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A modified 3D mean strain energy density criterion for predicting shale mixed-mode Ⅰ/Ⅲ fracture toughness

Journal of Rock Mechanics and Geotechnical Engineering 2024年第7期16卷 2411-2428页

作者： Kun Zheng chaolin wang Yu Zhao Jing Bi Haifeng Liu College of Civil Engineering Guizhou UniversityGuiyang550025China State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsChinese Academy of SciencesWuhan430071China

The fracture toughness of rocks is a critical fracturing parameter in geo-energy exploitation playing a significant role in fracture mechanics and hydraulic *** edge-notched disk bending(ENDB)specimens are employed to measure the entire range of mixed-modeⅠ/Ⅲfracture toughness of Longmaxi *** theoretically interpret the fracture mechanisms,this research first introduces the detailed derivations of three established fracture *** distinguishing the volumetric and distortional strain energy densities,an improved three-dimensional mean strain energy density(MSED)criterion is *** the critical volumetric to distortional MSED ratio decreases,the transition from tensiondominated fracture to shear-dominated fracture is *** results indicate that both peak load and applied energy increase significantly with the transition from pure mode I(i.e.,tension)to pure modeⅢ(i.e.,torsion or tearing)since mode-Ⅲcracking happens in a twisted manner and mode-Ⅰcracking occurs in a coplanar *** macroscopic fracture signatures are consistent with those of triaxial hydraulic *** average ratio of pure mode-Ⅲfracture toughness to pure mode-Ⅰfracture toughness is 0.68,indicating that the obtained mode-Ⅲfracture resistance for a tensionbased loading system is apparent rather than *** to the three mainstream fracture criteria,the present fracture criterion exhibits greater competitiveness and can successfully evaluate and predict mixed-modeⅠ/Ⅲfracture toughness of distinct materials and loading methods.

关键词： Longmaxi shale Hydraulic fracturing Fracture mechanisms Fracture criteria Mixed-modeⅠ/Ⅲfracture toughness Edge-notched disk bending

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Numerical Study of Flow Features Around Submerged Circular and Square Piles at Flat and Scoured Beds Using OpenFOAM

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Journal of Ocean University of China 2024年第4期23卷 897-914页

作者： wang chaolin WU Guoxiang wang Dianhe DU Shengtao ZHANG Zhiyong JIN Heng ZHU David Z. LIANG Bingchen Donghai Academy School of Civil&Environmental Engineering and Geography ScienceNingbo UniversityNingbo 315211China Key Laboratory of Estuary and Coast of Zhejiang Province and Zhejiang Institute of Hydraulics and EstuaryHangzhou 310020China Shandong Provincial Key Laboratory of Ocean Engineering and College of EngineeringOcean University of ChinaQingdao 266100China Shandong Water Conservancy Vocational College Rizhao 276826China School of Mechanical and Energy Engineering Ningbotech UniversityNingbo 315211China

Elucidating the flow features around piles in local scouring processes is crucial for studies of local scouring mechanisms and scour depth *** study details the flow turbulence characteristics of two submerged piles that are determined by solving the Navier-Stokes equations with the improved delayed detached eddy simulation *** model is verified by comparing experimental and numerical results for hydrodynamic parameters with the literature for both square-crossing piles(SCPs)and circular-crossing piles(CCPs).Original topographies of flat and scoured beds(i.e.,the initial and equilibrium scouring stages)are based on experimental results obtained by the authors in the present *** and CCP flow features in the scouring process are *** results indicate that during the scouring process,the time-averaged drag coefficient and root mean square(rms)of the lift coefficient increase linearly in the CCP test,while the rms of the lift coefficient in the SCP test decreases ***,the minimum pressure coefficient is always located in the upstream corners in the SCP case but moves from 72.5°to 79.5°when the scour hole is completely developed in the CCP *** flow behind the pile,which is generated by separated boundary layers above the top face of the pile,can reach the sand bed and turn the separated shear layers into patches of small vortices in the near-wake ***,the high shear stress zones are mainly at the scour edges under scoured-bed conditions.

