Influence of confined water on the limit support pressure of tunnel face in weakly water-rich strata

In the process of shield tunneling through soft soil layers,the presence of confined water ahead poses a significant threat to the stability of the tunnel face.Therefore,it is crucial to consider the impact of confined water on the limit support pressure of the tunnel face.This study employed the finite element method(FEM)to analyze the limit support pressure of shield tunnel face instability within a pressurized water-containing layer.Subsequently,a multiple linear regression approach was applied to derive a concise solution formula for the limit support pressure,incorporating various influencing factors.The analysis yields the following conclusions:1)The influence of confined water on the instability mode of the tunnel face in soft soil layers makes the displacement response of the strata not significant when the face is unstable;2)The limit support pressure increases approximately linearly with the pressure head,shield tunnel diameter,and tunnel burial depth.And inversely proportional to the thickness of the impermeable layer,soil cohesion and internal friction angle;3)Through an engineering case study analysis,the results align well with those obtained from traditional theoretical methods,thereby validating the rationality of the equations proposed in this paper.Furthermore,the proposed equations overcome the limitation of traditional theoretical approaches considering the influence of changes in impermeable layer thickness.It can accurately depict the dynamic variation in the required limit support pressure to maintain the stability of the tunnel face during shield tunneling,thus better reflecting engineering reality.

Modification of rock mass rating system:Interbedding of strong and weak rock layers

Rock mass classification systems are the very important part for underground projects and rock mass rating(RMR) is one of the most commonly applied classification systems in numerous civil and mining projects. The type of rock mass consisting of an interbedding of strong and weak layers poses difficulties and uncertainties for determining the RMR. For this, the present paper uses the concept of rock bolt supporting factor(RSF) for modification of RMR system to be used in such rock mass types. The proposed method also demonstrates the importance of rock bolting practice in such rock masses. The geological parameters of the Shemshak Formation of the Alborz Tunnel in Iran are used as case examples for development of the theoretical approach.

Parameter inversion and location determination of evolutionary weak layer for open-pit mine slope

In light of the complex and dynamic mechanical properties of evolving weak strata in open-pit mines,and the consequent difficulty of determining their mechanical parameters,this study uses the ultimate balance theory,along with the back analysis method combined with monitoring data on field displacement,to carry out parameter inversion using the FLAC3D numerical simulation software.The edge slope of a working pit of the Weijiamao open-pit mine was used as research object to this end.As the results obtained by the constitutive model were consistent with the field monitoring data,the evolving weak strata in the slope and the position of the landslide in the mine could be obtained.The landslide was directed northeast.The mechanism of the edge slope of the working pit was identified as unloading shear failure,and the feasibility of the method of parameter inversion was verified.The internal friction angle φand cohesion C of evolving weak strata in the slope of the open-pit mine were also obtained,where this compensated for the deficiency of laboratory tests and enabled the transformation from qualitative to quantitative analysis.This can provide a reliable basis for the safe operation of open-pit mines.

Numerical analysis of loess and weak intercalated layer failure behavior under direct shearing and cyclic loading

The mechanical behavior of the joints inside a loess layer is greatly important in weak intercalation studies owing to its involvement in a wide range of landslides in the loess region in China.The shear behavior of the joints in the loess stratum during direct shear and cyclic loadings was investigated using the PFC2D discrete element software.Loess mudstone and mudstone with weak intercalated layer materials were subjected to direct testing,and cyclic shear tests were conducted with consideration to the influence of normal stress and shear velocity.The macroscopic properties and damage patterns were obtained for six numerical configurations;namely,loess-weathered mudstone with 0°,10°,and-10°joints and weathered mudstone with 0°,10°,and-10°weak intercalated layers.The numerical test results revealed that,in the direct shear tests,the shear stress and shear displacement of the samples increased with the normal stress.In the cyclic shear tests with a total cycle number N=20,the shear stress-shear strain curve of the six different configurations exhibited a hysteresis loop.The numerical tests also revealed that,under cyclic shear,the normal stress and shear velocity affected the shear strength.The degree of damage increased as the shear velocity decreased from 0.1 mm/s to 0.005 mm/s for all six numerical configurations.Compared with the damage pattern of the direct shear tests,the damage of the cyclic shear tests mainly comprised shear cracks and fractures,some shaking consolidation settlement and fewer shear strain occurred around the joints.In the direct shear tests,more compression cracks and fractures occurred in the samples.The damage mainly developed along the joints,and shearing-off damage occurred.The results obtained by this study further elucidate the failure mechanism and microscopic damage response of the joints in the loess stratum in Northwest China.

