Theoretical and numerical simulation investigation of deep hole dispersed charge cut blasting

Drilling and blasting methods have been used as a common driving technique for shallow-hole driving and blasting in rock roadways.With the advent of digital electronic detonators and the need for increased production efciency,the traditional blasting design is no longer suitable for deep hole blasting.In this paper,a disperse charge cut blasting method was proposed to address the issues of low excavation depth and high block rate in deep hole undercut blasting.First,a blasting model was used to illustrate the mechanism of the deep hole dispersive charge cut blasting process.Then,continuous charge and dispersed charge blasting models were developed using the smooth particle hydrodynamics-fnite element method(SPHFEM).The cutting parameters were determined theoretically,and the cutting efciency was introduced to evaluate the cutting efect.The blasting efects of the two charging models were analyzed utilizing the evolution law of rock damage,the number of rock particles thrown,and the cutting efciency.The results show that using a dispersed charge improves the cutting efciency by about 20%and the rock breakage for the deep hole cut blasting compared to the traditional continuous charge.In addition,important parameters such as cutting hole spacing,cutting hole depth and upper charge proportion also have a signifcant impact on the cutting efect.Finally,the deep hole dispersed charge cut blasting technology is combined with the digital electronic detonator through the feld engineering practice.It provides a reference for the subsequent deep hole cutting blasting and the use of electronic detonators in rock roadways.

Experimental Study Optimizing Hole Cleaning-Cuttings Transport in Oil Drilling Engineering

With a clear understanding of the drilling fluid techniques and the cutting taking mechanism, a new advanced model is set up for analyzing field data and quantitative forecast of cutting taking mechanism. Therefore, a number of values affecting the drilling rate and the hole cleaning are studied over a wide range of parameters. Drilling data obtained under high borehole pressure conditions are analyzed to determine the causes of the reduction in rate of penetration (ROP) as the borehole pressure increases, which in some cases is caused by the buildup of rock debris under the bit. The theoretical achievement and testing conclusions can be very instructional for horizontal well drilling. Much higher annular velocities are required for effective hole cleaning in directional wells than in vertical wells. High viscosity muds are observed to provide better transport than low viscosity muds.

Numerical simulation of parallel hole cut blasting with uncharged holes

The cavity formation and propagation process of stress wave from parallel hole cut blasting was simulated with ANSYS/LS-DYNA 3D nonlinear dynamic finite element software. The distribution of element plastic strain, node velocity, node time-acceleration history and the blasting cartridge volume ratio during the process were analyzed. It was found that the detonation of charged holes would cause the interaction of stress wave with the wall of uncharged holes. Initial rock cracking and displacement to neighboring uncharged holes become the main mechanism of cavity formation in early stage.2008 University of Science and Technology Beijing. All rights reserved.

Optimization on cut-hole of mining tunnel excavation

The efficiency of excavation a mining tunnel is definitely linked with modes of cut-holes. According to experience and methods of engineering analogy, the double-wedge cut, the 9-hole cut and the single spiral cut were determined originally by considering the production conditions and blasting environment of the mining tunnels of the-74 m horizontal in the Da-ye iron mine. Based on acquired modes of cut-holes, the effect of the cut was studied, on the one hand, by a numerical simulation method with the aid of LS-DYNA3D, a nonlinear dynamic finite element program; on the other hand, a spot experiment was carried out in the mining tunnels. Both the numerical simulation and the spot experiment demonstrated and agreed that a single spiral cut provides the optimum excavation effect.

Endoscopic ultrasound-guided cutting of holes and deep biopsy for diagnosis of gastric infiltrative tumors and gastrointestinal submucosal tumors using a novel vertical diathermic loop

AIM To report on a more accurate diagnostic possibility offered by endoscopic ultrasound-guided cutting of holes and deep biopsy(EUS-CHDB) for pathologic diagnosis of gastric infiltrative tumors and gastrointestinal submucosal tumors.METHODS Ten consecutive patients who were suspected of having gastric invasive tumors or gastrointestinal submucosal tumors underwent EUS-CHDB with a novel vertical diathermic loop. We reviewed their medical data and analysed the effectiveness and safety of this new method. The final diagnosis was based on the surgical pathology or clinical/imaging follow-up. RESULTS EUS-CHDB was performed successfully in all the ten patients. Neither severe haemorrhage nor perforation occurred in any patient. Among the ten patients, there were three cases of gastric linitis plastica, one case of gastric lymphoma, five cases of gastrointestinal stromal tumors(GISTs), and only one case of chronic non-atrophic gastritis. That is, nine(90%) of the cases treated by EUS-CHDB showed positive findings.CONCLUSION EUS-CHDB may be a technically feasible and safe option for patients with gastric infiltrative tumors or gastrointestinal submucosal tumors. EUS-CHDB may be used as a remedial or even preferred biopsy method for submucosal lesions.

