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(1)

Rehabilitation or Replacement?

That Is The Question

Chris L. Windley PE Greg Anderson, PE

94th Annual Conference

(2)

Overview

—  Project Background

—  Existing Sewer Condition

—  Flow Projections and Impact

—  Replacement/Rehabilitation Alternatives

—  Evaluation of Rehabilitation Technologies

(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

(4)
(5)

Existing Sewer Condition

—  2012 CCTV and limited manhole inspections indicated

significant corrosion in the majority of the pipe sections.

(6)

Existing Sewer Condition

—  Limited inspections on 4 manholes

—  Moderate hydrogen sulfide corrosion in the concrete 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

(9)

Replacement/Rehabilitation Alternatives

—  CORPUD initiated an evaluation of multiple rehabilitation

technologies and replacement methods for large-diameter 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

(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

(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

(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 spray-in-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 50-100 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

(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 Excellent. Structural strength of the slipline pipe is independent of the host pipe.

Corrosion Resistance High

Expected Useful Life 50-100 years

Construction Factors May not require bypass pumping. Requires excavation of installation pits depending on material/length of

push.

Social Costs Residents could be impacted by noise and limited access due to staging of equipment.

(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

(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

(19)

Rehabilitation - Geopolymer Centrifugally

Sprayed-In-Place Pipe

Evaluation Criteria Geopolymer Coating

Flow Capacity/Diameter Range Negligible. Geopolymer application will only be ½-inch thicker than original deteriorated thickness of concrete pipe

Structural Integrity Excellent

Corrosion Resistance High, but limited age on existing applications in sanitary sewer

Expected Useful Life 50-100 years

Construction Factors 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

Social Costs Does not require excavation pits on both sides. Residents could be impacted by noise and limited access due to staging of equipment.

(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 1971.

—  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 Cured-In-Place Pipe

Flow Capacity/Diameter Range 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 Structural Integrity Excellent

Corrosion Resistance High

Expected Useful Life 50-100 years

Construction Factors Required onsite resin impregnation will significantly affect the cost of installation. May require bypass pumping if parallel line is not available to convey flow. Social Costs Does not require excavation pits, however due to the

size of the CIPP liner tops of manholes will need to be removed.

(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

(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  

(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

(28)

Contact Information: Chris Windley, PE 919-233-8091 cwindley@mckimcreed.com Greg Anderson, PE 757-965-2848 ganderson@mckimcreed.com

References

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