Deadman Anchor Burial Depth by Soil Type: What's Actually Published

No field manual, engineering study, or manufacturer publishes one burial depth that covers every soil. What’s actually published: a commercial ground anchor plate whose maker states roughly 2,500 lb at 24 inches in soft sand and more than 6,000 lb at 36 inches in that same sand, and separately reports measuring over 7,000 lb at that 36-inch depth, an industrial log-deadman standard built for multi-ton cable-logging tension, and soil-mechanics data explaining why sand and clay don’t behave the same way at any depth. Below is what’s documented, soil by soil, and where the data simply doesn’t exist yet.

Deadman Off-Road, Pull-Pal, and Crosby are trademarks of their respective owners; RiggingOps is not affiliated with or endorsed by any of them.

RiggingOps is not a licensed rigger, a certified recovery instructor, or an engineering authority, and this page is not hands-on field testing. It’s a synthesis of published field manuals, engineering research, and manufacturer documentation, with every figure traced back to its source below. Verify any number here against your own equipment’s documentation, the soil in front of you, and a qualified professional before you rely on it. Follow your winch manufacturer’s instructions first; where this page differs from your manual, the manual wins.

What a Deadman Anchor Is, and When It’s the Right Call

A deadman anchor is an object (a log, a steel plate, an improvised buried object) buried in the ground with a line running to the surface, used as a winch anchor point when nothing already rooted to the ground is available. FM 5-125, the US Army’s rigging manual, defines it directly: “You can construct a deadman from a log, a rectangular timber, a steel beam, or a similar object buried in the ground with a guy line or sling attached to its center. This guy line or sling leads to the surface of the ground along a narrow upward sloping trench.”

It isn’t the buried object’s own weight that holds the load. It’s the undisturbed soil in front of it, which has to shear or be pushed aside before the anchor can move. That’s why this entire page is organized around soil, not around what you bury.

Our winch anchor points with no tree guide lays out the full anchor hierarchy for vehicle recovery, and a deadman sits at the bottom of it. Exhaust a tree, rock, or existing structure first. Try a second vehicle next. A buried deadman or a commercial ground anchor is the right call only when none of that exists, on open desert, dunes, or a flat gravel wash with nothing to hook to. That guide also covers how to use a winch correctly; this page picks up specifically on depth, soil, and why a deadman fails, which that broader guide doesn’t cover at the same depth.

What Actually Governs Holding Power

FM 5-125 lists the governing factors directly. Under the heading “The holding power of a deadman is affected by,” it gives five: frontal bearing area, mean (average) depth, angle of pull, deadman material, and soil condition. The manual states the depth and angle relationship in one sentence: “The holding power increases progressively as you place [the] deadman deeper and as the angle of pull approaches a horizontal position.”

FM 5-125’s own reference table quantifies exactly how much angle changes the outcome, even holding depth and soil constant. This table is scanned from a 2001 print manual and OCR’d by archive.org rather than published as born-digital text, so treat the numbers as read from a scanned table, not clean text-sourced data, and note it describes “ordinary soil” generically, not any specific soil type:

Source: FM 5-125, Table 4-2, “Holding power of deadmen in ordinary soil”

Two things stand out in this table. First, depth compounds fast: at a 1:4 slope, holding power goes from 1,500 psf at 3 feet to 8,400 psf at 7 feet, more than five times the holding power for about 2.3 times the depth. Second, angle matters almost as much as depth: at the same 7-foot depth, a vertical pull holds 3,200 psf while a 1:4 slope holds 8,400 psf, over 2.6 times more, from geometry alone. Neither of these numbers is soil-type-specific, and FM 5-125 is engineering guidance for military rigging loads, not a vehicle-recovery spec. It’s included here to show the mechanics, not as a number to dig to.

Why Soil Type Changes the Answer: Cohesion vs. Friction

The reason a single depth number can’t work across sand, clay, and everything between them is that different soils resist a buried object through different physical mechanisms. Oregon State University’s Oregon OSHA-funded guide, authored by forest engineering researchers Francisca Belart, Jeff Wimer, and Ben Leshchinsky, explains it directly: “Soils with high clay and silt content tend to be cohesive when loaded quickly… Soils with high sand or gravel content tend to be more frictional… The larger the weight of overlying soil on a deadman anchor, the larger the friction that may be mobilized to resist anchor forces, and the more stable an anchor will be.”

Their published soil-property table gives this a number. Cohesion and friction angle are the two values that drive a soil’s resistance in standard geotechnical models:

Source: Oregon State University / Oregon OSHA, Guidelines for Safe Multi-Stump and Deadman Anchors

Every clay entry has a 0-degree friction angle: clay holds an anchor through cohesion (the soil particles sticking to each other), not friction. Every granular (sand/gravel) entry has 0 psi cohesion: sand holds through friction and the weight of soil pressing down, not stickiness. That’s a mechanical difference, not just a numeric one, and it’s the underlying reason this same source states there “is not a one easy answer” for burial depth: a formula built around cohesion behaves completely differently from one built around friction, even before moisture, density, or compaction enter the picture. On moisture specifically, the same guide notes a saturated clay loses shear strength under load, while saturated sand and gravel can shed water fast enough during loading to keep most of their friction intact.

