共查询到20条相似文献，搜索用时 15 毫秒
1.
地下衬砌洞室对Rayleigh波的放大作用 总被引：5，自引：3，他引：5
本文利用波函数展开法,给出了半空间中圆形衬砌洞室引起的Rayle igh波散射问题的一个级数解,并通过对求解技术的改进,获得了高频解答。论文通过入射波长、洞室直径、衬砌刚度和埋置深度等参数分析,研究了地下洞室对Rayle igh波的放大作用。数值结果表明,地下洞室情况下地表位移幅值可以达到无洞室情况的2.6倍以上;多数情况下,柔性衬砌洞室情况地表位移幅值最大,无衬砌洞室情况次之,刚性衬砌情况最小。 相似文献
2.
Detecting underground cavities using microtremor data: physical modelling and field experiment 
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下载免费PDF全文 In this paper, we study the possibilities of the use of microtremor records in the detection and delineation of near‐surface underground cavities. Three‐dimensional physical modelling data showed that the averaging amplitude spectra of a large number of microtremor records makes it possible to evaluate the frequencies and amplitudes of compressional standing waves generated by microtremor in the space between the ground surface and underground cavities. We illustrate how these parameters can be used to estimate the shape of the underground cavity horizontal projection. If the compressional wave velocity in the enclosing rock is known, it is possible to evaluate the depth to the cavity top using the frequencies of the standing waves. The results of the field experiment confirmed the possibility of underground cavities detection using microtremor data. 相似文献
3.
The scattering and diffraction of plane SV waves underground, circular, cylindrical cavities at various depths in an elastic half space is studied in this paper. The cavities, studied here, are at depths of two to five cavity radii, measured from the surface to the center of the cavity. Fourier-Bessel series are used to satisfy the wave equation and the boundary conditions. When the angle of incidence of the plane SV wave exceeds the critical angle, surface waves are generated, which are expanded in terms of Fourier series, which also involve Bessel functions. The surface displacement amplitudes and phases that are presented show that the results depend on the following parameters: (1) The angle of incidence, θβ; (2) the ratio cavity depth to the cavity radius, h/a; (3) the dimensionless frequency of the incident SV wave, η; and (4) Poisson's ratio, v. The presence of the cavity in the half space results in significant deviation of both the displacement amplitudes and phases on the nearby half space surface from that of a uniform half space. 相似文献
4.
5.
Marijan Dravinski 《地震工程与结构动力学》2003,32(5):653-670
Scattering of plane harmonic waves by a three‐dimensional basin of arbitrary shape embedded within elastic half‐space is investigated by using an indirect boundary integral equation approach. The materials of the basin and the half‐space are assumed to be the most general anisotropic, homogeneous, linearly elastic solids without any material symmetry (i.e. triclinic). The unknown scattered waves are expressed in terms of three‐dimensional triclinic time harmonic full‐space Green's functions. The results have been tested by comparing the surface response of semi spherical isotropic and transversely isotropic basins for which the numerical solutions are available. Surface displacements are presented for a semicircular basin subjected to a vertical incident plane harmonic pseudo‐P‐, SV‐, or SH‐wave. These results are compared with the motion obtained for the corresponding equivalent isotropic models. The results show that presence of the basin may cause significant amplification of ground motion when compared to the free‐field displacements. The peak amplitude of the predominant component of surface motion is smaller for the anisotropic basin than for the corresponding isotropic one. Anisotropic response may be asymmetric even for symmetric geometry and incidence. Anisotropic surface displacement generally includes all three components of motion which may not be the case for the isotropic results. Furthermore, anisotropic response strongly depends upon the nature of the incident wave, degree of material anisotropy and the azimuthal orientation of the observation station. These results clearly demonstrate the importance of anisotropy in amplification of surface ground motion. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
6.
平面SV波在饱和土半空间中圆柱形孔洞周边的散射 总被引：3，自引：1，他引：2
在Biot饱和多孔介质动力学理论的基础上,利用Fourier—Bessel级数展开法,得到SV波在饱和土半空间中圆柱形孔洞周边的散射问题的解析解答。与已有相关问题的解析解答进行对比,验证了此解的正确性,并给出算例,分析了入射频率对柱面上的应力集中因子的影响。 相似文献
7.
Effect of underground cavities on surface earthquake ground motion under SH wave propagation 总被引：2，自引：0，他引：2
A theoretical approach is presented to study the antiplane seismic response of underground structures, subjected to the incidence of both plane and cylindrical waves. The structure is assumed to be a circular inclusion embedded in a homogenous, isotropic and linear visco‐elastic halfspace. The inclusion may consist either of a cavity, with or without a ring‐shaped boundary, or it may be filled in with a linear‐elastic material, without loss of generality. The analytical solution is obtained using expansions of wave functions in terms of Bessel and Hankel functions, relying on the technique of images and the use of Graf's addition theorem to enforce the boundary conditions. The effects of underground cavities on surface earthquake ground motion are studied as a function of the size of the cavity, its embedment depth, the frequency content of the excitation, the incidence angle and the distance from the axis of symmetry of the cavity itself. A simple application of Rayleigh's method allows us to verify that the ground surface response is dominated by the fundamental vibration mode of the portion of soil between the cavity and ground surface itself, in the frequency range of interest for engineering purposes. A simple relationship to estimate the fundamental natural frequency as a function of the embedment depth of the cavity is given. Finally, amplification factors on response spectra are obtained, to provide a practical insight into the effect of an underground cavity on surface ground motion during real earthquakes. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
8.
