Excavation projects by definition are dangerous operationsthat require caution and planning, especially when theexcavation is intended to create a work space for personnelsuch as for underground installation repair or installation.Creating a safe working area for every excavation project presentsunique challenges for the contractor or municipality’s safetypersonnel and the work crew.
Many underground utility contractors own some type oftrench protection device, such as steel trench shields or perhapsaluminum hydraulic shores. Municipality DPWs frequently ownaluminum trench shields that can be moved with a rubber-tirebackhoe. However, it is not practical or even responsible forthe contractor or municipality to assume their own shoringor shielding equipment can be safely used for every excavationsituation or site condition they encounter.
Excavation parameters vary greatly from project to project;including soil type, adjacent structures or buildings, and the everpresent existing underground utilities that need to be located,marked and factored into the choice of trench protection systemor device. When contractors and municipalities face excavationchallenges that are beyond the capabilities of their own fleet oftrench safety equipment, they must rely on rental equipment tofill in the gaps.
In today’s market, many shoring options are available throughtrench safety equipment rental companies or even directlyfrom a shoring equipment manufacturer. Trench “stores” andmanufacturers have a well-trained sales team to assist the contractoror municipality in matching the best shoring option or solution toany specific excavation project.
This is particularly true of equipment representatives who havespecialized training from the manufacturer. Experienced shoringspecialists should be able to solve any excavation and safetyconflicts by addressing issues encountered on the jobsite — and itis never a one-size-fits-all solution.
A good shoring specialist will obtain as much information aspossible from the contractor or municipality’s designated safety officialor engineering team before proposing a shoring system. The followingare some important points to consider when designing a safe andappropriate shoring system for a particular excavation project.
Is this a shielding or shoring situation?
Although commonly used synonymously, shielding and shoringare two separate protective systems with their own rules regardingproper use within OSHA standards. Shielding is a protective systemutilizing a trench shield or “trench box” installed in the excavationto protect (shield) the workers from the hazards of a cave-in.Shoring is a protective system that utilizes structural members orhydraulic pressure that prevents the trench walls from caving in.An experienced shoring specialist can help choose the method bestsuited for the situation.
What is the work to be performed in the excavationand what is the proposed size and depth?
The shoring specialist has many options available from themanufacturer and the size and depth of the excavation willdetermine the best option to choose. Official manufacturerauthorized equipment distributors offer equipment for small andshallow excavations, long pipe runs, crossing utilities, limitedaccess and extreme depths, to name a few excavation challenges.Rental companies with a close association with the manufacturer’steam of engineers will have access to a solution to almost anyproblem encountered.
What size excavation equipment is available?
When renting underground protection and production products,it is critical to factor in the size and capacity of the excavationand earth moving equipment that will be used on the project. Tominimize costs to the customer, an experienced shoring specialistwill match the shielding or shoring system to the heavy equipmentthat will be used to install the shoring system.
The equipment distributor should be able to provide trench safetyequipment that corresponds with the excavator and other heavymachines commonly used for different excavation operations. Forexample, a modular aluminum shielding system such as Build-ABoxis light enough for installation and extraction using a tractorbackhoe. Comparatively, a steel trench shield 28 ft long rated foran excavation up to 30 ft deep weighs more than 15,000 lbs, butthat’s well within the capacity of a typical sized track excavator thata contractor may already have in his fleet,thus eliminating the need to rent “big iron”in addition to the shoring system.
Are there any overhead utilities orother obstructions?
The proposed shoring or shieldingequipment should address all concerns ofthe project including overhead obstructions.In most cases, options are available to utilizedifferent rigging options to stay withinOSHA standards regarding safe distancesfrom overhead power lines and the like.The system should be designed to providefor safe working distance from overheadhazards during assembly, installation andremoval of the shoring system.
Are there any buried utilitieswithin excavation limits that needto be accommodated?
Dealing with utilities crossing or runningparallel to the proposed excavation cancause costly delays and repairs if notaddressed properly. These utilities can alsocreate a long and frustrating day for theforeman and the contractor-designatedsafety person (referred to as the “competentperson” on excavation projects). Somesystems such as vertical hydraulic shoringare designed to install so crossing utilitiespass through the trench with relative ease.
For larger and deeper projects withcrossing utilities, a sheeting frame systemsuch as Shore-Trak is an efficient and costeffectivesolution. Sheeting frame systemscantilever corrugated steel sheets belowa waler frame, providing better visibilityduring installation around existingutilities. Sheeting frames allowing efficientinstallation with the excavator, thuseliminating the need for a sheeting driver.
What are the limitations of theshoring or shielding equipment?
All manufactured shoring and shieldingequipment has limitations for properuse. These limitations are found in themanufacturer’s tabulated data suppliedwith the system. Trench shields areconstructed with a maximum allowabledepth of use in different soil typesconsistent with OSHA classifications.Hydraulic shoring tabulated dataprovided by the manufacturer includesa chart specifying maximum cylinderspacing for different soil conditions.
Other systems available through a rentaltrench store, such as Slide Rail Systemsand sheeting frames, will include tabulateddata for the proposed configuration.Most shoring and shielding manufactureswill provide tabulated data stamped by aregistered Professional Engineer. In somecases, a Professional Engineered shoringsystem is required and the shoring specialistshould be familiar with the restrictions andrequirements dictated in the tabulated data.
These items address the most commondifficulties encountered on most excavationprojects and should be viewed as theminimum amount of information thatneeds to be collected before determiningthe proper and safe shoring solution. In anycase, the contractor or municipality shouldprovide as much information to the shoringspecialist as possible when renting trenchsafety equipment.
Mike Ross is a Shoring and Shielding Specialistin Efficiency Production’s Special OperationsShoring Division.