Highway Functional Classification

Highways are classified according to their functions in terms of the service they provide. The classification system facilitates a systematic development of highways and the logical assignment of highway responsibilities among different jurisdictions. Highways and streets are categorized as rural or urban roads, depending on the area in which they are located. This initial classification is necessary because urban and rural areas have significantly different characteristics with respect to the type of land use and population density, which in turn influences travel patterns. Within the classification of urban and rural, highways are categorized into the following groups:

• Principal arterials
• Minor arterials
• Major collectors
• Minor collectors
• Local roads and streets

Freeways are not listed as a separate functional class since they are generally classified as part of the principal arterial system. However, they have unique geometric criteria that require special design consideration.

Functional System of Urban Roads

Urban roads comprise highway facilities within urban areas as designated by responsible state and local officials to include communities with a population of at least 5000 people. Some states use other values, for example, the Virginia Department of Transportation uses a population of 3500 to define an urban area. Urban areas are further subdivided into urbanized areas with populations of 50,000 or more and small urban areas with populations between 5000 and 50,000. Urban roads are functionally classified into principal arterials, minor arterials, collectors, and local roads.
A schematic of urban functional classification is illustrated in Figure 1 for a suburban environment.

Urban Principal Arterial System

This system of highways serves the major activity centers of the urban area and consists mainly of the highest-traffic-volume corridors.
It carries a high proportion of the total vehicle-miles of travel within the urban area including most trips with an origin or destination within the urban area. The system also serves trips that bypass the central business districts (CBDs) of urbanized areas.

Fig 1 : Schematic Illustration of the Functional Classes for a Suburban Road Network

All controlled-access facilities are within this system, although controlled access is not necessarily a condition for a highway to be classified as an urban principal arterial.
Highways within this system are further divided into three subclasses based mainly on the type of access to the facility: (1) interstate, with fully-controlled access and gradeseparated interchanges; (2) expressways, which have controlled access but may also include at-grade intersections; and (3) other principal arterials (with partial or no controlled access).

Urban Minor Arterial System

Streets and highways that interconnect with and augment the urban primary arterials are classified as urban minor arterials. This system serves trips of moderate length and places more emphasis on land access than the primary arterial system. All arterials not classified as primary are included in this class.

Although highways within this system may serve as local bus routes and may connect communities within the urban areas, they do not normally go through identifiable neighborhoods. The spacing of minor arterial streets in fully developed areas is usually not less than 1 mile, but the spacing can be 2 to 3 miles in suburban fringes.

Urban Collector Street System

The main purpose of streets within this system is to collect traffic from local streets in residential areas or in CBDs and convey it to the arterial system. Thus, collector streets usually go through residential areas and facilitate traffic circulation within residential, commercial, and industrial areas.

Urban Local Street System

This system consists of all other streets within the urban area that are not included in the three systems described earlier. The primary purposes of these streets are to provide access to abutting land and to the collector streets. Through traffic is discouraged on these streets.

Functional System of Rural Roads

Highway facilities outside urban areas comprise the rural road system. These highways are categorized as principal arterials, minor arterials, major collectors, minor collectors, and locals. Figure 2 is a schematic illustration of a functionally classified rural highway network.

Fig 2 : Schematic Illustration of a Functionally Classified Rural Highway Network

Rural Principal Arterial System

This system consists of a network of highways that serves most of the interstate trips and a substantial amount of intrastate trips. Virtually all highway trips between urbanized areas and a high percentage of trips between small urban areas with populations of 25,000 or more are made on this system.

The system is further divided into freeways (which are divided highways with fully controlled access and no at-grade intersections) and other principal arterials not classified as freeways.

Rural Minor Arterial System

This system of roads augments the principal arterial system in the formation of a network of roads that connects cities, large towns, and other traffic generators, such as large resorts. Travel speeds on these roads are relatively high with minimum interference to through movement.

Rural Collector System

Highways within this system carry traffic primarily within individual counties, and trip distances are usually shorter than those on the arterial roads. This system of roads is subdivided into major collector roads and minor collector roads.

Rural Major Collector System

Routes under this system carry traffic primarily to and from county seats and large cities that are not directly served by the arterial system. The system also carries the main intracounty traffic.

Rural Minor Collector System

This system consists of routes that collect traffic from local roads and convey it to other facilities. One important function of minor collector roads is that they provide linkage between rural hinterland and locally important traffic generators such as small communities.

Rural Local Road System

This system consists of all roads within the rural area not classified within the other systems. These roads serve trips of relatively short distances and connect adjacent lands with the collector roads.

Materials for pavement construction

Soil

Every pavement, other than those on bridges, self-evidently includes soil. The most basic design requirement of any pavement is that the underlying soil is adequately protected from applied loads. Thus, no pavement engineer can avoid the need to understand soil. The following list features some key facts.

Soils vary from heavy clays, through silts and sands to high-strength rocky
materials.
Soils are not usually consistent along the length of a road or across any pavement
site.
Soils are sensitive to water content to differing degrees.
Water content will vary during the life of a pavement, sometimes over quite short
timescales, in response to weather patterns.
Some soils are highly permeable; some clays are virtually impermeable.

