In transport engineering, subgrade is the native material underneath a constructed road, pavement or railway track. It is called formation level; the term can refer to imported material, used to build an embankment. Subgrades are compacted before the construction of a road, pavement or railway track, are sometimes stabilized by the addition of asphalt, portland cement or other modifiers; the subgrade is the foundation of the pavement structure. The load-bearing strength of subgrade is measured by California Bearing Ratio test, falling weight deflectometer backcalculations and other methods. Subsoil Track bed
Wattle and daub
Wattle and daub is a composite building material used for making walls, in which a woven lattice of wooden strips called wattle is daubed with a sticky material made of some combination of wet soil, sand, animal dung and straw. Wattle and daub has been used for at least 6,000 years and is still an important construction material in many parts of the world. Many historic buildings include wattle and daub construction, the technique is becoming popular again in more developed areas as a low-impact sustainable building technique; the wattle is made by weaving thin slats between upright stakes. The wattle may be made as loose panels, slotted between timber framing to make infill panels, or made in place to form the whole of a wall. In different regions, the material of wattle can be different. For example, in Mitchell Site on the northern outskirts of the city of Mitchell, South Dakota, willow has been found as the wattle material of the walls of the house. Reeds and vines can be used as wattle material.
The origin of the term wattle describing a group of acacias in Australia, is derived from the common use of acacias as wattle in early Australian European settlements. Daub is created from a mixture of ingredients from three categories: binders and reinforcement. Binders hold the mix together and can include clay, chalk dust and limestone dust. Aggregates give the mix its bulk and dimensional stability through materials such as mud, crushed chalk and crushed stone. Reinforcement is provided by straw, hay or other fibrous materials, helps to hold the mix together as well as to control shrinkage and provide flexibility; the daub may be by treading -- either by humans or livestock. It is applied to the wattle and allowed to dry, then whitewashed to increase its resistance to rain. Sometimes there can be more than one layer of daub. Still in Mitchell Site, the anterior of the house had double layers of burned daub; this process has been replaced in modern architecture by lath and plaster, a common building material for wall and ceiling surfaces, in which a series of nailed wooden strips are covered with plaster smoothed into a flat surface.
In many regions this building method has itself been overtaken by drywall construction using plasterboard sheets The wattle and daub technique was used in the Neolithic period. It was common for houses of a Linear pottery and Rössen cultures of Central Europe, but is found in Western Asia as well as in North America and South America. In Africa it is common in the architecture of traditional houses such as those of the Ashanti people, its usage dates back at least 6000 years. There are suggestions that construction techniques such as lath and plaster and cob may have evolved from wattle and daub. Fragments from prehistoric wattle and daub buildings have been found in Africa, Europe and North America. A review of English architecture reveals that the sophistication of this craft is dependent on the various styles of timber frame housing; as discussed earlier, there were two popular choices for wattle and daub infill paneling: close-studded paneling and square paneling. Close-studding panels create a much more narrow space between the timbers: anywhere from 7 to 16 inches.
For this style of panel, weaving is too difficult, so the wattles run horizontally and are known as ledgers. The ledgers are sprung into each upright timber through a system of augered holes on one side and short chiseled grooves along the other; the holes are drilled at a slight angle towards the outer face of each stud. This allows room for upright hazels to be tied to ledgers from the inside of the building; the horizontal ledgers are placed every two to three feet with whole hazel rods positioned upright top to bottom and lashed to the ledgers. These hazel rods are tied a finger widths apart with 6–8 rods each with a 16-inch width. Gaps allow key formation for drying. Square panels are large, wide panels typical of some timber frame houses; these panels may be square in shape, or sometimes triangular to accommodate arched or decorative bracing. This style does require wattles to be woven for better support of the daub. To insert wattles in a square panel several steps are required. First, a series of evenly spaced holes are drilled along the middle of the inner face of each upper timber.