Gustiness and coherent structure under weak wind period in atmospheric boundary layer

Statistical analysis of turbulent and gusty characteristics in the atmospheric boundary layer under weak wind period has been carried out.The data used in the analysis were from the multilevel ultrasonic anemometer-thermometers at 47 m,120 m,and 280 m levels on Beijing 325 m meteorological tower.The time series of 3D atmospheric velocity were analyzed by using conventional Fourier spectral analysis and decompose into three parts:basic mean flow(period > 10 min),gusty disturbances(1 min < period < 10 min)and turbulence fluctuations(period < 1 min).The results show that under weak mean wind condition:1)the gusty disturbances are the most strong fluctuations,contribute about 60% kinetic energy of eddy kinetic energy and 80% downward flux of momentum,although both the eddy kinetic energy and momentum transport are small in comparison with those in strong mean wind condition;2)the gusty wind disturbances are anisotropic;3)the gusty wind disturbances have obviously coherent structure,and their horizontal and vertical component are negatively correlated and make downward transport of momentum more effectively;4)the friction velocities related to turbulence and gusty wind are approximately constant with height in the surface layer.

A theory for the formation of weak double layer

Solitary electrostatic waves with ion acoustic speed were frequently observed by satellites in the auroral acceleration region. In this paper, the nonlinear ion acoustic waves are studied in the plasma which is composed of warm electrons with the Boltzman distribution and cold ions of equal density. The characteristics of solitary-likc structure in the ion acoustic frequency range are derived with the methods of reductive perturbation and phase plane analysis. The results show that nonlinear ion acoustic waves may develop to a symmetric solitary structure which is compressive and no net potential drop when dissipation does not exist, and in the case with dissipation it may evolve to compressive solitary-like structure with asymmetric shape. produce net potential drop and form weak double layer. The above theoretical results are consistent with observations.

Weak Interactions and 2D Layer Structure of a New Ion-pair Complex Bis(1-benzyl-4-methylquinolinium)-bis(maleonitriledithiolato)nickel(Ⅱ)

A new ion-pair complex, [BzMeQ1]2[Ni（nmt）2]1（[BzMeQ1]^＋ = 1-benzyl-4-ntethylquino- linium, mnta- -- maleonitriledithiolate） has been synthesized and structurally characterized by IR, ESI-MS and X-ray diffraction methods. Complex 1 is of triclinic, space group PI, with a = 9.079（2）, b = 10.154（2）, c = 11.243（2）A, α= 81.58（1）, β= 69.63（1）, γ = 68.02（1）°, V= 940.1（3）A3, Dc = 1.427 g/cm^3, Z = 1, F（000） = 418 and R = 0.0442. A 2D layer structure is formed via the cation-cation π…π and C-H…π interactions observed in the solid state of the complex.

Single-borehole measuring method for broken rock zone in gently inclined thin layer weakness structure

According to the structural characteristics of gently inclined thin layer rock mass in which lots of weak interlayer existed,the concept of gently inclined thin layer weakness structure was proposed.If single-borehole measuring method of the acoustic along the conventional arrangement mode was used in measuring the broken rock zone in this structure,the change of the relationship curves (Vp-L) between acoustic p-wave velocity (Vp) and borehole depth (L) would present the irregular feature due to the mechanical characteristics of layered rock mass and harmful effects of weak interlayers,and the scope of broken rock zone couldn't be defined quickly.Based on the analysis of the me- chanical characteristics of layered rock mass,the propagation rule of acoustic and distri- butions characteristics of plastic zone and slip zone in layered rock mass,new arrange- ment mode of acoustic measuring boreholes for broken rock zone in gently inclined thin layer weakness structure was proposed.Namely,the measuring boreholes in two sides were parallel to the strata,the measuring boreholes in the roof and floor perpendicular to the strata.Besides the controlling depth of the measuring boreholes in the scope of the large plastic zones or the large slip zones should be increased.Engineering example showed that new acoustic measuring boreholes arrangement mode had the better appli- cability and could determine the scope of the broken rock zone in the gently inclined thin layer weakness structure quickly.

