The magnetic relaxation effect on TEM responses of a two-layer earth

We have simulated ungrounded horizontal loop transient responses of a two-layer earth consisting of a magnetically viscous layer above (model 1) or below (model 2) a nonmagnetic layer. The transient responses of a two-layer magnetically viscous earth can be computed using the superposition principle because magnetic relaxation and eddy current responses are independent at electrical conductivities typical of the real subsurface. The transients are presented and analyzed in the form of Y = f(h1) functions, where h1 is the upper layer thickness and Y is the response (at some fixed time) of a two-layer ground normalized to that of a uniform ground with its magnetic viscosity as in the upper (model 1) or lower (model 2) layer. In model 1, the Y function increases as magnetic viscosity grows in the upper layer while the latter is thinner than the loop size, but the magnetic relaxation responses of a thicker upper layer are almost identical to that of a uniform magnetically viscous ground. In model 2, the Y responses are likewise almost identical to that of a uniform magnetically viscous ground (h1 = 0) as far as the thickness of the upper layer remains small, but they decrease, first slowly and then ever more rapidly, after the layer becomes 15–20% thicker than the transmitter size. The effective sounditng depth in a magnetically viscous ground being controlled by the size of the transmitter, it is reasonable to use geometrical sounding to resolve the vertical distribution of magnetic viscosity.     

Joint inversion of IP-affected TEM data

A numerical experiment was applied to explore the potentialities and limitations of joint inversion of IP-affected transients measured with different loop configurations above a uniform half-space with a Cole-Cole complex conductivity. One of us calculated 200 m × 50 m and 50 m × 50 m loop responses of a uniform polarizable conductor with varied Cole-Cole parameters and imposed synthetic Gaussian noise that simulated measurement errors. Then the generated pseudo-experimental data passed to the other co-author who performed single and joint 1D inversion twice: first being unaware of the “true” underlying models and then after being told that they all were represented by a uniform polarizable earth. More than a half of the fitted models provided a good idea of the true models though misfit was quite large in some cases. The fit was better in single inversion with a priori information available, and improved further through joint inversion of central-loop and coincident-loop responses. Joint inversion with a priori information known was of good quality even at a chargeability as low as 0.02. The standard error in joint inversion was times the measurement error and depended mainly on fitting errors for smaller-loop data. The reason is that the smaller-loop transients included a non-monotonous interval where the signal changed rapidly under the effect of fast-decaying induced polarization.     

TEM最简化反演及在研究永久冻土层中的应用

阐述了基于烟圈理论的最简化反演方法和磁源TEM测深一维经验式反演方法,这两种方法可由观测数据直接反演,不需要初始模型。结合中国东北永久冻土层勘查研究课题,对TEM原始探测数据进行了反演解释。两种反演结果对揭示沿剖面横向、纵向的电性层变化,体现了较好的一致性,可为分析、划分不同电性界面的变化趋势提供参考依据。     

Inversion of heterogeneous anisotropic magnetotelluric responses

Inversion of laterally heterogeneous MT responses collected by a dense synchronous 2D array allows a new approach to estimating electrical anisotropy. The procedure includes solving an overdetermined equation system, assuming distant-dependent anisotropy in a smooth approximation. Inversion is performed using an effective conductivity tensor which approximates some limited domain of the survey polygon. The algorithm for simulating 2D array MT responses with the effective conductivity tensor approach implies correlation of surface components of the EM field measured simultaneously at all stations within the chosen domain of the survey polygon. The suggested technique of data acquisition and processing ensures reconstruction of the full conductivity tensor from laterally variable components of the EM field.     

移动荷载下黏弹性半空间体上双层板的动力响应

采用黏弹性半空间体上无限大双层板模型模拟路面结构,通过三重Fourier积分变换得到单位脉冲荷载作用下路面动力响应的Green函数。根据线性系统的叠加原理,利用广义Duhamel积分推导出移动荷载作用下路面动力响应的解析解。采用自适应Simpson法编制了计算奇异、振荡函数的广义积分计算程序,完成了路面动力响应从波数-频率域到时间-空间域的转换。结合算例,对移动荷载作用下路面的振动规律进行研究,讨论上、下层板厚度和板材料的弹性模量对路面动力响应的影响,明确了路面结构的振动特性,研究结果可为路面结构的设计、施工提供理论指导。     

