Experimental and numerical investigation of groundwater head losses on and nearby short intersections between disc-shaped fractures

Discrete fracture models are used for investigating precise processes of groundwater flow in fractured rocks,while a disc-shaped parallel-plates model for a single fracture is more reasonable and efficient for computational treatments.The flow velocity has a large spatial differentiation which is more likely to produce non-linear flow and additional head losses on and nearby intersections in such shaped fractures,therefore it is necessary to understand and quantify them.In this study,both laboratory experiments and numerical simulations were performed to investigate the total head loss on and nearby the intersections as well as the local head loss exactly on the intersections,which were not usually paid sufficient attention or even ignored.The investigation results show that these two losses account for 29.17%-84.97%and 0-73.57%of the entire total head loss in a fracture,respectively.As a result,they should be necessarily considered for groundwater modeling in fractured rocks.Furthermore,both head losses become larger when aperture and flow rate increase and intersection length decreases.Particularly,the ratios of these two head losses to the entire total head loss in a fracture could be well statistically explained by power regression equations with variables of aperture,intersection length,and flow rates,both of which achieved high coefficients of determination.It could be feasible through this type of study to provide a way on how to adjust the groundwater head from those obtained by numerical simulations based on the traditional linear flow model.Finally,it is practicable and effective to implement the investigation approach combining laboratory experiments with numerical simulations for quantifying the head losses on and nearby the intersections between disc-shaped fractures.     

Shaking table test of subgrade slope reinforced by gravity retaining wall with geogrids

Gravity retaining wall with geogrids has showed excellent seismic performance from Wenchuan great earthquake. However, seismic damage mechanism of this kind of wall is not sufficiently clear. In view of this, a large shaking table test of the gravity retaining wall with geogrids to reinforce the subgrade slope was carried out, and based on the Hilbert-Huang transform and the marginal spectrum theory, the energy identification method of the slope dynamic failure mode was studied. The results show that the geogrids can effectively reduce displacement and rotation of the retaining wall, and it can effectively absorb the energy of the ground movement when combined with the surrounding soil. In addition, it also reveals the failure development of the gravity retaining wall with geogrids to reinforce the subgrade slope. The damage started in the deep zone near the geogrids, and then gradually extended to the surface of the subgrade slope and other zones, finally formed a continuous failure surface along the geogrids. The analysis results of the failure mode identified by the Hilbert marginal spectrum are in good consistency with the experimental results, which prove that the Hilbert marginal spectrum can be applied to obtain the seismic damage mechanism of slope.

     

真三轴单面临空下煤岩组合体冲击破坏特征试验研究

煤岩复合承载结构所处的应力边界条件不同,冲击地压在巷道中的显现特征和前兆规律亦不相同。采用高频振动采集及孔内成像三轴动静载试验系统,开展了高静载和动静载耦合作用下煤岩组合体真三轴单面临空试验,分析了煤岩组合体界面处力学特征和强度条件,探究了不同应力边界下煤岩组合体的破坏形态、动力显现特征和声发射信号的演变规律。研究结果表明:(1)受煤岩变形相互制约的影响,交界面处砂岩强度被"弱化"。当界面处煤体裂隙尖端的应力大于"弱化"后砂岩强度时,裂隙将穿过煤岩界面发育至砂岩中,砂岩呈现出屈曲层裂、劈裂成板的破坏形态。(2)高静载作用下,煤岩组合体变形破坏特征和声发射信号具有明显的前兆规律,组合体发生承载失效前煤体局部颗粒弹射动能增大、弹射颗粒块度降低,声发射信号由"高频低能"向"高频高能"转变,组合体的破坏形态以剪切-张拉复合破坏为主。(3)受冲击动载影响,顶底板砂岩夹持作用减弱,煤体裂纹尖端应力得不到有效积聚,裂纹扩展到煤岩交界面时被阻隔,组合体以煤样的张拉破坏为主,声发射信号呈现出"高频高能"的特点,但大多集中在冲击破坏之后,导致组合体动力破坏难以预测。(4)与纯静载作用相比,虽然动静载耦合作...     

大倾角煤层分层综采再生顶板破断规律研究

针对大倾角厚软煤层下分层安全综采问题,结合淮南矿区潘北煤矿1212（3）大倾角厚软煤层分层综采下分层工作面地质与工程条件,综合运用基于数字散斑、声发射监测与分布式光纤传感技术的物理模拟试验、基于煤系地层赋存禀赋建模技术的数值模拟试验相结合的研究手段,开展了下分层开采再生顶板破断倾向分区演化、再生岩体变形声发射能量与光纤应变响应规律及应力分布特征研究。结果表明：再生顶板破断由其破断岩块滑移、低中位悬臂梁和高位铰接岩梁断裂组成,双梁破断是引起下分层支架失稳的关键所在。下分层中上部双梁破断声发射能量呈高度聚集且持续时间短,光纤感知低位悬臂梁破断且中上部光纤应变峰值高,下分层中上部是支架与再生顶板稳定性控制的重点区域。下分层下部再生顶板破断岩块充填密实且粒径小,是架间与架前岩块漏冒多发区域。下分层再生顶板中形成高应力组成的应力拱,距采空区高度约30 m,双梁破断主要发生在拱内,拱中岩体破断对支架具有一定的冲垮作用。     

