{"http:\/\/dx.doi.org\/10.14288\/1.0395693":{"http:\/\/vivoweb.org\/ontology\/core#departmentOrSchool":[{"value":"Applied Science, Faculty of","type":"literal","lang":"en"},{"value":"Non UBC","type":"literal","lang":"en"},{"value":"Engineering, School of (Okanagan)","type":"literal","lang":"en"}],"http:\/\/www.europeana.eu\/schemas\/edm\/dataProvider":[{"value":"DSpace","type":"literal","lang":"en"}],"https:\/\/open.library.ubc.ca\/terms#identifierCitation":[{"value":"Sensors 21 (2): 344 (2021)","type":"literal","lang":"en"}],"http:\/\/purl.org\/dc\/terms\/creator":[{"value":"Shen, Peiwu","type":"literal","lang":"en"},{"value":"Tang, Huiming","type":"literal","lang":"en"},{"value":"Zhang, Bocheng","type":"literal","lang":"en"},{"value":"Ning, Yibing","type":"literal","lang":"en"},{"value":"Su, Xuexue","type":"literal","lang":"en"},{"value":"Sun, Sixuan","type":"literal","lang":"en"}],"http:\/\/purl.org\/dc\/terms\/issued":[{"value":"2021-01-25T18:32:30Z","type":"literal","lang":"en"},{"value":"2021-01-06","type":"literal","lang":"en"}],"http:\/\/purl.org\/dc\/terms\/description":[{"value":"Cyclic wetting and drying treatment is commonly used to accelerate the weakening process of reservoir rock. The weakening is reflected in strength variation and structure variation, while the latter receives less attention. Based on a series of cyclic wetting and drying tests, this study tentatively applied the uniaxial compressive test, computed tomography (CT) test and digital image correlation (DIC) test to investigate the weakening of slate in a reservoir area. Test results show that the weakening is mainly reflected in the reduction of compressive strength, followed by the decrease of ability to resist cracking and elastic deformation. The weakening seems more likely to be caused by structure variation rather than composition change. Two failure modes, e.g., splitting and splitting-tension, are concluded based on the crack paths: the splitting failure mode occurs in the highly weathered samples and the splitting-tension failure mode appears in the low-weathered samples. The transition zones of deformation are inside samples. The nephogram maps quantify the continuous deformation and correspond to the aforementioned structure variation process. This study offers comprehensive methods to the weakening investigation of slate in reservoir area and may provide qualitative reference in the stability evaluation of related slate rock slope.","type":"literal","lang":"en"}],"http:\/\/www.europeana.eu\/schemas\/edm\/aggregatedCHO":[{"value":"https:\/\/circle.library.ubc.ca\/rest\/handle\/2429\/77168?expand=metadata","type":"literal","lang":"en"}],"http:\/\/www.w3.org\/2009\/08\/skos-reference\/skos.html#note":[{"value":"sensorsCommunicationWeakening Investigation of Reservoir Rock by CoupledUniaxial Compression, Computed Tomography and DigitalImage Correlation Methods: A Case StudyPeiwu Shen 1,2, Huiming Tang 1,3,*, Bocheng Zhang 1, Yibing Ning 1, Xuexue Su 1 and Sixuan Sun 1\u0001\u0002\u0003\u0001\u0004\u0005\u0006\u0007\b\u0001\u0001\u0002\u0003\u0004\u0005\u0006\u0007Citation: Shen, P.; Tang, H.; Zhang,B.; Ning, Y.; Su, X.; Sun, S. WeakeningInvestigation of Reservoir Rock byCoupled Uniaxial Compression,Computed Tomography and DigitalImage Correlation Methods: A CaseStudy. Sensors 2021, 21, 344. https:\/\/doi.org\/10.3390\/s21020344Received: 12 December 2020Accepted: 31 December 2020Published: 6 January 2021Publisher\u2019s Note: MDPI stays neu-tral with regard to jurisdictional clai-ms in published maps and institutio-nal affiliations.Copyright: \u00a9 2021 by the authors. Li-censee MDPI, Basel, Switzerland.This article is an open access articledistributed under the terms and con-ditions of the Creative Commons At-tribution (CC BY) license (https:\/\/creativecommons.org\/licenses\/by\/4.0\/).1 Department of Engineering Geology and Geotechnical Engineering, Faculty of Engineering,China University of Geosciences, Wuhan 430074, China; pwshen@cug.edu.cn (P.S.);zhangbocheng@cug.edu.cn (B.Z.); yeebingning@cug.edu.cn (Y.N.); suxuexue@cug.edu.cn (X.S.);20151000308@cug.edu.cn (S.S.)2 School of Engineering, University of British Columbia, Kelowna, BC V1V 1V7, Canada3 Three Gorges Research Center for Geohazards, Ministry of Education, China University of Geosciences,Wuhan 430074, China* Correspondence: tanghm@cug.edu.cnAbstract: Cyclic wetting and drying treatment is commonly used to accelerate the weakening processof reservoir rock. The weakening is reflected in strength variation and structure variation, whilethe latter receives less attention. Based on a series of cyclic wetting and drying tests, this studytentatively applied the uniaxial compressive test, computed tomography (CT) test and digital imagecorrelation (DIC) test to investigate the weakening of slate in a reservoir area. Test results showthat the weakening is mainly reflected in the reduction of compressive strength, followed by thedecrease of ability to resist cracking and elastic deformation. The weakening seems more likely tobe caused by structure variation rather than composition change. Two failure modes, e.g., splittingand splitting-tension, are concluded based on the crack paths: the splitting failure mode occurs inthe highly weathered samples and the splitting-tension failure mode appears in the low-weatheredsamples. The transition zones of deformation are inside samples. The nephogram maps quantifythe continuous deformation and correspond to the aforementioned structure variation process. Thisstudy offers comprehensive methods to the weakening investigation of slate in reservoir area andmay provide qualitative reference in the stability evaluation of related slate rock slope.Keywords: reservoir rock; cyclic wetting and drying; CT; DIC; strength variation; structure variation1. IntroductionIn reservoir area, the fluctuating reservoir water level is one typical cyclic wettingand drying to the rock of reservoir bank slope, which expedites the physical weatheringprocess and further induces the reservoir geohazards (e.g., landslide, collapse and debrisflow). Most of the reservoir geohazards appear after impounding [1\u20133], and thus, theinvestigation on the weakening of rock exposed to cyclic wetting and drying has receivedmuch concern [4\u20136]. The weakening of rock resulted from cyclic wetting and drying canbe reflected in two aspects: strength variation and structure variation. Currently, thestrength variation in rock can be measured by various mechanical tests [7\u201311], e.g., theuniaxial compressive test, triaxial compressive test and direct shear test. Consideringthat most natural rocks are in the stress state of compression, the compressive tests aremore commonly used. However, the structure variation in rock is rarely tested. Forthis consideration, two non-destructive and non-contact methods including the computedtomography (CT) and digital image correlation (DIC) are utilized in this study, to investigatethe internal and external structure variations of weakened reservoir rock.The CT method is applied to obtain the reconstruction image of an object [12\u201314]. Inthe scanning, an X-ray beam is used to scan a certain thickness of object, the penetratingSensors 2021, 21, 344. https:\/\/doi.org\/10.3390\/s21020344 https:\/\/www.mdpi.com\/journal\/sensorsSensors 2021, 21, 344 2 of 14X-ray is then received by a detector and is further converted into visible light and electricalsignal so that one computer can recognize and process. The CT method was first usedin medical diagnosis [12,15\u201318]. With the perfection of theory and operation, the