Identification and Correction for MT Static Shift Using TEM Inversion Technique

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不规则回线源层状介质瞬变电磁场正反演研究及应用

不规则回线内任一点的电磁场可以看成是其内部多个圆形回线在该点的电磁场之和,因此,只要求出不规则回线内各个圆形回线在该点的电磁场,将它们叠加就可得出不规则回线在该点的电磁场。此种方法的关键是如何在不规则回线内划分圆形回线。采用的方法是首先在不规则回线内以测点为圆心做一个圆,这时整个回线被分为圆内和圆外两部分;然后再将回线内圆外的部分划成众多的小圆形,此时就将求解不规则回线的电磁场转化为求解圆形回线的电磁场。     

双层地基水平受荷桩受力变形分析

基于双层地基中的水平受荷桩的特性,对其受力变形进行了分析。将水平受荷桩视为竖直放置的弹性地基梁,基于Winkler弹性地基梁理论,考虑桩土共同工作得到水平受荷桩位移控制微分方程及其幂级数解答,进而根据内力与位移的连续条件得到了由桩顶受力及变形条件表示任一深度处桩身的水平位移、转角、弯矩及剪力的计算矩阵表达式。通过一具体算例将幂级数解计算结果与《公路桥涵地基与基础设计规范》推荐的简化计算公式计算结果进行了比较。结果表明：当第1层地基土的厚度在某一定值时,《规范》简化计算方法所得结果与幂级数解接近;但当层厚不在该值附近时,两个方法计算结果存在差异。     

Modeling of unsaturated granular flows by a two-layer approach

Flows of partially saturated grain-fluid mixtures over complex curved topography are commonly observed in nature. However, comprehensive understanding of the physics behind them is to date out of reach. To investigate their dynamic process, a two-layer approach is proposed, in which the fluid-saturated granular layer is overlaid by the pure granular material. More specifically, the lower layer is described by a two-phase mixture theory of density preserving solid and fluid constituents. For the upper layer, the single-phase granular mass is treated as a frictional Coulomb-like continuum, and the dilation effect and the influence of the interstitial air are ignored. The capillarity effects and grains-size segregation are not considered in both the layers. The lower and upper layers interact at an interface which is a material surface for the fluid phase, but across which the mass exchange for the granular phase may take place. The granular mass exchange across the layer interface is parameterized by an entrainment type postulate. In addition, the classical jump conditions are employed to connect both layers at the interface dynamically. Furthermore, we perform the depth-averaged technique for the saturated grain-fluid mixture lower layer and the pure granular upper layer, respectively, to simplify the governing equations established. It is demonstrated that the resulting model equations can be reduced to most of the existing single-layer pure granular flow models and saturated two-phase single-layer debris flow models. Numerical solutions demonstrate that the present two-layer model can describe flows of partially saturated grain-fluid mixtures and the transition process of a saturated grain-fluid mixture into an under-saturated state.     

斜支撑支护基坑与相邻地下室有限土体土压力反演分析

为探讨斜支撑支护基坑与相邻地下空间有限土体土压力分布规律,对某基坑现场监测数据进行反演分析。研究基于试算法改进后的三次样条法,运用Matlab软件进行反演计算得到支护结构弯矩值和桩后土压力值,结果表明：受有限土体位移模式、非极限状态、边界条件的影响,有限土体主动土压力在开挖面以上,呈现明显的\     

TEM investigation of a microcline from a nepheline syenite

Chess-board (“tiled”) microcline crystals from a nepheline-bearing syenite from Ilimaussaq, W. Greenland, were investigated using transmission electron microscopy (TEM) and were found to consist of a mosaic of slightly misoriented domains, which bear no obvious relationship to the optical microstructure. Part of the misorientation of most pairs of neighbouring domains involves a small rotation about c. However, some are related to adjacent domains by the albite twin law, the pericline law, or diagonal association. This microcline could have crystallized with triclinic symmetry which could account for the differences between the microstructure of this microcline and M-twinned microcline. Metasomatism may explain both the optical microscope and TEM scale structures of this microcline. Examination of the electron diffraction patterns of areas of microcline which contain both diagonally associated and twinned domains draw attention to the fact that each of the few orientations in an M-twinned crystal is related to one of the other orientations by diagonal association. The formation of common cross-hatch twinned microstructures are discussed with reference to diagonal association.     

