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Khogali, W. E. I.; Elhussein H. Mohamed
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MANAGING UTILITY CUTS: ISSUES AND CONSIDERATIONS
by
Walaa E.I. KHOGALI1 and Elhussein H. MOHAMED2
Institute for Research in Construction, National Research Council Canada 1500 Montreal Road, Ottawa, CANADA K1A 0R6
Abstract Résumé
The escalating cost of repairing road damage resulting from poorly performing restored utility cuts within the right-of-way of urban roads is creating serious financial stress on cities and utility companies alike. Despite the fact that utility cuts are normally restored based on specific design and construction practices, they continue to perform poorly in many cases. As a result disagreement between cities and utility providers emerged and led to litigation in a number of cases. The research project presented here was developed in response to the need of improving the long-term performance of restored utility cuts by identifying and resolving technical difficulties involved in the restoration process.
In depth review of the literature, preliminary engineering analysis and consultation with stakeholders (cities and utilities) revealed that the absence of a sufficient engineering practice has been the main cause behind current restoration problems. There are instances where design and construction specifications set forth by city engineers were not adhered to, which many believe is the reason behind the reported premature failures. Nonetheless, the review of many existing restoration practices indicates that even when such specifications are followed, performance of restored utility cuts remain unsatisfactory. Analysis of current practices indicates that existing technical specifications can not guarantee adequate performance. Accordingly, management systems developed to enforce these specifications were not fruitful. This paper provides a detailed analysis of the present situation highlighting inadequacies in current restoration practices and exploring possible solutions. It also presents a new format for establishing a sound engineering practice that can be managed effectively. The new solution involves the development of a unified North American guide for best practice capable of addressing site-specific conditions including conventional and innovative construction materials, environmental conditions, and local construction practice and expertise. These guidelines will be performance-based and will form a sound base for the development of effective policies and maintenance management systems capable of addressing the local needs of each city.
Keywords: Utility cuts, restoration, backfill, road damage, performance-based
1
Dr. Walaa E.I. Khogali is a Research Officer at the National Research Council Canada. He is actively involved in the field of rehabilitation of urban roads. His current research activities focus on the characterization of road foundation material for urban use. He can be reached at walaa.khogali@nrc-cnrc.gc.ca or at (613) 993-3787.
2
Dr. Elhussein H. Mohamed is a Research Officer at the National Research Council Canada. He is currently involved in the field of urban roads rehabilitation. He can be reached at
1 Introduction
Operations in the public right-of-way by utility companies necessitate proper co-ordination between these companies and public road authorities to ensure the responsible utilization of this public resource by all parties involved. Of paramount importance are the issues related to public safety, riding comfort, aesthetics and cost-effectiveness of the implemented reinstatement strategy. Every day a substantial number of utility cuts are dug and restored in every city worldwide either to install new services or to repair and upgrade existing facilities. The majority of these facilities are located underneath urban roads. Over the past 50 years, many studies carried out by several municipalities and utility companies have indicated that the life expectancy of an urban street may be reduced by these utility cuts. Although there is no agreed-upon quantitative evaluation of the effect on pavement life, the strong perception on the part of public road authorities is that roadway performance is adversely affected by reinstated utility cuts; because they result in increased maintenance costs to the public agencies. The problem persists and is growing in magnitude. This situation brought about bitter disputes between cities/municipalities and utility companies, which resulted in the evolution of a litigious environment.
This paper describes an analysis of the current situation, including the economics and size of the problem, and presents prospects that may provide cost-effective and sound engineered solution(s) that can be practically implemented.
2 Situation Analysis
In analyzing the current situation, the authors will be addressing the following issues: size of the utility cut restoration problem and its economic impact,
current state-of-practice, and
future challenges and proposed solutions.
2.1 Size of the Problem
Today, there is a growing trend to cut urban streets open to service and maintain the deteriorating utility networks of underground facilities worldwide. In a recent paper presented by Jones (1999), it is reported that more than 100,000 excavations are dug and the roadway restored every year in Camden Borough (a district of London, UK). It is also been reported that utility works in the U.K. rank as the second major cause of traffic disruptions with estimated delay costs of $13 billion dollars. A similar yet more staggering finding is the one reported by the New York City Transportation Commissioner: more than 250,000 cuts a year are made in the streets of NY City. This number increases by 8% each year. These statistics, and many more, serve to confirm and substantiate the fact that there is definitely an increasing need to access the underground facilities for maintenance and rehabilitation of these aging systems. This in turn creates serious financial stress on cities and utility companies alike.
