Roof collapse mechanism of weak surrounding rock for deep-buried tunnels under high geostress conditions

High geostress,a typical attribute of tunnels located at significant depths,is crucial in causing stress-induced failure and influencing the stability of the tunnel crown.This study developed an analytical method for the failure mechanism that occurs in deep-buried tunnel roofs,taking into account the influence of geostress.The limit analysis theory was utilized for deriving analytical solutions about the geometry of the collapsing surface and the limit supporting pressure.The collapsing surface obtained by the analytical solution was validated by the findings of the physical model test,which shows a high level of agreement with the actual one.An extensive investigation was done to explore the effects of the lateral pressure coefficients,the tunnel buried depth,the geological conditions of the surrounding rock,the long-short axis ratio,and the size of the tunnel profile.The findings indicate that an increase in the lateral pressure coefficient from 0.5 to 1.5 results in a reduction in the height of the collapsing zone by 2.08 m and the width of the collapsing zone by 1.15 m,while simultaneously increases the limit supporting pressure by 18.9%.The proposed upper bound method accurately determines the limit supporting pressure and the geometry of the collapsing surface,which aligns well with the results acquired through numerical modelling and on-site monitoring in actual engineering applications.The proposed analytical method can serve as a reference for similar crown failure issues of deep-buried tunnels.

Comparison of vibrations induced by excavation of deep-buried cavern and open pit with method of bench blasting

The measured data of vibrations induced by excavation of deep-buried cavern and open pit with method of bench blasting were analyzed by Fourier Transform and Wavelet Transform,and the characteristics of vibrations induced under these two circumstances were studied.It is concluded that with the similar rock condition and drilling-blasting parameters,vibration induced by bench blasting in deep-buried cavern has a higher main frequency and more scattered energy distribution than that in open pit.The vibration induced by bench blasting in open pit is mainly originated from the blast load,while the vibration induced by bench blasting in deep-buried cavern is the superposition of vibrations induced by blast load and transient release of in-situ stress.The vibration induced by transient release of in-situ stress increases with the stress level.

Fisher discriminant analysis model and its application for prediction of classification of rockburst in deep-buried long tunnel

A Fisher discriminant analysis （FDA） model for the prediction of classification of rockburst in deep-buried long tunnel was established based on the Fisher discriminant theory and the actual characteristics of the project. First, the major factors of rockburst, such as the maximum tangential stress of the cavern wall σθ, uniaxial compressive strength σc, uniaxial tensile strength or, and the elastic energy index of rock Wet, were taken into account in the analysis. Three factors, Stress coefficient σθ/σc, rock brittleness coefficient σc/σt, and elastic energy index Wet, were defined as the criterion indices for rockburst prediction in the proposed model. After training and testing of 12 sets of measured data, the discriminant functions of FDA were solved, and the ratio of misdiscrimina- tion is zero. Moreover, the proposed model was used to predict rockbursts of Qinling tunnel along Xi＇an-Ankang railway. The results show that three forecast results are identical with the actual situation. Therefore, the prediction accuracy of the FDA model is acceptable.

Mechanical Properties of Deep-buried Marble Material Under Loading and Unloading Tests

The mechanical properties are essentially different when rock material is subjected to loading or unloading conditions. In this study, loading and unloading tests with various confining pressures are conducted to investigate the mechanical properties of marble material samples taken from the deep diversion tunnels of Jinping II Hydropower Station. The stress-strain relationship, failure characteristics and strength criterion are compared and analyzed based on the experiment results. The results show： in the loading and unloading test, peak strength, lateral strain, axial strain and plastic deformation increase significantly as the confining pressure increases. Lateral strain increased significantly and obvious lateral dilatancy can be observed to the change of confining pressure; The fracture mode is mainly the single shear fracture for the triaxial compression test and post-peak test, angle between the failure surface and the ends of the rock material becomes smaller as the confining pressure increases. Hock-Brown strength criterion reflects the strength characteristics of marble material under two different unloading conditions, and has some supplementary effects to the rock material of mechanical field.

