Thermal-hydro-mechanical coupling stress intensity factor of brittle rock

A new calculation formula of THM coupling stress intensity factor was derived by the boundary collocation method, in which an additional constant stress function was successfully introduced for the cracked specimen with hydraulic pressure applied on its crack surface. Based on the newly derived formula, THM coupling fracture modes （including tensile, shear and mixed fracture mode） can be predicted by a new fracture criterion of stress intensity factor ratio, where the maximum axial load was measured by self-designed THM coupling fracture test. SEM analyses of THM coupling fractured surface indicate that the higher the temperature and hydraulic pressure are and the lower the confining pressure is, the more easily the intergranular （tension） fracture occurs. The transgranular （shear） fracture occurs in the opposite case while the mixed-mode fracture occurs in the middle case. The tested THM coupling fracture mechanisms are in good agreement with the predicted THM coupling fracture modes, which can verify correction of the newly-derived THM coupling stress intensity factor formula.

Failure behavior of highly stressed rocks under quasi-static and intensive unloading conditions

Unloading failure of rocks,especially highly stressed rocks,is one of the key issues in construction of underground structures.Based on this,analytical models for rocks under quasi-static and intensive unloading conditions are established to study the failure behavior of highly stressed rocks.In case of rock failure under quasi-static unloading,the rock mass ahead of working face is regarded as an elasto-brittle material,and the stress-displacement curves are used to characterize the tensile fracture of peak-stress area.It is observed that,when intensive unloading happens,there is an elastic unloading wave（perturbation wave） propagating in the rock mass.If the initial stress exceeds the critical stress,there will be a fracture wave,following the elastic unloading wave.To study the propagation feature of fracture wave,the conservation laws of mass,momentum and energy are employed.Results show that the post-peak deformation,strength and energy dissipation are essential to the failure process of highly stressed rocks.

Prevention and forecasting of rock burst hazards in coal mines

Rock bursts signify extreme behavior in coal mine strata and severely threaten the safety of the lives of miners, as well as the effectiveness and productivity of miners. In our study, an elastic-plastic-brittle model for the deformation and failure of coal/rock was established through theoretical analyses, laboratory experiments and field testing, simulation and other means, which perfectly predict sudden and delayed rock bursts. Based on electromagnetic emission (EME), acoustic emission (AE) and microseism (MS) effects in the process from deformation until impact rupture of coal-rock combination samples, a multi-parameter identification of premonitory technology was formed, largely depending on these three forms of emission. Thus a system of classification for forecasting rock bursts in space and time was established. We have presented the intensity weakening theory for rock bursts and a strong-soft-strong (3S) structural model for controlling the impact on rock surrounding roadways, with the objective of laying a theoretical foundation and establishing references for parameters for the weakening control of rock bursts. For the purpose of prevention, key technical parameters of directional hydraulic fracturing are revealed. Based on these results, as well as those from deep-hole controlled blasting in coal seams and rock, integrated control techniques were established and anti-impact hydraulic props, suitable for roadways subject to hazards from rockbursts have also been developed. These technologies have been widely used in most coal mines in China, subject to these hazards and have achieved remarkable economic and social benefits.

Use of double edge-cracked Brazilian disk geometry for compression-shear fracture investigation of rock

A new specimen geometry-the double edge-cracked Brazilian disk and a relevant fracture analysis byweight function method are proposed for the investigation of rock fracture caused by compression-shear loading. Notonly can the mixed mode fracture with any ratio of KⅠ/KⅡ be achieved, but also the pure mode Ⅱ crack extensioncan be obtained. The combined mode fracture analysis for this geometry shows that diametral compression in the far-field can induce a compression-shear stress state in the singular stress field ahead of crack tips. Experimental investi-gations conducted on marble specimens show that the pure mode Ⅱ crack extension can be obtained when the dimen-sionless crack length a＞0.7 and the inclined crack angle 5°≤ψ≤40°. Normalized mode Ⅰ and mode Ⅱ stress inten-sity factors decrease from -0.45 and 2.47 at ψ=5° to -1.65 and 1.52 at ψ=40°, respectively. The strains at threepoints of specimen are also measured in order to investigate the influence of stress singularity on initial crack exten-sion. The results show that the principal orientations of strain at three points are very stable in the loading process.The derived formulae are quite explicit, and the specimen geometry is easy to fabricate and convenient to achieve thepure mode Ⅱ crack extension. Therefore, it can hopefully be used to obtain mode Ⅱ fracture toughness of rock.

