<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE article  PUBLIC "-//NLM//DTD Journal Publishing DTD v3.0 20080202//EN" "http://dtd.nlm.nih.gov/publishing/3.0/journalpublishing3.dtd"><article xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" dtd-version="3.0" xml:lang="en" article-type="research article"><front><journal-meta><journal-id journal-id-type="publisher-id">WJET</journal-id><journal-title-group><journal-title>World Journal of Engineering and Technology</journal-title></journal-title-group><issn pub-type="epub">2331-4222</issn><publisher><publisher-name>Scientific Research Publishing</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="doi">10.4236/wjet.2023.112018</article-id><article-id pub-id-type="publisher-id">WJET-124796</article-id><article-categories><subj-group subj-group-type="heading"><subject>Articles</subject></subj-group><subj-group subj-group-type="Discipline-v2"><subject>Chemistry&amp;Materials Science</subject><subject> Engineering</subject></subj-group></article-categories><title-group><article-title>
 
 
  Rock Stress Measurement Methods in Rock Mechanics—A Brief Overview
 
</article-title></title-group><contrib-group><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Mohammed</surname><given-names>Sazid</given-names></name><xref ref-type="aff" rid="aff1"><sup>1</sup></xref><xref ref-type="corresp" rid="cor1"><sup>*</sup></xref></contrib><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Khaled</surname><given-names>Hussein</given-names></name><xref ref-type="aff" rid="aff1"><sup>1</sup></xref></contrib><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Khalid</surname><given-names>Abudurman</given-names></name><xref ref-type="aff" rid="aff1"><sup>1</sup></xref></contrib></contrib-group><aff id="aff1"><addr-line>Mining Engineering Department, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia</addr-line></aff><pub-date pub-type="epub"><day>15</day><month>03</month><year>2023</year></pub-date><volume>11</volume><issue>02</issue><fpage>252</fpage><lpage>272</lpage><history><date date-type="received"><day>27,</day>	<month>February</month>	<year>2023</year></date><date date-type="rev-recd"><day>6,</day>	<month>May</month>	<year>2023</year>	</date><date date-type="accepted"><day>9,</day>	<month>May</month>	<year>2023</year></date></history><permissions><copyright-statement>&#169; Copyright  2014 by authors and Scientific Research Publishing Inc. </copyright-statement><copyright-year>2014</copyright-year><license><license-p>This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/</license-p></license></permissions><abstract><p>
 
 
  The current brief review paper on rock stress measurement methods is very crucial factors in mining, civil infrastructure, geothermal energy, nuclear underground disposal, large underground oil storage caverns, etc as well as in geology and geophysical area. Measurement of 
  in situ rock stress is 
  a 
  very challenging and difficult quantity and not possible to measure directly. Measure the deformation or displacements or hydraulic factors by perturbing the rock and converting the measured quantity into rock stress. There are two main categories for measuring methods: direct and indirect methods. The most common methods of direct in situ stress techniques 
  are 
  briefly described including advantage
  s
  , disadvantages and limitation
  s
  . Moreover, authors included the application of Artificial Intelligence (AI) for rock stress measurement methods.
 
</p></abstract><kwd-group><kwd>Rock Stress</kwd><kwd> In Situ Stress</kwd><kwd> Hydraulic Fracturing</kwd><kwd> Flat Jack and Artificial  Intelligence</kwd></kwd-group></article-meta></front><body><sec id="s1"><title>1. Introduction</title><p>Understanding of the rock stress is of great importance and central concern in rock mechanics. Rock stress has a strong connection to a variety of issues in civil, mining, petroleum engineering, and geology and geophysics. <xref ref-type="table" rid="table1">Table 1</xref> listed of activities where rock stresses play a critical role [<xref ref-type="bibr" rid="scirp.124796-ref1">1</xref>] [<xref ref-type="bibr" rid="scirp.124796-ref2">2</xref>] . The stability of underground openings such as mines, shafts, tunnels, or caverns in civil and mining engineering projects is largely determined by the distribution and magnitude of rock stresses [<xref ref-type="bibr" rid="scirp.124796-ref2">2</xref>] [<xref ref-type="bibr" rid="scirp.124796-ref3">3</xref>] . Excessive magnitude of rock stress around underground openings (stress concentrations) can result in the failure of the rock mass locally or on a larger scale, causing roof collapse, sidewall movement and/or ground subsidence [<xref ref-type="bibr" rid="scirp.124796-ref4">4</xref>] [<xref ref-type="bibr" rid="scirp.124796-ref5">5</xref>] [<xref ref-type="bibr" rid="scirp.124796-ref6">6</xref>] . There are a number of publications published since long time regarding the rock stress problems in civil and mining projects and a large amount of literature exists on the subject of rock stresses and these factors [<xref ref-type="bibr" rid="scirp.124796-ref2">2</xref>] [<xref ref-type="bibr" rid="scirp.124796-ref6">6</xref>] - [<xref ref-type="bibr" rid="scirp.124796-ref17">17</xref>] .</p><p>Rock stress is enigmatic and fictitious quantities and can be classified into in situ stresses and induce stresses (<xref ref-type="fig" rid="fig1">Figure 1</xref>). The other terms used for in situ stress are natural, primitive or virgin, which exist in rock mass before any disturbances of human activities. Alternatively the induce stresses are generated due to human activities in or on the rock for build of engineering structures, i.e., tunnel, surface or underground mining, caverns, highway slopes etc [<xref ref-type="bibr" rid="scirp.124796-ref18">18</xref>] . Overall, in situ stresses are product of geological events which have several cycle of thermal, mechanical and physicochemical geological processes and majorly contributed for in situ stresses. Different classifications of in situ stresses have been proposed by several authors. According to Voight (1966), in situ stresses can be divided into two main categories: gravitational and tectonic [<xref ref-type="bibr" rid="scirp.124796-ref19">19</xref>] . This tectonic stress can be further broken down into two subgroups: current and residual, whereas Obert (1968) composed in situ stresses into internal and external stresses [<xref ref-type="bibr" rid="scirp.124796-ref20">20</xref>] .</p><table-wrap id="table1" ><label><xref ref-type="table" rid="table1">Table 1</xref></label><caption><title> Activities requiring knowledge of rock stress [<xref ref-type="bibr" rid="scirp.124796-ref1">1</xref>] [<xref ref-type="bibr" rid="scirp.124796-ref21">21</xref>] </title></caption><table><tbody><thead><tr><th align="center" valign="middle" >Civil and Mining Engineering</th></tr></thead><tr><td align="center" valign="middle" >Stability of underground excavations (tunnels, mines, caverns, shafts, stopes, haulages)</td></tr><tr><td align="center" valign="middle" >Drilling and blasting</td></tr><tr><td align="center" valign="middle" >Pillar design</td></tr><tr><td align="center" valign="middle" >Design of support systems</td></tr><tr><td align="center" valign="middle" >Prediction of rock bursts</td></tr><tr><td align="center" valign="middle" >Fluid flow and contaminant transport</td></tr><tr><td align="center" valign="middle" >Dams</td></tr><tr><td align="center" valign="middle" >Slope stability</td></tr><tr><td align="center" valign="middle" >Energy development</td></tr><tr><td align="center" valign="middle" >Borehole stability and deviation</td></tr><tr><td align="center" valign="middle" >Borehole deformation and failure</td></tr><tr><td align="center" valign="middle" >Fracturing and fracture propagation</td></tr><tr><td align="center" valign="middle" >Fluid flow and geothermal problems</td></tr><tr><td align="center" valign="middle" >Reservoir production management</td></tr><tr><td align="center" valign="middle" >Energy extraction and storage</td></tr><tr><td align="center" valign="middle" >Geology/Geophysics</td></tr><tr><td align="center" valign="middle" >Orogeny</td></tr><tr><td align="center" valign="middle" >Earthquake prediction</td></tr><tr><td align="center" valign="middle" >Plate tectonics</td></tr><tr><td align="center" valign="middle" >Neotectonics</td></tr><tr><td align="center" valign="middle" >Structural geology</td></tr><tr><td align="center" valign="middle" >Volcanology</td></tr><tr><td align="center" valign="middle" >Glaciation</td></tr></tbody></table></table-wrap><p>External stresses contained gravitational and tectonic stresses (regional stresses), whereas internal stresses contained of residual stresses. Various other author classified the in situ stresses almost in same categories [<xref ref-type="bibr" rid="scirp.124796-ref17">17</xref>] [<xref ref-type="bibr" rid="scirp.124796-ref22">22</xref>] [<xref ref-type="bibr" rid="scirp.124796-ref23">23</xref>] [<xref ref-type="bibr" rid="scirp.124796-ref24">24</xref>] . This paper included the general agreement of all authors and followed the Fairhurst, (2003) classifications.