Excavators are a common item of plant that can be used on construction sites to excavate and load most types of soil. Before beginning excavation works, there must be a plan for the areas that require excavating as well as where the excess material will be stored.
Very broadly, types of excavating plant can be categorised as:
Generally, the choice of excavating plant will depend on:
- The quantity of material to be excavated.
- The type and condition of the soil.
- The weather conditions.
- The speed of excavation required.
- The depth of the excavation.
- The material disposal method (side cast or cart away).
 Hydraulic excavators
These are tracked machines with a slewing capacity of 360-degrees, capable of adapting to a wide range of different requirements. The typical bucket size is 1 m3.
Face shovels are characterised by a boom and bucket arm that extends and swings upwards from the front. It can be used to excavate any kind of soil, including rock that has been loosened by blasting. It is usual for an additional haulage vehicle to be required for spoil removal, as well as a low loader transport lorry for travelling between sites. Face shovels are limited to an excavation depth of 300-400 mm below their own track or wheel level.
A backacter is fitted with a boom and bucket arm or a dipper arm that excavates downwards. They are most suited to trench, foundation and basement excavations. The depth of the dig can be up to 6-7 m, although arm extensions can be added if further depths are required. In excavation operations where the bucket width is equal to the trench width, increased accuracy and high productivity rates can be achieved.
Hydraulic clamshells are used in situations that are too difficult for a backacter, such as dredging and caisson sinking. They are suited to excavating very loose soils, as the bucket grabs and lifts rather than scoops and lifts.
Draglines are fitted with a basic crane jib which uses a rope or chain to control a drag bucket which is swung out to the excavation position and hauled or dragged back towards the power unit. It is best suited to bulk excavation in loose or waterlogged soils below its own track level.
Also known as a skimmer, a trenching machine is used for excavating long trenches, such as those necessary for pipelines. They will normally dig trenches 0.25-1.5 m wide and up to depths of 3 m, where a high degree of accuracy is required. The machine moves forwards when excavating with buckets either mounted on a wheel at the front, or on a chain which is carried by a jib.
These are the most common ‘JCB digger’ machines, intended for small to medium-sized excavation works. They are fitted with loading/excavating front buckets with widths up to 2 m and a rear backacter bucket that has a 180-degree arc of operation. Both are hydraulically controlled by the operator/driver. Use of the backacter bucket requires that the machine is raised off its axles using rear-mounted hydraulic outriggers or jacks.
The machine is flexible in that it can be fitted, usually on the backacter dipper arm, with a variety of bucket widths and attachments such as bulldozer blades, scarifiers, grab buckets and post-hole auger borers.
 Related articles on Designing Buildings Wiki
- Bituminous mixing and laying plant.
- Building foundations.
- Cherry pickers.
- Compressed air plant.
- Concreting plant.
- Construction plant.
- Construction tools.
- Crane supports.
- Earth-moving plant.
- Forklift truck.
- Power float.
- Pumps and dewatering equipment.
- Rubble chute.
- Temporary works.
- Trenching equipment.
- Types of crane.
- Types of roller.
 External references
- ‘Introduction to Civil Engineering Construction’ (3rd ed.), HOLMES, R., The College of Estate Management, (1995)
- ‘Building Construction Handbook’ (6th ed.), CHUDLEY, R., GREENO, R., Butterworth-Heinemann, (2007)
Featured articles and news
CEOs and high-level executives explain who they expect to be the most successful players in the future of construction.
What are package contracts and how are they broken down? Find out in our introductory article.
Identifying sustainable shoreline protection solutions in the face of rising sea levels and storms in the US.
Budget documents state modern methods of construction will be favoured for public infrastructure schemes from 2019.
A walk-through exhibition of an emergency humanitarian shelter is officially opened at BRE's Innovation Park.
How to work safely on a construction site during winter.
Housing is the big winner in Chancellor Philip Hammond's Autumn Budget.
The winner of our BSRIA competition, Tomorrow's challenges in today's buildings, is.... Bob Hendrikx. A big thank you to everyone that took part.
Committee of MPs accuses government of dealing billpayers a 'bad hand' over the guaranteed power price.
In 1992, the Joint Fire Code was first published. What influence does it still have on construction sites today?
"Companies will have to adapt or go out of business" - how are virtual reality and big data disrupting digital construction?
International Well Building Institute and BRE collaborate on multiple levels to advance human health through better buildings.
"The industry has tried moving away from prescriptivism to focus on performance, but maybe that’s no longer working".