The Role of Excavation in the Construction Industry
What Is Excavation?
The term “excavation” has a number of different meanings, and may relate to archaeology, medicine, or the construction industry. For our purposes, we’ll consider only the latter.
It’s the process of removing rock, earth and other materials using equipment such as backhoes and bulldozers. Excavators may also use explosives as necessary.
In the construction industry, excavation is used to make way for building foundations, roads, and reservoirs. Experienced contractors usually handle excavation jobs using heavy equipment and advanced techniques, to ensure it’s completed efficiently and in a timely fashion.
Before excavation can begin, the site must be carefully inspected to ensure that the natural features and artifacts there are preserved during the process. Excavators also survey the ground and top levels to ensure the integrity of the soil.
The company then draws up plans defining the depth and size of the excavation. These plans are used to define the boundaries of the excavation on the site. Corner benchmarks are used to mark the boundaries of the building site.
The excavation process also includes the construction of dewatering wells to control groundwater in the vicinity of the site, which is removed using a series of interconnected trenches. Protection bunds are built to contain potentially harmful liquids as the main portion of a spill containment system.
Types of Excavation
There are four types of excavation based on the types of material excavated.
– The exposed surface area is removed to make the site suitable for bearing structural loads. Apart from the topsoil, decaying matter and vegetation are also removed to prevent the soil from becoming compressible.
– This type of excavation removes the layer of soil directly below the surface. This material is often set aside and used to make foundations and embankments.
– Excavators remove hard materials with the aid of explosives or using methods such as drilling, using heavy machinery or by hand.
– “Muck” is a combination of soil and water that makes the surface unsuitable for construction. Hence it has to be removed.
Excavation can also be classified based on the purpose for which it’s conducted.
– This type of excavation removes sediment below the water level. It usually takes place in bodies of water, such as lakes and rivers.
Cut and fill excavation
– In this type of excavation, the topsoil and earth are stripped and stockpiled. The material becomes fill for elevated sections and embankments. It’s also used to create a level surface for the construction, with the higher surfaces cut and the material moved to lower ones.
Purposes of Excavation
– The top layer of the soil is excavated to remove undesirable materials such as roots and vegetation.
– This involves stripping material from an area where a roadway is to be built, or using cut-and-fill methods to build adjoining embankments.
Drainage or structure excavation
– This involves excavating a trench to direct rainwater away from the construction site.
– The excavator removes material to prepare the site to receive the abutments and footings of bridges. The types of excavation involved may include dry, rock and wet, and might also require blasting and drilling if conducted underwater.
– This involves strengthening or dredging an existing waterway channel to prepare for construction of a bridge or drainage project.
– This involves excavating trenches to prepare for strip foundations or burying utility lines.
– This involves excavating material for use in another site that has insufficient earth, such as roadway embankments.
– This involves removing debris and sediments from a site that is below the water level. It’s conducted for a variety of purposes, including civil engineering projects, land reclamation, and creating trenches for laying underground cables and pipes.
– This involves either removing material from the site or bringing in additional material to ensure that the surface over which the rail bed will be laid is level.
– This involves adding additional material to raise the level of the surface so it can be used as a road.
– The upstream and downstream sides of the site where the dam will be built have to be excavated of rock and soil. The material may be stockpiled for later use in the dam body.
– These protective walls are built with material such as rocks and soil, that are excavated from another site.
– This involves underwater dredging to build a waterway. Excavation of an existing waterway may also be done when the government builds a new drainage structure or bridge.
– This involves using excavated material to build up the berm to the desired level.
– This involves removing material from the surface to create a level base, or adding material from another excavation to ensure the desired slope.
The Scope of Excavation Work
Residential – Subdivision
– Constructing subdivisions requires major excavation work, since you’re not only building houses, but also developing the land around them. Site development services are also required.
Commercial and Industrial Sites
– Both types of construction projects should not be lumped together, since they have different requirements and challenges. However, generally, they’re considered to be large-scale excavation projects that also require site development.
– The scope of excavation work depends on the size of the building being constructed and the purpose for which it will be used. In general, however, school construction projects are considered major ones that require large scale excavation, as well as site development.
– The scope of excavation depends on what the church will be used for. Churches that are primarily places of worship are generally small to medium scale projects. Those that want to allow for a greater range of activities, such as providing leisure facilities for young parishioners, will require more land, and thus a greater scope for excavation.
– Since local, municipal, and federal facilities make up a range of construction types, the scope of excavation depends on the type of facility. For instance, detention facilities will be considered major excavation projects, while courthouses may be considered small to medium scale ones.
