The term construction industry is used worldwide to cover what is a collection of industries with very different practices, brought together temporarily on the site of a building or civil engineering job. The scale of operations ranges from a single worker carrying out a job lasting minutes only (e.g., replacing a roof tile with equipment consisting of a hammer and nails and possibly a ladder) to vast building and civil engineering projects lasting many years that involve hundreds of different contractors, each with their own expertise, plant and equipment. However, despite the enormous variation in scale and complexity of operations, the major sectors of the construction industry have a great deal in common. There is always a client (known sometimes as the owner) and a contractor; except for the very smallest jobs, there will be a designer, either an architect or engineer, and if the project involves a range of skills, it will inevitably require additional contractors working as subcontractors to the main contractor (see also the article “Organizational factors affecting health and safety” in this chapter). While small-scale domestic or agricultural buildings may be built on the basis of an informal agreement between the client and builder, the vast majority of building and civil engineering work will be carried out under the terms of a formal contract between the client and contractor. This contract will set out details of the structure or other work that the contractor is to provide, the date by which it is to be built and the price. Contracts may contain a great deal besides the job, the time and the price, but those are the essentials.
The two broad categories of construction projects are building and civil engineering. Building applies to projects involving houses, offices, shops, factories, schools, hospitals, power and railway stations, churches and so on—all those kinds of structures that in everyday speech we describe as “buildings”. Civil engineering applies to all the other built structures in our environment, including roads, tunnels, bridges, railways, dams, canals and docks. There are structures that appear to fall into both categories; an airport involves extensive buildings as well as civil engineering in the creation of the airfield proper; a dock may involve warehouse buildings as well excavation of the dock and raising of the dock walls.
Whatever the type of structure, building and civil engineering both involve certain processes such as building or erection of the structure, its commissioning, maintenance, repair, alteration and ultimately its demolition. This cycle of processes occurs regardless of the type of structure.
Small Contractors and the Self-employed
While there are variations from country to country, construction is typically an industry of small employers. As many as 70 to 80% of contractors employ less than 20 workers. This is because many contractors start out as a single tradesperson working alone on small-scale jobs, probably domestic ones. As their business expands, such tradespeople start to employ a few workers themselves. The workload in construction is rarely consistent or predictable, as some jobs finish and others start up at different times. There is a need in the industry to be able to move groups of workers with particular skills from job to job as the work requires. Small contractors fulfil this role.
Alongside the small contractors there is a population of self-employed workers. Like agriculture, construction has a very high proportion of self-employed workers. These again are usually tradespeople, such as carpenters, painters, electricians, plumbers and bricklayers. They are able to find a place in either small-scale domestic work or as part of the workforce on bigger jobs. In the boom construction period of the late 1980s, there was an increase in workers claiming to be self-employed. This was partly because of tax incentives for the individuals concerned and use by contractors of so-called self-employed who were cheaper than employees. Contractors were not faced with the same level of social security costs, were not required to train self-employed persons and could get rid of them more easily at the end of jobs.
The presence in construction of so many small contractors and self-employed individuals tends to militate against effective management of health and safety for the job as a whole and, with such a transitory workforce, certainly makes it more difficult to provide proper safety training. Analysis of fatal accidents in the United Kingdom over a 3-year period showed that about half the fatal accidents happened to workers who had been onsite for a week or less. The first few days on any site are especially hazardous to construction workers because, however experienced they may be as tradespeople, each site is a unique experience.
Public and Private Sectors
Contractors may be part of the public sector (e.g., the works department of a city or district council) or they are part of the private sector. A considerable amount of maintenance used to be done by such public works departments, especially on housing, schools and roads. Recently there has been a move to encourage greater competition in such work, partly as a result of pressures for better value for money. This has led firstly to a reduction in the size of public works departments, even their total disappearance in some places, and to the introduction of mandatory competitive tendering. Jobs previously done by public works departments are now done by private-sector contractors under severe “lowest tender wins” conditions. In their need to cut costs, contractors may be tempted to reduce what are seen as overheads such as safety and training.