Dissolution mechanism of a deep-buried sandstone reservoir in a deep water area:A case study from Baiyun Sag,Zhujiang River(Pearl River)Mouth Basin

Dissolution mechanism and favorable reservoir distribution prediction are the key problems restricting oil and gas exploration in deep-buried layers.In this paper,the Enping Formation and Zhuhai Formation in Baiyun Sag of South China Sea was taken as a target.Based on the thin section,scanning electron microscopy,X-ray diffraction,porosity/permeability measurement,and mercury injection,influencing factors of dissolution were examined,and a dissolution model was established.Further,high-quality reservoirs were predicted temporally and spatially.The results show that dissolved pores constituted the main space of the Paleogene sandstone reservoir.Dissolution primarily occurred in the coarse-and medium-grained sandstones in the subaerial and subaqueous distributary channels,while dissolution was limited in fine-grained sandstones and inequigranular sandstones.The main dissolved minerals were feldspar,tuffaceous matrix,and diagenetic cement.Kaolinization of feldspar and illitization of kaolinite are the main dissolution pathways,but they occur at various depths and temperatures with different geothermal gradients.Dissolution is controlled by four factors,in terms of depositional facies,source rock evolution,overpressure,and fault activities,which co-acted at the period of 23.8–13.8 Ma,and resulted into strong dissolution.Additionally,based on these factors,high-quality reservoirs of the Enping and Zhuhai formations are predicted in the northern slope,southwestern step zone,and Liuhua uplift in the Baiyun Sag.

Numerical simulation of zonal disintegration of surrounding rock in the deep-buried chamber

Zonal disintegration is the phenomenon of cyclical rupture zone and nonrupture zone in the surrounding rock of a deep-buried chamber,which is different from that of a shallow chamber.Based on the finite difference software FLAC3D,the numerical simulation of surrounding rock with different mechanical parameters was conducted by using the SU model(Bilinear Strain-Softening Ubiquitous-Joint).The influences of buried depth,cohesion,and internal friction angle of surrounding rock on zonal disintegration were analyzed to reveal the influence law.The results show that:(1)after the chamber excavation,multiple rupture zones gradually extend from the chamber surface or adjacent periphery to the deep surrounding rock.In the extension process,a single rupture zone may be forked into two or even multiple rupture zones,which cross each other and form the zonal disintegration zone.(2)Zonal disintegration is affected by bothσ(in situ stress)and U_(cs)(uniaxial compression strength).Smaller U_(cs)and largerσwill lead to zonal disintegration.(3)The zoning fracture is not obvious in the case ofσ≤U_(cs).In the reverse case,zoning fracture appears remarkably in the surrounding rock around the chamber.These results reveal the influence law of zonal disintegration and provide theoretical support for the design of deep-buried chambers.

Analytical solution for steady seepage into a circular deep-buried mountain tunnel with grouted zone in anisotropic strata

Due to the existence of a large number of discontinuous fractures and interfaces in tunnel surrounding rocks,the groundwater inflow into tunnel generally presents significant anisotropy.Therefore,it is of great significance to consider the anisotropic permeability when dealing with water gushing-induced engineering accidents in water-rich mountain tunnels with large burial depth.In this study,based on the complex variable method and the seepage flow theory,a theoretical model of water inflow into a deep-buried circular tunnel in a fully saturated,anisotropic and semi-infinite aquifer is developed.The influence of grouted zone,initial support and secondary lining is fully considered.By comparison to the existing analytical methods and numerical results,the reliability of this proposed analytical solution is well validated.It is indicated from the parametric study that the groundwater inflow into tunnel presents an upward trend with an increasing value of the strata permeability in the vertical direction.Moreover,the water inflow rate and the total water head decrease with the growth of the thickness of grouting circle.It is suggested that reasonable grouting thickness and permeability should be controlled to enhance the grouting effect.This study provides a practical method for estimating the water inflow into a deep-buried,grouted and lined mountain tunnel considering the anisotropic strata permeability.

