Influence of maximum principal stress direction on the failure process and characteristics of D-shaped tunnels

To investigate the failure process and characteristics of D-shaped tunnels under different maximum principal stress directions θ, true-triaxial tests were conducted on cubic sandstone samples with a through D-shaped hole. The test results show that the failure process can be divided into 4 periods: calm, buckling deformation, gradual buckling and exfoliation of rock fragment, and formation of a V-shaped notch. With an increase in θ from 0° to 90°, the size of the rock fragments first decreases and then increases, whereas the fractal dimension of the rock fragments first increases and then decreases. Meanwhile, the failure position at the left side shifts from the sidewall to the corner and finally to the floor, whereas the failure position at the right side moves from the sidewall to the spandrel and finally to the roof, which is consistent with the failure position in underground engineering. In addition, the initial vertical failure stress first decreases and then increases. By comparing the results, the failure severities at different maximum principal stress directions can be ranked from high to low in the following order: 90°>60°>30°>45°>0°.     

满堂扣件式钢管脚手架应力传递规律试验研究

满堂扣件式钢管脚手架在混凝土工程模板施工中有着广泛的应用,具有拆装方便、周转次数多、经济效益显著等诸多优点。本文通过3×3跨的满堂式扣件钢管脚手架加载实验,在施加不同荷载的情况下,研究脚手架某一立杆扣件处的应力传递规律。采用数值模拟和现场监测等分析方法,分析在不同的荷载作用下,架体内部钢管立柱的应力传递规律,其结论和研究方法可为研究类似架体的受力性能提供借鉴和参考,同时为现场关键点监控和远程安全预警系统开发提供相应的理论依据。     

有效应力作用下单裂隙渗透规律的实验研究

通过对单裂隙试件进行的渗透性实验，提出了考虑岩石物性参数的渗透系数表达式，并根据实验结果建立了在有效应力作用下裂隙闭合量Δｂ与渗透系数ｋｆ和有效应力σｃ的关系式。这对深入研究裂隙渗流，简化有限元计算，解决工程实际问题具有一定的指导意义。     

基于能量原理的岩爆机理及应力状态分析

讨论了岩石破坏与能量耗散、能量释放的内在联系.基于能量原理,指出了岩爆发生的机制与特点,证明岩爆是发生在储存有高弹性应变能的硬脆性岩体中的地质灾害.结合圆形洞室围岩应力分布,分析了发生岩爆的地下洞室围岩的应力状态及相应的灾变位置.     

润扬悬索桥钢箱梁受力分析及实验研究

为了研究大跨度悬索桥扁平钢箱梁的工作行为与受力性能,以主跨1490m的润扬悬索桥为研究对象,基于大型有限元分析软件ANSYS建立了该桥的三维有限元整体计算模型,并对其进行了各种工况下的非线性静力分析．在此基础上运用子模型方法,基于局部精细模型计算了钢箱梁的各关键部位的应力．理论和试验结果都表明,该桥钢箱梁各关键部位在车载作用下的应力水平都比较低,但其顶板和顶板U形肋出现的应力疲劳值得重视．     

An investigation of machine learning techniques to estimate minimum horizontal stress magnitude from borehole breakout

Borehole breakout is a widely utilised phenomenon in horizontal stress orientation determination, and breakout geometrical parameters, such as width and depth, have been used to estimate both horizontal stress magnitudes. However, the accuracy of minimum horizontal stress estimation from borehole breakout remains relatively low in comparison to maximum horizontal stress estimation. This paper aims to compare and improve the minimum horizontal stress estimation via a number of machine learning (ML) regression techniques, including parametric and non-parametric models, which have rarely been explored. ML models were trained based on 79 laboratory data from published literature and validated against 23 field data. A systematic bias was observed in the prediction for the validation dataset whenever the horizontal stress value exceeded the maximum value in the training data. Nevertheless, the pattern was captured, and the removal of systematic bias showed that the artificial neural network is capable of predicting the minimum horizontal stress with an average error rate of 10.16% and a root mean square error of 3.87 MPa when compared to actual values obtained through conventional in-situ measurement techniques. This is a meaningful improvement considering the importance of in-situ stress knowledge for underground operations and the availability of borehole breakout data.     

不同卸荷应力路径下岩体破坏特征试验研究

隧道施工引起围岩应力释放的问题值得关注，目前对不同开挖方式引起隧道围岩强度及破坏的研究较少．因此，通过采用岩石三轴试验机，模拟隧道的不同开挖工况，针对不同卸荷应力路径下的岩石强度及破坏特征进行了深入研究，提出了相应的结论，可为后续理论研究提供试验参考．     

不同卸荷应力路径下岩体破坏特征试验研究

隧道施工引起围岩应力释放的问题值得关注,目前对不同开挖方式引起隧道围岩强度及破坏的研究较少.因此,通过采用岩石三轴试验机,模拟隧道的不同开挖工况,针对不同卸荷应力路径下的岩石强度及破坏特征进行了深入研究,提出了相应的结论,可为后续理论研究提供试验参考.     