关键词： flat bed scoured bed local scour OpenFOAM bed shear stress

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NMR-based analysis of the effect of moisture migration on sandstone pore structure under alternating wetting and drying conditions

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International Journal of Mining Science and Technology 2024年第08期 1135-1150页

作者： Huasu wang Jing Bi Yu Zhao chaolin wang Jiabao Ma College of Civil Engineering Guizhou University

The wetting-drying(W-D) cycle is a type of water–rock interaction. The pore structure of rock, such as shape, size, distribution and pore throat, affects fluid storage and transport. Fractal theory and experimental research on the evolution characteristics of pore damage during the wet-dry erosion process are highly important for determining W-D damage. The mass and velocity of liquid migration are related to the pore size, porosity, fluid properties, etc. Experimental data show that the water absorption quality and velocity in rocks decrease with the number of wet-dry cycles. At the same test time, the mass and velocity of the SI water absorption method are smaller than those of the FI method. Under these two conditions, the amount and rate of water absorption represent the degree of water–rock *** the pore evolution during the wet-dry cycling, an equation describing the motion of liquid in porous media was derived based on the imbibition-type separation model. The experimental data are in excellent agreement with the calculated values of the model. Permeability characteristics can affect the area and degree of rock deterioration as well as the development rate of pores and microcracks. Based on the interaction between permeability and pores, quantitative analysis of the weakening process(local damage) of rocks under W-D cycles can provide good reference indicators for evaluating the stability of geotechnical engineering.

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外部水源作用下岩石液氮冻结试验研究

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岩土工程学报 2024年第2期46卷 415-425页

作者：谭智勇王超林龙安发贵州大学土木工程学院贵州贵阳550025

地下工程施工常遇到砂土交错和地下水丰富的软弱地层问题,液氮低温可使岩土体迅速冻结以达到土层稳定和加固目的,但液氮在快速冻结的同时也会导致周围岩土体物理力学性质受到劣化,因此,探究超低温作用下外部水源对岩石劣化作用的影响对... 详细信息

地下工程施工常遇到砂土交错和地下水丰富的软弱地层问题,液氮低温可使岩土体迅速冻结以达到土层稳定和加固目的,但液氮在快速冻结的同时也会导致周围岩土体物理力学性质受到劣化,因此,探究超低温作用下外部水源对岩石劣化作用的影响对于工程施工的长期稳定和安全具有重要意义。为研究外部水源对岩石低温劣化作用影响,对不同饱水条件下的岩样进行液氮冷浸处理后开展超声波试验、核磁共振试验和单轴压缩试验。试验结果表明:①岩样在冻结状态下仍存在损伤,且损伤程度随岩样恢复室温后进一步增加;②液氮冷浸时间40 min左右对岩样劣化作用最明显;③外部水环境导致干燥岩样劣化程度增加、而饱和岩样劣化程度降低;④当岩石外部存在水源时,长时间(>30 min)的液氮冷浸作用会增加岩石的强度,而短时间(≤30 min)的液氮冷浸处理会劣化岩石的强度。

关键词：液氮冻结损伤孔隙结构岩石强度

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水流强度对淹没式方桩局部冲刷特性的影响

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河海大学学报（自然科学版） 2024年第2期52卷 92-100页

作者：杜升涛王超琳杨博王振鲁梁丙臣宁波大学土木工程与地理环境学院浙江宁波315211 中国海洋大学山东省海洋工程重点实验室山东青岛266101 中国海洋大学工程学院山东青岛266101

为研究不同水流强度作用下淹没式方桩的局部冲刷特性及流场变化,开展了非均匀沙条件下的桩基局部冲刷试验,分析了桩周的冲刷地形、冲刷深度变化规律;利用OpenFOAM对不同水流强度下的桩周流场进行了模拟,讨论了桩前马蹄涡、桩周回流和下... 详细信息

为研究不同水流强度作用下淹没式方桩的局部冲刷特性及流场变化,开展了非均匀沙条件下的桩基局部冲刷试验,分析了桩周的冲刷地形、冲刷深度变化规律;利用OpenFOAM对不同水流强度下的桩周流场进行了模拟,讨论了桩前马蹄涡、桩周回流和下降水流的分布特点。结果表明:在清水冲刷条件下,桩周的冲刷坑深度、沙丘高度和受冲刷影响区域大小均随水流强度的增大而增大;在平衡冲刷地形下,高水流强度冲刷后桩周流动更加复杂,冲刷坑内的涡流强度大幅度提高;当水流强度接近1时,粗颗粒泥沙对细颗粒的屏蔽效应会在一定程度上影响桩周最大冲刷深度。

关键词：方桩局部冲刷水流强度流场特性模型试验 OpenFOAM

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冻融环境下基于声发射的砂岩各向异性劣化机理分析

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中国地质灾害与防治学报 2024年第1期35卷 132-142页