All this leads to one thing – uncertainty. However clever one tries to be in understanding and characterising soils, it is quite impossible to be 100% sure of the properties at a given time or in a given location.

This uncertainty makes life considerably harder. Nevertheless, it is necessary to categorise each soil type encountered in as realistic a way as possible, and there are two fundamental areas in which soil behaviour affects pavement performance. These are :

stiffness under transient (i.e. moving wheel) load
resistance to accumulation of deformation under repeated load, likely to be
related to shear strength.

Granular material

Granular material is unbound material with relatively large particle sizes, and includes natural gravel, crushed rock and granulated industrial by-products such as slag from steel production. Soils are technically granular materials, albeit often with a very small particle size (2 mm or less for clay), but the key difference is that a soil is not, in general, ‘engineered’ in any way.

A granular pavement layer, on the other hand, will be selected and quite possibly deliberately blended to give a particular combination of particle sizes. It can also be mixed with a predetermined amount of water. One would
therefore naturally expect that much of the uncertainty inherent in soil properties is removed in the case of a granular material.

However, it may still be difficult to predict performance accurately, as different material sources, most commonly different rock types, might be expected to exhibit slightly different properties due to their different
responses to crushing or their differing frictional properties.

Nevertheless, a granular material will be a much more controlled and predictable component than the soil.
Even the water-content variation of a granular material will be a little more predictable, in both magnitude and effect, than in the case of soil.

However, the properties of granular material of interest to the pavement engineer are actually more or less the same as those of soil, namely

stiffness under transient load
resistance to accumulation of deformation under repeated load, related to shear
strength.

Hydraulically-bound material

Nowadays, the availability of Portland cement, and substitutes such as fly ash or ground granulated blast-furnace slag, means that it can be economical to use such a binding agent to strengthen a granular material. These binders are known as ‘hydraulic’ binders, as they require the presence of water for the cementing action to take place.

Cement technology is a vast subject in its own right and involves several different chemical reactions, the most important of which are the conversion of tricalcium silicate (c. 50% of Portland cement) and dicalcium silicate (c. 25%) into hydrates (forming strong solids) by reaction with water, also generating calcium hydroxide and heat. The
first reaction is rapid; the second is slower. The reader should refer to specialist literature for details.

Hydraulically-bound materials, including so-called pavement-quality concrete (hereafter referred to as PQC) at the upper end of the strength spectrum, introduce a quite different type of behaviour and totally different design requirements. They possess a key property that is lacking in soils and granular materials, namely the ability to withstand tension.

Individual particles are rigidly bonded together by the binding agent, and a definite tensile force is required to break that bond. In the case of a strong concrete, all the large particles are well bonded into a continuous matrix of fine aggregate and cement paste, and the whole material is solid and rigid. It has a stiffness that is still partly
governed by the contacts between the large particles, but which is also heavily dependent on the qualities of the surrounding cementitious matrix.

In the case of a weaker hydraulically-bound material, the binding effect may be less complete and there may be many particle contacts that remain unbound, giving a certain freedom of movement
within the material and a reduced stiffness and strength.

Nevertheless, even a weak hydraulically-bound material will remain as a solid, with negligible permanent deformation
until the bonds are fractured, that is until the tensile strength is overcome. The key properties for the pavement engineer are, therefore

stiffness
tensile strength.

One further property that could arguably be added is fatigue resistance, that is, the resistance of the material to failure under repeated load at a stress level less than its failure strength. However, the relationship with tensile strength is so close that it is hardly a separate property.

It would also have been possible to add curing rate (the rate of strength gain), as this certainly affects the construction process and economics significantly, and thermal expansion coefficient, as this property strongly influences the tendency of a hydraulically-bound material to crack under day–night temperature variation, requiring the introduction of movement joints in concrete pavements

Bitumen-bound material

This is a material almost unique to pavement engineering, amaterial whose beneficial properties were discovered almost by accident, but a material which is now very much at the centre of pavement technology. There are countless stories as to when bituminous products were first used on roads, such as the accidental spillage of tar outside Derby iron works in 1901.

Although mastics including natural asphalt had been used on footways since the 1830s, they were not stable enough for roads, and it was not until around 1900–1901 that the first usages of tar-bound stone occurred at approximately similar dates in the USA and Europe. Lay (1990) gives further information.

While proportions differ around the world, typically some 90% of paved highways have a bitumen-bound surface layer; whatever the make-up beneath the surface, bitumen and bitumen-bound materials (referred to hereafter as asphalts) currently play a major role.

And asphalt is quite different from concrete or any hydraulically-bound material. Bitumen is a binding agent, like Portland cement and the other hydraulic binders, but it has very different properties. Whereas hydraulic binders create a rigid material that cannot deform appreciably unless it first cracks, bitumen remains a viscous liquid at
normal in-service temperatures. It therefore has the ability to ‘flow’.

