Failure analysis and control technology of intersections of large‑scale variable cross‑section roadways in deep soft rock

In deep underground mining,achieving stable support for roadways along with long service life is critical and the complex geological environment at such depths frequently presents a major challenge.Owing to the coupling action of multiple factors such as deep high stress,adjacent faults,cross-layer design,weak lithology,broken surrounding rock,variable cross-sections,wide sections up to 9.9 m,and clusters of nearby chambers,there was severe deformation and breakdown in the No.10 intersection of the roadway of large-scale variable cross-section at the−760 m level in a coal mine.As there are insufcient examples in engineering methods pertaining to the geological environment described above,the numerical calculation model was oversimplifed and support theory underdeveloped;therefore,it is imperative to develop an efective support system for the stability and sustenance of deep roadways.In this study,a quantitative analysis of the geological environment of the roadway through feld observations,borehole-scoping,and ground stress testing is carried out to establish the FLAC 3D variable cross-section crossing roadway model.This model is combined with the strain softening constitutive(surrounding rock)and Mohr–Coulomb constitutive(other deep rock formations)models to construct a compression arch mechanical model for deep soft rock,based on the quadratic parabolic Mohr criterion.An integrated control technology of bolting and grouting that is mainly composed of a high-strength hollow grouting cable bolt equipped with modifed cement grouting materials and a high-elongation cable bolt is developed by analyzing the strengthening properties of the surrounding rock before and after bolting,based on the Heok-Brown criterion.As a result of on-site practice,the following conclusions are drawn:(1)The plastic zone of the roof of the cross roadway is approximately 6 m deep in this environment,the tectonic stress is nearly 30 MPa,and the surrounding rock is severely fractured.(2)The deformation of the roadway progressively increases from small to large cross-sections,almost doubling at the largest cross-section.The plastic zone is concentrated at the top plate and shoulder and decreases progressively from the two sides to the bottom corner.The range of stress concentration at the sides of the intersection roadway close to the passageway is wider and higher.(3)The 7 m-thick reinforced compression arch constructed under the strengthening support scheme has a bearing capacity enhanced by 1.8 to 2.3 times and increase in thickness of the bearing structure by 1.76 times as compared to the original scheme.(4)The increase in the mechanical parameters c andφof the surrounding rock after anchoring causes a signifcant increase inσt;the pulling force of the cable bolt beneath the new grouting material is more than twice that of ordinary cement grout,and according to the test,the supporting stress feld shows that the 7.24 m surrounding rock is compacted and strengthened in addition to providing a strong foundation for the bolt(cable).On-site monitoring shows that the 60-days convergence is less than 30 mm,indicating that the stability control of the roadway is successful.

Study on the relation between damage and permeability of sandstone at depth under cyclic loading

The damage and permeability evolution of rock under stress is of great significance to engineering safety.In this paper,the evolution law of rock damage and permeability is studied by means of acoustic emission (AE) seepage experiment on deep roof sandstone with cyclic loading.Characterization of damage uses the changes in acoustic emission fractal characteristics and compression parameter which based on elastic modulus.The experimental results show that the AE events has fractal characteristic,in which the AE b-value and correlation dimension can represent the damage of rock.When the fractal characteristic value of AE increases,it indicates that the rock is in the compaction stage and the damage is not obvious.When the fractal characteristic value of AE drops,it indicates that the rock was damaged,and the permeabilityincrease.Under the cyclic load increasing step by step,the elastic modulus first increases and then decrease.Introducing compression parameter C to characterize the state of compaction and damage,it is obtained that the rock damage state and hydrostatic permeability show a power law function relationship with porosity and have the same monotonicity.When compression parameter is less than zero,the evolution law of permeability and damage can be described by functional relationship between hydrostatic permeability K and compression parameter C.

Three-dimensional spatial and temporal distributions of dust in roadway tunneling

To study the three-dimensional spatial and temporal distributions of dust in tunneling roadways,and to solve the problems of inadequate time and limited number of monitoring points,this paper designs a device for the real-time monitoring and storage of data on the concentrations of dust at multiple measuring points in the same section of a tunnel.The proposed device can measure the total concentration of dust and that of respirable dust in real time at different instances and locations,and using different working procedures.These measurements are used to study the temporal and spatial migration of dust.The results show that there was a sharp fluctuation zone 0–25 m from the heading face,about 25–40 m was high speed subsidence,beyond 40 m was gentle subsidence,The change of respiratory dust is much smoother.At different distances from the heading face,the total dust concentration exhibited a process of“violent oscillation–rapid descent–stable descent,”while the respirable dust exhibited a process of“fluctuating ascent–gradual subsidence.”Changes in the concentrations of total dust and respirable dust dust were consistent at different positions in the same section of the tunnel.The concentration of dust near the wall was low,and those along the sidewalk and air duct of the roadway were slightly higher than in the middle.The concentration of dust farther down the air duct decreased more slowly than that in the remaining lines of measurement.Small amounts of dust featuring large particles settled quickly.High concentrations of dust were observed to be intermittent,and the background value of dust concentration within 100 m of heading face was between 0.5 and 3 mg/m3.

三轴加卸载下层理砂岩的脆性特性

准确定量表征煤或岩石的脆性对有效估测深部工程的开挖效率具有重要意义。层理砂岩在全生命周期演化过程中所受到的应力演化特征必然会伴随有能量演化过程。因此,基于上述能量演化特征,本文提出“三阶段”三轴加卸载应力路径,获得损伤演化规律,并定义了脆性指数BI16。研究结果表明:1)围压可以提高层理砂岩的承载力和塑性变形抵抗能力。此外,加载方式和围压对塑性体积变形的抵抗能力存在显著影响,而倾角对其影响则较小。2)层理砂岩在常规三轴加载条件下的峰前损伤演化过程可划分为三个阶段。同时,层理砂岩在三轴加卸载条件下的峰前损伤演化过程则可划分为四个阶段。3)层理砂岩的整个变形过程会显著影响其脆性,且脆性是动态的、并非恒定的。上述研究结论可为准确估算深地工程的开挖效率提供依据。