Frozen Ground & Winter Excavation

Frozen soil can look as hard as rock, but it doesn’t stay that way. Below the frozen crust the soil may be soft, wet or unstable, and a thaw can turn a solid wall into a collapse. Winter excavation needs extra care, extra inspections and a plan for what happens when temperatures rise.

• Construction
• Excavation
• Cold Weather

Why frozen ground fools people

• Frost is only on the surface. The frost layer may be a few inches to a few feet deep, depending on the climate and the winter. The soil under it isn’t frozen and is no stronger than in summer. Once the trench goes below the frost line, the frozen layer can break off the top.
• Thawing weakens soil. Soil that freezes and thaws repeatedly loses strength and generally has to be treated as the weakest class, Type C, by the competent person. See Soil Classification.
• Frost is brittle. A frozen wall can fail suddenly, with little warning and no slow cracks to read. See Cave-In Warning Signs.
• Sun, equipment heaters, a warm day or rain can start a thaw in hours.

Extra inspections

• The competent person must inspect the excavation, the adjacent areas and protective systems daily before work, and again after anything that could change conditions. In winter those include freezing, thawing, rain, snow and rising temperatures. See Competent Person Inspections.
• Check for cracks, sloughing, bulging walls, water seeping and thawing spots. Pull workers out if there are signs of danger until it’s fixed.
• Watch the forecast. A warm spell or rain after a deep freeze is a high-risk time.

Digging in frozen ground

• Use the right equipment, such as ripper teeth, breakers or saws, to break the frost, and keep people clear of flying chunks.
• Don’t use open fires or fuel-burning heaters inside trenches. They produce carbon monoxide and can ignite other hazards. See Trench Atmospheres and Carbon Monoxide.
• If ground heaters, blankets or thawing pads are used, follow the manufacturer’s directions, keep electrical equipment GFCI-protected and watch for soft spots from thawing. See GFCI.
• Locate utilities before digging. Frozen ground can make marks, paint and flags hard to see. Call 811 and keep the tolerance zone clear. See Call 811.

Ice, snow and slips

• Clear snow and ice from ladders, ramps, walkways and edges, and use sand or salt. See Extension Ladders.
• Snow can hide the edge of an excavation, spoil piles and holes. Mark and fence the edges. See Barriers & Fall Protection at Excavation Edges.
• Ice cleats and good boots help. See Ice Cleats.
• Frozen spoil piles can slide or roll when they thaw. Keep them back at least 2 feet from the edge. See Access, Egress & Spoils.

Water and thaw

• Melting snow and ice add water to the trench and can undercut walls. See Dewatering.
• Frozen water lines, drains and pipes can break during work, or when they thaw, and flood the excavation.
• Cold weather can freeze hydraulic hoses and make equipment slow to respond, so warm up machines properly.

Backfilling in winter

Don’t backfill with frozen clumps, snow or ice. They leave voids and settle badly when they thaw, which damages pipes and pavement. Use proper fill and compact in lifts. See Backfilling & Compaction.

Cold stress

Cold wears people down and slows thinking. Provide warm-up breaks, layers and hot drinks. See Cold Stress and Cold Weather Clothing.

Winter excavation checklist

• Soil classified by the competent person, with freeze and thaw taken into account
• Protective system in place for any trench 5 feet or deeper
• Extra inspections after freezing, thawing, rain or snow
• Edges, ramps and walkways cleared of ice and marked
• No fuel-burning heaters in the trench; atmosphere tested when needed
• Warm-up breaks and cold stress plan for the crew

Last updated: October 4, 2026