CTmethod was introduced into the field of rock mechanics, which benefits the developmentof rock mechanics [19\u201323]. Currently, the application of the CT method in rock mechanicsfocuses on the visualization of rock damage, rock composition, rock stress state and rocktest process, etc. [19,21,22,24,25]. The DIC method is developed to measure the full-fielddisplacement of objects [26\u201330]. In the measurement, the point of the region of interest(ROI) between the reference image and current image is tracked, so that the displacementof this point and then the full field can be determined. Since the DIC method has a widerange of applications, some scholars applied the method to rock mechanics, and the currentresearches on the combination of the DIC method and rock mechanics concentrate on thedeformation of rocks under various test conditions [31\u201335].The application of CT and DIC methods contributes to the development of rockmechanics. In general, the CT method is suitable for internal structure investigation, whilethe DIC method is fit for external structure investigation. However, the application of themethods is often independent, and the comprehensive investigation of natural rock basedon coupled mechanical treatment, CT method and DIC method is lacking, let alone thereservoir rock subject to physical weathering.The Miaowei hydropower station in Yunnan province, southwestern China, operatedin 2018. With the impounding of reservoir, some reservoir bank slopes have slid, whichthreatens the people and buildings nearby (Figure 1). Field investigation shows that mostof the exposed rocks are slate and are steeply inclined with various weathering levels(Figure 2). This study investigated the weakening characteristics of slate in the Miaoweireservoir area using the coupled uniaxial compressive test, CT test and DIC test. As shownin Figure 3, the cyclic wetting and drying test was first conducted to make the samplesin different levels of weathering; then, the uniaxial compressive test was carried out tolearn the strength variation of samples, and the CT test and DIC test were executed tostudy the internal and external structure variation of samples; finally, one comprehensiveunderstanding of the weakening characteristics of slate in the Miaowei reservoir area wasinvestigated.Sensors 2021, 21, x FOR PEER REVIEW 2 of 16   eration, two non-destructive and non-contact methods including the computed tomogra-phy (CT) and digital image correlation (DIC) are utilized in this study, to investigate the internal and external structure variations of weakened reservoir rock. The CT method is applied to obtain the reconstruction image of an object [12\u201314]. In the scanning, an X-ray beam is used to scan a certain thickness of object, the penetrating X-ray is then received by a detector and is further converted into visible light and electrical signal so that one computer can recognize and process. The CT method was first used in medical diagnosis [12,15\u201318]. With the perfection of theory and operation, the CT method was introduced into the field of rock mechanics, which b nefits th  development of rock mechanics [19\u201323]. Currently, the ap licatio  of the CT method in rock mechanics focuses on the visualization of rock damage, rock composition, rock stress stat  and rock t st pro-cess, etc. [19,21,22,24,25]. The DIC method is developed to measure the full-field displace-ment of objects [26\u201330]. In the measurement, the point of the region of interest (ROI) be-tween the reference image and current image is tracked, so that the displacement of this point and then the full field can be determined. Since the DIC method has a wide range of applications, some scholars applied the method to rock mechanics, and the current re-searches on the combinatio  of the DIC method and rock mechanics concentrate on the deformation of rocks under variou  test conditions [31\u201335]. The application of CT and DIC methods contribut s to the developme t of ro k me-chanics. In general, the CT method is suitable for internal structure investigation, while the DIC method is fit for external structure investigation. However, the application of the methods is often independent, and the comprehensive investigation of natural rock based on coupled mechanical treatment, CT method and DIC method is lacking, let alone the reservoir rock subject to physical weathering. The Miaowei hydropower station in Yunnan province, southwestern China, oper-ated in 2018. With t  impounding of r servoir, some reservo r bank slopes have slid, which threatens the people and buildings nearby (Figure 1). Field investigation shows that most of the exposed rocks are slate and are steeply inclined with various weathering levels (Figure 2). This study investigated the weakening characteristics of slate in the Mi-aowei reservoir area using the coupled uniaxial compressive test, CT test and DIC test. As shown in Figure 3, the cyclic wetting and drying test was first conducted to make the samples in different levels of weathering; then, the uniaxial compressive test was carried out to learn the strength variation of samples, and the CT test and DIC test were executed to study the internal and extern l structure variation of sample ; finally, one c mprehen-sive understanding of the weakening characteristi s of slate in the Miaowei rese voir are  was investigated.  Figure 1. Location of Miaowei reservoir area in Yunnan province and two landslide sites. Figure 1. Location of Miaowei reservoir area in Yunnan province and two landslide sites.Sensors 2021, 21, 344 3 of 14Sensors 2021, 21, x FOR PEER REVIEW 3 of 16    Figure 2. Exposed rocks of reservoir bank slopes in Miaowei reservoir area.  Figure 3. Flow chart of this study. 2. Sample Preparation and Test Methods 2.1. Sample Preparation The samples tested in this study are slate from the Miaowei reservoir area, with a natural density of 2.74 g\/cm3 and the mineral composition of sericite, chlorite and quartz. In order to maintain the natural state, the fresh slate rock blocks after field sampling were sealed by plastic wrap and then boxed by foam board for transportation. As shown in Figure 4a,b, the rock blocks were finally cut into cube samples with the size of 50 mm \u00d7 50 mm \u00d7 100 mm (length \u00d7 width \u00d7 height) to fulfill laboratory test requirements, the samples were resealed and six identical samples named C0, C2, C4, C6, C8 and C10 were prepared in this study. Figure 2. Exposed rocks of reservoir bank slopes in Miaowei reservoir area.Sensors 2021, 21, x FOR PEER REVIEW 3 of 16    Figure 2. Exposed rocks of reservoir bank slopes in Miaowei reservoir area.  Figure 3. Flow chart of this study. 2. Sample Preparation and Test Methods 2.1. Sample Preparation The sa ples tested in this study are slate from the Miaowei reservoir area, with a natural density of 2.74 g\/cm3 and the mineral composition of sericite, chlorite and quartz. In order to maintain the natural state, the fresh slate rock blocks after field sampling were sealed by plastic wrap and then boxed by foam board for transportation. As shown in Figure 4a,b, the rock blocks were finally cut into cube samples with the size of 50 mm \u00d7 50 mm \u00d7 100 mm (length \u00d7 width \u00d7 height) to fulfill laboratory test requirements, the samples were resealed and six identical samples named C0, C2, C4, C6, C8 and C10 were prepared in this study. Figure 3. Flow chart of this study.2. Sample Preparation and Test Methods2.1. Sample PreparationThe samples tested in this study are slate from the iao ei reservoir area, itha natural density of 2.74 g\/cm3 and the mineral composition of sericite, chlorite andquartz. In order to maintain the natural state, the fresh slate rock blocks after field sam-pling were sealed by plastic wrap and then boxed by foam board for transportation. Asshown in Figure 4a,b, the rock blocks were finally cut into cube samples with the size of50 mm\u00d7 50 mm\u00d7 100 mm (length\u00d7width\u00d7 height) to fulfill laboratory test requirements,the samples were resealed and six identical samples named C0, C2, C4, C6, C8 and C10were prepared in this study.Sensors 2021, 21, 344 4 of 14Sensors 2021, 21, x FOR PEER REVIEW 4 of 16    Figure 4. Sample preparation by cutting (a), sample size (b) and cyclic wetting and drying test (c). 