Definition - What does Vertical Stress mean?
Vertical stress is one of the principle stresses experienced by confined underground formations. The other stresses are minimum and maximum horizontal stresses. The magnitude and direction of these stresses depend on tectonic conditions and influence rock failure. Stresses in underground formations are not uniform and change in magnitude based on direction.
The stresses are generally compressive, anisotropic and non-homogenous.
Trenchlesspedia explains Vertical Stress
The three principle stresses mentioned above increase as depth increases. The principle vertical stress also known as overburden stress is a result of the weight of rock overlying a certain point of measurement. Fractures always form perpendicular to the minimum in-situ stress and in almost all cases, the vertical stress equals the weight of the overburden per unit area.
In some cases, higher sub-surface vertical stresses are created by upward forces greater than the overburden weight. At shallow depth, the minimum stress is the vertical stress causing fractures in the horizontal direction.