Objectives To analyze the influence of karst caves on the construction of large-section tunnels,and to investigate the deformation,failure,and water inrush characteristics of tunnel surrounding rock under various occurrence states of karst caves.Methods Based on the Shuangbei Tunnel project,considering the stress-damage-seepage coupling effect of the surrounding rock,numerical simulations were conducted using FLAC3D software.The simulations analyzed the displacement,failure zone,water-conducting fracture channels,and water inflow characteristics of the large-section tunnel surrounding rock under five factors and four levels:the angle between the karst cave and the tunnel center,the clear distance between the karst cave and the tunnel,the diameter of the karst cave,the water pressure in the karst cave,and the initial permeability coefficient of the rock mass surrounding the karst cave.The range analysis method was system-atically used to evaluate the impact of karst caves on the deformation,failure,and water inrush degree of the tunnel surrounding rock.Results The results show that:under conditions without a karst cave,the maximum displacement of the tunnel surrounding rock is 104.1 mm,the failure zone exhibits a"butterfly-shaped"distribution,with failure width and height of 7.0 m and 25.9 m,respectively.When a dry(water-free)karst cavity exists near the tunnel,the plastic zone of the surrounding rock expands and extends toward the karst cave,and the maximum displacement increases by approximately 30%～42%.When a water-rich,high-pressure karst cave exists near the tunnel,one or several water-conducting fracture channels form in the rock mass between the tunnel and the karst cave,and the maximum displacement of the surrounding rock exceeds 1,000 mm.The range values for the influence of the five karst cave occurrence parameters on the maximum displacement of the tunnel surrounding rock are 215.8,443.4,453.1,869.3,and 227.5 mm,respectively.The range values for the influence on the failure area of the tunnel surrounding rock are 351.8,102.1,372.5,243.3,and 166.4 m²,respectively.The range values for the influence on the total water inflow of the tunnel surrounding rock are 1 797.3,2 829.4,1 747.6,2 336.5,and 2 816.0 m³/h,re-spectively.Conclusions When karst caves near the tunnel contain no groundwater,their impact on the sta-bility of the large-section tunnel surrounding rock is relatively small.When groundwater is present,there exists a critical water pressure value that triggers the formation of water-conducting fracture channels between the tunnel and the karst cave,leading to overall sliding instability and water inrush.Among the five karst cave occurrence parameters,the water pressure in the karst cave determines the final displacement magnitude of the tunnel surrounding rock.The diameter of the karst cave and the angle between the karst cave and the tunnel center are key parameters affecting the extent and degree of failure of the tunnel surrounding rock.The clear distance between the karst cave and the tunnel,the initial permeability coefficient of the rock mass surrounding the karst cave,and the water pressure in the karst cave are the most important parameters controlling local and overall water inflow into the tunnel.

In order to study the deformation and failure law of bolt-mesh support roadway under roof impact load,taking 250104 transport roadway of Huating Coal Mine as background,FLAC3D was used to analyze the variation characteristics of stress,deforma-tion and plastic zone of surrounding rock of bolt-mesh support roadway under different impact load wave velocities,angles and off-set distances.The results show that:under the impact of roof load,the plastic zone of roadway roof and rock mass on both sides will gradually expand to upward and both sides,and its maximum displacement will increase exponentially;with the increase of the wave velocity of the roof impact load,the maximum displacement of the roadway roof and two sides will gradually increases exponen-tially;with the increase of impact angle of roof impact load,the maximum displacement of the roadway roof and two sides presents an"S-shaped"growth curve,and the impact angle of 90° has the most adverse impact on the stability of the surrounding rock of the roadway with bolt-mesh support;with the increase of the impact offset distance of roof impact load,the maximum displacement of roadway roof and impact side rock will increase first and then decrease.When the impact offset distances is equal to 5.0 m,it will pose the greatest threat to roadway safety.

