Numerical analysis on mechanical difference of sandstone under in-situ stress,pore pressure preserved environment at depth

Deep in-situ rock mechanics considers the influence of the in-situ environment on mechanical properties,differentiating it from traditional rock mechanics.To investigate the effect of in-situ stress,pore pressure preserved environment on the mechanical difference of sandstone,four tests are numerically modeled by COMSOL:conventional triaxial test,conventional pore pressure test,in-situ stress restoration and reconstruction test,and in-situ pore pressure-preserved test(not yet realized in the laboratory).The in-situ stress restoration parameter is introduced to characterize the recovery effect of in-situ stress on elastic modulus and heterogeneous distribution of sandstone at different depths.A random function and nonuniform pore pressure coefficient are employed to describe the non-uniform distribution of pore pressure in the in-situ environment.Numerical results are compared with existing experimental data to validate the models and calibrate the numerical parameters.By extracting mechanical parameters from numerical cores,the stress-strain curves of the four tests under different depths,in-situ stress and pore pressure are compared.The influence of non-uniform pore pressure coefficient and depth on the peak strength of sandstone is analyzed.The results show a strong linear relationship between the in-situ stress restoration parameter and depth,effectively characterizing the enhanced effect of stress restoration and reconstruction methods on the elastic modulus of conventional cores at different depths.The in-situ pore pressurepreserved test exhibits lower peak stress and peak strain compared to the other three tests,and sandstone subjected to non-uniform pore pressure is more prone to plastic damage and failure.Moreover,the influence of non-uniform pore pressure on peak strength gradually diminished with increasing depth.

Failure mechanism of bolting support and high-strength bolt-grouting technology for deep and soft surrounding rock with high stress

In deep underground mining, the surrounding rocks are very soft with high stress. Their deformation and destruction are serious, and frequent failures occur on the bolt support. The failure mechanism of bolt support is proposed to solve these problems. A calculation theory is established on the bond strength of the interface between the anchoring agent and surrounding rocks. An analysis is made on the influence law of different mechanical parameters of surrounding rocks on the interfacial bond strength. Based on the research, a new high-strength bolt-grouting technology is developed and applied on site. Besides, some helpful engineering suggestions and measures are proposed. The research shows that the serious deformation and failure, and the lower bond strength are the major factors causing frequent failures of bolt support. So, the bolt could not give full play to its supporting potential. It is also shown that as the integrity, strength, interface dilatancy and stress of surrounding rocks are improved, the bond strength will increase. So, the anchoring force on surrounding rocks can be effectively improved by employing an anchoring agent with high sand content, mechanical anchoring means, or grouting reinforcement. The new technology has advantages in a high strength, imposing pre-tightening force, and giving full play to the bolt supporting potential. Hence, it can improve the control effect on surrounding rocks. All these could be helpful references for the design of bolt support in deep underground mines.

Failure mechanism and control technology of water-immersed roadway in high-stress and soft rock in a deep mine

Aiming at soft rock ground support issues under conditions of high stress and long-term water immersion, the ground failure mechanism is revealed by taking the deep-water sumps of Jiulong Mine as the engineering background and employing field investigation, tests of rock structure, mechanical properties and mineral composition. The main factors leading to the surrounding rock failure include the high and complex stress state of the water sumps, high-clay content and water-weakened rock, and the unreasonable support design. In this paper, the broken and fractured rock mass near roadway opening is considered as ground small-structure, and deep stable rock mass as ground large-structure. A support technology focusing on cutting off the water, strengthening the small structure of the rock and transferring the large structure of the rock is proposed. The proposed support technology of interconnecting the large and small structures, based on high-strength bolts, high-stiffness shotcrete layer plugging water,strengthening the small structure with deep-hole grouting and shallow-hole grouting, highpretensioned cables tensioned twice to make the large and small structures bearing the pressure evenly,channel-steel and high-pretensioned cables are used to control floor heave. The numerical simulation and field test show that this support system can control the rock deformation of the water sumps and provide technical support to similar roadway support designs.