Processes Used Include…
– This process involves removing soil, dirt, and other material from the surface of the excavation site, using tools such as shovels.
– This process involves removing material from a shallow underwater surface as preparation for building structures, such as piers and bridges.
– This involves digging a trench for the purpose of laying and maintaining cables, conduits, or pipes underground.
Site Preparation and Development
– This is the broad term used for a series of processes used to prepare the land for construction, which includes:
Land clearing/site clearing
– This involves removing obstructions such as brush and trees from the land. Methods used include pushover, burning and cutting and grinding.
– This involves preparing the surface for construction. It starts by removing weak materials from the surface, and then evaluating the sub-grade soil for its load-bearing capacity and potential for volume changes when exposed to freezing or moisture. If the subgrade is of poor quality, it can be replaced with more suitable excavated soil. Implementing moisture control methods can also ensure continued soil quality.
– The topsoil is removed from the excavation site for disposal, or it can be stockpiled for later use.
– This involves distributing soil on the site to draw water runoff away from the base of the structure. This will prevent erosion and water damage.
– This involves returning material such as soil and rocks to the construction site, to strengthen and support the foundation of a structure.
This type of excavation involves driving tunnels or subsurface openings. These can be done for creating drainage tunnels for sewage, or for managing storm water by creating runoff. Tunnels can also be excavated to create underground transport systems such as subways or pedestrian walkways.
– This type of excavation involves digging trenches for laying of pipes and cables for water and power utilities. Trenches where there are existing service lines can also be dug up for repair purposes.
– This involves trenches dug for water drainage where there is not enough surface drainage. The trench has to be dug such that when the pipes are laid, the water drains to the appropriate location and does not drain to an adjoining yard.
Storm water runoff and storm water management
– When water from weather events such as storms is not absorbed into the ground, it can pool and result in erosion and water damage to the property. To manage storm water, drainage systems must be created to direct the excess precipitation away from the property, and to a cleaning facility. The cleaned water can be recycled into a local water system, or released into a nearby body of water.
– These are large-scale excavation projects that have to be handled carefully to avoid accidents such as tunnel collapses and damaging overhead surfaces.
The Role of the Civil Engineer in Excavation Projects
Civil engineers are responsible for major public works such as buildings, and infrastructure projects such as roads, bridges and water supply projects. They generally specialize in a particular technical area such as environmental engineering, transportation, structural engineering, and engineering mechanics.
At the construction site, civil engineers oversee the excavation and ensure that it’s completed safely. They start by assessing the site, looking at factors such as the strength and weight of the soil, and what type it is, the presence of groundwater, and vibrations or surcharges from nearby vehicles or buildings.
The site engineer will also consider the possibility that the excavation could damage or disturb nearby services or structures, and make plans to ameliorate these effects. For instance, they could recommend that the site use smaller machines during excavation that will not generate powerful vibrations.
The engineer is also responsible for the design of the shoring in the excavation. The shoring should be stable to ensure the pit will not collapse while the excavation is being completed.
Well-designed shoring systems will not only speed up the work, but also ensure the safety of the workers. Shoring is commonly used when constructing building foundations to support the surrounding loads until the underground levels are completed.
Equipment Used in Excavation
– This piece of heavy equipment moves earth for short distances of up to two miles. It has a wagon and a gate with a blade. As the wagon moves forward, the blade scrapes up excavated material such as earth. This is forced into the wagon and taken to a disposal area once it’s full.
– This machine moves materials such as rock, asphalt, and debris into a dump truck or other type of machinery. Compact front-end loaders can be attached to tractors, so they can perform the functions of dedicated loaders.
– These machines transport and dispose of loose material. An open-box bed houses the materials, which has hinges that lift the front to deposit the material on the ground behind the truck.
– This machine creates a level surface for a construction project using a long blade. It’s used to “finish grade” since it can more precisely set the surface.
– This machine has a blade in front to move large amounts of excavated materials. It may also have a “ripper” in the rear for loosening materials that are densely compacted.
– This piece of excavating equipment has a digging bucket attached to an arm that digs up unwanted material from the construction site.
– These machines are used when there’s need for equipment with a longer reach, or for underwater excavation.
– These machines dig trenches and come in two types. The chain trencher uses a chain wrapped around a fixed arm as the digging tool, while wheeled trenchers use a metal wheel with teeth.
– This machine compresses the various materials at construction sites. The three main types are the road roller, which compacts crushed rock to use in foundations as the base layer; the plate compactor, used to make level grades; and the jumping jack which compacts backfill in trenches dug for gas or water pipes.
– Also known as skid steer loaders, these machines use attachment options to perform various functions ranging from earthmoving to landscaping.
What is Site Development?
