Patrick W. Saltmarsh Tim Hunt, CHST Dir. of Envt’l, Safety Health and Safety Corporate Director W. J. L. Derenzo French Excavating Corp. Companies
Know Your Soil Type
O
SHA classifies soils by type. Type A, B, C-60, and C-80. The characteristics and materials that make up the soil will determine which type you are working with. OSHA describes the different types of soils as: Type A soil is cohesive and has a high unconfined compressive strength; 1.5 tons per square foot or greater. Examples of Type A soil include clay, silty clay, sandy clay, and clay loam. Soil cannot be classified as Type A if it is fissured, if it has been previously disturbed, if it has water seeping through it, or if it is subject to vibration from sources such as heavy traffic or pile drivers. Type B soil is cohesive and has often been cracked or disturbed, with pieces that don't stick together as well as Type A soil. Type B soil has medium unconfined compressive strength, between 0.5 and 1.5 tons per square foot. Examples of Type B soil include angular gravel, silt, silt loam, and soils that are fissured or near sources of vibration, but could otherwise be Type A. Type C soil is the least stable type of soil. Type C includes granular soils in which particles don't stick together and cohesive soils with a low unconfined compressive strength; 0.5 tons per square foot or less. Examples of Type C soil include gravel and sand. Because it is not stable, soil with water seeping through it is also automatically classified as Type C soil, regardless of its other characteristics. Most OSHA compliance investigators believe that an excavator working on excavating the soils generates vibration. Thus if any excavation of soils occurs with machinery, it cannot be classified as Type A. So for just about all work, the best soil can be classified as would be Type B. In New England, we assume all soils to be Type C. Soil classifications are made by JULY, 2021
the Competent Person on site. They are required to perform at least one visual and one manual test. OSHA provides options for acceptable visual and manual tests. The most common visual tests include inspecting the soil as it is being removed, inspecting the spoil pile, and the color and makeup of the excavation walls. While visually inspecting the soils, the competent person looks to see if the soil is staying clumped together while being excavated. The trench walls can be inspected for signs of layering different soil types, water seeping through, and any fissures present. The most common manual tests are the plasticity test, the thumb penetration test, and the use of a penetrometer. The thread test, which shows if the soil is cohesive, is when the competent person takes a moist soil sample and rolls it into a thread that is 1/8” thick and 2” long. The competent person then takes continued on page 61
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