Tunnel in the context of "Road design"

Infrastructure is the set of facilities and systems that serve a country, city, or other area, and encompasses the services and facilities necessary for its economy, households and firms to function. Infrastructure is composed of public and private physical structures such as roads, railways, bridges, airports, public transit systems, tunnels, water supply, sewers, electrical grids, and telecommunications (including Internet connectivity and broadband access). In general, infrastructure has been defined as "the physical components of interrelated systems providing commodities and services essential to enable, sustain, or enhance societal living conditions" and maintain the surrounding environment.

Especially in light of the massive societal transformations needed to mitigate and adapt to climate change, contemporary infrastructure conversations frequently focus on sustainable development and green infrastructure. Acknowledging this importance, the international community has created policy focused on sustainable infrastructure through the Sustainable Development Goals, especially Sustainable Development Goal 8 "Industry, Innovation and Infrastructure".

Gunpowder, also commonly known as black powder to distinguish it from modern smokeless powder, is the earliest known chemical explosive. It consists of a mixture of sulfur, charcoal (which is mostly carbon), and potassium nitrate (saltpeter). The sulfur and charcoal act as fuels, while the saltpeter is an oxidizer. Gunpowder has been widely used as a propellant in firearms, artillery, rocketry, and pyrotechnics, including use as a blasting agent for explosives in quarrying, mining, building pipelines, tunnels, and roads.

Gunpowder is classified as a low explosive because of its relatively slow decomposition rate, low ignition temperature and consequently low brisance (breaking/shattering). Low explosives deflagrate—burning at subsonic speeds—whereas high explosives detonate, producing a supersonic shockwave. Ignition of gunpowder packed behind a projectile generates enough pressure to force the shot from the muzzle at high speed, but usually not enough force to rupture the gun barrel. It thus makes a good propellant but is less suitable for shattering rock or fortifications with its low-yield explosive power. Nonetheless, it was widely used to fill fused artillery shells (and used in mining and civil engineering projects) until the second half of the 19th century, when the first high explosives were put into use.

Coastal erosion is the loss or displacement of land, or the long-term removal of sediment and rocks along the coastline due to the action of waves, currents, tides, wind-driven water, waterborne ice, or other impacts of storms. The landward retreat of the shoreline can be measured and described over a temporal scale of tides, seasons, and other short-term cyclic processes. Coastal erosion may be caused by hydraulic action, abrasion, impact and corrosion by wind and water, and other forces, natural or unnatural.

On non-rocky coasts, coastal erosion results in rock formations in areas where the coastline contains rock layers or fracture zones with varying resistance to erosion. Softer areas become eroded much faster than harder ones, which typically result in landforms such as tunnels, bridges, columns, and pillars. Over time the coast generally evens out. The softer areas fill up with sediment eroded from hard areas, and rock formations are eroded away. Also erosion commonly happens in areas where there are strong winds, loose sand, and soft rocks. The blowing of millions of sharp sand grains creates a sandblasting effect. This effect helps to erode, smooth and polish rocks. The definition of erosion is grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles.

The Tunnel of Eupalinos or Eupalinian aqueduct (Greek: Ευπαλίνιον όρυγμα, romanized: Efpalinion orygma) is a tunnel of 1,036 m (3,399 ft) length running through Mount Kastro in Samos, Greece, built in the 6th century BC to serve as an aqueduct. The tunnel is the second known tunnel in history which was excavated from both ends (Ancient Greek: ἀμφίστομον, romanized: amphistomon, "having two openings"), and the first with a geometry-based approach in doing so. Today it is a popular tourist attraction. The tunnel is inscribed on the UNESCO World Heritage List along with the nearby Pythagoreion and Heraion of Samos, and it was designated as an International Historic Civil Engineering Landmark in 2017.

Rapid transit, mass rapid transit (MRT) or rail rapid transit (RRT) and commonly referred to as metro, is a type of high-capacity public transport that is generally built in urban areas. A grade separated rapid transit line below ground surface through a tunnel can be regionally called a subway, tube, metro or underground. They are sometimes grade-separated on elevated railways, in which case some are referred to as el trains – short for "elevated" – or skytrains. A common alternative term for rapid transit in North America is heavy rail. Rapid transit systems are usually electric railways that, unlike buses or trams, operate on an exclusive right-of-way, which cannot be accessed by pedestrians or other vehicles.

Modern services on rapid transit systems are provided on designated lines between stations typically using electric multiple units on railway tracks. Some systems use guided rubber tires, magnetic levitation (maglev), or monorail. The stations typically have high platforms, without steps inside the trains, requiring custom-made trains in order to minimize gaps between train and platform. They are typically integrated with other public transport and often operated by the same public transport authorities. Some rapid transit systems have at-grade intersections between a rapid transit line and a road or between two rapid transit lines.

A water supply network or water supply system is a system of engineered hydrologic and hydraulic components that provide water supply. A water supply system typically includes the following:

1. A drainage basin (see water purification – sources of drinking water)
2. A raw water collection point (above or below ground) where the water accumulates, such as a lake, a river, or groundwater from an underground aquifer. Raw water may be transferred using uncovered ground-level aqueducts, covered tunnels, or underground pipes to water purification facilities..
3. Water purification facilities. Treated water is transferred using water pipes (usually underground).
4. Water storage facilities such as reservoirs, water tanks, or water towers. Smaller water systems may store the water in cisterns or pressure vessels. Tall buildings may also need to store water locally in pressure vessels in order for the water to reach the upper floors.
5. Additional water pressurizing components such as pumping stations may need to be situated at the outlet of underground or aboveground reservoirs or cisterns (if gravity flow is impractical).
6. A pipe network for distribution of water to consumers (which may be private houses or industrial, commercial, or institution establishments) and other usage points (such as fire hydrants)
7. Connections to the sewers (underground pipes, or aboveground ditches in some developing countries) are generally found downstream of the water consumers, but the sewer system is considered to be a separate system, rather than part of the water supply system.

Water supply networks are often run by public utilities of the water industry.

A level crossing is an intersection where a railway line crosses a road, path, or (in rare situations) airport runway, at the same level, as opposed to the railway line or the road etc. crossing over or under using an overpass or tunnel. The term also applies when a light rail line with separate right-of-way or reserved track crosses a road in the same fashion. Other names include railway level crossing, railway crossing (chiefly international), grade crossing or railroad crossing (chiefly American), road through railroad, criss-cross, train crossing, and RXR (abbreviated).

There are more than 100,000 level crossings in Europe and more than 200,000 in North America.

The Yablonoi Mountains or Yablonovy Mountains (Russian: Яблоновый хребет, Buryat: Яабланай шэлэ нуруу, Yaablanai shele nuruu; Mongolian: Хэнтий нуруу, Khentii nuruu) are a mountain range, in Transbaikal (mainly in Zabaykalsky Krai, Khentii province), Siberia, Russia, Mongolia. The range is sparsely inhabited with most settlements engaged in mining. The area is especially rich in tin. The city of Chita lies between the Yablonoi Mountains to the west and the Chersky Range to the east.

The Trans-Siberian Railroad passes the mountains at Chita and runs parallel to the range before going through a tunnel to bypass the heights.