In construction areas loaders are also used to transport building materials - such as bricks, pipe, metal bars, and digging tools - over short distances.

Loaders are also used for snow removal, using their bucket or a snowbasket, but usually using a snowplow attachment. They clear snow from streets, highways and parking lots. They sometimes load snow into dump trucks for transport.

High-tip buckets are suitable for light materials such as chip, peat and light gravel and when the bucket is emptied from a height.

Unlike backhoes or standard tractors fitted with a front bucket, many large loaders do not use automotive steering mechanisms. Instead, they steer by a hydraulically actuated pivot point set exactly between the front and rear axles. This is referred to as "articulated steering" and allows the front axle to be solid, allowing it to carry greater weight. Articulated steering provides better maneuverability for a given wheelbase. Since the front wheels and attachment rotate on the same axis, the operator is able to "steer" his load in an arc after positioning the machine, which can be useful. The tradeoff is that when the machine is "twisted" to one side and a heavy load is lifted high, it has a greater risk of turning over to the "wide" side.

Front loaders gained popularity during the last two decades, especially in urban engineering projects and small earthmoving works. Many engineering vehicle manufacturers offer a wide range of loaders, the most notable are those of John Deere, Caterpillar, Case, Volvo, Komatsu and Liebherr.

Popular additions to compact utility tractors and farm tractors are Front End Loaders, also referred to as a FEL. Compact utility tractors, also called CUTs are small tractors, typically with 18 to 50 horsepower and used primarily for grounds maintenance and landscape chores. There are 2 primary designs of compact tractor FELs, the traditional dogleg designed style and the curved arm style.

John Deere Tractor manufactures a semi-curved loader design that does not feature the one piece curved arm, but also is not of the traditional two piece design. New Holland Ag introduced a compact loader with a one piece curved arm on its compact utility tractors, similar one piece curved arm loaders are now available on compact tractors on many brands including Case/Farmall, and some Montana and Kioti tractors. Kubota markets traditional loader designs on most of its compact tractors but now features a semi-curved loader design similar to the John Deere loader design on several of its small tractors.

While the Front End Loaders on CUT size tractors are capable of many tasks, given their relatively small size and low capacities when compared to commercial loaders, the compact loaders can be made more useful with some simple options. A Toothbar is commonly added to the front edge of a loader bucket to aid with digging. Some loaders are equipped with a Quick Attach (QA) system, the QA system allows the bucket to be removed easily and other tools to be added in its place. Common additions would include a set of Pallet Forks for lifting pallets of goods or a Bale Spear for lifting hay bales.

A skid loader is a small loader utilizing four wheels with hydraulic drive that directs power to either, or both, sides of the vehicle. Very similar in appearance and design is the track loader, which utilizes a continuous track on either side of the vehicle instead of the wheels. Since the expiration of Bobcat's patent on its quick-connect system, newer tractor models are standardizing on that popular format for front end attachments.

Telescopic handler

A telescopic handler, or telehandler, is a machine widely used in agriculture and industry. It is similar in appearance and function to a forklift, with the increased versatility of a single telescopic boom that can extend forwards and upwards from the vehicle. On the end of the boom the operator can attach one of several attachments, such as a bucket, pallet forks, muck grab, or lift table.

The most common attachment for a tele-handler is pallet forks and the most common application is to move loads to and from places out of reach for a conventional forklift. For example, telehandlers have the ability to remove palletized cargo from within a trailer and to place loads on rooftops and other high places. The latter application would otherwise require a crane, which is not always practical or time-efficient.

The advantage of the telehandler is also its biggest limitation: as the boom extends or raises while bearing a load, it acts as a lever and causes the vehicle to become increasingly unstable, despite counterweights in the rear. This means that the lifting capacity quickly decreases as the height and/or length of the boom increase. A vehicle with a 5,000lb capacity with the boom retracted may be able to lift as little as 400lb with it fully extended. The operator is equipped with a load chart which helps him determine whether a given task is possible, taking into account weight, boom angle and height. Failing this, most telehandlers utilize a computer which uses sensors to monitor the vehicle and will warn the operator and/or cut off further control input if the limits of the vehicle are exceeded. Some machines are also equipped with front outriggers similar to those installed on mobile cranes, which extend the lifting capability of the equipment while stationary.

Telehandlers were pioneered by the Matbro company at Horley in Surrey, England who developed them from their articulated cross country forestry forklifts. At first they had a centrally mounted boom on the front section, with the driver's cab on the rear section, as in the Teleram 40, but the rigid chassis design with a rear mounted boom and cab to the side has become more popular.

Track loader

A track loader is an engineering vehicle consisting of a tracked chassis with a loader for digging and loading material. The history of track loaders can be defined by three evolutions of their design. Each of these evolutions made the track loader a more viable and versatile tool in the excavation industry. These machines are capable in nearly every task, but master of none. A dozer, excavator, or wheel loader will out perform a track loader under a set of conditions, but the ability of a track loader perform almost every task on a job site is why it remains a part of many company's fleets.

