NZ Forest Road Engineering Manual

Forest road engineering terminology

Abney level: A handheld clinometer used to measure a slope.
Adverse grade: The uphill grade in the direction that a loaded truck would travel. Conversely, favourable grade refers to the uphill grade that an unloaded truck would travel.
AEP: Annual exceedance probability. The chance of a flood of a given size (or larger) occurring in any one year. Usually expressed as a percentage.
Aggregate: Material formed from a mass of fragments or particles loosely compacted together, or mechanically crushed, angular rock used for forest road surfacing.
Angle of repose: The angle between the horizontal and the maximum slope that soil assumes through natural processes. It generally applies to dry granular soils.
Apron: A hard (generally concrete) surface layer constructed at the entrance or outlet of a river crossing structure. Can be augmented with rocks to improve fish passage.
Arterial road: The main road in a forest to which multiple secondary roads will connect.
Assessment of effects: A process of systematically identifying the effects of a proposed activity or activities on the environment.
Auger: A helical (spiral) shaped drill used to bore holes into the ground for the purpose of obtaining soil samples.
Backfill: Soil or other material used to replace material removed during construction.
Balanced road section: An excavation technique used on gentle to moderate slopes where the excavated cut material is used to make the adjacent fill on a section of road. On a balanced road section, the cut material is equal to the compacted fill material.
Bankfull channel width: The distance across a river channel, formed by the dominant channel-forming flow, with a recurrence interval seldom outside a 1 to 2-year range (measured at a right angle to the channel flow).
Base course: The bottom layer of road surface rock in a two-layer surfacing system. The base course is the layer between the subgrade and the surface (running) layer of crushed rock.
Batters: Constructed slopes of uniform gradient.
Battery culvert: A river crossing structure made by using multiple culverts that allow the free flow of water through the culverts in low flow conditions, and water and debris to flow over the top of the entire structure in high flow.
Bearing strength: The amount of weight that a soil or subgrade can safely support without plastic (permanent) deformation.
Bed invert gradient: The waterway bed slope where the rise or fall of the horizontal distance of a river channel is measured in metres.
Bedrock: The continuous body of rock, of a relatively great thickness, that underlies the overburden soils.
Bench: A ledge cut to contain fill, or a step cut into a batter to make it more stable.
Benchmark: A term used in surveying to infer a reference point. For example, to signify a starting point.
Berm: A raised or engineered structure parallel to the edge of the road or track, designed to contain and direct surface water runoff and sediment.
Birds nest: a. A wire rope that has over-spooled from a drum to the point where it is tangled; b. Logging residues stacked on, or over, the edge of a landing.
Borrow: Any excavation from outside the construction batter limits shown on the drawings.
Borrow pit: An area smaller than a quarry where material has been dug out.
Broad-based dip: A shallow depression dug across a road to facilitate road surface drainage without interrupting vehicle passage.
Brush cut: To clear away brush from a trail, survey line, or tree before working.
Bulk fill: Material placed in the form of fill, from the ground surface after clearing and removing of top soil.
Bunding: A secondary containment system to contain and prevent leakage around an operation or storage facility.
Camber: The gradual downward slope from the centre of a crowned road.
Catch point: The point at which a road cut or fill slope intercepts the natural ground.
Catchment: An area where water is collected by the natural landscape. Gravity causes all rain and runoff in the catchment to run downhill where it naturally collects in creeks, rivers, lakes or the sea. Also referred to as a watershed or drainage basin.
Centreline: The centre of a planned or established road.
Clay: Soil finer than 0.002 mm that exhibits plasticity with a range of water contents. It usually exhibits considerable strength, depending on the presence of other soil materials when air-dried.
Clearing: An area within a roadway clearing limit where standing and dead vegetation have been removed. This is the first step of construction on a forest road.
Cobble: Rock fragments, usually rounded, with an average diameter of 75-300 mm.
Cold deck: A pile or deck of logs stored for some time between phases of the operation. For example, processing and loading, or skidding and processing.
