ارزیابی مهندسی ابزار زیرسطحی برای پروژه بزرگراه: تجزیه و تحلیل سود هزینه

Accurate location of buried utility infrastructures is a vital issue for utility owners, utility managers and engineers, designers, and contractors that perform new installations, repairs, and maintenance on highway projects. Unreliable information on underground utilities can result in undesirable consequences such as property damage, claims, and other social and environmental problems. Subsurface utility engineering (SUE) is becoming a significant method for reducing the potential for underground utility conflicts at the project planning phase. SUE accurately identifies, characterizes, and maps underground utilities through four quality levels. This study presents a SUE benefit–cost analysis (BCA) to encourage a better understanding of SUE and the use of SUE. Eleven main benefit factors and two cost factors are identified and estimated on twenty-two SUE projects and eight non-SUE projects from Pennsylvania Department of Transportation (PennDOT) districts. In addition, this study reveals the relationship between benefit–cost ratio and complexity levels of buried utilities.

As human society has flourished in modern times, more and more infrastructure systems have been constructed to meet an ever-increasing demand. However, the expansion of infrastructure has resulted in many problems in the construction industry. Underground utility damage at construction sites has been one of the major problems (Lew and Anspach, 2000). In general, the utility damage has been caused by inaccurate underground information. Existing records and visible feature surveys by site visit are typically 15–30% off the mark, and sometimes considerably worse (Stevens and Anspach, 1993). A one-call system was developed to solve the problem of inaccurate existing records. However, the information provided by one-call systems has not effectively met the need to accurately locate underground utilities. This one-call system only provides the information on buried utilities of members. In other words, information on existing utilities of non-members is not available in the one-call system. In addition, utility owners/operators who are notified by the one-call center incorrectly mark or even fail to mark their utility locations sometimes. Old utilities also may not be discovered under this system. Two or three days, timing of utility locations before actual construction, also may not be enough for utility companies to accurately locate and mark their underground utilities. Failure to use the one-call system at all is a further problem in utility damage during construction (Sterling, 2000). Subsurface utility engineering (SUE) is an engineering process that utilizes new and existing technologies to accurately identify, characterize, and map underground utilities early in the development of a project (ASCE, 2002). As shown in Fig. 1, SUE is divided into four quality levels which are represented by different combinations of traditional record, site survey, geophysical technology, and vacuum excavation system. The accuracy and reliability of underground information increase from quality level D to quality level A, but the costs increase from quality level D to quality level A (Jung, 2009). SUE can be the most suitable and reliable method for reducing risks associated with uncertain underground information through geophysical technologies and non-destructive methods. This study takes an in-depth analysis of highway projects executed by districts of the Pennsylvania Department of Transportation (PennDOT). The key objective of this study is to perform a detailed benefit–cost analysis (BCA) to provide a better understanding of SUE and encourage the use of SUE. Eleven main benefit factors and two cost factors are identified and estimated on 22 SUE projects and 8 non-SUE projects. In addition, this study reveals the relationship between benefit–cost analysis and the varying complexity levels of buried utilities. The BCA can help owners and designers to select SUE for their underground projects. Full-size image (23 K) Fig. 1. Quality levels of SUE.

This study presents the background information of previous studies on BCA of SUE. Previous studies utilized only SUE projects to quantify cost savings of SUE. Those studies inferred SUE benefits from utility conflicts that were revealed by SUE. However, the mere identification of utility conflicts does not necessarily result in a cost being incurred that is considered as a SUE benefit. In this study, non-SUE projects with problems were used to determine the cost savings of SUE because direct costs incurred by problems related to utilities can be considered as SUE benefits. From 22 SUE projects and 8 non-SUE projects from various PennDOT districts, the results of the study revealed that $11.39 can be saved for every $1 spent on SUE in some road projects. A ratio of 1.65% was determined as the ratio of SUE cost to total project cost. This means that SUE can provide accurate utility information to encourage cost savings with reasonable cost. Project relocation cost is the most important item to the cost savings, representing 40.33% of total savings. This study shows that there is no relationship between project cost and B/C, nor any relationship between project cost and complexity level. However the results indicate that there is a strong relationship between complexity levels of buried utilities at the construction sites and B/C of SUE. The greater the complexity level of buried utility, the higher the SUE benefits. For 30 projects, the average of B/C of complexity level 4 projects is 8.47 and the average of B/C of complexity level 5 projects is 17.83. A small difference in complexity levels resulted in a great difference in benefits of SUE. For projects with complexity level 5, the most accurate utility information is required to reduce risk and maximize benefits. The results of this study can help owners and designers to save project cost by selecting SUE for their underground projects and utilize the utility impact rating form. This study contributes to SUE research not only by conducting a benefit–cost analysis of SUE, but also by revealing the relationship between B/C and complexity level. However, more in-depth verification should be conducted by expanding the number of SUE and non-SUE projects. Although the benefit–cost analysis was conducted with actual SUE and non-SUE projects, more accurate analysis can be made through more rigorous investigations. Future studies can pursue the selection of geophysical techniques, because the available techniques vary according to soil and construction site conditions. For SUE quality levels A and B, a decision-support tool to select appropriate geophysical techniques should be developed for managers, designers, and engineers for successful SUE projects.