Design specifications and selection issues in the application of Trenchless Technology for water and sewer mains

Transcription

1 The Caribbean Water and Wastewater Association in association with The Florida Section American Water Works Association Improving the Quality of Life with Water & Waste Management Solutions August 24-28, 2015 Miami, Florida Design specifications and selection issues in the application of Trenchless Technology for water and sewer mains David Boyce Chartered Engineer Over the past thirty to forty years, the development of trenchless technologies has been adopted both in the United States and Europe for water and sewer mains rehabilitation programmes. These techniques ranged from renovation of part of the fabric, upgrading performance of the pipe network, rectification of local damage and installation of a new pipeline system without incorporating the new fabric. The use of trenchless technology has however been limited to a few projects within the English speaking Caribbean Region, such as the case of the Barbados South Coast Sewerage Project, and generally installation of crossings and services in some of the utilities. With respect to wastewater, the trenchless technology can be truly a no dig activity. The renovation system can be inserted by robotic means. There is generally no need for major excavations. Water mains however do not generally have access manholes, and current structural renovation systems usually require the removal and subsequent replacement of service connections and in line fittings such as branches and valves. All of these activities require local excavation and so it is more a case of trenchless, meaning less trench rather than no dig. However experience in Europe has shown that limiting excavation to small pits can still produce significant benefits over full trench methods. In light of the need to replace the aging water and wastewater systems across the region, especially within the now highly trafficked and built-up cities, this paper examines the application of various trenchless technologies that could be used for reconstruction of the networks within such urban settings. The presentation consider the example of previous studies and investigations carried out by Genivar (2007) with respect rehabilitation of water and wastewater mains within the city of Port of Spain, where a multiplicity of services still exist such as water, sewer, fire fighting and telecommunication along several streets. In presenting a case for trenchless technology, the basis for the design, application of suitable specifications and selection issues will be discussed within the following context: Rational for replacement of the infrastructure due to faulty and leaking joints and inadequate capacity Design considerations in the application of trenchless technology taking into account, external loading and integrity of the methods to withstand variable and high operating pressures Renewal vs Replacement selection options such as non structural coatings, structural and non structural linings and out right replacement. Specifications and benefits of this technology which include environmental preservation, minimization of traffic and pedestrian disruptions and cost containment due to controlled excavations 1

2 WATER AND SEWERAGE SYSTEM A study undertaken by Genivar stated that based on the 2000 census Port of Spain has a population of 49,031. The Downtown Port of Spain area comprises 1,169 households with a population of 4,316 people. In addition a total of 2,887 businesses and 24 institutional facilities were indentified. In addition an estimated 200,000 commuters access Port of Spain daily. The area is therefore heavy trafficked and the grid network is shown in Figure 1. The Downtown Port of Spain water distribution system dates back to as early as 1900 s. The distribution system was also redesigned and reconstructed during the 1960 s by Howard Humphries during a major expansion and upgrade of the downtown area. Water lines in the downtown area range from 3 to 12 and are comprised primarily of cast iron mains. The system comprises both trunk mains 12 and distribution mains < 12. The sewer network dates back to 1860 s. The majority of the system was installed in the 1960 s when a major expansion and upgrade was undertaken by Metcaff and Eddy. The sizes range in diameter from 125mm to 250mm and range in depth from 1.5m to 2.7m. The main trunk lines are approx. 1500mm in dia. and range from 4.5m 6m. Figure 1. Adopted from Study carried out by Genivar