An ability to flow may seem a rather undesirable quality in a material that is aiming to bind rock particles together, and it does indeed lead to the possibility that an asphalt can deform – hence the phenomenon known as ‘rutting’ or ‘tracking’. However, it also overcomes some of the difficulties encountered with rigid hydraulically-bound materials.

For a start, the expansion and contraction with day–night temperature variation is accommodated simply by a small viscous strain within an asphalt, meaning that no movement joints are required, and that thermally-induced cracking will only occur under the most extreme temperature conditions (continental winters, deserts).

Asphalts are also able to accommodate any moderate movement within the foundation, for example, minor differential settlement in an embankment, movement that might lead to the fracture of a rigid concrete slab. Furthermore, the tendency of asphalt to flow can be controlled by proper mixture design such that rutting is avoided.

However, despite the flexible nature of asphalt, it can still crack. It is impossible to define a tensile strength, as this will vary with temperature and rate of loading; the relevant parameter is the ‘fatigue characteristic’, defining resistance to cracking under repeated load. The key properties required for design are therefore:

stiffness
resistance to deformation under repeated load
fatigue characteristic.

Other materials

The fourmaterial types introduced so far represent the basic building blocks available to the pavement engineer. However, it is worth referring here to a couple of materials that do not fit so easily into any of the four categories.The first is block paving. Blocks are often made of concrete and so could have been introduced under ‘hydraulically-bound materials’.

On the other hand, they can be cut fromnatural stone or may comprise fired clay bricks.Moreover, the discontinuous nature of block paving means that the properties of the parent material are less important than the effects of the discontinuities. The blocks themselves may have the properties of concrete, for example, a stiffness modulus of some 40 GPa, but the effective layer modulus once the discontinuities are taken into account may be as little as 500MPa.

The second special case is a hybrid material, known in the UK as grouted macadam and in the USA as resin-modified pavement; it is also sometimes known as ‘semi-flexible’ material. This too does not fit neatly into any of the previous categories, as it combines an asphalt skeleton with a cementitious grout, filling the voids in the asphalt mixture.

It therefore utilises both bituminous and hydraulic binders. Having a two-stage production process the material tends to be expensive, and is used in particular heavyduty applications such as bus lanes and industrial pavements. As will be demonstrated later, it actually resembles an asphalt much more than a concrete, but it is nevertheless
distinct.

Block paving and grouted macadam are bulk-use materials at the expensive end of the range.
There are also specialist products that are only used in small quantities to strengthen, or in some way improve, a pavement layer.Here one could include steel reinforcement of concrete.

There are also reinforcing products designed for asphalt; some are steel, others polymeric or made of glass fibre.Asimilar range of products is available for the reinforcement of granular materials. Generically, these products are known as geogrids and their use is widespread in some areas, for example, as a means of stabilising roads over very soft ground.

Geotextiles comprise a closely related range of products, produced in various ways and forming continuous layers separating two different pavement materials (commonly the soil and a granular layer). These too can have a reinforcing function, but their most common use is simply as a separator, ensuring that fine soil particles do not migrate up into the pavement and that stones from a granular layer do not lose themselves in the soil.

The entire spectrum of geogrids and geotextiles is known under the collective name of geosynthetics and, although geosynthetics are specialist products, it is the responsibility of the pavement engineer to understand how (and whether) they work in particular applications rather than relying solely on the, sometimes not unbiased, opinion of a supplier.

The long history of the paved highway

It is impossible to know where or when the wheel was invented. It is hard to imagine that Stone Age humans failed to notice that circular objects such as sections of tree trunk rolled.

The great megalithic tombs of the third millennium BC bear witness to ancient humans’ ability to move massive stones, and most commentators assume that tree trunks were used as rollers; not quite a wheel but a similar principle!

However, it is known for certain that the domestication of the horse in southern Russia or the Ukraine in about 4000 BC was followed not long afterwards by the development of the cart.

It is also known that the great cities of Egypt and Iraq had, by the late third millennium BC, reached a stage where pavements were needed. Stone slabs on a rubble base made an excellent and long-lasting pavement surface suitable for both pedestrian usage and also traffic from donkeys, camels, horses, carts and, by the late second millennium BC, chariots.

Numerous examples survive from Roman times of such slabbed pavements, often showing the wear of tens of thousands of iron-rimmed wheels. Traffic levels could be such that the pavement had a finite life.

Even in such ancient times, engineers had the option to use more than simply stones if they so chose – but only if they could justify the cost! Concrete technology made significant strides during the centuries of Roman rule and was an important element in the structural engineer’s thinking.

Similarly, bitumen had been used for thousands of years in Iraq as asphalt mortar in building construction. Yet neither concrete nor asphalt was used by pavement engineers in ancient times, for the excellent reason that neither material came into the cheap, high-volume category. As far as the pavement engineer was concerned, economics dictated that the industry had to remain firmly in the Stone Age.

Even in the days of Thomas Telford and John Loudon Macadam – the fathers of modern road building in the UK – the art of pavement construction consisted purely of optimising stone placement and the size fractions used.

