Soil Testing for Construction

What is Soil Testing?

Soil testing is an essential part of pre-construction to determine the properties and characteristics of the soil at a construction site. A series of tests are used in conjunction with each other to help engineers and construction professionals make informed decisions about foundation design, structural stability, and other aspects of the project.

Why is Soil Testing Important Before Construction?

In summary, soil testing provides essential information for informed decision-making throughout the construction process by minimizing risks, enhancing safety, optimizing design, and contributing to the overall success of the project. Investing in thorough soil testing is a fundamental step in ensuring the quality, durability, and safety of any construction endeavor.

Who Does Soil Testing?

Soil testing is typically conducted by geotechnical engineers and technicians, construction companies, government agencies and academic and research institutions. These professionals have the expertise and training to collect soil samples, perform laboratory tests, and analyze the results to assess the properties and behavior of the soil at a construction site. These individuals and companies play a crucial role in providing accurate and reliable information for engineering and construction projects. It’s important to note that soil testing is a specialized field that requires knowledge of soil mechanics, geology, and engineering principles. Professionals in this field use their expertise to ensure the safe and effective design and construction of infrastructure, buildings, and other structures.

• Geotechnical Engineers: Geotechnical engineers are responsible for planning, coordinating, and interpreting soil tests. They design the testing program, supervise field investigations, analyze laboratory data, and use the results to make informed recommendations for foundation design, slope stability analysis, earthwork, and other aspects of construction.
• Construction Companies: Larger construction companies may have in-house geotechnical teams or may subcontract soil testing to specialized geotechnical consulting firms. These firms have the necessary equipment and expertise to conduct field investigations, collect samples, and perform laboratory tests.
• Geotechnical Consulting Firms: These firms specialize in geotechnical engineering and offer a range of services, including site investigations, soil testing, and geotechnical analysis. They work with architects, engineers, developers, and contractors to provide essential soil information for construction projects.
• Government Agencies: Government departments responsible for infrastructure development, transportation, and environmental protection may also conduct or oversee soil testing for public projects. They ensure that construction activities adhere to regulatory standards and environmental considerations.
• Academic and Research Institutions: Universities and research institutions may conduct soil testing for educational purposes, research studies, or to support specific projects related to soil behavior and geotechnical engineering.

Types of Soil Testing for Construction

While there are various soil tests available, here are some of the most common:

1. Sieve Analysis – ASTM C136, AASHTO T 27: The distribution of particle sizes in a soil sample is a fundamental characteristic used for classification. This test determines the distribution of soil particle sizes. It helps classify the soil into different categories, namely gravel, sand, silt, and clay. The results are presented in a graphical form known as a “gradation curve” or “particle size analysis.”
2. Atterberg Limits – ASTM D4318, AASHTO T 90: The Atterberg limits are used to assess a soil’s consistency and plasticity. The Atterberg Limits consist of three key parameters: the liquid limit (LL), the plastic limit (PL), and the plasticity index (PI). These limits help classify soils and provide valuable information for engineering and construction purposes. This test determines critical water contents, or in the case of PI, range of water contents, at which soils exhibit different properties. These limits help classify the soil’s behavior, such as its plasticity, shrinkage, and swelling characteristics. Determining Atterberg Limits is a crucial step in assessing the consistency and plasticity of fine-grained soils, such as clays and silts.
3. Soil Classification – ASTM D2487, AASHTO M 145: Soil classification involves categorizing soils based on their physical characteristics, i.e., particle size and engineering properties, i.e., Atterberg limits. This classification is essential for various engineering and construction purposes, as different soil types behave differently under load, have varying drainage characteristics, and affect the stability of structures. The most common system for classifying soils in the field of geotechnical engineering is the Unified Soil Classification System (USCS). The American Association of State Highway and Transportation Officials (AASHTO) classification system is also widely used.
4. Proctor Compaction Test – ASTM D698, AASHTO T99 & ASTM D1557, AASHTO T180: Also known as the Standard Proctor Test or Modified Proctor Test, this test determines the maximum dry density (MDD) and optimum moisture content (OMC) of a soil sample when compacted. These values are important for designing and controlling the compaction of soils in construction. When chemically stabilizing soil, it is important to understand that the Modified Proctor generally results in a lower moisture requirement compared to the Standard Proctor, so enough water must be present to ensure complete hydration.
5. California Bearing Ratio (CBR) Test – ASTM D1883, AASHTO T 193: The CBR test evaluates the strength of a soil sample by measuring its resistance to penetration by a standard plunger under controlled conditions. It is commonly used to assess the suitability of subgrade soils for road and pavement construction.
6. Unconfined Compressive Strength (UCS) Test – ASTM D 2166, AASHTO T 208: The UCS test is a laboratory test used to determine the shear strength and load-bearing capacity of a soil sample under axial compression. It is an important test in geotechnical engineering and soil mechanics to assess the strength properties of cohesive soils, such as clays and silts, that do not easily maintain their shape when unconfined. When lime is used to improve soil conditions, ASTM D5102 should be referenced.
7. Optimum Moisture Testing: Optimum moisture content (OMC) testing is an important procedure in geotechnical engineering and construction to determine the moisture content at which a soil attains its maximum density during compaction. This information is crucial for achieving proper compaction of soil layers in various construction activities, such as road and pavement construction, embankments, and foundations. The goal is to achieve the highest possible density and strength while minimizing the potential for future settlement. A Proctor test is used to determine the relationship between the moisture content and the dry unit weight (density) of a soil during compaction.

Mintek believes in choosing the right product for each specific project, so we encourage every customer to utilize our Innovation Center for site soil testing. Our technical experts are available to provide additional insight to your jobsite soils and how to best achieve the results you desire. Check out our Geotechnical Support page for more information on our Innovation Center services or to get in contact with our technical experts.