Crane mat and temporary works glossary

Also called Aluminium outrigger mat, Modular aluminium mat

A crane mat manufactured from structural aluminium alloy, usually as extruded modules that interlock and stack in layers to reach a required safe working load and plan area. Aluminium is one of four materials in common use for crane mats — with timber, steel and engineering plastics — and is chosen where handling weight, a rating published per configuration and indifference to water matter more than purchase price.

Also called Timber mat, Swamp mat, Access mat

Site shorthand for a heavy timber mat, typically hardwood baulks bolted or banded together, laid so plant can travel or stand on soft, wet or unmade ground. Bog mats are access and ground protection products first: they are usually supplied by size and species rather than against a published safe working load, which is the difference that matters when one ends up under an outrigger.

Also called Outrigger mat, Ground protection mat

A load-spreading panel, usually rectangular, placed on the ground beneath a crane’s outriggers, tracks or wheels to reduce the bearing pressure transmitted to the ground and prevent it failing or the plant sinking. Crane mats are made from various materials — including timber, steel, aluminium and UHMWPE/HDPE plastics — and are sized according to the load to be spread and the ground conditions on site.

The amount a mat, pad or structural element bends or displaces under load. Some deflection is normal and expected in any material; the concern in ground protection is whether it is small enough, and recovers fully once the load is removed, so that it does not damage the ground or affect the stability of the plant standing on it.

Also called Uneven settlement, Out-of-level settlement

Settlement that differs from one bearing point to another, so a machine or structure goes out of level rather than settling evenly. For a crane on outriggers it is the more dangerous of the two: the machine was levelled before the lift, and a foot that settles further than its neighbours tilts it while it is loaded.

Also called Allowable bearing pressure

The maximum bearing pressure the ground can safely support without excessive settlement or failure, established through site investigation and geotechnical assessment. It varies significantly with soil type, moisture content and previous ground disturbance, and is the key figure used to size crane mats and outrigger pads.

Also called Bearing pressure, GBP

The load per unit area transmitted from a foundation, outrigger, track or mat down into the supporting ground, usually expressed in kilonewtons per square metre (kN/m²). Comparing the applied bearing pressure against the ground’s bearing capacity is the basic calculation behind every ground protection decision.

Also called Geotechnical desk study, Trial pit, Plate bearing test

The process of establishing what the ground on a site is and what it can carry, running from a desk study of historical maps, geological records and previous reports, through trial pits and boreholes, to in-situ tests such as the plate bearing test and the Standard Penetration Test. It is where the allowable bearing pressure used to size crane mats and outrigger pads comes from.

Also called Half Loader Spreader Module, Half-loader configuration

A spreader module built into an aluminium crane mat that moves a high outrigger load away from the centre of the mat and spreads it across two positions, lowering the pressure reaching the ground. On ALIMATS® it is also a configuration category: half-loader builds reach higher safe working loads than the standard build over the same plan area.

Also called kPa, Kilonewtons per square metre, kN/m²

The unit UK ground bearing figures are written in: one kilopascal (kPa) is one kilonewton per square metre, so kPa and kN/m² are the same unit under two names. One tonne per square metre is 9.81 kPa, and one kilopascal is about 20.9 pounds per square foot — the conversion needed to read ground pressure figures published for the American market.

Also called Load spreading, Load distribution

The principle of distributing a concentrated load, such as an outrigger point load, over a larger ground area so the resulting bearing pressure is reduced to within the ground’s safe bearing capacity. Crane mats and outrigger pads work by load spread, and the degree achieved depends on a mat’s size, thickness and stiffness.

Also called Dispersion angle, Load dispersal angle, 45 degree rule

The angle at which a load is assumed to disperse outwards as it passes down through a mat, pad or layer of engineered fill, used to work out the area over which it finally bears on the ground. A 45° dispersion is the assumption most commonly seen in UK lift planning, but it is an assumption the temporary works designer makes and owns — it is not a property of the mat.