Dynamic fracture behavior of rock under impact load using the caustics method

We studied the dynamic fracture mechanical behavior of rock under different impact rates. The fracture experiment was a three-point bending beam subjected to different impact loads monitored using the reflected caustics method. The mechanical parameters for fracture of the three-poim bending beam specimen under impact load are analyzed. The mechanism of crack propagation is discussed. Experimental results show that the dynamic stress intensity factor increases before crack initiation. When the dynamic stress intensity factor reaches its maximum value the crack starts to develop. After crack initiation the dynamic stress intensity factor decreases rapidly and oscillates. As the impact rate increases the cracks initiate earlier, the maximum value of crack growth velocity becomes smaller and the values of dynamic stress intensity factor also vary less during crack propagation. The results provide a theoretical basis for the study of rock dynamic fracture.

A swirling jet from a nozzle with tangential inlets and its characteristics in breaking-up rocks

In order to apply a swirling jet to a PDC drill bit, the nozzle performance influenced by nozzle inlet geometric parameters and rock breaking tests under submerged conditions were studied. Numerical simulation was used to study the influence of the nozzle structure on the swirling intensity and nozzle discharge coefficient. Simulation results indicate that spreading angle of the swirling jet is greater than that of＂ the non-swirling jet, and the swirling intensity of the jet is strongly influenced by the length of the nozzle body but weakly by the number of tangential inlets. Rock breaking tests were conducted to evaluate the performance of the swirling jet. It is found that the swirling jet shows a lower threshold pressure to break the rock samples and could break rock more efficiently compared with the non-swirling jet.

Analysis on Fracture Mechanics of Unstable Rock

Unstable rock is a kind of global geological disaster with high frequency. This paper, considering three kinds of combined loads which are gravity, fracture water pressure and seismic force, constructs a unstable rock mechanics model and it uses a fracture mechanics method to deduce the composite stress intensity factor of the type I - II. Based on the maximum circumferential stress theory, this article calculates the theo-retical fracture angle by triangle universal formula.

A Study on Propagation Mechanism of Fracture Systems in Rock Masses by Discontinuity Displacement Method

The main task of fracture mechanics of rock masses is the study on the propagating mechanism of fractures in rock masses , which can be efficiently conducted by discontinuty displacement (DD) numerical evaluation . Firstly ,the element stress and displacement are analysed and the principle and steps of the numerical calculation of stress intensity factor and fracture extension force are introduced .The numerical results of parallel and echelon fracture systems ,which are compared with real field fractures .are presented. Finally . a simple engineering application example is presented .

Experimental Research on Large Diameter Cast-in-Place Piles Embedded in Rock

This paper expatiated the field test of large diameter cast in place piles embedded in soft rock, including static loading test, high or low strain dynamic test, measurement of stresses and strains of pile body, and pressure measurements between pile tip and soft rock. The relative in situ test problems are discussed. Based on the limit equilibrium theory and the load transfer equation, a synthesis method of analyzing the ultimate carrying capacity of single large diameter pile is put forward. The research results show that the key to determining the ultimate carrying capacity of single pile with a large diameter is the analysis of the intensity of soft rock.

Mass Balance of Major Elements in Relation to Weathering in Soils Developed on Igneous Rocks in a Semiarid Region,Northwestern Iran