Sonia L. Parvanova Petia S. Dineva George D. Manolis Frank Wuttke 《Bulletin of Earthquake Engineering》2014,12(2):981-1005
In this work, we examine the seismic response of multiple tunnels reinforced with liners and buried within the elastic homogeneous half-plane in the presence of surface relief. The seismic waves are upward propagating, time-harmonic, horizontally polarized shear (SH) waves. More specifically, we examine: (a) the scattered wave fields along the free surface and inside the half-plane with the embedded tunnels; (b) the dynamic stress concentration factors that develop at the soil-liner interfaces; (c) the stresses and displacements that develop inside the tunnel liners. We use a sub-structuring technique that is based on the direct boundary element method to model each constituent part of the problem separately. Then, assembly of the full problem is accomplished through the imposition of compatibility and equilibrium conditions at all interfaces. Next, a detailed verification study is carried out based on comparisons against available analytical and/or numerical results for a series of test examples. Subsequently, detailed numerical simulations are conducted and the results of these parametric studies reveal the influence of the following key parameters on the soil-tunnel system response: (a) the shape of the free-surface relief; (b) the depth of placement of the tunnels and their separation distance; (c) the SH-wavelength to tunnel diameter ratio; (d) the elastic properties of the tunnel lining rings and (e) the dynamic interaction effects between the free-surface relief and the tunnels. 相似文献
9.
半无限空间中稳态P波在衬砌周围的散射 总被引：8，自引：0，他引：8
本文采用多级坐标和复变函数方法针对半无限空间中P波在一衬砌周围的散射问题提出了一种近似求解分析方法。具体做法是利用一个半径很大的圆来逼近半空间的直边界，将待解问题转化为全空间中P波在一圆孔和一衬砌周围的共同散射问题。我们预先写出问题波函数的一般形式解，利用边界条件并借助复数傅立叶级数展开把问题化为求解波函数中未知系数的无穷线性代数方程组，进而讨论了衬砌内外边界处动应力集中系数针对不同条件组合的分布和变化情况。算例结果表明：本文方法对于研究与P波（SV波）有关的散射问题是可行的。 相似文献
10.
Based on the plane complex variable theory and the image technique, an analytical solution is presented for scattering of plane harmonic P, SV or Rayleigh waves by a shallow lined circular tunnel in an elastic half space. The major contribution of this study is the treatment of the orthogonality of the boundary conditions along the half surface and the cavity wall. In terms of the image technique, the scattered waves by the half surface are simulated as transmitting from the image source of the origin of the tunnel. Using two different conformal mapping functions, we obtained the complex-valued stresses and displacements of the elastic medium and the liner in the image domain, respectively. The boundary value problem results in a set of infinite algebraic equations. The accuracy of the present approach is verified by comparing the present solution results with the available published data. Parametric study indicates that the embedment depth, the shear modulus and the thickness of the liner have significant influences on the dynamic response of the liner and the medium. 相似文献
11.
本文首先讨论了压力空腔和爆炸中心的等价问题。计算层状介质中的空腔爆炸所产生的位移场时,可先求介质的单位脉冲响应,然后将其与等价的爆炸点源函数做褶积。对于均匀的半空间,自由面位移的暂态解是由三个无量纲的参数所决定的;由此可导出远场位移的精确解。本文也讨论了爆炸点附近的运动。最后还导出多层介质中空腔爆炸所产生的表面位移谱的形式解。 相似文献
12.
Amplification of in-plane seismic ground motion by group cavities in layered half-space (Ⅰ) 下载免费PDF全文
下载免费PDF全文 Amplification of in-plane seismic ground motion by underground group cavities in layered half-space is studied both in frequency domain and time domain by using indirect boundary element method (IBEM), and the effect of cavity interval and spectrum of incident waves on the amplification are studied by numerical examples. It is shown that there may be large interaction between cavities, and group cavities with certain intervals may have significant amplification to seismic ground motion. The amplification of PGA (peak ground acceleration) and its PRS (peak response spectrum) can be increased up to 45.2% and 84.4%, for an example site in Tianjin, under the excitation of Taft wave and El Centro wave; and group cavities may also affect the spectra of the seismic ground motion. It is suggested that the effect of underground group cavities on design seismic ground motion should be considered. 相似文献
13.
采用波函数展开法给出了板的横截面处孔洞在平面P波入射下动应力集中问题的解。本文使用大圆弧假定法来满足板中的自由表面的边界条件。数值结果表明,上表面和孔洞间的距离与下表面和孔洞间的距离都对结果有影响。如果孔洞半径相对板的厚度很小,解近似等于孔洞全空间解。所给出的解是半解析解。因此能被用来验证诸如BEM,FEM,FDM等数值法。 相似文献
14.
