Effect of Water Saturation on the Damage Failure and Acoustic Emission Characteristics of White Sandstone

HU Yu-bo, FANG Jing-nian, XU Rong-chao, HAO Xiao-hong, YAN Zhen, ZHOU Wen-peng, LI Zhen

Journal of Changjiang River Scientific Research Institute ›› 2024, Vol. 41 ›› Issue (11) : 163-171.

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Medical Journal of the Chinese People's Armed Police Forces
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Journal of Changjiang River Scientific Research Institute ›› 2024, Vol. 41 ›› Issue (11) : 163-171. DOI: 10.11988/ckyyb.20231215
Rock-Soil Engineering

Effect of Water Saturation on the Damage Failure and Acoustic Emission Characteristics of White Sandstone

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Abstract

The instability and failure of surrounding rock in water-bearing weak strata are often closely related to the effects of water. To deeply reveal the influence and mechanical mechanism of water saturation on rock damage and failure, uniaxial compression tests on white sandstone under dry and water-saturated conditions were carried out. Through comparative analysis, the effects and mechanisms of water saturation on strength, deformation, stress thresholds, strain energy, and acoustic emission characteristics were studied. The results showed the following when the white sandstone was water-saturated: (1) Uniaxial compressive strength and elastic modulus decrease, while Poisson’s ratio increases.(2) The normalized crack initiation stress (σci/σf) decreases. The analysis shows that the softening effect of water weakens the bonding between mineral particles, making new cracks easier to initiate, thus leading to a decrease in σci/σf.(3) The normalized crack damage stress (σcd/σf) decreases. Based on the analysis of the AE b-value, the proportion of small-scale ruptures increases. The increase in the proportion of small-scale fractures makes it easier for microcracks to coalesce into macrofractures, leading to a decrease in σcd/σf.(4) The total energy (U), elastic energy (Ue), and dissipated energy (Ud) at peak strength decrease, and the ratio of elastic energy to total energy (Ue/U) also decreases.(5) The analysis based on AE RA value (ratio of rise time to amplitude) and AF value (average frequency) shows that the proportion of shear fractures increases after water saturation, making it easier to produce intragranular fractures. The research results provide important insights into the failure mechanisms of water-saturated rocks.

Key words

white sandstone / water saturation / stress thresholds / energy evolution / damage failure / acoustic emission

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HU Yu-bo , FANG Jing-nian , XU Rong-chao , et al . Effect of Water Saturation on the Damage Failure and Acoustic Emission Characteristics of White Sandstone[J]. Journal of Yangtze River Scientific Research Institute. 2024, 41(11): 163-171 https://doi.org/10.11988/ckyyb.20231215