Experimental study on similarity materials for soft rock of deep-buried tunnels

When every parameter is properly scaled down in accordance with some similarity coefficients, it is possible to study the physical-mechanical properties of rock mass with a scale model. To identify the key mechanisms of soft rock in deep buried tunnels, the proper sand, binder and ratio were selected. During the process, the model manufacture technology was introduced and typical tests were done and the results were presented. The physical and meehanieal properties effects caused by each composition were discussed. It is shown that the physical and mechanical properties of chosen ratio material such as uniaxial compressive strength tests, elasticity modulus, tensile strength, internal frictional angle, and Poisson＇s ratio meet with similarity relationship well. The physical and mechanical properties of deep soft rock are simulated successfully.

Forecasting of water yield of deep-buried iron mine in Yanzhou, Shandong

This paper compares analytical and numerical methods by taking the forecasting of water yield of deep-buried iron mine in Yanzhou, Shandong as an example. Regarding the analytical method, the equation of infinite and bilateral water inflow boundary is used to forecast the water yield, and in the case of numerical simulation, we employed the GMS software to establish a model and further to forecast the water yield. On the one hand, through applying the analytical method, the maximum water yield of mine 1 500 m deep below the surface was calculated to be 13 645.17 m3/d; on the other hand, through adopting the numerical method, we obtained the predicted result of 3 816.16 m3/d. Meanwhile, by using the boundary generalization in the above-mentioned two methods, and through a comparative analysis of the actual hydro-geological conditions in this deep-buried mine, which also concerns the advantages and disadvantages of the two methods respectively, this paper draws the conclusion that the analytical method is only applicable in ideal conditions, but numerical method is eligible to be used in complex hydro-geological conditions. Therefore, it is more applicable to employ the numerical method to forecast water yield of deep-buried iron mine in Yanzhou, Shandong.

Stress wave propagation and incompatible deformation mechanisms in rock discontinuity interfaces in deep-buried tunnels

Complex weak structural planes and fault zones induce significant heterogeneity,discontinuity,and nonlinear characteristics of a rock mass.When an earthquake occurs,these characteristics lead to extremely complex seismic wave propagation and vibrational behaviors and thus pose a huge threat to the safety and stability of deep buried tunnels.To investigate the wave propagation in a rock mass with different structural planes and fault zones,this study first introduced the theory of elastic wave propagation and elastodynamic principles and used the Zoeppritz equation to describe wave field decomposition and develop a seismic wave response model accordingly.Then,a physical wave propagation model was constructed to investigate seismic waves passing through a fault,and dynamic damage was analyzed by using shaking table tests.Finally,stress wave attenuation and dynamic incompatible deformation mechanisms in a rock mass with fault zones were explored.The results indicate that under the action of weak structural planes,stress waves appear as a complex wave field decomposition phenomenon.When a stress wave spreads to a weak structural plane,its scattering may transform into a tensile wave,generating tensile stress and destabilizing the rock mass;wave dynamic energy is absorbed by a low-strength rock through wave scattering,which significantly weakens the seismic load.Wave propagation accelerates the initiation and expansion of internal defects in the rock mass and leads to a dynamic incompatible deformation.This is one of the main causes for large deformation and even instability within rock masses.These findings provide an important reference and guide with respect to stability analysis of rock mass with weak structural planes and fault zones.

秸秆绳不开沟深埋还田机切土刀的设计与试验

为解决北方寒地秸秆直接还田难腐解、还田均匀性差以及影响机械化作业播种质量等问题,提出先将作物秸秆加工成秸秆(草)绳后再应用专用设备将草绳深埋还田的新思路。介绍了秸秆绳不开沟深埋还田机整机结构与工作原理,重点对切土刀的结构参数进行了理论分析与设计,并对切土刀切削土壤进行了有限元动力学分析。以作业深度、作业速度为影响因素,以切削阻力为试验指标,进行仿真模拟试验,获得了两因素对切削阻力的影响规律及回归方程。通过田间试验验证了切土刀设计的合理性,为样机设计和新机型的开发提供参考。