Mechanism and practice of rock control in deep large span cut holes

Deep large span cut holes are difficult to stabilize. The 7801 cut hole in the Lu'an Wuyang Mine was used as this project's background. The main factors affecting large span cut hole stability are analyzed. Pre- stressed bolting theory was used to design a roof control method for a large span roadway. By reducing the span and applying equal strength coordinated supports the rock could be stabilized. The control prin- ciples and methods are given herein along with the analysis. A double micro arch cross section roadway is defined and its use in solving the current problem is described. Beam arch theory was used to build a model of the double micro arch cross section roadway. A support reverse force model for the arch foot intersection was also derived. A support method based upon reducing the width of the large span in the cut hole is presented. These results show that the reduced span of the roadway roof plus the use of cable anchors and single supports gives an effective way to control the large span cut hole. On site monitoring showed that the reduced span support from the double micro arch cross section roadway design had a significant effect. The roadway surface displacement was small and harmful deformation of the cut hole was effectively controlled. This will ensure its long term stability.

Experimental research on characteristics of hole reaming and side cutting of one-cone bits

The hole reaming and side cutting characteristics of offset one-cone bit and conventional one- cone bit were investigated on simulated drilling experimental equipment. The borehole diameter was a little larger than the bit diameter due to side force. However, the reaming effect was not very apparent, whether drilling with an offset or conventional one-cone bit. The side cutting displacement increased gradually with increasing depth of drilling and side force. The side cutting displacement of offset onecone bits was larger than that of conventional ones under the same conditions of weight-on-bit （WOB）, rotary speed, side force and borehole depth.

Influence of delay interval on blasting efficiency of parallel hole cuts with an empty hole

Time interval of short delay ignition is an important factor to affect theefficiency of blasting cuts. The motion process of rock pieces in the cut cavity is analyzed, amechanical model to calculate the delay time of parallel hole cuts is presented for tunnel blasting,and a theoretical method to determine the volume ratio (the clearage rate) of the rock pieceswithin the cut cavity at different moments is proposed for the blasting cut with an empty hole.Numerical analysis results show that the optimal delay interval is proportional to the boreholedepth. The suggested results are of practical value to the optimal design of the delay interval inmillisecond blasting related to the parallel hole cuts with an empty hole.

Cuttings transport: Back reaming analysis based on a coupled layering-sliding mesh method via CFD

Inadequate hole cleaning is one of the main reasons for inefficient operations in extended-reach drilling.The mechanism of cuttings transport under the back reaming operation,which is frequently adopted to remove the cuttings,has been investigated in this study.To this end,a coupled layering-sliding mesh method with the Eulerian-Granular approach has been established innovatively.The dynamic layering method has been employed to simulate the axial motion of the pipe,whereas the sliding mesh method has been used to simulate the pipe rotation.The back reaming operation of a connector-furnished pipe has been simulated,and the sensitive parameter analysis has been conducted.The results thus obtained demonstrate that the increase in the initial bed height,inclination,and the diameter and length of the connector causes a significant increase in the cuttings concentration.In addition,the cuttings concentration is observed to decrease significantly with the pipe rotation speed.Furthermore,two main factors contribute towards the cuttings accumulation around the connector,namely,the difference in the cross-sectional area and the pushing effect of the connector—like a“bulldozer”.The“bulldozer”effect of the connector dominates when the tripping velocity is significant compared to the velocity of the cuttings.Conversely,the effect of the difference in the cross-sectional area becomes the leading factor for cuttings accumulation.The“bulldozer”effect of the connector causes a more severe impact on hole cleaning.In both cases,increasing the tripping velocity only mildly affects the cuttings concentration.It is therefore suggested that the tripping velocity should be slower than that of the sand during the back reaming operation.Furthermore,increased fluid velocity might lead to a higher accumulated cuttings concentration around the connector when the cuttings bed has not entirely passed through the connector.A significant flow rate can be safely applied after the cuttings have passed through the connector furnished with a large diameter,such as the bottom hole assembly.This exploration serves as an essential guide to predicting and controlling tight spots while back reaming.