With the development of underground engineering, dynamic disasters, such as rock bursts, are becoming increasingly serious. Bolt-grouting combined support is one of the common support methods, aiming at the prevention and control of dynamic disasters in fractured surrounding rock of underground engineering. However, the design of bolt-grouting supports is based mainly on experience, and the antishock characteristics need further study for fractured rock masses reinforced by bolt-grouting, which provides a scientific basis for the design of surrounding rock roadway reinforcement. Therefore, we carried out an experimental study on the dynamic mechanical properties of bolted and grouted red sandstones containing prefabricated fractures with different dip angles. The test results show that the dynamic peak strength and the deformation capacity decrease with increasing of fracture dip angle. Compared with the unreinforced samples, the dynamic peak strength and dynamic peak strain of bolt and grouting reinforced samples are improved, and the reinforced rock samples have higher impact resistance and deformation capacity. As the fracture dip angle increases, the incident energy, reflection energy, and transmission energy all show a decreasing trend. Bolt and grouting play the role of energy absorption and increasing antishock, and the dissipation rate of bolted-grouted rock samples is improved. The failure mode of the unreinforced samples is shear failure, the damage of which is more severe than that of bolt and grouting reinforced samples. For the bolt-grouting samples, tensile failure is observed at a low strain rate, and shear failure occurred at a high strain rate.

In order to study the water-inrush disaster law of collapse column under the influence of interstitial material activation, a return air roadway of Shenhua Group was taken as the research object. The strength reduction and permeability mutation caused by rock destruction inside and outside collapse column and activation and loss of fillings were considered. FLAC3D simulation was used to study the characteristics of displacement, permeability coefficient, pore water pressure and water inflow of collapse column and surrounding rock in the process of roadway excavation. On this basis, the influence of fillings packed height of collapse column on water inrush was analyzed. The results show that: with the increase of the distance between roadway and collapse column fillings layer, the width and depth of the activated loss of collapse column fillings in the roadway floor will be larger and larger, resulting in the rock displacement between collapse column water-conducting layer and roadway bottom is increasing and the overall slip trend appears. Finally, when the roadway driving face exceeds 1 m of the collapse column central axis, the high-pressure water of the collapse column injects water into the roadway through the activation and loss channel of fillings. And the water inrush has the characteristics of large volume, suddenness and hysteresis. The larger the fillings packed height of collapse column is, the later the water inrush time node of collapse column relative to roadway excavation surface is. However, when the fillings packed height of collapse column reaches 22 m, water inrush will not occur in the collapse column.

课程思政建设是高校全面提高人才培养质量的重要任务,也是每门专业课课程改革中的首要任务.在立德树人的教育理念下,专业课程与思想政治教育形成协同效应,在课程教学中与思想政治育人同向同行.围绕"工程力学"课程思政的育人目标,结合课程内容,着力寻找专业伦理、职业操守、人文精神、家国情怀、社会主义核心价值观等德育元素的融入点.提出了课程思政的教学方法和手段,探索了"工程力学"课程思政考核方式,为"工程力学"课程思政教学提供了参考.

The filling material of the karst collapse column (KCC) is easy to be activated by mining. During this process, the mechanical properties of KCC fillings change, and its water resisting capacity constantly deteriorates and thus often leads to water inrush disaster. In this study, the samples of KCC fillings were taken on-site and then were remolded by the consolidation drainage method. The variation laws of the compressive strength, tensile strength, cohesive stress, internal friction angle, and permeability of the filling samples with respect to the consolidation pressure and moisture content were tested and analyzed. Based on an engineering example, the yield and activation and particle loss of the filling material of the KCC are analyzed. A mechanism for the lagging water inrush of KCC in the process of mining is proposed. The main results of the present study can be concluded concisely as follows. (1) The KCC fillings show obvious soft rock characteristics in the process of uniaxial compression and Brazilian split. The ratio of the uniaxial compressive strength to splitting tensile strength is between 12 : 1 and 8 : 1. The larger the consolidation pressure or the smaller the moisture content, the larger the ratio. (2) With the increase of consolidation pressure or the decrease of moisture content, the uniaxial compressive strength, elastic modulus, splitting tensile strength, cohesive stress, and internal friction angle of the filling material of the KCC increase linearly, while its permeability increases exponentially. (3) When the crack field of the surrounding rocks of the stope is connected with the KCC, its filling material will continue to yield, activate, and migrate under the fluid-solid coupling effect and finally result in the lagging water inrush from the KCC.

