隧道掘进爆破振动对地表影响的小波包分析

基于现场实测隧道掘进爆破振动信号数据,采用小波包分析技术对振动信号进行小波包能量谱分析,得到爆破振动信号能量在各频带上的分布。通过比较各点分析结果可以发现隧道掘进爆破地震波能量主要集中在切向与径向。在沿隧道掘进方向随着与掌子面之间距离的增大地震波的主频下降,能量主要集中频带也越来越窄,并且向低频带发展;而在垂向上地震波主频随着埋深的减小而减小,同时地震波的能量主要集中频带也越来越窄并且向低频带发展。最后从能量的角度探讨隧道掘进爆破地震波沿各个方向的衰减规律。     

沉底水雷爆炸威力的数值计算

采用冲击波物理中的阻抗匹配镜像线方法处理物质交界面,利用无网格光滑粒子流体动力学法(smoothed particle hydrodynamics,SPH)方法模拟沉底装药的水下爆炸过程,得到了不同方向不同爆距处的峰值压力反射系数,分析了爆炸流场参量分布和变化规律,研究了不同水底砂层厚度和不同装药量对爆炸冲击波传播和流...     

Torque reduction during the excavation of dense cohesionless soils

In this paper, water jet has been used to achieve a reduction in the magnitude of the excavation torque, also known as the torsional resistance, imparted on the cutting wing of an excavation machine during rotational excavation of cohesionless soils. This was accomplished by injecting a controlled water jet along the front plane of the cutting wing during the excavation of a model sandy ground. Experimental excavation was performed on compacted completely saturated sand samples using a prototype excavation machine and the torque required for excavation was measured. Within the experimental limitations, the results showed that water jet could successfully be used to reduce torque during excavation of dense sandy soils.     

隧洞开挖爆破地震反应谱特征研究

利用地震工程中应用比较成熟的反应谱理论对隧洞开挖爆破地震进行研究。针对反应谱计算中必须输入加速度数据的问题,对实测爆破振动速度数据进行数值微分计算,并采用小波分析方法消噪得到准确、清晰的加速度时程曲线,继而将其用于反应谱计算。结合不同工程中大量的爆破振动监测资料,对隧洞开挖爆破地震反应谱进行分析。结果表明:隧洞开挖爆破地震反应谱都有一些共同的特征,反应谱曲线一般存在一个明显的峰值点,峰值对应的周期集中在几毫秒到几十毫秒的区间内。另外,在归纳、整理大量地下工程开挖爆破地震反应谱的基础上,得到了隧洞开挖爆破地震的设计反应谱。     

考虑固结的基坑开挖回弹问题有限层求解

在综述前人有关基坑变形研究成果的基础上,指出开挖回弹量直接影响到基坑的稳定性和建筑物的后期沉降,但相关研究很少考虑土体在开挖过程中的固结影响.现引入固结有限层法,通过增加开挖部分的耦合矩阵和开挖部分的渗透矩阵,建立三维横观各向同性土体考虑固结的开挖回弹问题的有限层求解格式,并编制了相应的计算程序,以分析开挖过程中坑底土体的动态固结过程和负孔压的消散规律,研究固结对坑底土体回弹的影响程度.结果表明坑底土体的孔压随时间逐步消散,从负孔压慢慢消散到零,且符合Mandel-Cryer效应,坑底的回弹量随时间不断增加,且中心点回弹量较大,边缘点回弹量相对较小,总体成中心对称的倒锅底形.     

Assessment of the displacement field along a surface crack in a flat plate using optical techniques

Experimental Techniques - Structural components may contain cracks, and for these components a crack tip represents a highly singular stress. The evaluation of the associated strain gradient is...     

Effect of bucket-wheel scale on excavation forces and soil motion

Bucket-wheels enable planetary rovers to perform lightweight digging operations in support of sustained space exploration. Using an excavation tool whose performance scales well for robots of varying sizes builds confidence in a wide range of future digging missions, much as scaled versions of the rocker-bogie suspension have enabled mobility for Mars rovers of vastly different sizes. Bucket-wheel excavation force increases approximately with the cube of excavation dimensions. The excavation forces were measured for bucket-wheels of different scales at proportionate depths and advance speeds, and these results were compared to predictions by excavation models. Analytical and empirical investigated models exhibit force scaling tendency similar to experiment despite their independent backgrounds. Soil particle motion imaging shows that a curved shear interface is prevalent for the conditions tested. This agrees with literature and allows the application of analytical models.     

Developing an excavation torque model for dense cohesionless soils

Torque encountered during the rotary excavation of soils (e.g., when using the DJM method for deep soft ground improvement) poses a serious detrimental effect not only to the excavating machines but also to the viability of a project as a whole. Consequently, this research investigates ways and means of realizing the reduction of torque encountered during the excavation of cohesionless soils. In this paper, the development of a torque model for a rotary excavation of cohesionless soils is proposed. Whereas in most of the soil tillage theories (i) the cutting tool is usually partially exposed at the surface, and (ii) excavation is generally longitudinal, this model is significant because; (i) the excavation process is radial, and (ii) the blade is completely immersed in the excavated medium. Various theories for the prediction of forces acting during the interaction of cutting tools and soils in conjunction with localized modeling of all the other forces, applied and adopted to suit this excavation geometry, have been applied in the development of the torque model. Experimental data was obtained from excavation experiments performed on compacted completely saturated sand samples. Within the experimental and theoretical limitations, the results showed that this model represented the excavation process.     