</p><p>The details of each types of in situ stress can be obtained through the reference book of Amadei and Stephansson (1997) [<xref ref-type="bibr" rid="scirp.124796-ref1">1</xref>] . One of the sources of in situ stress is tectonic forces. Tectonic stress can be felt like earthquake (i.e., active tectonic stress), however, it can occur silently in most cases (i.e., passive tectonic stress) either at plate-scale or broad regional scale as shown in <xref ref-type="fig" rid="fig2">Figure 2</xref> [<xref ref-type="bibr" rid="scirp.124796-ref25">25</xref>] . Passive tectonic stress may create greater vertical and horizontal stress thus it is the safety key for underground constructions, i.e., mining drift, caverns and tunnels etc. [<xref ref-type="bibr" rid="scirp.124796-ref26">26</xref>] .</p><p>Residual stresses (lock-in stresses) are the stresses that persist in a material even when no external loads or temperature gradients are present. These stresses are not caused by any external stimuli, but rather are inherent in the material itself. Residual stresses and strains can build up strain energy internally, which can have a major impact on the stability of rock structures, such as underground openings and surface excavations [<xref ref-type="bibr" rid="scirp.124796-ref25">25</xref>] . The stress brought by gravity’s force on a rock mass is known as gravitational stress. This stress is mainly caused by the weight of the overlying rocks and the self-weight of the rock mass. Gravitational stress can cause a significant amount of stress to be present in the rock mass, which can lead to instability and potential failure of the rock mass [<xref ref-type="bibr" rid="scirp.124796-ref27">27</xref>] . Terrestrial stress is the sum of all the stresses acting on a rock mass, including gravitational, tectonic, residual, and atmospheric stresses. These stresses can cause deformation in the rock mass, resulting in instability and potential failure [<xref ref-type="bibr" rid="scirp.124796-ref21">21</xref>] [<xref ref-type="bibr" rid="scirp.124796-ref28">28</xref>] .</p><p>Heidbach et al. (2018) presented the present-day in situ stress field on world map [<xref ref-type="bibr" rid="scirp.124796-ref29">29</xref>] . This project initiated in 1986 and continuous working in different phases. The latest phase end in 2016 and provided the World Stress Map (WSM) [<xref ref-type="bibr" rid="scirp.124796-ref29">29</xref>] . Authors outlined the 2016 WSM database release in detail and analyze the patterns of global and regional stress (<xref ref-type="fig" rid="fig3">Figure 3</xref>). For example, the WSM contained data on the present-day stress field of Saudi Arabia, primarily from petroleum wells in the country. According to the map, the majority of Saudi Arabia is in a region of normal to high tectonic stress, with some areas of very high stress in the northeast and southwest. Additionally, the WSM indicates that the region has seen a lot of activity in recent years, with many earthquakes recorded in the region over the past decade. This paper classifies methods under two main categories direct in situ measurement methods and indirect methods as shown in <xref ref-type="fig" rid="fig4">Figure 4</xref>. This paper will discuss methods of both categories with an emphasis on review of direct methods.</p></sec><sec id="s2"><title>2. In Situ Measuremnt Methoeds</title><p>There are two main categories for in situ stress measurement methods which are indirect and direct methods. The indirect methods based on the observation of rock behavior without any major disturbance of rock, i.e., core discing, statistics data, borehole breakout etc. Whereas disturb the rock by develop crack or crack opening, and induced strain. The examples are Hydraulic fracturing and relief methods (<xref ref-type="fig" rid="fig4">Figure 4</xref>).</p><p>In this paper, brief review description is presented for indirect methods and direct methods, but more emphasized on direct methods. Indirect methods of measuring in-situ stress include the use of statistics from collected data (database), back analysis of large rock volumes, core discing, the acoustic method (Kaiser effect), strain recovery methods and borehole breakouts. Each of these methods has its own advantages and limitations, and they can be used in combination to achieve a more comprehensive understanding of the subsurface conditions (<xref ref-type="table" rid="table2">Table 2</xref>). For example, statistic of measured data (database) can be employed in hydraulic fracturing field data to improve the accuracy of determining the shut-in pressure or estimating the in situ tensile strength of hydraulic fractures [<xref ref-type="bibr" rid="scirp.124796-ref30">30</xref>] [<xref ref-type="bibr" rid="scirp.124796-ref31">31</xref>] . While core discing can provide detailed information about the stress state of a specific rock formation [<xref ref-type="bibr" rid="scirp.124796-ref32">32</xref>] as shown in <xref ref-type="fig" rid="fig5">Figure 5</xref>. The conditions for core discing are high in situ stresses and the brittle rock. The thickness of the chips depends on stress intensity. As stresses increases, the size of disc decreases and in extreme cases, the discs can become so thin. Borehole breakout is a phenomenon that occurs when the rock is unable to sustain the compressive stress concentrations around a borehole (<xref ref-type="fig" rid="fig6">Figure 6</xref>). Borehole breakouts can be used to identify the direction of maximum horizontal stress. This results in breakage of the wall on two diametrically opposed zones, called ‘breakout’. In relief method the large rock volumes (back analysis) can be used to estimate the magnitude of the in-situ stress [<xref ref-type="bibr" rid="scirp.124796-ref33">33</xref>] [<xref ref-type="bibr" rid="scirp.124796-ref34">34</xref>] . The main issue with relief methods is that they only involve a small volume of rock, making the measured stresses vulnerable to shifts due to tiny changes in the mineral composition and rock grain size. To obtain more accurate results, it is possible to measure the local or average stresses over a larger volume of rock by overcoring multiple strain gages in a large-diameter bored raise at various heights [<xref ref-type="bibr" rid="scirp.124796-ref35">35</xref>] [<xref ref-type="bibr" rid="scirp.124796-ref36">36</xref>] . Over the years, the Acoustic method (Kaiser Effects) approach has been researched as a viable technique for identifying in situ stressors. The approach is based on an observation Kaiser made in 1950 and strain recovery methods are used to determine the anisotropy of the rock formation and the orientation of the principal stress axes.</p><table-wrap id="table2" ><label><xref ref-type="table" rid="table2">Table 2</xref></label><caption><title> Advantages and limitations of indirect in situ stress measurement methods</title></caption><table><tbody><thead><tr><th align="center" valign="middle" >Method</th><th align="center" valign="middle" >Advantages</th><th align="center" valign="middle" >Limitations</th></tr></thead><tr><td align="center" valign="middle" >Statistic of Measured Data (Database)</td><td align="center" valign="middle" >Can be used to analyze a large amount of data quickly and efficiently.</td><td align="center" valign="middle" >Results can be affected by outliers or incorrect data.</td></tr><tr><td align="center" valign="middle" >Core Discing</td><td align="center" valign="middle" >Can be used to determine rock properties such as strength and stiffness. Operated at 10<sup>-3</sup> m<sup>3</sup> rock volume.