为研究渗流与蠕变的相互耦合作用对软土基坑开挖的影响,文章以深圳地铁11号线前海湾站基坑工程为背景,基于FLAC3D中的渗流和蠕变分析模式,对不同计算条件下软土基坑的桩后水压力、桩位移、地表沉降以及坑底隆起等的变化规律展开研究.研究结果表明:(1)渗流和蠕变作用均会对基坑开挖变形产生较大影响,只有综合考虑这两者间的相互影响,才能保证基坑开挖模拟计算结果与实际相符合;(2)基坑开挖过程中,基坑两侧桩最大位移值和位置都与开挖时间呈指数衰减关系,而基坑两侧地表最大沉降除会在每次降水过程中急速增大外,其余时段则与开挖时间保持相对缓慢的线性增长关系;(3)随着潜水水位埋深的增加,基坑两侧地表最大沉降和桩体最大位移都将线性减小.

Taking the concrete as an example, this paper studies the shear characteristics of the cohesive soil and rigid base. A series of shear tests are conducted by the refitted DSJ-2 electric four-joint equal stress direct shear apparatus. The results in the shear tests are contrastively analyzed. The results show that under the condition of simple shear tests, the constitutive relation of structural interface between the clay and concrete is rigid, and the residual strength is obvious. Under the condition of direct shear tests, the shear stress-displacement curves present hyperbolic connection. There is obvious strain hardening phenomenon, no obvious peak strength and residual strength. Under the two experimental conditions, the peak shear strength of the interface increases with an increase in the normal stress. With increasing moisture content, the peak shear strength of the interface decreases. The internal friction angle and cohesion of the structural interface decrease with increasing moisture content, and the relationship between internal friction angle, cohesion of the structural interface and moisture content are nonlinear. The peak shear strength of the direct shear tests is greater than that of the simple shear tests.

为了研究裂隙砂岩力学特性,利用颗粒流(PFC)软件构建含不同几何状态的裂隙试样模型,分析裂隙几何状态对裂隙试样力学特性和变形特性的影响.结果表明:相比于完整试样,裂隙试样的峰值强度、弹性模量、峰值轴向应变均有所降低,泊松比明显提高;裂隙试样峰值强度、弹性模量随着岩桥宽度的增加逐渐增加,随着岩桥倾角增加,裂隙试样弹性模量呈现先减小后增大的变化规律,当岩桥倾角与裂隙倾角相同时,裂隙试样的弹性模量、峰值强度最小;裂隙试样泊松比随着岩桥宽度、围压的增加逐渐降低,随着围压增加,裂隙试样峰值强度、峰值轴向应变逐渐增加;裂隙的存在弱化了试样的力学特性,改变了试样的变形特性,岩桥宽度越小,弱化能力越强,相比于岩桥宽度对裂隙试样的影响程度,岩桥倾角对试样的影响程度较小.

采用升级改造后的DSJ-2型直剪仪,在不同法向应力水平下,开展了不同含水量的粘性土与不同介质性质的地下结构物接触界面的单剪试验,探索揭示粘土含水量变化对接触界面的剪切力学行为影响规律.研究结果表明:随着粘土含水量的增大,基底刚度较大时,剪应力-剪切位移曲线应变硬化现象愈来愈明显,反之,愈来愈不明显.剪切法向应力处于较低水平时,粘土的含水量对刚度较大的混凝土基底界面剪应力峰值强度影响更明显,反之,刚度相对较小的木材基底更明显.不同性质基底同粘土单剪时,随其含水量的不断提高,接触界面的内摩擦角均是不断降低,但其降低幅度不尽相同,结构物的刚度对接触界面内摩擦角起控制作用.随着粘土含水量的增大,接触界面的粘聚力总体变化规律为先增大,增大到某一峰值点后降低,界面的粘聚力由土体与结构物共同控制,且同结构物的刚度大小和界面自身特性均密切相关.

