In transport engineering, subgrade is the native material underneath a constructed road, [1] pavement or railway track (US: railroad track). It is also called formation level.
The term can also refer to imported material that has been used to build an embankment.
Subgrades are commonly compacted before the construction of a road, pavement or railway track
A road is a thoroughfare for the conveyance of traffic that mostly has an improved surface for use by vehicles and pedestrians. Unlike streets, whose primary function is to serve as public spaces, the main function of roads is transportation.
Transportation engineering or transport engineering is the application of technology and scientific principles to the planning, functional design, operation and management of facilities for any mode of transportation in order to provide for the safe, efficient, rapid, comfortable, convenient, economical, and environmentally compatible movement of people and goods transport.
Tarmacadam is a road surfacing material made by combining crushed stone, sand, and tar, patented by Welsh inventor Edgar Purnell Hooley in 1902. It is a more durable and dust-free enhancement of simple compacted stone macadam surfaces invented by Scottish engineer John Loudon McAdam in the early 19th century. The terms "tarmacadam" and tarmac are also used for a variety of other materials, including tar-grouted macadam, bituminous surface treatments and modern asphalt concrete.
The Shell pavement design method was used in many countries for the design of new pavements made of asphalt. First published in 1963, it was the first mechanistic design method, providing a procedure that was no longer based on codification of historic experience but instead that permitted computation of strain levels at key positions in the pavement. By analyzing different proposed constructions, the procedure allowed a designer to keep the tensile strain at the bottom of the asphalt at a level less than a critical value and to keep the vertical strain at the top of the subgrade less than another critical value. With these two strains kept, respectively, within the design limits, premature fatigue failure in the asphalt and rutting of the pavement would be precluded. Relationships linking strain values to fatigue and rutting permitted a user to design a pavement able to carry almost any desired number of transits of standard wheel loads.
Highway engineering is a professional engineering discipline branching from the civil engineering subdiscipline of transportation engineering that involves the planning, design, construction, operation, and maintenance of roads, highways, streets, bridges, and tunnels to ensure safe and effective transportation of people and goods. Highway engineering became prominent towards the latter half of the 20th century after World War II. Standards of highway engineering are continuously being improved. Highway engineers must take into account future traffic flows, design of highway intersections/interchanges, geometric alignment and design, highway pavement materials and design, structural design of pavement thickness, and pavement maintenance.
A road surface or pavement is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a road or walkway. In the past, gravel road surfaces, macadam, hoggin, cobblestone and granite setts were extensively used, but these have mostly been replaced by asphalt or concrete laid on a compacted base course. Asphalt mixtures have been used in pavement construction since the beginning of the 20th century and are of two types: metalled (hard-surfaced) and unmetalled roads. Metalled roadways are made to sustain vehicular load and so are usually made on frequently used roads. Unmetalled roads, also known as gravel roads, are rough and can sustain less weight. Road surfaces are frequently marked to guide traffic.
A railway track or railroad track, also known as a train track or permanent way, is the structure on a railway or railroad consisting of the rails, fasteners, railroad ties and ballast, plus the underlying subgrade. It enables trains to move by providing a dependable surface for their wheels to roll upon. Early tracks were constructed with wooden or cast iron rails, and wooden or stone sleepers; since the 1870s, rails have almost universally been made from steel.
Asphalt concrete is a composite material commonly used to surface roads, parking lots, airports, and the core of embankment dams. Asphalt mixtures have been used in pavement construction since the beginning of the twentieth century. It consists of mineral aggregate bound together with bitumen, laid in layers, and compacted.
The base course or basecourse in pavements is a layer of material in an asphalt roadway, race track, riding arena, or sporting field. It is located under the surface layer consisting of the wearing course and sometimes an extra binder course.