To conduct any utility works project involving the maintenance/installation of underground facilities, two alternatives for access are available to do the work: trenchless technology and “open-cut & restore” technique. Trenchless technologies are attractive in that they cause minimum disturbance to traffic and have a low impact on the environment and least inconvenience to the public. On the other hand, some obstacles that hinder the frequent use of
these technologies include:
• Risk of construction failures due to unexpected underground obstacles (sub-surface detection methods are still in their infancy) or sandy soil conditions;
• Limitations of boring equipment: size of pit hole, minimum offset from street curb, maximum length of boring span, availability of skilled equipment operators;
• Absence of maps or drawings that provide accurate underground information (safety concerns); and
• High initial cost and short history of proven success.
Cut and reinstatement technique is the second alternative that is currently in wide use. However, satisfactory performance using this approach is still a far-fetched goal. Although, many research projects by both city administrations and by utility companies (Zeghal et al. 1999; Zeghal and Mohamed 1998) were completed, the practice has not improved. The reasons behind the lack of success will be discussed in detail in the following section.
2.2 Economic Impact
An important factor to consider when dealing with public utility works, including reinstatement of utility cuts, involves the selection of appropriate planning horizons for the economic analysis of utility projects. Present value analysis of utility systems in North America, by both public and private agencies, is typically limited to a 10-year horizon. This does not reflect the true long-term nature of these systems, which is in part due to the immense capital investment and pay-back involved and the anticipated service life periods for these facilities that are measured in decades (McKim 1999). Failure to recognize long-term welfare economics as a key decision tool when dealing with utility cut restoration projects contributes in part to the failure of producing positive economic results.
There are three types of costs that are associated with utility works projects (Jones 1999): 1. Direct Costs, which encompass planning, design, contracting costs, diversion of existing
facilities, permanent reinstatement and professional charges.
2. Indirect Costs, which include reduction in road service life, increase in road maintenance requirements, damage to adjacent property and disruption to businesses directly affected by the works.
3. Social Costs, which include environmental loss associated with air pollution, noise, vibration, the loss of amenity and the disruption to commercial and private traffic together with increased level of traffic accidents.
The estimate of direct costs, which are usually recoverable, can be done with great accuracy. However, some indirect costs and all social costs are difficult, if not impossible, to assess and quantify. Furthermore, the latter costs are usually irrecoverable which puts the burden on public road authorities to try to minimize such costs when approving any kind of utility works projects.
2.3 Utility Cut Restoration
The process of utility cut restoration involves three elements: planning and co-ordination,
management schemes, and construction.
Previous studies managed to successfully advance planning and co-ordination activities related to utility cuts (APWA 1996,1997). However, research results in support of management issues from
earlier studies are scarce. Management can be carried out effectively only if the performance of a restored utility cut can be predicted accurately. Performance prediction involves the same tools as those used for the design and analysis of structures. Analytical models can be used to analyze the structure and predict road deterioration trends associated with materials of known characteristics, construction and design specifications. Design and construction practices are commonly examined in isolation of management requirements. Consequently, management issues receive little or no attention while developing models for analysis and design focusing only in providing support for construction issues. The absence of such link between management and current design and construction practices made it difficult for construction practices to effectively support management decisions related to permit issuance and contract settlement, all requiring prediction of potential performance of the reinstated cut.
2.4 Unresolved Issues in Construction Practice
A successful construction practice dealing with the restoration of utility cuts should include the following components:
• structural design approach based on sound engineering fundamentals,
• material selection based on known material response to external stimuli,
• well defined failure mechanisms and quantifiable performance based on predictable indicators, and
• controlled in-field practice involving construction equipment usage and reliable construction specifications that can be related to the performance of the system.
Currently no restoration procedure/technique possesses all of the above components. The following is a critique of the most common restoration procedures considering the above-discussed requirements.
