Displacement of surrounding rock in a deep circular hole considering double moduli and strength-stiffness degradation

The problem of cavity stability widely exists in deep underground engineering and energy exploitation.First,the stress field of the surrounding rock under the uniform stress field is deduced based on a post-peak strength drop model considering the rock’s characteristics of constant modulus and double moduli.Then,the orthogonal non-associative flow rule is used to establish the displacement of the surrounding rock under constant modulus and double moduli,respectively,considering the stiffness degradation and dilatancy effects in the plastic region and assuming that the elastic strain in the plastic region satisfies the elastic constitutive relationship.Finally,the evolution of the displacement in the surrounding rock is analyzed under the effects of the double modulus characteristics,the strength drop,the stiffness degradation,and the dilatancy.The results show that the displacement solutions of the surrounding rock under constant modulus and double moduli have a unified expression.The coefficients of the expression are related to the stress field of the original rock,the elastic constant of the surrounding rock,the strength parameters,and the dilatancy angle.The strength drop,the stiffness degradation,and the dilatancy effects all have effects on the displacement.The effects can be characterized by quantitative relationships.

鞘状碳纳米管人工肌肉纤维在弱电流刺激下的驱动性能提升机制

电热驱动的鞘状人工肌肉已经展示出广阔的应用前景.当受到高电流产生的焦耳热影响时,它们的鞘层会膨胀和软化,有效地释放芯部纤维内储存的扭转能量,这种现象显著地提高了驱动性能.本工作制备了一种包裹在聚二甲基硅氧烷(PDMS)鞘层中的预捻碳纳米管(CNT)人工肌肉纤维.施加频率为0.25 Hz的50 mA电流,其可以产生13.28%的收缩变形和9.82 MPa的收缩应力,功率密度为3.8 W g^(−1).得益于非螺旋结构,CNT纤维@PDMS的运行速率可达42%s^(−1),我们据此开发了快速运行的开关和仿生臂.有趣的是,我们观察到即使在较弱的电流不足以诱导驱动所需的PDMS鞘层膨胀和软化的情况下,CNT纤维@PDMS的驱动性能也有所改善.为了解释这一现象,我们提出了一种鞘层致密化机制.当电流通入CNT纤维时,其内部CNTs间产生的安培吸引力也会引发驱动,PDMS鞘层在固化过程中产生沿CNT纤维径向分布的收缩应力,会使CNTs间距减小,从而提升安培吸引力.我们通过检测CNT纤维@PDMS在不同温度下的驱动行为、内部微观结构、力学和电学性能的变化证实了这种致密化机制的存在,并分析了整个驱动过程中能量的变化.

Shear behaviour of anchored jointed rock mass under different engineering conditions considering damage and joint surface morphology

According to different geological conditions and engineering disturbance,three dimensional numerical models of anchored jointed rock mass with two kinds of boundary conditions of constant normal load(CNL)and constant normal stiffness(CNS)were constructed considering the ductility damage of rockbolt,the stiffness degradation of grouting layer and the joint surface roughness.The effects of anchorage angle,joint surface morphology,and boundary conditions on the shear performance of anchorage system were analyzed,and the failure characteristics under different working conditions were revealed.Finally,the analytical solution of shear strength of anchored system was established.Results show that the larger the anchorage angle is,the more serious the necking phenomenon of rockbolt will be.The damage degree of the bonding layer and the horizontal displacement of the bedding rock mass decrease with the increase of the joint surface roughness.The CNL condition is to instantaneously apply high normal stress,and the CNS condition is to gradually form a high normal stress environment through the superposition of increment on the basis of the initial value,which can resist greater transverse load.This is equivalent to enhancing the ductility of the rockbolt.The shear strength of the system increases with the increase of normal stress and normal stiffness.Ignoring the normal stiffness will underestimate the shear strength.

Monitoring and evaluation of disaster risk caused by linkage failure and instability of residual coal pillar and rock strata in multi-coal seam mining

Comprehensive research methods such as literature research,theoretical analysis,numerical simulations and field monitoring have been used to analyze the disasters and characteristics caused by the linkage failure and instability of the residual coal pillars-rock strata in multi-seam mining.The effective monitoring area and monitoring design method of linkage instability of residual coal pillar-rock strata in multi-seam mining have been identified.The evaluation index and the risk assessment method of disaster risk have been established and the project cases have been applied and validated.The results show that:①The coal pillar will not only cause disaster in singleseam mining,but also more easily cause disaster in multi-seam mining.The instability of coal pillars can cause not only dynamical disasters such as rock falls and mine earthquakes,but also cause surface subsidence and other disasters.②When monitoring the linkage instability of residual coal pillar-rock strata,it is not only necessary to consider the monitoring of the apply load body(key block),the transition body(residual coal pillar)and the carrier body(interlayer rock and working face),but also to strengthen the monitoring of the fracture development height(linkage body).③According to the principles of objectivity,easy access and quantification,combined with investigation,analysis,and production and geological characteristics of this mining area,the main evaluation indexes of the degree of disaster caused by linkage instability of residual coal pillar-rock strata are determined as:microseismic energy,residual coal pillar damage degree,fracture development height.And the evaluation index classification table was also given.④According to the measured value of the evaluation index,the fuzzy comprehensive evaluation method was used to calculate the disaster risk degree in the studied mine belongs to class III,that is,medium risk level.The corresponding pressure relief technology was adopted on site,which achieved a good control effect,and also verified the accuracy and effectiveness of the risk evaluation results.

Quantitative analysis of parameters’influence on the stability of coal roadway clamped by upper and lower soft rock with extra thickness

In this paper,a physical model of coal roadway which is clamped by upper and lower softrock with extra thickness was built according to the characteristics of soft rock strata in china's western mining area.Then,a series of orthogonal numerical experiments were carried out by selecting the strength and stiffness parameters of soft rock and coal seam as well as the in situ stress of soft rock strata as experimental factors and roadway displacements(convergence displacements of sides,displacement of roof to floor)as experimental indexes.By constructing the F statistics with different inspection levels,evaluation method for influence of the experimental factors on stability indexes were defined.Thus,influence degrees of specified parameters on the stability of roadway were divided into five classes as follows:highly significant influence,significant influence,relatively significant influence,little significant influence,and no influence respectively which realize the quantitative analysis of the influence degrees of experimental factors.The finite element calculation results showed that main failure mode of coal roadway that usually showed as tension failure of coal seam in roof and deformation factors of coal seam had the most remarkable effect on roadway displacements.The conclusions provide theoretical basis for further analysis of the mechanism of"roof burst"in roadway maintenance.