Fatigue Behavior of Open-Holed CFRP Laminates with Initially Cut Fibers

Carbon fiber-reinforced plastic (CFRP) laminates with initially cut fibers (ICFs) have good formability without large degradation of static strength;however, their fatigue behavior has not been investigated thus far. In this paper, we investigated fatigue behavior and damage progress of open-holed CFRP laminates with ICFs having interlayers. Three types of CFRP laminates were employed: a laminate without ICF fabricated using an autoclave (Continuous-A), a laminate with ICF fabricated using an autoclave (ICF-A) and a laminate with ICF fabricated using press molding (ICF-P). First, fatigue test was conducted to obtain S (maximum stress)-N (the number of cycles to failure) curves in order to reveal fatigue strength. The fatigue tests for several specimens were interrupted at three prescribed numbers of cycles to observe damage progress. It is found that the Continuous-A laminate shows little strength degradation in the S-N curve while fatigue strength in both ICF laminates is decreased by approximately 30% at N of 106. In contrast, the damage progress of the ICF-P laminate is the least among the three laminates while the delamination progress at both edges and around the hole in the Continuous-A laminate is the most prominent.

孔洞缺陷对TC4切削加工影响的仿真研究

为研究孔洞缺陷对TC4材料切削加工的影响,使用有限元切削仿真方法对切削过程的应力应变、切屑形态和切削力特点和规律进行研究。通过热力耦合仿真、数据分析、时频分析等方法对含缺陷材料切削过程中的参数的研究,研究结果表明:位于切削路径上的缺陷,在切削完后缺陷处表面出现应力集中,位于切削路径上的缺陷处表面应力值相比无缺陷时明显减大;缺陷位于表层区域时,由于缺陷导致材料内部结构变化,切屑断裂,切屑形态剧烈变化;当缺陷位于切削路径上和表层区域时,切削至缺陷处时切削力发生突变,切削状态发生失稳,并且位于表层区域的缺陷对切削力的突变影响最大;最后通过Choi-Williams时频分析对含不同位置缺陷切削仿真得到的切削力信号进行分析,观察到不同位置缺陷情况下切削力波动的时频信号,判断缺陷的位置。

沿空留巷密集钻孔切顶机理及关键参数确定方法

为实现密集钻孔切顶条件下沿空留巷顶板结构安全稳定,研究正常情况与密集钻孔条件下顶板岩层结构受力状况,基于岩石断裂理论和弹性理论分析回采前后顶板密集钻孔孔间围岩受力分布及其破断过程,明确密集钻孔切顶机理及相邻钻孔的孔间集中应力相互作用机制,推导工作面端头弧形三角板结构巷道侧边界密集钻孔孔间围岩的拉剪应力计算公式。在此基础上,分析不同参数对孔间围岩所受拉剪应力的影响作用,提出沿空留巷密集钻孔切顶关键参数确定方法。研究表明:密集钻孔主要通过回采前后钻孔周围应力条件改变来增加钻孔围岩拉剪应力集中程度,引起孔间裂隙扩张联通,形成切缝线破断关键岩层。回采前钻孔主要受水平挤压应力影响,回采后钻孔受力逐渐转变为采空区顶板回转下沉产生的拉剪应力为主,钻孔孔间围岩状态随之由孔间围岩弱化阶段过渡到孔壁裂纹成形阶段,再转变为孔间围岩破断阶段。密集钻孔孔间围岩所受拉剪应力大小主要取决于关键岩层厚度及钻孔孔径与孔间距之比,与钻孔高度及间距成负相关,与角度及直径正相关。据此提出了密集钻孔关键参数确定方法,并根据龙滩矿3124 N工作面坚硬顶板条件设计了密集钻孔切顶留巷方案,确定钻孔长度为8.3 m,角度为15°,钻孔直径为48 mm,间距为500 mm。留巷后巷道顶帮变形可控且整体稳定性较好,由此可证明密集钻孔布置参数较为合理,密集钻孔关键参数确定方法有效可行。