References

List( Publishing order | Descend order by publishing year | Descend order by cited within ) Chart analysis
[1]
刘新荣, 傅晏, 王永新, 等. 水-岩相互作用对库岸边坡稳定的影响研究[J]. 岩土力学, 2009, 30(3): 613-616, 627.
(LIU Xin-rong, FU Yan, WANG Yong-xin, et al. Stability of Reservoir Bank Slope under Water-rock Interaction[J]. Rock and Soil Mechanics, 2009, 30(3): 613-616, 627. (in Chinese))
Cited in this article [1]
[2]
肖诗荣, 卢树盛, 管宏飞, 等. 三峡库区凉水井滑坡地质力学模型研究[J]. 岩土力学, 2013, 34(12): 3534-3542.
(XIAO Shi-rong, LU Shu-sheng, GUAN Hong-fei, et al. Study of Geomechanical Model of Liangshuijing Landslide in Three Gorges Reservoir Area[J]. Rock and Soil Mechanics, 2013, 34(12): 3534-3542. (in Chinese))
Cited in this article [1]
[3]
CAI X, ZHOU Z, TAN L, et al. Water Saturation Effects on Thermal Infrared Radiation Features of Rock Materials during Deformation and Fracturing[J]. Rock Mechanics and Rock Engineering, 2020, 53(11): 4839-4856.
Cited in this article [1]
[4]
LI Z, XU R. An Early-warning Method for Rock Failure Based on Hurst Exponent in Acoustic Emission Microseismic Activity Monitoring[J]. Bulletin of Engineering Geology and the Environment, 2021, 80(10):7791-7805.
Cited in this article [1]
[5]
ZHANG X P, WONG L N Y, WANG S J, et al. Engineering Properties of Quartz Mica Schist[J]. Engineering Geology, 2011, 121(3/4): 135-149.
Cited in this article [1]
[6]
周翠英, 邓毅梅, 谭祥韶, 等. 饱水软岩力学性质软化的试验研究与应用[J]. 岩石力学与工程学报, 2005, 24(1): 33-38.
(ZHOU Cui-ying, DENG Yi-mei, TAN Xiang-shao, et al. Experimental Research on the Softening of Mechanical Properties of Saturated Soft Rocks and Application[J]. Chinese Journal of Rock Mechanics and Engineering, 2005, 24(1): 33-38. (in Chinese))
Cited in this article [1]
[7]
郭慧敏. 饱水-风干循环作用下砂岩力学性质劣化规律[J]. raybet体育在线 院报, 2020, 37(1): 90-94.
https://doi.org/10.11988/ckyyb.20180841
Abstract
水库在建成运营过程中,水库内水位反复升降对库岸边坡安全性产生影响。为探究饱水-风干循环作用下水库边坡岩体力学性质的劣化规律,以某水库边坡水位变幅带砂岩为试验对象,进行岩石三轴压缩试验。引入劣化率概念探究水岩作用对砂岩力学性质的影响,并借助电镜扫描技术分析了砂岩在水岩作用下的劣化机理。研究表明:水岩作用程度相同时,砂岩峰值抗压强度随围压增大而变大;相同围压条件下,随饱水-风干/循环次数增多,砂岩峰值抗压强度、黏聚力、内摩擦角变小,且三者数值与循环次数N之间的变化规律符合指数分布。当水岩作用增强时,峰值抗压强度劣化率最小值为31.35%,黏聚力、内摩擦角劣化率分别为30.61%和15.37%;水库水位升降对砂岩峰值抗压强度、黏聚力影响较内摩擦角大,三者劣化率与循环次数N之间的变化规律同样符合指数分布。在砂岩三轴压缩试验基础上,对水岩作用下岩石劣化机理进行了研究。研究成果对于受水位反复升降影响的水库边坡安全性治理具有一定参考价值。
(GUO Hui-min. Deterioration of Mechanical Properties of Sandstone under Cyclic Water Saturation and Drying[J]. Journal of Changjiang River Scientific Research Institute, 2020, 37(1): 90-94. (in Chinese))
Cited in this article [1]
[8]
王桂林, 任甲山, 曹天赐, 等. 干湿循环下溶隙灰岩单轴压缩损伤破裂特征[J]. raybet体育在线 院报, 2024, 41(2): 105-114, 122.
(WANG Gui-lin, REN Jia-shan, CAO Tian-ci, et al. Effect of Dry-wet Cycles on Damage and Failure Characteristics of Karst-fissured Limestone under Uniaxial Compression[J]. Journal of Changjiang River Scientific Research Institute, 2024, 41(2): 105-114, 122. (in Chinese))
Cited in this article [1]
[9]
闫章程, 孙辉, 李利平, 等. 灰岩单轴压缩过程中干燥与饱水状态对声发射特征的影响[J]. raybet体育在线 院报, 2020, 37(4): 109-114, 121.
https://doi.org/10.11988/ckyyb.20190049
Abstract