</td><td align="center" valign="middle" >Sample size is limited and may not be representative of the entire formation.</td></tr><tr><td align="center" valign="middle" >Borehole Breakouts</td><td align="center" valign="middle" >Can be used to determine the orientation of stress in the rock surrounding the borehole. Operated at 10<sup>−2</sup> - 10<sup>2</sup> m<sup>3</sup> rock volume.</td><td align="center" valign="middle" >Results can be affected by borehole deviation and the presence of drilling-induced fractures.</td></tr><tr><td align="center" valign="middle" >Relief of Large Rock Volumes (Back Analysis)</td><td align="center" valign="middle" >Can be used to determine the location and size of large rock volumes. Operated at 10<sup>2</sup> - 10<sup>3</sup> m<sup>3</sup> rock volume.</td><td align="center" valign="middle" >Results can be affected by the accuracy of the data and the assumptions made during the analysis.</td></tr><tr><td align="center" valign="middle" >Acoustic Method (Kaiser Effect)</td><td align="center" valign="middle" >Can be used to determine the mechanical properties of rock. Operated at 10<sup>−3</sup> m<sup>3</sup> rock volume.</td><td align="center" valign="middle" >Results can be affected by the presence of fluid in the pores of the rock.</td></tr><tr><td align="center" valign="middle" >Strain Recovery Methods</td><td align="center" valign="middle" >Can be used to determine the deformation of rock. Operated at 10<sup>−3</sup> m<sup>3</sup> rock volume.</td><td align="center" valign="middle" >Results can be affected by the accuracy of the data and the assumptions made during the analysis.</td></tr></tbody></table></table-wrap></sec><sec id="s3"><title>3. Hydraulic Methods</title><p>Hydraulic methods are one of the most widely used techniques for measuring in-situ stress levels. This method involves injecting pressurized liquids into an existing fracture in a rock formation, causing it to widen and create new fractures. By measuring the pressure response of these fractures, the stress levels of the material can be determined. Conventional or classical hydraulic fracturing and hydraulic tests on pre-existing fractures (HTPF) are two of the most used methods for measuring stress levels using hydraulic methods.</p><sec id="s3_1"><title>3.1. Conventional (Classical) Hydraulic Fracturing (HF)</title><p>Hydraulic fracturing (HF) was used in the 1940s, originally to stimulate production from low permeable oil-bearing formations. In 1957, Hubbert and Willis developed the classical concept of hydraulic fracturing to be useful for in-situ stress measuring. HF is the best-known method to evaluate in-situ stress at deeper levels [<xref ref-type="bibr" rid="scirp.124796-ref33">33</xref>] . A straddle packer is used to seal off a section of a borehole, which is usually no longer than 1 meter in length. This sealed off section is then pressurized with a fluid, usually water, at a slow rate. This causes tensile stresses to build up at the borehole wall until it ruptures, initiating a hydro fracture.</p><p>HF is used to measure the in-situ stress of subsurface rock by propagating a fracture in the rock. Two fractures begin on opposing sides of the borehole’s perimeter, with the fracture plane typically parallel to the borehole axis. The direction of the fracture is identified by looking at the traces on the borehole wall, and it spreads in the direction of least resistance. The components recorded in a vertical borehole are two of the primary stresses, and this orientation is related to the direction of the highest horizontal stress in vertical or sub-vertical boreholes [<xref ref-type="bibr" rid="scirp.124796-ref33">33</xref>] . This technique is two-dimensional and only measures the greatest and least normal stresses in the plane perpendicular to the borehole axis as presented in <xref ref-type="fig" rid="fig7">Figure 7</xref>. The setup of HF is provided under the next method which is hydraulic tests of pre-existing fractures (HTPF) since both share same setup as presented in <xref ref-type="fig" rid="fig8">Figure 8</xref>.</p><p>HF is an effective and cost-efficient in-situ stress measurement method, allowing for direct and accurate measurements at depths not accessible by other methods. It can measure stress in multiple orientations, providing a more comprehensive analysis of the stress field and its impact. Additionally, it is fast and non-destructive, making it a great option for stress measurements [<xref ref-type="bibr" rid="scirp.124796-ref37">37</xref>] . HF method can provide high confidence measurement of in-situ stress at several kilo meters depths [<xref ref-type="bibr" rid="scirp.124796-ref33">33</xref>] . “Rummel has successfully determined in situ stresses by hydraulic fracturing at a depth of approximately 6 km, using aluminum packers”. So far, hydraulic fracturing has been successfully used to measure in-situ stress at a depth of up to 9 km. <xref ref-type="fig" rid="fig8">Figure 8</xref> shows the technique of HF [<xref ref-type="bibr" rid="scirp.124796-ref38">38</xref>] .</p><p>On the other hand, the main drawback of using hydraulic fracturing as an in-situ stress measurement method is that it has the potential to cause damage to the surrounding rock. Additionally, the measurements obtained may be affected by factors such as temperature, pore pressure, and the presence of fractures in the rock [<xref ref-type="bibr" rid="scirp.124796-ref37">37</xref>] .</p></sec><sec id="s3_2"><title>3.2. Hydraulic Tests on Pre-Existing Fractures (HTPF)</title><p>Hydraulic Tests on Pre-existing Fractures (HTPF) is a method of measuring the horizontal stress in the rock mass by using hydraulic pressure to reopen existing fractures in the rock [<xref ref-type="bibr" rid="scirp.124796-ref39">39</xref>] [<xref ref-type="bibr" rid="scirp.124796-ref40">40</xref>] . It is used to determine the depth and orientation of existing fractures, and to measure the in-situ stress in the surrounding rock. The HTPF method can be used to measure the stress in the horizontal, vertical, and diagonal directions, and can provide information about the magnitude of the stresses in the rock [<xref ref-type="bibr" rid="scirp.124796-ref39">39</xref>] . Valette and Cornet presented both the theoretical foundations and practical implementation of HTPF, eliminating the need to create new fractures in the rock mass by instead re-opening existing fractures [<xref ref-type="bibr" rid="scirp.124796-ref33">33</xref>] .</p><p>Combining the HF and HTPF methods is often beneficial when the borehole is parallel to one of the principal stresses (typically the vertical direction). The HF method can be used to accurately determine the direction and magnitude of the minimum principal stress, while the HTPF results can be used to estimate the magnitude of the maximum horizontal principal stress and the vertical stress components, without taking into account either pore pressure or tensile strength [<xref ref-type="bibr" rid="scirp.124796-ref40">40</xref>] . When cost and time are the most important considerations, the HTPF method should replace hydro-fracturing only when the borehole axis is not expected to be parallel to the principal stresses, or when there are significant weak points in the rock mass [<xref ref-type="bibr" rid="scirp.124796-ref41">41</xref>] .</p></sec></sec><sec id="s4"><title>4. Relief Methods</title><p>The core purpose of relief methods is to detach a piece of rock from the stress environment in the surrounding rock mass and observe its response [<xref ref-type="bibr" rid="scirp.124796-ref1">1</xref>] . Relief methods can be categorized into two main groups: surface relief methods and borehole relief methods.</p><sec id="s4_1"><title>4.1. Surface Relief Methods</title><p>The rock’s response to stress reduction is measured by surface relief techniques like the flat jack method and the curved jack methods, which measure the distance between gauges (pins) on the rock surface before and after the relief. This technique is most appropriate for measuring tunnel surfaces, and for more information, readers should refer to Amadei and Stephansson [<xref ref-type="bibr" rid="scirp.124796-ref33">33</xref>] . Surface relief methods have a few drawbacks. Humidity and dust can affect the accuracy of the gages or pins used. Additionally, the strain or displacement measurements are taken from a rock surface that could have been altered due to the effects of weathering or the excavation process. To connect localized stresses in the sides of the excavation to the more distant stress components, estimates of stress concentration factors must be utilized [<xref ref-type="bibr" rid="scirp.124796-ref1">1</xref>] .