浅埋深综放工作面采空区“三带”分布研究

为研究浅埋深综放工作面采空区“三带”分布规律,在串草圪旦煤矿6101综放工作面采空区埋设束管,对采空区“三带”进行了现场实测。实测结果表明:由于煤层埋深浅、地表起伏大、进风侧存在地表漏风,进风侧采空区“三带”明显滞后于回风侧,进回风两侧氧化带宽度分别为87.8 m和61.4 m。利用FLUENT软件对实测条件下该工作面采空区“三带”进行了数值模拟,模拟结果和现场实测结果基本一致。同时模拟了不漏风条件下该工作面采空区“三带”分布,此时采空区散热带、氧化带范围大幅度减小,进风侧采空区氧化带稍大,而工作面中部和回风侧“三带”分布基本一致。

深埋藏锌多金属矿床开拓方案的选择

随着中国社会的不断进步和发展,对资源的开发与利用更加的科学化、合理化、智能化和绿色化。我国目前依然处于工业化和城镇化的发展阶段,对金属资源有一定的需求。对于埋藏较深的锌多金属矿床的开发与利用显得尤为重要,合理的开拓方案更是重中之重,开拓方案的选择涉及到基建期工程量、矿山建设投资及矿山投产的时间。综合矿体的赋存条件、基建投资、经济效益等多方面因素,对该矿两个矿区同时建设或接续开采、对一矿是否分期开采进行了充分的论证与分析,为同类矿山提供参考。

基于围岩应力状态的超大断面隧道深浅埋判定研究

随着目前公路隧道跨度越来越大,而超大跨扁平隧道由于其特殊的形状,使得拱部受力较上圆形隧道更为不利且开挖的影响范围也更大,因此现有深浅埋分界方法的适用性尚需考证。研究采用数值计算与经验公式方法,对比不同跨度、不同围岩级别下超大跨扁平隧道的深浅埋分界,得到适用于此工程的判定方法,同时确定其深浅埋分界范围。研究结果表明:1)主应力旋转轴理论与规范经验法相互补充、相互验证,具有着一定的可操作性,大跨扁平隧道深浅埋分界的判定应结合2种方法综合得到;2)当隧道跨度在19 m左右时,Ⅲ级围岩深浅埋分界值为6 m,Ⅳ级围岩深浅埋分界值为14 m,Ⅴ级围岩深浅埋分界值为34 m。

埋藏过程对深层-超深层碎屑岩成岩作用及优质储层发育的影响——以准噶尔盆地南缘下白垩统清水河组为例

以准噶尔盆地南缘下白垩统清水河组为例,综合利用岩石薄片、扫描电镜、电子探针、稳定同位素组成及流体包裹体等技术手段,开展前陆盆地埋藏过程对深层—超深层碎屑岩成岩作用及优质储层发育影响的研究。研究表明,清水河组依次经历了“缓慢浅埋”、“构造抬升”、“渐进深埋”与“快速深埋”4个埋藏阶段。“缓慢浅埋”与“构造抬升”不仅能够缓解储层颗粒间的机械压实作用,还有利于长期保持开放型的成岩体系;既能够促进大气淡水对储层易溶组分的充分溶解,还能够抑制溶蚀产物的沉淀。晚期“快速深埋”过程促成流体超压的发育,一方面有效地抑制压实、胶结作用对原生孔隙的破坏,另一方面也促进储层微裂缝的大量发育,提高了晚期有机酸充注产生的溶蚀效果。基于孔隙度演化史的定量恢复,证实长期“缓慢浅埋”与“构造抬升”过程对深层—超深层优质碎屑岩储层发育的贡献最大,其次为晚期“快速深埋”过程,“渐进深埋”过程则几乎没有贡献。

