在平面波的作用下地下洞室的振动加速度分布规律研究

利用模型试验和理论研究了在平面应力波的作用下,地下洞室振动加速度分布规律.结果表明:当洞室受到拱顶正上方平面波作用时,拱顶径向振动加速度是4个测量数据中最大的,是振动最激烈的地方;当入射方向从拱顶向左侧偏移至水平方向,迎爆侧的径向加速度都比背爆侧的径向加速度大;当入射方向在拱顶时,切向振动加速度从拱顶至侧墙是先增加后减小,入射方向在拱腰处,拐角的切向振动加速度应该注意;对比洞室的径向加速度和切向振动加速度,洞室的振动加速度允许峰值是由径向加速度控制.这将对实际工程进行抗爆设计非常有意义.     

小净距隧道后行洞爆破对先行洞的振动影响分析

为分析后行洞爆破施工时对先行洞造成的影响,依托蒙古道隧道工程并以大断面小净距隧道为研究对象,进行有限元数值模拟。结合现场测试对现场爆破后振动测试信号进行HHT分析,确定了爆破振动影响信号的时频特征。研究表明：当后行洞在进行爆破施工时,先行洞初期支护的垂直振动速度和切向振动速度都明显的小于径向振动速度;后行洞迎爆侧的径向振动速度明显大于背爆侧,后行洞爆破的最大振动速度相对应的频率主要集中在20～80 Hz之间。受后行洞爆破影响,小净距隧道的先行洞迎爆一侧的拱脚处出现拉应力易导致隧道衬砌出现拉伸破坏,建议在该部位进行喷射钢纤维混凝土等措施进行加强。     

小近距隧道扩挖爆破作用下邻洞振动响应研究

在小近距隧道扩挖工程中,隧道爆破引起邻洞振动,对既有隧道结构稳定性造成较大影响。为研究爆破作用下邻洞隧道振动响应特征,依托浙江省温岭市楼山隧道扩挖工程,采用现场振动测试试验和数值模拟方法,研究爆破作用下邻洞隧道振动特征及衰减规律,并对比了爆破隧道与邻洞隧道振动响应差异性。结果表明:爆破掏槽段炸药引起的隧道振动最大。在爆破近区,隧道扩挖爆破对邻洞隧道振动响应的影响更大。邻洞隧道的迎爆侧离爆源近,隧道振动强度大;既有隧道空间对振动衰减作用较大,背爆侧的振动强度相对较小。     

爆破应力波对邻近圆形隧道的动力扰动特征

开挖爆破产生的地震波会诱发邻近隧道的动力响应,威胁邻近地下结构的稳定性。针对爆破应力波引起邻近隧道的质点振动和动应力集中效应,采用数值模拟方法,分析了爆破地震波中的P波对邻近圆形隧道的动力扰动特征。计算结果表明,应力波通过圆洞时,围岩中的主应力方向和动应力集中系数分布形态均与等效静态加载时相似,附加的动应力仅对圆洞洞壁附近围岩的主应力量值产生影响,而对洞壁以外围岩的主应力量值和主应力方向都将产生影响。其次,应力波通过圆洞时还将诱发振动速度集中现象,围岩质点的振动方向与波的传播方向总体一致,其振速集中系数与动应力集中系数的分布特征不同,且其最大值点位置相差约90°,这表明质点振动速度最大的位置并非动应力集中系数最大的位置。另外,圆洞洞壁最大振速集中系数随正则化波数的增加而增大,而最大动应力集中系数随正则化波数的增加而先增大后减小。     

钢管混凝土单圆管拱模型重力失真影响振动台试验研究

为了研究重力失真对振动台试验相似模型地震响应的影响,基于人工质量的混合模型相似理论,以缩尺比为1:10的钢管混凝土单圆管拱结构为试验模型,通过设置5种不同人工质量为重力失真度参数,采用5种不同时间压缩比的地震波及人工波,进行了纵向、横向地震模拟振动台试验。试验结果表明:重力失真对拱结构模型第一阶频率相似的影响显著,重力失真度越大,模型第一阶频率相似系数试验值和理论值之间的误差也越大;输入波的频率比较小时,重力失真度越小的模型加速度响应越大,加速度峰值时间越延后;重力失真度和输入波的频率比对模型横向（Y向）加速度响应的影响要大于纵向（X向）的影响;通过调整模型配重及输入波的频率比,可减小模型的重力失真对加速度响应的影响。     

爆破动力作用下小净距隧道围岩振动效应分析

以渝长高速公路武隆小净距隧道掘进爆破为背景,应用FLAC3D数值模拟法进行隧道掘进爆破条件下的前洞围岩振动效应分析.通过计算结果与试验数据的对比分析,证明了应用此计算方法进行振动强度分析的可行性.进一步分析表明,全断面不同循环进尺爆破方案引起振动速度的分布规律基本相同;在爆破掌子面前,前洞迎爆侧边墙上的最大振动速度沿隧道轴线方向随水平距离增大有明显的放大现象,最大振动速度发生在爆破掌子面前面10 m左右前洞断面迎爆侧的边墙上;在爆区附近,前洞迎爆侧围岩上的振动速度是背爆侧的6-10倍.     