为研究裂隙的存在对岩体破坏模式的影响,本文对含有不同几何状态的裂隙细砂岩进行了单轴压缩试验,分析了单轴压缩条件下,岩桥倾角和岩桥宽度对裂隙细砂岩试样裂纹起裂、扩展过程以及破坏模式的影响;结果表明:从整体来看,在单轴压缩条件下,裂隙细砂岩试样的破坏模式主要有拉伸破坏、剪切破坏、拉剪组合破坏3种;随着岩桥宽度的增加,裂隙细砂岩试样裂纹发育的起始位置从1条裂隙的尖端转化为2条裂隙的尖端,裂隙细砂岩试样的破坏模式由剪切破坏模式经过拉剪组合破坏模式后向拉伸破坏模式过渡;随着岩桥倾角的增加,裂隙细砂岩试样裂纹发育的起始位置从2条裂隙的尖端转化为1条裂隙的尖端,裂隙细砂岩试样的破坏模式由拉剪破坏逐渐向剪切破坏过渡;裂纹的发育和扩展在应力-应变曲线上都有所体现,应力-应变曲线的每一次波动都对应裂纹的发育或扩展;试验结果为裂隙岩体工程提供了一定的指导意义.

The effects of saturation on post-peak mechanical properties and energy features are main focal points for sandstones. To obtain these important attributes, post-peak cyclic loading and unloading tests were conducted on sandstone rock samples under natural and saturated states using the RMT-150B rock mechanics testing system. After successful processing of these tests, comparisons of stress-strain, strength, deformation, damage, and degradation of mechanical properties, wave velocity, and energy features of sandstone were conducted between natural and saturated states. The results show that saturation has evident weakening effects on uniaxial cyclic loading and unloading strength and elastic modulus of post-peak fracture sandstone. With the increase of post-peak loading and unloading period, the increases in amplitude of peak axial, lateral, and volumetric strains are all enhanced at approximately constant speed under the natural state. The increase in amplitude of axial peak strain is also enhanced at approximately constant speed, while the amplitudes of lateral and volumetric peak strains increase significantly under the saturated state. Compared with the natural state, the increase in amplitude of saturated samples’ peak lateral and volumetric strains, and the post-peak cyclic loading and unloading period all conform to the linearly increasing relationship. Under natural and saturated states, the damage factor (the plastic shear strain) of each rock sample gradually increases with the increase of post-peak cyclic loading and unloading period, and the crack damage stress of each rock sample declines rapidly at first and tends to reach a constant value later with the increase in plastic shear strain. Under natural and saturated states, the wave velocities of rock samples all decrease in the process of post-peak cyclic loading and unloading with the increase in plastic shear strain. The wave velocities of rock samples and plastic shear strain conform to the exponential relationship with a constant. Saturation reduces the total absorption energy, dissipated energy, and elastic strain energy of rock samples.

为适应新时期环境下高等教育对培养人才的要求,从材料力学课程的课堂教学入手,讨论了在学时较少的现状下如何通过转变教学观念和精炼教学内容提高课堂教学的效率和培养学生的学习能力;讲述了如何用提高教学趣味性的手段激发学生学习的积极性;同时也对力学模型和"云课堂"两种实用性强、可行性高的课堂教学方法进行了探讨.

根据工程力学专业所开设的MATLAB课程特点,探讨MATLAB实践教学与工程力学本科毕业论文的相互促进作用,并举实例说明两者的结合,目的是激发学生对毕业设计的兴趣;有利于学生创新思维的培养,提高学生分析和解决实际问题以及理论联系实际的能力;锻炼学生在工程设计中应用MATLAB的能力,提高学生毕业论文的质量.

