Stress evolution and support mechanism of a bolt anchored in a rock mass with a weak interlayer

By applying experimental method, the bolt stress and supporting mechanism is studied during the deformation process of a rock mass containing a weak interlayer. The force measuring bolt is installed manually and instrumented five pairs of symmetrical strain gauges. The experimental results show that the fully grouted bolt suffers tensile, compressive, bending and shear stress at the same time. The bolt stress evolution is closely related to the deformation stages of the rock mass which are very gradually varying stage, gradually varying stage at the pre-peak and suddenly varying stage at the post peak stage.The axial compressive stress in the bolt is mainly induced by the moment. Thus, in most cases the axial compressive stress is distributed on one side of the bolt. For axial stresses, induced by the axial force and the bending moment at the post-peak stage, three types of changing are observed, viz. increasingincreasing type, decreasing-increasing type and increasing-decreasing type. The stress characteristics of the bolt section in the weak interlayer are significantly different from those in the hard rock. The failure models of the anchored bolt are tensile failure and shear failure, respectively. The bolt not only provides constraints on the free surface of the rock mass, but also resists the axial and lateral loading by the bending moment. This study provides valuable guidelines for bolting support design and its safety assessment.

Breaking and mining-induced stress evolution of overlying strata in the working face of a steeply dipping coal seam

The breaking features and stress distribution of overlying strata in a steeply dipping coal seam(SDCS)differ significantly from those in a near-horizontal one.In this study,the laws governing the evolution of vertical stress release and shear stress concentration in the overlying strata of coal seams with different dip angles are derived via numerical simulation,rock mechanics tests,acoustic emissions,and field measurements.Thus,the stress-driven dynamic evolution of the overlying strata structure,in which a shear stress arch forms,is determined.Upon breaking the lower pari of the overlying strata,the shear stress transfers rapidly to the upper part of the working face.The damaged zone of the overlying strata migrates upward along the dip direction of the working face.The gangue in the lower part of the working face is compacted,leading to an increase in vertical stress.As the dip angle of the coal seam increases,the overlying strata fail suddenly under the action of shear stresses.Finally,the behavioral response of the overlying strata driven by shear stresses in the longwall working face of an SDCS is identified and analyzed in detail.The present research findings reveal the laws governing the behavior of mine pressure in the working face of an SDCS,which in turn can be used to establish the respective on-site guidance.

4D-stress evolution of tight sandstone reservoir during horizontal wells injection and production: A case study of Yuan 284 block,Ordos Basin,NW China

To investigate the 4D stress change during injection and production in tight sandstone reservoirs, a multi-physical fields modeling method is proposed considering the reservoir heterogeneity, hydraulic fracture and complex injection-production system. The 4D stress evolution of tight sandstone reservoir in Yuan 284 block of Huaqing oilfield, Ordos Basin,during injection-production in horizontal well network is investigated by modeling coupled flow and geomechanics. Results show:(1) Induced by injection and production, the 3D stress increases near the injectors but decreases near the producers, and the horizontal stresses are distributed in obvious strips along their respective stress directions.(2) The horizontal stress difference is the highest at the horizontal wellbore beside injectors during injection and production, while it is the lowest in undeveloped zone between the injectors, and the orientation of maximum horizontal principal stress changes the most near the injectors, which is distributed radially.(3) The hydraulic fracture in re-fracturing well was observed to be asymmetrical in geometry and deflected as the stress changed. The results provide theoretical guidance for horizantal well network modification and re-fracturing optimization design in tight sandstone reservoir.

Cretaceous Stress Fields Evolution and Its Geodynamic Implications in Jiaolai Basin, Northern China

The Tan-Lu fault zone(TLFZ)along the East China continental margin experienced sinistral movement at the beginning of Early Cretaceous(ca.145)due to fast oblique subduction of the Izanagi Plate in the Pacific Ocean.It can

Evolution of the Late Cenozoic Tectonic Stress Regime in the Tianshui Basin,Northeast Tibetan Plateau

The Tianshui Basin,located inside the western Qinling orogenic belt and northeastern margin of the Tibetan Plateau （Fig.1）,is a NE-trending Late Cenozoic basin,which documents the neotectonic response of the northeastward growth of Tibetan Plateau.

Surrounding Rock Failure Mechanism and Control Technology of Gob-Side Entry with Triangle Coal Pillar at Island Longwall Panel in 15 m Extra-Thick Coal Seams

Taking the return air roadway of Tashan 8204 isolated island working face as the background, the evolution law of the stress field in the surrounding rock of the widened coal pillar area roadway during the mining period of the isolated island working face is obtained through numerical simulation. The hazardous area of strong mine pressure under different coal pillar widths is determined. Through simulation, it is known that when the width of the coal pillar is less than 20 m, there is large bearing capacity on the coal side of the roadway entity. The force on the side of the coal pillar is relatively small. When the width of the coal pillar ranges from 25 m to 45 m, the vertical stress on the roadway and surrounding areas is relatively high. Pressure relief measures need to be taken during mining to reduce surrounding rock stress. When the width of the coal pillar is greater than 45 m, the peak stress of the coal pillar is located in the deep part of the surrounding rock, but it still has a certain impact on the roadway. It is necessary to take pressure relief measures to transfer the stress to a deeper depth to ensure the stability of the triangular coal pillar during the safe mining period of the working face. This provides guidance for ensuring the stability of the triangular coal pillar during the safe mining period of the working face.