Physical simulation and application of a new TEM configuration

In some applications, especially for tunnel surveys and ancient tomb investigations, the scale of survey location is so small that it is impossible to lay a large enough transmitter loop for detection. A small-scale and high-power Transient Electromagnetic (TEM) transmitter configuration must be adapted to detect longer distance or greater depth. Redesigning the TEM surveying configuration may facilitate improving signal penetration and precision of TEM soundings. Based on physical simulation, a newly designed special-loop-source TEM survey configuration has been introduced, which employs four square apertures within a single large transmitter loop to excite stronger fields. The primary and secondary fields have been measured using both the new special-loop system and standard normal single loop TEM configuration for different receiver-transmitter separations and for different target depths. The response curves were compared, revealing that the primary field intensity and the secondary field response were improved by the special-loop transmitter system as compared to the standard system. The new special-loop configuration can be used for tunnel TEM prediction and other TEM investigations. A case study was conducted on tunnel forecasting in Hubei Province, China. This terra TEM survey showed that it is an effective and successful method for exploring and predicting challenging geological structures ahead of a tunnel wall during excavation.     

挡土墙主动土压力分布与侧压力系数

采用库仑土压力理论的假设：挡土墙土压力是由墙后填土在极限平衡状态下出现的滑动楔体产生,在该滑动楔体上沿竖向取水平薄层作为微分单元体,通过作用在单元体上的水平力、竖向力和力矩平衡条件,建立挡土墙上土压力强度的一阶微分方程式,给出了土侧压力系数、土压力强度、土压力合力和土压力合力作用点高度的理论公式,并分析了填土内摩擦角和墙背摩擦角对土侧压力系数、土压力强度、土压力合力、土压力合力作用点和墙底抗倾稳定性的影响。     

Experimental study of migration of potassium ion through a two-layer soil system

A barrier system based on the hydraulic trap design concept for a landfill was proposed. To study the field scenario in which a clay liner is underlain by a granular layer functioning as a secondary leachate drain layer, a laboratory advection–diffusion test was performed to investigate factors controlling the transport of contaminants in a two-layer soil system. The soils used for this study were Ariake clay and, the underlying layer, Shirasu soil from the Kyushu region of Japan. Potassium (K⁺) was selected as the target chemical species with an initial concentration of 905 mg L⁻¹. The effective diffusion coefficients (D _e) of K⁺ for Ariake clay and Shirasu soil were back-calculated using an available computer program, Pollute V 6.3. Values of D _e derived from this experiment are consistent with previously published ones. The Ariake clay has lower D _e than the Shirasu soil. The hypothesis that mechanical dispersion can be considered negligible is reasonable based on both the observation that the predicted values well fit the experimental data and the analyses of two dimensionless parameters. Parametric analyses show that transport of K⁺ through soils is controlled by advection–diffusion rather than diffusion only, whereas at low Darcy velocity (i.e., ≤10⁻⁹ m s⁻¹), transport of K⁺ will be controlled by diffusion. Applications of the test results and parametric analysis results in practical situations were reviewed.     

Modeling pressure pipe embedded in two-layer soil by a half-plane BEM

In this paper, an elastostatic half-plane boundary element method (BEM) formulation was applied to analyze the stress behavior of underground pressure pipes, embedded in two-layer soils. In the use of this method, only the boundary of pipe and interfaces were required to be discretized. In this regard, first, a computer code was prepared based on a multi-region substructuring process in the BEM scheme. Then, the efficiency and applicability of the method as well as the prepared algorithm were verified by solving some practical examples and comparing the results with those of the published works. Finally, a parametric study was done to evaluate the effect of pipe depth and determine the soil stress distribution. The studies showed that the half-plane BEM was in good agreement with the existing solutions and its capability was very favorable for elastostatic problems including semi-infinite domain. It is obvious that this method can be practically used to analyze the geotechnical underground buildings in substituting the full-plane BEM formulation.     

Stability assessment of a circular earth dam

Stability of a circular earth dam is assessed for radial cracking potential and static slope stability using continuum mechanics‐based three‐dimensional numerical models. Comparisons of numerical model results for a circular water tank with vertical walls and different radii with their analytical counterparts are included to support the validity of the ideas and their implementation in the continuum mechanics‐based computer program used. Effects of sloping wall faces and Poisson's ratio on computed deformations and stresses are also included. The same numerical models are used to assess stability of a circular dam in terms of factor‐of‐safety and associated failure surface. Three‐dimensional slope stability analysis results are compared with continuum based two‐dimensional slope stability analysis results to assess the magnitude of 3D effects. Example problems are included to illustrate the use of ideas presented. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.     