The first track loaders were built from track tractors with scratch built loaders. The first loaders were cable operated like the bulldozers of the era. These track loaders lacked the ability to dig in hard ground, but so did the dozers of the day. They were mostly used for moving stockpiled material and loading trucks and rail cars.

The first major design change to track loader came with the integration of hydraulic systems. Using hydraulics to power the loader linkages increased the power of the loader. More importantly, the loaders could apply downpressure to the bucket, vastly increasing their ability to dig unworked ground. Most of the track loaders were still based on a bulldozer equivalent. The weight of the engine was still on the front half of the tracks along with the heavy loader components. This caused many problems with heavy wear of the front idler wheels and the undercarriage in general. The Caterpillar 983 track loader, the second largest track loader ever built, was notorious for heavy undercarriage wear.

The hydrostatic drive system was the second major innovation to affect the the design of track loaders.

Track loaders have become very sophisticated machines, using hydrostatic transmissions and electro-hydraulic controls to increase efficiency. Until the rise in popularity of excavators, track loaders had little competition digging and loading jobs.

Now, the lower owning and operating costs, versatility and acquisition costs of hydraulic excavators are making track loaders a "thing of the past"..

Trencher (machine)

A trencher is piece of construction equipment used to dig trenches, typically for laying pipes or cable, or for drainage. Trenchers may range in size from walk-behind models, to attachments for a skid loader or tractor, to very heavy tracked engineering vehicles.

Trenchers come in different sizes and may use a different digging implement, depending on the required width and depth of the trench and the hardness of the surface to be cut.

Wheel Trencher

Wheel trenchers may be mounted on tracks or rubber tires, and utilize a number of buckets mounted on a wheel that moves in a circular motion to excavate material. Wheel trenchers are the fastest method of excavating and are cheaper to operate and maintain than chain type trenchers.

Chain trencher

A chain trencher cuts with a digging chain that is driven around a rounded metal frame, or boom. It resembles a giant chainsaw. This type of trencher can cut ground that is too hard to cut with a bucket-type excavator.

The angle of the boom can be adjusted to control the depth of the cut. To cut a trench, the boom is held at a fixed angle while the machine creeps backward.

A rockwheel

A rockwheel is a toothed metal wheel—effectively a giant circular saw. Rockwheels can cut harder ground than a chain trencher, including cutting through solid stone. They are also used to cut pavement for road maintenance and to gain access to utilities under roads.

The teeth on a rockwheel are removable and made of high strength steel (HSLA steel, tool steel or high speed steel) or tungsten. When the machine is under heavy use, the teeth may need to be replaced frequently, even daily.

Portable trencher

Landscapers and lawn care specialist may use a portable trencher to install landscape edging and irrigation lines. They may also be used to install utility connections just beneath the surface such as coaxial cables. These machines are lightweight (around 200 pounds) and are easily maneuverable compared to other types of trenchers. The cutting implement may be a chain, or a blade similar to a rotary lawn mower blade oriented so that it rotates in a vertical plane.

A trencher may be combined with a drainage pipe or geotextile feeder unit and backfiller, so drain or textile may be placed and the trench filled in one go.

Tunnel boring machine

A tunnel boring machine (TBM) is a machine used to excavate tunnels with a circular cross section through a variety of soil and rock strata. They can bore through hard rock, sand, and almost anything in between. Tunnel diameters can range from a metre (done with micro-TBMs) to 19 metres. Tunnels of less than a metre or so in diameter are typically done by horizontal directional drilling rather than TBMs.

Tunnel boring machines are used as an alternative to drilling and blasting (D&B) methods in rock and conventional 'hand mining' in soil. A TBM has the advantages of limiting the disturbance to the surrounding ground and producing a smooth tunnel wall. This significantly reduces the cost of lining the tunnel, and makes them suitable to use in heavily urbanized areas. The major disadvantage is the upfront cost. TBMs are expensive to construct, difficult to transport and require significant infrastructure. The biggest is built by Herrenknecht AG of Schwanau, Germany to dig the 57km Gotthard Base Tunnel. It has a diameter of 19 meters.

History

The first successful tunnelling shield was developed by Sir Marc Isambard Brunel to excavate the Thames Tunnel in 1825. However, this was only the invention of the shield concept and did not involve the construction of a complete tunnel boring machine, the digging still having to be accomplished by the then standard excavation methods.

The very first boring machine ever reported to have been built was Henri-Joseph Maus' Mountain Slicer. Commissioned by the King of Sardinia in 1845 to dig the Fréjus Rail Tunnel between France and Italy through the Alps, Maus had it built in 1846 in an arms factory near Turin. It basically consisted of more than 100 percussion drills mounted in the front of a locomotive-sized machine, mechanically power-driven from the entrance of the tunnel. Unfortunately, the Revolutions of 1848 irremediably affected the funding of the project and the tunnel was not completed until 10 years later, by using also innovative but rather less expensive methods such as pneumatic drills.