Compaction: The process of applying pressure or vibration to soil or aggregate to strengthen it, resulting in increased density (tonnes per m3).
Cone Penetration Test (CPT): An in-situ test for determining soil properties. It consists of slowly pressing a steel cone into the soil to measure the penetration resistance.
Corduroy road: A structured load-bearing surface where logs are laid horizontally and parallel, with no void areas. Corduroy roads are an engineered road construction technique used in places where the substrate is very weak, and where the load must be spread if the road is to be trafficable. This can be used on skid trails or landings, or with adequate surfacing also on haul roads.
Crest vertical curve: The transition between an uphill and downhill grade, an uphill to less extreme uphill grade, or a downhill to a less extreme downhill grade.
Cross-ditch: A shallow channel excavated or bladed diagonally across the surface of a road (or skid trail), to lead water off the road and prevent soil erosion. On smaller skid trails they are also referred to as water bars.
Cross-drain culvert: A pipe that carries water from road ditches and discharges on the downhill side.
Crossfall: The cross slope for roads that are not crowned.
Crowned: A road surface that is sloped from the centre of the road to the inside and outside road edges to achieve road surface drainage.
Crushed rock: Angular rock used for road surfacing. Often mechanically crushed to a specified range of rock particle sizes.
Culvert: a. A pipe or box structure that conveys a stormwater flow under a forestry road or forestry track; b. The entire structure used to channel a water body under a forestry road or forestry track.
Cut: An excavation within the construction batter limits shown on the drawings and above the final subgrade surface. The cut includes side cuts and batters.
Cut slope: The inside road slope cut into the face of the hill slope.
Cut-off or cut-out: Shallow channels or earth mounds constructed across a road, track or firebreak to divert and control runoff. Cut-offs are constructed to minimise sediment movement and scouring by preventing the accumulation of sufficient flow and velocity to support erosion. Unlike water bars, cut-offs are normally used in impermeable soils and are not used for retaining runoff.
Daylighting: The process of removing trees to allow sunlight to dry out a roadway or landing.
Debris trap: A structure designed to catch and temporarily store harvest residues from flowing water. Also known as a slash trap or woody debris trap.
Degree of saturation: The degree to which the voids in a soil mass contain fluid. Usually expressed as the ratio of water volume to total void volume.
Dilatancy: The phenomenon of expansion of cohesionless soils when subjected to shearing deformation.
Ditch: An engineered channel, often dug at the toe of a fill batter, running parallel to the edge of a road surface. It is designed to catch stormwater runoff from the road surface and carry it to suitably located and constructed discharge points. Often incorrectly called a water table, water table drain, drain or roadside drain.
Drainage (stormwater) culvert: The culvert below the road profile that cross-drains water from the roadside drain at the inner edge of a forestry road or forestry track to its outer edge.
Duff: Accumulated surface litter on the forest floor.
Earthworks: As defined by the NES-PF: a. A disturbance of the surface of the land by the movement, deposition, or removal of earth (or any other matter constituting the land, such as soil, clay, sand, or rock) in relation to plantation forestry; b. Includes the construction of forestry roads, forestry tracks, landings and river crossing approaches, cut and fill operations, maintenance and upgrade of existing earthworks, and forestry road widening and realignment; c. Does not include soil disturbance by machinery passes, forestry quarrying, or mechanical land preparation.
Ecosystem: The complex ecological community and environment forming a functional whole in nature.
Embankment: Soil, aggregate or rock material placed on a prepared ground surface and constructed to grade. The embankment is the fill material on the downhill side of the road, or, on fill sections, the entire road.
End haul: Moving excavated roadway material a distance (usually by dump truck) to a designated soil dump site. Often used with full bench construction instead of side-casting the cut directly onto the slope.
Energy dissipater: A structure, usually made of rock or logs, that dissipates the energy of water discharged from a culvert. If constructed from large angular rock it is referred to as ‘rip rap’.
