In the trenches

If you need to dig a trench along a narrow strip of earth between two buildings, you have two options. A hard-working laborer may be able to impress you with the speed and precision of a hand-dug trench, but where there's room to run, a compact trenching machine can do the job at considerable savings of time and money.

Before all else! Before you trench any site, you must do one thing without exception: Have the location of existing subsurface utility lines confirmed and marked prior to trenching. If you don't already know the number to call in your location, the web site provides links to many marking services around the country.

You don't think you need to call? Let me set my pride aside and tell you a story. Recently, I supervised the trenching of a long, looped irrigation mainline. Having cut all of the irrigation trenches in one area, I asked the trencher operator to make an additional, adjacent 10-foot cut to facilitate the installation of a new 4-inch drain line.

As someone who specifies verification of all sub-surface utilities on every irrigation plan I do, I was shocked and amazed when the trencher severed the main electrical service to the house. Fortunately, the trencher operator was not injured. After spending nearly a thousand of my own dollars to have a new sub-panel installed, my clients had electricity again. One five-minute phone call could have saved us all a lot of grief.

Trencher anatomy The two basic types of compact trenchers are ride-on and walk-behind. Walk-behind units are smaller and more appropriate fortight spaces. Most trenchers of either type have three basic operation systems:

* The ground drive, which enables you to transport the machine and drives the machine while trenching. * Trenching articulation, including on-off, drive traction, and boom and chain-drive controls.

* A spoil-handling auger that windrows trenched soil adjacent to the trench for easy backfilling.

Beyond this, machines vary widely in terms of the number and sophistication of options. Your choices include the type of chain and boom controls, digging depth and width, horsepower, safety features and many other options.

Some of the most basic compact trenchers-disc trenchers or, as some manufacturers call them, earth saws-use a motor-driven spinning disc with digging teeth. These typically produce narrow, shallow trenches, so their use is limited to smaller applications. However, they are adequate for small piping as well as some wiring, and their price and size make them economical options for small-scale uses.

If you purchase a trencher, carefully evaluate the options available to you and balance these with your usual trenching requirements and your budget.

The right machine for the job Whether you rent a machine or just select one from your "stable," site characteristics and the required trench size largely determine the type of trencher you'll need for a particular job.

* Access. If you're working on a new (unbuilt) site, access is generally not an issue. Therefore, neither is the size of your trencher. However, communication is important. Make sure project managers and other contractors know of your access needs and work timelines or else they may build over your equipment access.

If you're working on built property, you may need to remove a portion of fence or wall to access the site. If you can, try to rebuild the portion of removed fence or wall as a gate or removable panel to facilitate future access needs.

Compact trenchers, as the term implies, don't need a lot of access room. Although machines vary in width, an average walk-behind is 36 inches wide. A 48-inch-wide access path provides comfortable room if you need to make sharp turns. By contrast, most sit-down trenchers need 60 inches or more for comfortable access.

"Mini-loaders" are becoming increasingly popular with landscape installers. These machines are designed to accept a variety of attachments, including trenchers. They may be small skid steers, or they may be track-driven. In either case, their narrow width-several mini-loaders are 36 to 40 inches wide if equipped with narrow tires-makes them suitable for many of the tight spaces where you'd use a walk-behind trencher.

* Required trench size. The trench depth and width you need are determined by two primary factors: utility trench codes and the size (diameter) of piping or conduit. Remember that you will need a trench somewhat wider than the pipe with which you will be working so that you have room to work with fittings in the trench. Many factors determine proper trench depth and local codes may require a certain minimum depth. However, for most landscape applications, nearly all walk-behind trenchers can achieve the depth you require. Even small disc trenchers can dig as deep as 10 or 12 inches-deep enough for small sprinkler pipe and some wiring applications.

Obviously, trench depth and width vary by machine. Most walk-behind trenchers can cut trenches from 3.5 to 12 inches wide and up to 48 inches deep. Ride-on trenchers can cut trenches up to 16 inches in width and up to 60 inches deep.

Fortunately, sites where you need a compact trencher (where access and operating space are limited), such as residential jobs, also tend to be those where the smaller capacity of a compact trencher is adequate. However, it's always better to have a little more trenching capacity than you think you'll need. If nothing else, this may allow you to do the job faster.

Operation Like all field operations, trenching works best when you plan ahead. Make room for the equipment, chalk or paint the desired trench paths, leave plenty of room for turning the machine, and, if possible, try to avoid tight turns.

Once you're at the site, start the machine, back it off its trailer and move it into position using the ground transport system. Field movement of the machine is best with the boom and digging chain out front and the transmission in forward. Conversely, trenching is most effective with the machine pulling the boom and digging chain behind it with the transmission in reverse.

