Numerical simulation of attenuation and group velocity of guided ultrasonic wave in grouted rock bolts

In this paper, the guided ultrasonic wave propagating in grouted rock bolts was simulated with finite element method. An 800 mm partially grouted cylindrical rock bolt model was created. Dynamic input signals with frequency from 25 to 100 kHz were used to excite ultrasonic wave. The simulated waveform, group velocity and amplitude ratio matched well with the experimental results. This model made it possible to study the behaviour of the guided waves in the grouted bolt along its central axis. Analysis of the simulated results showed that the group velocity in grouted rock bolts is constant along the grouted length, and the boundary effect on the group velocity is negligible. This paper also presents methods to determine the attenuation coefficient from simulation and to determine the boundary effect on attenuation at the bolt ends. The analysis showed that the attenuation of the guided wave propagating inside the grouted bolts is similar to the theoretical solution in steel bar with infinite length. After correction for the boundary effects the grout length of a grouted rock bolt can be determined using the measured attenuation, with sufficient accuracy.     

Analysis of a guided wave along a conducting structure in a borehole

A guided wave along a borehole is often observed in borehole radar measurements. These guided waves deform the antenna pattern and can cause artefacts in radar measurements. A water-filled borehole or a conducting logging cable can function as a waveguide for electromagnetic waves under some conditions. We describe the theoretical characteristics of such a guided wave in a borehole and compare them with our experiments. The measured signal discussed was obtained with a directional borehole radar. This radar uses a cylindrical conformal array antenna as receiver and is a model of a conducting structure in a borehole. The induced field around the borehole was compared with the theory. The most fundamental symmetrical and asymmetrical modes were TM₀₁ and HE₁₁, and they were identified in the measured signals using time–frequency distribution analysis and by observation of the azimuthal field distribution of the magnetic field.     

Seismic wave propagation in viscoelastic and saturated rock

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Seismic wave propagation in viscoelastic and saturated rock

Considering engineering practice, the viscoelastic two-phase model is adopted, seismic wave propagation in saturated rock is studied. Not only the effect of the viscosity of rock skeleton but also the effect of ground water on the propagation of the seismic wave can be considered by this model, the propagation characteristics of seismic wave in saturated rock can be understood comprehensively and the model is more reasonable than other model by which seismic wave propagation is studied. The effect of frequency, water content and viscosity constant on the wave velocity and attenuation are studied by numerical examples and some valuable conclusions are drawn.     

A continental channel wave,guided by the intermediate layer in the crust

Summary A study has been made of a new channel wave, denotedLi, using a total of 83 observations from the seismic records of Swedish stations, mainly from earthquakes at normal depth.Li resembles theLg waves in several respects: it propagates only through continental structures, it has a similar particle motion, i.e. mainly transverse horizontal, and only slightly larger period. ButLi has a higher velocity, 3.79±0.07 km/sec, and it is believed to propagate in the intermediate layer in the crust in a way similar to the propagation of theLg waves in the granitic layer.Li is identical withS ^* in records of near-by earthquakes in the same way asLg2 is identical withSg. Li usually exhibits no clear dispersion.

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Zusammenfassung Es wurden Untersuchungen angestellt über eine neue Kanalwelle, welcher die BezeichnungLi gegeben wurde, wobei insgesamt 83 Erdbebenregistrierungen von schwedischen Stationen Verwendung fanden. Hauptsächlich waren es Erdbeben mit normaler Herdtiefe. DieLi-Wellen haben in verschiedener Hinsicht Ähnlichkeit mit denLg-Wellen: Sie pflanzen sich nur im Bereich kontinentaler Struktur fort und sie haben eine ähnliche Partikelbewegung, d.h. hauptsächlich horizontaltransversal.Li hat eine nur unwesentlich höhere Periode als dieLg-Wellen. AberLi hat eine wesentlich höhere Geschwindigkeit, 3.79±0.07 km/sec, und es ist anzunehmen, dass sie sich in der Basaltschicht der Kruste in ähnlicher Weise fortpflanzt wieLg in der Granitschicht.Li ist identisch mitS ^* in Aufzeichnungen von Nahbeben, so wieLg2 identisch mitSg ist.Li weist gewöhnlich keine deutliche Dispersion auf.