Ephemeral river flows: Water flow in a river or stream that only occurs during and immediately after rain.
Erosion: The process of dislodging and transporting soil particles by wind, flowing water or rain.
Erosion susceptibility classification: A system within the NES-PF that determines the risk of erosion on land across New Zealand, based on environmental characteristics. These include rock type and slope. Land is classified into four categories of erosion susceptibility according to the level of risk: Low (green), moderate (yellow), high (orange), and very high (red).
Excavation: Removing earth from an area.
Fifty-year flood: A flood event that has a 2% probability of occurring annually. The scale of this projected flood will determine the dimensions of several components of roads built around rivers, such as bridges and culverts.
Fill: Soil or aggregate, placed to raise the land surface, normally under a strict compaction regime. It can be used to build a structure above natural ground level, as with fill sections on the downhill side of a road.
Fill slope: An area on the downhill side of a roadway (or both sides in a through fill section) that must have excavated material placed on them to build a road section up to grade.
Filter (or buffer) strip: Land adjacent to a water body; its vegetative cover is used to filter the sediments out of surface runoff water from cutover or roads.
Flagging: Coloured plastic ribbons, which can be attached to trees or stakes to make boundaries, stakes and other markers visible.
Flume, or fluming: An open channel or conduit, made from plastic, galvanised corrugated steel, and sometimes concrete, or timber, which is used to carry runoff from earthworks over loose fill or erodible material so that it can be discharged onto less erodible surfaces.
Ford: A hard surface on the bed of a river, permanently or frequently overtopped by water, that allows the crossing of a river by machinery or vehicles.
Fording: The act of driving across the bed of a river.
Forest infrastructure: Structures and facilities that are required for the operation of the forest. These include roads, forestry tracks, river crossings, landings, fire breaks, stormwater and sediment control structures, and water runoff controls.
Forest road: A road designed for forest activities. Requirements may change over a rotation because the width, grade, strength and pavement surface will be different for general forestry activities than for a road that allows a fully laden logging truck to safely traverse it, and that has all-weather access. The term forest road does not include roads managed by a local authority.
Forest track: As defined by the NES-PF, a track that allows the passage of forestry machinery or vehicles, but does not provide the width, grade, strength, or pavement surface to allow a fully laden logging truck to safely traverse it. It may also lack all-weather access.
Frost heave: The heaving of the ground due to the formation of ice lenses.
Gabion: A cage, cylinder or box filled with rocks, concrete, or sand and soil for use in civil engineering and road building.
Geotextiles: Synthetic fabrics designed for use in soil stabilisation and control.
Gradation: The graph showing the proportions by mass of a soil or fragmented rock distributed in specified particle-size ranges.
Grade (slope): The tangent of the angle from the land surface to the horizontal. Grades are typically specified for new road constructions.
Granular fill material: Material which has been placed in the fill, and which contains less than 35% passing a 60µm sieve (fines = silts and clays).
Gravel: Particles of rock between 5-75 mm in size. They can be rounded, semi-rounded or angular.
Green strip: An uncut strip of timber left along rivers and roads. Also known as buffer strip, leave strip, or streamside management zone.
Grizzly: A rock screen device often used during gravel extraction or at a rock truck loading area.
Grubbing: Digging and removing stumps, roots and duff within the clearing limits of the roadway.
Heading up: A hydraulic head of water above the culvert inlet that occurs when the nominal capacity of the culvert is exceeded.
Headwall: A wall built at the upstream end of a culvert.
Heave: The expansion or displacement of soil caused by phenomena such as moisture absorption, removal of pressure, driving of piles, frost action, and/or loading of an adjacent area.
Highway truck: A truck designed to haul a load that does not exceed legal highway limits.
Horizontal curve: A circular curve used to change the horizontal direction of a road.
Hot deck: A landing where the processing of stems to logs is done in conjunction with the loading out activity.
Hydro-seeding: A seed mulch and water mix sprayed onto fills and batters
In-situ: The in-place or undisturbed properties or state of a soil.