爆破地震波作用下圆形洞室围岩振动速度分布规律

为了探究岩石开挖爆破地震波作用下邻近圆形洞室的动力响应规律,采用FLAC3D数值模拟软件研究爆破地震波作用下不同埋深圆形隧道洞壁和地表振动速度的缩放规律,以及对不同频率平面简谐P波入射时,隧道洞壁及地表振动速度的分布规律进行研究,并通过理论计算结果的对比分析,检验了数值模拟的可靠性。研究结果表明:隧道埋深会引起隧道洞壁及地表振动速度产生缩放效应:隧道埋深较浅时,隧道洞壁上半部分缩放效应大于下半部分,振动速度放大系数随埋深增加而减小;埋深较深时时,隧道洞壁各位置质点振动速度放大效应随埋深的增加呈现递增规律;地表振动速度放大系数峰值随隧道埋深的增加向背爆侧偏移;迎爆侧洞壁振动速度随入射波频率增加呈增大趋势;地表振动速度放大系数峰值随入射波频率增加向爆源方向偏移。     

爆炸载荷作用下临界震塌爆距公式研究

坑道震塌破坏机制复杂,是工程中亟待解决的难题之一。为了得到便于工程应用的临界震塌爆距计算公式以及影响临界震塌爆距的主要因素,在常用经验公式的基础上,通过拟合爆距与洞跨比影响系数,将经验公式显化,推导的修正公式不需要反复迭代试算,使用方便。利用ANSYS/LS-DYNA有限元分析软件对坑道正上方装药爆炸进行数值模拟,得出临界震塌爆距,其结果与修正公式相比较,表明修正公式与模拟结果吻合较好,可用于临界震塌爆距的计算。数值模拟临界震塌爆距随洞室跨度的变化,结果表明:洞室跨度越大,临界震塌爆距越大,且趋于某一极限值;洞室跨度小于15 m时临界震塌爆距随洞跨的增大增幅较快。     

深部岩体中切槽爆破机理实验分析

深部岩体爆破致裂是初始应力场和爆炸动态载荷叠加作用结果,采用动静组合加载试验装置和焦散线实验系统,在PMMA模型试件中施加初始静态应力场和爆炸动态载荷,探讨炮孔切槽与水平方向成不同角度(0°,45°和90°)下,初始应力场对爆生裂纹扩展规律的影响效应。实验结果表明:①初始压应力场中,切槽孔的存在改变了圆形炮孔周边应力集中;②0°角时,初始应力场降低了裂纹尖端应力集中,抑制裂纹的扩展,且应力越大,抑制效应越明显,但不改变爆生裂纹的扩展方向;③45°角时,初始应力场改变了裂纹扩展模式,由Ⅰ型断裂向混合型转变,随着应力越大,Ⅱ型断裂越明显,且裂纹向最大主应力方向偏转;④90°角时,初始应力场提高了裂纹尖端应力集中,促进裂纹的扩展,且应力越大,促进效应越明显,不改变爆生裂纹的扩展方向。研究结果为深部岩体中开展切槽爆破技术提供理论指导。     

减震沟对爆炸塔内空爆振动减震效果试验研究

为研究减震沟对爆炸塔内炸药空爆振动的减震效果,设计不同药量和药包悬置高度的3组、7次爆炸振动试验。结果表明:无减震沟时,地表振动速度表现为垂向径向切向,地表振动频率符合振动在岩土介质的传播规律;减震沟对水平方向的减震效果约为垂直方向的2倍;在减震沟附近存在振动分区和垂向振动滞后现象,在振速增大的区域内存在有减震沟时振速大于无减震沟时,振动频率随距离的增加先增大后减小。减震沟的减震效果受药量影响大于药包悬置高度的影响(药量越大减震效果越明显);对振速进行回归拟合时,有减震沟时地表振动衰减系数K和衰减指数α约为无减震沟时的1/10和1/2,减震沟外侧拟合优度约为0.65,表明萨道夫斯基公式回归拟合仅适用无减震沟侧,不适合有减震沟侧。     

