slänthållfasthet

Slänthållfasthet, literally “layer strength,” is a term used in geology, coastal engineering and civil construction to describe the resistance of a layered medium—such as a sandy beach or dune—to shear motion that tends to separate the layers. The concept is particularly relevant for loose, two‑ or three‑dimensional assemblages of grains that have been deposited in discrete strata by waves, currents or wind. When the layers are inclined relative to the shear direction, the tensile stresses acting along the interfaces can overcome the cohesion of the sediment, leading to slippage and failure of the layered structure.

The value of slänthållfasthet depends on several interrelated factors. Particle size and roundness control interlocking; finer, angular grains generally yield higher resistance. Moisture content introduces capillary forces that greatly increase layer cohesion, a phenomenon exploited in road construction where moisture‑tight identical layers must remain stable under load. The angle of internal friction, determined by grain shape and packing density, influences how much shear stress the interface can absorb. Organic binders or cementing material, such as silt or clay horizons, raise the interface strength considerably. Finally, intrusion of water or ice can create suction or ice lubrication that either augments or diminishes cohesion, depending on temperature and saturation.

Measurement of slänthållfasthet typically involves laboratory shear tests on core samples, in situ core shear apparatus, or numerical simulation of layer bending. The outcomes guide design decisions for retaining walls, seawalls and dune protection, as well as the assessment of landslide potential on soft, layered slopes. In coastal management, adjusting berm height and vegetation placement can alter the effective layer strength, mitigating erosion without extensive hard‑engineering measures.