大跨越架空输电导线铝部应力分布试验

为了掌握大跨越架空输电导线铝部应力空间分布特性,以JLHA1/G6A-500/280型特强钢芯铝合金导线为研究对象,采用铝股丝表面激光刻槽,内嵌高灵敏、超大复用容量超弱光纤光栅,搭建了大跨越输电导线铝部应力试验平台,研究了不同张力条件下大跨越架空输电导线铝部应力分布规律,建立了大跨越导线实体有限元模型,分析了铝股应力分布特征,并验证了试验结果的正确性。结果表明:导线承受张力作用时,外层铝股和次外层铝股应力不同,外层铝股应力小于次外层铝股应力,导线同层铝股应力基本相同;铝股应力随导线张力的增大呈线性增大趋势,张力每增大1%,铝股应力增大约10%。不同导线张力作用时钢股和铝股应力均呈现环状分层特性,铝股平均应力小于钢股平均应力,铝部和钢股应力比约为3∶7;外层和次外层铝合金股丝应力沿圆周向分布不均匀,建议大跨越导线线型设计时考虑铝股丝分层特性。

地震作用下含弱层顺向坡响应规律分析

以抚顺西露天矿南帮含弱层顺向坡作为参考原型,利用FLAC3D软件模拟实际地震动及地震动输入、斜坡模型的边界条件、岩体参数以及网格模型划分,对含弱层顺向坡进行数值模拟计算,通过监测点的加速度和速度探讨含弱层顺向坡在地震作用下的响应规律。研究结果表明:(1)地震作用下对于含单一弱层斜坡响应特征起到决定性的影响因素是弱层的厚度,在地震荷载作用下影响斜坡的稳定程度要大于单一弱层倾角的影响。(2)通过弱层与斜坡坡面的相交部位监测点2#在水平方向速度可以得出,厚度对于X方向的速度大小影响程度较大。(3)对于地震作用下双弱层特性斜坡的响应规律分析时,弱层与斜坡相交部位的破坏响应规律会随着坡高的增大而有所变化,双弱层监测点3#的加速度幅值变化及速度变化程度均比双弱层监测点2#明显。地震作用下顺向坡的响应规律与含有弱层的倾角、厚度和弱层的数量位置有关,在对斜坡的治理与防护的过程中应当充分考虑地震与弱层特性的耦合作用对斜坡稳定性的影响。

打印路径对3D打印混凝土构件力学性能的影响

在3D打印混凝土配合比研究基础上,对打印路径进行了优化设计。采用三种路径打印成型构件,评估了打印路径对3D打印混凝土构件力学性能的影响,并分析了打印构件的力学各向异性,提出了力学各向异性系数,确定了最佳受力方向。此外,通过SEM分析了打印构件的层间界面对力学性能的影响。结果表明:3D打印混凝土构件在Z方向受力最大,打印路径优化后,可有效改善层间薄弱面;打印构件在层间界面处的水化产物未能充分填充,存在空隙、气泡、裂缝等缺陷,使打印构件的力学性能降低。

长期运行引水隧洞开裂衬砌受力影响规律与承载特性

衬砌裂缝是引水隧洞中常见的病害之一,衬砌开裂会对隧洞衬砌承载力和安全性造成不同程度的影响。以长期服役的东江水源工程引水隧洞衬砌为研究对象,通过现场检测确定了全洞段裂缝的产状、分布规律和开裂特征。利用ANSYS软件中的软弱薄层单元,建立了开裂衬砌的三维数值模型,得出贯穿型纵向裂缝的位置变化对衬砌结构安全性的影响,系统分析了衬砌的承载特性。结果表明,衬砌开裂条件下,衬砌结构局部开裂区的安全系数降低最为显著,尤其是拱肩位置的裂缝对结构的危害程度远大于边墙、拱顶裂缝;另外,裂缝的产生会对其他未开裂部位的受力特性及稳定性产生影响。数值模拟结果良好地体现了裂损衬砌对隧洞结构的影响规律,与现场检测结果一致,为长期服役下隧洞结构病害防治提供了参考。