2.4.1 Structural Analysis and Material Selection Issues
The majority of restoration procedures currently available were derived from guidelines developed by the American Association of State Highway and Transportation Officials (AASHTO), originally intended for the design of highway pavements. AASHTO standard specifications offer the most widely used road material classification system and structural design guidelines. The material classification system was based on a number of physical properties, and the design on empirical models that were derived using results of the AASHTO road test. In the absence of effective analytical support in the early 1960s, road tests represented the only viable means for quantifying performance as influenced by material type, layer thickness and traffic loading. Since few construction materials, one subgrade, one (standard) truck and one environmental condition were considered in the AASHTO test, the use of the developed empirical models for design purposes was limited. In addition, physical properties of a material alone cannot depict accurately the characteristic response of a pavement layer constructed with a typical material and exposed to traffic and environmental loading. Mechanistic response of each material type to these external stimuli needs to be considered. Quality control measures that are required for enforcing design specifications do not guarantee control over performance if based on physical properties alone. Consequently, implementation of AASHTO specifications in regions with different soil types, construction materials and practice as well as environmental and traffic conditions resulted in numerous incidents of premature road failures. The same shortcomings that accompanied the implementation of AASHTO standards for highway
pavement design and construction seem to afflict on utility cut restoration. As a result of the unsatisfactory performance of AASHTO Standards, the US National Cooperative Highway Research Program (NCHRP) launched a new initiative aimed at developing a new design standard (2002 Guide).
Modifications of AASHTO specifications, such as those developed by the Ministry of Transportation of Ontario (MTO), are attempts at accounting for local conditions (provincial level), but they still fall short in capturing the effect of numerous local conditions prevailing in different municipalities. The empirical nature of the developed construct supporting the current design and the fact that the standards were mainly based on the results of the road test of the 1960s, limit the potential for achieving the modification that will improve the practice of restoring utility cuts.
2.4.2 Impact of Road Digging
The fact that AASHTO standards were developed for designing new roads and not for rehabilitating old ones may explain the lack of success in engineering utility cut excavation and restoration using these standards. Some of the elements needed for effective analysis and design, which are missing in the current practices, include the following:
• Road cuts involve digging through the asphalt surface, granular base and sub-base and subgrade soil to reach buried facilities. Removal of materials used in these layers reduces lateral support to the materials in the uncut road sections. This is expected to weaken the support the excavated material provides to the pavement structure. It also causes the soil along the sides of the trench to sloughs into the hole reducing the support for the pavement edges. There are indications linking the digging process to loss of structural integrity and poor performance by restored utility cuts. In current practices, there are neither a mechanism to evaluate the impact of digging and soil removal nor design or construction specifications to reduce its effects.
• Sensitivity of digging and compaction equipment to the characteristics of utility cuts has not been well investigated. The tight workspace dictates the use of equipment smaller than that used in the construction of conventional roads. There is no guarantee that such equipment is capable of satisfying current construction specifications. Furthermore, there are many innovative materials such as flowable fills and soil modifiers whose characteristics and behaviour may deviate from standards established by AASHTO. Potential performance and construction requirements of these materials are not yet well known.
• Pavement cutting, which precedes the digging of soils, did not receive attention in previous investigations. Few studies attempted to develop specifications for cutting tools to allow for a choice between two or more methods, because there is no clear understanding of the impact that asphalt cutting techniques have on the performance of restored utility cut.
2.4.3 Quality Control
The majority of the reviewed management schemes call for enforcing technical specifications to guarantee effective execution of construction contracts, which in turn is expected to produce acceptable performance of the restored utility cut. However, the current quality control measures employed are not capable of providing such a guarantee, i.e., adequate performance. Currently used tests were developed based on physical properties of loose and laboratory-compacted construction materials. Because of inadequate theoretical support to the
developed control measures and the large number of variables known to influence performance of a restored utility cut, not accounted for in current practices, these tests failed to guarantee control over quality and performance. To illustrate this point, let us examine Figure 1, which displays the results of an earlier research work that investigated the ability of current design and
quality control measures to account for seasonal variation effects on the performance of roads (Khogali 1995). In this figure, the characteristic response of the material to load was measured using the resilient modulus, a mechanistic parameter that describes the stress-stain behaviour of
F i g . 1 : T y p i c a l R e s i l i e n t M o d u l i f o r a C o h e s i v e S o i l M a t e r i a l ( E f f e c t o f S e a s o n a l V a r i a t i o n s ) M o i s t u r e C o n t e n t ( % ) 8 1 0 1 2 1 4 1 6 1 8 2 0 2 2 Dr y De nsi ty ( kg/m 3 ) 1 6 5 0 1 7 0 0 1 7 5 0 1 8 0 0 1 8 5 0 1 9 0 0 1 9 5 0 2 0 0 0 S o i l G r o u p # 1 S = 1 0 0 % S = 9 0 % 9 9 % M a x D r y D e n s i t y 9 5 % M a x D r y D e n s i t y S o i l G r o u p # 1 O M C - % 1 4 . 7 M D D - k g / m 3 1 8 5 1 D e p t h - m 0 . 1 6 L L - % 3 0 . 0 P I - % 1 2 . 7 S o i l T y p e S C 1 . B l a c k d o t s r e f e r t o l a b o r a t o r y t e s t e d s a m p l e s 2 . # b e s i d e b l a c k d o t r e p r e s e n t s M r in M P a 8 1 2 2 1 4 1 0 @ σσσσd = 1 4 k P a & σσσσ3 = 1 4 k P a
cohesive and granular materials. The resilient modulus (Mr) of three test specimens of a silty sand material were determined and plotted against a moisture-density relation background. The three Mr values: 81MPa, 22MPa and 14MPa, which were obtained at three different levels of moisture: 14.3%, 15.4% and 15.9% were determined using only one dry density (98% of maximum Proctor density.) As can be seen, the modulus value varies considerably at the same level of observed dry density. This observation serves to emphasize the point that control tests that specify only a field density measure will not be sufficient to guarantee performance.