Engineering research has shown that the surrounding rock of deep roadways experienced many times of post-peak cyclic loading and unloading. So studying on rock mechanical characteristics of post-peak loading and unloading is helpful to control the deep surrounding rocks. The test using RMT-150B rock mechanics testing system, to experiment on the mechanical properties of sandstone of post-peak cyclic loading and unloading. The results show that: the stress–strain curves of post-peak cyclic loading and unloading have significant plastic hysteretic loops. The area of plastic hysteretic loops gloss back. The enveloping outer enclosure of cycle loading curve is the similar as the stress–strain curves of strain softening stage when the samples failure, which shows that post-peak failure of rocks have significant memory. With the increase of cycles, the cumulative deterioration parameters are gradually increased, and the ultimate bearing capacity, elastic of loading section of samples and cumulative deterioration parameters conform with the exponential attenuation function with constant term. With the increase of surrounding pressure, the total energy, dissipated energy and elastic energy of samples are gradually increased. With the increase of cycles, the total energy, dissipated energy and elastic energy of samples all are gradually decreasing, the rate of reduction decreases gradually. The samples exist in vertical splitting and transverse shear combination failure under the post-peak uniaxial cycles, or exist in shear failure under the post-peak triaxial cycles. The shear plane exists slip traces.

In order to make an exploration of the evolutionary regularity of the deformation and fracture of the deep-level soft rectangular rock roadways,the paper has first of all tested and obtained the microscopic parameters of the mudstone particles and the cementation in the PFC2D via the numerical simulation of mono-axial and tri-axial compression tests based on the geological condition of a sample deep-level mudstone roadway.And,then,we have worked out the spatialdistribution patterns and the development characteristics of the deformation and fracture of the surrounding rocks in such soft rock roadway under the different mudstone microstructures while taking into account the distribution status-in-situ of the mudstone particles and pore structure.The results of our numerical simulation show that:(1) The different spatial orders of the rock microscopic particles tend to cause asymmetric deformation-fractures in three distinct fracture patterns and five distinct deformation patterns.(2) The process for the surrounding rocks to get fractured is that,at first,there may appear a tendency for micro cracks in the weak places of the shallow surrounding rocks randomly,and then the minor cracks here and there in the rocks would result in a lot of shear slip bands.And,next,with the extension and expansion of such shear slip bands,the fracture zones would begin to develop upwardly and downwardly across the roadway.And,finally,the entire surrounding roadway would be broken into lots of meshed ruptures.(3) During the different periods of the rectangular roadway excavation,the radial displacement of the surrounding rocks tends to be related with the exponential decay with the distance prolonging from the crack point of the roadway's top surface,while the average displacement of the shallow surrounding rock on the roof tends to be significantly greater than that of the two sides.(4) There may also exist minor probability that the greatest displacement may occur near the central point while highest probability of displacement tends to occur within the sphere of 0.25 m near the middle part of the four corners of the rectangle.(5) With the prolonging of the excavation time,the total number of cracks and the magnitude of displacement would be likely to exhibit a feature of variation of the exponential decay.

The given paper is inclined to disclose the evolutionary regularity of the stress,displacement and rupture to be caused by the different lateral pressure coefficients via a discrete particle element software known as PFC3D,in hoping to uncover the effect of the lateral pressure coefficient on the stability of the deep rocks in the background of a deep circular roadway.The results of our study show that,(1) with the increase of the lateral pressure coefficients,the main stress difference between the shallow rock on the roof or the floor and the deep rock therein tends to increase gradually,which may lead to changes little by little and later the change tends to decrease first and then increase correspondingly.What is said above implies that,at the same burial depth,the high lateral pressure coefficient may not always result in failure in regard to the two sides of the roadway rock,rather,it may cause the rock on the roof subjected to the high shear stress,which is naturally detrimental to the stability of roof rock.(2) The greater the lateral pressure coefficient,the smaller the possibility of the vertical displacement of the roof rock,and the lower the diminishing regularity of the roof rock collapsing from the dome to the outside would be,and,in contrast,the greater the horizontal displacement of the rock on the two sides will be,which seems to the opposite to the rule of vertical displacement.(3) It would be more likely for the roadway roof or the floor rock to get fractured in case the lateral pressure coefficient becomes bigger.And,consequently,the greater the lateral pressure coefficient,the greater the rupture range will be.While roadway rock on the two sides tends to rupture under different lateral pressure coefficients,its rupture range tends to be reduced slightly with the increase of the lateral pressure.(4) With the increase of the different lateral pressure coefficients,the probability of the surrounding rock cracks in the circular roadway tends to grow exponentially in the relation to the excavation time length.And,in turn,the total probability rate of the surrounding rock cracks will turn to be in a parabolic relation to the lateral pressure coefficient from the day when the roadway excavation were completed.

