Early knowledge of the precise location of these networks for which there are often no precise surveys, even when they are not very old, can help achieve savings, but above all gain time and avoid interference during construction. In particular, the significant foreseeable development of optic fibre telecommunications networks requires precise knowledge of existing networks to be able to use high yield machines.

The timing of this article is opportune to sensitize engineers to these problems.

The inability to obtain reliable underground utility information has been a troublesome problem for highway designers in the United States for many years. Now there is a solution. There is a new engineering process called - Subsurface Utility Engineering-.

Subsurface utility engineering incorporates new and existing technologies to accurately locate and map underground utilities during early design of a highway project.

Developed by a Virginia firm, Subsurface Utility Engineering was first used in Fairfax County in Virginia in 1980. The Virginia Department of Transportation began using it on highway projects in 1984. Both still use it extensively. At the present time, 27 State highway agencies are using Subsurface Utility Engineering. Several more considering using it in the near future. In addition, many city and county highway agencies are using it on their highway projects.

Activities

Three major activities are involved in the use of Subsurface Utility Engineering. These activities are called designating, locating, and data management.

• Designating is the us of surface geophysical techniques to determine the existence and horizontal position of underground utilities.
• Locating is the use of non-destructive digging equipment at critical points along a subsurface utility's path to determine the precise horizontal and vertical position of buried utilities.
• Data Management involves surveying utility information obtained by designating and locating to project control and transferring it into highway agency's computer-aided design and drafting (CADD) system or onto its project plans.

Quality Levels of Information

These activities provide "quality levels" of information. Quality levels may be though of as degrees of risk, or, how much information is really needed before planning, designing, and constructing a highway project.

Highway plans typically contain disclaimers as to the accuracy of the utility information. The use of quality levels allows project owners to certify on the plans that a certain quality level of information has been provided.

There are four quality levels as follows:

• Quality Level D (QL-D) is the most basic level of information for utility locations. This information comes solely from existing utility records. It may provide an overall "feel" for the congestion of utilities, but is often highly limited in terms of comprehensiveness and accuracy. Its usefulness should be confined to project planning activities.
• Quality Level C (QL-C) is probably the most commonly used level of information. It is obtained by surveying visible utility facilities, such as manholes, valve boxes, etc., and then correlating this information to the QL-D records information. It is not unusual when using QL-C to find that many underground utilities have been either omitted or erroneously plotted. Its usefulness should be confined to rural projects where utilities are not prevalent, or are not too expensive to repair or relocate.
• Quality Level B (QL-B) is obtained through the professional selection, application, and interpretation of surface geophysical techniques to identify virtually all utilities within the project limits. This is "designating." The information obtained in this manned is surveyed to project control. Its usefulness is maximized during the preliminary design of a project, where slight adjustments in the design can produce dramatic cost savings.
• Quality Level A (QL-A) information is the highest level of accuracy presently available. It provides precise three-dimensional plan and profile mapping of utilities and related structures when exact information is needed for final design decisions. This information can only be obtained by exposing subsurface utility to daylight or by using reliable records that would guarantee to contain the original and exact reproduction of the construction as well as an accessible topographic system. This is the locating - stage. Vacuum excavation is the preferred non destructive method to expose underground utility networks and other structures.
  

Proper Use of Subsurface Utility Engineering

When used properly, subsurface engineering works as follows:

• The highway agency and a Subsurface Utility Engineering provider enter into a contract for professional engineering services.
• The highway agency authorizes the provider to:
  -Obtain existing records from utility owners.
  -Plot utility information on plan sheets using utility records (DL-D information) and visual indications (QL-C information).
  -Apply applicable surface geophysical techniques (designating) to determine the existence and horizontal position of underground utilities within the project limits (QL-B information). At this point two-dimensional horizontal information is provided to the designer and decisions can be made on where to place storm drainage systems, structures, cut and fill, and other design features in order to avoid conflicts with existing utilities. Slight adjustments in the design can produce substantial cost savings by eliminating many utility relocations and moving excavation work away from critical utilities.
  -Use nondestructive digging equipment (such as vacuum excavation) at critical points along a subsurface utility's path (locating) to determine the precise horizontal and vertical position of buried utilities (QL-A information). This involves physically uncovering the utility using a small hole measuring about 20 x 20 centimeters square at the top. Not only does this allow the underground utility to be accurately surveyed (top and bottom), but also provides information on its type, size, and condition. The designer now knows where the critical utilities are positioned in three dimensions and can make small adjustments in design elevations or horizontal locations and avoid the need to relocate utilities or excavate near them.
  -Survey utility information to project control and transfer it into the highway agency's CADD system or onto its final plans.
  -Professionally authenticate the complete work product. The work product is insured against errors and omissions.
  

Benefits

The use of Subsurface Utility Engineering benefits highway agencies and utilities in the following ways:

• It reduces utility relocations necessitated by highway construction. Accurate underground utility information early in the design of a project makes it possible to design around many potential conflicts.
• It eliminates unexpected conflicts with underground utilities during construction. As a result, there are fewer project delays and subsequent contractor claims, and fewer disruptions of utility service.
  

