Direktskjærprøving

Direktskjærprøving, also known as direct shear testing, is a laboratory test used in soil mechanics and geotechnical engineering to determine the shear strength of a soil sample. This shear strength is a critical parameter for assessing the stability of foundations, slopes, and other structures built on or with soil.

The test involves placing a soil sample within a shear box, which is typically a metal container split into two halves. The sample is subjected to a normal load, simulating the forces acting on the soil in situ. Subsequently, a shear force is applied horizontally across the plane separating the two halves of the shear box, causing the soil to fail in shear. The shear force is gradually increased until failure occurs, or until a predetermined displacement is reached.

During the test, the applied shear force and the resulting horizontal displacement are continuously recorded. By repeating the test on identical samples with different normal loads, a relationship between normal stress and shear stress at failure can be established. This data is then plotted on a graph, forming a Mohr-Coulomb failure envelope. The parameters of this envelope, namely the angle of internal friction (phi, φ) and the apparent cohesion (c), represent the shear strength characteristics of the soil.

Direktskjærprøving is a relatively simple and quick test, making it a common choice for routine soil investigations. However, it has limitations, such as the inherent assumption of a single, pre-defined failure plane and the inability to accurately model complex stress conditions found in real-world scenarios. Despite these limitations, it provides valuable information for preliminary design and comparative studies.