It is widely known that open excavation methods are prone to danger, not just to workers but also to pedestrians and vehicles using the same route in which the project is operating. Trenchless technology has quickly eliminated that problem; but like everything else, it has its share of hazards that need to be either eliminated or guarded against. Eliminating hazards is almost impossible, but thanks to guidelines laid down by the government, OSHA, and concerned municipal authorities, these hazards can be safely avoided, provided they are followed.
One of the biggest challenges encountered in almost any trenchless operation is the possibility of striking underground utilities. Resulting accidents can have very serious consequences, even the loss of life. There is an uncertainty in estimating what may be encountered underneath the surface. It is very important, therefore, to have a thorough knowledge of the existing utilities that pass through the location of the proposed route of trenchless operation. Local one-call centers or Dig Safe have an approximate location of the utilities to plan the new route, however, some lateral pipelines, and water and sewer pipelines may not be registered with them. Also, they do not provide the depth of the utility. Carrying out a thorough geotechnical investigation including bore pits, and vacuum excavation to expose the marked utilities at regular intervals is, therefore, very essential. (Learn more in “The Science of Getting it Right: Locating Underground Utilities.”)
Irrespective of the type of trenchless method used, safety guidelines should be strictly followed. Most of the trenchless methods require the excavation of at least 2 pits, one for the insertion of the equipment, and the other for the exit and pullback of the pipe. Depending on the soil condition, trench boxes or other engineered systems are used to provide stability to the pit for the purpose of placing machinery, pipes and workers. Shoring, shielding and sloping are protective systems that allow for safe working area and prevent collapse of the surrounding soil. Below is a general safety guide that can be used for trenchless projects right from set up to completion. (Learn more in “When Ground Improvement is Needed During Trenchless Rehabilitation.”)
Site Set Up and Jacking Pits
Though trenchless construction does not require excavation, space is needed to operate the equipment, which is often placed in an excavated pit. The site selected for beginning the project should be such that there is minimum disruption to pedestrian and vehicular traffic. Vibration caused by the machinery, cranes and traffic if any near the pit should be taken into consideration when preparing the jacking pit. The excavated pit should be well supported with shores and braces. Shoring systems exert hydraulic or mechanical pressure on the walls of the pit, thus providing adequate safety for machinery and men. For water bearing soils or installations that run deep, watertight caissons should be installed. All excavations should be demarcated and barricaded with signs and guard rails. The excavated pit should be large enough to accommodate the jacking system, lubrication unit, slurry tanks, pipe storage area, crane, generator, etc. Equipment to be operated above the excavation area should be kept well away from the pit edge to prevent slipping into the pit. The shoring and bracing system should be designed keeping in mind the lateral loads that it may encounter from equipment weight.
Locating and Demarcating Existing Utilities
A geotechnical report is the ideal method to locate underground utilities other than gathering information from municipal records and other agencies like Dig Safe that keep track of installations. These identified utilities should be properly marked so that it is visible along the path of the bore. They should also be exposed at regular intervals to ensure that the utility line is actually passing that way. Sometimes, laterals connecting homes and offices are not marked and could lead to cross boring problems that can be fatal to workers and may cause heavy financial loss leading to the failure of the project. Cables should also be identified and marked to prevent electrical shocks while drilling. (Read on in “Why a Detailed Geotechnical Report Means Success for Your Trenchless Project.”)
Many processes are simultaneously conducted during the drilling operation. Workers and small equipment should be kept clear of the drill head, auger or cutter head. Workers operating near such machinery should be well protected with safety gear, shoes and helmets because loose fitting gear can be potentially dangerous. Also, stepping or straddling over running machinery can have serious consequences.
Appropriate tools like pipe tongs should be used for connecting or disconnecting augers or pipes. The machine operator at no time should leave the machine while it is running by locking it in the operating position, and the operator should be aware and alert of his surroundings and should be quick to shut it down if any worker is seen to be in a dangerous situation. All personnel operating equipment like excavators, cranes, etc, should be experienced and knowledgeable of safe operating procedures with proper certification and licensing where applicable.
The Drill Path
The drill head, cutter head or auger should be constantly tracked. Interference sources like traffic signal loops, electric fences, underground metal tanks, etc. should be identified so that it is not confused with any obstacles on the drill path. The communication between the drill operator and the tracking personnel should be open at all times so that any potential obstacle is instantly communicated and accidents are avoided. Any change in the bore path indicated by the reading instruments should be immediately noted and the operation halted till the problem is identified and rectified. Cross boring into gas or chemical pipelines can be very dangerous. To prevent the possibility of getting electrocuted if the drill head touches electric cables, none of the workers, at any time, should come into direct contact with the drill string when it is being pushed into the ground. (Learn more in “A Complete Guide to the Usage and History of Drill Bits and Tooling.”)
While working with equipment that run on fuel, especially in jacking pits, exhausts generated from the machinery can create a harmful atmosphere for the workers operating in the pit. Sufficient circulation of air using exhaust systems should be ensured so that fresh air is always available. Gas monitors should be used to detect the presence of harmful gasses like hydrogen sulfide and carbon monoxide, which if found to be above safe levels should call for a shutdown of the operation until gas venting can be established and the working conditions are safe again.
Completion of Work
Once the work is completed, all equipment and tools should be safely dismantled and removed from the site. Excess material should be safely disposed of to prevent runoff during a monsoon or heavy rain fall. If hazardous material is encountered during the excavation process, safe disposal methods should be adopted. To the furthest extent possible, the excavated sites should be restored to its original condition. Any work area or pits to be left open should be clearly guarded and marked to prevent accidents to pedestrians and vehicles, with a perimeter placed around them or temporary cover.
As per OSHA excavation regulations, all workers should be well protected with safety gear, and insured. Accidents at site can prove to be fatal for workers as well as for the reputation of the contractor. Safety should be the first consideration right from the planning phase. Improperly protected sites often lead to disastrous consequences and unnecessary loss of life, financial profits and environmental damage. The best way to ensure safe working procedures are followed is to make sure that all personnel involved in the operation are well aware of safety procedures before working on the project. They should also be made aware of possible hazards that they may encounter, and instructed on how to react for their safety and the safety of others.