渠式切割水泥土连续墙的应用和发展

作为超深、等厚、连续、可靠的截水挡土帷幕,渠式切割水泥土连续墙在国内有广泛应用。本文概括了渠式切割水泥土连续墙在国内的引进、应用和发展历程。结合对国内200多个既有应用案例的统计分析,研究了渠式切割水泥土连续墙的施工设备保有情况、成墙深度范围、常用墙体厚度和主要应用场景;罗列了渠式切割水泥土连续墙在复杂地层施工的辅助措施以及典型案例;指出了渠式切割水泥土连续墙在敏感环境微扰动施工的控制要点;介绍了渠式切割预制装配式混凝土连续墙的设计要求和用途,尤其是内插预制板材的截面设计和制造工艺;最后用工程实例表明渠式切割预制装配式混凝土连续墙同时继承了渠式切割微扰动和地下连续墙支护刚度好的特点,无论是切割成墙期间还是土方开挖期间,施工对周边环境的影响都较小。

石门揭煤局部防突措施研究进展及展望

随着矿井开采深度的增加,瓦斯突出问题日益凸显,如何快速安全地进行石门揭煤,是保障煤矿安全生产的重要目标。选取中国知网数据库中近30年相关文献为样本,基于图谱分析法,分析了石门揭煤局部防突领域中的研究热点;对防突措施的研究进展和不足之处进行了系统探析,分析发现低温冷冻技术从降低煤层储能及提高煤体强度2个角度实现防突。煤与瓦斯突出事故的发生是煤层储能失稳后突破了煤体抵抗能力导致的,基于目前局部防突领域存在的技术难题以及人工冻结存在的不足,结合智能化技术,提出智能“钻-抽-注”一体化措施,通过信号基站及局域网络进行实时监控及预警,实现精准防突;通过建立多物理场耦合模型、理论分析及工程实践验证3方面相结合,掌握冷冻条件下煤岩体瓦斯赋存状态及运移规律,为低温冷冻技术在石门揭煤局部防突中的应用提供理论依据;借助智能液氮冻结系统,实现“一孔多功能”,为石门揭煤局部防突工作提供新的选择和支持,从而快速、安全揭开突出危险性煤层。

GFRP材料螺旋铣孔时的制孔质量研究

采用传统钻孔方法对GFRP(玻璃纤维增强材料)进行加工时易产生毛刺、撕裂和分层等缺陷,而螺旋铣孔方法可以有效避免这些缺陷产生。运用螺旋铣孔方法对GFRP进行制孔试验,得到切削速度、刀具公转转速、轴向进给螺距对孔壁表面粗糙度以及孔径尺寸误差的影响规律,对比分析了螺旋铣孔和钻孔的孔口缺陷。试验结果表明:影响孔壁表面粗糙度的切削参数由大至小依次为切削速度>刀具公转转速>轴向进给螺距;切削速度、刀具公转转速、轴向进给螺距与孔壁表面粗糙度均呈正比关系;影响孔径尺寸误差的切削参数依次为刀具公转转速>轴向进给螺距>切削速度;螺旋铣孔的入口侧缺陷较多,钻孔时的孔口缺陷更多出现在出口侧。

深孔聚能预裂爆破切顶卸压机理与应用

为解决悬顶导致的煤柱及邻近巷道高应力和大变形问题,结合工作面顶板地质条件,提出深孔聚能预裂爆破切顶卸压专项方案,采用数值模拟及现场试验对卸压效果开展综合研究。研究结果表明,煤层顶板在切顶后垂直应力减幅为21.62%,预裂切顶措施可显著降低煤柱及邻近巷道围岩应力水平。试验发现,炮孔内轴向贯穿裂缝明显,可实现采空区顶板及时垮落。顶底板在切顶后累计位移量减幅达59.27%,巷道两帮及顶底板移近变形得到有效控制,煤柱垂直应力增量显著降低。实践证明,采用深孔聚能预裂爆破切顶卸压效果显著,可大幅提高作业效率,为类似矿压防治工程提供借鉴。

Cutting edge preparation of microdrills by shear thickening polishing for improved hole quality in electronic PCBs

