In the construction industry, soil excavation is one of the most hazardous tasks. On average, 40 construction workers die each year in trenching cave-ins. An environmental professional will prepare a Soil Management Plan for each project to avoid these accidents. That will include detailed specifications for soil classification and backfill procedures. Click https://www.levelgroundexcavation.com/ to learn more.
Soil classification is the process of grouping soils with similar ranges of properties into units that can be geo-referenced and mapped. It is important for soil excavation because it allows engineers to understand how each soil type might behave on an engineering project site, which can help plan and construct a trench. Soil is a complex natural resource with many different physical and chemical properties. Therefore, proper soil classification is essential to avoid costly mistakes that might occur during excavation.
Professionals use a few major types of soil classification systems. One of the most popular is the Unified Soil Classification System or USCS. This system divides soil into orders, suborders, great groups, subgroups, families, and series. It also describes the physical and chemical characteristics of soil that influence management.
A visual inspection of a soil sample is an integral part of the classification process. During a visual inspection, a person examines the color and texture of the soil in a clump of spoil. They look for signs of fissured or crack-like earth. They note if the ground has been disturbed by underground water, utility lines, or other vibration sources.
The next step of the process is a manual soil sample test. That can be done using a simple ribbon or thumb test or an instrument that measures the strength of a soil sample. This test helps determine whether the soil is cohesive, which can affect trench safety. Cohesive soil is classified as Type A, while non-cohesive soil is classified as Type B.
A competent worker must perform at least one visual and one manual test of the soil before excavating it. In addition, the skilled worker must also conduct a laboratory soil classification. The laboratory soil classification subjects the samples to standard lab tests and indexes them into specific ASTM or AASHTO soil groups. The results of these tests can be used for engineering designs such as foundations or pavements and to identify potential hazards for employees.
One of the most important factors in soil excavation is estimating the maximum allowable slope for a hole. That is based on the slope angle of a pit’s bank or edge wall and the top safe pitch for the soil type. That will help protect employees during the excavation process by preventing trench collapse.
OSHA sets the minimum slope requirements. However, a competent person must use their experience and knowledge of the site conditions to determine the safest slope for the soil. That may require a geotechnical report, soil tests, or independent testing to determine the soil type, moisture content, and friction angle.
Cohesion, permeability, shear strength, and the existence of rock are other important factors to consider when assessing the excavation slope. Once this information is known, a design can be made to calculate the safe slope for the excavation.
If the minimum slope requirements are exceeded during an excavation, it can cause a cave-in of the bank or the trench wall. That can result in serious injury or death of workers.
While working in an excavation, the worker must be constantly vigilant to signs that the soil is unsafe for continued digging. Often, these signs are obvious and may include warnings from utility markings or conduit, pipe, or other underground structures that have been exposed during the digging process. Other indicators may consist of the presence of water in the excavation or a change in the consistency of the soil that indicates it has been weakened by weather or other causes.
During the bid process, the competent person must choose a safe method of support for the walls and banks of the excavation. This decision will affect the price of the bid and can be costly if the wrong support is selected. It is also very important to regularly test the soil consistency to ensure it is safe to continue excavating. Otherwise, sloughing and trench collapse can occur with little or no notice during the excavation process. That can be especially hazardous in windy areas or if the soil becomes dry and weak.
Trench excavations may be wide or narrow, and the width affects how much labor and machinery is needed. The depth of the trench can also influence how expensive it is to excavate and backfill, as well as how likely a cave-in is to occur. Tracks should be as narrow as possible while allowing enough room to make pipe joints and properly tamp backfill material around the pipes.
The soil type in a trench also impacts how safe it is to work there. Soil with a high unconfined compressive strength is more stable, and the sides of the track can withstand more pressure without collapsing.
In general, trenches less than 5 feet deep in rock require a protective system, but if the track is in non-cohesive soil and is at least 6 feet deep, a competent person can determine that a defensive strategy isn’t required.
A competent person must design and implement a protective system when the trench is deeper than that. Typical scenarios include sloped or benched walls, shields and support systems, stairways, ladders, or ramps that allow workers to escape the trench.
During construction, the sides of the trench should be sloped or benched as necessary to prevent cave-ins. Dropping the trench walls is usually done by removing soil from the face of the track at an inclined angle away from the excavated area. At the same time, benching involves cutting back the trench wall in sections and then reshaping it with a bench.
The backfill used in trenches should be class A compacted select excavation materials, and the top 12 inches should be tamped with a light piston. That ensures that the backfill is densely packed and it can withstand pressure.
Trenches should be backfilled as soon as possible to keep workers safe. That reduces the chance of a cave-in and allows crews to continue working on pipe installation. The soil must also be inspected before workers go back into the trench, and it should be closed immediately if a hazardous condition is identified.
Trench depth plays a major role in excavation safety. It’s one of the main factors influencing whether shoring and other protective systems are required. In addition, it can affect the potential for bottom heaving and squeezing and the stability of adjacent structures. These problems can lead to cave-ins, entrapment, and other serious injuries and fatalities.
A competent person must inspect the trench before workers enter it and, as conditions change, ensure that protective systems are in place. They must also be able to identify existing and predictable hazards and working conditions that are unsanitary, hazardous, or dangerous to workers and are authorized to take prompt corrective measures to eliminate them.
In addition, workers must be provided with safe means of access and egress. That includes ladders, steps, and ramps placed within 25 feet of all workers for excavations 4 feet or deeper. The job site must also be properly marked, and signs should be posted to warn people of the dangers. Workers must also be able to see each other, which can be accomplished through high-visibility clothing.
Another major concern with soil excavation is the potential for workers to be struck by vehicles or equipment. That can occur when workers are positioned too close to trench edges or when material is stored too close. Construction site managers must provide each worker with personal protective equipment, including hard hats, eye protection, and hearing protection.
Accidents involving construction vehicles are common on sites and can be especially deadly when an excavator is engaged. Using spotters or flaggers to direct vehicular traffic and keeping equipment, materials, and excavated soil away from the trench can help prevent this type of incident. In addition, workers should wear high-visibility clothing when working around vehicles and always look over their shoulders before moving.
Besides the issues above, soil conditions can shift throughout an excavation. That’s why it’s important to inspect the trench regularly, regardless of whether or not shoring is needed. The competent person must also test the soil’s unconfined compressive strength before each worker enters the track and as conditions change.