     

Propagation characteristics of blast-induced shock waves in a jointed rock mass

The propagation characteristics of blast-induced shock waves in a jointed rock mass have been monitored and studied. Accelerometers were set up on a rock surface along three lines, at 0°, 45° and 90° with respect to the orientation of the predominant joint strikes. Cylindrical charges were detonated in a charge hole, and ground accelerations in both vertical and radial directions at various points on the rock surface were recorded. Results show that rock joints have significant effects on the propagation characteristics of blast-induced shock waves. The amplitude and principal frequency of shock waves attenuate with the increase of distance from the charge centre, and the increase of incident angle between the joint strike and the wave propagation path. The measured data were compared with the empirical equations of shock wave attenuation proposed by other authors. The mechanism of rock joint effect, the attenuation of shock waves in relation to the propagation distance, the charge weight and the incident angle, are discussed in this paper.     

Propagation characteristics of converted refracted wave and its application in static correction of converted wave

Three-component seismic exploration through P-wave source and three-component geophone is an effective technique used in complicated reservoir exploration. In three-component seismic exploration data processing,one of the difficulties is static correction of converted wave. This paper analyzes propagation characteristics of non-converted and converted refracted waves,and discovers a favor-able condition for the formation of converted refracted wave,i.e. the velocity of overlaying medium S wave is much lower than that of underlying medium S wave. In addition,the paper proposes the static correction method of converted wave based on PPS converted refracted wave,and processes the real three-component seismic data with better results of static correction of converted wave.     

Propagation and stability of wave motions in rotating magnetic systems

Recent developments in the study of linear wave motions in rotating magnetic systems are reviewed. Particular attention is paid to the relationship between motions in diffusionless and diffusive systems. The influence of the geometry of the system is also stressed.     

岩石样品中超声波传播数值模拟及分析

为了深入研究超声波速度测试中超声波在岩石样品中的传播规律,对岩石超声波速度实验采用交错网格有限差分算法进行了数值模拟.选取了适合于超声波震源的差分精度、稳定性条件和吸收边界.通过模拟波形与实验记录波形的对比分析,结果表明:激发器和接收器直接位于岩心与探头接触面时,接收到的波形中干扰波较少,合成记录波形特征明显,易于分析;使用雷克子波作为超声波数值模拟的震源子波,计算得到实际首波初至时间为21.55μs,而波形图中首波初至时间为23.90μs,这是由于子波自身的长度使得波初至时间比实际波初至的时间晚;相对于岩心与探头接触面的反射波,岩心柱体与空气接触面的反射波对有效波形信号的影响更大.     

The frictional properties of joints in rock

Summary The conditions for sliding over artificial joint surfaces have been studied experimentally by cutting rock cylinders at various angles to their axes and studying slip over these surfaces in a triaxial testing apparatus. The types of joint used were: (i) filled with plaster to simulate a soft joint filling, (ii) bare surfaces ground approximately flat, and (iii) natural surfaces across which shear failure had taken place. The results agreed reasonably well with the simple theory for a constant coefficient of friction. Measured coefficients of friction lie in the range 0.5–0.8 and differ by surprisingly little between the various surfaces. The surfaces across which sliding has taken place exhibit interesting slickenside phenomena. Subsidiary failures frequently occur which cut across the joint surfaces.     

Seismic images and rock properties of the very shallow structure of Campi Flegrei caldera (southern Italy)

In September 2001, an extensive active-seismic investigation (Serapis experiment) was carried out in the Gulfs of Naples and Pozzuoli, with the aim of investigating and reconstructing the shallow crustal structure of the Campi Flegrei caldera, and possibly identifying its feeding system at depth. The present study provides a joint analysis of the very shallow seismic reflection data and tomographic images based on the Serapis dataset. This is achieved by reflection seismic sections obtained by the 3D data gathering and through refined P-velocity images of the shallowest layer of Pozzuoli Gulf (z < 1,000 m). From the refined Vp model, the overall picture of the velocity distribution confirms the presence of a complex arc-shaped anomaly that borders the bay offshore. The deeper part of the anomaly (beneath 700 m, with Vp > 3,500 m/s) correlates with units made up of agglomerate tuffs and interbedded lava, which form the southern edge of the caldera, which was probably formed following the two large ignimbritic eruptions that marked the evolutionary history of the area under study. The upper part of the anomaly that tends to split into two parallel arcs is correlated with dikes, volcanic mounds and hydrothermal alteration zones noted in previous shallow reflection seismic analyses. The depth of the transition between the upper and lower parts of the anomaly is characterized by an abrupt Vp increase on the one-dimensional (1D) profiles extracted from the 3D tomographic model and by the presence of a strong reflector located at about 0.6/0.7 s Two Way Time (TWT) on Common Mid Point gathers. The move-out velocity analysis and stack of the P–P and P–S reflections at the layer bottom allowed to estimate relatively high Vp/Vs values (3.7 ± 0.9). This hypothesis has been tested by a theoretical rock physical modeling of the Vp/Vs ratio as a function of porosity suggesting that the shallow layer is likely formed by incoherent, water saturated, volcanic and marine sediments that filled Pozzuoli Bay during the post-caldera activity.     

