Shear Strength of Soil Calculator
Compute shear strength soil using validated scientific equations. See step-by-step derivations, unit analysis, and reference values.
Formula
tau = c + (sigma - u) * tan(phi)
Shear strength tau equals the cohesion c plus the effective normal stress (total normal stress sigma minus pore water pressure u) multiplied by the tangent of the friction angle phi. This is the Mohr-Coulomb criterion in effective stress form. When excess pore pressure is present, the effective stress is reduced, lowering the available shear strength.
Frequently Asked Questions
What is the difference between drained and undrained shear strength?
Drained shear strength applies when pore water can freely drain during loading, so no excess pore pressure builds up. This condition uses effective stress parameters c-prime and phi-prime and governs long-term stability. Undrained shear strength (Su or cu) applies when loading is too fast for drainage, common in saturated clays under rapid loading. In undrained conditions, the friction angle is effectively zero, and all resistance comes from cohesion. The choice between drained and undrained analysis depends on the loading rate relative to the permeability of the soil.
What is soil composition and how is it measured?
Soil is composed of minerals (45%), organic matter (5%), water (25%), and air (25%). Texture is classified by percentages of sand (0.05-2mm), silt (0.002-0.05mm), and clay (less than 0.002mm) using the USDA soil texture triangle. Loam, an ideal garden soil, has roughly equal parts of each.
Is my data stored or sent to a server?
No. All calculations run entirely in your browser using JavaScript. No data you enter is ever transmitted to any server or stored anywhere. Your inputs remain completely private.
How accurate are the results from Shear Strength of Soil Calculator?
All calculations use established mathematical formulas and are performed with high-precision arithmetic. Results are accurate to the precision shown. For critical decisions in finance, medicine, or engineering, always verify results with a qualified professional.
Is Shear Strength of Soil Calculator free to use?
Yes, completely free with no sign-up required. All calculators on NovaCalculator are free to use without registration, subscription, or payment.
How do I interpret the result?
Results are displayed with a label and unit to help you understand the output. Many calculators include a short explanation or classification below the result (for example, a BMI category or risk level). Refer to the worked examples section on this page for real-world context.