2.5 Management Schemes
Regardless of the numerous findings provided by previous studies, there are still disagreements between municipalities and utilities as to what constitutes acceptable practice. Each considers studies sponsored by the other as biased investigations. This fact combined with the other unresolved construction issues reviewed above rendered the use of currently implemented management schemes fruitless.
The following are three recommendations that need to be considered to reduce confusions about various reinstatement issues:
• Future solutions should be developed through joint research ventures that involve both parties.
• Development of performance-based specifications is the preferred way to solve the conflict between municipalities and utility providers.
• In developing performance-based specifications, the requirements of management must be considered. Analytical tools will be needed to provide the following:
guidelines for material selection (based on actual material behaviour),
a method for structural design of the reinstatement (based on sound engineering principles and taking into consideration the unique nature of urban streets and site specifics), and
an effective system for performance prediction.
3 IRC/CRREL Initiative
A consortium project was recently launched by the Institute of Research in Construction (IRC) of the National Research Council of Canada and the Cold Regions Research and Engineering Laboratories (CRREL) of the US Army Corp of Engineers to resolve issues associated with construction and management of utility cut restoration. Participants in the consortium come from all sectors of the stakeholder groups (cities/municipalities, utility providers, equipment manufacturer and material suppliers) within North America. To date, the accumulated funds for the project, whose targeted budget is US $2.5 million, stands at US $1.4 million. Efforts are still ongoing to secure the remaining funds.
The initiative as planned is designed to achieve the following benefits:
• lower road maintenance costs,
• smoother roads with fewer closures for maintenance/rehabilitation activities,
• engineered solutions for local conditions,
• applicable throughout North America,
• basis for performance-based specifications, and
• promote consistent policies and eliminate dispute among stakeholders.
3.1 Overview of Consortium Project
Based on the needs identified in this paper, a comprehensive research project was developed and initiated to address the concerns of the different stakeholders involved in the reinstatement of utility cuts. The project consists of two information-gathering tasks and four major interconnected research components. The information-gathering phase includes a state-of-the-art literature review and a survey questionnaire. The format for acquiring information and expertise from practitioners was designed and is currently being distributed to project participants to collect information regarding local reinstatement practices covering both construction techniques and management schemes used. Analysis of the survey data is expected to reveal information that can be used to identify failure patterns and to interpret observed performance history of techniques and materials that work and others that are less successful. Another use of the survey data, together with input from the literature search, is to identify factors that are critical to the performance of restored utility cuts for further analysis.
The four research components of the project were designed to respond to the specific elements of the problem, including the pavement structure, the material used as backfill and the construction-related variables, all of which influence the performance of the restored utility cuts. A state-of-the-art analytical model was developed to handle the structural analysis tasks. This model is capable of accommodating the identified variables related to the above-mentioned elements, i.e., structure, material and construction. The outcome of this exercise is damage prediction, which will be used to quantify the performance of road system. Analytical modeling is intended for use with other several tasks to overcome possible limitations resulting from the inductive use of experimental data that were obtained from specific sites.