2.2. Test Methods The tests including cyclic wetting and drying, uniaxial compression, DIC and CT were orderly conducted to investigate the weakening of samples. Although these test methods have been applied to rock mechanics, it should be noted that the cyclic wetting and drying test can speed up the weathering process of samples, but it cannot fully meet the weathering conditions of natural rocks. The uniaxial compression test is convenient to carry out and provides visual conditions for the real-time deformation observation of samples, however, most natural rocks are always in triaxial stress state. The CT test can be conducted to observe the internal deformation of samples, but cannot provide real-time observation data, while the DIC test can record the continuous deformation of sam-ples in real time, but cannot monitor the inside deformation of samples. Therefore, these test methods need to be combined to make up for the shortcomings. These test methods are detailed in the following three parts. 2.2.1. Cyclic Wetting and Drying Test The cyclic wetting and drying test was conducted to accelerate the weathering pro-cess of samples so that significant weakening occurred. The samples named C0, C2, C4, C6, C8 and C10 were designed to respectively experience 0, 2, 4, 6, 8 and 10 cycles of wet-ting and drying, for the sake of possessing stepped levels of weakening. As shown in  Figure 4c, the test includes two parts: (1) wetting and (2) drying. For the former, the sam-ples were unpacked and then placed in containers with distilled water fully submerged, the wetting is set to room temperature and lasts 72 h without disturbance in each cycle and the water was replaced once per cycle. For the latter, the samples after wetting were moved to an oven with the temperature of 110 \u00b0C and the drying lasts 72 h without dis-turbance, the samples after each drying were air-cooled to room temperature in the oven. The wetting and drying were duplicated to designed cycles (0, 2, 4, 6, 8 and 10 cycles) so as to obtain six samples possessing stepped levels of weakening. The related controlling parameters of the cyclic wetting and drying test in this study are summarized in Table 1.   Figure 4. Sample preparation by cutting (a), sample size (b) and cyclic wetting and drying test (c).2.2. Test MethodsThe tests including cyclic wet ing and drying, uniaxial compres ion, DIC and CTwere orderly conducted to investigate the weakening of samples. Although these testmethods have been applied to rock mechanics, it should be noted that the cyclic wet ingand drying test can spe d up the weathering proces of samples, but it can ot ful y me tthe eatheri . The uniaxial compre sion test is convenientto carry out and provides visual conditions f r r l-ti defor atio observation ofsamples, however, most natural rocks are always in triaxi l stress state. The CT test can beconducted to observe th int r al deformation of samples, but cannot pr vide real-timeobservation data, while t e DIC test can record the continuous deformation of samplesin real time, but cannot monitor the inside deformation of samples. Therefore, these testmethods need to be combined to make up for the shortcomings. These test methods aredetailed in the following three parts.2.2.1. Cyclic Wetting and Drying TestThe cyclic wetting and drying test was conducted to accelerate the weathering processof samples so that significant weakening occurred. The samples named C0, C2, C4, C6, C8and C10 were designed to respectively experience 0, 2, 4, 6, 8 and 10 cycles of wetting anddrying, for the sake of possessing stepped levels of weakening. As shown in Figure 4c,the test includes two parts: (1) wetting and (2) drying. For the former, the samples wereunpacked and then placed in containers with distilled water fully submerged, the wettingis set to room temperature and lasts 72 h without disturbance in each cycle and the waterwas replaced once per cycle. For the latter, the samples after wetting were moved to anoven with the temperature of 110 \u25e6C and the drying lasts 72 h without disturbance, thesamples after each drying were air-cooled to room temperature in the oven. The wettingand drying were duplicated to designed cycles (0, 2, 4, 6, 8 and 10 cycles) so as to obtain sixsamples possessing stepped levels of weakening. The related controlling parameters of thecyclic wetting and drying test in this study are summarized in Table 1.Sensors 2021, 21, 344 5 of 14Table 1. Controlling parameters of cyclic wetting and drying test.Treatments Contents ParticularsWettingTest site Geotechnical laboratorySoak solution Distilled waterTemperature Room temperatureDuration 72 hDryingTest site Geotechnical laboratoryHeating mode Electric dry ovenTemperature 110 \u25e6CDuration 72 h2.2.2. Uniaxial Compressive TestThe uniaxial compressive test was conducted to explore the strength variation ofweakened samples, which also provides a reference for the later structure variation analysis.The samples were tested on the Mechanics Testing System 815 produced by MTS SystemsCorporation (Eden Prairie, MN, USA). As shown in Figure 5, the Mechanics Testing System815 is supported by five subsystems, e.g., the computer system, hydraulic system, loadingsystem, pore pressure system and confining pressure system, and the related systemstructure diagram is shown in Figure 6. In this study, the computer system, hydraulicsystem and loading system were activated to complete the uniaxial compressive test, thetest was computer-controlled and the data was automatically recorded and processed(Figure 7). In the test, the laboratory temperature was about 25 \u25e6C and the loading wasdisplacement-controlled. The travel rate of the pressure head when contacting the samplewas set to 0.002 mm\/s so that the deformation of samples was easier to be caught by adigital camera. Other parameters of the operation are default values and more controllingparameters of the Mechanics Testing System 815 are displayed in Table 2. It is noted that thecracking stress, uniaxial compressive strength and elastic modulus were tested to analyzethe strength variation. The cracking stress corresponds to the stress when crack initiatesin samples, the uniaxial compressive strength is the maximum strength of samples undercompression and the elastic modulus is the ability of samples to resist elastic deformation.Sensors 2021, 21, x FOR PEER REVIEW 5 of 16   Table 1. Controlling parameters of cyclic wetting and drying test. Treatments Conte ts Particulars Wetting Test site Geotechnical laboratory Soak solution Distilled water Temperature Room temperature Duration 72 h Drying Test site Geotechnical laboratory Heating mode Electric dry oven Temperature 110 \u00b0C Duration 72 h 2.2.2. Uniaxial Compressive Test The uniaxial compressive test was conducted to explore the strength variation of weakened s mples, which