作者：刘兵郑坤王超林毕靖连帅龙贵州大学土木工程学院贵州贵阳550025

在冻融环境下,层理岩石的破裂对寒区工程稳定性存在一定的威胁,容易发生工程事故。将平行、垂直层理砂岩在0,20,40,60次冻融循环处理后,进行了单轴压缩和声发射试验,研究了不同层理砂岩的力学性质和岩石变形破坏过程中声发射特征参数的... 详细信息

在冻融环境下,层理岩石的破裂对寒区工程稳定性存在一定的威胁,容易发生工程事故。将平行、垂直层理砂岩在0,20,40,60次冻融循环处理后,进行了单轴压缩和声发射试验,研究了不同层理砂岩的力学性质和岩石变形破坏过程中声发射特征参数的变化情况。结果表明:随着冻融作用的加强,两组试样的纵波速度都逐渐变小,孔隙率逐渐变大;平行组试样的抗压强度下降比例和应变增大比例都大于垂直组试样,说明平行组试样的劣化程度高于垂直组试样;两组不同层理砂岩在冻融循环作用下的声发射振铃计数演化曲线趋势变化一致,可分为三个阶段:平静阶段、阶梯式增长阶段、骤增阶段。不同层理方向的砂岩单轴破坏模式不同。平行组试样声发射b值变化呈倒“V”型,而垂直组试样声发射b值变化呈正“V”型,基于RA-AF值变化特征表明平行层理黄砂岩基本以拉伸破坏为主,而垂直层理砂岩在未处理时以拉伸破坏和剪切破坏为主,在60次冻融循环处理后,也以拉伸破坏为主。研究成果为寒区岩土工程的安全评估提供科学依据。

关键词：层理砂岩冻融循环声发射破坏机理

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某电站锅炉水冷壁T23管泄漏原因分析及处理

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电力设备管理 2024年第5期 81-83页

作者：王朝林胡玉璋皖能合肥发电有限公司

某电站锅炉在投运一年后,其锅炉水冷壁T23管焊缝发生泄漏和裂纹的现象。在充分考虑T23钢的材料的焊接性的基础上,结合宏观和微观组织的检验对泄漏进行了分析和讨论。焊缝中含有较多高硬度的马氏体组织,是其产生裂纹的内因;水冷壁鳍片焊... 详细信息

某电站锅炉在投运一年后,其锅炉水冷壁T23管焊缝发生泄漏和裂纹的现象。在充分考虑T23钢的材料的焊接性的基础上,结合宏观和微观组织的检验对泄漏进行了分析和讨论。焊缝中含有较多高硬度的马氏体组织,是其产生裂纹的内因;水冷壁鳍片焊缝的横向收缩应力、刚性梁结构的拘束应力等水平方向的附加应力是导致焊缝开裂的外因。最后提出了相应措施,为类似问题的解决和预防提供一定的参考。

关键词：锅炉水冷壁 T23 泄漏

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Study on damage-stress loss coupling model of rock and prestressed anchor cable in dry-wet environment

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International Journal of Mining Science and Technology 2023年第12期33卷 1451-1467页

作者： Yu Zhao Huasu wang Jing Bi Zhijun Wu chaolin wang Jiabao Ma College of Civil Engineering Guizhou UniversityGuiyang 550025China School of Civil Engineering Wuhan UniversityWuhan 430072China

The loss of anchoring force is one of the problems to be solved *** anchorage loss is a key factor causing the failure of anchoring engineering,so it is crucial to study the time-dependent variation of anchoring *** dry and wet(D-W)conditions have a significant effect on deformation of *** anchoring system is composed of anchoring components and rock mass,and thus rock deformation has a significant impact on the loss of anchoring *** rock deformation under the effects of D-W cycles is a prerequisite to understanding the factors that influence loss of anchoring force in anchor *** this study,we designed an anchoring device that enabled real-time monitoring of the variation in strain during D-W periods and rock *** magnetic resonance(NMR)measurements showed that under D-W conditions,the increment in porosity was smaller for prestressed rock than unstressed *** trends of prestress loss and strain variation are consistent,which can be divided into three characteristic intervals:rapid attenuation stage,slow attenuation stage and relatively stable *** the same stress level,the rate of stress loss and strain for the soaking specimen was the highest,while that of the dried specimen was the *** the same D-W cycling conditions,the greater the prestress,the smaller the strain loss rate of the rock,especially under soaking *** characteristics of pore structure and physical mechanical parameters indicated that prestress could effectively suppress damage caused by erosion related to D-W *** study reveals the fluctuation behavior of rock strain and prestress loss under D-W conditions,providing a reference for effectively controlling anchoring loss and ideas for inventing new anchoring components.