A material characterization format was outlined to investigate the characteristic response of various backfills, unbound aggregate and asphalt concrete materials to different traffic and environmental stimuli. Mechanical testing techniques/protocols were developed to capture the influence of seasonal variations on the evaluated response, considering moisture and temperature effects. Pertinent physical properties of the materials, to be used in conjunction with the results from mechanical tests as inputs to the analytical model, were specified. Results obtained from material testing will be used in pilot field experiments and in the design of various reinstatement options for evaluation in the accelerated loading facility located at CRREL.
Field experiments were planned to study local construction-related practices and to test the effectiveness of the proposed instrumentation techniques that need to be used in the accelerated loading phase. A non-destructive testing (NDT) plan was outlined to be carried out as part of the field experiments to develop a method of analysis that can later be used to relate the actual performance of the restored cuts to the structural condition of the road system as assessed by NDT techniques.
A controlled full-scale experiment at the CRREL facility was outlined to study a number of construction variables and to evaluate the performance of cuts restored using various reinstatement techniques. Results obtained from this experiment are direct means for evaluating performance and, when compared with performance predictions provided by structural analysis, will help validate the analytical model.
A flowchart of the research approach is shown in Figure 2. Further details regarding the specifics of the research components can be found elsewhere (Zeghal and Mohamed 1998).
Fig 2: Research Approach Laboratory Investigation
(Material Characterization)
Mechanical Tests Physical Tests
Pilot Field Experiments (Based on Local Practices)
Site Selection/Planning (5) Instrumentation
NDT Testing
Analytical Investigation
(Micro Mechanics Damage - Based Model)
Structural Analysis Damage Prediction
Deliverables
Material Selection Guidelines Structural Design Procedure Construction QC/QA Measures
Performance Prediction Scheme (Management)
Accelerated Loading Tests
Experiment Design Construct Sections
Instrumentation/HVS/NDT Data Collection and Analysis
Literature Search Survey
Questionnaire Design Distribution & Analysis
4 Summary and Concluding Remarks
This paper presented an overview of problems associated with the current state-of-practice of utility cut restoration. The discussion included an insight into the size of the problem and its economic impact on a worldwide scale. The paper also highlighted some of the unresolved issues connected to current construction practices and commented on the influence they have on current management schemes.
An in-depth literature search, preliminary engineering analysis and consultation with stakeholders revealed that the absence of a sufficient engineering practice has been the main cause of current restoration problems. Review of existing restoration practices indicated that design and construction specifications adopted by most cities do not guarantee adequate performance. Management issues received little or no attention while developing models for analysis and design focusing only in providing support for construction issues. Accordingly, management systems developed to enforce the current construction specifications were not successful.
This paper also explored a new format for establishing sound engineering practices that can be managed effectively. The new solution involves a new initiative by IRC/CRREL that aims at the development of a unified North-American guide for best-practice capable of addressing site-specific conditions including conventional and innovative construction materials, environmental conditions, and local construction practice and expertise. These guidelines will be performance-based and will form a sound basis for the development of effective policies and maintenance management systems capable of addressing the local needs of each city. Specific benefits of the new initiative are:
• lower road maintenance costs,
• smoother roads with fewer closures for maintenance/rehabilitation activities,
• engineered solutions for local conditions,
• cost effective solutions,
• applicable throughout North America,
• basis for performance-based specifications, and
• promote consistent policies and eliminate dispute among stakeholders.
5 References
American Public Works Association, (1996) Excavation in the right-of-way: A Guide to Co-ordination and Regulation, Special Report.
American Public Works Association, (1997) Managing Utility Cuts, Special Report.
Jones, C.J.F.P. (1999) Policy, Incentives and Barriers to the Use of Trenchless Technology, in Life Extension Technologies Workshop, New York City, August 25-26, USA.
Khogali, W.E.I. (1995) Assessing Seasonal Variations in Cohesive Subgrade Soils. Ph.D. Dissertation, University of Alberta, Edmonton, Canada.
McKim, R. (1999) Why New Technologies Meet Resistance, in Life Extension Technologies Workshop, New York City, August 25-26, USA.
Zeghal, M. and H.H. Mohamed (1998) Reinstatement of Utility Cuts: An Innovative Solution to an Old Problem, APWA International Public Works Congress: NRCC/CPWA Seminar Series “Innovations in Urban Infrastructure”. Las Vegas, USA.
Zeghal, M., Khogali, W.E.I. and H.H. Mohamed (1999) Road Cut Management Study: Evaluation of Restoration Techniques, Final Report, NRCC Client Report. Ottawa, Canada.