This research is peer-reviewed, not just an extension pamphlet: the same authors and underlying model appear in a companion paper published in the Canadian Journal of Forest Research, Deadman anchoring design for cable logging: a new approach, 50(3): 342-357 (2020). A later correction (10.1139/cjfr-2021-0205) replaces one diagram in that paper and leaves its equations, charts, and capacity figures unchanged. The freely readable copy linked in our sources is the authors’ submitted manuscript, not the typeset version of record.

Burial Depth by Soil Type: What’s Actually Published

This is the honest breakdown. Two soils have real, sourced numbers. Three don’t, and we’re saying so rather than repeating a folklore figure.

For hardpack specifically, that’s the one condition with a direct, apples-to-apples manufacturer comparison against sand: Deadman Off-Road’s own instructions say 18 inches in hardpack “might yield the same or more” capacity than 24 inches in soft sand. That is the manufacturer’s stated expectation for its own product, not a reported measurement and not a universal ratio.

The Trench and Cable-Angle Geometry, and Why Each Part Matters

The two sources agree on the load path and differ on one detail worth knowing about. FM 5-125 instructs: “dig a hole at right angles to the guy line and undercut 15 degrees from the vertical at the front of the hole facing the load… Make the guy line as horizontal as possible, and ensure that the sloping trench matches the slope of the guy line. The main or standing part of the line leads from the bottom of the deadman. This reduces the tendency to rotate the deadman upward out of the hole.” The USDA Forest Service/Oregon State University Deadman Anchor Quick Reference gives the same logic in field-instruction form: excavate perpendicular to the direction of pull for maximum resistance, maintain vertical trench walls, cut a notch for the line no wider than necessary where it exits the ground, and never disturb the front vertical wall of the trench, because “it will reduce anchor capacity.”

The mechanical reasoning behind each rule, not just the step:

• Perpendicular orientation puts the full frontal bearing area of the buried object square against the pull direction, maximizing the soil mass it has to push through to move. Dig at an angle to the pull and you cut that resisting area down.
• An intact, undisturbed front face is the actual load-bearing surface, and this is the one place the two sources differ: FM 5-125 says to undercut that face 15 degrees from vertical so it leans back over the load, while the USDA/OSU Quick Reference says to maintain vertical trench walls. Both are protecting the same thing, a face of undisturbed soil to bear against. Oregon State University models that resistance as passive earth pressure; FM 5-125 never uses the term, but its instruction to leave the front of the hole facing the load intact serves the same function. Disturb that face while digging or backfilling and you have reduced the anchor’s capacity before attaching a line.
• The line exiting from the base of the buried object, at a low angle, keeps the pull direction close to horizontal, which FM 5-125’s own table above shows increases holding power substantially over a steeper pull, and it prevents the buried object from rotating upward and out of the hole under tension, the mechanism both sources describe as the trigger for uplift failure.
• A narrow exit notch limits how much of the front wall gets disturbed at the surface, where the soil is least confined and easiest to loosen.

If you’re rigging a deadman through a snatch-block redirect (say, pulling a second vehicle through a block anchored to a buried deadman), the geometry above still applies, but the load the soil has to hold changes. Our winch redirect anchor force page documents that a block can load whatever’s holding it at up to roughly double the winch’s single-line pull, per Crosby’s published Angle Factor table. Dig and rig for that doubled resultant load, not the winch’s rated line pull, whenever a redirect is part of the setup.

Purpose-Built Ground Anchors vs. Improvised Buried Objects: The Real Decision

The soil-type table above is also the argument for buying a purpose-built anchor instead of improvising one. A commercial ground anchor plate is the only category in this research with a manufacturer publishing its own depth-versus-capacity figures for its own product (Deadman Off-Road’s numbers above). That sidesteps the depth-uncertainty problem this whole page documents: you’re working from a manufacturer’s own stated figures for its own product, not a folklore number or an industrial spec built for a different scale of load entirely.

A buried log has real engineering backing too, but only at industrial cable-logging scale: the USDA Forest Service/Oregon State University Deadman Anchor Quick Reference calls for a trench at least 5 feet deep and a log at least 16 feet long and 18 inches in diameter, sized for multi-ton yarding tension, not a stuck 4x4. The installation logic (perpendicular trench, undisturbed front wall, staged backfill, daily inspection) scales down fine as technique. The depth and log-size numbers do not scale down as a spec; they’re the wrong order of magnitude for a vehicle recovery.

A buried spare tire or traction board has no manufacturer or field-manual backing at all. The spare-tire technique is a genuine off-roader practice, but it’s forum-sourced and anecdotal, not documented anywhere we could find. Burying a traction board as an anchor has no source support whatsoever: every manufacturer instruction we found for traction boards (MaxTrax and similar) describes them solely in their designed use, as a ramp under a tire, never as a burial anchor, so we’re not presenting that as a real option here.

