A Trenching and Excavation Revolution Is Underfoot
The trenching and excavation equipment industry is experiencing a technology revolution with the introduction of new digging techniques learned from the oil industry - it’s known under a few names: hydro excavation, hydro vac excavation, vacuum excavation, or suction excavation.
The basic technology comes from the sewer cleaning industry that uses a machine called a combination sewer cleaner. A sewer jetter pumping high pressure water through selected sewer nozzles mounted on a long jetter hose cuts through and loosens ground soil, essentially digging trenches using water pressure. A long vacuum hose sucks up the loosen soil into the vacuum tank truck.
Hydro excavation has clear advantages over standard slot trenching and excavation machines.
Hydro excavating slot trenching is a safe and non-destructive method of trenching for telecommunication cables, sewer lines, and pipeline installations.
- Slot trenching locates;
- Slot trenching installations;
- Drain tile slot trenching;
- Pipeline slot trenching.
Hydro excavators work with precision, digging clean holes that require less restoration work. Daylighting can reduce restoration costs, which amount to more than 30% of a project's cost.
A well trained hydro excavation technician working with other operations can significantly accelerate the projects timeline and reduce costs normally associated with damaged infrastructure using traditional trenching and excavation machinery.
Hydro excavators come equipped with extended water and vacuum hoses enabling crews to reach worksites as far as 350 feet away and down to depths below 40 feet. Site accessibility in remote areas coupled with difficult soil conditions such as rocky soils, clays, frozen ground are no match for hydro trenching and excavation crews.
Hydro Trenching and Excavation Practices
Potholing or daylighting, is essentially digging a hole to expose underground infrastructure to locate horizontal and vertical facilities. These horizontal and vertical locates are typically marked on surveys. The locates may also be identified by traditional survey coordinates or GPS or tape measuring distances from permanent features in three horizontal directions.
Municipalities and utility companies consider hydro excavators as an essential step of underground construction for all types of trenching and excavation.
Potholing with a backhoe has the potential of striking underground infrastructures. Backhoes are inexact and cumbersome; even the most skilled backhoe operator risks hitting and damaging the utility they were trying to locate and repair.
Backhoes are not the preferred method of daylighting, but if necessary it requires a spotter during the entire excavation. The spotter communicates to the backhoe operator when buried utilities are sited.
Manual digging a test hole for daylighting is defined as a worker hand holding a shovel and digging into soil. Hand digging is time-consuming and labor-intensive. The main advantage of digging is that it uses less expensive equipment and is relatively safer locating utilities. As with any trenching and excavation, caution should be practiced near live utilities.
Vacuum excavators are a non-destructive method of locating underground utilities. Either high pressure air or water is utilized to loosen soil and a vacuum system collects the soils.
Do we use air or water to excavate?
Air vacuum excavators use kinetic energy and high velocity airstream to expand and loosen soil. The loosened soil and rock are vacuumed up by a powerful vacuum hose and tank. This is how test holes are created and daylighting buried utilities. Holes vary in shape and size, however a typical measure is 6 inches to 12 inches in diameter and 4-6 feet deep. Air excavation has certain advantages over hydro vacuum excavation. Air excavation is quicker in most soils and eliminates the need for disposing wet soil. Since the soil remains dry it can be re-used for backfill. As well air methods are considered safer for operators and underground infrastructure. Disadvantages of air excavation: they are not productive in all soil types specifically wet and heavy clay.
Water or Hydro Excavation
Water vacuum excavation or hydro excavation systems dig holes using high pressure water to loosen the soil. The wet soil and slurry is lifted into a vacuum tank via a powerful vacuum hose. As with air systems, a typical hole measures 6 inches to 12 inches in diameter. The hole depth is dependent on the vacuum performance. High pressure water is effective in loosening wet heavy clay. Heated water enables excavation in frozen ground giving productivity throughout the year. A hydro excavator must use caution with high pressure water given its power to cut through harder soils, therefore potentially damaging utilities.
Trenching and Excavation Safety
Before digging, call 811 for utility locates throughout the states, the call system that coordinates the locations of all utilities.
Once obtained, construction drawings for new or existing facilities should be used during daylighting operations. Construction drawings need to be compared to locate paint marks to ascertain if facilities shown have been identified in the field. If drawings and physical marks do not match, further daylighting may be needed to confirm locations.
Keep all contact names and phone numbers of underground utility providers in hand.
If locate marks are incorrectly designated and new utilities are exposed, then the facility owner or state should be informed. Furthermore the vacuum excavator company should document the locates of the utility and inform the facility owner. If the utility is not found through daylighting, using construction drawings and locate marks, the facility owner needs to be contacted.
Protection During Exposure
Most state statutes require trenching and excavation within 2 feet of located utilities be cautiously performed. Backhoe excavation should not be allowed within 2 feet of existing facilities.
Exposed utilities can sag or shift when soil supporting and protecting the utility is removed. Utilities now unsupported , due to daylighting, needs to be supported by shoring. The utility needs to be protected from falling objects that may cut or damage the utility.
Backfill and Soil Remediation
Once underground utilities have been exposed by the hydro vac services company, the hole should be backfilled within 24 hours unless otherwise directed. Sediment controls should be used during daylighting activities to prevent stormwater pollution. The hole needs to be clean and dry before backfilling.
Check your local state safety guidelines manuals or OSHA training online for safe trenching and excavation practices.
Related article: Trenchless Sewer Repair - The Future Is Here