关键词： D-W cycles Anchoring force loss Coupled model Pore structure Prestressed device

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三轴循环加卸载条件下砂岩能量和孔隙演化

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水利水电技术（中英文） 2024年第3期55卷 184-195页

作者：刘腾龙毕靖王超林党爽沈明轩贵州大学土木工程学院贵州贵阳550025

【目的】为了对考虑复杂应力环境下的岩土工程破坏特征演化及稳定性加固提供指导依据,【方法】对砂岩进行循环加卸载试验,基于宏观三轴压缩试验和微观核磁共振试验研究砂岩能量和孔隙演化规律。【结果】结果显示:砂岩在三轴循环加卸载... 详细信息

【目的】为了对考虑复杂应力环境下的岩土工程破坏特征演化及稳定性加固提供指导依据,【方法】对砂岩进行循环加卸载试验,基于宏观三轴压缩试验和微观核磁共振试验研究砂岩能量和孔隙演化规律。【结果】结果显示:砂岩在三轴循环加卸载下偏应力-应变曲线出现了明显的滞回环,试样峰值强度与围压成正相关关系,并且试件延性破坏程度随初始围压增加而增强;基于能量密度准则,径向能量表现出相似的变化规律,耗散能均在最后一个阶段明显增加,且径向总能量和径向弹性应变能差距变大;基于核磁共振理论,发现试件T_2谱和核磁成像灰度值变化规律一致。【结论】结果表明:从滞回环和能量密度准则揭示了岩石在试验过程中的能量损耗特征和岩石的破坏是因为岩石储存弹性应变能的能力达到极限导致能量的急剧释放;从微观核磁共振成像结合试件宏观破坏特征分析,两者在破坏形态上高度一致,增加初始围压可以提高试件循环次数从而致使试件峰值强度增大。

关键词：偏应力-应变曲线滞回环能量密度耗散比核磁成像 T_(2)谱破坏形式影响因素

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Mutual impact of true triaxial stress, borehole orientation and bedding inclination on laboratory hydraulic fracturing of Lushan shale

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Journal of Rock Mechanics and Geotechnical Engineering 2023年第12期15卷 3131-3147页

作者： Yongfa Zhang Anfa Long Yu Zhao Arno Zang chaolin wang College of Civil Engineering Guizhou UniversityGuiyang550025China Helmholtz Centre Potsdam GFZ German Research Centre for GeosciencesPotsdam14473Germany

Unconventional resources like shale gas has been the focus of intense research and development for two decades. Apart from intrinsic geologic factors that control the gas shale productivity (e.g. organic matter content, bedding planes, natural fractures, porosity and stress regime among others), external factors like wellbore orientation and stimulation design play a role. In this study, we present a series of true triaxial hydraulic fracturing experiments conducted on Lushan shale to investigate the interplay of internal factors (bedding, natural fractures and in situ stress) and external factors (wellbore orientation) on the growth process of fracture networks in cubic specimens of 200 mm in length. We observe relatively low breakdown pressure and fracture propagation pressure as the wellbore orientation and/or the maximum in situ stress is subparallel to the shale bedding plane. The wellbore orientation has a more prominent effect on the breakdown pressure, but its effect is tapered with increasing angle of bedding inclination. The shale breakdown is followed by an abrupt response in sample displacement, which reflects the stimulated fracture volume. Based on fluid tracer analysis, the morphology of hydraulic fractures (HF) is divided into four categories. Among the categories, activation of bedding planes (bedding failure, BF) and natural fractures (NF) significantly increase bifurcation and fractured areas. Under the same stress regime, a horizontal wellbore is more favorable to enhance the complexity of hydraulic fracture networks. This is attributed to the relatively large surface area in contact with the bedding plane for the horizontal borehole compared to the case with a vertical wellbore. These findings provide important references for hydraulic fracturing design in shale reservoirs.

关键词： True triaxial hydraulic fracturing experiment In situ stress state Bedding planes Natural fractures Wellbore orientation Shale reservoirs

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