also provides a reference for the later structure variation anal-ysis. The sa ples ere te ted n the M cha ics Testing System 815 produced by MTS Syste s Corporation (Eden Prairie, MN, USA). As shown in Figure 5, the Mechanics Te t-ing System 815 is supported by five subsystems, e.g., th  comput r system, hydraulic sys-tem, loading system, pore pressure system and confining pressure system, and the related system structure diagram is shown in Figure 6. In this study, the computer system, hy-draulic system and loading system were activated to complete the uniaxial compressive test, the test was computer-controlled and the data was automatically recorded and pro-cessed (Figure 7). In the test, the laboratory temperature was about 25 \u00b0C and the loading was displacement-controlled. The travel rate of the pressure head when contacting the sample was set to 0.002 mm\/s so that the deformation of samples was easier to be caught by a digital camera. Other parameters of the operation are default values and more con-trolling parameters of the Mechanics Testing System 815 are displayed in Table 2. It is noted that the cracking stress, uniaxial compressive strength and elastic modulus were tested to analyze the strength variation. The cracking stress corresponds to the stress when crack initiates in samples, the uniaxial compressive strength is the maximum strength of samples under compression and the elastic modulus is the ability of samples to resist elas-tic deformation.  Figure 5. Apparatus for uniaxial compressive test. Figure 5. Apparatus for uniaxial compressive test.Sensors 2021, 21, 344 6 of 14Sensors 2021, 21, x FOR PEER REVIEW 6 of 16    Figure 6. Structure diagram of Mechanics Testing System.  Figure 7. Digital image correlation (DIC) test and schematic diagram of test data processing. Table 2. Controlling parameters of Mechanics Testing System. Aspects Contents Particulars Operating conditions Uniaxial compression \u221240\u201360 \u00b0C Loading parameters Max. axial load 4600 kN Max. pore water pressure 70 MPa Servo valve sensitivity 290 HZ Data acquisition channels 10 Min. sampling time 50 \u03bcs Sample requirements Uniaxial compression 300 mm (Max. diameter)  600 mm (Max. height) 2.2.3. CT Test The CT test was conducted to investigate the internal structure variation of weakened samples. The samples were tested on the X-ray Inspection System v|tome|x s 240  (Figure 8) produced by GE Sensing and Inspection Technologies GmbH, Wunstorf, Ger-many. The system is computer-controlled and supported by four sets of software, e.g., the xs|control, datos|x acquisition, datos|x reconstruction and VGSTUDIO MAX; among which, the first three are built in the system and the last one is developed by Volume Graphics GmbH, Heidelberg, Germany. In the test, the xs|control was used to monitor and control the X-ray tube to scan, the datos|x acquisition was utilized to collect the two-dimensional (2D) CT image series (sectional projections) from the scanning, the datos|x Figure 6. Structure diagram of Mechanics Testing System.Sensors 2021, 21, x FOR PEER REVIEW 6 of 16    Figure 6. Structure diagram of Mechanics Testing System.  Figure 7. Digital image correlation (DIC) test and schematic diagram of test data processing. Table 2. Controlling parameters of Mechanics Testing System. Aspects Contents Particulars Operating conditions Uniaxial compression \u221240\u201360 \u00b0C Loading parameters Max. axial load 4600 kN Max. pore water pressure 70 MPa Servo valve sensitivity 290 HZ Data acquisition channels 10 Min. sampling time 50 \u03bcs Sample requirements Uniaxial compression 300 mm (Max. diameter)  600 mm (Max. height) 2.2.3. CT Test The CT test was conduct d to investigate the int rnal structure variation of weakened sampl s. The samples were t sted on the X-ray Inspectio  Syst m v|tome|x s 240  (Figure 8) produced by GE Sensi g and Inspection Technologies GmbH, Wunstorf, Ger-many. The system is computer-contr lled and supported by four sets of software, e.g., the xs|control, datos|x acquisition, datos|x r construction and VGSTUDIO MAX; among whic , the first three are built in the system and the last one is developed by V lume Graphics GmbH, Heidelberg, Germany. In the test, the xs|control was used to monit r and control the X-ray tube to scan, th  datos|x acquisition was utilized to collect the two-dimensional (2D) CT image series (sectional projections) from the scanning, the datos|x Figure 7. Digital image correlation (DIC) test and schematic diagram of test data processing.Table 2. Controlling parameters of Mechanics Testing System.Aspects Contents ParticularsOperating conditions Uniaxial compression \u221240\u201360 \u25e6CLoading parametersMax. axial load 4600 kNMax. pore water pressure 70 MPaServo valve sensitivity 290 HZData acquisition channels 10Min. sampling time 50 \u00b5sSa ple requirements Uniaxial compression 300 mm (Max. diameter)600 mm (Max. height)2.2.3. CT TestThe CT test was co ducted to investigate the internal structure variation of weakenedsamples. Th sampl s were t sted on the X-ray Inspection Syst m v|tome|x s 240 (Figure 8)produced by GE Sensing and Inspection Techn logies GmbH, Wunstorf, Germany. Thesystem is computer-controlled and supported by four sets of software, e.g., the xs|control,t s x isiti , datos|x reconstruction and VGSTUDIO MAX; among which, the firstthree are built in the system and the last one is developed by Volume Graphics GmbH,Heidelberg, Germany. In the test, the xs|control was used to monitor and control theX-ray tube to scan, the datos|x acquisition was utilized to collect the two-dimensional (2D)Sensors 2021, 21, 344 7 of 14CT image series (sectional projections) from the scanning, the datos|x reconstruction wasapplied to reconstruct the three-dimensional (3D) volumes of samples from the sectionalprojections and the VGSTUDIO MAX was developed for visualization and post-processingbased on the reconstructed 3D volumes of samples. The samples can be scanned andreconstructed by the system since the X-ray displays dissimilar penetration ability to solidphase and gas phase. In general, the solid phase indicates the rock matrix of samplesand the gas phase represents the crack (damage) of samples. The solid phase and the gasphase were combined to obtain the distribution of damage, so that further investigationon the internal structure variation was conducted (Figure 9). In this study, the laboratorytemperature is 20 \u25e6C, and the voltage and current of the X-ray tube are set to 120 kVand 90 \u00b5A, respectively. Other parameters of the operation are default values and morecontrolling parameters of the system are displayed in Table 3.Sensors 2021, 21, x FOR PEER REVIEW 7 of 16   reconstruction was applied to reconstruct the three-di ensional (3D) volumes of samples from the sectional projections and the VGSTUDIO MAX was developed for visualization and post-processing based on the reconstructed 3D volumes of samples. The samples can be scanned and reconstructed by the system since the X-ray displays dissimilar penetra-tion ability to solid phase and gas phase. In general, the solid phase indicates the rock matrix of samples and the gas phase represents the crack (damage) of samples. The solid phase and the gas phase were combined to obtain the distribution of damage, so that fur-ther investigation on the internal structure variation was conducted (Figure 9). In this study, the laboratory temperature is 20 \u00b0C, and the voltage and current of the X-ray tube are set to 120 kV and 90 \u03bcA, respectively. Other parameters of the operation are default values and more controlling parameters of the system are displayed in Table 3.  