Testing TEM systems using a large horizontal loop conductor

Testing TEM systems has to include field experiments with physical models commensurate to the real transmitter–receiver configurations and to the target subsurface features. A large horizontal loop closed across a known resistance is a convenient model in this respect. It is convenient to lay in the field, it has manageable parameters, and its natural response is easy to calculate.A field-size experiment and numerical modeling were applied to investigate the model wire loop response to eddy current in a uniform conductive ground, both at early and late times. The higher the resistivity of the ground the larger the time range in which the measured response matches the predicted one, other things being equal.The experiments show that (i) closed loops laid near a transmitter–receiver system are applicable to test the quality of the latter as a tool for TEM or other similar resistivity surveys; (ii) current induced in the model loop can be used to infer the resistivity of the ground; (iii) a closed loop slows down the growth and reduces the amplitude of voltage induced at early times in a receiver loop or in a multiturn coil.     

地震波阻抗反演方法之改进与三阶段、九步骤反演方法的初步实践

地震波阻抗反演在储层预测中发挥了重要作用,它是确保地震数据、测井曲线、速度和地质信息正确综合的首要技术。地震反演的方法很多,对当前石油工业界常用的5种地震波阻抗反演方法的技术关键、适用性进行了分析和对比。由于受地震资料、地质条件和勘探开发程度的制约,现有波阻抗反演方法各具适应性,并不能很好地解决油田储层地震预测问题。为此,提出了一种新的工作思路--三阶段、九步骤反演方法。 应用该方法在松辽盆地GLB地区PTH油层的勘探部署和储量评价中取得较好效果,可预测1~2 m薄储层,对于国内类似地质条件的薄储层预测具有一定的借鉴意义。     

Hybrid Inversion Method to Estimate Hydraulic Transmissivity by Combining Multiple-Point Statistics and a Direct Inversion Method

Inversion methods that rely on measurements of the hydraulic head h cannot capture the fine-scale variability of the hydraulic properties of an aquifer. This is particularly true for direct inversion methods, which have the further limitation of providing only deterministic results. On the other hand, stochastic simulation methods can reproduce the fine-scale heterogeneity but cannot directly incorporate information about the hydraulic gradient. In this work, a hybrid approach is proposed to join a direct inversion method (the comparison model method, CMM) and multiple-point statistics (MPS), for determination of a hydraulic transmissivity field T from a map of a reference hydraulic head \(h^\mathrm {(ref)}\) and a prior model of the heterogeneity (a training image). The hybrid approach was tested and compared with pure MPS and pure CMM approaches in a synthetic case study. Also, sensitivity analysis was performed to test the importance of the acceptance threshold \(\delta \), a simulation parameter that allows one to tune the influence of \(h^\mathrm {(ref)}\) on the final results. The transmissivity fields T obtained using the hybrid approach take into account information coming from the hydraulic gradient while simultaneously reproducing some of the fine-scale features provided by the training image. Furthermore, many realizations of T can be obtained thanks to the stochasticity of MPS. Nevertheless, it is not straightforward to exploit the correlation between the T maps provided by the CMM and the prior model introduced by the training image, because the former depends on the boundary conditions and flow settings. Another drawback is the growing number of simulation parameters introduced when combining two diverse methods. At the same time, this growing complexity opens new possibilities that deserve further investigation.     

全波形时间域航空电磁探测分辨率

时间域航空电磁系统的传统记录方式存在不能探测高导异常等不足。以导电薄板为模型,研究了梯形波激励、全波形记录方式下的探测分辨率。采用等效涡流环近似方法,在计算了任意位置两线圈互感的基础上,实现了薄板电流关断期间和断开期间感应电动势的数值计算。数值计算表明:当存在覆盖层时,如果测量系统最小分辨率为5 nV/m2,在电流断开期间可检测目标体电导为1~400 S,在电流关断期间可检测目标体电导为0.1~1 000 S。时间域航空电磁系统采用全波形测量,可以拓宽电磁系统检测异常电导的分辨率孔径。