Also called Fill, Made-up ground

Ground that has been altered by human activity, typically by filling, dumping or reworking with material that is not naturally occurring in that location — demolition rubble, old foundations or uncompacted fill, for example. Made ground is often unpredictable and weaker or less consistent than undisturbed natural ground, so it is a common trigger for additional ground protection or investigation.

Also called Outrigger float, Crane pad, Spreader pad

A load-spreading pad placed directly under an individual outrigger foot, smaller and more localised than a full crane mat, used to reduce the bearing pressure at that specific point. “Float” is an alternative term for the same component, used particularly in mobile crane hire.

Also called Concentrated load

A load applied, or treated as applied, at a single concentrated location rather than spread over an area — the load from an individual outrigger foot, for example. Point loads generally produce much higher local bearing pressures than the same total load applied as a uniformly distributed load, which is why they are the critical case for crane mat sizing.

Also called Punching failure, Local shear failure

A local failure in which a concentrated load pushes a plug of material through the element supporting it, rather than that element bending or the ground settling under it — an outrigger foot through a thin pad, or a mat through a firm crust into softer material below. It is governed by what lies directly beneath and around the loaded area, so a larger mat of the same thickness does not necessarily prevent it.

Also called Track mat, Temporary roadway

Lighter, often modular matting laid end to end to create a temporary road or path for tracked or wheeled plant to travel across soft or sensitive ground, as distinct from a crane mat, which supports a stationary load at a single fixed position. Trackway is generally sized for distributed traffic loading rather than the concentrated point loads a crane mat must resist.

Also called UDL

A load treated as spread evenly across an area rather than concentrated at a single point — the loading from a general work platform or from stored materials over a floor or ground area, for example. UDLs generally produce lower local bearing pressures than an equivalent point load, which is why point loads such as outrigger feet are usually the governing case for crane mat design.

An engineered surface built up to provide a stable base of sufficient bearing capacity for a crane or other plant to work from, typically used where the natural or made ground alone is not adequate. A working platform is itself a piece of temporary works, and its design should be checked and certified before plant is brought onto it.

Also called AP

The individual responsible for the overall planning and management of a lifting operation, including selecting the crane, assessing ground conditions and approving the lift plan. On complex or high-risk lifts the appointed person is often a separate role from the crane supervisor; on simpler lifts, one person may hold both responsibilities.

Also called Counterweight

Additional weight, such as concrete or steel blocks, added to a crane or piece of plant to increase stability and counteract the overturning effect of a load. Ballast increases the loads transmitted to the ground through tracks, wheels or outriggers, so it must be accounted for in ground-bearing calculations, not just the load being lifted.

Also called Concrete pump stabiliser, Concrete pump outrigger

The outrigger legs a truck-mounted concrete boom pump extends to spread its footprint and support the reaction loads generated while pumping, similar in principle to a crane’s outriggers. Because boom pumps can impose high, sustained point loads while stationary for long pours, their stabiliser pads often need the same ground protection as crane outriggers.

Also called BS 7121-1:2016, Safe use of cranes

BS 7121 is the British Standard series giving the code of practice for the safe use of cranes, and BS 7121-1:2016 is its general part: safe systems of work, selection, erection and dismantling, maintenance, inspection, thorough examination, operation, and the planning and management of lifting operations. It is the document a UK appointed person’s lift planning is normally built on.

Also called C703, Crane stability on site

CIRIA C703, Crane stability on site (second edition), is the UK industry guide to keeping a crane stable on site, covering type and choice of crane, loading cases, ground conditions and foundation details. It is one of very few UK references written about the ground under a crane rather than about the crane itself.

Also called CS

The person on site responsible for directing the crane operation once the lift plan has been approved by the appointed person, including confirming the crane is correctly positioned, ballasted and set up before lifting begins. On smaller or more straightforward lifts, the appointed person and crane supervisor may be the same individual.

Also called Safety factor

The ratio between a material’s or structure’s actual capacity and the maximum load it is designed to carry, built in to allow for uncertainties in loading, material variability and workmanship. A stated safe working load already has an appropriate factor of safety applied, so it should never be further derated on assumption, nor exceeded on the assumption that spare capacity remains.