3 CONDITION ASSESSMENT Investigation carried out by WASA 2 indicated that the pipeline network is deficient due to (i) aged network greater than 50 years (ii) undersized and encrusted (iii) lack of transmission grid within downtown (iv) lack of redundancy (v) low system pressures experienced generally and (vi) limited piping configuration in place to utilize storage reservoirs effectively in downtown POS. Evaluation of the sewer system by Genivar indicated that a high proportion of the sewers surveyed exhibited significant deterioration and in some lengths, broken pipes and significant sagging was noted. The hydraulic evaluation indicated that over 70 percent of the collection sewers are hydraulically undersized. Water and Wastewater System Infrastructure Upgrade The upgrading required is summarized in Table 1 Water System Wastewater Collection System Proposed Est. km Existing Proposed Est. Km Transmission 39,755 Upgraded Sewers 20,000 Distribution 33,700 Table 1. Compiled from Wasa 2 and Genivar Studies A number of issued were identified by the Consultant Genivar (2007) that has to be taken into consideration during the construction stage. Stormwater control Excavation for sewers often intercepts storm water collection and disposal, which has to be maintained. In addition many gullies type drain systems in downtown Port of Spain currently connect to the sanitary sewers increasing the flows that have to be handled by the sewers Maintaining connections The existing connections taken to be mostly of the same vintage as the sewers will have to be rerouted to the new sewer and in most instances replaced. While this work is undertaken effectively temporary means of managing the sanitary waste from the existing buildings will be required. Road Reinstatement Surface restoration is an integral component of the work for sewer installation in the area. The existing pavement has significant older subsurface installation, deterioration of curbs, etc. Traffic and Business Disruption The streets are narrow and busy. Excavation to install sewers in these areas will essentially prevent vehicular access and retard pedestrian movements to the entire city blocks. Work at intersections will restrict traffic in all directions at intersections. In addition where businesses are cut off, it will be necessary to provide alternative means of ingress and egress. Damage to Other Services Generally sewers are the deepest utility, thus when sewers are to be replaced the resulting excavation often causes damage to adjacent utilities. Existing telecommunication services and a fire fighting system will have to be taken into consideration, with options to upgrade or replace. 3

4 PLANNING FOR THE CONSTRUCTION The planning and implementation of the water and wastewater reconstruction should take a number of issues into account that are in the best interest of safety, efficiency, operability, and cost. The assessment should include the knowledge and experience of construction of this complexity. The extent of the construction issues identified suggests that the use of trenchless technology should be a major consideration for undertaking the works. Characteristics that lend itself to the trenchless methods include the following factors 3 Size of Contract The size of the contract can preclude some technologies, as it may not be economical to have specialized equipment and personnel travel long distances for smaller contracts. Initial mobilization and demobilization for some specialty technologies can be expensive. With larger contracts, more options are available for various technologies. Risk Assessment An understanding of the project risks, including environmental issues and risks associated with the applicable construction techniques, is essential for the success of the project. The risk assessment process requires identification, quantification, evaluation/assessment, response development and control, and documentation. Major risk within sections of POS relates to open and deep trenching adjacent to existing utilities, possible collapse of adjacent old buildings and complete destruction of the road network, which would attract new investments. Local Availability Local availability would be a critical factor, as there is limited local presence of some of the newer technologies. This should however not be a major problem due to the extensive works required over the long term. Depth of Sewer The depth of a sewer plays a major role in determining the technologies available for rehabilitation or replacement. Trenchless technologies are frequently the least expensive for deeper sewers in an urban setting. The depth that begins to favour trenchless methods will vary depending on local and project conditions. This depth can range from 4 to 8 metres. Factors to consider include soil type, the depth to the water table, possible utility conflicts, road surface conditions, and traffic volume. Factors that decrease the depth are poor soils, extensive road surface profiles, and high traffic volumes. Factors that favour increasing the depth include good soils, road surfaces needing improvement, and low traffic. The conditions in POS supports trenchless technology. Density of lateral Services The number of storm and wastewater sewer laterals connected to the sewer requiring remedial action plays a large role in determining possible remediation technologies. This assumes that even when a trenchless technology is used to rehabilitate or replace a sewer, the sewer laterals will be replaced using excavation methods (i.e., not using a trenchless technology). As a rule, a higher number of sewer laterals per length of sewer being rehabilitated favours open cut replacement as the most economic solution. However, using a different rehabilitation or replacement technology at a higher construction cost than the open cut method may be in the best interests of the community. When other issues are considered, such as traffic, impacts on commercial and industrial customers, environmental concerns, and safety issues, cost may be less of a factor. 3 4