为探究水岩耦合条件下的声发射规律,通过开展干燥与饱水灰岩单轴压缩条件下的声发射监测试验,并结合快速傅里叶变换、短时傅里叶变换与离散小波变换这3种常用的声发射信号分析方法,对比分析了干燥与饱水灰岩的时域参数、频率特征与典型破裂信号的时频特征。结果表明:水对于岩石的变形破坏特征影响显著,相对于干燥状态,饱水试样的单轴抗压强度下降明显,且幅值、能量以及振铃计数等基本时域特征参数均呈现出大幅降低的特点;岩样破坏前,干燥与饱水灰岩都表现出由“高主频、低幅值”向“低主频、高幅值”过渡的总体变化趋势;干燥岩样破坏前主频值高于饱水岩样,完全破坏后却低于饱水岩样,主频下降幅度大,而饱水岩样的主频值波动较小,频率较为稳定。研究结果对于工程尺度的防突机构声发射监测具有一定的参考价值。
(YAN Zhang-cheng, SUN Hui, LI Li-ping, et al. Acoustic Emission Characteristics in Dry and Water-saturated Limestones under Uniaxial Compression[J]. Journal of Yangtze River Scientific Research Institute, 2020, 37(4): 109-114, 121. (in Chinese))
https://doi.org/10.11988/ckyyb.20190049
Cited in this article [1] Abstract
Acoustic emission monitoring of dry and water-saturated limestone under uniaxial compression was performed in this research to explore the acoustic emission law under water-rock coupling conditions. Signal analysis method inclusive of fast Fourier transform, short-time Fourier transform, and discrete wavelet transform were adopted to compare and analyze the time domain, frequency domain and time-frequency characteristics of the dry and water-saturated limestone specimens. Results showed that water had a notable influence on the deformation and failure characteristics of limestone. Compared with that in dry state, limestone in water-saturated state had markedly lower uniaxial compressive strength and basic time domain characteristic parameters such as amplitude, energy and ringing count. Before failure, the dry and water-saturated limestones both presented an overall trend of transition from “high main frequency and low amplitude” to “low main frequency and high amplitude”. Before failure, the value of main frequency of dry limestone was higher than that of water-saturated limestone; whereas after complete destruction, the main frequency of dry limestone declined sharply and became lower than that of water-saturated limestone. The main frequency of water-saturated limestone was stable with small fluctuation.
[10]
邓朝福, 刘建锋, 陈亮, 等. 不同含水状态花岗岩断裂力学行为及声发射特征[J]. 岩土工程学报, 2017, 39(8): 1538-1544.
(DENG Chao-fu, LIU Jian-feng, CHEN Liang, et al. Mechanical Behaviors and Acoustic Emission Characteristics of Fracture of Granite under Different Moisture Conditions[J]. Chinese Journal of Geotechnical Engineering, 2017, 39(8): 1538-1544. (in Chinese))
Cited in this article [1]
[11]
朱俊, 邓建辉, 黄弈茗, 等. 饱和大理岩特征强度试验研究[J]. 岩石力学与工程学报, 2019, 38(6): 1129-1138.
(ZHU Jun, DENG Jian-hui, HUANG Yi-ming, et al. Experimental Study on the Characteristic Strength of Saturated Marble[J]. Chinese Journal of Rock Mechanics and Engineering, 2019, 38(6): 1129-1138. (in Chinese))
Cited in this article [1]
[12]
HUANG S, HE Y, LIU G, et al. Effect of Water Content on the Mechanical Properties and Deformation Characteristics of the Clay-bearing Red Sandstone[J]. Bulletin of Engineering Geology and the Environment, 2021, 80(2): 1767-1790.
Cited in this article [1]
[13]
HUANG S, HE Y, LIU X, et al. Experimental Investigation of the Influence of Dry-wet, Freeze-thaw and Water Immersion Treatments on the Mechanical Strength of the Clay-bearing Green Sandstone[J]. International Journal of Rock Mechanics and Mining Sciences, 2021,138: 104613.
Cited in this article [1]
[14]
杨科, 张寨男, 池小楼, 等. 循环载荷下含水砂岩裂纹演化与损伤特征试验研究[J]. 岩土力学, 2022, 43(7): 1791-1802.