针对现有研究无法有效评价裂隙分布特征对围岩变形破裂影响程度的问题,以一个软岩巷道工程为背景,考虑裂隙的5种形态分布特征:距巷道的中心距离、方位角、倾角、长度和宽度,并在此基础上进行PFC3D正交数值模拟试验设计.结果表明:当裂隙穿过巷道时,斜向裂隙更容易导致巷道周边岩体发生大变形或局部垮塌,其危险程度要大于水平裂隙,更大于竖向裂隙;当裂隙未穿过巷道时,如裂隙附近岩体处于相对容易破裂的位置,则巷道岩体就会在裂隙距巷道表面最近的位置产生一条新的连通至巷道表面的破裂通道;裂隙方位角和裂隙宽度是影响巷道表面围岩收敛变形的最主要因素,而裂隙方位角和裂隙长度则对巷道横断面围岩的破裂扩展起着决定性作用.

Since engineering rock mass is under high stress conditions, it has strong time-dependent effect due to continuously high ground stress after excavation and rupture. The study of creep properties after its post-peak is significant in both theory and practice. Firstly, the uniaxial pre-peak yield and post-peak rupture unloading tests are conducted on the intact rock samples using RMT-150B rock mechanics test system. Then the rock samples with different damage degrees are prepared under conditions of pre-peak yield and post-peak rupture. Lastly, uniaxial creep tests on the prepared rock samples are conducted to obtain uniaxial creep mechanical properties by using RLW-2000 microcomputer servo rock triaxial rheology testing system. From experimental results, velocities of all damaged rock samples show different degrees of reduction by comparing with the velocities of intact rock samples. Under each stress level, instantaneous dependent variable of the damaged rock samples gradually increases with the increase of the stress level, and there is linear relationship between the instantaneous dependent variable and stress level. It is found that the instantaneous dependent variable of post-peak damaged and rupture rock sample is significantly greater than that of pre-peak yield and damaged rock sample under the same stress level. Generally, each creep deformation gradually increases with the increase of the stress level under all stress levels, which meets exponential function relationship. The creep deformation of post-peak damaged and rupture rock sample is substantially greater than the pre-peak yield and damaged rock sample under the same stress level, Moreover, the difference of the creep deformation between post-peak damaged rock sample and pre-peak yield and damaged rock sample increases with increasing the load. The instantaneous deformation modulus of damaged rock sample steadily improved with the increase of stress level, furthermore, the instantaneous modulus changes linearly with the stress level. The instantaneous modulus of deformation at each stress level is obviously different, the higher the degree of rock damage, the lower the instantaneous modulus of deformation. For the damaged rock samples under all levels, the improved Nishihara model can be used to simulate uniaxial creep characteristics.

为了改善高强素混凝土的脆性破坏行为,通过钢纤维与碳纳米管的混掺试验,分别进行了空白试样和高强钢纤维碳纳米管混凝土的立方体和轴心抗压试验,得到了单轴受压应力-应变关系曲线,并由此建立了本构方程.试验结果表明:HSPC的棱柱体试件破坏形态为典型的脆性破坏;HSSFCNRC属于典型的塑性破坏.其次,两者的轴压比(轴心与立方体抗压强度之比)均随强度提高而提高,但HSPC的峰值应变、弹性模量和泊松比均比HSSFCNRC小;第三,由于HSPC的脆性和压力试验机的局限性,所采集到的下降段曲线上数据点远较后者少得多,而且后者也较前者的曲线平缓得多.这些特征指标,均说明了钢纤维与碳纳米管已有效改善了HSPC的脆性破坏行为,可为相关工程应用奠定基础.