Lammonsiirtoilmiö

Lammonsiirtoilmiö, a Finnish term, translates to "snowdrift phenomenon" or "laminae shift phenomenon" in English. It refers to a specific type of instability observed in certain layered materials, particularly in fine-grained soils and snowpack. This phenomenon occurs when a weaker layer within a stratified material is subjected to shear stress, causing it to slide relative to adjacent, stronger layers.

The process is initiated by a critical stress threshold being reached within the weaker lamina. Once this threshold is surpassed, the shear strength of the layer is overcome, leading to macroscopic displacement. This sliding can propagate along the interface between layers, potentially causing significant structural deformation or failure. In snow science, the lammonsiirtoilmiö is a critical factor in understanding avalanche formation, as weak layers in the snowpack can fail and trigger slab avalanches. In geotechnical engineering, it is relevant to the stability of slopes and foundations composed of layered sediments.

Factors influencing the occurrence and severity of lammonsiirtoilmiö include the material properties of each layer (such as cohesion, friction angle, and plasticity), the thickness of the layers, and the applied stress regime. The presence of pore water pressure can also significantly reduce the effective stress and shear strength of a layer, making it more susceptible to sliding. Understanding and predicting this phenomenon is crucial for hazard assessment and risk management in environments prone to its effects.