(YANG Ke, ZHANG Zhai-nan, CHI Xiao-lou, et al. Experimental Study on Crack Evolution and Damage Characteristics of Water Bearing Sandstone under Cyclic Loading[J]. Rock and Soil Mechanics, 2022, 43(7): 1791-1802. (in Chinese))
Cited in this article [1]
[15]
徐荣超, 靳一鼎, 李日运, 等. 龙马溪页岩应力-应变门槛值的各向异性特征研究[J]. 岩土工程学报, 2021, 43(12): 2291-2299.
(XU Rong-chao, JIN Yi-ding, LI Ri-yun, et al. Anisotropic Characteristics of Stress and Strain Thresholds of Longmaxi Shale[J]. Chinese Journal of Geotechnical Engineering, 2021, 43(12): 2291-2299. (in Chinese))
Cited in this article [1]
[16]
周辉, 孟凡震, 卢景景, 等. 硬岩裂纹起裂强度和损伤强度取值方法探讨[J]. 岩土力学, 2014, 35(4): 913-918, 925.
(ZHOU Hui, MENG Fan-zhen, LU Jing-jing, et al. Discussion on Methods for Calculating Crack Initiation Strength and Crack Damage Strength for Hard Rock[J]. Rock and Soil Mechanics, 2014, 35(4):913-918,925. (in Chinese))
Cited in this article [1]
[17]
ZHANG X P, LÜ G G, LIU Q S, et al. Identifying Accurate Crack Initiation and Propagation Thresholds in Siliceous Siltstone and Limestone[J]. Rock Mechanics and Rock Engineering, 2021, 54(2): 973-980.
Cited in this article [1]
[18]
郭孔灵, 杨磊, 盛祥超, 等. 水力耦合作用下含三维裂隙类岩石材料的破裂力学行为及声发射特征[J]. 岩土力学, 2019, 40(11): 4380-4390.
(GUO Kong-ling, YANG Lei, SHENG Xiang-chao, et al. Fracture Mechanical Behavior and AE Characteristics of Rock-like Material Containing 3-D Crack under Hydro-mechanical Coupling[J]. Rock and Soil Mechanics, 2019, 40(11): 4380-4390. (in Chinese))
Cited in this article [1]
[19]
LI Y, LIU G, QIN T, et al. Progressive Failure and Fracture Mechanism of Sandstone under Hydraulic-mechanical Coupling[J]. Shock and Vibration, doi:10.1155.2020.8866680
Cited in this article [1]
[20]
YAO Q, CHEN T, JU M, et al. Effects of Water Intrusion on Mechanical Properties of and Crack Propagation in Coal[J]. Rock Mechanics and Rock Engineering, 2016, 49(12): 4699-4709.
Cited in this article [1]
[21]
谢和平, 彭瑞东, 鞠杨. 岩石变形破坏过程中的能量耗散分析[J]. 岩石力学与工程学报, 2004, 23(21): 3565-3570.
(XIE He-ping, PENG Rui-dong, JU Yang. Energy Dissipation of Rock Deformation and Fracture[J]. Chinese Journal of Rock Mechanics and Engineering, 2004, 23(21): 3565-3570. (in Chinese))
Cited in this article [1]
[22]
谢和平, 鞠杨, 黎立云, 等. 岩体变形破坏过程的能量机制[J]. 岩石力学与工程学报, 2008, 27(9): 1729-1740.
(XIE He-ping, JU Yang, LI Li-yun, et al. Energy Mechanism of Deformation and Failure of Rock Masses[J]. Chinese Journal of Rock Mechanics and Engineering, 2008, 27(9): 1729-1740. (in Chinese))
Cited in this article [1]
[23]
郭佳奇, 刘希亮, 乔春生. 自然与饱水状态下岩溶灰岩力学性质及能量机制试验研究[J]. 岩石力学与工程学报, 2014, 33(2):296-308.
(GUO Jia-Qi, LIU Xi-liang, QIAO Chun-sheng. Experimental Study of Mechanical Properties and Energy Mechanism of Karst Limestone under Natural and Saturated States[J]. Chinese Journal of Rock Mechanics and Engineering, 2014, 33(2):296-308. (in Chinese))
Cited in this article [1]
[24]
夏冬, 杨天鸿, 王培涛, 等. 循环加卸载下饱和岩石变形破坏的损伤与能量分析[J]. 东北大学学报(自然科学版), 2014, 35(6): 867-870.
https://doi.org/10.12068/j.issn.1005-3026.2014.06.024
Abstract
以中关铁矿深部饱水闪长岩单轴循环加卸载的室内力学试验结果为基础，结合线弹性损伤力学理论，针对饱和岩石在单轴循环加卸载作用下的变形、损伤及能耗特性进行了研究.结果表明:每一级加载与卸载过程的应力-应变曲线均呈内凹形，随着循环次数及应力水平的增加，塑性滞回曲线向应变增大的方向移动，且应变中不可恢复的变形逐渐减小；轴向应变、横向应变和体应变的绝对损伤参数与累积损伤参数均随循环次数及应力水平的增大而增大，且三者的变化趋势基本一致；能量耗散值与循环的次数近似呈线性关系，后一循环的能耗不等于前几次循环能耗之和.
