Direct Shear Test Analyzer
Our soil & sediment mechanics calculator computes direct shear test accurately. Enter measurements for results with formulas and error analysis.
Reviewed by Daniel Agrici, Founder & Lead Developer
Formula
tau = c + sigma * tan(phi)
This Direct Shear Test Analyzer computes results from your provided inputs using the calculator's underlying model.
Frequently Asked Questions
What is the direct shear test?
The direct shear test is a laboratory geotechnical test used to determine the shear strength parameters of soil, specifically cohesion (c) and the angle of internal friction (phi). A soil specimen is placed in a split box where the upper half is displaced horizontally while a normal load is applied vertically. The test is performed at several different normal stresses, and the peak shear stress at failure is recorded for each. Plotting shear stress versus normal stress and fitting a straight line yields the Mohr-Coulomb failure envelope.
What are the limitations of the direct shear test?
The direct shear test forces failure along a predetermined horizontal plane, which may not be the weakest plane in the soil. Drainage conditions cannot be precisely controlled, making it difficult to determine truly undrained or drained parameters for fine-grained soils. The stress distribution on the failure plane is non-uniform, with stress concentrations at the edges. Despite these limitations, the test is widely used because it is simple, fast, inexpensive, and provides reasonable shear strength parameters for many practical applications.
What is the difference between peak and residual shear strength?
Peak shear strength is the maximum shear stress a soil can sustain before failure occurs, corresponding to the highest point on the shear stress versus horizontal displacement curve. Residual shear strength is the constant shear stress that the soil maintains at large displacements after the peak has been exceeded. Dense sands and overconsolidated clays show significant peak-to-residual strength reduction due to dilation and particle rearrangement. The residual friction angle is important for analyzing reactivated landslides and pre-existing shear surfaces.
References
Reviewed by Daniel Agrici, Founder & Lead Developer · Editorial policy