Research on Mechanism of Rock Burst Generation and Development for High Stress Rock Tunnels

Through the investigation and analysis of high stress distribution in surrounding rock during the excavation of rock tunnels,the key factors to cause rock burst and the mechanism of rock burst generation and development are researched. The result shows that the scale and range of rock burst are related with elastic deformation energy storied in rock mass and the characteristics of unloading stress waves. The measures of preventing from rock burst for high stress rock tunnels are put forward.

Engineering rock mechanics practices in the underground powerhouse at JinpingⅠhydropower station

Based on the analyses of data obtained from the underground powerhouse at Jinping I hydropower station, a comprehensive review of engineering rock mechanics practice in the underground powerhouse is first conducted. The distribution of strata, lithology, and initial geo-stress, the excavation process and corresponding rock mass support measures, the deformation and failure characteristics of the surrounding rock mass, the stress characteristics of anchorage structures in the cavern complex, and numerical simulations of surrounding rock mass stability and anchor support performance are presented. The results indicate that the underground powerhouse of Jinping I hydropower station is characterized by high to extremely high geo-stresses during rock excavation. Excessive surrounding rock mass deformation and high stress of anchorage structures, surrounding rock mass unloading damage, and local cracking failure of surrounding rock masses, etc., are mainly caused by rock mass excavation. Deformations of surrounding rock masses and stresses in anchorage structures here are larger than those found elsewhere： 20% of extensometers in the main powerhouse record more than 50 mm with the maximum at around 250 mm observed in the downstream sidewall of the transformer hall. There are about 25% of the anchor bolts having recorded stresses of more than 200 MPa. Jinping I hydropower plant is the first to have an underground powerhouse construction conducted in host rocks under extremely high geo-stress conditions, with the ratio of rock mass strength to geo-stress of less than 2.0. The results can provide a reference to underground powerhouse construction in similar geological conditions.

Study on the Deformation Mechanism of a Soft Rock Tunnel

The large deformation of soft rock tunnel is one of the key problems to be overcome in the tunnel construction stage.In the present study,the deformation mechanism of a representative tunnel and some related countermeasures are investigated using field tests and engineering geological analysis.Owing to the scarce performances of methods based on other criteria such as small pipe spacing,anchor bolt length and steel frame spacing,a new support scheme is implemented and optimized.Results show that shear failure and bedding sliding are produced under high horizontal stress conditions.The low strength of the surrounding rock results in the uneven convergence of both sides of the tunnel.With the aforementioned new support scheme,however,most of such problems can be mitigated leading to good stability properties and ensuing economic advantages.

高地应力软岩隧道初支侵限诱因及控制措施研究

高地应力软弱围岩隧道施工易发生软岩大变形不良地质灾害,进一步引发掌子面失稳塌方、初支结构破坏、钢拱架弯折、初支结构侵限等不良现象,严重影响施工安全,阻碍工期。依托九绵高速白马隧道工程,结合工程特点,从围岩自身力学特性及高地应力软岩变形特征方面深入分析了白马隧道初支侵限机理,并针对此特点,提出了一套适用于软岩大变形初支结构侵限专项施工方案。研究结果表明,由于地下水的侵蚀,炭质千枚岩发生软化,岩体力学性质变差,自承能力降低,在高地应力持续作用下,围岩发生挤压大变形,进一步诱导初支侵限。变更支护方案后,6 m锚杆结合小导管注浆加固对围岩变形有一定控制作用,但6 m锚杆无法将松动区岩块锚固在稳定母体中,不能充分发挥锚杆悬吊能力,对围岩变形控制效果有限,无法满足现场围岩变形需求,建议采用8 m长锚杆。初支拆换过程中应实时监测围岩变化情况,明确围岩变化方向、速率、累计值等,并根据现场实时监测数据反馈施工,实时调整支护参数,确保施工质量。