In-slope: A road surface sloped toward the ditched side, or the inside shoulder, of a road.
Intermittent river: A river that does not flow year-round. It is commonly dry three or more months per year.
Landing (pad, skid): An area of land where logs or tree lengths extracted from a forest are accumulated, processed, and loaded for removal.
Landslide: The downward and outward sliding or movement of a mass of earth or rock, or a mixture of both. Also referred to as mass wasting.
Lift: A layer of soil or road surface rock.
Loam: A mixture of sand, silt, or clay, or a combination of any of these, with organic matter.
Loess: A uniform aeolian (relating to or arising from the action of the wind) deposit of silty material. It has an open structure and relatively high cohesion due to cementation of grains. A characteristic of loess deposits is that they can stand with nearly vertical slopes.
Main road: A road that supports a high level of traffic, usually well built and well designed. They can also be referred to as primary or arterial roads
Maintenance (upgrade): As defined by the NES-PF, it includes activities that reshape and upgrade existing forestry infrastructure, the installation and maintenance of water runoff control measures, and/or road metalling. It does not include road widening or realignment.
Meandering line: The survey line at the high-water mark on navigable lakes and rivers.
Moisture content (MC): The moisture content of soil, normally reported as the weight of water relative to the weight of soil in percent. If it is reported relative to the volume of water, it is called the volumetric MC.
Mud: The mixture of soil and water in a fluid state.
Mulch: A covering of loose organic material applied over the soil surface to protect it.
Normally consolidated soil: A soil that has never been subjected to an effective pressure greater than the existing effective overburden pressure.
Off-highway trucks: Trucks designed to handle loads exceeding legal highway size and weight restrictions. These trucks are not driven on highways but are used in logging operations conducted on private roads.
Off-tracking: The different paths that the front and rear wheels on a logging truck, tractor-trailer, or other vehicle take when cornering. The rear or trailer wheels take a shorter path than the front wheels around the curve, corner or turn, so the driver has to compensate for this by taking the curve, corner or turn wider. Because of off-tracking, curves will need to be wider than segments of road.
Optimum moisture content (OMC): The water content at which a soil can be compacted to a maximum dry unit weight using a specific compaction effort.
Organic soil: Soil with a high organic content, normally greater than 25% by weight. In general, organic soils are highly compressible and have poor load-sustaining properties.
Outslope: A road surface sloped to the outside shoulder. In general, an outsloped road needs no ditch because the slope of the road itself sheds runoff water away from the road.
Overburden: The overlying soil and rock that is excavated and removed to allow construction of the underlying material.
Penetrometer: A device used for indirectly testing the load-carrying capacity of soil by measuring its resistance to an object being forced into the soil with a standard force.
Percolation: The movement, under hydrostatic pressure, of water through soil or rock, excluding movement through large openings such as solution channels.
Perennial river: A river that is a continually or intermittently flowing body of freshwater, in which the intermittent flows provide habitats for the continuation of the aquatic ecosystem.
Pioneer road: A temporary access roadway constructed within the clearing limits to provide for clearing, grubbing, and timber removal activities.
Plan and profile drawings: Drawings that show both horizontal (plan) and vertical (profile) delineation of a road survey or geometric design.
Porosity: The ratio of volume of voids in a rock or soil to its total volume.
Primary logging road: A road designed and maintained for a high level of use. Typically an all-weather gravel road that is part of a permanent road system.
Proctor curve: The relationship between dry unit weight and water content of a soil for a given compaction effort.
Quarry: A large deep pit where rock is blasted, ripped or excavated and extracted.
Ravelling: The movement of soil or aggregate, usually caused by erosion on cut and fill slopes.
Reconstruction: The rebuilding of existing roads, beyond normal maintenance activities.
Relief culvert: A secondary pipe that carries water during high flow event after the primary culvert has reached capacity.