The distinction between public and private sectors may also apply to clients. Central and local government (along with transportation and public utilities if under the control of central or local government) may all be clients for construction. As such they would generally be thought to be in the public sector. Transportation and utilities run by corporations would usually be considered to be in the private sector. Whether a client is in the public sector sometimes influences attitudes towards inclusion of some items of safety or training in the cost of construction work. Recently public- and private-sector clients have been under similar constraints as regards competitive tendering.
Work across National Boundaries
An aspect of public-sector contracts of increasing importance is the need for tenders to be invited from beyond national boundaries. In the European Union, for example, large-scale contracts beyond a value set out in Directives, must be advertised within the Union so that contractors from all member countries may tender. The effect of this is to encourage contractors to work across national boundaries. They are then required to work in accordance with the local national health and safety laws. One of the aims of the European Union is to harmonize standards between member states in health and safety laws and their application. Major contractors working in parts of the world subject to similar regimes must therefore be familiar with health and safety standards in those countries where they carry out work.
In buildings, the designer is usually an architect, although on small-scale domestic housing, contractors sometime provide such design expertise as is necessary. If the building is large or complex, there may be architects dealing with design of the overall scheme as well as structural engineers concerned with design of, for example, the frame, and specialist engineers involved with design of the services. The architect for the building will ensure that sufficient space is provided in the right places in the structure to permit installation of plant and services. Specialist designers will be concerned to ensure that the plant and services are designed to operate to the required standard when installed in the structure in the places provided by the architect.
In civil engineering, the lead in design is more likely to be taken by a civil or structural engineer, although in high-profile jobs where visual impact may be an important factor, an architect may have an important role in the design team. In tunnelling, railways and highways, the lead in design is likely to be taken by structural or civil engineers.
The role of the developer is to seek to improve the utilization of land or buildings and profit from that improvement. Some developers simply sell the improved land or buildings and have no further interest; others may retain ownership of land or even buildings and reap a continuing interest in the form of rents that are greater than before the improvements.
The skill of the developer is to identify sites either as empty land or under-utilized and out-of-date buildings where application of construction skills will improve their value. The developer may use his or her own finances, but perhaps more often exercises further skills in identifying and bringing together other sources of finance. Developers are not a modern phenomenon; the expansion of cities over the last 200 years owes a great deal to developers. Developers may themselves be clients for the construction work, or they may simply act as agents for other parties who provide finance.
Types of Contract
In the traditional contract, the client arranges for a designer to prepare a full design and specifications. Contractors are then invited by the client to tender or bid for doing the job in accordance with the design. The role of the contractor is largely confined to construction proper. The contractor’s involvement in questions of design or specification is then mainly a matter of seeking such changes as will make it easier or more efficient to build—to improve “buildability”.
The other common arrangement in construction is the design and build contract. The client requires a building (perhaps an office block or shopping development) but has no firm ideas on detailed aspects of its design other than the size of site, number of persons to be accommodated or scale of activities to be carried out in it. The client then invites tenders from either designers or contractors to submit both design and construction proposals. Contractors working in design and build either have their own design organization or have close links with an external designer who will work for them on the job. Design and build may involve two stages in design: an initial stage where a designer prepares an outline scheme which is then put out to tender; and a second stage where the successful design and build contractor will then carry out further design on detailed aspects of the job.
Maintenance and emergency contracts cover a wide variety of arrangements between clients and contractors and represent a significant proportion of the work of the construction industry. They generally run for a fixed period, require the contractor to do certain types of work or to work on a “call-off” basis (i.e., work that the client calls the contractor in to do). Emergency contracts are widely used by public authorities who are responsible for providing a public service that ought not to be interrupted; government agencies, public utilities and transportation systems make wide use of them. Operators of factories, particularly those with continuous processes such as petrochemicals, also make wide use of emergency contracts to deal with problems in their facilities. Having entered such a contract, the contractor undertakes to make available suitable workers and plant to carry out the work, often at very short notice (e.g., in the case of emergency contracts). The advantage to the client is that he or she does not need to retain workers on payroll or have plant and equipment that may only occasionally be used to deal with maintenance and emergencies.