深井高应力软岩巷道底鼓力学机理及控制技术研究

为解决林西矿深井高应力软岩巷道底鼓问题,论文通过理论分析和现场实测相结合方法,研究分析出了深井高应力软岩巷道底鼓力学机理及控制技术,得出了如下结论:(1)推导出了巷道两侧底板极限破坏深度、极限破坏宽度以及沿滑移面有效滑动力的计算公式;(2)判断出了林西矿1791-2工作面回风巷底板破坏为挤压流动性底鼓,全断面破坏鼓起形式;(3)分析出了巷道底鼓机理、底鼓原因以及控制途径;(4)提出了“顶、帮、底同治”控制巷道底鼓技术,顶帮采用高强预应力锚杆网+锚索支护,底板采用预应力锚索锚注加固+混凝土铺底技术;(5)现场工业试验表明巷道底鼓得到了有效遏止,能够满足正常使用要求。

高应力条件下煤矿开采安全技术的探讨

探讨了高应力条件下煤矿开采的安全技术。首先,分析了高应力环境的特点,包括岩层力学特性的变化、应力集中与能量积聚、地下环境的复杂性及煤层气体的动态变化;然后,深入研究了现有的煤矿开采安全技术,重点关注岩层控制技术、瓦斯监测与治理技术、应力监测与调控技术以及自动化与智能化开采技术;最后,着重介绍了高应力条件下创新的煤矿开采安全技术,包括微震监测技术、高应力区域无人机探测技术、高性能支护材料与技术以及高精度地质预测系统。这些技术的应用提升了煤矿开采的安全性和效率,对于煤炭行业的发展具有重要意义。

Optimization of construction scheme and supporting technology for HJS soft rock tunnel

For a soft rock tunnel under high stress in jointed and swell soft rock(HJS), two construction schemes pilot-tunneling enlarging excavation and step-by-step excavation were optimized using FLAC2 D, and the deformation effects of the two construction schemes were verified by field tests. Based on engineering geological investigation and mechanical analysis of large deformations, the complex deformation mechanisms of stress expansion and structural deformation of the soft rock tunnel were confirmed,and support countermeasures from the complex deformation mechanism converted to a single type were proposed, and the support parameters were optimized by field tests. These technologies were proved by engineering practice, which produced significant technical and economic benefits.

深部高水平应力巷道倾斜锚杆破断机制及加强支护时机

针对深部高水平应力下巷道倾斜锚杆承受弯曲、拉伸为主的复合荷载作用,易发生破断失效导致巷道局部失稳问题,以山东能源集团孙村煤矿2424工作面下平巷为工程背景,调研得到了倾斜锚杆破断特征,推导了内力与内力矩分布、破断危险断面位置及相当应力表达式,建立了以危险断面最大相当应力为指标的破断力学判据,揭示了不同锚固参数与侧压系数对最大相当应力的影响规律,即最大相当应力随侧压系数、锚固长度和预紧扭矩增大而增大,而随锚杆安装角度增大呈现先减小后增大再减小的趋势。在此基础上,利用FLAC软件内置Fish语言实现了对锚杆危险断面最大相当应力的表征,定义了以危险断面最大相当应力与许用应力比值表示的危险系数K,并以此为指标提出了加强支护时机确定方法,获得了不同加强支护时机下围岩变形破坏规律。随着加强支护时的危险系数K增大,锚杆危险断面最大相当应力、围岩整体变形量与集中应力先减小后增大,危险系数K较小时,浅部围岩弹性能积聚较大,自承载能力发挥不足;危险系数K过大时,围岩变形量大、破坏严重,整体稳定性差。确定了2424工作面下平巷合理加强支护时机为危险系数K取0.8,现场加强支护实践表明,在危险系数为0.8(超前工作面60 m)时进行加强支护,锚杆破断率减小了87.9%,围岩变形得到有效控制,稳定性明显提高。

基于机械激振方式进行高地应力软岩隧道应力释放效果研究

为解决高地应力软岩隧道的应力释放现有工艺存在的问题,提出一种新的超前应力释放方法。该方法采用机械激振的方式来对岩体进行预处理,完成应力的超前释放,从而减小隧道后续支护结构的变形。采用FLAC3D分析机械激振高地应力释放方法的实际适用情况,揭示激振方式、激振频率、激振幅值和激振时长4个因素对应力释放效果的影响规律。得出以下结论:1)通过对比隧道变形量,比选出双边错峰激振这一最优激振方式。2)激振频率为系统共振频率时,应力释放效果达到最佳,并随着激振幅值增大而增大;但当超过某一限值之后,应力释放效果略微下降并保持稳定。3)在激振一定时间后,振动影响范围内岩体所具有的地应力已充分释放完毕,此时继续激振并不会增大卸荷的影响范围。4)综合得出应力释放效果最优工况,通过组合激振参数,进一步验证了此种工法的有效性。

