Outrigger Setup on Fill Beside an Open Trench
A three-axle digger derrick is staged in a new subdivision to set a 40 ft Class 4 pole. The rear lot line slopes about 8 percent toward a 6 ft deep foundation excavation. The right rear outrigger would land on 3-week-old compacted fill that received 0.75 in of rain yesterday; the left front would sit on an asphalt driveway. A locate mark for a 2 in plastic gas main crosses the fill about 30 in deep, but the paint is faded and the ticket expires at noon. The crew plans full outrigger extension on 12 in by 12 in pads and intends to level with the machine frame controls. The bubble level shows about 2 degrees out of level. The operator says the pads will bridge the soft spot and wants to begin setting up immediately because the pole truck is waiting. The site competent person is off-site.
1. What must be resolved before any outrigger is extended?
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Do not extend outriggers until the site is evaluated as a system, not just as four pad locations. First, confirm the locate ticket is current and the gas main is marked accurately; faded paint and an expiring ticket are stop-work conditions until the utility or a qualified locator re-marks and the depth/alignment is confirmed. Second, assess the fill: 3-week-old fill after 0.75 in of rain may have low bearing capacity, and an 8 percent slope plus a 6 ft excavation means the right rear outrigger may be inside the trench influence zone. Third, determine whether the machine can be leveled within the manufacturer's limit; 2 degrees out of level is a warning, not a target. Fourth, establish who is competent to approve the setup. The operator's 'bridge the soft spot' plan assumes the pad spreads load without verifying that the soil can support it.
2. How should the outrigger layout and cribbing be changed?
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The goal is to move load away from the trench edge and onto competent soil. Reposition the machine so no outrigger is closer to the excavation than the competent person allows, and so the right rear outrigger is not over the gas main or on loose fill. Use larger, engineered load-spreading mats rather than small 12 in pads; do not stack loose blocks or rely on a single pad to bridge a soft spot. Fully extend outriggers as required by the load chart, but verify the machine is level within the manufacturer's tolerance using the level indicator, not the operator's judgment. If the slope cannot be corrected with proper cribbing, move to a different setup location. The gas main must be protected from concentrated outrigger load, and the trench must be barricaded or covered if workers could enter the influence zone.
3. What should the crew do if the right rear pad sinks about 2 in during the preload test?
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Stop the setup. A 2 in sink is evidence that the soil is yielding, not a minor settling issue. Retract the outrigger, remove the load from that corner, and inspect the pad and soil. Do not simply add another block under a loaded outrigger; that can create an unstable stack and hide the real bearing failure. Reposition the machine to a stronger area, use a larger load-spreading mat, and repeat the preload test while watching the pad and the trench edge. If the sink repeats, the location is unsuitable without an engineered solution. Re-level the machine, confirm all outriggers are deployed per the manufacturer, and document the event. Only then should the lift proceed.