Next, a continuous groove is cut along the middle of each inner face of the lower timber in each panel. Vertical slender timbers, known as staves, are inserted and these hold the whole panel within the timber frame; the staves are positioned into the holes and sprung into the grooves. They must be placed with sufficient gaps to weave the flexible horizontal wattles. In some places or cultures, the technique of wattle and daub were used with different materials thus has different names, including pug and pine and stud, hourdis and dab, pierrotage/bousillage and columage. Bajarreque and jacal are examples of structure built with the technique of daub. In the early days of the colonisation of South Australia, in areas where substantial timber was unavailable, pioneers' cottages and other small buildings were constructed with light vertical timbers, which may have been "native pine", driven into the ground, the gaps being stopped with pug. Another term for this construction is pug. "Mud and stud" is a similar process to wattle and daub, with a simple frame consisting only of upright studs joined by cross r
Adobe is a building material made from earth and organic materials. Adobe is Spanish for mudbrick, but in some English-speaking regions of Spanish heritage, the term is used to refer to any kind of earth construction. Most adobe buildings rammed earth buildings. Adobe is among the earliest building materials, is used throughout the world. Adobe bricks are rectangular prisms small enough that they can air dry individually without cracking, they can be subsequently assembled, with the application of adobe mud to bond the individual bricks into a structure. There is no standard size, in different regions. In some areas a popular size measured 8 by 4 by 12 inches weighing about 25 pounds; the maximum sizes can reach up to 100 pounds. In dry climates, adobe structures are durable, account for some of the oldest existing buildings in the world. Adobe buildings offer significant advantages due to their greater thermal mass, but they are known to be susceptible to earthquake damage if they are not somehow reinforced.
Cases where adobe structures were damaged during earthquakes include the 1976 Guatemala earthquake, the 2003 Bam earthquake, the 2010 Chile earthquake. Buildings made of sun-dried earth are common throughout the world Adobe had been in use by indigenous peoples of the Americas in the Southwestern United States and the Andes for several thousand years. Puebloan peoples built their adobe structures with handsful or basketsful of adobe, until the Spanish introduced them to making bricks. Adobe bricks were used in Spain from Iron Ages, its wide use can be attributed to its simplicity of design and manufacture, economics. A distinction is sometimes made between the smaller adobes, which are about the size of ordinary baked bricks, the larger adobines, some of which may be one to two yards long; the word adobe has existed for around 4000 years with little change in either pronunciation or meaning. The word can be traced from the Middle Egyptian word ɟbt "mud brick". Middle Egyptian evolved into Late Egyptian, Demotic or "pre-Coptic", to Coptic, where it appeared as τωωβε tōʾpə.
This was adopted into Arabic as الطوب aṭ-ṭawbu or aṭ-ṭūbu, with the definite article al- attached. Tuba, This was assimilated into the Old Spanish language as adobe via Mozarabic. English borrowed the word from Spanish in the early 18th century, still referring to mudbrick construction. In more modern English usage, the term "adobe" has come to include a style of architecture popular in the desert climates of North America in New Mexico, regardless of the construction method. An adobe brick is a composite material made of earth mixed with water and an organic material such as straw or dung; the soil composition contains sand and clay. Straw is useful in binding the brick together and allowing the brick to dry evenly, thereby preventing cracking due to uneven shrinkage rates through the brick. Dung offers the same advantage; the most desirable soil texture for producing the mud of adobe is 15% clay, 10–30% silt, 55–75% fine sand. Another source quotes 15–25% clay and the remainder sand and coarser particles up to cobbles 50 to 250 mm, with no deleterious effect.
Modern adobe is stabilized with Portland cement up to 10 % by weight. No more than half the clay content should be expansive clays, with the remainder non-expansive illite or kaolinite. Too much expansive clay results in uneven drying through the brick, resulting in cracking, while too much kaolinite will make a weak brick; the soils of the Southwest United States, where such construction has been used, are an adequate composition. Adobe walls are load bearing, i.e. they carry their own weight into the foundation rather than by another structure, hence the adobe must have sufficient compressive strength. In the United States, most building codes call for a minimum compressive strength of 300 lbf/in2 for the adobe block. Adobe construction should be designed so as to avoid lateral structural loads that would cause bending loads; the building codes require the building sustain a 1 g lateral acceleration earthquake load. Such an acceleration will cause lateral loads on the walls, resulting in shear and bending and inducing tensile stresses.
To withstand such loads, the codes call for a tensile modulus of rupture strength of at least 50 lbf/in2 for the finished block. In addition to being an inexpensive material with a small resource cost, adobe can serve as a significant heat reservoir due to the thermal properties inherent in the massive walls typical in adobe construction. In climates typified by hot days and cool nights, the high thermal mass of adobe mediates the high and low temperatures of the day, moderating the temperature of the living space; the massive walls require a large and long input of heat from the sun and from the surrounding air before they warm through to the interior. After the sun sets and the temperature drops, the warm wall will continue to transfer heat to the interior for several hou
Soil is a mixture of organic matter, gases and organisms that together support life. Earth's body of soil, called the pedosphere, has four important functions: as a medium for plant growth as a means of water storage and purification as a modifier of Earth's atmosphere as a habitat for organismsAll of these functions, in their turn, modify the soil; the pedosphere interfaces with the lithosphere, the hydrosphere, the atmosphere, the biosphere. The term pedolith, used to refer to the soil, translates to ground stone in the sense "fundamental stone". Soil consists of a solid phase of minerals and organic matter, as well as a porous phase that holds gases and water. Accordingly, soil scientists can envisage soils as a three-state system of solids and gases. Soil is a product of several factors: the influence of climate, relief and the soil's parent materials interacting over time, it continually undergoes development by way of numerous physical and biological processes, which include weathering with associated erosion.