Pricing of maintenance and emergency contracts may be on the basis of a fixed sum per annum, or on the basis of time spent carrying out work, or some combination.
Perhaps the most common publicly known example of such contractors is maintenance of roads and emergency repairs to gas main or power supplies that have either failed or been accidentally damaged.
Whatever the form of contract, the same possibilities arise for clients and designers to influence the health and safety of contractors by decisions made in the early stage of the job. Design and build perhaps permits closer liaison between the designer and contractor on health and safety.
Price is always an element in a contract. It may simply be a single sum for the cost of doing the job, such as building a house. Even with a single lump sum, the client may have to pay part of the price in advance of the job starting, to enable the contractor to buy materials. The price may, however, be on a cost-plus basis, where the contractor is to recover his or her costs plus an agreed amount or percentage for profit. This arrangement tends to work to the disadvantage of the client, since there is no incentive for the contractor to keep costs down. The price may also have bonuses and penalties attached to it, so that the contractor will receive more money if, for example, the job is completed earlier than the agreed time. Whatever form the price takes for the job, it is usual for payments to be made in stages as the work progresses, either on completion of certain parts of the job by agreed dates or on the basis of some agreed method of measuring the work. At the end of construction proper, it is common for an agreed proportion of the price to be kept back by the clients until “snags” have been put right or the structure has been commissioned.
During the course of the job, the contractor may encounter problems that were not foreseen when the contract was made with the client. These might require changes to the design, the construction method or the materials. Usually such changes will create extra costs for the contractor, who then seeks to recover from the client on the basis that these items become agreed “variations” from the original contract. Sometimes recovery of the cost of variations can make the difference for the contractor between doing the job at a profit or loss.
The pricing of contracts can affect health and safety if inadequate provision is made in the contractor’s tender to cover the costs of providing safe access, lifting equipment and so on. This becomes even more difficult where, in an attempt to ensure that they obtain value for money from contractors, clients pursue a vigorous policy of competitive tendering. Governments and local authorities apply policies of competitive tendering to their own contracts, and indeed there may be laws requiring that contracts can be awarded only on the basis of competitive tendering. In such a climate, there is always a risk that the health and safety of construction workers will suffer. In cutting costs, clients may resist a reduction in the standard of construction materials and methods, but at the same time be totally unaware that in accepting the lowest tender, they have accepted working methods that are more likely to endanger construction workers. Even in a situation of competitive tendering, contractors submitting tenders should have to make clear to the client that their bid adequately covers the cost of health and safety involved in their proposals.
Developers can influence health and safety in construction in ways similar to clients, firstly by using contractors who are competent in health and safety and architects who take health and safety into account in their designs, and secondly in not automatically accepting the lowest tenders. Developers generally want to be associated only with successful developments, and one measure of success ought to be projects where there are no major health and safety problems during the construction process.
Building Standards and Planning
In the case of buildings, whether housing, commercial or industrial, projects are subject to planning laws that dictate where certain types of development may take place (e.g., that a factory may not be built among houses). Planning laws may be very specific about the appearance, materials and size of buildings. Typically areas identified as industrial zones are the only places where factory buildings may be erected.
Often there are also building regulations or similar standards that specify in precise detail many aspects of the design and specification of buildings—for example, the thickness of walls and timbers, depth of foundations, insulation characteristics, size of windows and rooms, layout of electrical wiring and earthing, layout of plumbing and pipework and many other issues. These standards have to be followed by clients, designers, specifiers and contractors. They limit their choices but at the same time ensure that buildings are built to an acceptable standard. Planning laws and building regulations thus affect the design of buildings and their cost.
Projects to build housing may consist of a single house or vast estates of individual houses or flats. The client may be each individual householder, who will then normally be responsible for maintenance of his or her own house. The contractor will usually remain responsible for correcting defects in construction for a period of months after building is finished. However, if the project is for many houses, the client may be a public body, either in local or national government, with responsibility for providing housing. There are also large private bodies like housing associations for whom numbers of houses may be built. Public or private bodies with responsibilities for providing housing generally rent the finished houses to occupants, retaining a greater or lesser degree of responsibility for maintenance also. Building projects involving blocks of flats usually have a client for the block as a whole, who then lets out individual flats under a leasing arrangement. In this situation the owner of the block has responsibility for carrying out maintenance but passes on the cost to the tenants. In some countries ownership of individual flats in a block can rest with the occupants of each flat. There has to be some arrangement, sometimes through an estate management contractor, whereby maintenance can be carried out and the necessary costs raised among the occupants.
