CAVE-IN!
Increasing Job Site Safety & Reducing Costs
By David V. Dow

Excavation and trenching is statistically the most hazardous work in the U.S. construction industry. Frequent news stories from around the country attest to the danger. More than 100 workers are killed each year in trench cave-ins alone. Countless others are injured or maimed, physically and psychologically.

Recognizing the need for more effective regulations on excavation safety, the Occupational Safety and Health Administration (OSHA) published a revised federal standard in1990 to establish more clearly the requirements for protecting employees in excavations. The definitive standard greatly increases the flexibility you and your workers have in choosing protective systems.

Responsible contractors know that life-threatening cave-ins are clearly preventable. Such managers take precautions to ensure worker safety. Modern trench shoring and shielding devices provide for a quick and easy means of creating a safe and productive environment for below-ground workers. Most systems are adaptable to various trench depths and widths. Properly configured, installed, and maintained, shoring and shielding devices prevent accidents and ensure worker safety in the trenches.

Most cave-ins result from a superficial inspection of a site that indicated no apparent chance of a trench collapse. In fact, the vast majority of cave-ins actually occur in clay-based soils (where wall failures are not anticipated), as opposed to sandy conditions where failures normally would be indicated. Also, most cave-ins happen in trenches between five and 15 feet deep, where many managers and workers falsely believe they can quickly escape if a trench wall collapses.

Failure to support or shield the trench as excavation proceeds, even in apparently “good” soil, invariably exposes workers to great danger. For safety’s sake, all trenches should be considered potentially lethal, until adequately sloped, shored, or shielded.

You must consider several variables—all vitally important to assuring the selection of a safe and productive trench safety system—when determining the particular trench safety requirements of a particular job:
• Soil conditions
• Depth and width of the trench
• Ground water seepage: saturated or submerged soils
• Nearby utility services or structures
• Surcharge loads: stored material, equipment, traffic, spoil, etc.
• Vibrations
• Type of excavator to be used
• Working space requirements
• Potential changes in the weather.

AVAILABLE OPTIONS

Three alternatives are available for providing a safe working environment for trench workers: sloping, shoring, and shielding.

Sloping requires the cutting back of trench walls to an angle that will ensure no collapse into the work area. Shoring devices pre-load the trench walls and provide a positive restraint to soil movement, thus preventing cave-in hazards. Shielding devices are not designed to prevent trench wall collapse, but serve to “shield” workers should a cave-in occur.

SLOPING IS AN EXPENSIVE CHOICE

Although each of the three options are appropriate for specific projects, sloping generally proves the most expensive alternative when compared to shoring or shielding. To properly slope a trench often requires the acquisition of expensive right of way, along with the additional costs of excess excavation, refilling, compaction, and reinstatement. With a vertical cut, few, if any, of these factors are involved.

PRE-ENGINEERED . . . AND RELIABLE

Modern trench shoring and shielding hardware and practices yield three major benefits:
• They increase your job site safety.
• They help meet OSHA and other governmental regulations.
• They reduce costs and improve your crew’s productivity.

The first two reasons get a lot of attention from most jobsite managers. And well they should. But the third point—cost savings—is frequently overlooked. Trench shoring and shielding, properly used, can frequently “pay for themselves,” helping your crew work more efficiently and cost effectively.

Today’s trench shoring and shielding systems are generally pre-engineered, and the designs come with a history of proven reliability. Most modern devices ensure that at no point in your operation—initial excavation, system installation, system removal, back-filling, or compaction—is it necessary for personnel to be exposed to dangers in an unshored trench. Most systems are installed and removed from above the ground. Also, the range of systems available is large, enabling you to have a shield or shore of just about any conceivable combination of trench width and depth delivered right to your job site.

 ABOUT THOSE COST REDUCTIONS

In addition to the safety benefits of modern trench shoring and shielding systems, often overlooked advantages include increased productivity and reduced costs. As we discussed, the savings associated with a vertical cut compared to sloping are dramatic. Likewise, productivity increases greatly when you integrate the excavation and shoring operations. Pre-assembled systems are quick and easy to use, fewer skilled workers are involved, and your workforce is more productive when working in a well-shored or shielded environment—a place where they can focus on the tasks at hand.

AN EXAMPLE OF COST SAVINGS

The following example is based on numerous similar real-life situations that contractors and crews find themselves in.

Suppose that your company is bidding on a 400-linear-footsewer line that will cut across the parking lot of an existing shopping center. The sewer line must be 12 feet deep. It will not be necessary to remove or cut across any curbs, gutters or sidewalks. In addition, you will not have to remove any light poles, trees or shrubbery.

Your choices for trench protection are sloping or using a trench shield. Because you will be working in OSHA “Type B” soil, if you slope the angle will need to 1:1 (H:V). We are assuming that you will need three feet of width at the bottom of the trench to lay the sewer pipe.

Your costs to excavate, backfill, and restore the surface would be approximately $71,190, compared to $15,962 if you used a rented trench shield. Note: This example is of a trench needed for a sewer line, but the same savings apply for virtually any trench, regardless of depth, width, or utility service—water, gas, electrical, telephone, cable-TV, etc.

In conclusion, contractors can increase job-site safety and reduce their costs through proper selection of modern trench shoring and shielding equipment.

A Word About Aluminum Hydraulic Shoring…

Aluminum hydraulic shoring is a pre-engineered shoring system with aluminum hydraulic cylinders used in conjunction with vertical or horizontal rails. Such systems are designed to support the sidewalls of an excavation, thereby preventing cave-ins. Because hydraulic shoring is constructed of lightweight aluminum, it is easy to handle. The units are installed and removed from above ground, increasing worker safety throughout the shoring process. The equipment uses a gauge-regulated pump and a water-based pressurized fluid to evenly pre-load the trench walls.

A Word About Trench-Shielding…

A trench shield is a structure that protects employees within the structure because it is able to withstand the force imposed on it by a cave-in. Shields can be pre-manufactured or built on the job site in accordance with OSHA regulations. Professionally manufactured trench shields come in a wide variety of sidewall thicknesses, heights, lengths, and weights, and are usually constructed from steel or aluminum. With appropriate shield capacities, they can be stacked to accommodate virtually any depth and soil condition. In choosing a shield for a particular site, you should assure yourself that a qualified registered professional engineer designed the structure, and that the shield is capable of withstanding the most extreme lateral earth pressure that may be encountered on the job. Trench shields generally use quick-connect spreaders of fixed length. The spreaders determine the shield’s width. End panels may also be used on one or both ends to provide protection in three- or four-sided excavations. This all-around protection is particularly helpful when doing repair work or setting manholes or similar structures.

David Dow is a founding partner of Trench Safety. With offices in Tennessee and Arkansas, Trench Safety serves the utility and construction markets. E-mail David at dvdow@trenchsafety.com