Reno mattress: A double twisted hexagonal woven galvanized steel wire mesh compartmented basket with a rectangular mattress shape. Even distribution of the stone fill ensures that the reno mattress maintains intimate contact with the foundation soil.
Rill: A shallow channel cut into soil by the erosive action of flowing water.
Rip rap: Large dimension (usually) loose stone used to form a foundation for a breakwater or other structure.
Riparian zone: The margin and bank of a water body, including the area where direct interaction occurs between land and water systems, that is important for the management of water quality and ecological values.
River: As defined by the NES-PF, a river is a continually or intermittently flowing body of fresh water. It includes streams and modified watercourses, but does not include artificial watercourses such as irrigation canals, water supply races, canals for the supply of water for electricity power generation, or farm drainage canals.
River crossing: As defined by the NES-PF, a river crossing is a structure required for the operation of a plantation forest. It provides for vehicles or machinery to cross over a water body. It includes an apron and other structures and materials necessary to complete a river crossing. It does not include a stormwater culvert or a culvert under a forestry road or forestry track.
Road: a. A skid road in skidder or high-lead logging; b. A cleared path along which logs are hauled to the landing with one setting of the rigging; c. An access and haul route for vehicles.
Road grade: The slope of a road surface in the direction of travel, usually expressed in percent (in metres per 100 metres). For example, a 10% grade equals a change along the road of 10 metres vertical in 100 metres horizontal.
Road pattern: A characteristic arrangement of spur roads in relation to each other.
Road prism: The road geometry between the extreme points of excavation and/or fill, or between the top of the cut and the bottom of the fill.
Road template: Used to establish the shape and basic dimensions of the cross section of a road.
Roadbed: The road subgrade surface between the subgrade shoulders.
Roadway: The portion of a road within the limits of excavation and embankment.
Rock: Any igneous, sedimentary or metamorphic stone which is solidly bonded or cemented together, and which occurs in masses, ledges, seams or layers.
Sag vertical curve: The transition between a downhill and an uphill grade, or a steeper downhill and less severe downhill grade.
Scarification: a. A shallow loosening of the soil; b. The gravelling of a road surface.
Seasonal road: Used mainly during a specific season, such as a logging road used only during the dry season.
Secondary logging road: Designed for relatively little use. Typically, a dirt road with no gravel, used only during dry weather.
Sediment: Solid material that is: a. A mineral, or mineral and organic; b. In suspension, being transported, or has been moved from the site of origin by air, water, gravity, or ice and has come to rest on the earth’s surface, either above or below water.
Sediment control measures: Structures or measures to slow or stop water with sediment in it, so that the sediment drops out of suspension before the water from the site reaches a water body.
Sheep-foot roller: A steel drum roller with protruding metal plates (‘feet’) used for compacting clay soils.
Side cast: Non-compacted fill or spoil that has been excavated from a cut to create forestry infrastructure on the downhill slope from the infrastructure.
Sieve analysis: A series of sieves used to determine the particle size distribution of a soil.
Skid road: A road cut through the woods for skidding.
Skid trail: A skidder path through the forest.
Slash: Woody material or debris left behind after plantation forestry activities.
Slip: a. Material dislodged by the force of nature from outside the cut batter limits or from the fill slope shown on the drawings; b. Relative movement in the direction of travel at the mutual contact surface of the traction or transport device and the surface that supports it.
Slope ratio: The steepness of a slope expressed as a ratio of its horizontal to vertical distance ratio. For example, a 1:1 slope changes 1 metre horizontal to every 1 metre vertical (45 degrees).
Slope stability: The resistance of a natural or artificial slope to movement or failure.
Slough: Material that has eroded and ravelled from cut or fill slopes.
Slump: A failure of a natural or constructed slope.
Soffit: The lowest part of the span of a bridge.
Soil: The upper layer of earth in which plants grow. A black or dark brown material typically consisting of a mixture of organic remains, clay, and rock particles. Often thought of as anything that is not rock.
Soil adhesion: Soil sticking to foreign materials such as soil implements, tracks, or wheels.