Printed circuit boards(PCBs)are representative composite materials,and their high-quality drilling machining remains a persistent challenge in the industry.The finishing of the cutting edge of a microdrill is crucial to drill performance in machining fine-quality holes with a prolonged tool life.The miniature size involving submicron scale geometric dimensions,a complex flute shape,and low fracture toughness makes the cutting edge of microdrills susceptible to breakage and has been the primary limiting factor in edge preparation for microdrills.In this study,a newly developed cutting edge preparation method for microdrills was tested experimentally on electronic printed circuit boards.The proposed method,namely,shear thickening polishing,limited the cutting edge burrs and chipping on the cutting edge,and this in turn transformed the cutting edge’s radius from being sharp to smooth.Moreover,the edge–edge radius could be regulated by adjusting the processing time.PCB drilling experiments were conducted to investigate the influence of different cutting edge radii on wear,hole position accuracy,nail head value,and hole wall roughness.The proposed approach showed 20%enhancement in hole position accuracy,33%reduction in the nail head value,and 19%reduction in hole wall roughness compared with the original microdrill.However,a threshold is needed;without it,excessive shear thickening polishing will result in a blunt edge,which may accelerate the wear of the microdrill.Wear was identified as the primary factor that reduced hole quality.The study indicates that in printed circuit board machining,microdrills should effectively eliminate grinding defects and maintain the sharpness of the cutting edge as much as possible to obtain excellent drilling quality.Overall,shear thickening polishing is a promising method for cutting edge preparation of microdrills.Further research and optimization can lead to additional improvements in microdrill performance and contribute to the continued advancement of printed circuit board manufacturing.

不同堵塞条件下硬岩隧道直眼掏槽破岩效果数值模拟研究

为研究不同堵塞材料及堵塞长度对硬岩隧道直眼掏槽爆破效果的影响,依托工程实例,采用ANSYS/LS一DYNA仿真模拟软件建立三维数值模型,对5种不同堵塞条件展开研究。根据数值模型计算结果,对掏槽区域爆破裂纹拓展情况进行了定性分析,对典型部位的岩石受力情况进行了定量分析。结果表明:1)自由面岩石主要受拉应力作用产生裂纹,炮孔堵塞使得爆炸荷载整体作用时间延长,致使自由面上裂纹更加密集;2)位于炸药和堵塞材料之间空气段附近的围岩,先受爆炸应力波作用岩石被压碎,后受力在拉压应力之间多次转化,致使裂纹被放大,结合爆生气体发挥的“气楔”作用,使得裂纹几乎贯穿模型截面;3)炮孔堵塞后炸药段周围岩石受到的爆生气体作用应力值显著提升,比不堵塞时的炸药段周围岩石峰值应力高出1.31~2.34倍,炮孔堵塞使得爆生气体持续稳定发挥作用时的压应力值提高3.70~4.70倍;4)以黏土和水作为堵塞材料时,堵塞长度为40cm的直眼掏槽破岩效果优于堵塞长度为60cm的效果。研究成果可为优化硬岩隧道直眼掏槽爆破参数提供理论基础。

掏槽孔爆破作用下隧道掌子面应力传播与衰减规律研究

为明晰掏槽孔爆破作用下隧道掌子面应力传播与衰减规律,借助爆破试验分析隧道掌子面在掏槽孔爆破作用下水平方向、竖向和斜向的振动速度变化规律,同时采用ANSYS/LS-DYNA模拟掏槽孔爆破作用下隧道围岩同一截面内应力传播特点。研究结果表明:隧道掌子面边缘测点振动速度大于距爆源近测点振动速度,最小爆源距测点振动速度大于中间位置测点振动速度;隧道掌子面的拱顶和拱肩位置振动速度较大,上部测点振动速度大于下部测点;隧道掌子面应力主要集中在水平方向和竖向,纵向应力较小,水平方向和竖向应力变化时刻主要集中在0~5 ms,水平方向应力传播范围更广;隧道掌子面炮孔下方测点应力大于同爆源距上方测点。相关结论可为类似隧道动力响应分析提供参考。

竖井大直径空孔掏槽爆破的振动效应分析

大直径空孔对掏槽爆破及其振动效应有复杂的影响。以青岛地铁5号线沾化路竖井工程为背景,借助数值模拟与现场试验相结合等手段,揭示了直孔掏槽时大直径中空孔孔径和装药孔与中空孔距离的比值K对掏槽区破岩效果和地表振速响应规律的影响。研究结论表明:掏槽区爆破破岩和减振效果与K值之间存在显著的正相关性,且K值为1时大直径空孔掏槽爆破效果最为合理;采用大直径中空孔(Ф80 cm)掏槽,基于数码电子精确延时的逐孔起爆方式,可将实际工程地表质点峰值振速精准控制在0.3 cm/s以内;现场试验监测与数值模拟结果误差在8%左右,表明研究方法是合理可行的。研究结论能为城市闹市区地铁及竖井爆破振动有害效应精准控制提供依据和参考。