Times havemoved on; themassive exploitation of oil has meant that bitumen, a by-product from refining heavy crude oil, is now much more widely available. Cement technology has progressed to the stage where it is sufficiently cheaply available to be considered in pavement construction. However, there is no way that pavement engineers can contemplate using some of the twenty-first century’s more expensive materials – or, at least, they can be used only in very small amounts. Steel can only be afforded as reinforcement in concrete and, even in suchmodest quantities, it represents a significant proportion of the overall cost.

Plastics find a use in certain types of reinforcement product; polymers can be used to enhance bitumen properties; but always the driving force is cost, which means that, whether we like it or not, Stone Age materials still predominate.

Satellite positioning (GPS), advantages and disadvantages for site engineers

A 1960s surveying text book consulted in 1980 would reveal little change in twenty years. That is not true today, with modern technology, systems and software are being continually updated. Nowhere is this more obvious than with satellite positioning.

It has exploded onto the construction market changing some operations beyond all recognition. As technology improves, accuracy increases and costs come down it becomes more economical to employ it on smaller and smaller jobs.

What is it?

Satellite positioning is the determination of the position of a point using a satellite receiver. Satellite positioning is generally known as GPS or global positioning system after the American military system, which was fi rst available for public use.

Unlike most surveying and setting out tasks, the skill required of the operator is minimal. The skill with GPS is with the management of the system’s input and out put data. The satellite receiver does all the work in gathering the data and outputting or storing it as required. With setting out it can provide the operator with predetermined setting out coordinates.

How accurate is it?

Accuracy depends on the methods employed and the equipment used. For construction setting out centimetre level accuracy is achievable. This makes it suitable for many setting out tasks. Unlike traditional survey methods, each point is independent of the points around it, and therefore each point is of a similar accuracy.

Degradation of accuracy (due to creep) with distance from the main station is no longer a prob lem. If used in unsuitable conditions, accuracy may be compromised.
An error in one point is not passed on to adjacent points.

What are the advantages?

When used for setting out, a single engineer with a setting out pole equipped with a satellite receiver can set out points almost as fast as he can mark them. With a road centre-line for example, the operator can walk the route and mark centreline points at whatever frequency is required. The setting out information can be taken straight from the design on disk without the need to input a mass of figures.

Work is unaf fected by weather or daylight or a lack of it. Visibility between points is not required, so local obstructions (shrubbery, mechanical plant, low buildings, walls etc.) do not hinder the process. Productivity increases are considerable. As well as giving plan coordinates (Eastings and Northings), it will automatically provide heights as a mat ter of course.

Satellite systems can also be integrated into computer-controlled plant, in which, for example, a grader has the road design in its memory. The grader blade is automatically adjusted to give the correct earthwork
profile. This eliminates the need for a complete setting-out team along with their instruments, forest of timber-work, chainmen and their transport.

What are the disadvantages?

Cost is always an issue, but this has to be balanced against productivity. GPS is not suited to all locations. Due to the fact the position of the receiver is derived from observing a number of satellites, a clear view of the sky is necessary. This may make GPS unsuitable for city centre sites shielded by adjacent tall buildings.
A received signal may give inaccurate results if defl ected off the side of a building. GPS is not suitable for tunnelling work. However GPS can be used very effi ciently to establish a control either side of an obstruction under which tunnelling is required.

GPS does not work well in tree-covered areas, again due to the need for a clear line of sight to the sky.
The height element of the output is of a lower order of accuracy than the plan coordinates. Additionally, heights given are not above mean sea level (as with traditional levelling), but above the mathematical model of the Earth, WGS84 (World Geodetic System 1984).

Unfortunately, for Europe this does not run parallel to mean sea level. However the GPS output can be confi gured to give correct information. GPS is not suffi ciently accurate enough to obtain the 1 mm precision that can be
achieved with a theodolite.

The principal types of foundations

Isolated Footings

Footings are understood formed by a rigid rectangular base of stone or concrete of dimensions : width B and length L, in which the ratio of L/B will not exceed 1.5.

The foundation structure will support the column load. The bearing capacity of the footing may be stimated, and its dimensions selected ; thereafter, a forcast of the settlement is made.

To illustrate the case pf footing foundations, consider a building with nine columns (Fig 1) supported on isolated footings. In this case, the footings will work independently of each other. Therefore, it is required that the differential settlements between footings will not exceed the allowable total and differential settlement requirements.

Figure 1: Isolated Footings

The differential settlements may be reduced selecting properly the area of the footings, and at times, using the stiffness of the superstructure.

From the structural point of view, however, the superstructure should not be allowed to take high secondary stresses induced bu the differential settlements of the footinhs, except in very special casees.

Singles footing foundations, in general, will be user only in soils of low compressibility and in structures where the differential settlements between columns may be controlled by the superstructure flexibility, or including in the design og the building joints or hinges that will take the differential settlements and/or rotations, respectively, without damaging the construction.

Continuous Footings

When it is necessary to control within certain limits the magnitude of differential settlements between columns supported on footings, and when soil deposits of medium or low compressibility atre encountered, it is recommended to use continuous footings. They may be defined as resisting elements joining columns together by foundation beams.

