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In-situ stress is the natural pre-existing stress confined in the rock before it is drilled, excavated or affected by outside influences. The in-situ stresses originate in the earth crust due to different factors, mainly the weight of the overlaying rock layers and tectonic movements (see Figure 1). The other factors are summarized in Figure 2. The in-situ stress can vary within one rock mass from one location to another due to varying rock properties. It is important to determine the magnitude and direction of in-situ stresses before doing underground work or designing underground structures, see table 1 for their different applications. In-situ stress characterization is the science of estimating the stress magnitudes and determining the orientation of three principle stresses: maximum horizontal stress, minimum horizontal stress, and vertical stress.

In-situ stress is the natural pre-existing stress confined in the rock before it is drilled, excavated or affected by outside influences. The in-situ stresses originate in the earth crust due to different factors, mainly the weight of the overlaying rock layers and tectonic movements (see [[:File:GeoWikiWriteOff2021-Tayyib-Figure1.png|Figure 1]]). The other factors are summarized in [[:File:GeoWikiWriteOff2021-Tayyib-Figure2.png|Figure 2]]. The in-situ stress can vary within one rock mass from one location to another due to varying rock properties. It is important to determine the magnitude and direction of in-situ stresses before doing underground work or designing underground structures, see [[File:GeoWikiWriteOff2021-Tayyib-Table1.png|Table 1]] for their different applications. In-situ stress characterization is the science of estimating the stress magnitudes and determining the orientation of three principle stresses: maximum horizontal stress, minimum horizontal stress, and vertical stress.

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File:GeoWikiWriteOff2021-Tayyib-Figure1.png|{{Figure number|1}}Movement of the tectonic plate (Earth’s outer shell: Crust & Lithospheric Mantle) generate in-situ stress. (from Duarte & Schellart, 2016) [1]

File:GeoWikiWriteOff2021-Tayyib-Figure1.png|{{Figure number|1}}Movement of the tectonic plate (Earth’s outer shell: Crust & Lithospheric Mantle) generate in-situ stress. (from Duarte & Schellart, 2016) [1]

File:GeoWikiWriteOff2021-Tayyib-Figure2.png|{{Figure number|2}}Summary of the different factors causing rock stress. (from Amadei & Stephanson, 1997) [2]

File:GeoWikiWriteOff2021-Tayyib-Figure2.png|{{Figure number|2}}Summary of the different factors causing rock stress. (from Amadei & Stephanson, 1997) [2]

File:GeoWikiWriteOff2021-Tayyib-Table1.png|Table 1 Activities requiring knowledge of in-situ stresses. (from Amadei & Stephanson,1997 as cited in Zhang, L 2016) [3.0]

File:GeoWikiWriteOff2021-Tayyib-Table1.png|'''Table 1''' Activities requiring knowledge of in-situ stresses. (from Amadei & Stephanson,1997 as cited in Zhang, L 2016) [3.0]

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The maximum shear stress is given by the circle’s radius R:

The maximum shear stress is given by the circle’s radius R:

R= ½ (σ1 - σ3)

R= ½ (σ1 - σ3)

[[File:GeoWikiWriteOff2021-Tayyib-Figure6.png|thumbnail|Figure 6 Mohr Circle is used in two dimensions. The x and y coordinates give the normal and shear stresses that are acting on a plane of arbitrary orientation. (from Fossen, H., 2016) [4.0]]]  

[[File:GeoWikiWriteOff2021-Tayyib-Figure6.png|framed|center|{{Figure number|6}}Mohr Circle is used in two dimensions. The x and y coordinates give the normal and shear stresses that are acting on a plane of arbitrary orientation. (from Fossen, H., 2016) [4.0]]]  

===3-D Mohr Circle===

===3-D Mohr Circle===