Given its complexity and strong internal connectedness, soil ecologists regard soil as an ecosystem. Most soils have a dry bulk density between 1.1 and 1.6 g/cm3, while the soil particle density is much higher, in the range of 2.6 to 2.7 g/cm3. Little of the soil of planet Earth is older than the Pleistocene and none is older than the Cenozoic, although fossilized soils are preserved from as far back as the Archean. Soil science has two basic branches of study: pedology. Edaphology studies the influence of soils on living things. Pedology focuses on the formation and classification of soils in their natural environment. In engineering terms, soil is included in the broader concept of regolith, which includes other loose material that lies above the bedrock, as can be found on the Moon and on other celestial objects as well. Soil is commonly referred to as earth or dirt. Soil is a major component of the Earth's ecosystem; the world's ecosystems are impacted in far-reaching ways by the processes carried out in the soil, from ozone depletion and global warming to rainforest destruction and water pollution.
With respect to Earth's carbon cycle, soil is an important carbon reservoir, it is one of the most reactive to human disturbance and climate change. As the planet warms, it has been predicted that soils will add carbon dioxide to the atmosphere due to increased biological activity at higher temperatures, a positive feedback; this prediction has, been questioned on consideration of more recent knowledge on soil carbon turnover. Soil acts as an engineering medium, a habitat for soil organisms, a recycling system for nutrients and organic wastes, a regulator of water quality, a modifier of atmospheric composition, a medium for plant growth, making it a critically important provider of ecosystem services. Since soil has a tremendous range of available niches and habitats, it contains most of the Earth's genetic diversity. A gram of soil can contain billions of organisms, belonging to thousands of species microbial and in the main still unexplored. Soil has a mean prokaryotic density of 108 organisms per gram, whereas the ocean has no more than 107 procaryotic organisms per milliliter of seawater.
Organic carbon held in soil is returned to the atmosphere through the process of respiration carried out by heterotrophic organisms, but a substantial part is retained in the soil in the form of soil organic matter. Since plant roots need oxygen, ventilation is an important characteristic of soil; this ventilation can be accomplished via networks of interconnected soil pores, which absorb and hold rainwater making it available for uptake by plants. Since plants require a nearly continuous supply of water, but most regions receive sporadic rainfall, the water-holding capacity of soils is vital for plant survival. Soils can remove impurities, kill disease agents, degrade contaminants, this latter property being called natural attenuation. Soils maintain a net absorption of oxygen and methane and undergo a net release of carbon dioxide and nitrous oxide. Soils offer plants physical support, water, temperature moderation and protection from toxins. Soils provide available nutrients to plants and animals by converting dead organic matter into various nutrient forms.
A typical soil is about 50% solids, 50% voids of which half is occupied by water and half by gas. The percent soil mineral and organic content can be treated as a constant, while the percent soil water and gas content is considered variable whereby a rise in one is balanced by a reduction in the other; the pore space allows for the infiltration and movement of air and water, both of which are critical for life existing in soil. Compaction, a common problem with soils, reduces this space, preventing air and water from reaching plant roots and soil organisms. Given sufficient time, an undifferentiated soil will evolve a soil profile which consists of two or more layers, referred to as soil horizons, that differ in one or more properties such as in their texture, density, consistency, temperature and reactivity; the horizons differ in thickness and gene
Rammed earth known as taipa in Portuguese, tapial or tapia in Spanish, pisé in French, hangtu, is a technique for constructing foundations and walls using natural raw materials such as earth, lime, or gravel. It is an ancient method, revived as a sustainable building material used in a technique of natural building. Rammed earth is simple to manufacture, non-combustible, thermally massive and durable. However, structures such as walls can be laborious to construct of rammed earth without machinery, e. g. powered tampers, they are susceptible to water damage if inadequately protected or maintained. Edifices formed of rammed earth are on every continent except Antarctica, in a range of environments including temperate, semiarid desert and tropical regions; the availability of suitable soil and a building design appropriate for local climatic conditions are the factors that favour its use. Manufacturing rammed earth involves compressing a damp mixture of earth that has suitable proportions of sand, clay, and/or an added stabilizer into an externally supported frame or mold, forming either a solid wall or individual blocks.