Also called Lifting plan

A documented plan for a lifting operation, prepared or approved by the appointed person, setting out the sequence of work, the crane and equipment to be used, ground conditions and protection measures, exclusion zones, and the roles and responsibilities of those involved. A lift plan is required for anything beyond the most basic, repetitive lifting operations.

Also called Duty chart, Rated capacity chart

Manufacturer’s data, specific to an individual crane, showing the maximum load it can lift at a given radius and configuration, including how outrigger reactions vary with load and radius. The appointed person and crane supervisor use the load chart to confirm a lift is within the crane’s capacity and to calculate the ground loads that need to be spread by mats or pads.

Also called LOLER 1998, Lifting Operations and Lifting Equipment Regulations 1998

LOLER is the Lifting Operations and Lifting Equipment Regulations 1998, the UK regulations governing the strength and stability, positioning, marking, planning, supervision and thorough examination of lifting equipment used at work. Regulation 8 is the sentence lift planners quote: every lifting operation involving lifting equipment must be properly planned by a competent person, appropriately supervised and carried out in a safe manner.

Also called Mobile elevating work platform, Cherry picker, Scissor lift

A powered platform, such as a scissor lift or boom lift, that raises people to work at height. Like cranes, MEWPs transmit concentrated loads through wheels or outriggers and can require ground protection matting on soft, uneven or made ground to prevent sinking or instability.

Also called Stabiliser leg, Jack leg

An extending leg or beam fitted to a mobile crane, or to other plant such as boom pumps and some MEWPs, that is lowered to the ground to widen the machine’s effective base and provide stability while working. Outriggers transmit high, concentrated point loads to the ground, which is why they are typically set up on mats or pads.

Also called Outrigger load

The vertical load transmitted through an individual outrigger to the ground, which varies with the crane’s configuration, the load being lifted, and the radius at which it is working. Outrigger reactions, taken from the crane’s load chart, are the starting figures used to size mats or pads for a specific lift.

Heavy plant used to install piled foundations, typically imposing very high, concentrated ground loads through tracks or outriggers, often on ground that has not yet been fully engineered. Piling rigs commonly require substantial ground protection, particularly where they need to track across a site between pile positions.

Also called Working radius

In crane terminology, the horizontal distance from the crane’s centre of rotation to the centre of the load being lifted. A crane’s safe working load reduces as radius increases, which is why radius is one of the two key figures — with the resulting load — read from a load chart.

Also called SWL

The maximum load that a piece of equipment, mat, sling or lifting accessory is designed to carry safely, already incorporating an appropriate factor of safety. Safe working load should always be read together with the specific conditions it applies to — configuration, radius, ground support — since it is not necessarily a single fixed figure for every situation.

Also called Slewing

The rotation of a crane’s upper structure and boom around its vertical axis, allowing the load to be moved to a different position without moving the crane’s base. Slewing changes where the load sits relative to the base, which can alter the loads on individual outriggers even where the load and radius stay constant.

Also called Mini crane, Tracked mini crane

A compact, tracked crane with narrow tracks and outrigger-supported legs, designed to access confined spaces such as building interiors or narrow side passages that conventional mobile cranes cannot reach. Despite their small size, spider cranes can impose significant point loads through their tracks or outriggers and often need matting on delicate floor finishes or soft ground.

Also called BS 5975-1:2024, BS 5975-2:2024

BS 5975 is the British Standard code of practice for temporary works, and since December 2024 it has been published in two parts: BS 5975-1:2024 on the management procedures for controlling temporary works, and BS 5975-2:2024 on the design and implementation of falsework. The single-document edition, BS 5975:2019, was withdrawn on 18 December 2024.

Also called Construction (Design and Management) Regulations 2015

CDM 2015 is the Construction (Design and Management) Regulations 2015, the UK regulations setting out how construction projects are planned, managed and monitored and the duties held by clients, designers, principal designers, principal contractors and contractors. Regulation 19 is the one that reaches temporary works: any buttress, temporary support or temporary structure must be of such design and installed and maintained so as to withstand any foreseeable loads which may be imposed on it, and used only for the purposes for which it was designed and installed and is maintained.