冲击荷载下层状饱和无粘性土动孔压发展模式研究

为揭示饱和无黏性土层在冲击荷载作用下动孔压发展模式及其受土层条件的影响,基于自主研制的冲击荷载加载台装置,开展了不同土层条件层状饱和土冲击试验,对动孔压发展特征及土体沉降等进行了分析。结果表明:冲击荷载作用下,无粘性饱和土体动孔压发展呈明显两阶段,即瞬态响应和稳态响应阶段,其中稳态响应阶段动孔压发展又经历缓慢下降及快速下降两过程。单层土情形下,饱和砂土在冲击荷载后动孔压发生骤增,随着粒径的增大,动孔压峰值越大,但其消散用时则随粒径的增大而减小;双层土情形下,动孔压稳态响应阶段因上下土层渗透系数变化,在其下层土动孔压下降过程产生明显变化;当含有相对弱透水夹层时,受弱透水层影响,各测点动孔压下降段几乎在同一时刻均出现明显转折平台,使其下降的速率明显变小,且该现象弱透水层以上土体较其下部土体更为显著;含夹层时,试验过程出现明显非均匀分布的“水膜”,最大厚度可达2 cm左右。同时,每次冲击荷载下均伴随明显的土体沉降,随着冲击次数增加,土层沉降变化量逐渐减小。

基于弹性薄板理论的大南湖矿区弱胶结覆岩离层动态演化规律研究

以大南湖7#矿井为研究区,基于组合梁原理和弹性薄板理论对工作面离层发育位置进行预计,通过计算离层上下岩层组的挠度差,计算了离层的体积和破断距,利用GDEM模拟软件对工作面离层动态发育过程进行模拟。结果表明,离层发育于3煤顶板泥岩与上部厚层粗砂岩之间。依据薄板弹性理论,离层的最大挠度差约为721 mm,离层的体积约为297 m^(3),离层的位置随着工作面不断移动,并在工作面推进320 m左右的位置闭合,产生水害的可能性较小。

含软弱夹层凝灰岩滑坡稳定性计算——以松阳县呈田滑坡为例

含软弱夹层凝灰岩边坡受降雨影响诱发的滑坡一直是浙江省内公路边坡防治的主要对象。为进一步理解不同软弱夹层强度弱化模式对滑坡稳定性的影响,选取典型凝灰岩滑坡——浙江省松阳县呈田滑坡,采用Midas GTS NX有限元软件的强度折减法进行不同降雨条件下的滑坡变形分析,同时引入软弱夹层强度“S”型曲线弱化模型,并优化考虑裂隙水压和渗流力的耦合模型,对比讨论滑坡的稳定系数演化特征。结果表明,滑坡的变形迹象与数值模拟结果得到相互印证,随着降雨持续,变形带由后缘夹层不断向前缘演化扩展;强降雨导致富含黏土矿物的软弱夹层强度弱化是该滑坡失稳的主要原因。通过对比不同方式计算的边坡稳定系数,采用考虑软弱夹层强度“S”型曲线弱化模型计算的滑坡稳定系数随着后缘裂隙水头高度和结构面强度软化阶段表征参数(λL)的增加而快速减小,突出了滑坡变形失稳演化的时间效应,其更适用于滑坡风险评价工作;而采用极限平衡法计算的滑坡稳定系数,突出了计算结果的唯一性,适合于以安全为前提条件的滑坡抢险的风险决策。

多弱层顺倾软岩边坡控制开采技术

针对多弱层顺倾软岩边坡下部压煤问题,从边坡变形风险可控以及资源回收最大化角度出发,在分析地质资料和弱层层位的基础上,结合单一弱层的控制开采技术,提出了多弱层顺倾软岩边坡控制开采技术;以扎尼河露天矿北端帮边坡为工程背景,基于极限平衡理论,分析了北端帮边坡的稳定性,对多弱层控制的顺倾软岩边坡控制开采方案进行了研究。研究表明:通过多弱层顺倾软岩边坡控制开采技术的实施,可在采场深部增加内排物料形成“中间桥”工艺,对深部弱层形成“压覆”,对整体边坡形成“支撑”,保证边坡沿各弱层滑动均得以控制,实现多弱层顺倾软岩边坡煤炭高效回收以及蠕动形变的稳定性控制。

Persistent mixing bursts in the equatorial Pacific thermocline induced by persistent equatorial waves