邻桩爆破引发井巷支护结构破坏的分析及防范措施

在分析邻桩爆破时岩柱、支护结构破坏类型的基础上 ,根据应力波叠加和入射空穴而散射的动应力集中原理 ,建立了圆形井巷周边切向动应力集中的力学模型。利用该模型和波函数解法 ,计算了井巷相邻侧爆破引起的周边最大应力 ,推荐了能保持岩柱稳定、围岩—支护结构抗塌、抗裂的邻桩间距。在施工中 ,根据不同桩径、围岩性质 ,采取不耦合装药、调整单响药量和岩柱宽度等措施 ,确保了工程质量和安全。     

Inertia-induced radial confinement in an elastic tubular specimen subjected to axial strain acceleration

This paper extends the study in [10] on the stress state in an elastic solid specimen subjected to axial strain acceleration to a tubular cylindrical specimen. A perturbation solution is presented, based on which, it is found that the radial confinement stress induced by the compressive axial strain acceleration decreases with the increase of the inner radius of the tubular specimen. It is shown that the radial stress distribution predicted by perturbation solution can be used to estimate the distribution of the maximum radial stress in tubular specimen. The solutions presented in this paper can be used to estimate the radial confinement stress and additional axial stress due to the existence of axial strain acceleration in split Hopkinson pressure bar tests of brittle materials using tubular specimens.     

圆柱壳非圆大开孔的应力集中研究

本文以薄圆柱壳大开孔应力集中问题的理论解为基础,利用保角映射方法对圆柱壳非圆大开孔的应力集中问题进行研究。在给出映射函数的基础上,对承受不同外部载荷下开椭圆大孔圆柱壳孔边应力集中系数进行了数值计算,并与相应的圆柱壳小开孔理论解进行了比较。结果表明：大开孔解答更具有合理性。     

Exploding pressure vessel test on zylon/epoxy composite

The efficiency of zylon/epoxy composites under radial load for the reinforcement of high-field magnet coils is studied using the exploding pressure vessel technique. Under the combined stresses in tangential and radial directions, the behaviour of zylon/epoxy composite is well described by the theory of orthotropic cylindrical shells when the pre-stress effects are considered. The ultimate tensile strength of the zylon/epoxy shell with a fibre-filling factor of 90% is found to be 4.8 GPa. The bursting pressure (maximal radial stress) is, for a given filling factor, a monotonically increasing function of the ratio of the shell thickness to inner radius. The beneficial effects of the pre-stress during winding on the reinforcement are discussed.     

Analysis of the energy and damage evolution rule for sandstone based on the particle flow method

We use the particle flow code PFC3D to simulate the triaxial compression of sandstone under various radial stresses and loading strain rates to determine the triaxial stress-strain curves, crack propagation path, and contact forces to investigate the failure process of sandstone. We analyze the energy and damage evolution during triaxial compression. The results indicate that the tension and shear-induced cracks increase with the increase of radial stress under the same loading strain rate. Both normal and tangential contact forces exhibit strong anisotropy and increase with radial stress and strain rate. The normal contact force has an approximately symmetrical distribution with respect to the horizontal plane, whereas the tangential contact force has an approximately symmetrical distribution with respect to the axis. For the characteristics of the energy evolution, the boundary energy density, strain energy density, and dissipated energy density all increase linearly with the radial stress, and the boundary energy density increases at the fastest rate, followed by the strain energy density and dissipated energy density. In the post-peak stage the primary energy consumption is the dissipated energy. After that, in the remaining stage the strain energy decreases gradually. By analyzing the evolution of the damage variables in the prepeak area we observed that the damage variable followed an exponential relationship with the axial strain. When the loading strain rate is constant, the damage variable corresponding to the same strain value decreases with increase of radial stress. The results indicate that the increase in radial stress delays the damage acceleration. In contrast, the effect of the loading strain rate on the damage variable is small. The findings reveal the internal structural evolution of rocks during deformation and failure.

