Underground Shield

Some successful products and equipment have sprung from the experience of contractors, engineers and field workers in the utility industries.

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By Paul Hull

This Innovative Shield can Speed Underground Work Safely.

Some successful products and equipment have sprung from the experience of contractors, engineers and field workers in the utility industries. Trenchless technologies, fall protection equipment and many tools for linemen could be cited. The Terra Shield is like that. The inventor of Terra Shield (and president of the company) is Bob Wegener, professional engineer in more than 20 states with two decades in the civil engineering field. The product he envisaged in his work– and has now finalized–is one that provides the means and method to expedite utility work underground, while limiting its impact on the motoring public and reducing construction time and costs during the project by a dramatic amount.

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The accuracy of the shield is controlled by the excavator operator from the cab.

On many roadway and highway projects, and on water and wastewater extension projects, common reasons for delay have been the difficulties presented by utility support and relocation issues. Congestion of local traffic is not simply inconvenient; it can harm businesses and their customers. It can damage the company's image and customer rapport. Whether the difficulties involve the moving and transportation of goods or access for customers to businesses, they are detested by local authorities and the community, and by the contractors. In addition to the inconvenience of many utility projects in crowded locations, there is the aspect of safety. One initial advantage of Terra Shield is that it virtually eliminates the need for workers to go into trenches, while the automated control systems for the excavator reduce the intensity of labor operations to a minimum. Perhaps most impressive for utilities and their contractors or field crews is the fact the Terra Shield gives protection and access under existing utilities without exposure or deterioration of the utility conduit. This is critical when dealing with older asbestos tiles, as it eliminates any hazardous waste issues.

The Shielding Process

Terra Shield is inserted under the existing conduit with either a static or dynamic installation tool. Trusses are installed the length of the intended excavation, with patented, threaded J rods used to connect the Terra Shield to the trusses. Tighten nuts on the J rods to compress a load under the conduit and prevent movement during the excavation process. The Terra Shield not only supports the conduit in place, but its ½" thick barrier acts as a protective shield against accidental contact with the conduit while the work is performed below. After the job is done, the Terra Shield is left in place and the J rods and trusses are removed for future projects.

To drive the shield into its specified place under the conduits, a static driver or a vibratory driver could be used. With a static driver, 50 tons of hydraulic force is used–which is excellent for placing the shield in sensitive areas where fragile conduit or soil movement is an engineering concern. With static drive there is virtually no soil movement. The vibratory driver offers drive forces from 16 to 60 tons and can be used is almost any soil conditions. Utilities will understand the reliability and efficiency of the driving process when they learn that the Terra Shield driver is a derivative of the principles used in HMC excavator-mounted hammers, used so successfully for many pole installations and other utility projects nationwide. HMC has produced a machine that can pick up a Terra Shield sheet and place it and drive it into position quickly, in most cases in less than two minutes.

The Exclusion Zone

Of great importance in this innovative technique is the Exclusion Zone. This is created by using sensors on the Terra Shield driver and the excavator boom and stick. It prevents any penetration of the Terra Shield into a zone predetermined by the utility owner. If the sensors show penetration into the exclusion zone, the driver is shut down immediately. The in-cab LED display for the operator gives a virtual image of the installation. Terra Shield has recently upgraded its Auto Steer system to help installers identify and protect not only the primary conduit being supported, but also any peripheral conduit in the immediate area.

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All control comes from the operator in the excavator, with electronic help.

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The shield, with its exclusion zone ready to warn, prepares to go under the conduit.

In the most recent product development, Terra Shield has launched the Auto Steer to allow for multiple exclusion zones. This multiple targeting feature allows the placement of any number of additional exclusion zones prior to installation–meaning more speed and more safety. After the primary conduit is located and the Primary Exclusion Zone is in place, the Auto Steer touch screen can be switched to Secondary Targeting. Using the top left corner of the primary circuit as a starting point (X = 0 Y + 0), the operator enters the dimensions for the top center of the next circuit identified. Then, the dimensions of the secondary circuit and the diameter of the Exclusion Zone desired are entered. This technique can be repeated any number of times until all known adjacent conduits are protected. If the projected path of the shield comes into contact with any exclusion zones as the Terra Shield is installed, the operation will be halted and the Auto Steer screen will flash red, indicating which zone is in danger of contact.

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This close-up shows the HMC drive unit for the protective shield.

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The process of shielding can be achieved quickly and safely.

The Terra Shield seems to be a happy combination of technology and experience. Originating from the field experience of a civil engineer, it was developed to provide a solution to an everyday challenge faced by the telecommunication and power sectors of our utility industry.

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