</p></sec><sec id="s4_2"><title>4.2. Flat Jack Method</title><p>Flat jack is one of the earliest techniques used in rock mechanics to measure in-situ stress within the rock mass [<xref ref-type="bibr" rid="scirp.124796-ref17">17</xref>] . During the 1950s and 1960s, it was suggested to assess the deformability of rock masses and it soon became widely used for calculating stresses [<xref ref-type="bibr" rid="scirp.124796-ref1">1</xref>] . One of the earliest methods of stress measurement in rock mechanics was the flat jack method [<xref ref-type="bibr" rid="scirp.124796-ref1">1</xref>] . Flat jacking is a method used to determine the in situ stress and also used in finding engineering properties of existing structures for structural evaluation. It is also used to determine compressive strength of masonry structures.</p><p>A flat jack is a thin, hydraulic load cell that is inserted into a typical mortar joint, in which a slot has been formed (<xref ref-type="fig" rid="fig9">Figure 9</xref>). When pressurized, the flat jack exerts stress on the surrounding masonry and by measuring surface deformations, information on the existing state of stress as well as the stiffness and strength of the masonry can be obtained. This method directly measures the actual state of compressive stress present within the masonry and is useful for determining stress gradients present within a masonry wall or column [<xref ref-type="bibr" rid="scirp.124796-ref42">42</xref>] . Mechanically, the route taken by the rock during a flat jack test can be represented as illustrated in <xref ref-type="fig" rid="fig1">Figure 1</xref>0. The rock is thought to be elastic and to be compressed perpendicular to the jack surface [<xref ref-type="bibr" rid="scirp.124796-ref1">1</xref>] . The original spacing between two reference pins is marked as d<sub>o</sub>, and the unidentified normal stress is marked as σ (at point A), When the slot is cut, the normal stress across the slot is reduced from σ to zero (at the free surface), and the distance between the pins is reduced by a magnitude of 2d (at point B). The pins restore to their initial position once the jack is pressured to the cancellation pressure pc. (<xref ref-type="fig" rid="fig1">Figure 1</xref>1). The main benefit of the flat jacking technique was that it could be used with a basic extensometer (i.e., located between points A and B) without having to create unique tools or sensors that could fit into a narrow hole [<xref ref-type="bibr" rid="scirp.124796-ref17">17</xref>] .</p><p>Other advantages of flat jacking method are relatively straight forward, cost-effective, and can be implemented without needing to calculate the elastic modulus. On the other hand, flat jacking can only be used at the surface of the excavation, where rock is likely to be overly stressed, leading to an unreliable estimate [<xref ref-type="bibr" rid="scirp.124796-ref43">43</xref>] . A refined version of flat jacking method was done by Jaeger and Cook to make it suitable for measuring in-situ stress at deeper levels. The maximum depth they measure stress at was 7 m [<xref ref-type="bibr" rid="scirp.124796-ref17">17</xref>] . The advantages, disadvantages and limitation of flat jack methods are tabulated in <xref ref-type="table" rid="table3">Table 3</xref>.</p><table-wrap id="table3" ><label><xref ref-type="table" rid="table3">Table 3</xref></label><caption><title> The advantages and disadvantages of flat jacking method</title></caption><table><tbody><thead><tr><th align="center" valign="middle" >Advantages</th></tr></thead><tr><td align="center" valign="middle" >- Direct measurement of the compressive stress present within the masonry. - Useful for determining stress gradients within a masonry wall or column. - Can be used to determine the in-situ stress and compressive strength of masonry structures. - Provides information on the existing state of stress as well as the stiffness and strength of masonry.</td></tr><tr><td align="center" valign="middle" >Limitations</td></tr><tr><td align="center" valign="middle" >- Requires the cutting of a slot in the masonry, which may cause damage to the structure. - Can be time-consuming and labor-intensive. - Requires specialized equipment and trained personnel to perform the test.</td></tr><tr><td align="center" valign="middle" >Suitable for:</td></tr><tr><td align="center" valign="middle" >- Evaluation of existing masonry structures such as walls and columns. - Determining the in-situ stress and compressive strength of masonry structures. - Structural evaluation of existing structures.</td></tr></tbody></table></table-wrap></sec><sec id="s4_3"><title>4.3. Borehole Relief Methods</title><p>Borehole relief methods (also known as overcoring methods) are used to measure in situ stress based on the stress relief around the borehole. This method involves drilling a borehole into the ground, then measuring the amount of relief in the external forces around the borehole. The relief of external forces can then be used to estimate the magnitude of the in-situ stress as well as the lateral pressure coefficient [<xref ref-type="bibr" rid="scirp.124796-ref44">44</xref>] . Borehole relief methods involve three types: overcoring of measuring cells in pilot holes, borehole slotting and overcoring of boreholes bottom cells.</p><p>Overcoring of Measuring Cells in Pilot Holes</p><p>Based on overcoring principle, overcoring of measuring cells in pilot holes can be broken down into three further categories: soft inclusion cells, deformation meters to measure wall displacements during overcoring, and stiff/solid cells [<xref ref-type="bibr" rid="scirp.124796-ref33">33</xref>] .</p><p>- Soft Inclusion Cells</p><p>Soft inclusion cells are a technique used to measure in-situ stresses in rocks and soils by inserting a soft, pliable material into a borehole and measuring the deformation of the material to calculate the stress in the surrounding rocks [<xref ref-type="bibr" rid="scirp.124796-ref45">45</xref>] as shown in <xref ref-type="fig" rid="fig1">Figure 1</xref>2 and <xref ref-type="fig" rid="fig1">Figure 1</xref>3.</p><p>The core concept of a soft cell is based on the linear elasticity theory for continuous, homogeneous, and isotropic rocks. By measuring at least six strain components on the borehole wall in different orientations, it is possible to determine the total stress tensor at the test location. Moreover, there are recognized theories for detecting stress in anisotropic rocks [<xref ref-type="bibr" rid="scirp.124796-ref33">33</xref>] .</p><p>Based on the aforementioned concept, the most often used instruments are the CSIR cell, CSIRO cell, and Borre Probe cell [<xref ref-type="bibr" rid="scirp.124796-ref33">33</xref>] . In good rock conditions, these devices have a range of between 10 and 50 meters from existing free surfaces. Unbroken cores at least 150 to 300 millimeters in length are required to provide accurate results. In vertical water-filled boreholes up to depths of 500 to 1000 meters, many adaptations of the CSIR triaxial strain cell have been proposed and tested as presented in <xref ref-type="table" rid="table4">Table 4</xref> [<xref ref-type="bibr" rid="scirp.124796-ref1">1</xref>] [<xref ref-type="bibr" rid="scirp.124796-ref33">33</xref>] .</p><table-wrap id="table4" ><label><xref ref-type="table" rid="table4">Table 4</xref></label><caption><title> Characteristics of the most common soft overcoring cells</title></caption><table><tbody><thead><tr><th align="center" valign="middle" >Instrument</th><th align="center" valign="middle" >No of active gauges</th><th align="center" valign="middle" >Measuring depths</th><th align="center" valign="middle" >Continuous logging</th></tr></thead><tr><td align="center" valign="middle" >CSIR cell</td><td align="center" valign="middle" >12</td><td align="center" valign="middle" >10 - 50 m</td><td align="center" valign="middle" >No</td></tr><tr><td align="center" valign="middle" >CSIRO cell</td><td align="center" valign="middle" >9/12</td><td align="center" valign="middle" >Up to 1000 m</td><td align="center" valign="middle" >Yes, by cable</td></tr><tr><td align="center" valign="middle" >Borre probe cell</td><td align="center" valign="middle" >9</td><td align="center" valign="middle" >Up to 30 m</td><td align="center" valign="middle" >Yes, built in data logger.