What does excavation mean in the Dirt World?

What is Excavation in Construction_Featured Image

Most people think of construction as a vertical endeavor. But excavation—moving dirt, rock, and other material—is arguably the most important part of any construction project. 

Defining excavation in construction 

The word “excavate” comes from “ex” + “cavare” literally meaning “to hollow out, like a cave”1.  While most excavation projects don’t involve digging any caves, excavating always includes moving earth, rock, and other surface material. 

Nearly every vertical construction project starts with digging or excavating, and that’s just the most visible construction work. Excavation is also necessary for all environmental restoration, mitigation, mining, exploration, heavy highway, bridge, and landfill projects.

During this stage of construction, backhoes, excavators, loaders, crushers, graders, draglines, and other heavy equipment may be used to remove material and prepare the site for building.

What are the steps in the excavation process?

Before excavation begins, the excavation site must be surveyed and evaluated for environmental hazards and habitat requirements. Next, the size and depth of the designated excavation area, according to the contractor’s plans, must be clearly marked for the heavy equipment operators. The primary pieces of heavy equipment used in excavation are the excavator and the dozer. On most construction projects, excavation will also require dump trucks, bulldozers, and wheel loaders to transport material around or away from the job site.

The following is a breakdown of the excavation process:

  1. Set out corner benchmarks

Corner benchmarks provide the excavation site with a measurement of level. These benchmarks are marked on permanent structures like footers, slabs, trees, or roads. 

2. Survey ground and top levels

Once benchmarks are established, surveyors mark the top and ground levels with lime powder. 

3. Excavate to the approved depth

While excavation uses an excavator and a dozer, smaller heavy equipment, like the skid steer, is ideal for compact projects in smaller spaces. Technically, digging by hand is also excavating. Tunneling companies like Midwest Mole sometimes have to perform hand-tunneling on more specialized tasks. The best construction workers are willing to work with equipment or by hand—whatever the job requires. 

4. Dress loose soil

The soil must be measured for density and quality, and then appropriate reinforcement methods like trenching and shoring are applied. Blount is one company that specializes in shoring in an area of the country with notoriously unstable soils, the Southwestern desert.

5. Make up to cutoff level

The existing ground level is the profile of the pre-construction ground; the cutoff level is the profile of the vertical limit of excavation, and the finished ground level is the profile of the post-construction ground after backfill. According to the plans, making it up to the cutoff level means backfilling the excavated areas with aggregate material (like sand, soil, or gravel) up to the required level.

6. Dewater and dig interconnected trenches

Drainage is a huge concern of every construction project. There are two ways contractors typically deal with drainage issues on the jobsite: Dewatering and Trenching.  An excavator will dig paths for water that correspond with gravity, so water is directed away from the work area.

7. Establish and mark building boundaries

Transferring ideas from paper to the ground on the jobsite with white spray paint enables the operator on an excavation project to dig within the proper boundaries. Understanding the importance of the center line, both from a vertical and a horizontal point of view, is vital both for the operator and everyone else involved in the project.

8. Bunds and drains construction

A bund is an embankment or a causeway that allows runoff water to flow without destroying nearby organic material. Contoured bunds and drains prevent soil erosion by intercepting surface water runoff.  

Excavation requires skill

Excavation is used on almost every construction project. Residential foundations, commercial site preparation, man-made lakes, and mining sites require excavation. During this portion of construction, the earth's surface is dug up, rearranged, and smoothed out to prepare for vertical or sub-surface construction.

Like many parts of the construction process, excavation requires skill, experience, and attention to detail. Those working in excavation have to learn skills from reading the blueprints and operating heavy equipment to using special techniques and creativity when dealing with tricky soil conditions.

Types of excavation

Moving dirt is a big job. The more dirt, the more costly the job and the more important it is to use time efficiently.  Designing a project that saves money and time requires a thorough understanding of the types of excavation necessary for a given project.  

It is helpful to think about excavation by classifying it according to two distinct features: excavation by material and by purpose.

Excavation by material

Topsoil

Topsoil excavation is the removal of the immediately exposed layer of earth. This includes topsoil and vegetation like trees, bushes, and grasses. 

Rock

Rock excavation is just what it sounds like—removing rock from a site. This type of excavation uses drilling and blasting. It requires hammer attachments, drills, or explosives to break up the rock so that it can be removed. Rock is defined by layers in excess of 18,” with boulders larger than ½ of a cubic yard in diameter. 

Muck

Muck excavation is the removal of excessively wet and undesirable soil. Muck is unstable because of its high water content and cannot usually be used to bear loads or create embankments. Muck can be dried out by spreading it over a large area and leaving it to dry or by stabilizing it with other material.

Earth

Earth excavation used to construct embankments and foundations removes the layer of soil immediately beneath the topsoil and on top of the rock layer. Earth is distinguished from rock by its capacity to be plowed, ripped, or broken apart into small enough pieces to be quickly loaded into hauling units and removed or incorporated into an embankment or foundation. 

Unclassified

Unclassified is the catch-all category for any combination of the previous materials. When a job requires unclassified excavation, those performing the work must be prepared to move earth, regardless of what type of material is encountered.

Excavation by purpose

Defining excavating by purpose is helpful for understanding the end goal of the job. Here are some of the most common ways of defining excavation by purpose. 

Cut-and-Fill

Cut-and-fill excavation describes the removal of earth from one part of a job site to another and then utilizing that same material from the depression made by excavation to create embankments or slopes. 

Trenching

A trench is a narrow cut, cavity, or depression made on the earth’s surface. Trenching excavation usually involves digging in a pre-set, narrow line that may require shoring to keep people on the worksite safe. Trenching is great for foundation footings, drainage, utilities, and other applications.

Basement

Basement excavation, or footing excavation, is where digging is done to create the foundation for a building. This type of excavation is usually done close to grade and as neatly as possible to cast concrete accurately and without forms. This type of excavation takes particular skill and firm soil.

Dredging

Dredging involves the removal of underwater material, usually with the help of a dragline. A dredging project is done with the help of excavators, backhoes, and barges.

Precision earthmoving

Everything from warehouses to skyscrapers starts down low, in the dirt. The quality of built structures that help societies to flourish begins with precision earthmoving. Excavating often goes unseen, but without excavation, we wouldn’t be able to make anything that requires a level grade or a strong foundation.

Excavation is physical. Practical. Complex. It requires a thorough knowledge of how different soil types act and which heavy equipment should be used for moving material. This is a basic overview of what excavation means in construction, but excavation is an art form that can take a lifetime to master.