船舶应急抛锚贯入深度计算方法对比分析

船舶应急抛锚贯入深度对海底管线的埋深有着重要的参考价值,为深入研究当前船舶应急抛锚贯入深度计算方法在相同工况下的特点及适用性,对基于Young公式和基于有限元模拟的船舶应急抛锚贯入深度计算方法进行分析并作对比。结果表明,两种方法的计算结果总体一致,但基于有限元模拟的船舶应急抛锚贯入深度计算方法得到的贯入深度值较大,这可为相关的海底原油管线保护埋深设置时,船舶应急抛锚贯入深度计算提供参考。

深埋松散特厚煤层巷道变形及全锚索梯次让压支护技术研究

针对深埋藏松散特厚煤层巷道围岩变形与破坏的显著问题,往昔采用的传统锚杆支护方式显然难以遏制其变形趋势。为改变当前深埋巷道的支护状况,进一步强化围岩承载能力,对巷道围岩的变形特点及其破坏成因展开了详尽的分析。在此基础上,提出了新颖的全锚索梯次让压支护技术。现场应用结果表明,这一支护方案实施之后,巷道围岩的变形得到了显著控制,围岩裂隙发育的程度相对适中,顶板下沉及两帮收敛的最大累计值分别为58 mm和120 mm,巷道围岩的变形状况完全满足正常的使用需求。

深埋煤层回采巷道支护参数优化设计

深部煤层受高地应力及采动应力的影响,巷道围岩破碎松散,支护问题较为突出,围岩变形速度快,持续变形时间较长。以古城煤矿3103轨道顺槽的支护方案为研究对象,通过数值计算对支护参数进行优化,采用巷道顶帮强支、强护,底板弱支、弱护,围岩钻孔卸压的“强+弱+卸”三位一体综合围岩控制技术,巷道围岩变形量有所减小,两帮支护效果较为明显,围岩变形量分别减少了37%和14%,优化支护方案符合煤矿的安全生产要求,保证了巷道在掘进过程中安全可靠性。

叠落式暗挖隧道连接方法比选分析

在地铁叠落隧道中,上下层隧道的受力和变形是设计控制的核心问题,因为下层隧道在深埋情况下承担着上部结构传递的荷载,因此关乎着叠落隧道工程建设的成败。传统的叠落隧道模型无法考虑施工过程中下层隧道变形对上层隧道内力、变形的连带影响,且无法考虑上层隧道刚度、承载力、变形的发挥对下层隧道产生的“遮拦效应”。因此,针对目前叠落隧道在设计方法上的不足,为探究上下层隧道不同连接方式对工程的影响,提出了一种更为贴近实际且可以精确地计算下层隧道在深埋情况下承担上部结构传递的荷载的设计模型,并依托北京市某地铁区间暗挖段深埋叠落隧道,采用有限单元法分别建立了带有弹性连接的模型和传统的叠落隧道模型,并进行了计算,分析了不同方法得出的衬砌变形量与内力,然后通过与传统模型曲线进行对比,验证了该方法的正确性。分析结果表明:连接模型计算的内力大于传统模型,传统模型的计算结果受参数选取的影响偏于保守,不够安全;连接模型能够较为真实地反映岩石与上下层隧道开挖的相互作用,从而模拟出岩石地层中暗挖隧道的实际受力状态,所得结论对于同类型地铁叠落隧道工程的设计具有一定的指导意义,同时解决了在设计叠落隧道时传统模型选取单一隧道计算其内力与变形的局限性,提高了叠落隧道结构分析的准确性。

异形钢护筒围护大直径深埋地下管道改迁技术研究与应用

随着地下空间的快速开发,地下工程建设的深度也在增加,实际工程中面临着一大批大直径深埋管道的改迁问题。为了安全可靠地对大直径深埋地下管道进行改迁割接,研究1种异形钢护筒结构对地下管道改迁的施工技术;分别从异形钢护筒内径与企口尺寸、壁厚、下沉激振力、坑底MJS地基加固、地下管道走向边界定位等方面做出具体分析。在宁波市鄞州大道综合管廊工程中,运用该施工技术,对1条横穿盾构轴线的DN1600原水管,完成顺利改迁。通过工程实践,验证该技术适用于淤泥质软土地区大直径深埋地下管道改迁,并具有良好的经济效益与社会效益。