In the United States, the first boring machine to have been built was used in 1853 during the construction of the Hoosac Tunnel. Made of cast iron, it was known as Wilson's Patented Stone-Cutting Machine, after its inventor Charles Wilson. It drilled 10 feet into the rock before breaking down. The tunnel was eventually completed more than 20 years later, and as with the Fréjus Rail Tunnel, by using less ambitious methods.

In the early 1950's, F.K. Mitry won a dam diversion contract for the Oahe Dam in Pierre, South Dakota, and consulted with James S. Robbins to dig through what was the most difficult shale to excavate at that time, the Pierre Shale. Robbins built a machine that was able to cut 160 feet in 24 hours in the shale, which was ten times faster than any other digging speed at that time.

The breakthrough that made tunnel boring machines efficient and reliable was the invention of the rotating head, conceptually based on the same principle as the percussion drill head of the Mountain Slicer of Henri-Joseph Mau, but improving its efficiency by reducing the number of grinding elements while making them to spin as a whole against the soil front. Initially, Robbins' tunnel boring machine used strong spikes rotating in a circular motion to dig out of the excavation front, but he quickly discovered that these spikes, no matter how strong they were, had to be changed frequently as they broke or tore off. By replacing these grinding spikes with longer lasting cutting wheels this problem was significantly reduced. Since then, all successful modern tunnel boring machines have rotating grinding heads with cutting wheels.

Description

The support structures at the rear of a TBM. This machine was used to excavate the main tunnel of the Yucca Mountain nuclear waste repository in Nevada.

A tunnel boring machine (TBM) typically consists of one or two shields (large metal cylinders) and trailing support mechanisms. At the front end of the shield is a rotating cutting wheel. Behind the cutting wheel is a chamber where, depending on the type of the TBM, the excavated soil is either mixed with slurry (so-called slurry TBM) or left as is. The choice of TBM type depends on the soil conditions. Systems for removal of the soil (or the soil mixed with slurry) are also present.

Behind the chamber there is a set of hydraulic jacks supported by the finished part of the tunnel which push the TBM forward. The action here is much like an earthworm. The rear section of the TBM is braced against the tunnel walls and used to push the TBM head forward. At maximum extension the TBM head is then braced against the tunnel walls and the TBM rear is dragged forward.

Behind the shield, inside the finished part of the tunnel, several support mechanisms which are part of the TBM are located: dirt removal, slurry pipelines if applicable, control rooms, and rails for transport of the precast segments. The cutting wheel will typically rotate at 1 to 10 rpm (depending on size and stratum), cutting the rock face into chips or excavating soil (muck). Depending on the type of TBM, the muck will fall onto a conveyor belt system and be carried out of the tunnel, or be mixed with slurry and pumped back to the tunnel entrance. Depending on rock strata and tunnel requirements, the tunnel may be cased, lined, or left unlined. This may be done by bringing in precast concrete sections that are jacked into place as the TBM moves forward, by assembling concrete forms, or in some hard rock strata, leaving the tunnel unlined and relying on the surrounding rock to handle and distribute the load.

While the use of a TBM relieves the need for large numbers of workers at increased pressure, a caisson system is sometimes formed at the cutting head.Workers entering this space for inspection, maintenance and repair need to be medically cleared as "fit to dive" and trained in the operation of the locks.

Shields

Modern TBMs typically have an integrated shield. The choice of a single or double shielded TBM depends on the type of rock strata and the excavation speed required.

Double shielded TBMs are normally used in unstable rock strata, or where a high rate of advancement is required. Single shielded TBMs, which are less expensive, are more suitable to hard rock strata.

Urban tunnelling and near surface tunnelling

Urban tunnelling has the special challenge of requiring that the ground surface be undisturbed. This means that ground subsidence must be avoided. The normal method of doing this is to maintain the soil pressures during and after the tunnel construction. There is some difficulty in doing this, particularly in varied rock strata (e.g., boring through a region where the upper portion of the tunnel face is wet sand and the lower portion is hard rock).

TBMs with positive face control are used in such situations. There are three common types: Earth pressure balance (EPB), Bentonite slurry (BS), and compressed air (CA). The compressed air method is the oldest, but is falling out of favour due to the difficult working conditions it imposes. Both types (EPB and BS) are clearly preferred over open face methods in urban environments as they offer far superior ground control.

When tunnelling in urban environments other tunnels and deep foundations need to be addressed in the early planning stages. The project must accommodate measures to mitigate any detrimental effects to other infrastructure.

Traction: Off-the-road tires and Tracks

Heavy equipment requires specialized tires for various construction applications. While many types of equipment have continuous tracks applicable to more severe service requirements, tires are used where greater speed or mobility is required. An understanding of what equipment will be used for during the life of the tires is required for proper selection. Tire selection can have a significant impact on production and unit cost. There are three types of off-the-road tires, transport for earthmoving machines, work for slow moving earth moving machines, and load and carry for transporting as well as digging. Off-highway tires have six categories of service C compactor, E earthmover, G grader, L loader, LS log-skidder and ML mining and logging. Within these service categories are various tread types designed for use on hard-packed surface, soft surface and rock. Tires are a large expense on any construction project, careful consideration should be given to prevent excessive wear or damage.

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