Continious footings are arraged by joining two or more columns together with beams.

The vertical differential displacements may be controlled via beam stiffness (Fig 2). The selection of the foundation beams, either running in one direction or the other along columns rows, depends largely on the layout of the column loads, and othe functional requirements concerning the structural and architectural design of the project.

Figure 2: Continuous Footings

For heavier loads, and when the project calls foor stiffness in both directions (namely, along column rows A, B and C also rows 1,2 and 3), the foundations is given stiffness with beams in both directions (Fig 3).

Figure 3: Continuous Footings

In this case, it may be observed that the footing slabs will cover practically all the foundation. This type of foundation using continuous footings is advantageous in soils of medium compressibility, where it is necessary to control differential movements between colomns.

The foundation beams are designed with the necessary stiffness to fulfill the differential settlements requirements.

Raft Foundation

When the loads are so largee that continious footings will occupy close to 50% of projected area of the building, it is more economical to use a continuous mat covering the entire area, as shown in Fig 4. The total load in this case may be assumed uniformly distributed in the area covered by the building.

The soil reaction is determined on the basis of a safe bearing capacity. The total and differential settlements may be investigated considering the stiffness of tthe raft or foundation slab is a matter of economy, compatible with the allowable differential settlements.

Figure .4 : Mat Foundations

Flexibility is important to obtain economy ; however, restrictions in differential vertical displacements between colmuns may call for certain slab stiffness, either by making it thicker or by placing foundation beams joining columns rows.

The beams can be designed with the required stiffness to reduce differential displacements.

This type of foundation may be used generally in soil deposits of medium compressibility ; however, in certain instances, the surface raft foundation may be used in soils of high and very high compressibility, where large total settlements may be allowed.

This type of foundation may be used efficiently in reduucing differential settlement.

Compensated Foundations

In soil deposits of medium, high and very high compressibility and low bearing capacity, compensated foundations are indicated.

This type of foundation requires a monolithic box foundation, as shown in Fig 5. When the water table is close to the ground surface, water proofing is necessary to use the buoyancy effect in designing the foundation.

Figure .5 : Compensated Foundation

In the design of compensated foundations, it should be borne in mind that the soil should be consedered as a material of two phases, namely : a solid and liquid phase.

Therefore, in a compensated foundation, the compensation is made by adding two effects :

Substitution of the submerged weight of solids.
The buoyancy effect by weight of liquid displaced.

Both effects are used to equalize the total weight of the building. The volume of the concrete box forming the foundation strructure annd basements will displace a weight of liquid that, according to Archimedes’ principal, will contribute in floating the foundation up to this value, reducing the load applied to the solid phase.

The load taken by the solid phase will, however, deform the soil because of the change in effective stresses induced in the soil structure. It shoul be investigated from the point of view of bearing capacity of the soil and total and differentioal settlements, as previously discussed for other foundations.

Compensated Foundations with Friction Piles

When a compensated foundation as described is not sufficient to support the load with the allowable total settlement, in spite of desigin the foundation with sufficient stiffness to avoid detrimental differential settlements within the foundation itself, friction piles may be used in addition to the concept of compensation.

This case may be present in deposits of high or very high compressibility extending to great depth. The piles will reinforce the upper part of the soil where a higher comopressibility is encountered.

The applicability of this foundation calls for a soil that varies from very high compressibility at the upper part of the deposit, to medium or low compressibility at the bottom (Fig 6).

Figure 6: Compensated friction pile Foundation

Point Bearing Pile Foundations

When the loads to be supported are higher than those a compensated friction pile foindation can take, the nit will be required to find a deep-seated hard stratum of low to very low compressibility and high shear strenth, where piles can be driven to point bearing. One can distinguish two cases of point bearing foundations (Fig 7 and Fig 8).

The first case is recognized when the hard stratum of convenient thickness is found underlain by materials of medium compressibility. In these cases the piles should be evenly distributed as shown in Fig 7. After solving the problem of point bearing of the piles in the hard stratum, there still existas the problem of finding if the lower compressible soil stratum will have a safe bearing value, and also if the total and differential settlements will be within the allowable values specified for the foundation in question.

This type of foundation should be designed with sufficient stiffness to control differential settlements.

The second type of pile fooundation is recognized wwhen the point bearing piles rest in a firm deposit of low compressibility extending to great despth (Fig 8). In this case, it is economical to use groups of piles to solve the foundation problem.

Figure 7 : Point Bearing Piles

Figure 8 : Point Bearing Piles in groups

The columns will rest on single footings supported on the piles. The piles driven in the firm stratum develop laterad friction contributing to the mechanical properties on shear strengh of the depostigs in whttich the are driven, on the spacing of the piles, on the length of penetration into the bearing stratum, and on the state of density and confinement of such stratum.

Pier Foundations

Pier foundations are used to support very heavy loads in buried soil deposits of very low compressibility (Fir 9). Their load capacity is a function of the mechanical properties of the soil under the base of the pier, and of the confining stress of the bearing stratum. Actuelly, the bearing capacity of such an element is determined as a deep-seated isolated footing.