Soil compaction: a. Increased soil density resulting from the packing effect of machines moving over the soil; b. Disturbs soil structure and can cause decreased tree growth, increased water runoff, and soil erosion.
Soil failure: The alteration or destruction of the soil structure by mechanical forces such as in shearing, compression, or tearing.
Spoil: The by-product of excavations and earthworks.
Spur road: Supports a low level of traffic, such as a level that would serve one or two landings.
Stabilisation: a. Seeding; b. Vegetative cover, mulch, or slash cover; c. Compacting, draining, roughening, or armouring by the placement of rock or the use of other rigid materials.
Stormwater control measures: Structures or measures to manage stormwater on formed surfaces; primarily to reduce the volume or velocity of water runoff so as to reduce its power to entrain sediment.
Stream morphology: Refers to shapes of river channels and how they change in shape and direction over time.
Stumping: The removal/excavation of tree stumps from the ground, usually associated with the construction of infrastructure.
Subgrade: The native material underneath a constructed road or the finished surface prior to applying the improvement layer. Also called the formation layer.
Subgrade: The layers of roadbed on which the base or surface course are placed. On an unsurfaced road, the finished subgrade is the wearing surface. That is, the top layer of a road surface.
Subsoil: The layer of soil with low organic matter content found at depths of 25 cm or more below the surface of the ground. Its colour varies from brown, yellow-brown, red and olive. It contains speckled colour patterns where poorly drained.
Surface course: The top layer of a road surface, also referred to as the ‘running surface’.
Tangent: A straight segment of road between two horizontal curves.
Temporary bridge: A single-span bridge that is in place for up to two years.
Temporary river crossing: A river crossing that is in place for up to two months. It includes a corduroy, which is a structure made by laying a culvert in the bed of a river to carry the water flow, creating a running surface approach using logs placed parallel to the culvert. It does does not include a bridge or ford.
Through cut: A roadway section cut through a ridge; it will have cut slopes above both sides of the road.
Through fill: An elevated roadway section with fill slopes below both sides of the road.
Time of concentration: A concept used in hydrology to measure the response of a watershed to a rain event. It is defined as the time needed for water to flow from the most remote point in a watershed to the watershed outlet. It is a function of the topography, geology, and land use within the watershed.
TM61 method: An empirical method for estimating a design flood peak discharge in an ungauged New Zealand catchment.
Topo (Topographic map): A map that shows the elevation contours of the ground.
Topsoil: The layer of material immediately below the ground surface. It includes vegetation, turf and humus or other organic matter.
Traffic volume: The number of vehicles passing per day over a given section of road. In general, the more traffic volume, the more road surfacing will be needed.
Turnout: A short auxiliary lane on a single-lane road which allows meeting vehicles to pass each other. It is usually designed for ease of access for the unloaded truck so that the loaded truck can proceed.
Undercut: An excavation from just below the subgrade surface. This may be an extension of the depth of cut in a cut area.
Vertical curve: A transition between two road grades, such as between uphill and downhill grades. A vertical curve is designed with flatter parabolic, or non-circular, curve, unlike a horizontal curve, which is designed as a portion of a whole circle.
Water bar: A structure installed in the road surface to divert road surface water off the road. Water bars are constructed from subgrade soil or other materials, such as rubber strips and timber.
Water body: A river, lake, stream, pond, wetland, or aquifer, or any part thereof, that is not located within the coastal marine area (RMA).
Water quality: The chemical, physical, biological and radiological characteristics of water. It is a measure of the condition of water relative to the requirements of one or more biotic species and/or any human need or purpose.
Water runoff control measures: Structures or measures to reduce the volume or velocity of water runoff, and consequently reduce its power to gather up and transport sediment.
Wearing surface (of a road): Refers to the surface on which vehicle wheels run.
Well-graded: Describes a soil composed of a variety of different particle sizes.
Yarding road: The path followed by a turn of logs yarded by a cable method.

Contents

Forest road engineering terminology