On level ground and in problem-free soil, trenching machines track well on their own, but you may need to nudge them sideways occasionally to keep them in line. Across slopes you may need to provide almost constant sideways pressure to achieve an acceptable trench. If so, be careful! Don't bind the chain in the trench by over-pulling or pushing, and don't strain your body. Stretch before you operate the machine and keep your knees bent during operation. Fortunately, most plastic pipe and tubing is flexible, letting you "snake" it through trenches. Therefore, an absolutely straight trench is not usually mandatory.

If the wheels of the trencher are spinning, the tires may be over-inflated. You may need to slow down the trencher's rate of travel. The optimal speed of the chain and trencher depend on digging conditions, trench depth and width, and type of trencher. The trencher should dig fairly smoothly if its speed is appropriate. The ground drive of some trenchers includes axle locks for greater traction, as well as adjustable wheel widths for greater stability.

The chain and teeth The chain--which, after all, is what actually digs the trench--is a critical component of any trencher. Regardless of which trencher you ultimately select, chain options let you vary trench width or adapt to specific soil qualities or constraints. By selecting the right combination of teeth, you can overcome most soil challenges including tree roots, troublesome fill material (sub-surface building debris, paving pieces), extremely sandy soils (which are especially difficult on slopes), soils with cobblestone-size or larger aggregates and clay soils, both hard and mucky.

The teeth of the chain do the actual digging. Most trencher chains employ cup teeth, which may comprise some or all of the teeth of the chain. As the name implies, cup teeth efficiently scoop out dirt from the trench. In relatively soft soil, cup teeth alone are adequate for most jobs and may be vital in sandy soil.

However, a few manufacturers make chains with sharp carbide teeth designed for breaking through tougher soil or soil with buried debris. Consolidated Carbide (Lake Havasu, Ariz.) manufactures carbide chain teeth designed for increasing production, particularly in hard ground. However, John Walgren, president of Consolidated Carbide, notes that an additional benefit of carbide teeth's greater durability is extended life span in normal digging conditions. That makes carbide teeth popular with equipment rental companies.

Some carbide teeth are welded directly to the chain whereas other teeth, carbide or cup, bolt onto the chain. When bolt-on teeth wear down or break, it is simple to bolt on new ones. Chains that have teeth welded directly to the chain must be repaired by welding. Using bolt-on teeth, you can devise various combinations of cup and carbide teeth for optimum performance in certain digging conditions. Some operators add hard facing to cup teeth to lengthen their lifespan, but it is possible that this could decrease digging performance. Trencher manufacturers usually offer you a variety of chain and teeth options on new models as well as for replacement parts.

Chain tension is a critical factor. Walgren says that proper tensioning is the "golden rule" of trenchers. Similar to chainsaws, trencher chains must be neither too tight nor too loose. Poorly adjusted chains wear out much more quickly. Walgren notes that experienced operators develop a "feel" for proper chain tension. Nevertheless, trencher owner manuals usually provide specifications for chain tension. You should check and adjust chain tension periodically because chains stretch with normal use and require tightening to maintain proper tension.

Chains, regardless of the condition of the teeth, eventually will need replacement. For example, Ditch Witch recommendations state that when a chain stretches more than 3 percent of its compressed length, it's time for a new one. Determine this by laying the chain on a level surface and pushing from the ends so that you remove all the slack. Measure its length. Then stretch the chain by pulling its ends and measure its length once more. If the stretched length is more than 3 percent longer than the compressed length, replace the chain. Sprockets also may need periodic replacement due to normal wear.

Trencher chains are designed to operate "dry," so oiling trencher chains is not a recommended practice. Oil actually can increase wear because it attracts dirt particles and causes them to stick to the chain.

Other options Some projects preclude the use of a trencher and necessitate other ways of creating a trench. Extending utilities under a paved surface or foundation is possible with directional boring or pneumatic piercing, which can bore a hole at the desired sub-surface depth for a substantial distance. Some trenchers, including a few walk-behinds, even allow you the option of replacing the digging "head" with a boring unit.

Laying roll cable or tubing with a vibratory plow is another "trencherless" technology. By plowing at the desired depth, this machine vibrates enough space to mechanically insert the desired cable, tubing or pipe into the soil with relatively little disturbance. Thus, no backfilling is necessary.

Safety Remember that safety is a concern with trenchers as with all power equipment. When you operate a trencher, avoid loose clothing that could catch in moving parts, and always wear eye protection. Do not remove protective shields or disconnect safety switches, and make sure the engine is turned off before performing any adjustments or maintenance.

Steve McGuirk is a landscape architect with the Madrone Lanscape Group (Soquel, Calif.).

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