Figure 8. Apparatus for computed tomography (CT) test.  Figure 9. Schematic diagram of CT processing.   Figure 8. Apparatus for computed tomography (CT) test.Sensors 2021, 21, x FOR PEER REVIEW 7 of 16   reconstruction was applie  to reconstruct the thre -dimensional (3D) volum s of samples from the sectional projection  and th  VGSTUDIO MAX was developed f r visualization and post-proc s ing based on the reconstructed 3D volu es of samples. The samples can be scanned and reconstructed by t e system since the X-ray disp ays dissimilar p netra-tion ability to solid phase and gas phase. In general, the solid ph se indic tes the rock matrix of sample  and the gas phase rep sents the crack (d mag ) of samples. The solid phase and the gas pha e were combined to obtain the distribution of damage, so that fur-ther investiga ion on the internal structure variation w s conducted (Figure 9). In this study, the laboratory temperature is 20 \u00b0C, and the voltage and current of the X-ray tube are set to 120 kV and 90 \u03bcA, respectively. Other parameter  of the operation are def ult values and more controlling parameters of the system are displayed in Table 3.  Figure 8. Apparatus for computed tomography (CT) test.  Figure 9. Schematic diagram of CT processing.   Figure 9. Schematic diagram of CT processing.Sensors 2021, 21, 344 8 of 14Table 3. Controlling parameters of X-ray inspection system v|tome|x s 240.Aspects Contents ParticularsOperating conditions Temperature and Relativehumidity (RH) 10\u201330\u25e6C, 25\u201370 RHX-ray parametersMax. voltage 240 kVMax. power 320 WMin. focal length 4.5 mmDetail detectability <1 \u00b5mMax. voxel resolution <2 \u00b5mGeometric magnification (3D) 1.46\u2013100\u00d7Sample manipulatorNumber of axes 5Rotation 0\u2013360\u25e6Max. sample weight 10 kgMax. sample size 260 mm \u00d7 400 mm(diameter \u00d7 height)Axis speed 0.01\u201380 mm\/s2.2.4. DIC TestThe DIC test was conducted to investigate the external structure variation of weakenedsamples, which is completely different from the uniaxial compressive test since the DICtest makes the deformation process reappeared and visible. As shown in Figure 5, thecompression process of specimens was recorded by a digital camera (24 frames per secondand 1920 \u00d7 1080 pixels per frame), which is the basis for further DIC analysis. The basicprinciple of DIC analysis is to track the displacement of target points (pixels) between thereference image (without deformation) and current images (with deformation) (Figure 7).Specifically, the video recording the full deformation process of one sample was firstconverted to a series of digital pictures; then, the image showing the sample withoutdeformation was set as the reference image, while the images displaying the sampleexperiencing continuous deformation were used as the current images, the number ofcurrent images can be determined by the required deformation interval of one sample. Afterthat, the correlation criteria was applied to catch the displacement vectors of target pointsin the ROI; finally, the continuous deformation process of one sample can be quantified byregional deformation, which was intuitively represented by the isograms and nephogrammaps. The DIC test was conducted based on an open-source DIC algorithm [28] and tworepresentative samples with an obvious difference in weakening level were tested.3. Results3.1. Strength VariationFigure 10a\u2013c shows the cracking stress, uniaxial compressive strength, elastic modulusand weight versus the cycles of wetting and drying. In this study, it is noted that the crack-ing stress, uniaxial compressive strength and elastic modulus show an overall decreasingtrend with the growth of cycles of wetting and drying. However, the cracking stress andelastic modulus have fluctuant variation trends, the uniaxial compressive strength shows amore monotonous variation trend; specifically, the cracking stress seems to vary between53.5 and 26.1 MPa, the uniaxial compressive strength likely changes between 66.8 and137.5 MPa and the elastic modulus seems to alter between 6.7 and 22.5 MPa. The differenceindicates that the cyclic wetting and drying has the greatest impact on the compressivestrength of samples, while in the long term, the cyclic wetting and drying also weakens theability of samples to resist cracking and elastic deformation. Figure 10d also demonstratesthat cyclic wetting and drying has almost no effect on the weight of samples since all thesamples basically remain unchanged in terms of weight. The result further reveals that theweakening of the samples experiencing cyclic wetting and drying is not mainly reflectedin the erosion of composition, but may be the change of structure, which can be furtherexplored from the CT test and DIC test.Sensors 2021, 21, 344 9 of 14Sensors 2021, 21, x FOR PEER REVIEW 9 of 16   weight of samples since all the samples basically remain unchanged in terms of weight. The result further reveals that the weakening of the samples experiencing cyclic wetting and drying is not mainly reflected in the erosion of composition, but may be the change of structure, which can be further explored from the CT test and DIC test.   (a) (b)   (c) (d) Figure 10. Correlations of cracking stress (a), uniaxial compressive strength (b), elastic modulus (c) and weight (d) versus cycles of wetting and drying. 3.2. Structure Variation The structure variation is embodied in the exterior damage and interior damage of samples, which is jointly analyzed by the DIC test and CT test. The samples after the uni-axial compressive test provide the most intuitive material for the analysis of exterior dam-age. Figure 11 shows the samples and the corresponding damage sketches after the uni-axial compressive test. It is obtained that the samples with lower weathering levels tend to display more complex failure modes. In particular, the samples experiencing fewer cy-cles of wetting and drying possess more obvious cracks on the surface and the cracks are more widespread; usually, the cracks get coalescent on the surface and cause greater dam-age. With the increasing of cycles of wetting and drying, the cracks on the surface of sam-ples are less coalescent and the related damage levels decrease. These cracks not only ap-pear on the surface of samples, but also inside the samples, which can be seen from  Figure 12. Figure 12 shows the continuous longitudinal sections of two representative samples after two and eight cycles of wetting and drying respectively, and the red line at the bottom right corner indicates the position of each longitudinal section in the top view. It is observed that most of the cracks inside samples are coalescent. The sample after fewer cycles of wetting and drying contains more cracks that are interlaced, compared with the sample experiencing more cycles of wetting and drying. This phenomenon is because as Figure 10. Correlations of cracking stress (a), uniaxial compressive strength (b), elastic modulus (c) and weight (d) versuscycles of wetting and drying.3.2. Structure VariationThe structure variation is embodi d in the exterior damage and interior damage ofsamples, which is jointly analyzed by the DIC test and CT test. The samples after theuniaxial compressive test provide the most intuitive material for the analysis of exteriordamage. Figure 11 shows the samples and the corresponding damage sketches after theuniaxial compressive test. It is obtained that the samples with lower weathering levels tendto display more complex failure