</td></tr></tbody></table></table-wrap><p>The Borre Probe is a soft stress cell, which is used to measure the stress field within a single borehole measurement. It works by measuring the strains induced by overcoring in the rock and then calculating the stress from the measured strains. The Borre Probe is different from other stress cells in that it does not measure displacement but rather strains. This means that the Borre Probe is more accurate than other stress cells in determining the stress field in a single borehole [<xref ref-type="bibr" rid="scirp.124796-ref39">39</xref>] [<xref ref-type="bibr" rid="scirp.124796-ref43">43</xref>] . All three of these instruments have the advantage of being able to measure the 3D state of stress from a single measurement point as shown in <xref ref-type="fig" rid="fig1">Figure 1</xref>4 and <xref ref-type="fig" rid="fig1">Figure 1</xref>5. This is a major benefit that they all share [<xref ref-type="bibr" rid="scirp.124796-ref33">33</xref>] .</p><p>- Deformation Meters</p><p>The theory behind deformation meters is the same as it is for soft inclusion cells for measuring displacements. After being over cored, the instrument is inserted into a pilot hole. Instead of measuring strain during overcoring, these sensors measure one or more variations in pilot hole diameter. The Sigra in situ stress tool and the USBM gage are two commercial deformation-type gages (IST) [<xref ref-type="bibr" rid="scirp.124796-ref33">33</xref>] .</p><p>- STIFF/SOLID CELLS</p><p>The disparity in material qualities between the rock and inclusion material causes stiff/solid cells, which are less common than the other two categories, to generally have problems [<xref ref-type="bibr" rid="scirp.124796-ref33">33</xref>] . Overcoring techniques performed in a borehole are among the most popular ways to relieve stress. The US Bureau of Mines stress gauge is one stress-measurement tool that makes use of the idea of overcoring. The USBM gauge is simply a cylindrical instrument with three pairs of pistons that are diametrically opposed and evenly distributed around the circumference. These pistons are coupled to cantilevers within the tool, which deflection is gauged by strain gauges. A tiny borehole, about the same diameter as the gauge (38 mm), is driven into the rock to be used with the USBM gauge. The pistons are initially tensioned to create adequate contact with the borehole walls before the gauge is placed into the hole (<xref ref-type="fig" rid="fig1">Figure 1</xref>6(a)). Then, a drill bit with a bigger diameter (usually 150 mm) is used to overcore this small hole to a depth that extends at least one overcore diameter past the gauge (<xref ref-type="fig" rid="fig1">Figure 1</xref>6(b)). A nearly stress-free circular rock zone will be produced by the overcoring process. The three sets of cantilevers monitor the radial deformation of the (inner) borehole as the stresses acting on this annular region are released [<xref ref-type="bibr" rid="scirp.124796-ref46">46</xref>] .</p><p><xref ref-type="table" rid="table5">Table 5</xref> denoted all direct methods of in situ stress measurement techniques advantages and limitations.</p></sec></sec><sec id="s5"><title>5. Use the Artificial Intelligence In-Situ Stress Measurement</title><p>One way in which Artificial intelligence (AI) can be used in in-situ stress measurement is through the application of machine learning algorithms to data collected from boreholes [<xref ref-type="bibr" rid="scirp.124796-ref47">47</xref>] [<xref ref-type="bibr" rid="scirp.124796-ref48">48</xref>] . Boreholes are drilled into the subsurface and instruments are used to measure various parameters, such as rock strength, pore pressure, and temperature [<xref ref-type="bibr" rid="scirp.124796-ref47">47</xref>] . These data can be used to train machine learning models, which can then be used to make predictions about the stress state at other locations in the subsurface (<xref ref-type="fig" rid="fig1">Figure 1</xref>7). Overall, AI can greatly enhance</p><table-wrap id="table5" ><label><xref ref-type="table" rid="table5">Table 5</xref></label><caption><title> Advantages and limitations of direct in-situ stress measurement Methods</title></caption><table><tbody><thead><tr><th align="center" valign="middle" >Method</th><th align="center" valign="middle" >Advantages</th><th align="center" valign="middle" >Limitations</th></tr></thead><tr><td align="center" valign="middle" >Relief (Overcoring)</td><td align="center" valign="middle" >Most developed technique in both theory and practice. Operated at 10<sup>−</sup><sup>3</sup> - 10<sup>−</sup><sup>2</sup> m<sup>3</sup> rock volume.</td><td align="center" valign="middle" >Scattering due to small rock volume. Requires drill rig. Only 2D.</td></tr><tr><td align="center" valign="middle" >Doorstopper</td><td align="center" valign="middle" >Works in jointed and high stressed rocks.</td><td align="center" valign="middle" >Only 2D. Requires drill rig.</td></tr><tr><td align="center" valign="middle" >Flat jacking</td><td align="center" valign="middle" >Direct measurement of the compressive stress present. Both 2D/3D within the masonry. Useful for determining stress gradients within a masonry wall or column. Operated at 0.5 - 2 m<sup>3</sup> rock volume.</td><td align="center" valign="middle" >Requires the cutting of a slot in the masonry, which may cause damage to the structure. Can be time-consuming and labor-intensive. Requires specialized equipment and trained personnel to perform the test.</td></tr><tr><td align="center" valign="middle" >Hydraulic fracturing (HF)</td><td align="center" valign="middle" >Measurements in existing hole. Low scattering in the results. Involves a fairly large rock volume. Quick. Operated at 0.5 - 50 m<sup>3</sup> rock volume.</td><td align="center" valign="middle" >Only 2D. The theoretical limitations in the evaluation of σ<sub>h</sub>. Disturbs water chemistry. Only 2D.</td></tr><tr><td align="center" valign="middle" >HTPF</td><td align="center" valign="middle" >Measurements in existing hole. Can be applied when high stresses exist and overcoring and hydraulic fracturing fail. Both 2D/3D. Operated at 1 - 10 m<sup>3</sup> rock volume.</td><td align="center" valign="middle" >Time-consuming. Requires existing fractures in the hole with varying strikes and dips.</td></tr></tbody></table></table-wrap><p>the efficiency, accuracy and robustness of in-situ stress measurement, by providing a fast and efficient way to analyze data and make predictions about the subsurface stress state.</p><p>There is a case study in this field, a geometric equation for borehole deformation under stress was developed using the basic principles of elasticity. The relationship between in situ stress and borehole deformation was then established, and a prediction model for in situ stress was proposed. Numerical simulations were used to analyze the deformation effect in different types of rock. The study also used an artificial neural network to predict the shear wave time difference using logging parameters such as density and natural gamma radiation. The results showed that the borehole geometry under stress was quasi-elliptic and that the predicted geometry was consistent with the actual geometry. The overall error of the in situ stress predicted using this method was less than 9.2%, with the highest accuracy in coal seams. This suggests that the proposed method is feasible [<xref ref-type="bibr" rid="scirp.124796-ref49">49</xref>] . Also, there are another paper aims to compare and improve the minimum horizontal stress estimation through various machine learning regression techniques, including parametric and non-parametric models. The study was based on 79 laboratory data and validated against 23 field data. The results showed that the artificial neural network was able to predict the minimum horizontal stress with an average error rate of 10.16% and a root mean square error of 3.87 MPa, which is a meaningful improvement compared to conventional in-situ measurement techniques [<xref ref-type="bibr" rid="scirp.124796-ref50">50</xref>] . On the other hand, an AI-based methodology is proposed to identify geomechanical parameters from borehole injection pressure curves obtained during hydraulic fracturing tests. A genetic algorithm minimizes the difference between observed and predicted pressure curves while an artificial neural network substitutes hydraulic fracture simulations to reduce computational time. A recursive strategy predicts pressure curves and a hyperparameter tuning technique selects appropriate neural network parameters. The framework was applied to a KGD problem and confirmed its ability to identify geomechanical parameters from fracturing tests [<xref ref-type="bibr" rid="scirp.124796-ref51">51</xref>] .