What are the best practices for evaluating soil composition and quality before excavation?

2 Assess the soil texture

The next step is to assess the soil texture, which is the relative proportion of sand, silt, and clay in the soil. Soil texture affects the porosity, permeability, water retention, and compaction of the soil. You can use a soil texture triangle to classify the soil texture based on the percentage of sand, silt, and clay. For example, a soil with 40% sand, 40% silt, and 20% clay is called a loam. A soil with 70% sand, 10% silt, and 20% clay is called a sandy clay loam. The ideal soil texture for construction is usually a well-graded mixture of sand, silt, and clay that has good drainage and strength.

3 Evaluate the soil structure

The third step is to evaluate the soil structure, which is the arrangement and aggregation of soil particles into larger units called peds. Soil structure affects the aeration, infiltration, erosion, and root penetration of the soil. You can use a visual inspection or a hand test to determine the soil structure by observing the shape, size, and cohesion of the peds. The common shapes of soil structure are granular, blocky, platy, prismatic, columnar, and single-grained. The ideal soil structure for construction is usually granular or blocky, which have good porosity and stability.

4 Measure the soil moisture

The fourth step is to measure the soil moisture, which is the amount of water in the soil. Soil moisture affects the shrinkage, swelling, frost heave, and bearing capacity of the soil. You can use a moisture meter or a gravimetric method to measure the soil moisture by comparing the weight of wet and dry soil samples. The common indicators of soil moisture are the natural moisture content, the field capacity, the wilting point, and the saturation point. The ideal soil moisture for construction is usually moderate and consistent, which prevents excessive movement and deformation of the soil.

5 Test the soil organic matter

The fifth step is to test the soil organic matter, which is the decomposed material from plants and animals in the soil. Soil organic matter affects the nutrient availability, pH, cation exchange capacity, and biological activity of the soil. You can use a colorimetric test or a loss-on-ignition method to measure the soil organic matter by estimating the carbon content or the weight loss of soil samples after burning. The common measures of soil organic matter are the organic carbon content, the organic matter content, and the humus content. The ideal soil organic matter for construction is usually low and uniform, which reduces the variability and instability of the soil.

6 Sample the soil quality

The final step is to sample the soil quality, which is the overall condition and function of the soil. Soil quality affects the sustainability, productivity, and environmental impact of the construction project. You can use a soil survey or a soil test to sample the soil quality by collecting and analyzing representative soil samples from different depths and locations of the site. The common parameters of soil quality are the pH, the electrical conductivity, the nutrient levels, the salinity, the sodicity, and the contamination. The ideal soil quality for construction is usually neutral, balanced, and clean, which ensures the health and safety of the site and the surrounding ecosystem.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?