     

Investigating Creep Performance and Predicting Rupture Time for Rotating FGM Disc under Different Thermal Gradients

A mathematical model is developed to describe the steady state creep in a rotating Al-SiC_p disc having a non-linear thickness profile and distribution of SiC particles along the radial direction. The model is used to investigate the effect of imposing three different kinds of radial temperature profiles viz. linear, parabolic and exponential with fixed values of inner and outer surface temperatures, on the creep stresses and strain rates. It is noticed that by increasing the temperature exponent (n_T), the radial stress (over the entire radius) and tangential stress (near the inner radius) increase in the disc. However, the tangential stress decreases near the outer radius. The radial and tangential strain rates in the functionally graded (FG) disc reduce significantly with the increase in exponent n_T. Besides reduction in the magnitude, the distribution of strain rates also become relatively more uniform throughout with the increase in n_T. It is concluded that FG disc operating under exponential temperature profile performs better. It is also revealed that amongst several FG discs operating under radial thermal gradients, with different values of temperature exponent (n_T) but having the same average and fixed outer surface temperature, the FGM disc with lower value of n_T exhibits the maximum creep life.     

中应变率加载下云杉各向异性力学行为研究

采用高速加载INSTRON设备对云杉开展100 s-1~102 s-1中应变率压缩实验,研究了材料沿顺纹、横纹径向、弦向、以及径(弦)切面内与顺纹呈15°、30°、45°、60°和75°夹角方向的力学性能。实验表明随着加载方向由顺纹向横纹径(弦)向变化,材料屈服强度逐渐减小,应力-应变曲线塑性流动段由"塑性软化"向"塑性硬化"转变;试件沿不同方向压缩屈服强度表现出较强应变率敏感性。冲击压缩下云杉宏观破坏模式与加载方向相关,沿顺纹方向加载时,试件中部向外膨胀,产生褶皱、纤维屈曲折断;当载荷方向与顺纹夹角逐渐增大时,材料失效模式体现为木材纤维分层滑移、撕裂。采用简化Hill强度理论对中低应变率下云杉空间屈服行为进行了理论描述,不同应变率下云杉空间屈服面为椭圆柱曲面,屈服曲面半径长度随应变率提高而增加。实验与理论分析表明,云杉沿空间不同方向具有各向异性力学特性,屈服强度受应变率和加载方向影响较大,而破坏模式则主要依赖于载荷方向。     

一类非均布荷载作用下双层厚壁圆筒光滑接触时的应力解析解

采用复变函数方法,给出了双层厚壁圆筒外壁受有一类两向不等压非均布径向压力,内壁受有均布压力作用时平面问题的应力求解方法。在两层圆筒光滑接触的假定下,获得双层厚壁圆筒的应力解析解。通过算例分析了不同弹性模量组合时圆筒内不同截面的切向应力与径向应力分布规律,研究结果表明:当内壁均布压力较小时,两层圆筒的内壁处切向应力沿环向均呈余弦分布,且都在内壁的最小地应力方向承受最大压应力,在最大地应力方向承受最大拉应力;径向应力沿径向在圆筒0#x000b0;、45#x000b0;、90#x000b0;截面处分别呈近似#x0201c;M#x0201d;状、#x0201c;菱形#x0201d;、#x0201c;W#x0201d;状分布;随着内外层弹性模量比值的增大,内层圆筒内壁附近切向应力增大,径向应力在最小地应力方向增大,在最大地应力方向减小,而在外层筒分布规律相反。采用内软外硬的弹性模量组合,能有效的减小圆筒内层内壁处的应力集中程度。     

Differences in wood material responses for radial and tangential direction as measured by dynamic mechanical thermal analysis

Wood is a complex cellular structure with different properties in the radial and tangential direction. Many researchers have measured dynamic properties in the longitudinal direction and a few in the radial direction but very little data can be found in the literature on dynamic mechanical properties in the tangential direction. The purpose of the work presented in this paper was to investigate the dynamic mechanical behaviour in the radial and tangential directions of wood (Pinus sylvestris). Testing was done in tension at 1 Hz with a Dynamic Mechanical Thermal Analyser. Properties in radial and tangential direction were different. The radial direction showed a higher elastic modulus and lower loss factor levels at temperatures between –120°C and 80°C. The tangential direction had on average a higher peak temperature than the radial direction for a loss factor peak around –80°C. It is the opposite of synthetic composites where the stiffer direction has a higher peak temperature. A loss factor peak at around 0°C was seen, most significantly in the tangential direction. This peak has scarcely been reported in the literature before. The distance between annual rings did not significantly affect the dynamic behaviour in the tangential direction.     

地下双洞室在SV波入射下动力响应问题解析解

采用波函数展开法给出了地下双洞室在平面SV波入射下动力响应二维问题的一个解析解，数值结果表明：当两个洞室之间距离较近时，洞室之间的相互作用对地下双洞室的动应力集中具有显著的放大作用，两个洞室情况动应力集中系数可能达到单个洞室的5．2倍以上，动应力集中系数的峰值位于两个洞室相对的区域内。