Generally, loose clasts or boulders only experience environmental stresses, up to the point where their mass may begin to impart some type of gravitational stress of significance. any place where there is evidence of weathering. Bedrock may experience any of these three broad types of stress-loading down to the bottom of the Critical Zone – i.e. the hydrosphere, atmosphere, or biosphere.

Environmental stresses arise due to interactions of rock with other Earth systems – i.e. Gravitational stresses, sometimes termed topographic stresses, arise due to topography or overburden that exerts gravitational forces (e.g. Tectonic stresses arise from the motion of tectonic plates in Earth's crust (see, for example, the world stress map, Heidbach et al., 2019). There are three primary categories of stress-loading that rocks experience: tectonic, gravitational and environmental, or combinations thereof. These stresses in turn, occur due to forces (stress-loading) acting on the rock. Martha-Cary (Missy) Eppes, in Reference Module in Earth Systems and Environmental Sciences, 2021 3.1 Origins of stressesĬrack propagation that comprises mechanical weathering occurs due to stresses that arise in rock, both bedrock and loose clasts. The theory predicts that a crack will propagate in order to lower the total energy of the system, by dissipating the elastic strain energy due to loading into the creation of a new surface. Crack propagation may be described using the energy criterion theory ( Griffith, 1920) which is based on thermodynamic and energy balance. Fracture occurs when the applied stress is sufficient to break the atomic bonds of the solid ( Anderson, 1995 Scholz, 2002). To study fracture mechanics, three important variables have to be taken into account: the applied stress, the size of the initially present flaw, and the fracture toughness ( Anderson, 1995). A short review of the fundamentals of crack propagation in linear elastic material is given, followed by a discussion on the effects of environmental conditions on propagation velocity.

Crack propagation may occur at low stress and is usually characterized by a slow propagation, so it is often referred to as subcritical crack propagation or stress corrosion. However, as it will be presented here, slow crack propagation in rocks is affected by the environment and the fluid chemistry and can be seen as mechanical phenomenon facilitated by chemical effects. Jean-Pierre Gratier, in Advances in Geophysics, 2013 3.2.1.2 Subcritical Crack PropagationĬrack propagation is described using fracture mechanics theory and would therefore have its place in the mechanical compaction section.

Principle app crack