Figure 9 : Pier Foundation

The piers, columns-like elements cast in place, in most cases carry high loads of 500 ton or moore ; therefore, the compressibility of the deposit on which the are resting should be very low, in order that they may be recommended.

Pier shafts may be used from dimensiosn are also a function of the procedure used to perform the excavation, and of the way the hydraulic conditions are handled. The density of the material wherre these elements aare bearing may be altered during excavations if an upward water flow is produced. Specially important is the case when the material is a cohesionless fine sediment or when the cohesion is small, in which case it is necessary to perform the excavation using a pneumatic system, introducing air under sufficient high pressure to balance the flow of water toward the bottom of the excavation, preserving the natural confining and density connditions of the bearing stratum.

Usually, if precautions are taken in the installation of these elements, the settlements will be very small. The settlement, however, may be estimated knowing the stress-strain characterictics of the strata encouontered under the base of the piers. The nagative friction on these elements may take large proportions : hence, it shoul be estimated.

When these rigid elements are used in seismic regions to support loads through deposits of high and very high compressibility, it is necessary to investigate the effect ot the horizontal motion of the soil mass during earthquakes. The horizontal drift forces against the piears because of soil displacement should not be overlooked. In occasions, rigid elements have been damaged because of the strong horizontal motions produced bu the earthquakes.

Sand Pier Foundations

The solution of foundations using sand pier or sand piles is shown in Fig 10.

Figure 10 : Sand Piers

This type of foundation is used to increase the load capacity of the soil by reducing its compressibility and increasing its shear strength capacity properties. This type of pile may be used in loose or medium dense sand deposits.

The improvement of the subsoil is a function of the volume of sand introduced at the time thses elements are installed. Usually first a hole is driven in the ground, then sand is introduced and highly compacted in layers, using a heavy ram.

The sand element will take the load because of the lateral confinement given by the subsoil. The deformation of these elements may be estimated by means of the stress-strain properties of the sand ussed, considering the pier as a long sand cylinder laterally confined bu the soil. This type of foundation is only recommended in places where the cost of cement is very high, and good aggregates to fabricate concrete are difficult to obtain.

SOIL NAILING TECHNIQUE AND TYPES

Soil nailing is a construction technique that we use to reinforce soil to make it more stable. We use this technique for slopes, excavations, retaining walls etc. to make it more stable.

In this technique, soil is reinforced with slender elements such as reinforcing bars which are called as nails. These reinforcing bars are installed into pre-drilled holes and then grouted.

These nails are installed at an inclination of 10 to 20 degrees with vertical.

Soil nailing is used to stabilize the slopes or excavations where required slopes for excavation cannot be provided due to space constraints and construction of retaining wall is not feasible. It is just an alternate to retaining wall structures.

As the excavation proceeds, the shotcrete, concrete or other grouting materials are applied on the excavation face to grout the reinforcing steel or nails. These provide stability to the steep soil slope.

Types of Soil Nailing:

There are various types of soil nailing techniques:

Grouted Soil Nailing:

In this type of soil nailing, the holes are drilled in walls or slope face and then nails are inserted in the pre-drilled holes. Then the hole is filled with grouting materials such as concrete, shotcrete etc.

Driven Nails:

Driven nailing is used for temporary stabilization of soil slopes. In this method, the nails are driven in the slope face during excavation. This method is very fast, but does not provide corrosion protection to the reinforcement steel or nails.

Self drilling Soil Nail:

In this method, the hollow bars are used. Hollow bars are drilled into the slope surface and grout is injected simultaneously during the drilling process. This method of soil nailing is faster than grouted nailing. This method provides more corrosion resistance to nails than driven nails.

Jet Grouted Soil Nail:

In this method, jets are used for eroding the soil for creating holes in the slope surface. Steel bars are then installed in this hole and grouted with concrete. It provides good corrosion protection for the steel bars (nails).

Launched Soil Nail:

In this method of soil nailing, the steel bars are forced into the soil with very high speed using compressed air mechanism. The installation of soil nails are fast, but control over length of bar penetrating the ground is difficult.

These points must be noted for installation of soil nails:

Soil Nails must penetrate beyond the slip plane into the passive zone typically for 4 to 5m.
The spacing of soil nails in horizontal or vertical direction must be related to strength of the soil. Extra soil nails should be installed at the edge of any surface being stabilized.
Soil nailing should start immediately after excavation. Any delay may lead to collapse of soil slope.

Learn What Is Photogrammetry And Its Various Applications

In this article, we are presenting a brief introduction to what is photogrammetry and its various applications for those who are new to this technology.

What is Photogrammetry?

In a straightforward language, Photogrammetry is a technology that combines photography and geometry. It has a significant impact on the current architectural works.

As the name implies, Photogrammetry is a 3-Dimensional coordinate measuring method that makes use of photographs as the primary medium for measurement. The classical definition of the Photogrammetry is the simple process of deriving metric information about an object through measurements made on the photograph of that object.