Experimental investigation on hard rock fragmentation of inserted tooth cutter using a newly designed indentation testing apparatus

This investigation aims to explore the effects of stress conditions and rock cutting rates on hard rock fragmentation through indentation tests on a newly designed triaxial testing apparatus. This apparatus was designed to realize a triaxial loading and indentation test of cylindrical specimens using inserted tooth cutter. The boreability and crushing efficiency of granite rock was investigated by analyzing the change rules of the thrusting force, penetration depth, characteristics of chippings and failure patterns. Several quantitative indexes were used to evaluate rock boreability in this investigation. The granite rock samples all had a chiselled pit and a crushed rock core. Under initial stress conditions, only flat-shape chippings were stripped from the rock surface when the thrusting force reached 20 kN. The rock cutting special energy had a close correlation with the initial stress conditions and inserted tooth shape. Moreover, a thrusting force prediction model was proposed in this paper. The contribution of this study is that for the first time the influence mechanism of the initial triaxial stress conditions on rock fragmentation is investigated using an inserted tooth and the newly designed testing apparatus. This study has a crucial importance for practical underground hard rock crushing in geoengineering.     

A critical review on the developments of rock support systems in high stress ground conditions

Extreme ground behaviour in high-stress rock masses such as rockburst prone and squeezing ground conditions are encountered in a range of underground projects both in civil and mining applications.The occurrence of such ground behaviour types are difficult to predict and special design and construction measures must be taken to control them. Determining the most appropriate support system in such grounds is one of the major challenges for ground control engineers because there are many contributing factors to be considered, such as the rock mass parameters, the stress condition, the type and performance of the support systems, the condition of major geological structures and the size and geometry of the underground excavation. The main characteristics and support requirements of rockburst-prone and squeezing ground conditions are herein critically reviewed and characteristics of support functions are discussed. Different types of energy-absorbing rockbolts and other support elements applicable for ground support in burst-prone and squeezing grounds are introduced. Important differences in the choice and economics of ground support strategies in high-stress ground conditions between civil tunnels and mining excavations are discussed. Ground support benchmarking data and mitigation measures for mines and civil tunnels in burst-prone, squeezing and heavily swelling grounds conditions are briefly presented by some examples in practice.     

基于非线弹性CSIRO地应力测量技术及应用

在地下工程的中尤其深部工程,地应力是指导开挖的重要参数之一,因此,地应力测量工作至关重要.CSIRO地应力测量法是国际岩石力学学会推荐的地应力测量方法之一.针对三山岛金矿深部巷道近千米花岗岩钻机取芯,精密加工成标准圆柱试件,进行单、三轴压缩试验,获取霍克布朗-准则强度准则曲线,重点设计单岩样多围压阶梯弹性段加载试验.通过试验数据计算获得岩石弹性模量和泊松比等物理力学参数,引入体积模量K和剪切模量G等变形参量,且随平均应力不断增大成非线性变化的关系,应用双曲线函数模型建立变形参量与平均应力的本构关系■.公式中K_0/G_0为初始变形模量,K_0/G_0+1/a为平均应力无限大时趋近值,1/b为变形模量初始增长率,三参数都具有明确的物理意义.基于此公式推导考虑岩石非线弹性变形特征的CSIRO地应力测量法中高压双轴公式,通过三山岛金矿深部花岗岩解除岩芯高压双轴加载试验验证此公式的适用性.     

孙村煤矿-1300m深部围岩冲击倾向性及防治对策研究

通过实验室方法研究了新汶矿务局孙村煤矿-1300m深部水平的冲击倾向性,提出了孙村煤矿未来深部开采时冲击地压防治对策.     

锦屏二级水电站施工排水洞岩爆数值模拟

岩爆是一种极为复杂的动力失稳现象.在深埋隧洞的勘察设计和施工过程中,高地应力及其诱发的频繁岩爆,是影响隧道洞室稳定的重要因素之一.作为四川雅砻江锦屏二级水电站的重要的临时工程,施工排水洞在进入埋深1600m后就发生多次岩爆, 严重制约了工程的进展,为了研究岩爆发生机理与高地应力之间的关系以及更好地预测岩爆在隧洞内发生的位置,运用渐进破坏过程数值分析软件RFPA(realistic failure process analysis)对施工排水洞进行初步的应力分析,得出与现场实测相吻合的初始地应力拟合曲线.同时,隧洞开挖引起应力重分布而产生的围岩破坏的数值模拟也很好的印证了现场发生的岩爆情况,表明基于渐进破坏过程数值分析的RFPA可以真实地模拟高地应力下岩爆机理.     