A falling weight deflectometer (FWD) is a testing device used by civil engineers to evaluate the physical properties of pavement in highways, local roads, airport pavements, harbor areas, railway tracks and elsewhere. The data acquired from FWDs is primarily used to estimate pavement structural capacity, to facilitate overlay design or determine if a pavement is being overloaded. Depending on its design, a FWD may be contained within a towable trailer or it may be built into a self-propelled vehicle such as a truck or van. Comprehensive road survey vehicles typically consist of a FWD mounted on a heavy truck together with a ground-penetrating radar and impact attenuator.
In highway engineering, subbase is the layer of aggregate material laid on the subgrade, on which the base course layer is located. It may be omitted when there will be only foot traffic on the pavement, but it is necessary for surfaces used by vehicles.
The California Bearing Ratio (CBR) is a measure of the strength of the subgrade of a road or other paved area, and of the materials used in its construction.
The track bed or trackbed is the groundwork onto which a railway track is laid. Trackbeds of disused railways are sometimes used for recreational paths or new light rail links.
The R-Value test measures the response of a compacted sample of soil or aggregate to a vertically applied pressure under specific conditions. This test is used by Caltrans for pavement design, replacing the California bearing ratio test. Many other agencies have adopted the California pavement design method, and specify R-Value testing for subgrade soils and road aggregates.
Cellular confinement systems (CCS)—also known as geocells—are widely used in construction for erosion control, soil stabilization on flat ground and steep slopes, channel protection, and structural reinforcement for load support and earth retention. Typical cellular confinement systems are geosynthetics made with ultrasonically welded high-density polyethylene (HDPE) strips or novel polymeric alloy (NPA)—and expanded on-site to form a honeycomb-like structure—and filled with sand, soil, rock, gravel or concrete.
The Aircraft Classification Number (ACN) – Pavement Classification Number (PCN) method is a standardized international airport pavement rating system promulgated by the ICAO in 1981. The method has been the official ICAO pavement rating system for pavements intended for aircraft of apron (ramp) mass greater than 5700 kg from 1981 to 2020.
Paver base is a form of aggregate used in the construction of patios and walkways whose topmost layer consists of mortarless pavers. The first layer in the construction of such a surface is called the subgrade—this is the layer of native material underneath the intended surface. It is usually compacted and stabilized. If the final pavement is to have vehicle traffic, a layer of subbase of crushed stone or concrete must come next—this layer will even out the subgrade and will bear the heaviest load from the pavement above. Next comes the base course composed of crushed gravel varying from 0.75 in (1.9 cm) down to dust-particle size. It too is typically compacted and evened. The next layer will be the paver base, composed of coarse sand and typically between 6 and 12 in thick, depending on anticipated traffic. The pavers are then laid on top of this, and then a uniform, fine-grained sand is poured between them.
The wearing course, also known as a friction course or surface course, is the upper layer in roadway, airfield, and dockyard construction. The term 'surface course' is sometimes used slightly different, to describe very thin surface layers such as chip seal. In rigid pavements the upper layer is a portland cement concrete slab. In flexible pavements, the upper layer consists of asphalt concrete, that is a construction aggregate with a bituminous binder. The wearing course is typically placed on the binder course which is then laid on the base course, which is normally placed on the subbase, which rests on the subgrade. There are various different types of flexible pavement wearing course, suitable for different situations.
Pavement milling is the process of removing at least part of the surface of a paved area such as a road, bridge, or parking lot. Milling removes anywhere from just enough thickness to level and smooth the surface to a full depth removal. There are a number of different reasons for milling a paved area instead of simply repaving over the existing surface.
The Neoloy Geocell is a Cellular Confinement System (geocell) developed and manufactured by PRS Geo-Technologies Ltd. Geocells are extruded in ultrasonically welded strips. The folded strips are opened on-site to form a 3D honeycomb matrix, which is then filled with granular material. The 3D confinement system is used to stabilize soft subgrade soil and reinforce the subbase and base layers in flexible pavements. Cellular confinement is also used for soil protection and erosion control for slopes, including channels, retention walls, reservoirs and landfills.
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