modes. In particular, the samples experiencing fewer cyclesof wetting and drying possess more obvious cracks on the surface and the cracks are morewidespread; usually, the cracks get coalescent on the surface and cause greater damage.With the increasing of cycles of wetting and drying, the cracks on the surface of samplesare less coalescent and the related damage levels decrease. These cracks not only appearon the surface of samples, but also inside the samples, which can be seen from Figure 12.Figure 12 shows the continuous longitudinal sections of two representative samples aftertwo and eight cycles of wetting and drying respectively, and the red line at the bottom rightcorner indicates the position of each longitudinal section in the top view. It is observedthat most of the cracks inside samples are coalescent. The sample after fewer cycles ofwetting and drying contains more cracks that are interlaced, compared with the sampleexperiencing more cycles of wetting and drying. This phenomenon is because as the cyclesof wetting and drying increase, the initial micro-cracks gradually propagate along foliationplanes, which finally causes pre-damage in samples before the uniaxial compressive test.Once the samples are subjected to external compression, the developed micro-cracks tendto quickly grow into macro-cracks along foliation planes, which eventually leads to theSensors 2021, 21, 344 10 of 14rapid destruction of samples; however, for the samples experiencing fewer cycles of wettingand drying, most of the micro-cracks do not go through the pre-damage along foliationplanes; thus, the micro-cracks have the opportunity to fully propagate and interlace undercompression, which results in the wide distribution of cracks and the high damage levelsof samples.Sensors 2021, 21, x FOR PEER REVIEW 10 of 16   the cycles of wetting and drying increase, the initial micro-cracks gradually propagate along foliation planes, which finally causes pre-damage in samples before the uniaxial compressive test. Once the samples are subjected to external compression, the developed micro-cracks tend to quickly grow into macro-cracks along foliation planes, which even-tually leads to the rapid destruction of samples; however, for the samples experiencing fewer cycles of wetting and drying, most of the micro-cracks do not go through the pre-damage along foliation planes; thus, the micro-cracks have the opportunity to fully prop-agate and interlace under compression, which results in the wide distribution of cracks and the high damage levels of samples.  Figure 11. Samples after uniaxial compressive test and related crack sketches.  Figure 12. Spatial distribution of cracks inside samples, red line at bottom right corner indicates longitudinal section\u2019s position in top view. Figure 11. Samples after uniaxial compressive test and related crack sketches.Sensors 2021, 21, x FOR PEER REVIEW 10 of 16   the cycles of wetting and drying increase, the initial micro-cracks gradually propagate along foliation planes, which finally causes pre-damage in sa ples before the uniaxial compressive test. Once the samples are subjected to external compression, the developed micro-cracks tend to quickly grow into macro-cracks along foliation planes, which even-tually leads to the rapid destruction of samples; however, for the samples experiencing fewer cycles of wetting and drying, most of the micro-cracks do not go through the pre-damage along foliation planes; thus, the micro-cracks have the opportunity to fully prop-agate and interlace under compression, which results in the wide distribution of cracks and the high damage levels of samples.  Figure 11. Samples after uniaxial compressive test and related crack sketches.  Figure 12. Spatial di tribu  of cracks inside samples, red line at bottom right corner indicates longitudinal section\u2019s position in top view. Figure 12. Spatial distribution of cracks inside samples, red line at bottom right corner indicateslongitudinal section\u2019s position in top view.Sensors 2021, 21, 344 11 of 14It is concluded that the samples behave both by splitting failure mode and splitting-tension failure mode. For the splitting failure mode, the crack path basically followsfoliation planes, the cracks are far apart and generally do not interfere with each other. Thisfailure mode appears in the samples that have experienced more cycles of wetting anddrying. For the splitting-tension failure mode, the crack path is partly along foliation planesand partly between foliation planes. This is because the crack spacing is small and thesplitting along foliation planes easily transforms into tension between foliation planes. Thisfailure mode arises in the samples that have undergone fewer cycles of wetting and drying.The above results from direct observation and the CT test can be further verified inthe DIC test. Figures 13 and 14 show the nephogram maps of axial displacement of thesamples, the same as in Figure 12. The compressive direction defaults to be positive andthe units are in millimeters. As the test time shows in the lower middle of each frame,the sample experiencing more cycles of wetting and drying takes less test time to reachdestruction compared with the sample undergoing fewer cycles, which corresponds to theaforementioned analysis. From the perspective of axial displacement, it is clear that theobvious deformation areas are relatively scattered at the beginning\u2014this is because thepositions of micro-cracks are random. As compression continues, the obvious deformationareas gradually get connected due to the coalescence of cracks and the deformation isbasically along foliation planes. After that, the deformation areas of a sample that hasexperienced more cycles expand along foliation planes until the sample is entirely splitand destroyed, then the deformation areas gradually disappear, and the test is over. Thedeformation of a sample that has undergone fewer cycles of wetting and drying continues,and the deformation areas are further connected; at this time, the coalescence areas tendto stagger foliation planes until the split-tension failure runs through the entire sample,then the deformation areas disappear, and the sample is destroyed. The results from theDIC test correspond to the results from the CT test, which together reveal the structurevariation of samples.The results from the CT test can be used not only to verify the macroscopic failuremodes of samples, but also to analyze the evolution modes of local cracks inside samples.As shown by the cracks in circles of Figure 12, the same crack will show different evolutionmodes during the propagating process inside samples; specifically, a single crack may gen-erate multiple branch cracks inside one sample, and multiple branch cracks may eventuallygather into one crack. The turning point of this change generally appears inside samplesrather than on the surface. This phenomenon indicates that the stress state inside onesample is not the same, and usually makes the failure mode of a sample more complicated.For the single-crack region, the propagation of a crack will cause the sample to show a puredeformation mode (e.g., splitting mode), while for the multi-crack region, the propagationof a crack will cause the sample to show a combined deformation mode (e.g., splitting-tension mode), the transition zone of deformation is generally inside the sample and isdifficult to be observed in conventional mechanical tests. The evolution phenomenon of acrack in a sample has a good corresponding relationship with the engineering geologicalcondition; for