</p><p>Another study that used machine learning to predict in-situ stresses from logging data was conducted by Ibrahim et al. 2021 [<xref ref-type="bibr" rid="scirp.124796-ref52">52</xref>] . In this study, the researchers collected logging data from boreholes drilled in the subsurface. They then used machine learning algorithms, such as Random Forest or Support Vector Machine, to train models on this data.</p><p>These models were able to predict the in-situ stresses at different locations in the subsurface with high accuracy. The results of this study showed that machine learning can be a powerful tool for in-situ stress prediction and can improve the efficiency and accuracy of subsurface stress measurements. However, the practical use of these AI models is still a concern as many require some level of expertise to be used, as they are not in a form of simple mathematical equations. There is still a need to explore advanced AI methods and the limited availability of data for AI simulations is also a major challenge [<xref ref-type="bibr" rid="scirp.124796-ref53">53</xref>] .</p></sec><sec id="s6"><title>6. Conclusion</title><p>Knowledge of in situ stress have major impact to any infrastructure project related mining, civil engineering, geothermal, large underground opening etc. Therefore, this paper given a brief review of the in situ stress measurement methods and more emphasized on most common methods. Each method has their limitation for applicability. In direct methods are commonly used by experts without disturbing the rock mass. Some area where no access of underground opening for direct measurement of in situ stress, hydraulic fracturing tends to be appropriate choice at greater depth up to several kilometers. Applicable of HTPF technique if large amount of intersection of fracturing existing, which remove the ambiguity associate with conventional hydraulic fracturing. Relief methods used for in situ stress measurement where underground accessibility possible. Some methods can be carried out directly on rock core sample in laboratories without visiting the project site. At last authors tried to link Artificial Intelligence (AI) for measure the in situ stress which will be remain a major and interesting topic in rock mechanics.</p></sec><sec id="s7"><title>Acknowledgements</title><p>The authors acknowledge the blind reviewer who makes possible our manuscript up to acceptance level in esteem journal. Also, very thankful to editor of WJET and SCIRP publisher for their kind support from submission to accepting the MS.</p></sec><sec id="s8"><title>Conflicts of Interest</title><p>The authors declare no conflicts of interest regarding the publication of this paper.</p></sec><sec id="s9"><title>Cite this paper</title><p>Sazid, M., Hussein, K. and Abudurman, K. (2023) Rock Stress Measurement Methods in Rock Mechanics—A Brief Overview. World Journal of Engineering and Technology, 11, 252-272. https://doi.org/10.4236/wjet.2023.112018</p></sec></body><back><ref-list><title>References</title><ref id="scirp.124796-ref1"><label>1</label><mixed-citation publication-type="other" xlink:type="simple">Amadei, B. and Stephansson, O. (1997) Rock Stress and Its Measurement. Springer, Berlin. https://doi.org/10.1007/978-94-011-5346-1</mixed-citation></ref><ref id="scirp.124796-ref2"><label>2</label><mixed-citation publication-type="other" xlink:type="simple">Singh, P.K., Wasnik, A.B., Kainthola, A., Sazid, M. and Singh, T.N. (2013) The Stability of Road Cut Cliff Face along SH-121: A Case Study. Natural Hazards, 68, 497-507. https://doi.org/10.1007/s11069-013-0627-9</mixed-citation></ref><ref id="scirp.124796-ref3"><label>3</label><mixed-citation publication-type="other" xlink:type="simple">Hoek, E. and Brown, E.T. (2019) The Hoek–Brown Failure Criterion and GSI— 2018 Edition. Journal of Rock Mechanics and Geotechnical Engineering, 11, 445-463.  
https://doi.org/10.1016/j.jrmge.2018.08.001</mixed-citation></ref><ref id="scirp.124796-ref4"><label>4</label><mixed-citation publication-type="other" xlink:type="simple">Ansari, T., Kainthola, A., Singh, K.H., Singh, T.N. and Sazid, M. (2021) Geotechnical and Micro-Structural Characteristics of Phyllite Derived Soil; Implications for Slope Stability, Lesser Himalaya, Uttarakhand, India. Catena, 196, Article ID: 104906.  
https://doi.org/10.1016/j.catena.2020.104906</mixed-citation></ref><ref id="scirp.124796-ref5"><label>5</label><mixed-citation publication-type="other" xlink:type="simple">Sazid, M., Wasnik, A., Singh, P., Kainthola, A. and Singh, T.N. (2012) A Numerical Simulation of Influence of Rock Class on Blast Performance. International Journal of Earth Sciences and Engineering, 5, 1189-1195.</mixed-citation></ref><ref id="scirp.124796-ref6"><label>6</label><mixed-citation publication-type="other" xlink:type="simple">Sazid, M. and Singh, T.N. (2015) Numerical Assessment of Spacing–Burden Ratio to Effective Utilization of Explosive Energy. International Journal of Mining Science and Technology, 25, 291-297. https://doi.org/10.1016/j.ijmst.2015.02.019</mixed-citation></ref><ref id="scirp.124796-ref7"><label>7</label><mixed-citation publication-type="book" xlink:type="simple">Adams, J. and Bell, J.S. (1991) Crustal Stresses in Canada. In: Slemmons, D.B., Engdahl, E.R., Zoback, M.D. and Blackwell, D.D., Eds., Neotectonics of North America, Geological Society of America, Inc., Boulder.</mixed-citation></ref><ref id="scirp.124796-ref8"><label>8</label><mixed-citation publication-type="book" xlink:type="simple">Franklin, J.A. and Hungr, O. (1978) Rock Stresses in Canada Their Relevance to Engineering Projects. In: Franklin, J.A. and Hungr, O., Eds., Geomechanik gebirgsbildender Vorgange und deren Auswirkungen auf Felsbauten ober und unter Tage [Geomechanics of Orogenetic Events and Their Effects on the Construction of Rock Structures on Subsurface and Underground], Springer, Vienna, 25-46.  
https://doi.org/10.1007/978-3-7091-4160-1_3</mixed-citation></ref><ref id="scirp.124796-ref9"><label>9</label><mixed-citation publication-type="other" xlink:type="simple">Lee, C.F. (1981) In-situ Stress Measurements in Southern Ontario. 22nd U.S. Symposium on Rock Mechanics, Cambridge, 29 June-2 July 1981, 465-472.</mixed-citation></ref><ref id="scirp.124796-ref10"><label>10</label><mixed-citation publication-type="other" xlink:type="simple">Lee, C.F. and Lo, K.Y. (1976) Rock Squeeze Study of Two Deep Excavations at Niagara Falls. Rock Engineering for Foundation and Slopes, 116-140  
https://cedb.asce.org/CEDBsearch/record.jsp?dockey=0265474</mixed-citation></ref><ref id="scirp.124796-ref11"><label>11</label><mixed-citation publication-type="other" xlink:type="simple">Lo, K.Y. and Morton, J.D. (1976) Tunnels in Bedded Rock with High Horizontal Stresses. Canadian Geotechnical Journal, 13, 216-230.</mixed-citation></ref><ref id="scirp.124796-ref12"><label>12</label><mixed-citation publication-type="other" xlink:type="simple">Carlsson, A. and Olsson, T. (1982) Rock Bursting Phenomena in a Superficial Rock Mass in Southern Central Sweden. Rock Mechanics, 15, 99-110.</mixed-citation></ref><ref id="scirp.124796-ref13"><label>13</label><mixed-citation publication-type="other" xlink:type="simple">Hast, N. (1958) The Measurement of Rock Pressure in Mines. Norstedts Forlag, Stockholm.</mixed-citation></ref><ref id="scirp.124796-ref14"><label>14</label><mixed-citation publication-type="other" xlink:type="simple">Myrvang, A.M. (1993) Rock Stress and Rock Stress Problems in Norway. Rock Testing and Site Characterization, 3, 461-471.  
https://doi.org/10.1016/B978-0-08-042066-0.50025-2</mixed-citation></ref><ref id="scirp.124796-ref15"><label>15</label><mixed-citation publication-type="other" xlink:type="simple">Stephansson, O. (1993) Rock Stress in the Fennoscandian Shield. Rock Testing and Site Characterization, 3, 445-459.  