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15.
The simulation of the seismic response of heterogeneous sedimentary basins under incident plane waves is computed using the Indirect Boundary Element Method (IBEM). To deal with these kinds of basins we used approximate analytical expressions for the two-dimensional Greens functions of a medium with constant-gradient wave propagation velocity. On the other hand, for the homogeneous half space underlying the sedimentary basin, the full space Greens functions were used. The response of semi-circular heterogeneous basins under incident SH waves is explored by means of the displacements in the frequency-space diagrams and synthetic seismograms. Moreover, we compared these results with those obtained for other homogeneous semi-circular models. The principal differences among them are pointed out. This simulation provided interesting results that displayed a complex amplification pattern in a rich spectrum of frequencies and locations. The maximum amplitudes levels were found around the edges of the heterogeneous sedimentary basins. In time domain some features characterize the seismic response of the basin which include enhanced generation and trapping of surface waves inside the sediments, and the reduced emission of seismic energy to the hard rock. In the heterogeneous models the lateral reflections of surface waves greatly influence the total displacements at the free surface in comparison with the homogeneous models where the displacements have a shared influence among both vertical and lateral reflections. 相似文献
16.
An up to date literature survey on the dynamics of underground structures is presented briefly. The dynamic response of large three-dimensional underground structures to external or internal dynamic forces or to seismic waves is numerically determined by the frequency domain boundary element method. This method is used to model both the structure and the soil medium, which are assumed to behave as linear elastic or viscoelastic bodies. The full-space dynamic fundamental solution is employed in the formulation and this requires a free soil surface discretization, confined to a finite portion around the area of interest, in addition to soil—structure interface and free structural surface discretizations. The dynamic disturbances can have a harmonic or a transient time variation. The transient case is treated with the aid of numerical Laplace transforms with respect to time. Various numerical examples involving lined cavities and long lined tunnels buried in the full- or the half-space subjected to harmonic or transient external forces or seismic waves are presented to illustrate the method and demonstrate its advantages. 相似文献
17.
Scattering of plane harmonic P, SV, or Rayleigh waves by a two-dimensional rough cavity completely embedded in an isotropic
elastic half-space is investigated by using a direct boundary integral equation method. The cavity’s roughness is assumed
to be in the form of periodic or random perturbations of arbitrary amplitude superimposed to a smooth elliptical shape. For
the randomly corrugated cavities the normal or the uniform probability distribution functions are assumed. Based on multiple
random cavity results, the corresponding average surface response is computed. These are compared with the corresponding periodically
corrugated and smooth cavity responses. The surface response is evaluated for different cavity shapes and incident waves and
for a range of frequencies. The surface motion results are used to determine the peak surface motion frequencies. They depend
strongly upon the basic inclusion shape (the principal axes) and the nature of the incident wave. Strong similarity in the
peak surface motion frequencies can be observed for the rough and smooth cavity models for both circular and elliptical shapes.
In order to quantify the importance of the cavity corrugation upon the surface motion, a roughness influence factor is defined
in terms of the rough and smooth cavity surface responses. This factor strongly depends upon the type of the incident wave,
the nature of the cavity corrugation, the basic cavity shape, and the frequency. The factor clearly shows the effect of the
cavity roughness upon the surface motion. 相似文献
18.
《Advances in water resources》2004,27(3):237-243
The problem of water flow around a tunnel cavity located in the saturated capillary fringe on top of a very permeable, freely draining substratum is considered for the critical non-leakage condition when there is uniform vertical downward flow through the upper surface of the saturated region. In this critical condition the soil–water pressure is equal to zero everywhere on the cavity wall that is also a streamline. The conditions at the upper fringe boundary are that the soil–water pressure is equal to the air-entry value of the soil and the flux through this surface is the uniform infiltration rate. The cavity surface and the fringe boundary which is elevated above the cavity position, are found through conformal mapping and the use of integral representations of non-standard mixed boundary-value problems. They are calculated for a range of infiltration rates and compared with those obtained by assuming the upper fringe boundary to be horizontal. The exact analysis given here gives larger tunnel cavities than those given by the approximate treatment of the problem. The results have application in the design of underground repositories against entry of seepage water, the construction of protective capillary barriers and in the design of interceptor drainage systems. 相似文献
19.
Introduction In recent years some big cities in China commonly build subways in central urban areas to improve crowded surface transportation, and the subways usually are large-scale group cavities composed by two parallel cavities. Construction of large-scale group cavities will certainly affect the design ground motion near the cavities, and further affect seismic safety of the existing build-ings nearby. So it is of significance to estimate this effect on seismic design of the buildings. H… 相似文献
20.
采用波函数展开法，给出了平面P波入射下半空间中洞室群对地面运动影响问题的一个级数解答. 数值结果表明，地下洞室群对附近地面运动具有显著的放大作用．建议地铁等地下工程在规划和设计时，考虑工程建设后对沿线地面运动的影响． 相似文献