含煤地层岩浆岩侵入体地震波场模拟

从地质特征出发分析了岩浆岩侵入对煤层的影响,在此基础上建立岩浆岩侵入模型进行地震叠前波场正演与成像处理,对岩浆岩侵入体不同厚度、岩浆岩对煤层不同的侵蚀程度、不同间距等多种模型进行地震正演模拟,分析了几种情况下的地震反射波特征及岩浆岩侵入对煤层反射波的影响.研究结果表明,岩浆岩侵蚀区地震波场复杂,高精度的成像结果是正确识...     

内日球子午面瞬态激波的传播特性

采用日球子午面内的二维三分量MHD模型,研究瞬态激波的传播特性,着重分析日球 电流片（HCS）、日球等离子体片（HPS）和低速流结构对激波传播的影响．结果表明,HCS 和HPS对激波传播几乎没有影响,而跨越HCS和HPS的低速流则显著改变激波的传播特性. 低 速流对激波的反射,导致激波扰动源一侧的激波速度加快、强度增强,低速流对激波透射的 阻碍作用导致激波扰动源异侧的激波滞后、强度减弱,但激波阵面的纬度跨度有所加宽．在 激波穿越过后,低速流区朝激波传播方向弯曲并受到骚扰,使得激波下游出现复杂的扰动结 构;对于激波扰动源同侧的激波下游,反射波与该处等离子体的相互作用同样会导致较为复 杂的扰动出现.     

Propagation of guided waves in a fluid layer bounded by two viscoelastic transversely isotropic solids

The analysis of Stoneley wave propagation in a fracture is essential for the identification and evaluation of fracture parameters from the borehole Stoneley wave. Also, it is important for many geophysics considerations, e.g. for tremor and long-period events observed in volcanoes and geothermal areas. In this paper, we investigate the guided waves propagation in a fluid layer lying between two viscoelastic vertically transversely isotropic media. The viscoelastic mechanism models the attenuation due to the presence of fluid saturation in the rock. A model based on the superposition of three inhomogeneous partial plane waves: one in the fluid and two heterogeneous waves in the solid is developed. The dispersion equation is obtained for this case. A numerical solution is carried out to obtain the guided wave velocity and attenuation coefficient. The results of this investigation show that there is a strong correlation between the velocity dispersion and attenuation of Stoneley wave and the anisotropic parameters of the medium especially in a sandstone (fast) medium.     

Propagation of the radiofrequency ground wave transient over a finitely conducting plane earth

Summary The introduction of precision radio navigation systems employing pulse techniques and the ever increasing interest in spherics have stimulated considerable interest in the propagation of the ground wave transient over the surface of the earth. The theory of the propagation of a transient radio frequency ground wave over a finitely conducting plane earth is presented for the particular case of theNorton surface wave by a consideration of a wave, interrupted abruptly at one point in time (t=0), a wave interrupted abruptly at two points in time (t=0,T ₂) and a wave interrupted at one point in time followed by an exponential decay. The first case is illustrated by several numerical examples of a cosine current wave applied to a vertical electric dipole source. It is apparent that the method of the inverse aplace transform for the particular cases considered yields some simple mathematical formulas.     

基于核Fisher判别的碎屑岩储层流体识别

流体识别是致密碎屑岩储层预测中的难点之一.本文把核Fisher判别分析用于致密碎屑岩储层流体识别,首先较全面的介绍了核Fisher判别分析理论基础,再利用测井属性参数计算出弹性属性参数,并将这两类参数作为特征变量,最后进行核Fisher判别分析建模和致密碎屑岩储层流体识别.四川盆地XC地区致密碎屑岩储层流体识别结果表明,对致密碎屑岩储层中的气层和气水同层两类线性不可分的样本数据,使用核Fisher判别分析均能实现分离,说明该方法在识别致密碎屑岩储层流体识时准确率高,具有很好的应用前景.     