Furthermore, photogrammetry is the science or the art of making measurements from the photographs. It means the measuring of features on photographs.

Photogrammetry uses the fundamental principles of triangulation called as Aerial Triangulation. In this method, a photograph gets snap from at least two different locations called “Line of sight,” and it can develop from each camera to points on the object.
The mathematical intersection of these lines can generate the 3D coordinates of the points of interest.

History of Photogrammetry

The Photogrammetry method was initially in use by the Prussian Architect in 1867 who designed some of the earliest topographic maps and some elevation drawings. The photogrammetry service in the topographic mapping is well-established but in the current scenario, the application of photogrammetry is common in the fields of architecture, engineering, forensic, underwater, medicine and much more for the production of accurate 3D data.

The term photogrammetry describes from the three simple words:
‘Photo’ – Light
‘gram’ – Drawing
‘metry’ – Measurement
“Photogrammetry means Light Drawing Measurement”

The output of this method is typically a map, drawings, measurement or a 3D model of some real-world objects. Many of the maps we are using are generated with the help of this technique, while the photographs are taken from the aircrafts.

Application of Photogrammetry

The categorization of the photogrammetry is based on the camera location during the actual photography. On these terms, we have Aerial Photogrammetry, Terrestrial Photogrammetry and Space Photogrammetry.
Now let’s understand each application of Photogrammetry in detail.

Aerial Photogrammetry

In this type of photogrammetry, the cameras are launch on a machine that flies aircraft and therefore takes pictures. These pictures are useful in generating the measurements. In this case, for the statistical comparisons, at least two photos of the same object or surface are clicked. This type of photography uses special design planes.

The aircrafts fly over a preset piece of land, pointed with a particular landmark. The camera speed is controlling accordingly to the speed of the plane. Also, the height of the plane from the land is initially defined. The stereo-plotter (an instrument that allows an operator to view two photos at once in a stereo view) processes the photographs. The photographs are also useful in automation processing for Digital Elevation Model (DEM) creation.

Terrestrial Photogrammetry

It is this kind of Photogrammetry technique in which the camera is usable in a stationary position, and hence photographs need to capture from a fixed, known position on or near the ground. The camera tilt and other specifications are in command. Photo Theodolite is a unique instrument that utilizes in exploring the photographs.

Space Photogrammetry

The space photogrammetry adapts all the aspects of extraterrestrial photography as well as measurements wherein the camera is non-moving on the earth or place on artificial satellite or in the space.

The term Photo Interpretation is applicable to that branch of photogrammetry wherein aerial or terrestrial photographs utilize to calculate, analyze, classify and interpret images of objects that are visible on the photographs. As a result, Photogrammetry is a combination of measurement and interpretation of a particular object.

Advantages of Photogrammetry

Photogrammetry has numerous advantages that are beneficial in modern construction as well as various other sectors like:

Covers large areas quickly.
The photogrammetry technique is cost-efficient.
The method is the easiest way to obtain or access information from the air.
The photographic images illustrate great details.

Application of Photogrammetry

To quickly verify the spatial positions of the ground objects.
To prepare topographical maps (surveying/mapping).
Helpful in Military/Artificial Intelligence.
For the interpretation of Geology/Archaeology.
Analysis of crop damages due to floods or other natural disasters.
To prepare a composite picture of ground objects.
To relocate existing boundaries of properties.
Helpful in the field of medicine.

The photogrammetry can generate a data set that will help many organizations or the stakeholders, therefore, helping to create most efficient and effective plan for any construction project.

Laser Scanning Technology and Its Advantages in Construction Industry

Laser Scanning is a method of collecting external data using a laser scanner which captures the actual distance of densely scanned points over a given object at breakneck speed. The process is usually known as a point cloud survey or as light detection and ranging (LIDAR, a combo of the words ‘light’ and ‘radar’).

Laser scanning is currently acquiring the impetus in the construction industry for its competency in helping Building Teams to collect tons of remarkably authentic information in a very short span of time. When done in a perfect way, Laser scanning can prove to be beneficial to all the involved parties in the life cycle of the project.

The laser scanning method can be used to create 3D representations that can be converted for use in 3D CAD modeling or BIM (Building Information Modeling).

While the construction industry is relatively gradual in adopting the newer technology, the designers and the construction professionals are challenging themselves to complete the project in rapid pace with the use technologies like BIM and custom-designed apps. The 3D laser scanning is less promoted technology in the adoption phase, though the AEC industry is now noticing the benefits of laser scanning can bring the boost in their projects.

Accuracy:

The laser scanning technology determines to be much quicker, more exact and inexpensive than the traditional survey measurement. The exactness of the process depends on the stability of the instrument base and the distance from the object.

Benefits of using the Laser Scanning Technology in Construction Industry

Laser Scanning has been a boon to the construction industry that allows obtaining a level of detail, accuracy which was not feasible with the other traditional methods. Let’s have a brief look at the benefits of implementing the Laser Scanning technology to build in a smarter way.