Additives such as lime or animal blood were used to stabilize it, while modern construction adds lime, cement, or asphalt emulsions. To add variety, some modern builders add coloured oxides or other materials, e.g. bottles, tires, or pieces of timber. The construction of an entire wall begins with a temporary frame, denominated the "formwork", made of wood or plywood, as a mold for the desired shape and dimensions of each section of wall; the form must be durable and well braced, the two opposing faces must be clamped together to prevent bulging or deformation caused by the large compressing forces. Damp material is poured into the formwork to a depth of 10 to 25 cm and compacted to 50% of its original height; the material is compressed iteratively, in batches or courses, so as to erect the wall up to the top of the formwork. Tamping was manual with a long ramming pole, was laborious, but modern construction can be made less so by employing pneumatically powered tampers. After a wall is complete, it is sufficiently strong to remove the formwork.
This is necessary if a surface texture is to be applied, e.g. by wire brushing, carving, or mold impression, because the walls become too hard to work after one hour. Construction is optimally done in warm weather so that the walls can harden; the compression strength of the rammed earth increases. Exposed walls must be sealed to prevent water damage. In modern variations of the technique, rammed-earth walls are constructed on top of conventional footings or a reinforced concrete slab base. Where blocks made of rammed earth are used, they are stacked like regular blocks and are bonded together with a thin mud slurry instead of cement. Special machines powered by small engines and portable, are used to compress the material into blocks. Presently more than 30% of the world's population uses earth as a building material. Rammed earth has been used globally in a wide range of climatic conditions. Rammed-earth housing may resolve homelessness caused by otherwise expensive construction techniques; the compressive strength of rammed earth is a maximum of 4.3 MPa.
This is more than sufficiently strong for domestic edifices. Indeed, properly constructed rammed earth endures for thousands of years, as many ancient structures that are still standing around the world demonstrate. Rammed earth reinforced with rebar, wood, or bamboo can prevent collapse caused by earthquakes or heavy storms, because unreinforced edifices of rammed earth resist earthquake damage poorly. See 1960 Agadir earthquake for an example of the total destruction which may be inflicted on such structures by an earthquake. Adding cement to soil mixtures poor in clay can increase the load-bearing capacity of rammed-earth edifices; the United States Department of Agriculture observed in 1925 that rammed-earth structures endure indefinitely and can be constructed for less than two-thirds of the cost of standard frame houses. Soil is a available and sustainable resource. Therefore, construction with rammed earth is viable. Unskilled labour can do most of the necessary work. While the cost of rammed earth is low, rammed-earth construction without mechanical tools is time-consuming and laborious.
One significant benefit of rammed earth is its high thermal mass: like brick or concrete, it can absorb heat during daytime and nocturnally release it. This action moderates daily temperature variations and reduces the need for air conditioning and heating. In colder climates, rammed-earth walls can be insulated with a similar insert, it must be protected from heavy rain and insulated with vapour barriers. Rammed earth can regulate humidity if unclad walls containing clay are exposed to an internal space. Humidity is regulated between 40% and 60%, the ideal range for asthma sufferers and for the storage of susceptible objects such as books; the material mass and clay content of rammed earth allows an edifice to breathe more than concrete edifices, which avoids problems of condensation but prevents significant loss of heat. Untouched, rammed-earth w
A soil horizon is a layer parallel to the soil surface, whose physical and biological characteristics differ from the layers above and beneath. Horizons are defined in many cases by obvious physical features colour and texture; these may be described both in absolute terms and in terms relative to the surrounding material, i.e. ‘coarser’ or ‘sandier’ than the horizons above and below. The identified horizons are indicated with symbols, which are used in a hierarchical way. Master horizons are indicated by capital letters. Suffixes, in form of lowercase letters and figures, further differentiate the master horizons. There are many different systems of horizon symbols in the world, it should be emphasised that no one system is more correct – as artificial constructs, their utility lies in their ability to describe local conditions in a consistent manner. Due to the different definitions of the horizon symbols, the systems cannot be mixed. Below, some of these systems will be described. In most soil classification systems, horizons are used to define soil types.
Some systems use entire horizon sequences for definition. Other systems pick out certain horizons, the “diagnostic horizons”, for the definition, e.g. the World Reference Base for Soil Resources, the USDA soil taxonomy and the Australian Soil Classification. Diagnostic horizons are indicated with names, e.g. the “cambic horizon” or the “spodic horizon”. The WRB, e.g. lists 37 diagnostic horizons. Of course, besides these diagnostic horizons, some other soil characteristics may be needed to define a soil type; some soils don’t have a clear development of horizons. A soil horizon sensu stricto is a result of soil-forming processes. Layers that do not have undergone such processes may be called “layers”; some soil scientists use the word layer in a more general way, including the horizons sensu stricto. Many soils have an organic surface layer, denominated with a capital letter; the mineral soil starts with an A horizon. If a well-developed subsoil horizon as a result of soil formation exists, it is called a B horizon.