https://doi.org/10.1016/B978-0-08-042066-0.50024-0</mixed-citation></ref><ref id="scirp.124796-ref16"><label>16</label><mixed-citation publication-type="other" xlink:type="simple">Stephansson, O., Sarkka, P. and Myrvang, A.M. (1986) State of Stress In Fennoscandia. Proceedings of the International Symposium on Rock Stress and Rock Stress Measurements, Stockholm, 1-3 September 1986, 21-32.  
https://urn.kb.se/resolve?urn=urn%3Anbn%3Ase%3Altu%3Adiva-40174</mixed-citation></ref><ref id="scirp.124796-ref17"><label>17</label><mixed-citation publication-type="journal" xlink:type="simple"><name name-style="western"><surname>Fairhurst</surname><given-names> C. </given-names></name>,<etal>et al</etal>. (<year>2003</year>)<article-title>Stress Estimation in Rock: A Brief History and Review</article-title><source> International Journal of Rock Mechanics and Mining Sciences</source><volume> 40</volume>,<fpage> 957</fpage>-<lpage>973</lpage>.<pub-id pub-id-type="doi"></pub-id></mixed-citation></ref><ref id="scirp.124796-ref18"><label>18</label><mixed-citation publication-type="other" xlink:type="simple">Kainthola, A., Singh, P.K., Wasnik, A. and Singh, T.N. (2012) Finite Element Analysis of Road Cut Slopes Using Hoek &amp; Brown Failure Criterion. International Journal of Earth Sciences and Engineering, 5, 1100-1109.</mixed-citation></ref><ref id="scirp.124796-ref19"><label>19</label><mixed-citation publication-type="other" xlink:type="simple">Voight, B. (1966) Interpretation of In-Situ Stress Measurements. 1st Congo International Society for Rock Mechanics (ISRM), September 1966, Lisbon, 48-332.</mixed-citation></ref><ref id="scirp.124796-ref20"><label>20</label><mixed-citation publication-type="other" xlink:type="simple">Obert, L. (1968) Determination of Stress in Rock. A State of the Art Report. ASTM Special Technical Publication NO. 429, 1966, 1-56.  
https://doi.org/10.1520/STP44677S</mixed-citation></ref><ref id="scirp.124796-ref21"><label>21</label><mixed-citation publication-type="journal" xlink:type="simple"><name name-style="western"><surname>Sazid</surname><given-names> M. </given-names></name>,<etal>et al</etal>. (<year>2017</year>)<article-title>Effect of Underground Blasting on Surface Slope Stability: A Numerical Approach</article-title><source> American Journal of Mining and Metallurgy</source><volume> 4</volume>,<fpage> 32</fpage>-<lpage>36</lpage>.<pub-id pub-id-type="doi"></pub-id></mixed-citation></ref><ref id="scirp.124796-ref22"><label>22</label><mixed-citation publication-type="other" xlink:type="simple">Bielenstein, H.U. and Barron, K. (1971) In-Situ Stresses. A Summary of Presentations and Discussions Given in Theme I at the Conference of Structural Geology to Rock Mechanics Problems. Department of Energy, Mines Branch, Ottawa.</mixed-citation></ref><ref id="scirp.124796-ref23"><label>23</label><mixed-citation publication-type="other" xlink:type="simple">Hyett, A.J., Dyke, C.G. and Hudson, J.A. (1986) A Critical Examination of Basic Concepts Associated with the Existence and Measurement of in Situ Stress. ISRM International Symposium, Stockholm, 31 August-3 September 1986, 387-391.</mixed-citation></ref><ref id="scirp.124796-ref24"><label>24</label><mixed-citation publication-type="other" xlink:type="simple">Price, N.J. and Cosgrove, J.W. (1990) Analysis of Geological Structures. Cambridge University Press, Cambridge.</mixed-citation></ref><ref id="scirp.124796-ref25"><label>25</label><mixed-citation publication-type="other" xlink:type="simple">Deb, D. and Verma, A.K. (2016) Fundamentals and Applications of Rock Mechanics. PHI Learning Pvt. Ltd., New Delhi.</mixed-citation></ref><ref id="scirp.124796-ref26"><label>26</label><mixed-citation publication-type="other" xlink:type="simple">Sperner, B., Müller, B., Heidbach, O., Delvaux, D., Reinecker, J. and Fuchs, K. (2003) Tectonic Stress in the Earth’s Crust: Advances in the World Stress Map Project. Geological Society London Special Publications, 212, 101-116.  
https://doi.org/10.1144/GSL.SP.2003.212.01.07</mixed-citation></ref><ref id="scirp.124796-ref27"><label>27</label><mixed-citation publication-type="other" xlink:type="simple">Sazid, M. (2019) Analysis of Rockfall Hazards along NH-15: A Case Study of Al-Hada Road. International Journal of Geo-Engineering, 10, Article No. 1.  
https://doi.org/10.1186/s40703-019-0097-3</mixed-citation></ref><ref id="scirp.124796-ref28"><label>28</label><mixed-citation publication-type="other" xlink:type="simple">Figueiredo, B., Lamas, L. and Muralha, J. (2016) Stress Field Assessment for Determining the Long-Term Rheology of a Granite Rock Mass. ISRM International Symposium on In-Situ Rock Stress, Tampere, 10-12 May 2016, 1-12.</mixed-citation></ref><ref id="scirp.124796-ref29"><label>29</label><mixed-citation publication-type="other" xlink:type="simple">Heidbach, O., et al. (2018) The World Stress Map Database Release 2016: Crustal Stress Pattern Across Scales. Tectonophysics, 744. 484-498.  
https://doi.org/10.1016/j.tecto.2018.07.007</mixed-citation></ref><ref id="scirp.124796-ref30"><label>30</label><mixed-citation publication-type="other" xlink:type="simple">(1982) Lawrence Berkeley National Laboratory, Determination of the State of Stress at the Stripa Mine, Sweden. https://escholarship.org/uc/item/4298625n</mixed-citation></ref><ref id="scirp.124796-ref31"><label>31</label><mixed-citation publication-type="other" xlink:type="simple">Ratigan, J.L. (1982) An Examination of the Tensile Strength of Brittle Rock. The 23rd U.S. Symposium on Rock Mechanics, Berkeley, 25-27August 1982, 423-440. 
https://doi.org/10.1016/0148-9062(83)91356-6</mixed-citation></ref><ref id="scirp.124796-ref32"><label>32</label><mixed-citation publication-type="other" xlink:type="simple">Perreau, P.J., Heugas, O. and Santarelli, F.J. (1989) Tests of ASR, DSCA, and Core Discing Analyses to Evaluate In-Situ Stresses. Middle East Oil Show, Manama, 11-14 March 1989, 325-336. https://doi.org/10.2118/17960-MS</mixed-citation></ref><ref id="scirp.124796-ref33"><label>33</label><mixed-citation publication-type="other" xlink:type="simple">Ljunggren, C., Chang, Y., Janson, T. and Christiansson, R. (2003) An Overview of Rock Stress Measurement Methods. International Journal of Rock Mechanics and Mining Sciences, 40, 975-989. https://doi.org/10.1016/j.ijrmms.2003.07.003</mixed-citation></ref><ref id="scirp.124796-ref34"><label>34</label><mixed-citation publication-type="other" xlink:type="simple">Dong, Q., Li, X., Jia, Y. and Sun, J. (2021) A Numerical Simulation of Blasting Stress Wave Propagation in a Jointed Rock Mass under Initial Stresses. Applied Sciences (Switzerland), 11, Article 7873. https://doi.org/10.3390/app11177873</mixed-citation></ref><ref id="scirp.124796-ref35"><label>35</label><mixed-citation publication-type="other" xlink:type="simple">Brady, B.H.B., Friday, R.G. and Alexander, L.G. (1976) Stress Measurement in a Bored Raise at the Mount Isa Mine. International Journal of Rock Mechanics and Mining Sciences &amp; Geomechanics Abstracts, 13, 123.  