A recent study by Liu et al.(2020)suggested that due to the saturation of equatorially trapped planetary waves with different dynamical types,temporal periods,meridional and baroclinic modes,complex layer structures of vertical velocity shear and hence turbulent mixing could frequently occur in the thermocline of the eastern equatorial Pacific.We investigated the occurrence of the interior turbulent mixing as indicated by shear instabilities,above the Equatorial Undercurrent(EUC)core at three equatorial sites along 140°W,170°W,and 165°E,respectively,based mainly on data from the Tropical Atmosphere and Ocean(TAO)mooring array.We found that turbulent mixing bursts persisted in the thermocline of all three sites.Specifically,the interior turbulent mixing layers(ITMLs)could occur in probability of approximately 68%,53%,and 48%at the three sites,respectively.The overall occurrence probability shows obvious and similar biannual variations at 140°W and 170°W,which is higher in boreal from late summer to winter and lower in spring.Vertically,the ITMLs are primarily located above the EUC core and prevail in deeper(shallower)layers from late summer to winter(spring).Most ITMLs(70%)lasted for hours to 3 days,and a few of them(15%)for more than 7 days.The thicknesses of ITMLs were concentrated between 15 and 55 m.At 165°E,the vertical distribution of ITML occurrence probability was different from that at 140°W and 170°W,as it did not show a preference for depths;the durations of ITMLs are short(also from hours to several days)and their thicknesses were between 5 and 25 m.These properties,particularly the high occurrence probability,and short durations demonstrated the persistence of thermocline mixing in the western to eastern equatorial Pacific thermocline and confirmed the generation mechanism by persistent equatorial waves as well.

邻洞爆破下软弱夹层对洞库稳定性的影响研究

为了研究邻洞爆破下软弱夹层对压气储能洞库稳定性的影响,基于弹塑性损伤理论框架,采用COMSOL Multiphysics数值仿真,将储气过程视为静态过程,考虑了岩石的塑性变形机制和刚度退化,通过对等效塑性应变表征岩石损伤变量的演化研究,分析夹层厚度、倾角和位置对内衬洞室稳定性的影响。结果表明:①随着夹层厚度的增加,靠近夹层部分的衬砌塑性应变增量增加,且最靠近夹层处受夹层影响最大。②夹层倾角从30°增加至90°过程中,会增加洞室左侧塑性变形,当夹层倾角小于45°时,倾角改变对质点峰值摇动速度PPV最大值影响较小,而当夹层倾角大于45°后,PPV最大值随夹角增加显著增大。③夹层距离洞室边界小于0.2 r时,距离的增加使最靠近夹层处衬砌最大塑性应变增量显著下降;间距大于0.2 r时,最大塑性应变增量随间距增加的变化较小,对稳定性影响相对较小。研究成果可以为压缩空气储能洞库的设计和施工提供参考。

车轴钢渗碳层深度弱磁检测技术研究

针对现有车轴钢渗碳层深度无损检测技术的工程局限性,提出一种弱磁检测方法,即利用渗碳层与其心部交界处应力集中且无法消除、进而对外表现出特定的磁感应强度的无损检测方法。通过采集不同样本车轴钢及其不同部位的磁场信号,分析磁感应强度幅值与深度的对应关系,构建弱磁检测数学模型。试验结果(标准厚度/检测厚度/绝对误差):花键外圆3.50 mm/3.57 mm/0.07 mm、杆部外圆4.30 mm/4.46 mm/0.16 mm、R角4.00 mm/3.86 mm/-0.14 mm,检测精度整体相对误差小于5%,满足工厂实际检测需求。

考虑土工复合材料衬垫系统的尾矿库稳定性分析

尾矿库库底铺膜层构成的土工复合材料衬垫系统往往形成薄弱层面威胁坝体的稳定性,在分析中需要重点关注。文章基于水工分析系统Autobank对铺膜面形成的衬垫薄弱层进行标记,在最危险滑动面的搜索中若搜索圆弧与衬垫薄弱层相交,则增加考虑该薄弱层与部分圆弧构成的复合滑动面,计算方法采用适用各种形状滑面的摩根斯顿法,以得到库身的最小抗滑稳定安全系数。算例分析结果表明:部分通过土工衬垫薄弱层的复合滑动面安全系数较小,且该平移滑动是完全可能发生的,为该剖面的最危险滑动面。本文结果可为尾矿库设计和运行提供科学依据,并为同类工程提供参考。