example, due to the influence of in-situ stress, the deformation of highand steep slate rock slopes often manifest as combined deformation modes including thecombined splitting and toppling deformation. Identifying the deformation zones of rockcan better study its engineering properties; however, the transition zone of deformation isalso not easy to be observed on site, which makes the current related researches mainlybased on generalized models. The analytical results in this study help to understand thedeformation process, failure mode and deformation transition zone of slate after cyclicwetting and drying, which may provide reference to the stability evaluation of slate rockslope in a reservoir area.Sensors 2021, 21, 344 12 of 14Sensors 2021, 21, x FOR PEER REVIEW 12 of 16    Figure 13. Nephogram maps of axial displacement of C2. Figure 13. Nephogram maps of axial displacement of C2.Sensors 2021, 21, x FOR PEER REVIEW 13 of 16    Figure 14. Nephogram maps of axial displacement of C8. The results from the CT test can be used not only to verify the macroscopic failure modes of samples, but also to analyze the evolution modes of local cracks inside samples. As shown by the cracks in circles of Figure 12, the same crack will show different evolution modes during the propagating process inside samples; specifically, a single crack may generate multiple branch cracks inside one sample, and multiple branch cracks may even-tually gather into one crack. The turning point of this change generally appears inside samples rather than on the surface. This phenomenon indicates that the stress state inside one sample is not the same, and usually makes the failure mode of a sample more com-plicated. For the single-crack region, the propagation of a crack will cause the sample to show a pure deformation mode (e.g., splitting mode), while for the multi-crack region, the propagation of a crack will cause the sample to show a combined deformation mode (e.g., splitting-tension mode), the transition zone of deformation is generally inside the sample and is difficult to be observed in conventional mechanical tests. The evolution phenome-non of a crack in a sample has a good corresponding relationship with the engineering geological condition; for example, due to the influence of in-situ stress, the deformation of high and steep slate rock slopes often manifest as combined deformation modes includ-ing the combined splitting and toppling deformation. Identifying the deformation zones of rock can better study its engineering properties; however, the transition zone of defor-mation is also not easy to be observed on site, which makes the current related researches mainly based on generalized models. The analytical results in this study help to under-stand the deformation process, failure mode and deformation transition zone of slate after cyclic wetting and drying, which may provide reference to the stability evaluation of slate rock slope in a reservoir area. 4. Conclusions This study tentatively used the coupled uniaxial compressive test, CT test and DIC test to investigate the weakening characteristics of reservoir rock. The test methods and apparatuses were first introduced in detail, then the strength and structure variations Figure 14. Nephogram maps of axial displacement of C8.4. ConclusionsThis study tentatively used the coupled uniaxial compressive test, CT test and DICtest to investigate the weakening characteristics of reservoir rock. The test methods andSensors 2021, 21, 344 13 of 14apparatuses were first introduced in detail, then the strength and structure variations basedon the tests were studied. Several valuable conclusions were obtained and summarized, asfollows.The physical weathering affects the strength of samples under compression, whichwas recorded in the uniaxial compressive test. The cracking stress, uniaxial compressivestrength and elastic modulus show decreasing variation trends with the increasing cyclesof wetting and drying. The weakening degree of compressive strength is higher than thatof the cracking resistance and elastic deformation resistance. The physical weathering ismore inclined to weaken the structure rather than erode the composition.The physical weathering varies the crack paths of samples under compression, whichwas visualized in the CT test and the DIC test. Both splitting failure mode and splitting-tension failure mode occurred in the samples, the former makes the crack path basicallyfollow foliation planes, and the latter causes the crack path to be partly along foliationplanes and partly between foliation planes. The samples with lower weathering levels pos-sess more widespread cracks on the surface and inside, and the cracks are more interlacedthan that of the samples with higher weathering levels. The transition zones of deformationare generally inside samples, which indicates the multiple stress states in samples undercompression. The quantified deformation process represented by nephogram maps helpsprove the aforementioned analytical results.The cyclic wetting and drying test, uniaxial compressive test, CT test and DIC testconducted in this study provide new insight into the mechanism investigation of weakeningof reservoir rock. The method can also be applied to other reservoir rocks for furtherqualitative rock stability evaluation.Author Contributions: This work was carried out as a collaboration among all the authors. Concep-tualization, P.S. and H.T.; funding acquisition, H.T.; supervision, H.T.; methodology, P.S.; test anddata, B.Z., Y.N., X.S. and S.S.; original draft, P.S.; revision, P.S. All authors have read and agreed tothe published version of the manuscript.Funding: This study was funded by the National Key Research and Development Program of China(grant no. 2017YFC1501305), the National Major Scientific Instruments and Equipment DevelopmentProjects of China (grant no. 41827808), and the National Natural Science Foundation of China (grantno. 41807263).Institutional Review Board Statement: Not applicable.Informed Consent Statement: Not applicable.Data Availability Statement: Not applicable.Acknowledgments: The authors appreciate the editor and reviewers for their comments and valuablesuggestions. All funding is also gratefully acknowledged.Conflicts of Interest: The authors declare no conflict of interest.References1. Li, C.; Fu, Z.; Wang, Y.; Tang, H.; Yan, J.; Gong, W.; Yao, W.; Criss, R.E. Susceptibility of reservoir-induced landslides and strategiesfor increasing the slope stability in the Three Gorges Reservoir Area: Zigui Basin as an example. Eng. Geol. 2019, 261, 105279.[CrossRef]2. Tang, H.; Wasowski, J.; Juang, C.H. Geohazards in the three Gorges Reservoir Area, China\u2013Lessons learned from decades ofresearch. Eng. Geol. 2019, 261, 105267. [CrossRef]3. Zou, Z.; Lu, S.; Wang, F.; Tang, H.; Hu, X.; Tan, Q.; Yuan, Y. Application of Well Drainage on Treating Seepage-Induced ReservoirLandslides. Int. J. Environ. Res. Public Health 2020, 17, 6030. [CrossRef] [PubMed]4. Shen, P.; Tang, H.; Huang, L.; Wang, D. Experimental study of slaking properties of red-bed mudstones from the Three GorgesReservoir area. Mar. Georesour. Geotechnol. 2019, 37, 891\u2013901. [CrossRef]5. Yao, W.; Li, C.; Zhan, H.; Zhou, J.Q.; Criss, R.E.; Xiong, S.; Jiang, X. Multiscale Study of Physical and Mechanical Properties ofSandstone in Three Gorges Reservoir Region Subjected to Cyclic Wetting-Drying of Yangtze River Water. Rock Mech. Rock Eng.2020, 53, 2215\u20132231. [CrossRef]6. Su, X.; Tang, H.; Huang, L.; Shen, P.; Xia, D. The role of pH in red-stratum mudstone disintegration in the Three Gorges reservoirarea, China, and the associated micromechanisms. Eng. Geol. 2020, 279, 105873. [CrossRef]Sensors 2021, 21, 344 14 of 147. Ulusay, R. The ISRM Suggested Methods for Rock Characterization, Testing and Monitoring: 2007\u20132014; Springer: Cham, Switzerland,2014.8. Zhang, Q.B.; Zhao, J. A review of dynamic experimental techniques and mechanical behaviour of rock materials. Rock Mech. RockEng. 