This page isn’t the place for the actual product comparison. Our winch anchor points with no tree guide covers Pull-Pal, Smittybilt, and ARB’s ground anchors with full specs, pros, cons, and a verdict on each. What matters here is the decision: a purpose-built plate has sourced depth data behind it, and an improvised buried object doesn’t, at vehicle scale, for any soil type covered in this research.

Failure Modes: Why a Deadman Pulls Out

A deadman fails one of three documented ways. Oregon State University’s engineering guide attributes all three to the same 1977 origin research from the USDA Forest Service (Prellwitz and Lee, “Deadman Anchors”):

1. Bending. The buried log or timber bends at the point of cable attachment if it’s too long and slender for the load. FM 5-125 codifies this as a design check before accepting any depth or sizing figure, capping the length-to-diameter ratio at 5 for logs and 9 for cut timber.
2. Shear. The wire rope or strap cuts into the log fiber, or into whatever it’s wrapped around, at the attachment point. Both FM 5-125 and the USDA/OSU sources recommend a steel bearing plate to spread the load and prevent this; FM 5-125 gives a worked bearing-plate example (a 1 1/16 x 9 1/2 x 10 inch plate for a 12 x 12 inch timber under a 3/4 inch cable).
3. Pullout, and the related but distinct failure, uplift. This is the only failure mode that depends on soil type and burial depth. Oregon State University’s guide explains the mechanism: “Pullout depends on the soil in which the deadman is buried. How much the soil weighs, its compaction and moisture… the resisting force on the trench is called the passive earth pressure.” Uplift happens at a steep pull angle, where the buried object is resisted only by its own weight and the soil directly above it. Pullout happens at a flatter pull angle, where a full wall of undisturbed soil resists the load instead. The same guide states plainly that “The lowest resistance between uplift and pullout, represents the deadman’s ultimate capacity from soil resistance,” meaning whichever of those two soil failure modes is weaker in your setup governs the soil side. That guide calculates structural capacity (the bending and shear modes above) separately and then takes the lower of the two, so soil geometry alone does not decide the anchor.

Shallow burial, a disturbed or loosened front trench wall, a steep pull angle, and saturated or thawing soil all push a deadman toward pullout or uplift faster. Depth, an undisturbed front wall, and a flatter pull angle are the three levers that push back against it, which is exactly why those three show up repeatedly across every sourced part of this page.

The Widely Repeated Numbers We Could Not Trace to a Primary Source

This topic is heavy with folklore, so it is worth naming plainly which numbers have a traceable source and which do not. A “24 to 36 inch” burial-depth rule of thumb circulates widely across off-road blogs and forums, and where it happens to overlap with Deadman Off-Road’s own stated figures (the 24-inch and 36-inch soft-sand numbers in the soil-type table above, which are that manufacturer’s expectations for its own plate), the overlap is coincidental to one product in one soil condition. It is not evidence of a universal depth standard, and shouldn’t be generalized to a buried log, tire, or a different soil.

One example worth naming directly: Off-Road Pull’s winch anchor guide states, in one place, “Dig a trench 2-3 ft deep perpendicular to the pull,” and elsewhere on the same page, “Buried deadman needs 36 inch depth minimum.” Those two figures contradict each other on the same page, with no source cited for either. That’s exactly the kind of repeated-but-unreconciled number this topic is full of, and we’re naming this specific example rather than repeating either figure as fact. The same page also states a rope exit angle of “15-20 degrees above horizontal” with no citation anywhere we could find backing that specific range.

We also checked construction and retaining-wall engineering sources that use the term “deadman anchor” for a structurally different application, holding back a retaining wall rather than resisting a winch pull. Pulling those numbers into a vehicle-recovery context without that distinction would be a fabrication trap: they’re a different structure, different load direction, and different design standard entirely, and this page doesn’t use them.

The honest summary, consistent with Oregon State University’s own framing: there is not a one easy answer for deadman burial depth. The design depends on log dimensions, soil characteristics, slope, angle of pull, and trench depth in combination, and no single number, no matter how often it is repeated, covers all of that at once. That same guide does supply nomographs and design charts as a quantitative method, so the absence of one universal depth is not an absence of engineering.

What’s Not Covered Here

This page covers the depth-and-soil side of a buried deadman anchor specifically. For the broader anchor-selection decision (when to use a deadman at all versus a tree, rock, second vehicle, or commercial ground anchor, plus full product picks for Pull-Pal, Smittybilt, and ARB, and how to bury a spare tire or log step by step), see winch anchor points with no tree. For winch rigging fundamentals, including anchor selection basics, see how to use a winch. For the math behind why a snatch-block redirect loads your anchor at up to double the winch’s line pull, see how much force a winch redirect puts on the anchor. For rated hardware at the connection point (why a shackle belongs there instead of a hook, and how Working Load Limit differs from Minimum Breaking Strength), see WLL vs MBS and what not to use for vehicle recovery. This page is part of our broader vehicle recovery techniques playbook, and our sourcing approach for every claim on this site is on the review methodology page.