This study was conducted to evaluate the weathering intensity of the major soils developed on igneous rocks in semiarid region of northwestern Iran.Eight parent materials were selected including monzodiorite,alkali granite,granodiorite,syenite,pyroxene diorite,hornblende andesite,pyroxene andesite,and dacite.Representative soil profiles were described and soil samples were collected and analyzed for selected chemical and physical properties and total concentrations of major elements and Zr,V,Ti and Y.Bulk densities as well as Ti,Zr and V concentrations were used to estimate the strain factors and mass balance equations were used to quantify the net result of pedogenic weathering,i.e.elemental loss and gain.The results of clay content and pedogenic iron variability as well as index of compositional variability(ICV),chemical index of alteration(CIA) and,A-CN-K and MFW ternary plots showed that the soils developed on volcanic rocks(hornblende andesite> pyroxene andesite> dacite) were more weathered than those on the plutonic parent rocks(alkali granite,granodiorite,monzodiorite,syenite,pyroxene diorite).The results of mass balance calculations based on the strain factors revealed that the Ca and Na depleted during weathering progress mostly from plagioclase grains.In the semiarid regions Ca is precipitated as pedogenic calcite in the soil horizons.K and Mg depletion is less than Ca and Na especially in the profiles on the hornblende andesite with the highest clay and LOI content.The results of this study clearly suggest that the behavior of K and Mg during the weathering cannot only be explained by the disintegration of the primary minerals,since they are fixed on the secondary clay minerals.Iron did not change in the soils compared to the parent material and was precipitated as the pedogenic iron and conserved in the soil horizons.Overall,the results on the weathering indicators and major elements mass balance enrichment/depletion in the study area confirmed that the soil profiles developed on volcanic rocks are more weathered than those on the plutonic igneous rocks.

类岩石试件三轴扰动破坏特性试验研究

为研究高应力围岩扰动破坏机制,开展了不同围压下类岩石试件的三轴常规压缩和三轴循环扰动试验,得到了试件的扰动应力–应变规律和变形破坏特征,并对试件开展了核磁共振(Nuclear Magnetic Resonance)成像试验,从微观角度进一步阐明了试件扰动破坏机理。研究结果表明:(1)试件在不同围压下均存在一个阈值强度,轴向荷载超过阈值强度后,轴向变形对扰动变得敏感,再次施加扰动会引起试件显著变形,当轴向荷载低于阈值强度时,变形对扰动不敏感。阈值强度与极限强度的比值可以反映试件的抗扰动能力,随着围压增大,该比值呈现逐步递减的规律,说明高围压下试件抗扰动能力下降,对扰动作用更敏感。(2)扰动作用下类岩石试件存在弱化效应,如常规三轴10MPa围压下试件表现出腰鼓破坏,而受扰动作用后,试件呈现斜切脆性破坏,与常规三轴5MPa围压下破坏形态相近。(3)岩石试件在高应力作用下进入塑性流动状态,内部颗粒重新排列,内部小孔隙与大孔隙的占比减少,而中孔隙的占比显著增多,试件内部孔隙率整体降低。

基于红外热像和振动信号的煤岩识别实验研究

针对现有煤岩识别技术存在的难以实际应用、易受信号干扰、成本高和实现复杂等问题,通过理论分析煤岩截割产热与煤岩硬度的关系,证明通过红外热像获取的截割温度变化来进行煤岩识别的合理性;搭建了掘进机截齿截割煤岩试验台,对不同硬度的普通煤层、煤岩交界处及中砂岩层进行长时间截割试验,通过红外热像仪和振动传感器分别获取截割温度和截割头振动信号并分析其变化规律。研究结果表明:①随着截割时间增加,截割温度逐渐升高;煤岩硬度越高,截割温度越高,且截割温度上升速率越快;在截割起始阶段无法通过截割温度识别煤岩,但在稳定截割时可根据截割温度特性识别煤岩。②截割头振动强度随着煤岩硬度增大而变大,但不随截割时间增加而产生明显变化,因此可弥补在截割起始阶段无法通过截割温度识别煤岩的不足。③通过单一截割温度或振动强度不能对煤岩进行准确识别,因此可在截割起始阶段和频繁出现闪温时通过振动强度来识别煤岩,而在截割稳定阶段通过红外热像获取的温度来识别煤岩。

四川盆地金秋气田:一个典型以中生界沉积岩为氦源岩的含氦-富氦气田

氦气成藏长期以来研究较少,成藏条件与成藏机理还不十分清楚,氦源岩类型和形成条件争议较大。通过解剖含氦-富氦的金秋气田认为:(1)金秋气田氦气含量主要分布在0.05%~0.10%,平均为0.07%,部分井含量超过0.10%,最高为0.20%。同位素分析认为氦气为壳源成因,没有幔源的贡献。(2)金秋气田是一个典型以中生界沉积岩为氦源岩的含氦-富氦气田。上三叠统须家河组和侏罗系具有较高的铀、钍元素含量和较大的地层厚度,在金秋地区具有较高的氦气生气强度,是形成含氦-富氦气藏的氦源基础。氦气应该主要来源于侏罗系储层,而非上三叠统须家河组烃源岩层系。(3)金秋气田含氦-富氦气田的形成受3个主要因素控制,具有高氦气生气强度的氦源岩提供了很好的物质基础;具有适度充注强度的烃类气体的存在有利于氦气富集;地层抬升剥蚀温、压下降导致的原位溶解氦气脱溶作用是氦气富集的有益补充。