Costs

Subsurface utility engineering typically costs about 10 percent of the total preliminary engineering cost, or about 1 percent of the total project costs, on projects where it was used.

The cost for QL-A information (i.e., locating, surveying, mapping) may vary from $300 to $650 per hole, depending upon the difficulty involved. In solid rock, it might cost more than in sand. They commonly dig through highway pavements to locate utilities using small holes measuring only about 20x20 centimeters at the top.

The cost for QL-B information (i.e., designating, surveying, mapping) is usually not as expensive as the QL-A information. As a rule, the designating information generally costs less than $3 per linear meter of utility designated. For example, the cost for designating 2,000 meters of gas line and 1,00 meters of telephone line would generally be less than $9,000.

Savings

Subsurface utility engineering saves money in many areas. Its use typically reduces the following costs:

• Utility relocation costs. Utility relocation costs may be reduced significantly using QL-B and QL-A information early in the design of a project to avoid or minimize utility relocations. Minor adjustments to a highway's design can be much less expensive than actual utility relocations in the field. Sometimes highway agencies pay for utility relocations, sometimes the utilities pay, and sometimes they share the costs. No matter who pays, both benefit from not having to relocate.
• Cost overruns. Nearly every project has cost overruns. Comprehensive and accurate utility information can reduce change orders, engineering redesign work, construction claims, and even contingency costs.
• Construction costs. Confidence in the location of utilities as shown on the construction plans may influence contractors to reduce their bid prices. Conscientious contractors will proceed cautiously in areas where utilities may exist and this takes more time. Time is money.
• Administrative costs. Administrative costs may be reduced. Insurance costs might go down it the insurers don't have to worry about costly utility conflicts. Financing might be easier to get and interest rates might even be influenced.
• Engineering costs. Subsurface utility engineering typically accounts for about 10 percent of the preliminary engineering costs on project where it is used. Generally, the savings come later during the utility relocation and construction phases. Even so, on some projects it has actually been found to be less expensive to use sub-surface utility engineering to obtain utilities information the traditional way.

The total overall savings on a typical project may approach 15 percent compared with costs from a project where Subsurface Utility Engineering is not used. Some States have experienced even greater savings as indicated below in the case studies.

Case Studies

The savings in time and money that can be realized by using Subsurface Utility Engineering are substantial. Here are some examples.

• On a major highway project in the City of Richmond, a provider for the Virginia Department of Transportation (VDOT) dug 156 test holes at locations where QL-B information indicated highway/utility conflicts were possible. Using the QL-A data obtained, VDOT's roadway and hydraulics designers determined that conflicts between proposed highway drainage facilities and existing utility lines would occur at 75 of the sites. As a result, minor design adjustments were made to highway drainage structures and 61 of the potential conflicts were eliminated. By making these changes, $731,425 worth of utility adjustments were avoided; whereas, the cost of digging the test holes was only $93,553, resulting in a savings of $637,872.
• In addition to the above cost savings, Subsurface Utility Engineering also helped VDOT reduce the time needed to design highways from 5 years to 4 years.
• The Florida Department of Transportation analyzed a major project in the City of Tallahassee where Subsurface Utility Engineering was used and found that it saved $e in contractor construction delay claims for every $1 spent for it.
• The company used Subsurface Utility Engineering during the design of 1.9 kilometers of a 138 kV electric pipeline through the downtown area of Columbus, Ohio. The cost of Subsurface Utility Engineering was less than $100,000. Subsequently, the successful bidder for construction of the pipeline stated that it had been possible to reduce its bid price by USD400,000 due to the accuracy and comprehensiveness of the utility information. Furthermore, there were no utility relocations, no utility change orders, no contractor claims, and no utility damages during the project. The project was finished ahead of schedule.
• The Maryland State Highway Administration (MSHA) has been using Subsurface Utility Engineering since 1989. On a highway project involving realignment of a highway and widening from 2 to 6 lanes, the use of Subsurface Utility Engineering enabled the MSHA to redesign the storm drainage system to minimize conflicts with utilities. Instead of impacting about 1,500 meters of each utility (gas, water, and sanitary), conflicts were reduced to about 120 meters each. The cost of Subsurface Utility Engineering was $56,000. Cost savings to MSHA and the utilities amounted to $1,340,000.
  

Other Uses

Subsurface utility engineering is not confined to highways. It can be used with good results on airport, railroad, transit, building construction, and any other public works projects where underground utilities may be encountered during excavation activities. In addition, it can be used for environmental purposes, such as detecting and mapping underground storage tanks, septic fields, and even contaminants (utility trenches provide preferential migration paths for contaminants).

Conclusions

The Federal Highway Administration's Office of Engineering believes:

• It is good engineering practice to use Subsurface Utility Engineering on every public works project where underground utilities are present.
• *The use of Subsurface Utility Engineering will significantly reduce utility relocations and accidental conflicts with underground utilities, and will save money, time, and lives.
• The use of Subsurface Utility Engineering will eventually result in nationwide cost savings exceeding $100 million per year in USA for highway work alone.

Credits
Author(s)
C. Paul Scott 

Publication(s)
Routes/Roads,
Issue 292, Volume IV,
October 1996