Often houses are built on a speculative basis, by a developer. Specific clients or occupants of those houses may not have been identified at the outset but come on the scene after construction has begun and purchase or rent the property like any other article. Houses are usually fitted out with electrical, plumbing and drainage services and heating systems; a gas supply may also be laid on. Sometimes in an attempt to cut costs, houses are only partially finished, leaving it to the purchaser to install some of the fittings and to paint or decorate the building.
Commercial buildings include offices, factories, schools, hospitals, shops—an almost endless list of different types of buildings. In most cases these buildings are constructed for a particular client. However, offices and shops are often built on a speculative basis like housing, with the hope of attracting buyers or tenants. Some clients require an office or shop to be totally fitted out to their requirements, but very often the contract is for the structure and main services, with the client making arrangements to fit out the premises using specialist contractors in office and shop fitting.
Hospitals and schools are built for clients who have a clear idea of precisely what they want, and the clients often provide design input into the project. Plant and equipment in hospitals may cost more than the structure and involve a great deal of design that has to satisfy stringent medical standards. National or local government may also play a part in the design of schools by laying down very detailed requirements on space standards and equipment as part of its wider role in education. National governments usually have very detailed standards as to what is acceptable in hospital buildings and plant. Fitting out of hospitals and similarly complex buildings is a form of construction work usually carried out by specialist subcontractors. Such contractors not only require knowledge of health and safety in construction in general, but also need expertise in ensuring that their operations do not adversely affect the hospital’s own activities.
Industrial building or construction involves use of the mass- production techniques of manufacturing industry to produce parts of buildings. The ultimate example is the house brick, but normally the expression is applied to building using concrete parts or units that are assembled onsite. Industrial construction expanded rapidly after the Second World War to meet the demand for cheap housing, and it is more commonly found in mass housing developments. Under factory conditions it is possible to mass produce cast units that are consistently accurate in a way that would be virtually impossible under normal site conditions.
Sometimes units for industrial construction are manufactured away from the construction site in factories that may supply a wide area; sometimes, where the individual development is itself very large, a factory is set up onsite to serve that sole site.
Units designed for industrial construction must be structurally strong enough to stand up to being moved, lifted and lowered; they must incorporate anchorage points, or slots to permit safe attachment of lifting tackle, and must also include appropriate lugs or recesses to permit the units to fit together both easily and strongly. Industrial construction demands plant for transporting and lifting units into position and space and arrangements to store units safely when delivered to site, so that units are not damaged and workers are not injured. This technique of building tends to produce visually unattractive buildings, but on a large scale it is cheap; a whole room can be assembled from six cast units with window and door openings in place.
Similar techniques are used to produce concrete units for civil engineering structures like elevated motorways and tunnel linings.
Some clients for industrial or commercial buildings containing extensive complex plant wish simply to walk into a facility that will be up and running from their first day in the premises. Laboratories are sometimes constructed and fitted out on this basis. Such an arrangement is a “turn-key” project, and here the contractor will ensure that all aspects of plant and services are fully operational before handing the project over. The job may be done under a design and build contract so that, in effect, the turn-key contractor deals with everything from design to commissioning.
Civil Engineering and Heavy Construction
The civil engineering of which the public is most aware is work on highways. Some highway work is the creation of new roads on virgin land, but much of it is the extension and repair of existing highways. Contracts for highway work are usually for state or local government agencies, but sometimes roads remain under the control of contractors for some years after completion, during which time they are permitted to charge tolls. If civil engineering structures are being financed by government, then both the design and actual construction will be subject to a high degree of supervision by officials on behalf of government. Contracts for construction of highways are usually let to contractors on the basis of a contractor being responsible for a section of so many kilometres of the highway. There will be a main contractor for each section; but highway construction involves a number of skills, and aspects of the job such as steel work, concrete, shuttering and surfacing may be subcontracted by the main contractor to specialist firms. Highway construction is also sometimes carried out under management contract arrangements, where a civil engineering consultancy will provide management for the job, with all the work being done by subcontractors. Such a management contractor may also have been involved in design of the highway.