抽芯储煤仓壁的强度分析

对抽芯储煤仓壁进行模型试验，通过试验结果分析其强度，并提出这种结构的计算方法。     

Laboratory tests to study the influence of rock stress confinement on the performances of TBM discs in tunnels

To clarify some aspects of rock destruction with a disc acting on a high confined tunnel face, a series of tests were carried out to examine fracture mechanisms under an indenter that simulates the tunnel boring machine (TBM) tool action, in the presence of an adjacent groove, when a state of stress (lateral confinement) is imposed on a rock sample. These tests proved the importance of carefully establishing the optimal distance of grooves produced by discs acting on a confined surface, and the value (as a ...     

沉积作用及应力历史对自重应力和沉降的影响

土体的沉积作用和应力历史会影响土体自重应力的确定,也会影响地基最终沉降量的确定。鉴于e-lnp比e-lgp坐标图能更方便、精确地描述线性问题,根据e-lnp坐标图推导沉积作用对成层土、正常固结土、超固结土的自重应力与沉降影响的计算式。用该计算式对昆明滇池国际会展中心部分深厚软土地基的自重应力和最终沉降量进行计算,并用计算结果和不考虑沉积作用及应力历史影响的计算结果进行对比分析,结果表明,沉积作用对深厚软粘土自重应力和最终沉降量计算值的影响非常显著,并且土体厚度越厚、上覆荷载越大,其影响越明显。     

转子轴封弹性槽形状及尺寸对应力集中的影响

计算了存在严重应力集中的转子轴封热弹性槽部位的热应力场。分析了弹性槽不同的结构形状对应力集中的影响,以及弹性槽不同的结构尺寸对应力集中的影响;对减小热弹性槽的应力集中程度提出了一些有益的建议。     

Effects of in-situ stress on the stability of a roadway excavated through a coal seam

Roadways excavated through a coal seam can exert an adverse effect on roadway stability. To investigate the effects of in-situ stress on roadway stability, numerical models were built and high horizontal stresses at varying orientations were applied. The results indicate that stress concentrations, roadway deformation and failure increase in magnitude and extent as the excavation angle with respect to the maximum horizontal stress increases. In addition, the stress adjacent to the coal-rock interface sharply varies in space and evolves with time; coal is much more vulnerable to deformation and failure than rock.The results provide insights into the layout of roadways excavated through a coal seam. Roadways should be designed parallel or at a narrow angle to the maximum horizontal stress. The concentrated stress at the top corner of the face-end should be reduced in advance, and the coal seam should be reinforced immediately after excavation.     

岩质边坡锚杆应力监测离心模型试验研究

基于离心模型试验方法,以m(重晶石粉)∶m(石英砂)∶m(石膏)∶m(水)=1.50∶1.00∶0.25∶0.50的质量比制备岩石替代材料,并制作3类典型岩质边坡的试验模型,通过应力监测方法研究岩质边坡失稳前的应力变化规律。试验结果为3类岩质边坡失稳前的应力变化曲线均较为平缓,监测预警易于把握,且具有相通性,均可采用Logistic曲线形式进行拟合;层状岩质边坡监测应以滑动面下部监测为主,结构面控制岩质边坡的破坏形式主要以拉剪破坏为主,试验选取的边坡类型监测应以上部结构面为主,碎裂结构岩质边坡应以边坡上部监测为主。综合离心模型试验结果表明,采用应力监测的方法评价公路岩质边坡的稳定性具有可行性。     

An experimental study of the incipient bed shear stress partition in mobile bed channels filled with emergent rigid vegetation

This paper investigates the bed shear stress based on the condition of the incipient motion of sediment in a uniform-flow flume covered with emergent rigid vegetation,which is represented by arrays of circular cylinders arranged in a regular pattern.A total of 148 tests are performed to observe the influence of the vegetation density,bed slope,flow depth and sediment size on the bed shear stress.The tests reveal that when the sediment is in incipient motion,the resistances acting on the flow passing the rigid vegetation contain the vegetation resistance and the bed shear stress.This shear stress could be divided into two parts:the grain shear stress and the shear stress caused by sand dunes,which are the deformed bedform with the sediment incipient motion.An empirical relationship between the shear stress of the sand dune and vegetation density,the Froude number,the apparent vegetation layer velocity is developed.