5 Surface Condition and other factors The condition of the ground surface can affect the method of rehabilitation chosen. Many communities, such as Scandinavia, France, Germany, Japan, Hong Kong, Singapore, and Thailand have no-cut policies for new pavements (prohibiting the use of open cut methods for several years after installation). 4 PIPELINE REPLACEMENT METHODS USING TRENCHLESS TECHNOLOGIES There are five general techniques for insitu pipe replacement. These include; pipe bursting, pipe implosion or crushing, pipe eating or reaming, pipe ejection and extraction and controlled line and grade system. There are two main Pipe Bursting methods; the pneumatic or hydraulic expansion and the static pull. The assessment carried out by Genivar suggested that existing mains and sewers would be upgraded and as such the pipe bursting technology which is appropriate will be discussed in detail. A summary of various technologies is given in Table 2.0 Pipe Bursting/Splitting Pipe Bursting and Splitting are well-established methods for trenchless replacement of worn out and undersized gas, water and sewer pipe. An existing pipe is replaced size-for-size or up-sized with a new pipe using the existing alignment (In-Line Replacement (Suleiman, 2010)). 5 The technique is the most cost effective when there are few lateral connections, when the old pipe is structurally deteriorated, and when additional capacity (larger diameter pipe) is needed. Pipe Bursting General Pipe bursting, which can be either pneumatic, hydraulic expansion or static pull, fractures a pipe and displaces the fragments outwards while a new pipe is drawn in to replace the old pipe, Figure 2 Figure 2 Pipe Bursting (Construction Updates, 2012) 6 Pipe Splitting Using essentially the same process as pipe bursting involves splitting the pipe in order to pull the replacement through. This technique is generally used when the host pipe material is not brittle; materials such as, but not limited to, steel and ductile iron. This method of trenchless pipe replacement is generally quick and smooth, allowing a perfect space for the new pipe to slide in after the split. The old pipe is forced upwards from the new pipe alignment, and becomes a protective barrier around the top half of the new pipe 5

6 Pipe Implosion and Crushing The Implosion System is similar to a bursting one in which it crushes the pipe while pulling through the replacement. In this two step process the old pipe is crushed inwards in the first step. In the second step the old pipe fragments are pushed outward by the bursting tool. The replacement pipe is dragged in behind the bursting head. This method is useful for replacing defective utility pipe, (ASTT, 2009a). 6 Figure 3. Figure 3 Pipe Implosion/Crushing Adopted for Reference 7 pp 11 Pipe Eating/Reaming The Pipe Eating system is designed to tunnel through the existing pipe and ground, crushing the pipe, whilst simultaneously inserting the new pipe into the bored out space. This method differs from a bursting operation. The crushed fragments of pipe mixed with soil are vacuumed out, as slurry, through the new pipe and out of the space. Figure 4. One of the main advantages of pipe eating technology is that the old pipe material is totally removed and the new pipe is accurately installed (ASTT, 2009a) 6 Figure 4 ECONOMIC AND ENVIRONMENTAL CONSIDERATIONS The cost of trenchless rehabilitation in many places around the world is decreasing as the market becomes more mature and development of technology plays a positive effect in reducing the unit rates. Meanwhile, open-cut methods are becoming more expensive as the indirect costs of fuels, spoil waste disposal and environmental and social impacts increase. Local Cost in Trinidad A recent Tender in Trinidad 2013 for replacement of an existing sewer in the City of San Fernando reflected a 5% reduction in cost for trenchless technology, indicated in Table 3 The pricing would not have taken into account social cost due to disruption, traffic and other environmental issues. Item Diameter length Open Cut Trenchless 1 525mm 61km 1,372,500 1,708, mm 107km 2,407,000 2,996, mm 210km 5,565,000 6,090, mm 480km 17,520,000 14,880, mm 60km 1,560,000 1,860,000 Other Cost 3150 $TT39,375,500 $TT37,234,000 Price 1US$=6$TT $TT67,804,000 $TT64,768,000 6