Construction of highways requires the creation of a surface whose gradients are suitable for the sort of traffic that will use it. In a generally level terrain, creation of the foundation of the highway may involve earthmoving—that is, shifting soil from cuttings to create embankments, building bridges across rivers and driving tunnels through mountainsides where it is not possible to go round the obstruction. Where labour costs are higher, such operations are carried out using mechanically powered plant such as excavators, scrapers, loaders and lorries. Where labour costs are lower, these processes may be carried out manually by large numbers of workers using hand tools. Whatever the actual methods adopted, highway construction requires high standards of route surveying and planning of the job.
Highway maintenance frequently requires roads to remain in use whilst repairs or improvements are carried out in part of the road. There is thus a hazardous interface between traffic movement and construction operations which makes good planning and management of the job even more important. There are often national standards for signage and coning off of roadworks and requirements as to the amount of separation there should be between construction and traffic, which may be difficult to achieve in a confined area. Control of traffic approaching roadworks is usually the responsibility of the local police, but requires careful liaison between them and the contractors. Highway maintenance creates traffic hold-ups, and accordingly contractors are put under pressure to finish jobs quickly; sometimes there are bonuses for finishing early and penalties for finishing late. Financial pressures must not undermine safety on what is very dangerous work.
Surfacing of highways may involve concrete, stone or tarmacadam. This requires a substantial logistical train to ensure that the required quantities of surfacing materials are in place in the right condition to ensure that surfacing proceeds without interruption. Tarmacadam requires special purpose spreading plant that keeps the surfacing material plastic while spreading it. Where the job is re-surfacing, plant will be required including picks and breakers so that the existing surface is broken up and removed. A final finish is usually applied to the surfaces of highways involving use of heavy powered rollers.
Creation of cuttings and tunnels may require use of explosives and then arrangements to shift the muck displaced by the blasting. The sides of cuttings may require permanent supports to prevent landslides or falls of ground onto the finished road.
Elevated highways often require structures similar to bridges, especially if the elevated section passes through an urban area when space is limited. Elevated highways are often constructed from cast reinforced concrete sections that are either cast in situ or cast in a fabrication area and then shifted to the required position onsite. The work will require large-capacity lifting machinery to lift cast sections, shuttering and reinforcing.
Temporary support arrangements or “falsework” to support sections of either elevated highways or bridges while they are being cast in position need to be designed to take into account the uneven loads imposed by concrete as it is poured. Design of falsework is as important as design of the structure proper.
Bridges in remote areas may be simple constructions from timber. More commonly today bridges are from reinforced concrete or steel. They may also be clad in brickwork or stone. If the bridge is to span a considerable gap, whether above water or not, its design will require specialist designers. Using today’s materials, the strength of the bridge span or arch is not achieved by mass material, which would be simply too heavy, but by skilful design. The main contractor for a bridge building job is usually a major general civil-engineering contractor with management expertise and plant. However, specialist subcontractors may deal with major aspects of the job like erection of steel work to form the span or casting or placing cast sections of the span in place. If the bridge is over water, one or both abutments that support the ends of the bridge may themselves have to be constructed in water, involving piling, coffer dams, mass concrete or stone work. A new bridge may be part of a new highway system, and approach roads may have to be built, themselves possibly elevated.
Good design is especially important in bridge building, so that the structure is strong enough to withstand the loads imposed on it in use and to ensure that it will not require maintenance or repair too frequently. The appearance of a bridge is often a very important factor, and again good design can balance the conflicting demands of sound engineering and aesthetics. Provision of safe means of access for maintenance of bridges needs to be taken into account during design.