Enhanced Planning and Designing

Using the laser scanning method, a tremendous boost in planning and designing is seen. The clashes between newly designed elements and existing conditions have been analyzed before the construction. The exactness of dimensions obtained from laser scans can also help improve planning by providing exact measurements for destruction and removal of components as well as assist in minimizing the waste materials.

Reduction in cost and Schedule

It has been seen that the 3D scanning can curtail the total project cost by 5% to 7%. The scanning can be performed in minimal hours to a few days, depending on the site as compared to several weeks in the traditional data collection methods.

Safety and Regulatory Agreement

The Laser scanning methods are often safer that the manual data collection method and are increasingly used to help satisfy with health, safety, and environmental responsibilities. The features such as remote sensing ability and quick data capture of the laser scanner trim the teams’ exposure to harmful environments. For example, when used in nuclear power plants, the laser scanner helps in reducing the size and the time of group’s exposure to the high radiation areas.

The laser scanning provides booming methods for surveying remote surfaces as well as complex geometrical surfaces are also surveyed with absolute ease. All the major providers of CAD 3D modeling and BIM have built compatibility that acknowledges their system to import the point cloud data into the 3D visual graphic material.

The use of drones with laser scanning has indeed become a recognized method of getting the exact detail of topography. LIDAR has been widely used for surveys from rail to the road vehicles. The instrument can easily operate at night when the targeted surfaces are less interfere with people and can produce outstanding accuracy.

What is 3D Concrete Printing? Its advantages and disadvantages

What is 3D Concrete Printing? It’s advantages and disadvantages

Imagine a 3D print you get, of your dream home before the actual construction starts, wow that’s amazing! You can then even make the changes if you wish to or can even design the better ideas. Yes, 3D printing proving to be a revolutionary tool in this behemoth world of construction technology and management.

The construction industry in today’s scenario is known for its ability to adapt quickly or frequently the new innovative ideas that can raise the building sector. One the most innovations in this area are 3D printing. Let’s have a close look at what 3D printing is and how can it be beneficial in transforming into a lean, responsive sector.

3D printing these days is gaining more and more traction and has potential to ease some of the aches of the construction technology and management industry. 3D printing, which is the domain of engineering possibly, could make an extreme change in the ways that our building structures are built. Yes, the 3D printing technique is being looked like a must-have technology in the construction industry.

First a quick look on…

What 3D Printing Means?

3D printing is a production method of creating solid objects from a digital source uploaded to a 3D printer. The printer intelligently reads the files and lays down consecutive layers of materials such as plastic, resins, concrete, sand, metals until the entire object is created.

Unlike inkjet printers, a 3D printer has containers of raw material, like plastic which forces out the exact patterns to lay down layers.

Currently, 3D printers are only used to create 3D models of structural designs, various prototypes, landscaping bricks or decorative components. Uses of 3D Printers in Construction Technology and Management

3D printers are already in use in the construction industry. Gigantic 3D printers have already been built that can use solid materials to manufacture a variety of the major structural components, even the whole buildings.

Initially, printers can only extrude one type of equipment at a time, but now with the advent in the technology world, more advanced printers have been built that can extrude multiple materials providing a significant level of speed and resilience that was not before.

The printers may manufacture wall sections that can snap together like Lego’s, or they may print formative stage that can be latterly filled to create a full-size wall. The printer can be shifted to a construction site to manufacture on demand.

Benefits of 3D Printing in Construction

The 3D printing benefits include:

Consumption of material is optimized.
Increases the ability to design a larger variety of customized homes and buildings.
The construction waste is saved.
Huge save in labour cost
Growth in productivity.
Faster construction.
Quality can be maintained.

Some disadvantages of 3D printing include:

Reduced employee number in theconstruction industryas the machine does most of the work.
A finite number of materials can be used since the printer cannot be able to print the required design in various materials.
Transportation of printers on job site becomes risky.
Any errors occur in a digital model can result in an uncertain situation on site during the printing or construction phase.

What is a Landslide?

Geologists, engineers, and other professionals often rely on unique and slightly differing definitions of landslides. This diversity in definitions reflects the complex nature of the many disciplines associated with studying landslide phenomena.

For our purposes, landslide is a general term used to describe the downslope movement of soil, rock, and organic materials under the effects of gravity and also the landform that results from such movement (please see figure 1 for an example of one type of landslide).

Figure 1. This landslide occurred at La Conchita, California, USA, in 2005. Ten people were killed. (Photograph by Mark Reid, U.S. Geological Survey.)

Varying classifications of landslides are associated with specific mechanics of slope failure and the properties and characteristics of failure types; these will be discussed briefly herein.

Figure 2. A simple illustration of a rotational landslide that has evolved into an earthflow. Image illustrates commonly used labels for the parts of a landslide (from Varnes, 1978, Reference 43).

There are a number of other phrases/terms that are used interchangeably with the term “landslide” including mass movement, slope failure, and so on. One commonly hears such terms applied to all types and sizes of landslides.
Regardless of the exact definition used or the type of landslide under discussion, understanding the basic parts of a typical landslide is helpful.

Figure 2 shows the position and the most common terms used to describe the unique parts of a landslide.