This is the process of adding improvements to a site that are necessary to support its primary activity. In the construction industry, site development is preparing a site for construction activities.
Integrated Site Development (ISD)
ISD involves a range of activities to ensure the land is ready for excavation and construction. These are:
Clearing, Grinding and Demolition
– These three activities involve removing material, debris, and unwanted structures from the site. A horizontal grinder takes wood waste and other types of debris and grinds them for disposal.
– This activity involves moving mass quantities of earth from the site to clear it in preparation for excavation.
Grading and excavation
– This activity prepares the site by creating a level base for excavation and construction, or ensuring a base that has a specified slope.
Sanitary sewer, storm sewer, and waterline
– This activity involves the construction of sewer and water lines. Sanitary sewers carry sewerage from plumbing to a wastewater treatment plant. Storm sewers carry drainage such as rainfall runoff, and discharge them into surface water bodies untreated.
Road and curb construction
– Roads and curbs are built to allow cars and other vehicles access to the site. Curbs may be combined with gutters to drain rainwater efficiently from roads.
Final Cleanup, testing and restoration
– At the end of the development process, the site is thoroughly cleaned up, and all debris is removed from the site, to ensure that it’s restored to as close to its natural state as possible. The site is tested to ensure the integrity of the site is maintained.
– This must be performed before the start of excavation and construction. It involves building rock creek dams, silt fences, and other control structures.
Other Services Provided by Most Excavation Companies
Most excavation companies also offer certain site development services. These include:
Concrete curb building/replacement
– Curbs channel water to drains to maintain sidewalk integrity and eliminating the need to build side ditches. Concrete is a popular construction material, since maintenance costs are nearly negligible and it’s very durable. The excavation company may build new curbs or replace ones damaged during construction.
– Asphalt is an affordable and sustainable material for paving sidewalks. It’s also durable enough to withstand harsh weather conditions, and can be dug up and reused. The excavation company may repave asphalt sidewalks and pavements that have been damaged.
– After construction has been completed in residential subdivisions, engineers from the excavation company produce a punch list. The contractor must complete the items on this checklist to the satisfaction of the clients before their final payment is given.
What is a “Punch List”?
A punch lists is a document prepared at the end of construction. It lists the work that the contractor must complete before they’re given the final payment, since it doesn’t conform to specifications enumerated in the contract. The remedial work ranges from work on installations that are incorrect and incomplete, to damage incurred to existing structures during the construction process.
What Are Some Excavation Hazards?
Despite all the safety precautions taken at construction sites, there are several inherent risks involved with excavation sites.
The most common of these are “cave-ins”
– These happen when the walls of the excavation collapse, and can happen without warning, endangering the safety of the workers. The walls of the excavation cave in because the dug-up soil no longer has any support, and gravity will eventually take over.
Accidental contact with underground or overhead electricity cables
– This hazard can result in accidental electrocution of workers, resulting in serious injury and even death.
Accidents involving construction equipment and other vehicles
– Equipment close to the edge of the excavation may fall into the pit, injuring or even killing workers.
Exposure to harmful gases
– The atmosphere in the excavation may become toxic when flammable or harmful gases are used near or in it. Workers may also suffer from oxygen deficiency as these gases build up in the pit. This is also a risk when the excavation is being performed close to a sewer or landfill.
Tripping or falling into the pit
– Workers near the edge of the excavation may accidentally trip on slippery soil, debris, or even construction equipment.
Collapse of adjacent structures
– The excavation may affect the integrity of nearby structures, causing them to collapse and injure workers and even bystanders at the site.
Flooding caused by hydrostatic testing
– The pit may fill with water, posing a drowning hazard to workers.
Compliance with Safety Standards
Excavation is an inherently risky activity, and workers are exposed to a variety of hazards. In order to ensure that excavation sites are as safe as possible, safety standards have to be put into place.
The main standards used by the industry come from the Occupational Safety and Health Administration of the Department of Labor. These define a set of requirements that will greatly reduce or prevent the risk of some of the most common hazards.
Before employers prepare a bid for a new construction project, the OSHA recommends that they prepare a safety checklist. The checklist will assess the amount of risk inherent in the project based on the location and type of excavation to be conducted. It will also help them to determine the kind and amount of safety equipment they’ll have to purchase to ensure the work is completed safely.
OSHA standards serve as the basis for individual workplaces to set their own safety guidelines. For instance, they commonly require that workers always wear protective equipment such as hardhats, goggles and gloves while on-site.
Many workers also suffer injuries not directly related to construction activities, such as accidentally coming into contact with live electrical wires. This has sparked moves to pass safety laws directly addressing these issues.