2014, 47, 1411\u20131478. [CrossRef]9. Dong, L.; Zhang, Y.; Ma, J. Micro-crack mechanism in the fracture evolution of saturated granite and enlightenment to theprecursors of instability. Sensors 2020, 20, 4595. [CrossRef]10. Wu, Q.; Jiang, Y.; Tang, H.; Luo, H.; Wang, X.; Kang, J.; Zhang, S.; Yi, X.; Fan, L. Experimental and Numerical Studies on theEvolution of Shear Behaviour and Damage of Natural Discontinuities at the Interface Between Different Rock Types. Rock Mech.Rock Eng. 2020, 53, 3721\u20133744. [CrossRef]11. Zou, Z.; Zhang, Q.; Xiong, C.; Tang, H.; Fan, L.; Xie, F.; Yan, J.; Luo, Y. In Situ Shear Test for Revealing the Mechanical Propertiesof the Gravelly Slip Zone Soil. Sensors 2020, 20, 6531. [CrossRef]12. Hounsfield, G.N. Computerized transverse axial scanning (tomography): Part 1. Description of system. Br. J. Radiol. 1973, 46,1016\u20131022. [CrossRef] [PubMed]13. Brenner, D.J.; Hall, E.J. Computed tomography-an increasing source of radiation exposure. N. Engl. J. Med. 2007, 357, 2277\u20132284.[CrossRef] [PubMed]14. Buzug, T.M. Computed tomography. In Springer Handbook of Medical Technology; Springer: Berlin\/Heidelberg, Germany, 2011.15. Abrams, H.L.; McNeil, B.J. Medical implications of computed tomography (CAT scanning). N. Engl. J. Med. 1978, 298, 255\u2013261.[CrossRef] [PubMed]16. Hounsfield, G.N. Computed medical imaging. Science 1980, 210, 22\u201328. [CrossRef]17. Hiriyannaiah, H.P. X-ray computed tomography for medical imaging. IEEE Signal Process. Mag. 1997, 14, 42\u201359. [CrossRef]18. Rao, P.M.; Rhea, J.T.; Novelline, R.A.; Mostafavi, A.A.; McCabe, C.J. Effect of computed tomography of the appendix on treatmentof patients and use of hospital resources. N. Engl. J. Med. 1998, 338, 141\u2013146. [CrossRef] [PubMed]19. Johns, R.A.; Steude, J.S.; Castanier, L.M.; Roberts, P.V. Nondestructive measurements of fracture aperture in crystalline rock coresusing X ray computed tomography. J. Geophys. Res. Solid Earth 1993, 98, 1889\u20131900. [CrossRef]20. Mees, F.; Swennen, R.; Van Geet, M.; Jacobs, P. Applications of X-ray computed tomography in the geosciences. Geol. Soc. 2003,215, 1\u20136. [CrossRef]21. Taud, H.; Martinez-Angeles, R.; Parrot, J.F.; Hernandez-Escobedo, L. Porosity estimation method by X-ray computed tomography.J. Pet. Sci. Eng. 2005, 47, 209\u2013217. [CrossRef]22. Yun, T.S.; Jeong, Y.J.; Kim, K.Y.; Min, K.B. Evaluation of rock anisotropy using 3D X-ray computed tomography. Eng. Geol. 2013,163, 11\u201319. [CrossRef]23. Yang, E.; Yun, T.S.; Kim, K.Y.; Moon, S.W.; Seo, Y.S. Estimation of the Structural and Geomechanical Anisotropy in Fault GougesUsing 3D Micro-Computed Tomography (\u00b5-CT). Sensors 2020, 20, 4706. [CrossRef] [PubMed]24. Kim, H.; Diaz, M.B.; Kim, J.Y.; Jung, Y.B.; Kim, K.Y. Stress Estimation through Deep Rock Core Diametrical Deformation and JointRoughness Assessment Using X-ray CT Imaging. Sensors 2020, 20, 6802. [CrossRef] [PubMed]25. Feng, X.T.; Chen, S.; Zhou, H. Real-time computerized tomography (CT) experiments on sandstone damage evolution duringtriaxial compression with chemical corrosion. Int. J. Rock Mech. Min. Sci. 2004, 41, 181\u2013192. [CrossRef]26. Chu, T.C.; Ranson, W.F.; Sutton, M.A. Applications of digital-image-correlation techniques to experimental mechanics. Exp. Mech.1985, 25, 232\u2013244. [CrossRef]27. Bruck, H.A.; McNeill, S.R.; Sutton, M.A.; Peters, W.H. Digital image correlation using Newton-Raphson method of partialdifferential correction. Exp. Mech. 1989, 29, 261\u2013267. [CrossRef]28. Blaber, J.; Adair, B.; Antoniou, A. Ncorr: open-source 2D digital image correlation matlab software. Exp. Mech. 2015, 55, 1105\u20131122.[CrossRef]29. Ferrer, B.; Mas, D. Parametric evaluation of errors using isolated dots for movement measurement by image cross-correlation.Sensors 2018, 18, 525. [CrossRef]30. Schreier, H.W.; Braasch, J.R.; Sutton, M.A. Systematic errors in digital image correlation caused by intensity interpolation. Opt.Eng. 2000, 39, 2915\u20132921. [CrossRef]31. Lenoir, N.; Bornert, M.; Desrues, J.; B\u00e9suelle, P.; Viggiani, G. Volumetric digital image correlation applied to X-ray microtomogra-phy images from triaxial compression tests on argillaceous rock. Strain 2007, 43, 193\u2013205. [CrossRef]32. Nguyen, T.L.; Hall, S.A.; Vacher, P.; Viggiani, G. Fracture mechanisms in soft rock: identification and quantification of evolvingdisplacement discontinuities by extended digital image correlation. Tectonophysics 2011, 503, 117\u2013128. [CrossRef]33. Munoz, H.; Taheri, A.; Chanda, E.K. Pre-peak and post-peak rock strain characteristics during uniaxial compression by 3D digitalimage correlation. Rock Mech. Rock Eng. 2016, 49, 2541\u20132554. [CrossRef]34. Zhou, X.P.; Wang, Y.T.; Zhang, J.Z.; Liu, F.N. Fracturing behavior study of three-flawed specimens by uniaxial compression and3D digital image correlation: sensitivity to brittleness. Rock Mech. Rock Eng. 2019, 52, 691\u2013718. [CrossRef]35. Liu, L.; Li, H.; Li, X.; Wu, D.; Zhang, G. Underlying mechanisms of crack initiation for granitic rocks containing a singlepre-existing flaw: insights from digital image correlation (DIC) analysis. Rock Mech. Rock Eng. 2020. [CrossRef]","type":"literal","lang":"en"}],"http:\/\/www.europeana.eu\/schemas\/edm\/hasType":[{"value":"Article","type":"literal","lang":"en"}],"http:\/\/www.europeana.eu\/schemas\/edm\/isShownAt":[{"value":"10.14288\/1.0395693","type":"literal","lang":"en"}],"http:\/\/purl.org\/dc\/terms\/language":[{"value":"eng","type":"literal","lang":"en"}],"https:\/\/open.library.ubc.ca\/terms#peerReviewStatus":[{"value":"Reviewed","type":"literal","lang":"en"}],"http:\/\/www.europeana.eu\/schemas\/edm\/provider":[{"value":"Vancouver : University of British Columbia Library","type":"literal","lang":"en"}],"http:\/\/purl.org\/dc\/terms\/publisher":[{"value":"Multidisciplinary Digital Publishing Institute","type":"literal","lang":"en"}],"https:\/\/open.library.ubc.ca\/terms#publisherDOI":[{"value":"10.3390\/s21020344","type":"literal","lang":"en"}],"http:\/\/purl.org\/dc\/terms\/rights":[{"value":"CC BY 4.0","type":"literal","lang":"en"}],"https:\/\/open.library.ubc.ca\/terms#rightsURI":[{"value":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/","type":"literal","lang":"en"}],"https:\/\/open.library.ubc.ca\/terms#scholarLevel":[{"value":"Faculty","type":"literal","lang":"en"}],"http:\/\/purl.org\/dc\/terms\/subject":[{"value":"reservoir rock","type":"literal","lang":"en"},{"value":"cyclic wetting and drying","type":"literal","lang":"en"},{"value":"CT","type":"literal","lang":"en"},{"value":"DIC","type":"literal","lang":"en"},{"value":"strength variation","type":"literal","lang":"en"},{"value":"structure variation","type":"literal","lang":"en"}],"http:\/\/purl.org\/dc\/terms\/title":[{"value":"Weakening Investigation of Reservoir Rock by Coupled Uniaxial Compression, Computed Tomography and Digital Image Correlation Methods: A Case Study","type":"literal","lang":"en"}],"http:\/\/purl.org\/dc\/terms\/type":[{"value":"Text","type":"literal","lang":"en"}],"https:\/\/open.library.ubc.ca\/terms#identifierURI":[{"value":"http:\/\/hdl.handle.net\/2429\/77168","type":"literal","lang":"en"}]}}