Excavation is full of multiple types of risk, both known and unknown. Every time a blade breaks ground, there is an inherent risk that could be caused by an underground utility, existing soil conditions, environmental conditions, or many other factors. This article walks through several hypothetical scenarios in what excavation risks to expect in the given conditions, ways to mitigate those risks, and the best courses of action to respond to hazards caused by those risks.
We’ll discuss the following risks:
- Underground utilities
- Soil contamination
- Rock excavation
- Heavy equipment around protected structures
- Excavations near high traffic roads
Excavation Around an Unknown Underground Utility
When operators are given the “green light” to excavate with no known utilities in the area, operators often work quickly to move as much soil as possible in the shortest timeframe possible. Newer utility installations typically feature a warning tape at least 12” above the buried utility with contact information for the utility owner. However, some older utilities (or newer utilities where the installer opted to not place any warning tape) have the potential to surprise contractors.
Contractors should always do preliminary research before cutting crews loose regarding utilities in the area. This includes contacting the local 811 to mark public utilities. More critical areas may require the use of a private contractor with additional sounding or ground-penetrating radar equipment to verify utility locations. While available information should be provided on the drawings and survey by the architect or engineer, a quick online search on publicly available GIS may prevent future headaches if a previously unmarked utility is discovered.
If a previously unmarked utility is damaged during excavation, the contractor should stop operations and immediately call the project manager and owner to notify them of the issue. The contractor should identify the utility type (i.e. storm sewer, gas, domestic water) and notify the appropriate authorities. If environmental assistance is needed (for sanitary sewer and gas), the state environmental department should be contacted and/or the steps noted in the architect or engineer’s stormwater pollution prevention plan (SWPPP) should be followed. Since the utility was unmarked and if there was no reasonable reason for the contractor to expect a utility in this location, these cases are typically not the fault of the contractor and often result in additional contract days and/or fees to rectify the situation.
Excavation Around a Known Underground Utility
When excavating around a known utility, contractors must take extra caution. Utilities are susceptible to damage when within the vicinity of heavy construction equipment, including crushing under a piece of equipment’s weight due to low cover or damage caused by equipment blades or teeth during excavation. Contractors should heavily weigh the option of seeking additional information about underground utilities in critical areas to mitigate excavation risk.
The degree of how much is known about a utility’s existing condition is important as well. Less expensive utility locating services may mark the location of the utility, but may not mark the utility depth, size, or material. It is typically advantageous for contractors and architects or engineers to seek additional utility information by potholing, or performing point excavations with a hydroexcavator to safely expose underground utilities to determine their depth. If hydroexcavation resources are not available, contractors may elect to deliberately dig at a single point with a small piece of equipment such as a mini-excavator to pinpoint the utility depth. Contractors should excavate along or parallel to the underground utility; excavating perpendicular to the utility increases the risk of an excavator bucket tooth snagging the pipe and causing damage to the utility. Damage caused to marked utilities will likely result in unpaid repair costs and contract time lost to the repair for contractors.
Excavation of Contaminated Soil
Contaminated soil presents a wide variety of excavation risks both to the safety of workers and to the health of the project. Contaminated soil can be an unexpected condition, an expected condition, or a known condition. An unexpected condition may be excavating a buried oil drum in a relatively rural location. An expected condition could be discovered oily soil near an abandoned gas station. A known condition would be a leaking underground storage tank (LUST) reported on a Phase 1 Environmental Site Assessment that is typically performed before the original owner of the property sells to a new owner. Another known condition could be caused by the contractor, such as spilling oil, fuel, or other fluids onto the ground without proper containment.
While the causes may vary, the treatment is typically the same; wear appropriate PPE such as respirators, excavate the contaminated soil and appropriately dispose of it in a landfill or other suitable location, and replace the void space with contaminant-free soil. More detailed and site-specific steps, such as the location of the nearest contaminant-accepting landfill, are typically provided in the architect or engineer’s SWPPP. Similar to utility damage, state environmental authorities should be contacted per the SWPPP in the event of contamination or a contaminated soil discovery.
The majority of risk stemming from rock excavation is contractual in nature, though there are safety additional safety measures that should be observed in some situations. Contractors should review geotechnical reports before bidding on projects to understand if rock excavation should reasonably be expected. Contractors should also thoroughly review the pay items or unit price specifications to understand if additional rock excavation is eligible for additional payment; some contracts explicitly state that no additional payments will be made for rock excavation.
If rock is encountered and must be removed, there are three methods to do so: ripping, pneumatically removing, and blasting. Ripping can be accomplished if the rock is a “softer” type of rock such as sandstone or shale and can be removed by the ripper attachment on a dozer or excavator. Pneumatic removal includes hammering or drilling with pneumatic attachments on heavy equipment. Pneumatic operations are time-consuming and require additional equipment and time to remove the crushed stone. Blasting is a much more expedient option than pneumatically crushing rock when allowable. However, there are myriad hazards to consider when blasting. One such hazard is damage to nearby structures, such as homes. Seismometers will often be required to be installed near homes to detect if detrimental forces from the blast reach nearby structures.
Maneuvering Heavy Equipment Around Protected Structures
A common note on construction drawings is for the contractor to “protect” a certain feature of the construction site, whether this is a bridge pier, a large tree, or some other valuable site feature. These features may be culturally or environmentally important, or simply expensive or complex if replacement was necessary.
Contractors can employ a variety of safety measures to ensure operators can identify protected features and avoid or more deliberately operate in these areas. A simple orange construction fence is a highly visible, inexpensive, and effective option for installing a boundary around protected site features. The architect or engineer may also dictate the type of protective measures installed around such assets, though the typical course of action is to rely on contractor means and methods to avoid potential lawsuits if an ineffective protective measure is prescribed. Operators may also request ground guides or other guidance to assist in navigating tight corners and blind spots. Failure to preserve protected site features bear a heavy cost, but even simple equipment tracking outside of construction boundaries may incur additional grading and seed/straw work.
Construction Signage Around Road Work
Road work is one of the most dangerous occupations due to the close vicinity to vehicles traveling at a high rate of speed. The more severe the interruption, the more dangerous the conditions. For example, a lane closure presents more hazards than a lane shift. Contractors must mitigate a variety of fair probability, high impact excavation risks to safely complete these projects. Bluntly stated, lives are on the line when deciding how much safety signage and barriers to install on road work projects.
The majority of contractors and engineers go heavy in safety features to make every effort to make road work sites as safe as possible. This includes barricading sites with jersey barriers, providing extremely bright lights and reflective vests for night work, and signaling lane shifts or lane closures miles in advance to give drivers ample warning to expect construction and the resultant traffic slowdowns. Harsher penalties are levied in construction zones in response to the number of fatalities and injuries occurring in these types of projects. The best rule of thumb for safety features on road work sites to apply the “p-factor”; the p stands for plenty.