(XIA Dong, YANG Tian-hong, WANG Pei-tao, et al. Analysis on Damage and Energy in Deformation and Fracture of Saturated Rock Subjected to Cyclic Loading and Unloading[J]. Journal of Northeastern University (Natural Science), 2014, 35(6): 867-870. (in Chinese))
Cited in this article [1]
[25]
李天斌, 陈子全, 陈国庆, 等. 不同含水率作用下砂岩的能量机制研究[J]. 岩土力学, 2015, 36(增刊2): 229-236.
(LI Tian-bin, CHEN Zi-quan, CHEN Guo-qing, et al. Study on Energy Mechanism of Sandstone under Different Water Content[J]. Rock and Soil Mechanics, 2015, 36(Supp. 2): 229-236. (in Chinese))
Cited in this article [1]
[26]
CAI X, ZHOU Z, DU X. Water-induced Variations in Dynamic Behavior and Failure Characteristics of Sandstone Subjected to Simulated Geo-stress[J]. International Journal of Rock Mechanics and Mining Sciences, 2020,130:104339.
Cited in this article [1]
[27]
张寅, 李哲, 宋士康, 等. 自然与饱水状态下砂岩压缩破坏力学特性及声发射特征[J]. 煤田地质与勘探, 2022, 50(2): 98-105.
(ZHANG Yin, LI Zhe, SONG Shi-kang, et al. Mechanical Properties and Acoustic Emission Characteristics of Sandstone under Natural and Saturated Conditions[J]. Coal Geology & Exploration, 2022, 50(2): 98-105. (in Chinese))
Cited in this article [1]
[28]
ZHANG X P, ZHANG Q, WU S. Acoustic Emission Characteristics of the Rock-like Material Containing a Single Flaw under Different Compressive Loading Rates[J]. Computers and Geotechnics, 2017, 83: 83-97.
Cited in this article [1]
[29]
高子兴, 夏冬, 杨意德, 等. 基于声发射监测的含水岩石动态损伤演化过程试验研究[J]. 采矿技术, 2018, 18(1): 51-55.
(GAO Zi-xing, XIA Dong, YANG Yi-de, et al. Experimental Study on Dynamic Damage Evolution Process of Water-bearing Rocks Based on Acoustic Emission Monitoring[J]. Mining Technology, 2018, 18(1): 51-55. (in Chinese))
Cited in this article [1]
[30]
夏冬, 杨天鸿, 王培涛, 等. 干燥及饱和岩石循环加卸载过程中声发射特征试验研究[J]. 煤炭学报, 2014, 39(7): 1243-1247.
(XIA Dong, YANG Tian-hong, WANG Pei-tao, et al. Experimental Study of Acoustic Emission Characteristics of Dry and Saturated Rocks during Cyclic Loading and Unloading Process[J]. Journal of China Coal Society, 2014, 39(7): 1243-1247. (in Chinese))
Cited in this article [1]
[31]
李博, 叶鹏进, 黄林, 等. 干燥与饱和岩石裂隙受压变形与声发射特性研究[J]. 岩土工程学报, 2021, 43(12): 2249-2257.
(LI Bo, YE Peng-jin, HUANG Lin, et al. Deformation and Acoustic Emission Characteristics of Dry and Saturated Rock Fractures[J]. Chinese Journal of Geotechnical Engineering, 2021, 43(12): 2249-2257. (in Chinese))
Cited in this article [1]
[32]
赵奎, 冉珊瑚, 曾鹏, 等. 含水率对红砂岩特征应力及声发射特性的影响[J]. 岩土力学, 2021, 42(4):899-908.
(ZHAO Kui, RAN Shan-hu, ZENG Peng, et al. Effect of Moisture Content on Characteristic Stress and Acoustic Emission Characteristics of Red Sandstone[J]. Rock and Soil Mechanics, 2021, 42(4):899-908. (in Chinese))
Cited in this article [1]
[33]
姚强岭, 王伟男, 杨书懿, 等. 含水率影响下砂质泥岩直剪特性及声发射特征[J]. 煤炭学报, 2021, 46(9): 2910-2922.
(YAO Qiang-ling, WANG Wei-nan, YANG Shu-yi, et al. Direct Shear and Acoustic Emission Characteristics of Sandy Mudstone under the Effect of Moisture Content[J]. Journal of China Coal Society, 2021, 46(9): 2910-2922. (in Chinese))
Cited in this article [1]
[34]
姚强岭, 王伟男, 李学华, 等. 水-岩作用下含煤岩系力学特性和声发射特征研究[J]. 中国矿业大学学报, 2021, 50(3): 558-569.