Method and apparatus for on-line estimation of soil parameters during excavation

Time-varying forces from soil–machine interactions cause stresses in the components of earthmoving machinery, which may cause damage to the machine. It is not always possible to know all the characteristics of a soil sample prior to excavation; however, by estimating necessary soil parameters, it is possible to predict the soil–machine interaction forces in a practical manner. This article presents the development of a simple apparatus and method for estimating the soil parameters from the cutting force measured by the novel bench-scale excavating tool, validation of the soil model, and comparison with other available techniques. The apparatus used to collect data of soil forces on a tool consists of an instrumented crank-slider mechanism equipped with a thin plate to fragment the soil, which is contained in a sample box. Using the Mohr-Coulomb earth pressure model to predict failure force during the interaction, two methods are used to minimize the error between the predicted and measured failure force, that allows to estimate soil parameters: First, the Newton–Raphson Method (NRM) is used to minimize the error, which allows estimation of two soil parameters (interface friction angles) on non-cohesive soil samples. Additionally, a new estimation scheme based on the NRM is presented, that uses an auxiliary equation, and allows estimation of up to three soil parameters, including interface friction angles and cohesion. Comparing the results obtained from the presented apparatus, it is confirmed that the friction angles are successfully estimated for two non-cohesive particulate materials. Additionally, it is shown that the new scheme demonstrates smaller error in estimating soil parameters for cohesive and non-cohesive soil samples than previously reported methods. The parameter estimation method is subsequently applied to determine the properties of highly cohesive oil sand, and delivers promising results.     

地应力对爆破过程中围岩振动能量分布的影响

对高地应力条件下隧洞爆破开挖过程中围岩振动信号进行小波包分析,得到了振动信号不同频带上的能量分布。实测资料分析结果表明,爆破开挖时,初始地应力动态卸载诱发的围岩振动的频率范围和爆破荷载诱发的围岩振动频率范围基本相同,但地应力卸载诱发的振动中,低频能量占较大的比例;开挖面上的卸载应力值的大小和卸载面的大小共同决定卸载效应的强弱,而这两个因素均与开挖面上的炮孔布置和起爆网络的连接有关。     

地铁隧道毫秒延时爆破环境振动特性研究

基于地铁隧道毫秒延时爆破环境振动特性现场试验,考虑爆破荷载的不规则特性,采用基于非对称加卸载准则的修正Davidenkov本构模型描述场地土体的动力非线性特性;通过改进Friedlander方程来模拟内源爆炸在圆柱形炮孔表面产生的瞬态空气冲击波;实现了包含毫秒延时爆破荷载输入和有限元-无限元耦合边界的地层-爆源体系三维精细化有限元模型,并与现场实测数据对比验证了该模型方法的有效性。对50 ms延时爆破和齐爆引起的环境振动特性进行了数值模拟,对比发现毫秒延时爆破不仅可以有效降低地表峰值振速,而且可以显著改变地表振动的频谱特性。毫秒延时爆破产生的地表振动频带较集中,对分散爆破振动能量的作用显著,且地表速度响应的主频较高,远离建筑结构自振频率,可显著降低爆破施工引起的邻近建筑物的结构振动水平。

     

爆破开挖振动下既有大型储油罐的动力响应

针对既有大型储油罐近区基础爆破开挖中的安全问题,采用ANSYS/LS-DYNA的隐式-显式顺序求解方法,结合流固耦合算法,研究了爆破振动下大型储油罐的动力响应规律。分析了罐壁不同位置的质点振速,由于质点振速分布情况较为复杂,不宜用局部质点振速判断罐壁危险点;总结了罐壁上应力的分布规律,结果显示爆破振动对储油罐的影响主要集中在迎爆侧下部,且在罐壁迎爆侧高度为3 m左右的位置最易发生象足屈曲;分析了不同频率爆破振动作用下满载储罐罐壁的质点振速,结果表明在爆破振动主频范围内,载荷频率远大于储罐固有频率条件下,罐壁上质点振速随着爆破振动频率的降低呈减小趋势;建立了储油罐罐壁质点振速与罐内液面高度的关系,结果表明降低液面高度可以有效提高储油罐的爆破振动安全阈值,爆破施工中邻近储罐储液高度不宜高于10 m。     

Fracture of the hanging wall of an excavation adjacent to a decline fault

Summary This paper presents the mathermatical modelling of a real rock mechanics problem concerning mining in the neighbourhood of the fault. The excavation starts at the fault surface and is carried out in the direction to the interior of the region.

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Bruch der überhängenden Wand beim Abbau in der Nähe von schrägen Verwerfungen

Übersicht Diese Arbeit stellt das mathematische Modell eines realen Problems der Felsmechanik vor, bei dem der Abbau in der Nähe von Verwerfungen erfolgt. Der Abbau beginnt an der Oberfläche der Verwerfung und wird in das Innere der Verwerfungszone weitergeführt.

     

Analytical study on long wave refraction over a dredge excavation pit

An analytical solution of the mild-slope wave equation is derived to describe long wave propagating over the idealized dredge excavation pit. The pit is assumed to be axisymmetrical and composed of a flat bottom and a convex slope. The convex slope is expressed by a simple power function. The problem is solved in the polar coordination system by the separation of variables. By the obtained solution, the characteristics of the wave refraction and reflection over the dredge excavation pit are discussed. The results show that wave amplitude is attenuated within and in the lee side of the pit and amplified at the rear flank of the pit due to wave refraction. The effects of the incident wave length and the shape of the pit on wave refraction are also discussed.