四川盆地东部下寒武统筇竹寺组烃源岩评价

四川盆地下寒武统筇竹寺组含油气系统已获探明储量超过1.3×10^(13)m^(3),但川东地区经历30年勘探仍未取得实质性突破。为厘清川东地区筇竹寺组烃源岩生烃条件,对新近钻井楼探1井、五探1井、马深1井、焦石1井和城口剖面等开展有机地球化学综合研究。结果表明:马深1井筇竹寺组厚度为358 m,底部黑色泥岩厚度约130 m;向北至盆地外缘杨坝剖面筇竹寺组厚度增加,总厚约400 m,但下部泥岩,总有机碳含量(质量分数)TOC>0.5%,厚度减小到50 m;川东地区筇竹寺组厚度110~150 m,下部黑色泥岩厚度约60 m。川北马深1井—福成地区筇竹寺组平均TOC含量为3.39%~3.44%;川东楼探1井—城口地区平均TOC含量相对较小,为0.52%~2.58%。盆地周缘筇竹寺组剖面等效镜质体反射率(R_(o))在2.22%~2.53%,盆地内钻井R_(o)在2.57%~3.10%;受古埋深影响,热演化程度由盆地外向盆地内呈增加趋势。进一步结合黑色泥岩产烃率、原始有机碳恢复系数等相关参数,计算得到川东地区生气强度由盆地内向东北方向呈现增加趋势,鹰探1井—楼探1井区生气强度在(10~20)×10^(8)m^(3)/km^(2);生气强度最大地区为城口区域,其生气强度达60×10^(8)m^(3)/km^(2)。结合典型钻井埋深沉降热史模拟表明,筇竹寺组烃源岩于志留纪(430 Ma)开始大量生烃,到三叠纪(250 Ma)进入生气阶段。综合研究表明,川东地区巴中—南江与城口地区两个生烃中心为下寒武统筇竹寺组含油气系统最有利生烃富集带。

典型岩溶小流域碳酸盐岩风化过程及其碳汇效应

碳酸盐岩风化过程是一个吸收大气CO_(2)的过程,具有碳汇效应。利用岩溶区水体的水文地球化学特征揭示碳酸盐岩风化过程、计算流域岩溶碳汇通量是全球变化研究的一个重要方面。以广西柳州官村地下河流域(GGW)为例,2021年4个季度的监测结果表明:(1)HCO_(3)^(-)和Ca^(2+)是主要的阴阳离子,阴阳离子当量浓度和TDS浓度反映了碳酸盐岩强烈的风化作用;(2)水化学时空分布特征显示,GGW的水化学类型为HCO_(3)-Ca型,水岩作用过程除了H_(2)CO_(3)风化碳酸盐岩外,还有H_(2)SO_(4)和HNO_(3)风化碳酸盐岩;(3)在研究H_(2)CO_(3)、H_(2)SO_(4)和HNO_(3)共同参与的水岩作用过程中,用δ13 C DIC计算H_(2)CO_(3)风化碳酸盐岩的CO_(2)消耗量为2.38 mmol·L^(-),CO_(2)净消耗量用[HCO_(3)^(-)]mol-[Ca^(2+)+Mg^(2+)]mol表示,平均净消耗量为1.98 mmol·L^(-),用CO_(2)净消耗量计算出的GGW无机碳汇强度(以CO_(2)计)C m为86.37 t·km^(-2)·a^(-);(4)不考虑外源酸作用,利用水化学径流法计算出的GGW无机碳汇强度(以CO_(2)计)C m为94.49 t·km^(-2)·a^(-),CO_(2)净消耗量是水化学径流法计算的CO_(2)汇量的91.41%;(5)碳汇强度为2008年的1.91倍,研究结果可为人工干预增加岩溶碳汇潜力评估提供一定的参考和借鉴。