(YAO Qiang-ling, WANG Wei-nan, LI Xue-hua, et al. Study of Mechanical Properties and Acoustic Emission Characteristics of Coal Measures under Water-rock Interaction[J]. Journal of China University of Mining & Technology, 2021, 50(3): 558-569. (in Chinese))
Cited in this article [1]
[35]
PALCHIK V, HATZOR Y H. Crack Damage Stress as a Composite Function of Porosity and Elastic Matrix Stiffness in Dolomites and Limestones[J]. Engineering Geology, 2002, 63(3/4): 233-245.
Cited in this article [1]
[36]
张晓平, 吕根根, 张旗, 等. 单轴压缩条件下硅质粉砂岩应力阈值研究[J]. 工程地质学报, 2020, 28(3): 441-449.
(ZHANG Xiao-ping, LÜ Gen-gen, ZHANG Qi, et al. Uniaxial Compression Test for Three Stress Thresholds of Siliceous Siltstone[J]. Journal of Engineering Geology, 2020, 28(3): 441-449. (in Chinese))
Cited in this article [1]
[37]
MARTIN C D, CHANDLER N A. The Progressive Fracture of Lac Du Bonnet Granite[J]. International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1994, 31(6): 643-659.
Cited in this article [1]
[38]
EBERHARDT E, STEAD D, STIMPSON B, et al. Identifying Crack Initiation and Propagation Thresholds in Brittle Rock[J]. Canadian Geotechnical Journal, 1998, 35(2): 222-233.
Cited in this article [1]
[39]
NICKSIAR M, MARTIN C D. Evaluation of Methods for Determining Crack Initiation in Compression Tests on Low-porosity Rocks[J]. Rock Mechanics and Rock Engineering, 2012, 45(4):607-617.
Cited in this article [1]
[40]
XU R, LI Z, JIN Y. Brittleness Effect on Acoustic Emission Characteristics of Rocks Based on a New Brittleness Evaluation Index[J]. International Journal of Geomechanics, 2022, 22(10):04022185.
Cited in this article [2]
[41]
LIU X, LIU Z, LI X, et al. Experimental Study on the Effect of Strain Rate on Rock Acoustic Emission Characteristics[J]. International Journal of Rock Mechanics and Mining Sciences, 2020, 133: 104420.
Cited in this article [2]
[42]
ZHANG Z H, DENG J H. A New Method for Determining the Crack Classification Criterion in Acoustic Emission Parameter Analysis[J]. International Journal of Rock Mechanics and Mining Sciences, 2020, 130: 104323.
Cited in this article [2]
[43]
XU R, ZHANG S, LI Z, et al. Experimental Investigation of the Strain Rate Effect on Crack Initiation and Crack Damage Thresholds of Hard Rock under Quasi-static Compression[J]. Acta Geotechnica, 2023, 18(2):903-920.
Cited in this article [1]
[44]
DONG L, ZHANG Y, BI S, et al. Uncertainty Investigation for the Classification of Rock Micro-fracture Types Using Acoustic Emission Parameters[J]. International Journal of Rock Mechanics and Mining Sciences, 2023, 162: 105292.
Cited in this article [1]
[45]
LI X F, LI H B, LIU L W, et al. Investigating the Crack Initiation and Propagation Mechanism in Brittle Rocks Using Grain-based Finite-discrete Element Method[J]. International Journal of Rock Mechanics and Mining Sciences, 2020, 127: 104219.
Cited in this article [1]
[46]
LI X F, LI H B, ZHAO J. 3D Polycrystalline Discrete Element Method (3PDEM) for Simulation of Crack Initiation and Propagation in Granular Rock[J]. Computers and Geotechnics, 2017, 90: 96-112.
Cited in this article [1]
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