Soil Classification Saves Lives

Construction work is an essential part of building our infrastructure, but it can also be hazardous. In the United States alone, over 800 construction workers lose their lives each year while on the job. Among the most dangerous aspects of construction is trenching, which claims the lives of 40 workers annually. The risk of death or serious injury due to trench cave-ins is a grim reality, but it is a preventable one. In this blog post, we will explore the importance of soil classification in trenching work and how it can save lives.

OSHA Video Explaining Soil Classification for Excavations in Construction

The Significance of Soil Classification

Trenching work requires a thorough understanding of the soil’s characteristics to ensure the proper implementation of safety measures. One cubic yard of soil can weigh as much as a car, approximately 3,000 pounds, and different types of soil possess varying levels of stability. Knowing the soil type enables construction workers to determine the appropriate techniques, such as sloping, benching, or shoring, to prevent cave-ins and protect their lives.

The Role of a Competent Person

According to the Occupational Safety and Health Administration (OSHA), employers must have a competent person on-site to determine the soil type. A competent person possesses the knowledge and authority to identify hazardous conditions and take corrective actions. They play a crucial role in ensuring the safety of workers by classifying soil accurately and implementing necessary protective measures.

Understanding Soil Types:

Type A, Type B, and Type C

Soils are classified into three main types:

Type A, Type B, and Type C, based on their stability and unconfined compressive strength.

1. Type A Soil: This is the most stable soil for excavation. Type A soil is cohesive, containing a high unconfined compressive strength of 1.5 tons per square foot or greater. Examples of Type A soil include clay, silty clay, sandy clay, and clay loam. However, soil cannot be classified as Type A if it is fissured, previously disturbed, subjected to water seepage, or exposed to vibrations from heavy traffic or pile drivers.
2. Type B Soil: Type B soil is also cohesive but is considered less stable than Type A. It has a medium unconfined compressive strength ranging between 0.5 and 1.5 tons per square foot. Examples of Type B soil include angular gravel, silt, silt loam, and soils that exhibit fissures or are exposed to nearby sources of vibration. However, if the soil meets the criteria for Type A classification but has one of these characteristics, it can still be considered Type B.
3. Type C Soil: Type C soil is the least stable and includes granular soils with particles that do not stick together. Additionally, cohesive soils with a low unconfined compressive strength of 0.5 tons per square foot or less fall under Type C. Examples of Type C soil include gravel and sand. Soil with water seepage is automatically classified as Type C, regardless of other characteristics.

Soil Testing Methods

To determine the soil type accurately, several testing methods can be employed. A competent person can conduct a visual inspection of the soil on the construction site and look for signs of cohesion, vibration sources, water seepage, previous disturbance, or fissures. This preliminary visual test helps identify factors that may affect soil stability.

The following are three common soil testing methods:

1. Plasticity Test: Also known as the pencil test, this method assesses the soil’s cohesion. It involves rolling a moist soil sample into a thread-like structure resembling a short pencil. If the sample can be held at one end without breaking, it indicates cohesive soil.
2. Thumb Penetration Test: This quick estimation method determines the compressive strength of a cohesive soil sample. By pressing the end of your thumb into a fresh clump of soil, you can gauge its resistance. The deeper the thumb sinks, the lower the compressive strength, with Type C soil allowing complete thumb penetration.
3. Pocket Penetrometer Test: For a more precise measurement of compressive strength, a pocket penetrometer is used. It provides numeric values by pushing a thin, metal piston into the soil sample. This test should be conducted on multiple samples from the same part of the excavation to ensure consistent results.

Applying Soil Classification for Worker Safety

By accurately classifying the soil type, a competent person can make informed decisions regarding the necessary protective measures in trenching work. This knowledge helps determine the appropriate methods of sloping, benching, or shoring to prevent cave-ins and safeguard workers’ lives.

Construction work, particularly trenching, poses significant risks to workers’ safety. However, through proper soil classification and the diligent implementation of safety measures, such risks can be mitigated. By understanding the characteristics of different soil types and conducting thorough soil testing, employers and competent individuals can create a safer working environment for construction workers. It is essential for every construction site to prioritize soil classification and take the necessary steps to protect the lives of those who build our world.