Tunnels are a specialized form of civil engineering. They vary in size from the Channel Tunnel, with over 100 km of bores from 6 to 8 m in diameter, to mini-tunnels whose bores are too small for workers to enter and which are created by machines launched from access shafts and controlled from the surface. In urban areas, tunnels may be the only way to provide or improve transport routes or to provide water and drainage facilities. The proposed route of the tunnel requires as detailed a survey as possible to confirm the kind of ground that the tunnel workings will be in and whether there will be groundwater. The nature of the ground, the presence of groundwater and the end use of the tunnel all influence the choice of tunnelling method.
If the ground is consistent, like the chalk-clay beneath the English Channel, then machine digging may be possible. If high groundwater pressures are not encountered during pre- construction survey, then it is usually unnecessary for the workings to be pressurized to keep out the water. If working in compressed air cannot be avoided, this adds considerably to costs because airlocks have to be provided, workers need to be allowed time to decompress, and access to workings for plant and materials may be made more difficult. A large tunnel for a road or railway in consistent non-hard-rock ground might be dug using a full-face tunnel-boring machine (TBM). This is really a train of different machines linked together and moving forward on rails under its own power. The front face is a circular cutting head that rotates and feeds spoil back through the TBM. Behind the cutting head are various sections of the TBM that place the segments of tunnel lining rings in position around the surface of the tunnel, grout behind the lining rings and, in a very confined space, provide all the machinery to handle and place ring segments (each weighing some tonnes), remove spoil, bring grout and extra segments forward and house electric motors and hydraulic pumps to power the cutting head and segment-placing mechanisms.
A tunnel in non-hard-rock ground which is not consistent enough to use a TBM, may be dug using equipment such as roadheaders that bite into the face of the heading. Spoil falling from the roadheader onto the tunnel floor are to be collected by diggers and removed by lorry. This technique permits digging of tunnels that are not circular in section. The ground in which such a tunnel is dug will not usually have sufficient strength for it to remain unlined; without some form of lining there might be falls from roof and walls. The tunnel may be lined by liquid concrete sprayed onto a steel mesh held in position by rock bolts (the “New Austrian tunnelling method”) or by cast concrete.
If the tunnel is in hard rock, the heading will be dug by means of blasting, using explosives placed into shot holes drilled into the rock face. The trick here is to use the minimum of blast to achieve a fall of rock in the position and sizes required, thereby making it easier to remove the spoil. On bigger jobs, multiple drills mounted on tracked bases will be used along with diggers and loaders to remove spoil. Hard rock tunnels are often simply trimmed to provide an even surface, but are not then further lined. If the rock surface remains friable with a risk of pieces falling, then a lining will be applied, usually some form of sprayed or cast concrete.
Whatever the method of construction adopted for the tunnel, the effective supply of tunnelling materials and removal of spoil are vital to the successful progress of the job. Large tunnelling jobs may require extensive narrow-gauge construction rail systems to provide logistical support.
Dams invariably contain large quantities of earth or rock to provide mass to resist the pressure from water behind them; some dams are also covered in masonry or reinforced concrete. Depending on the length of the dam, its construction often requires earthmoving on the very largest scale. Dams tend to be built in remote locations dictated by the need to ensure that water is available at a position where it is technically possible to restrict the flow of the river. Thus temporary roads may have to be built before dam building may start in order to get plant, materials and personnel to the site. Workers on dam projects may be so far from home that full-scale living accommodations have to be provided along with the usual construction site facilities. It is necessary to divert the river away from the site of the workings, and a coffer dam and temporary riverbed may have be created.
A dam constructed simply from earth or rock that has been shifted will require large scale excavation, digging and scraping plant as well as lorries. If the dam wall is covered by masonry or cast concrete, it will be necessary to employ high or long-reach cranes capable of depositing masonry, shuttering, reinforcing and concrete in the right places. A continuous supply of good-quality concrete will be necessary, and a concrete-mixing plant will be necessary alongside the dam workings, with the concrete either handled in batches by crane or pumped to the job.