An underlying loose, but poorly developed horizon is called a C horizon. Hard bedrock is denominated R. Most individual systems defined more layers than just these five. In the following, the horizons and layers are listed more or less by their position from top to bottom within the soil profile. Not all of them are present in every soil. Soils with a history of human interference, for instance through major earthworks or regular deep ploughing, may lack distinct horizons completely; when examining soils in the field, attention must be paid to the local geomorphology and the historical uses, to which the land has been put, in order to ensure that the appropriate names are applied to the observed horizons. O horizon The "O" stands for organic matter, it is a surface layer, dominated by the presence of large amounts of organic matter in varying stages of decomposition. In the Australian system, the O horizon should be considered distinct from the layer of leaf litter covering many vegetated areas, which contains no weathered mineral particles and is not part of the soil itself.
O horizons may be divided 3 categories: fibric and sapric. Oi horizons contain decomposed matter whose origin can be spotted on sight, Oe horizons contain intermediately decomposed organic matter, Oa horizons contain only well-decomposed organic matter, the origin of, not visible; the O horizon is greater than 20% organic matter by weight. P horizon These horizons are heavily organic, but are distinct from O horizons in that they form under waterlogged conditions; the "P" designation comes from peats. They may be divided into P2 in the same way as O horizons. A horizon The A horizon is the top layer of the mineral soil horizons referred to as'topsoil'; this layer contains dark decomposed organic matter, called "humus". The technical definition of an A horizon may vary between the systems, but it is most described in terms relative to deeper layers. "A" horizons may be darker in colour than deeper layers and contain more organic matter, or they may be lighter but contain less clay or pedogenic oxides.
The A is a surface horizon, as such is known as the zone in which most biological activity occurs. Soil organisms such as earthworms, arthropods, nematodes and many species of bacteria and archaea are concentrated here in close association with plant roots. Thus, the A horizon may be referred to as the biomantle. However, since biological activity extends far deeper into the soil, it cannot be used as a chief distinguishing feature of an A horizon; the A horizon may be further subdivided into A1, A2 and A3. E horizon “E”, being short for eluviated, is most used to label a horizon, leached of its mineral and/or organic content, leaving a pale layer composed of silicates or silica; these are present only in older, well-developed soils, occur between the A and B horizons. In systems where this designation is not employed, leached layers are classified firstly as an A or B according to other characteristics, appended with the designation “e”. In soils that contain gravels, due to animal bioturbation, a stonelayer forms near or
In geology, bedrock is the lithified rock that lies under a loose softer material called regolith within the surface of the crust of the Earth or other terrestrial planets. Bedrock refers to the substructure composed of hard rock exposed or buried at the earths surface, an exposed portion of bedrock is called an outcrop. Bedrock may have various chemical and mineralogical compositions and can be igneous, metamorphic or sedimentary in origin; the bedrock may be overlain by weathered regolith which includes soil and the subsoil. The surface of the bedrock beneath the soil cover is known as rockhead in engineering geology, its identification by digging, drilling or geophysical methods is an important task in most civil engineering projects. Superficial deposits can be thick, such that the bedrock lies hundreds of meters below the surface. Bedrock when exposed or within the subsurface may experience weathering and erosion by external factors. Weathering may be physical or chemical and alters the structure of the rock and may cause it to erode and or alter over time based on the interactions between the mineralogy and its interactions.
Bedrock may experience subsurface weathering at its upper boundary, forming saprolite. A geologic map of an area will show the distribution of differing bedrock types, rock that would be exposed at the surface if all soil or other superficial deposits were removed. Geology – The study of the composition, physical properties, history of Earth's components, the processes by which they are shaped. Outcrop Regolith – A layer of loose, heterogeneous superficial deposits covering solid rock Soil – mixture of organic matter, gases and organisms that together support life Weathering – Breaking down of rocks and minerals as well as artificial materials through contact with the Earth's atmosphere and waters Rafferty, John P. "Bedrock GEOLOGY". Encyclopedia Britannica. Encyclopedia Britannica. Retrieved 1 April 2019. Harris, The Gale Encyclopedia of Science. Ed. K. Lee Lerner and Brenda Wilmoth Lerner. Vol. 1. 5th ed. Farmington Hills, MI: Gale, 2014. P515-516. Media related to Bedrock at Wikimedia Commons