Someone with the training, knowledge and experience appropriate to a given task — such as inspecting a working platform or checking a lift plan — so that they can identify risks and judge whether work is being carried out safely. What counts as competent varies with the complexity and risk of the specific task in question.

Also called Temporary works design brief

A temporary works design brief is the statement of requirements issued to a temporary works designer before design starts, setting out what the temporary works has to do, the loads and constraints it must accommodate, the site conditions assumed, and the design parameters to be used. The brief is the input to the design; the design check is the scrutiny applied afterwards.

Also called Independent check, Category check

An independent review of a temporary works design carried out by someone not involved in producing the original design, to a level of scrutiny appropriate to the risk category of the works. The design check is a key control point before a permit to load or permit to use is issued.

Also called Permit to use

A formal, documented authorisation confirming that a temporary works item has been constructed, checked and approved, and may now be loaded or brought into use. Issuing the permit is normally the responsibility of the temporary works coordinator, following the required design check and any necessary inspection.

Also called Risk assessment and method statement, Method statement

RAMS is the paired risk assessment and method statement a contractor produces for a task: the risk assessment identifies the hazards and the controls, and the method statement sets out the sequence of work those controls are built into. RAMS covers how a task will be carried out, a lift plan covers the lifting operation itself, and a temporary works design covers whether the thing being loaded can take it.

Also called TW

Engineering works needed to allow permanent works to be constructed, but which are not part of the finished structure — excavation support, formwork, scaffolding and propping, for example, and the crane mats and outrigger pads used to support plant safely on site. Temporary works still need to be properly designed, checked and managed, even though they are removed once no longer required.

Also called TWC

The person appointed by a contractor to manage the overall temporary works process on a project or site, ensuring temporary works are designed, checked and given a permit to load or use before they are relied upon. The role is a management and coordination function, not necessarily a design role.

Also called TW register

A temporary works register is a project’s list of every temporary works item, recording for each one its design category, who designed it, who checked it, the status of that check and whether a permit to load has been issued. It is what a temporary works coordinator uses to know what exists on site and what is still outstanding.

Also called TWS

The person responsible for supervising a specific temporary works item on site, checking it is constructed, positioned and maintained in accordance with its design, and reporting to the temporary works coordinator. On smaller sites, the role may be combined with other site supervisory responsibilities.

Also called Aluminium crane mat material

The family of lightweight, corrosion-resistant metal alloys — aluminium combined with elements such as magnesium, silicon or zinc — used to manufacture structural products including crane mats. Aluminium alloys give a high strength-to-weight ratio compared with steel, so a mat with equivalent load-carrying capacity is significantly lighter to handle.

Also called Azobé, Lophira alata, Timber crane mat

A dense, naturally durable tropical hardwood (Lophira alata), widely used for crane mats and timber baulks because of its high strength and resistance to decay and abrasion. Ekki mats are heavier than aluminium or plastic mats of similar size, and their load capacity can vary with moisture content and natural defects such as knots and splits.

Also called Density, Compressive strength, Tensile strength

The four properties that decide how a mat or pad behaves under a crane: compressive strength, the stress a material carries before it crushes; tensile strength, the stress it carries in tension before it fails; modulus of elasticity, how much it deflects elastically before either happens; and density, how heavy it is to handle. Strength and stiffness are independent — a material can be strong and flexible, or stiff and brittle — and both matter, because a mat that has not failed can still deflect enough to concentrate its load.

Also called Plastic outrigger pad, Polyethylene mat, Nylon pad

Ultra-high-molecular-weight polyethylene (UHMWPE) and high-density polyethylene (HDPE) are engineering plastics used to manufacture lightweight ground protection mats and outrigger pads. They resist wear and moisture and do not absorb water or rot the way timber can, though their load capacity and stiffness differ from aluminium or timber alternatives and depend on the specific grade and thickness used.