Canals and docks
Construction and repair of canals and docks contain some aspects of other jobs that have been described, such as roadworks, tunnels and bridges. It is particularly important in canal building for surveying to be to the highest standard before work begins, especially regarding levels and to ensure that material that has had to be dug out can economically be used elsewhere in the job. Indeed the early railway engineers owed a great deal to the experience of canal builders a century before. The canal will require a source for its water and will either tap into a natural source such as a river or lake or create an artificial one in the form of a reservoir. Digging of docks may start on dry land, but sooner or later has to link up to either a river, a canal, the sea or another dock.
Canal and dock building requires excavators and loaders to open up the ground. Spoil may be removed by lorry or water transport may be used. Docks are sometimes developed on ground that has a long history of industrial use. Industrial wastes may have escaped into such ground over many years, and spoil removed in digging or extending the docks will be heavily contaminated. Work in repairing a canal or dock is likely to have to be carried out while adjacent parts of the system are kept in use. The workings may have to rely on coffer dams for protection. Failure of a coffer dam during extension of Newport Docks in Wales in the early years of this century resulted in nearly 100 deaths.
Clients for canals and docks are likely to be public authorities. However, sometimes docks are constructed for corporations alongside their major production plants or for corporate clients to handle a particular type of incoming or outgoing goods (e.g., motor cars). Repair and renovation of canals is nowadays often for the leisure industry. Like dams, both canal and dock construction may be in very remote situations, requiring provision of facilities for workers beyond those of a normal construction site.
Construction of railroads or railways historically came after canals and before major highways. Clients in railway construction contracts may be rail operators themselves or governmental agencies, if the railways are financed by government. As with highways, design of a railroad that is economical and safe to build and operate depends on good surveying beforehand. In general, locomotives do not operate effectively on steep gradients, and therefore those designing layout of the track are concerned with avoiding changes in levels, going round or through obstacles rather than over them.
Designers of railroads are subject to two constraints unique to the industry: first, curves in the track layout must generally conform to very large radii (otherwise trains cannot negotiate them); second, all the structures connected with the railway—its bridge arches, tunnels and stations—must be capable of accommodating the envelope of the largest locomotives and rolling stock that will use the track. The envelope is the silhouette of the rolling stock plus clearance to allow safe passage through bridges, tunnels and so on.
Contractors involved in building and repair of railroads require the usual construction plant and effective logistical arrangements to ensure that rail track and ballast as well as construction materials are always available in what may be remote locations. Contractors may use the track they have just laid to run trains supplying the works. Contractors involved in maintenance of existing operational railways have to ensure that their work does not interfere with the operations of the railway and endanger workers or the public.
The rapid expansion of air transportation since the middle of the 20th century has resulted in one of the biggest and most complex forms of construction: the building and extension of airports.
Clients for airport construction are usually governments at the national or local level or agencies representing the government. Some airports are built for major cities. Airports are rarely for private clients such as business corporations.
Planning the work is sometimes made more difficult because of environmental constraints that have been placed on the project in relation to noise and pollution. Airports require a lot of space, and if they are located in more heavily populated areas, creation of the runways and space for terminal buildings and car parks may require reinstatement of derelict or otherwise difficult land. Building an airport involves levelling a large area, which may require earth moving and even land reclamation, and then construction of a wide variety of often very large buildings, including hangars, maintenance workshops, control towers and fuel storage facilities, as well as terminal buildings and parking.
If the airport is being built on soft ground, buildings may require piled foundations. Actual runways require good foundations; hardcore supporting the surface layers of concrete or tarmac needs to be heavily compacted. Plant used on airport construction is similar in scale and type to that used in major highway projects, except that it is concentrated within a limited area rather than over the many miles of a highway.
Airport maintenance is a particularly difficult type of work where resurfacing the runways has to be integrated with continuing operation of the airport. Usually the contractor is allowed an agreed number of hours during the night when he or she can work on a runway that is temporarily taken out of use. All the contractor’s plant, materials and workforce have to be marshalled off the runways, prepared to move immediately to the work site at the agreed start time. The contractor must finish his or her work and get off the runways again at the agreed time when flights may resume. Whilst working on the runway, the contractor must not impede or otherwise endanger aircraft movement on other runways.