西部高强度开采矿区覆岩破坏发育高度分析

导水裂缝带是煤层顶板水害的主要通道,准确预测计算其发育高度是保障矿山安全生产的重要任务。在实测资料的基础上,通过采用理论分析和相似模拟等方法,揭示了西部高强度开采矿区采动覆岩的破坏类型、破坏关系及导水裂缝带的发育特征。结果表明:在薄基岩厚煤层高强度开采条件下,覆岩破坏类型为严重损坏类型。在采动覆岩中只存在“两带”形式,在采空区上方不存在岩层破坏后的具有一定隔水性的弯曲带,导水裂缝带直通地表,地表严重受损。覆岩以组合关键层的形式发生运移。在采动过程中组合关键层以滑落失稳的方式在岩层两端产生切落式破断,导致上覆基岩和松散层切落破断,地表产生台阶状裂缝。地表实测台阶状裂缝沿工作面推进方向的间距与井下周期来压步距相一致。综合考虑覆岩破坏的开采厚度与基岩厚度等关键性因素,提出了高强度开采导水裂缝带发育高度预测计算公式,其可靠性得到了现场实测与相似材料模拟结果的验证,研究结果对于神东矿区煤矿安全开采具有一定的指导意义。

三点弯曲载荷下岩体偏置斜裂隙的应力强度因子

地下巷道(硐室)顶板常因弯曲离层而破断,其破断位置与裂隙几何形态和位置密切关联。为揭示裂隙对岩层断裂的影响,建立了岩体偏置斜裂隙的三点弯曲模型,定义了裂隙的偏置系数和贯通率,分析了裂隙偏置系数、倾角和贯通率三者之间的关系,基于力学平衡原理和σ-K关系导出了偏置斜裂隙与偏置竖裂隙应力强度因子K的关系式。同时分析了裂隙倾角、贯通率和偏置系数对应力强度因子的影响规律。该方法可为裂隙影响下巷道(硐室)顶板的张拉断裂提供判定依据。

基于蠕变终止轨迹的岩石长期强度推算法

岩石长期强度是在长期荷载作用下岩石强度持续而有限趋于的一个稳定低限值,是评估岩土工程长期稳定性的一个重要指标。从蠕变终止轨迹理论出发,结合岩石常规三轴压缩和蠕变试验,介绍了一种相对简捷而准确的推算长期强度的方法;随后,以贵州花鱼洞大桥黄果树岸坡岩样为研究对象,详细给出了该方法用于推算岩石长期强度的具体步骤;最后,以既有文献实例为基础验证该方法的准确性。这一方法可用于快速而准确地确定工程岩石长期强度,研究结果可为有关理论研究和工程实践提供借鉴。

地下磷矿高强度开采地表生态环境演变与调控关键技术

地下磷矿高强度开采对地表生态环境的影响是一个备受关注的研究领域。该文通过对地下磷矿高强度开采地表生态环境演变与调控关键技术展开深入研究,旨在揭示该过程中的关键问题和解决方案。该文首先分析地下磷矿高强度开采对地表生态环境的影响,包括土地利用变化、植被破坏、土壤侵蚀及水资源受损等方面。在此基础上,该文提出针对地下磷矿高强度开采地表生态环境演变的调控关键技术。其中,针对土地利用变化,提出合理规划和管理地下矿山区域的用地结构,推动矿山生态恢复和重建;针对植被破坏,探讨生态恢复技术和植被保护措施,以增加植被覆盖率和保护濒危植物物种;针对土壤侵蚀,提出加强水土保持措施和开展土壤修复工作,减轻开采活动对土壤的破坏和侵蚀;针对水资源受损,探讨科学合理的水资源利用与保护措施,确保地下矿山开采不会对地表水资源造成长期损害。该文所提出的地下磷矿高强度开采地表生态环境演变与调控关键技术,提供一系列在实践中具有可操作性的措施,为地下磷矿开采领域及相关生态环境调控提供重要的参考依据。同时,也为其他类似矿产资源的高强度开采提供有益的借鉴和启示。希望该文的研究成果能够为促进地下磷矿开采的可持续发展和保护生态环境作出贡献。

煤柱回收工作面巷道围岩控制技术

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