7 Table 2 Adopted from Trenchless Technologies and Work Practices Review for Saskatchewan. Prepared for Communities of Tomorrow by PINTER & Associates pp57 7 7

8 Table 2 Cont d Adopted from Trenchless Technologies and Work Practices Review for Saskatchewan. Prepared for Communities of Tomorrow by PINTER & Associates pp57 7 8

9 Cost Categorization Apeldoorn (2012) 8 provided a more detailed anatomy of the costs associated with trenchless technologies, which paves the way for better cost-effectiveness analysis. He divides the costs into four main categories, namely; (i) direct, (ii) indirect, (iii) social quantifiable and (iv) social non quantifiable. Each category is sub-categorized to allow further breakdown of the associated costs. Apeldoorn (2012), presents a summary of cost comparisons of replacement methods, per linear foot installed, published by the Public Works Technical Bulletin, U.S Army Corps of Engineers, which compares these values to the cost of open-cut and trenchless technology rehabilitation methods, utilizing 1991 USEPA (United States Environmental Protection Agency) values, Table 4. Summary of Cost (US$) Comparisons of Replacement Methods per Linear Unit Installed (Appeldoorn, 2012) Table 4 Pipe Size Open Cut Trenchless Trenchless Cost Savings (mm) US$/Lm US$/Lm Average US$/Lm , , , , Trenchless Cost Vs Open Cut Cost (%) Social Costs Direct and indirect costs are easy to estimate, but if other limiting factors (such as soil type and pipe material etc) and/or other costs interfere, the costs associated with the trenchless technology may exceed that of the traditional open-cut method, especially in low traffic density areas and shallow depth conditions. Rahman et al. (2005) 9 showed that the open-cut method is capable of causing major disruption to commerce and the general public. As a result, identification and quantification of the costs associated with service disruption and inconveniences are the key to provide a proper comparison between different trenchless technologies and traditional open-cut construction methods. These social costs may include, but are not limited to: (i) disruption to traffic and to business activities; (ii) damage to existing paved surfaces (iii) adverse environmental impacts and (iv) disruption to normal life patterns of the people living, working and shopping around the construction zone. Examples of Trenchless Technology Cost-Effectiveness pp Current practices of many municipalities in North America favour trenchless technologies due to their apparent cost-effectiveness. The City of Windsor, Ontario, in June 2012 completed installation of 1,150 m of 900 mm diameter High- Density Polyethylene (HDPE) pipe along the busy Ojibway Parkway in the City s industrial west end, a route which is also a major commuting thoroughfare to Windsor s southern suburbs. Estimates of using Open-cut method indicated that the total project cost would be 20% to 40% higher than the current project cost of US$3,795,000. 9