Evolution of electrochemically induced stress and its effect on the lithium-storage performance of graphite electrode

The electrochemically induced stress is a key factor that affects the lithium-storage performance of electrode materials.In this study,the origin and evolution of the electrochemically induced stress of the graphite electrode were investigated by in situ experiments and simulations.An in situ optical experiment was performed to observe the electrode color to analyze the concentration and diffusion process of lithium ions inside the graphite electrode.An electrochemical-mechanical coupling model under the same experimental conditions was developed and verified by the experimental lithium concentration,and characterization of the spatiotemporal evolution of the potential,lithium concentration,and stress during the diffusion process was realized.The results showed that lithium intercalation leads to compressive stress,which presents a gradient distribution along the Li+diffusion path,and it exhibits a“piecewise”nonlinear growth trend with increasing lithiation time.In addition,as the potential decreases,the stress increases from slow to fast relative to the lithium-concentration increase,showing the characteristic of stages.The influence of stress on the lithium-storage performance is discussed using the local lithium-intercalation rate and phase-interface migration speed as the key parameters.The lithiation mechanism was analyzed from the perspective of the energy,and it was found that the two factors cause the slow diffusion in the late stage of lithiation,thus affecting the actual lithium-storage performance.This study will enhance the understanding of the electro-chemo-mechanical coupling mechanism and provide guidance for enhancing stress-regulated battery performance.

Deformation and failure characteristics of anchorage structure of surrounding rock in deep roadway

This paper investigated the stress evolution,displacement field,local deformation and its overall distribution,and failure characteristics of the anchorage structure of surrounding rock with different rockbolt spacing through the model experiments.The influences of the pre-tightening force and spacing of rockbolt on the support strength of the anchorage structure of surrounding rock were analyzed by the simulation using FLAC3D numerical software.The support scheme of the excavated roadway was then designed,and the effectiveness of this support scheme was further verified by the displacement measurement of the roadway.The results showed that the maximum displacement between the roof and floor of the west wing track roadway in Kouzidong coal mine,China is about 42 mm,and the maximum displacement between its both sides is about 72 mm,indicating that the support scheme proposed in this study can ensure the stability and safety of the excavated roadway.

鱼类及其他脊椎动物神经递质含量的比较研究

采用高效液相色谱法测定了变温动物(鱼、蛙、鳖)和恒温动物(鸡、狗、牛)脑和脊髓中多巴胺(DA)和5-羟色胺(5-HT)的含量。结果表明:(1)变温动物和恒温动物脑和脊髓中DA和5-HT含量存在较大差异。变温动物脑和脊髓中DA含量分别为(0.228±0.014)μg/g和(0.155±0.003)μg/g,5-HT含量分别为(0.465±0.139)μg/g和(0.104±0.004)μg/g;恒温动物脑和脊髓中DA含量分别为(0.258±0.015)μg/g和(0.236±0.018)μg/g;脑和脊髓中5-HT为(1.020±0.166)μg/g和(0.712±0.344)μg/g。(2)湖泊与池塘的鲢脑中DA含量分别为(0.197±0.018)μg/g和(0.073±0.012)μg/g,血液中肾上腺素(Ad)含量分别为(0.065±0.013)μg/g和(0.025±0.007)μg/g。这说明DA和Ad在鱼类环境应激中有重要作用。(3)从鱼类经鸟类到哺乳类纵向比较,其神经递质的含量是不同的。以进化论和全息论的观点来看,其中可能蕴藏着生物医药潜力。

On the Relationship of the Discrete Model of the Nuclei of Linear and Planar Defects and the Continuum Models of Defects in Crystalline Materials

A physical and mathematical model of the transition from a discrete model of linear and flat defects nuclei to continuum models of defects such as dislocations and disclinations and their combinations is presented, where the tensors of energy-momentum and angular momentum of an alternating field are considered, for which the type and structure of the Maxwell stress tensor σif αβ are given and the corresponding angular momentum tensor, using the dynamic equation for the evolution of internal stresses and the correlation between the stresses σif αβ in the defect core and the elastic stresses σelik in its environment, obtains elastic displacement and deformation fields identical to these fields from Burgers and Frank vectors of continuous models. The spectral density of the autocorrelation functions of the velocity of photoelectrons Ψβ⊥(β) and cations , which transforms into linear spectra as T → 0, is considered reflecting the existence of threshold values of oscillation and rotations currents of photoelectrons and cations at all stages of plastic deformation and fracture. The features of the process of sliding linear defects in metals are disclosed.