激振法对软岩高地应力超前释放数值模拟研究

针对高地应力软岩隧道的应力释放现状的缺点与不足,提出了一种新的超前应力释放方法,采用激振器进行机械激振的方式来对岩体进行预处理,完成应力的超期释放,从而有利于减小隧道后续开挖完成后衬砌的变形。并且针对隧道掘进机(tunnel boring machine,TBM)掘进技术,参考现有的井巷共振掘进技术,采用一种适配于TBM掘进系统的新设备,根据新设备的工艺以及作用方式,对激振过程进行了模拟分析,并且针对激振频率、激振幅值以及激振深度三个因素与应力释放的相关性进行了研究,得到了最有利于应力释放的频率、幅值与深度,并结合模拟后续隧道开挖所得到的隧道变形结果,进一步验证了此种工况组合的有效性,为该方法的后续实际应用提供了依据。

花岗岩实时高温真三轴的水力压裂

在干热岩资源开发中,水力压裂是提高热储层的渗透率与产热量的重要手段。然而,在高温高压环境下的水力压裂机理仍不清楚。本文在不同真三轴应力下对花岗岩进行了室温与200℃下的水力压裂试验,应用光学显微镜和核磁共振技术,表征了花岗岩试样水力裂缝从微观至宏观的特征形态,揭示了不同温度下的水力压裂机理。试验结果表明,在相同应力条件下,相对于室温下水力压裂,200℃下水力压裂能显著降低破裂压力与起裂压力,200℃下压裂曲线增压阶段明显偏离线性。在20 MPa的水平应力差下,200℃下水力压裂会形成具有多尺度裂纹的云状裂缝,而不是与室温下水力压裂类似的单一主裂缝。此外,核磁共振结果显示,在200℃水力压裂后的花岗岩试样中,微尺度裂纹的增加会导致压裂体积增加,这是由200℃水力压裂下孔隙压力的扩散导致微裂纹而造成的。

高应力软岩巷道底鼓机理及控制技术研究

以山西某矿机电房为工程背景,通过现场调研分析了高应力软岩巷道底鼓变形特征,并揭示了底鼓变形机理;通过建立巷道底板力学模型,求解了底板最大屈服破坏深度,得出了影响底板破坏深度的主要因素;利用FLAC3D模拟了不同底板支护方案下的巷道围岩应力、应变、塑性区分布规律;确定了“底板加强支护+帮顶协调支护”为原则的巷道整体修复原则,提出了以“浅部回填+中部锚固+深部注浆”为核心的底板控制技术。试验结果表明,巷道在30 d后达到稳定,底鼓最大变形量30 mm,两帮和顶板最大变形量均保持在100 mm以内,有效解决了高应力软岩条件下巷道底鼓灾变问题。

缓倾层状岩体大断面高铁隧道变形特征研究

隧道穿越缓倾层状围岩时,易发生剪切滑移、张拉破坏和弯折内鼓等现象,致使隧道施工过程中易发生拱顶掉块、塌方等问题。以重庆楠竹山隧道为工程依托,研究不同岩层倾角下隧道结构受力、变形特征以及塑性区分布规律,并探讨缓倾层状岩体隧道变形控制措施。研究表明:当缓倾层状岩体节理角度由0°增加至15°、30°时,隧道最大竖向位移变化不大,但节理角度增大对隧道水平位移的影响较大,最大水平位移主要发生在拱腰至边墙部位;隧道周边围岩塑性发展及破坏区受缓倾层状岩体节理角度的控制较为明显,当层状岩体倾角为0°、15°时,塑性区以压溃破坏为主,当层状岩体倾角为30°时,塑性区主要以层间剪切滑动破坏为主。研究有助于采取针对性措施以保证施工安全。