库车坳陷克拉苏构造带协同变形机制及盆山耦合关系

克拉苏构造带构造非常复杂,经过30余年的油气勘探开发,构造规律不清楚、构造圈闭不落实的问题仍然非常突出。本文通过大量三维地震资料的构造解释、建模及实钻资料验证,发现克拉苏构造带在剖面上呈分段分层变形、平面上呈雁列式展布特征。提出克拉苏构造带两种协同变形机制,较好地解释了在膏盐层调节作用下盐上、盐层、盐下3个构造层的差异变形现象。结合遥感影像及重力异常影像分析了盆山耦合关系,提出了南天山造山带的差异隆升推覆作用,南部温宿、新和、牙哈古隆起的阻挡作用和古近系膏盐层的调节作用是变形的3个主要影响因素,并据此较好地解释了克拉苏构造带构造圈闭平面展布格局。     

Design of optimal sand fences around a desert solar park—a case study from Phase IV of the Mohammed bin Rashid Al Maktoum Solar Park

Natural Hazards - Solar energy parks in desert areas must resist the encroachment of moving sand and burial by migrating dunes. It is therefore important to design economical, effective sand fences...     

Research on Reasonable Width of Coal Pillars of Non-equal Width Isolated Working Face Heading Goaf in Deep Mine

Geotechnical and Geological Engineering - Setting reasonable coal pillar is a key to ensure safe mining of island coal face heading goaf in deep mine. With the background of typical deeply buried...     

造山型金矿中富CO_(2)高内压流体包裹体完全均一温度的有效测定实验研究——以东天山玉峰金矿床为例SCIEI北大核心CSCD

形成于中-深成条件下的造山型金矿的成矿流体属于H_(2)O-NaCl-CO_(2)体系,金矿化阶段的石英中发育大量的富CO_(2)流体包裹体。长期以来,用常规冷热台对其进行显微测温热力学研究时,较高的内压力会造成绝大多数CO_(2)充填度>0.4的包裹体在尚未达到完全均一状态前就发生爆裂或泄露,导致所测的完全均一温度值明显偏离真实值,甚至无法测得完全均一温度,这制约了对造山型金矿床成矿条件的认知。针对该问题,本文以东天山玉峰金矿床富金矿石中的H_(2)O-NaCl包裹体(A型)和H_(2)O-NaCl-CO_(2)包裹体(AC型)为研究对象,介绍了利用最新型热液金刚石压腔(HDAC-VT型号)测试富CO_(2)高内压的AC型包裹体完全均一温度的实验流程与结果,并将实验数据与Linkam THMSG600冷热台测得的A型、AC型包裹体的完全均一温度进行了对比分析。实验结果表明,热液金刚石压腔能够有效阻止富CO_(2)流体包裹体在升温过程中发生爆裂、泄露等非弹性体积改变现象的发生,从而获得有效的完全均一温度。同时,本文还提出了一个新的压力-温度拟合线两线相交法,对热液金刚石压腔所测富CO_(2)流体包裹体的完全均一温度数据进行校正,以最大程度上减少外压力造成的影响,获得更为接近真实成矿流体的完全均一温度。基于此,获得玉峰金矿床的成矿温度和成矿压力分别为312~343℃和181~268 MPa。本文的实验研究工作显示了热液金刚石压腔在中-深成造山型金矿富CO_(2)成矿流体的研究领域具有重要应用前景。     

成矿流体动力学与大地构造环境的关系(英文)

热液矿床的形成需要大量流体,而流体的运移需要包括地势差、岩石变形、热梯度及热异常等多种驱动力。这些流体驱动力与构造环境及过程有密切关系。流体压力状态和热场及地势差的组合决定了压性构造环境流体以向上运动为主,如造山型成矿系统,而张性构造环境流体以对流为主,如VMS和SEDEX成矿系统。造山作用造成的地势差及水平挤压作用所产生的超压可以驱动流体侧向迁移数百公里,如MVT成矿系统。但是,具体的成矿流体动力学过程比较复杂,且随构造演化而变化。在经历过多个大地构造演化阶段的地区,如地洼区,老的成矿流体动力系统不断被新的系统叠加或取代;新的构造单元需要来自地幔的流体源补充才有利于成矿。成矿学研究的是成矿作用与大地构造的关系,而流体动力学系统与大地构造环境密切相关,因此,成矿流体动力学应成为成矿学的一个重要组成部分。     

An Review of International Climate Change Conference and Analysis on Recent Hot Issues

The international climate change negotiation has been carried out over 20 years. The issue of climate change has shifted from a scientific question into a complex political matter which is related to the sustainable development of mankind. Based on the overview of major processes and stages of international climate conferences, this paper analyzed the key measures that major countries have taken to address climate change, as well as the primary tasks of Paris climate conference and recent international actions. The recent international climate policy issues were also analyzed in order to provide suggestions for China’s activel participation in the development of a new round of international climate change system.