Shear wave velocity modelling in crustal rock for seismic hazard analysis

P-wave velocity data along with the thickness of sedimentary and crystalline layers within bedrock were collected from all global regions and presented in the Global Crustal Model CRUST2.0, published in 2001. This well-organised database provides invaluable potential contributions towards future seismic hazard modelling, particularly for stable continental regions (SCRs), where there is a scarcity of representative strong motion records for conventional modelling purposes. The P-wave velocity information presented in CRUST2.0 has been converted herein to S-wave velocity information. The latter is especially important for purposes of seismic hazard modelling. The value of the CRUST2.0 model has therefore been greatly enhanced by the important findings presented and further developed in this paper. By making the best use of available information on crustal conditions, the amplification behaviour of seismic waves affecting a region, an area or a site for any given earthquake scenario may be predicted. The developed methodology, which is intended for worldwide applications, has been illustrated by case studies in which model S-wave velocity profiles were developed for different geological regions within North America. The model profiles were found to be in excellent agreement with field measurements reported for each respective region.     

计算岩石波速空间平均的极限近似模型

本文在传统的岩石波速空间平均模型（Voight模型,Ruess模型,Hill模型和几何平均模型）的基础上,提出了一种极限近似模型.在这种模型中,它是利用作者提出的一个基于Hill模型（即代数平均模型）和几何平均模型的递推关系式,并利用这个关系式计算求出模型的极限近似值,该值介于Hill模型和几何平均模型之间,是具有典型代表意义的一个值.     

部分饱和孔隙岩石中声波传播数值研究

利用基于Biot理论的孔隙弹性介质的高阶交错网格有限差分算法,模拟了具有随机分布特征的多种流体饱和岩石中声波在中心频率分别为25,50,75,100kHz时的声场特点. 对于一个由两种成分（气和水）饱和的岩石模型, 假设含不同流体的孔隙介质随机分布在不同的宏观区域,该区域尺度远小于计算的声波波长;组成模型的两种随机分布介质具有相同的固体骨架参数、渗透率和孔隙度,但分别被具有不同压缩性、密度和黏滞系数特性的水和气饱和. 计算和统计分析结果表明,在两种孔隙成分随机分布的部分饱和条件下纵波速度比较复杂,除骨架参数外,其变化主要依赖于中心频率、各种孔隙成分饱和度及饱和介质的速度. 比较该随机分布模型、Gassmann理论模型和White的“气包”模型,发现三种模型得到的纵波速度和衰减规律有较好的定性对应关系. 其次,按照这种随机计算模型的处理方法,本文还首次计算了一个三种流体成分充填饱和的例子,即岩石模型中的孔隙被水、油和气部分饱和,计算时保持模型含水饱和度不变而只改变含油和含气饱和度. 在这种计算条件下,纵波速度随中心频率呈增大的趋势但有起伏变化. 声场快照显示了各种转换波在多种孔隙成分充填（两种和三种孔隙成分）岩石中的声场特征,复杂的水-油-气界面的非均匀分布对声场有重要影响,纵波能量主要转换形成了较为复杂的多种慢纵波和横波.     

Numerical experiments for the conductive properties of saturated rock

The reservoir evaluation as a key technology in oil exploration and production is based on the electrical transport property (ETP) of saturated rock that is described in a mathematical form with Arhcie’s equa-tion. But there have been increasing cases observed in many researches indicating that the ETP is non-Archie especially for the complex reservoir with low porosity and permeability. In this paper,the numerical experiments based on the Lattice Boltzmann method (LBM) have been employed to study the effect of porous structure and fluids on the ETP for revealing the nature of non-Archie phenomenon in micro-scale. The results of numerical experiments have proved that the saturation exponent n is a function of water saturation and porosity instead of being a constant in Archie’s equation. And then,a new formula has been developed for the EPT through combining the result of numerical simulation with that of laboratory measurements. The calculations from the new formula show very good agreement with laboratory measurements to demonstrate the efficiency of the new formula over the conventional methods in non-Archie rock.