高温及三轴应力下花岗岩体力学特性的实验研究

高温岩体地热开发及核废料的地下处置等需要对高温高压下花岗岩体的力学行为进行深入细致研究。采用自主研制的"20 MN伺服控制高温高压岩体三轴试验机",投入大量人力、财力和物力,历时0.5 a,系统深入地研究φ200 mm×400 mm的大尺寸花岗岩试样在高温三轴应力下的热变形和破坏特征及其热学和力学参数随温度的变化特征。研究结果表明:(1)在三维静水应力下,花岗岩的热变形可分为低温缓慢变形段、中高温快速变形段及高温平缓变形段等3个阶段。自由状态测定的热膨胀系数会过分夸大,或失真地估计岩石的热膨胀或热力作用,在应力状态下测定的热膨胀系数更能反映实际岩体状态。(2)在高温三轴应力条件下,花岗岩体受压表现出与常温下不一致的变形特征,即先是体积膨胀,当差应力超过一定值后则体积收缩。(3)花岗岩体在高温下的破坏形式是典型的剪切破坏,与常温下的破坏形式一致,但在高温和高围压条件下出现明显的延性转化。(4)在有围压条件下,花岗岩体的弹性模量随温度升高先是缓慢减小,然后快速减小,超过400℃后基本保持不变,与小试件的情况相似。

深部高地应力下岩石力学行为研究进展

越来越多的煤矿和金属矿进入深部开采.随着开采深度的增加,一系列工程灾害如岩爆、煤与瓦斯突出、顶板垮落、底板突水等日益严重,且深部开采中巷道与采场的维护理论也与浅部有十分明显的区别.人们认识到这种差别的根源在于岩石所处的赋存环境上的差异,深部与浅部在赋存环境上的差别是所谓"三高"即高地应力、高地温和高孔隙水压,尤其是高地应力条件下岩石表现出十分特殊的力学行为.简要介绍了深部开采现状、深部开采面临的技术难题以及深部岩体所处的高地应力环境,在此基础上,综述了深部高地应力条件下有关岩石力学性质的研究进展,包括高应力条件下岩石的脆-延转化特性、岩石的流变特性、岩石的强度特征、岩石的破坏特征尤其是岩爆等.文章最后指出深部条件下热-水-力耦合模型是一个值得关注的研究方向.

3种岩石高温后力学性质的试验研究

通过单轴压缩试验,对不同高温后熔结凝灰岩、花岗岩及流纹状凝灰角砾岩的力学性质进行了研究,分析比较3种岩石峰值应力、峰值应变及弹性模量随温度的变化规律,并研究了峰值应力与纵波波速、峰值应变与纵波波速的关系。试验升温等级设为20℃,200℃,400℃,600℃,800℃五级,升温速度为30℃/min。试验结果表明,高温后3种岩石的峰值应力、弹性模量均有不同幅度的降低,且经历的温度越高,降低的幅度越大。对于峰值应变,熔结凝灰岩、花岗岩的峰值应变随温度的升高而大幅度的增加;但对于流纹状凝灰角砾岩,峰值应变随着温度的升高在降低。此外,峰值应力与纵波波速、峰值应变与纵波波速的关系依赖于不同的岩石而表现出不同的规律。

异常高压气藏岩石应力敏感性及其对产能的影响

文章具体实测了克拉2异常高压气藏岩样不同覆压下的渗透率,根据其实测结果拟合出渗透率的应力敏感性幂函数表达式,总结了岩石渗透率随气藏压力或有效覆压的变化规律。考虑渗透率变化对气藏产能的影响,推导出新的产能方程。研究表明:克拉2气藏岩样应力敏感性高于大庆油田岩样,具有异常高压气藏岩石欠压实的特点。岩样的应力敏感性使产能降低,在克拉2 气藏的条件下,考虑应力敏感时的绝对无阻流量是渗透率为常数时的70%左右。该研究对深入了解异常高压气藏的产能及预测异常高压气藏的开发动态和采收率有一定意义。