https://doi.org/10.1016/0148-9062(76)90639-2</mixed-citation></ref><ref id="scirp.124796-ref36"><label>36</label><mixed-citation publication-type="other" xlink:type="simple">Chandler, N.A. (1993) Bored Raise Overcoring for in Situ Stress Determination at the Underground Research Laboratory. International Journal of Rock Mechanics and Mining Sciences &amp; Geomechanics Abstracts, 30, 989-992.  
https://doi.org/10.1016/0148-9062(93)90058-L</mixed-citation></ref><ref id="scirp.124796-ref37"><label>37</label><mixed-citation publication-type="book" xlink:type="simple">Gaone, F. M., Doherty, J. and Gourvenec, S. (2016) Self-Boring Pressuremeter Tests at the National Field Testing Facility, Ballina NSW. In Lehane, B.M., Acosta-Martínez, H.E. and Kelly, R., Eds., Geotechnical and Geophysical Site Characterisation, ISC’5, Vol. 1, Australian Geomechanics Society, 761-765.</mixed-citation></ref><ref id="scirp.124796-ref38"><label>38</label><mixed-citation publication-type="other" xlink:type="simple">Brudy, M., Zoback, M.D., Fuchs, K., Rummel, F. and Baumgartner, J. (1997) Estimation of the Complete Stress Tensor to 8 km Depth in the KTB Scientific Drill Holes Implications for Crustal Strength. Journal of Geophysical Research, 102, 18453-18475. https://doi.org/10.1029/96JB02942</mixed-citation></ref><ref id="scirp.124796-ref39"><label>39</label><mixed-citation publication-type="other" xlink:type="simple">Lindfors, U. and Ab, S. (2007) Svensk Karnbranslehantering AB Oskarshamn Site Investigation Hydraulic Fracturing and HTPF Rock Stress Measurements in Borehole KSH01A. https://skb.se/</mixed-citation></ref><ref id="scirp.124796-ref40"><label>40</label><mixed-citation publication-type="other" xlink:type="simple">Haimson, B.C. and Cornet, F.H. (2003) ISRM Suggested Methods for Rock Stress Estimation-Part 3: Hydraulic Fracturing (HF) and/or Hydraulic Testing of Pre-Existing Fractures (HTPF). International Journal of Rock Mechanics and Mining Sciences, 40, 1011-1020. https://doi.org/10.1016/j.ijrmms.2003.08.002</mixed-citation></ref><ref id="scirp.124796-ref41"><label>41</label><mixed-citation publication-type="other" xlink:type="simple">Hustrulid, W.A. and Johnson, G.A. (1990) Rock Mechanics Contributions and Challenges. CRC Press, London, 1082. https://doi.org/10.1201/9781003078944</mixed-citation></ref><ref id="scirp.124796-ref42"><label>42</label><mixed-citation publication-type="other" xlink:type="simple">Merrill, R.H., et al. (1964) Stress Determination by Flat Jack and Borehole Deformation Methods. U.S. Department of Interior, Bureau of Mines, RI 6400, 39.</mixed-citation></ref><ref id="scirp.124796-ref43"><label>43</label><mixed-citation publication-type="other" xlink:type="simple">Lin, H., Oh, J., Masoumi, H., Zhang, C., Canbulat, I. and Dou, L. (2018) A Review of in Situ Stress Measurement Techniques. Proceedings of the 18th Coal Operators' Conference, Mining Engineering, University of Wollongong, 95-102.</mixed-citation></ref><ref id="scirp.124796-ref44"><label>44</label><mixed-citation publication-type="other" xlink:type="simple">Mukai, A., Yamauchi, T., Ishii, H. and Matsumoto, S. (2007) In Situ Stress Measurement by the Stress Relief Technique Using a Multi-Component Borehole Instrument. Earth, Planets and Space, 59, 133-139.  
https://doi.org/10.1186/BF03352686</mixed-citation></ref><ref id="scirp.124796-ref45"><label>45</label><mixed-citation publication-type="other" xlink:type="simple">Liu, Q., Jiang, J., Zhang, C. and Zhu, Y. (2016) Analytical Investigation for in Situ Stress Measurement with Rheological Stress Recovery Method and Its Application. Mathematical Problems in Engineering, 2016, Article ID: 7059151.  
https://doi.org/10.1155/2016/7059151</mixed-citation></ref><ref id="scirp.124796-ref46"><label>46</label><mixed-citation publication-type="other" xlink:type="simple">Jaeger, N.G.W.C.J.C. and Zimmerman, R.W. (2007) Fundamentals of Rock Mechanics. 4th Edition, Wiley-Blackwell, Hoboken.</mixed-citation></ref><ref id="scirp.124796-ref47"><label>47</label><mixed-citation publication-type="other" xlink:type="simple">Gowida, A., Elkatatny, S. and Gamal, H. (2021) Unconfined Compressive Strength (UCS) Prediction in Real-Time While Drilling Using Artificial Intelligence Tools. Neural Computing and Applications, 33, 8043-8054.  
https://doi.org/10.1007/s00521-020-05546-7</mixed-citation></ref><ref id="scirp.124796-ref48"><label>48</label><mixed-citation publication-type="other" xlink:type="simple">Al Dhaif, R., Ibrahim, A.F. and Elkatatny, S. (2022) Prediction of Surface Oil Rates for Volatile Oil and Gas Condensate Reservoirs Using Artificial Intelligence Techniques. Journal of Energy Resources Technology, Transactions of the ASME, 144, Article 033001. https://doi.org/10.1115/1.4051298</mixed-citation></ref><ref id="scirp.124796-ref49"><label>49</label><mixed-citation publication-type="other" xlink:type="simple">Fang, X., Feng, H., Wang, Y. and Fan, T. (2022) Prediction Method and Distribution Characteristics of in Situ Stress Based on Borehole Deformation—A Case Study of Coal Measure Stratum in Shizhuang Block, Qinshui Basin. Frontiers in Earth Science (Lausanne), 10, 1-36. https://doi.org/10.3389/feart.2022.961311</mixed-citation></ref><ref id="scirp.124796-ref50"><label>50</label><mixed-citation publication-type="other" xlink:type="simple">Lin, H., et al. (2022) An Investigation of Machine Learning Techniques to Estimate Minimum Horizontal Stress Magnitude from Borehole Breakout. International Journal of Mining Science and Technology, 32, 1021-1029.  
https://doi.org/10.1016/j.ijmst.2022.06.005</mixed-citation></ref><ref id="scirp.124796-ref51"><label>51</label><mixed-citation publication-type="other" xlink:type="simple">Abreu, R., Mejia, C. and Roehl, D. (2022) Inverse Analysis of Hydraulic Fracturing Tests Based on Artificial Intelligence Techniques. International Journal for Numerical and Analytical Methods in Geomechanics, 46, 2582-2602.  
https://doi.org/10.1002/nag.3419</mixed-citation></ref><ref id="scirp.124796-ref52"><label>52</label><mixed-citation publication-type="other" xlink:type="simple">Ibrahim, A.F., Gowida, A., Ali, A. and Elkatatny, S. (2021) Machine Learning Application to Predict In-Situ Stresses from Logging Data. Scientific Reports, 11, Article No. 23445. https://doi.org/10.1038/s41598-021-02959-9</mixed-citation></ref><ref id="scirp.124796-ref53"><label>53</label><mixed-citation publication-type="other" xlink:type="simple">Lawal, A.I. and Kwon, S. (2021) Application of Artificial Intelligence to Rock Mechanics: An Overview. Journal of Rock Mechanics and Geotechnical Engineering, 13, 248-266. https://doi.org/10.1016/j.jrmge.2020.05.010%</mixed-citation></ref></ref-list></back></article>