Non-Destructive Air-Vacuum Excavation
This information provides the highest level of accuracy presently available. It involves “locating”; the use of non-destructive digging equipment to expose buried utilities at critical points. When surveyed and mapped, precise plan and profile information is available for use in making final design decisions. The use of nondestructive digging equipment, particularly vacuum excavation, eliminates damage to underground utility facilities traditionally caused by backhoes. By knowing exactly where a utility is positioned in three dimensions, the designer can often make small adjustments in design elevations or horizontal locations and avoid the need to relocate utilities. Additional information, such as the composition, condition, and size of the underground utility, soil contamination, pavement thickness, etc., also assist the designer and the utility owner in making important decisions.
Non-destructive Air-Vacuum Excavation is used to determine the exact horizontal and vertical location of facilities. The process involves removing the surface material over approximately a 1' x 1' area at the electronically determined approximate horizontal location produced during the designation stage. The air-vacuum process proceeds with the simultaneous action of compressed air-jets to loosen soil and vacuum extraction of the resulting debris.
This process ensures the integrity of the utility line during the excavation process, as no hammers, blades, or heavy mechanical equipment comes into contact with the utility line, eliminating the risk of damage to utilities and personnel. The process continues until the utility is uncovered. Normally, the following information (if applicable) is recorded for each vacuum excavation: the utility type, material, size, depth, condition, location (x, y, z), orientation, roadway section materials and depths, soil type and water table.
Air-Vacuum Excavation can also be used at a proposed boring location to excavate below the "utility window" which is usually eight feet. This reduces the risk to utilities during the initial drilling process. Soil samples can be taken during the air-vacuum excavation process. Frequently, contaminants move along utility line trenches. Air-vacuum excavation can be used to obtain soil samples adjacent to utility lines without risking damage.
Data Management
Equipped with this EXACT information, the Data Management aspect of SUE can begin. These four categories of invaluable information can be utilized to provide extremely accurate subsurface "photographs" for designers. The unique blending of all four of these distinct procedures produces the most exact CADD map possible. After concluding the air-vacuum stage, the exact utility data is then translated into a computer generated three-dimensional map. This computer-generated map then becomes a critical weapon for the designer, allowing for exact instructions to be crafted for excavation. The sum total of benefits to the client when SUE is utilized is the virtual elimination of utility breaks and work stoppages, cost overruns, safety hazards, adverse publicity, and the ensured health and safety of the general public all related to subsurface utility breaks.
When all of these procedures are blended together and applied, a clear and exact visual representation of the position of underground utilities in an area of excavation is produced. Each of these tools, applied independently, offers a limited and only partial representation of the subsurface utilities. The benefits derived from the application of these procedures are maximized when each is fully utilized to complement one another.
The two-fold end result of performing a complete SUE survey is:
- A precise subsurface map that eliminates utility breaks, safety hazards or claims, and public outcry, and
- Confidence to provide the client or owner with the best product while reducing design cost and compressing schedules.
Why Use SUE?
SUE is no longer a novelty. SUE is now recognized by the American Society of Civil Engineers (ASCE) as a viable and necessary component for the practice of civil engineering. Their national standards activity, Standard Guidelines for the Collection and Depiction of Existing Subsurface Utility Data, will have major ramifications regarding the allocation of risk for utility owners, constructors, and engineers. SUE will be a necessary process for every project designed by a civil engineer. The result will be that the reliability of utility data on plans is better defined.
Last Thoughts on SUE
- Did you know that no one really knows how many people are actually killed or injured every year as a result of utility breakage's?
- Did you know that today, many new projects are burying new facilities without creating actual "as-builts"?
- Did you know that in India we do not have legislation requiring a person to use one-call systems prior to excavation? However, there are few departments that require the contractor to obtain both the horizontal and vertical location prior to excavation?
- Did you know that on many projects, a "surprise discovery" rate of twenty-five percent or more is found, i.e., utilities not found on research or contract documents?
- Did you know that many training programs for directional drilling equipment does not mention that on projects where there is ambiguity or uncertainty regarding the contract plans and "one-call markout' a SUE professional should be considered as a safety precaution to find utilities?
- Did you know that on many major construction projects a designer is required to investigate the Subsurface Soil Conditions (geotechnical investigations) but very few consider investigating utility condition and use the owner's specification and plans?
- Did you know that many utility breakage's and interruptions have happened while a driller is performing a "geotechnical investigation"?
- Did you know that many utility breakages's occur during test-pitting operations while "searching" for the utilities?
- Did you know that the scrapes and scratches left on a pipe by mechanical excavation equipment could lead to the pre-mature pipe corrosion and possible failure? In June 1994, in US, an apartment building was destroyed by a gas line explosion because of such marks on the gas pipe.
- Did you know that most existing utility compilation plans are based on a compilation from random search of records and survey location of surface structures? (You are at a loss if a quick paving project has superseded the project.)
- Did you know that many communication companies do not provide copies of plans to surveyors, designers, and construction managers for utility location plan preparation?
- Did you know that budgetary cutbacks by municipalities and utility owners result in old documents not being revised to reflect current utility location?
- Did you know that incorrect information often winds its way into GIS System Networks?
- Did you know that Sue reduces liability? Use SUE to avoid being sued.
Indian Scenario:
Use of Ground Penetrating Radar (GPR or Georadar) is not new in India. Author himself has been involved in various projects using GPR for utility mapping since 1996, in India. GPR services are being used extensively by many trenchless contractors for obtaining prior information on existing utilities, which is an encouraging trend. A larger segment, however, is still operating without such information, resulting in costly damages to utilities. It is therefore required to arrive at a consensus among various service providers about making use of available technology to avoid damages and risks.
Like any indirect technique, GPR has its own limitations, and should therefore not be seen in isolation. Gathering of background information, use of additional tools discussed in the present paper and an understanding of the utility infrastructure is therefore a pre-requisite for a successful project.
For other technologies discussed above, under SUE, an internationally reputed company GeoSpec has confirmed their willingness to provide these services in India, in a communication with the author.
Conclusions:
Use of various techniques available for detection of underground utilities in a totally non-destructive manner reduces to a great extent the chances of damages during trenchless operations. The information thus obtained can also be used to create maps of a city’s utility infrastructure using latest tools of GIS and remote sensing, which can be updated on a regular basis as an when a new installation takes place. This would ensure an updated database for all times to come.
I would welcome suggestions, enquiries on any of the aspects covered under this paper on
iggs@mantraonline.com
Acknowledgment:
I am thankful to Mr Luv Sharma, Cosmic Technologies for his inputs on GIS and remote sensing aspects. I am also thankful to Mr Daran Rehmeyer, PE, CDT, GeoSpec, LLC, for his inputs on various aspects of SUE. I would also like to express my gratitude towards other directors of my company, IGG Services (P) Limited, Mr Abid Hasan and Mr P S Mukherjee for their contributions.