10 Mohamed et al. (2008) 10 presented a case study to examine the cost-effectiveness of trenchless technology compared to the open-cut method for replacing sewer pipes in the City of Troy, Michigan. Trenchless pipe bursting methods cost resulted in savings of 25.5 % of the total cost. DECISION SUPPORT FOR TECHNOLOGY SELECTION EPA (2011) 11 presented 8 (eight) case studies to show different selection processes in the United States. EPA (2011) points out the problem of limited number of commercial and/or public decision support models. The model that is commonly used is outlined in Figure 5. This provides a means to determine the likely method for the application of trenchless technology. TRENCHLESS TECHNOLOGIES AROUND THE WORLD The use of different trenchless technologies in many infrastructure projects is rapidly increasing worldwide. This is supported by the continuously increasing urbanization in both developed and less developed countries. The variety of trenchless technologies capable of handling different projects and site conditions offers an advantage over the traditional open cut. A survey of the trenchless market in North America (Underground Construction, 2007) 12 indicates that the percent of trenchless market ranges from 16.2% to 22.1% for the new construction of both water main and wastewater projects, respectively. The percent share for the rehabilitation projects ranges from 30.9% to 69.2%, wastewater and water main projects, respectively. A summary of different trenchless projects around the world was compiled by Ariaratnam, S.T, (2010). 7 Table 5 shows the wide aerial coverage and associated different types of infrastructures. CONCLUSION AND RECOMMENDATIONS In general, trenchless technologies outweigh traditional open-cut methods in high density urban areas, where access, traffic control and the cost of reinstatement of surfaces become more expensive, which adds up to the per metre of pipe price. The contribution of social costs relative to the project construction cost is estimated to range from 44% to 78% of the construction costs in the traditional open-cut method, whereas social costs for trenchless technologies ranges from 3% to 11% of construction costs. Those savings are added to the construction costs savings which amount to 20% - 40% of the total cost in cases using trenchless technologies, especially in heavily populated urban areas (pp94). 7 A direct relation exists between strong and sustainable communities and their infrastructure, in particular, underground assets dealing with water, wastewater and gas/energy. Modern methods for installing and replacing utility piping no longer involve digging up mass amounts of earth and no longer cause extensive surface disruption to the community or business activities. Trenchless technologies, equipment and standards are in place to ensure that these piping infrastructure systems can be quickly and without disruption, installed or replaced. The conditions within the urban settings of Port of Spain present the environment factors such as traffic, high business activities, population density, deep sewers, risk to adjoining properties. These issues could be resolved through a cost effective solution for replacement of the water and sewer network using Trenchless Technologies. 10

11 Figure 5 Model for Selection of Technologies Adopted from A Best Practice by National Guide to sustainable Municipal Infrastructure pp

12 Table 5 Adopted from Trenchless Technologies and Work Practices PINTER Associates Ltd for Saskatchewan Municipalities pg June

13 REFERENCES 1 Consultant Services for the Extension and Rehabilitation of Sewers and water Lines in Downtown port of Spain Genivar October Downtown Port of Spain Study Improving the Support Function to the Trinidad and Tobago Fire Services Prepared by Steve Joseph Operations Division Wasa Selection of Technologies for Sewer Rehabilitation and Replacement, A Best practice by the National Guide to Sustainable Municipalities and National Research Council, Date March Trenchless Technology Solutions for Professional Training Sessions prepared by: The Urban Utility Centre, by Mr. Robert Zlokovitz Senior Research Advisor, Professor Ilan Juran Executive Director, August Suleiman M. stevens, L Jahren C, Ceylan H, and Conway W Identification of Practices, Design Construction and Repair using Trenchless Technology, Institute for Transportation, Iowa State University IHRB Project TR Australian Society for Trenchless Technology (ASTT) (2009a0. Standard for Pipe Bursting, Document # CPJP8029-STD-002 September 7 Trenchless Technologies and Work practices. Review for Saskatchewan Municipalities. Prepared for Communities of Tomorrow by PINTER & Associates Ltd 03 June 2013 File Apeldoorn S (2012) Comparing the Costs Trenchless versus Traditional Methods, New Zealand Councilor Australasian Society for Trenchless Technology 9 Rahman S, Vanier D J, Newton L A (2005), MIP Report Social Cost Consideration for Municipal Infrastructure, management, NRC Publication Archive 10 Mohamed R, Najafi M and Hashemi B ( cost Comparison of open Cut and Trenchless Methods for Renewing sewer Lines, water Utility Infrastructure Management Newsletter Sept/October EPA (2011) Decision for Renewal of Wastewater Collection and water Distribution systems. US EPA Office of Research and Development, National Risk Management Research Laboratory Water Supply and Water Resources Division EPA/600/R-11/077 Washington D.C. 12 Timberlake M and Berry T (2012) Pipe Bursting Myths and Misconceptions, Underground Construction Volume 67, No 3 March. 13