When a crane lifts, virtually all of the load — the machine's weight plus the suspended load — transfers through a few small outrigger feet into the ground. That concentrated pressure can exceed 100 tons on a contact patch smaller than a dinner plate. Without proper support, the ground fails, the outrigger sinks, and the crane tips. Crane outrigger pads and rig mats exist to spread that point load to a safe bearing pressure. This is the highest-value, highest-risk application in the ground protection mat industry.
Why Point Load, Not Total Weight, Dictates Mat Selection
Two loading types matter on a job site:
- Point loading — small contact area, high pressure (outriggers, jack legs, stabilisers). This is the dangerous one. For point loading you care about stiffness, thickness, and structural design.
- Distributed loading — larger area, lower pressure (wide tires, long tracks). Here surface wear matters more.
A 100-ton crane does not apply 100 tons per square metre. It applies 100 tons through four outrigger pads, each perhaps 0.1 m² — yielding ground pressures that would instantly fail soft soil without a load-spreading mat.
Types of Crane & Rig Support Mats
1. Crane Outrigger Pads (Stabiliser Pads)
Dedicated PE pads placed directly under each outrigger foot. These use optimised bottom anti-slip teeth and a load-bearing structure to distribute vertical pressure. Available in HDPE, UHMWPE, and composite. Typical thicknesses range from 50 mm to over 150 mm for heavy lift operations.
2. Crane Mats (Timber or Composite)
Large, heavy mats (often 12–40 ft long) placed under crawler crane tracks. Traditionally hardwood (oak, Douglas fir, mixed hardwoods), increasingly composite for environmental and weight advantages. Steel-reinforced composite timber crane mats combine strength with environmental consideration.
3. Rig Mats
Interlocking modular platform systems for drill site stabilisation. Designed to support the entire drilling rig — mast, substructure, pumps, and crew — as a level working surface. Composite rig mats are replacing timber due to longer life and moisture resistance.
4. Cribbing Plates
Thicker engineered plates used for layered support (cribbing) under extreme loads. HDPE cribbing plates resist moisture and chemicals that would degrade timber cribbing.
Material Selection for Crane Pads
| Material | Best for | Key advantage | Watch out |
|---|---|---|---|
| HDPE pad | Medium cranes, mobile crane trucks | Cost-effective, non-conductive | Can deform under extreme point loads if too thin |
| UHMWPE pad | Heavy cranes, repeated lifts | Superior impact & abrasion resistance | Higher upfront cost |
| Composite crane mat | Crawler cranes, heavy lift platforms | Interlocking, reusable, eco-friendly | Heavier; needs handling equipment |
| Hardwood timber | Traditional heavy crane support | Familiar, high stiffness | Absorbs moisture, rots, environmental regs |
| Steel-reinforced composite | Maximum load distribution | Ultimate strength + composite benefits | Premium price |
Sizing Crane Outrigger Pads: The Bearing Capacity Rule
The required pad size depends on the allowable ground bearing pressure and the maximum outrigger reaction force. A simplified approach:
- Obtain the crane manufacturer's maximum outrigger load (often 80–150% of rated capacity in worst-case geometry)
- Determine the site's allowable soil bearing pressure (geotechnical report — typically 100–300 kPa for firm soil, far less for soft ground)
- Calculate minimum pad area = outrigger load ÷ allowable bearing pressure
- Select a pad with area ≥ calculated minimum, plus a safety factor
- Verify pad thickness/stiffness prevents excessive deflection (a pad that bends too much concentrates load at the edges)
Critical safety note
Never exceed the mat's rated capacity. A pad that is too small or too thin will not spread the load — the outrigger punches through, and the crane tips. Always confirm the mat's rated load against the crane's maximum outrigger reaction, not the average.
Load Capacity Tiers by Equipment
| Equipment | Typical load tier | Recommended mat |
|---|---|---|
| Mobile crane truck (20–40t) | Light–medium | HDPE outrigger pad, 50–80 mm |
| 40–80 ton crane | Medium | UHMWPE pad, 80–120 mm |
| 80 ton load mat | Heavy | Thick composite / UHMWPE, 120 mm+ |
| 120 ton ground mat | Extra heavy | Engineered composite crane mat |
| 150 ton rig mat | Extreme | Steel-reinforced composite rig mat |
| Crawler crane 300t+ | Extreme | Timber/composite crane mats, 12–40 ft |
Non-Conductive Mats: A Power-Line Safety Essential
For utility and transmission work near live power, non-conductive mats are mandatory. HDPE and UHMWPE are dielectric — they eliminate step-potential hazards that would occur with steel plates or wet timber. This is why composite mats are the default for power-line stringing, substation construction, and any lift near energised equipment.
Real-World Deployment: Heavy Lift Access
At the Sakhalin-2 oil and gas development in Russia, a reliable and portable composite matting system was needed to construct an LNG plant. Dura-Base mats created heavy-lift access pads for self-propelled modular transporters (SPMTs) to move massive modules across sandy terrain in extreme weather. The same composite system is used across US Gulf Coast heavy-lift projects.
In Queensland, Australia, an emergency required a 450-tonne crane to enter a rain-affected rail site. Composite matting was mobilised rapidly to support the critical lift — demonstrating that crane mat suppliers must combine engineering with rapid logistics.
Best Practices for Crane Pad Use
- Inspect ground before placement. Even the best mat fails on a void or uncompacted fill
- Level the mats. Outrigger loads on a tilted pad create lateral instability
- Use full-area support. Do not let an outrigger foot overhang the pad edge — that concentrates load and cracks the pad
- Monitor during the lift. Settling indicates ground failure; stop and re-pad immediately
- Store pads flat, out of direct UV when not in use to maximise lifespan
Frequently Asked Questions
How thick should a crane outrigger pad be?
It depends on the outrigger load and ground bearing capacity. As a guide: 50–80 mm HDPE for mobile cranes up to 40t; 80–120 mm UHMWPE for 40–80t cranes; 120 mm+ engineered composite for 80t+ and heavy lift operations. Always calculate based on the crane's maximum outrigger reaction, not rated capacity.
Can I use HDPE outrigger pads for steel-tracked cranes?
Outrigger pads support the outrigger feet (point loads), not the tracks. For crawler crane tracks, use full crane mats (timber or composite). HDPE outrigger pads are for wheeled mobile cranes with deployable outriggers.
Why are non-conductive crane pads required near power lines?
Steel plates and wet timber conduct electricity, creating step-potential hazards that can electrocute crew. HDPE and UHMWPE are dielectric, isolating the crane and crew from ground-fault currents — a regulatory requirement for energised-line work.
What is the difference between a rig mat and a crane mat?
A crane mat supports crawler crane tracks during lifts (long, heavy panels). A rig mat is a modular interlocking platform that supports an entire drilling rig — mast, substructure, and equipment — as a level working surface. Both are heavy-duty; rig mats prioritise modularity, crane mats prioritise length and stiffness.
Get a Quote for HDPE Ground Protection Mats
RUIYANG manufactures HDPE, UHMWPE and FRAS composite mats for construction, oilfield, mining, events and civil projects worldwide. Tell us your load, ground and quantity — we reply with specifications and factory-direct pricing.