typical pipe diameters smaller than the single replacement line the capital and social cost incurred to install the parallel lines in addition to rehabbing the existing lines outweighed the cost of a single replacement line. The Lower Walnut Creek Interceptor replacement is currently under design.

28 Contact Information: Chris Windley, PE Greg Anderson, PE