国内外隧道超前预报技术评析与推介

国内外的隧道地质超前预报技术正在发展之中，目前应用的负视速度法，水平剖面法，TSP、TGP等技术，由于观测方式和资料处理方法比较简单，不能准确确定掌子面前方围岩的波速，从而致使地质界面定位不准确，围岩工程类别划分缺乏依据，亟待改进.TRT与TST技术采用空间观测方式和偏移成像方法，技术比较先进，能解决了掌子面前方围岩速度结构可靠分析的问题，实现了隧道围岩地质结构的精确成像，适合复杂地质条件下的地质超前预报应用.目前的超前预报过于依赖地震方法，实际上地震方法对于解决构造问题比较有效，解决含水性问题不如电磁方法，高密度电法和瞬变电磁方法在超前预报领域会有广阔的应用前景.实际预报工作中要取得好的预报结果，必须提倡综合方法，提倡地质分析与工程物探相结合，地震方法与地磁方法相结合，共同解决不良地质构造、含水构造、含瓦斯气构造的超前预报问题.     

模糊聚类在不良地质洞段红外探水中的应用

在玉昆铁路柿花树隧道不良地质发育的洞段进行红外探水工作期间,常用的分析方法有时无法预判掌子面前方是否存在隐伏水体或含水构造。为了提高红外探水短距离预报的准确率,用模糊聚类法将掌子面测点场强的数据分类,根据开挖传递的地质信息,研究模糊聚类结果的变化规律、突水风险与岩体破碎程度之间的关系。实践证明,模糊聚类法和常用分析方法的结合,使红外探水取得了较好的预判效果。     

多辐射场源地空瞬变电磁法多分量全域视电阻率定义

本文针对多辐射场源地空瞬变电磁法理论,建立了相应的多分量全域视电阻率定义方法.分析了利用磁场强度进行多辐射场源地空系统全域视电阻率定义的优点,针对磁场强度的各个分量,提出了各自的全域视电阻率算法,实现了多分量、全时域、全空域视电阻率计算,并分析了偏移距对全域视电阻率的影响.通过调整源的相对位置及电流方向等参数,多辐射源瞬变电磁地空系统不仅可以加强不同分量信号强度,削弱随机干扰,还可更好地分辨地下异常体的位置.通过对所设计模型的处理,证实了多辐射场源地空系统多分量全域视电阻率算法的有效性,也验证了多辐射场源地空系统的优势.     

A study on the discrete image method for calculation of transient electromagnetic fields in geological media

We conducted a study on the numerical calculation and response analysis of a transient electromagnetic field generated by a ground source in geological media. One solution method, the traditional discrete image method, involves complex operation, and its digital filtering algorithm requires a large number of calculations. To solve these problems, we proposed an improved discrete image method, where the following are realized: the real number of the electromagnetic field solution based on the Gaver–Stehfest algorithm for approximate inversion, the exponential approximation of the objective kernel function using the Prony method, the transient electromagnetic field according to discrete image theory, and closed-form solution of the approximate coefficients. To verify the method, we tentatively calculated the transient electromagnetic field in a homogeneous model and compared it with the results obtained from the Hankel transform digital filtering method. The results show that the method has considerable accuracy and good applicability. We then used this method to calculate the transient electromagnetic field generated by a ground magnetic dipole source in a typical geoelectric model and analyzed the horizontal component response of the induced magnetic field obtained from the “ground excitation–stratum measurement” method. We reached the conclusion that the horizontal component response of a transient field is related to the geoelectric structure, observation time, spatial location, and others. The horizontal component response of the induced magnetic field reflects the eddy current field distribution and its vertical gradient variation. During the detection of abnormal objects, positions with a zero or comparatively large offset were selected for the drillhole measurements or a comparatively long observation delay was adopted to reduce the influence of the ambient field on the survey results. The discrete image method and forward calculation results in this paper can be used as references for relevant research.     

多辐射源地空瞬变电磁响应三维数值模拟研究

地空瞬变电磁法结合地面和航空电磁法的优点,可实现探测深度和工作效率的平衡.当前地空瞬变电磁法采用单一线源激发电磁辐射场,仅能从一个侧面与地质体耦合,难以获得地质体的全息影像.采用多辐射源是解决这一问题的途径.本文采用三维矢量有限元法对两个不同地质体多个辐射源情况下的地空瞬变电磁响应开展了模拟研究,分析了多辐射源在不同辐射方向、不同飞行高度电磁响应的分布特征.研究表明,由多辐射场源作为地空电磁法的发射源,通过分散布设的线源,可以在地下激发与地质体多方位耦合的电磁场,能够获得地下地质体多方位不同高度情况下的耦合信息.同时,多辐射场源能够增强源电磁场的辐射强度,减少单一线源体积效应影响,飞行高度较低时可获得较强的响应幅值,研究结果为多辐射地空瞬变电磁法深部精细探测提供理论依据.     

露天煤矿地下水电磁探测与类型判别

为准确确定露天煤矿地下水分布与类型,根据不同赋存条件电磁差异,基于磁场强度与电阻率参数进行异常划分与类型判别。以新疆某露天煤矿为例,采用高精度磁法通过磁异常强度确定烧变岩边界,并采用高密度电法和瞬变电磁法通过电阻率圈定低阻异常区,结合异常响应差异分别推断地下水分布范围与赋存类型。地面钻探验证探测成果的准确性。结果表明:露天煤矿烧变岩水与砂岩裂隙水电磁响应差异明显,基于磁场强度与电阻率的双参数综合电磁法能准确圈定其分布范围,并判别其赋存类型。     

TST隧道地震CT地质超前预报技术及应用

国内外的隧道地质超前预报技术正在发展之中,4目前应用的负视速度法,水平剖面法,TSP技术等,由于观测方式和资料处理方法比较简单,不能准确确定掌子面前方围岩的波速,从而致使地质界面定位不准确,围岩工程类别划分缺乏依据,亟待改进。本文提出的TST技术采用空间观测方式,资料处理方法采用偏移成像和走时反演成像,解决了掌子面前方围岩速度结构的分析问题,实现了隧道围岩地质结构的精确成像,适合复杂地质条件下的地质超前预报应用。     

坑(井)-地多参数电磁接收系统

坑（井）-地多参数电磁接收系统在地面、坑道、井中三维空间观测天然场源及人工源电磁信号,观测装置接近或穿过矿体,借助动源、大功率发射可获得更加明显的异常值,旨在加大探测深度的基础上提高深部分辨率,同时获取电阻率、极化率、复阻抗等参数.为坑（井）-地电磁成像方法现场数据采集提供硬件设备支持,针对坑道、井中电磁观测的特殊需求,开发了由不极化电极、非接触电极、小型感应式线圈、微型三分量音频磁传感器、地面-坑道电磁接收机、井中电磁接收机等组成的坑（井）-地多参数电磁接收系统,解决了传统不极化电极坑道硬岩表面接地困难和传统感应式磁传感器难以适应坑道狭窄空间的问题;通过多层次的室内、弱干扰条件下野外测试验证了接收系统的各项技术指标,接收机通道全频段噪声水平接近10 nV/rt（Hz）,微型三分量音频磁传感器体积压缩至32 cm×32 cm×32 cm;强干扰条件下的矿山试验验证了接收系统的可靠性、适用性及先进性.     

Numerical analysis of multicomponent responses of surface-hole transient electromagnetic method

We calculate the multicomponent responses of surface-hole transient electromagnetic method. The methods and models are unsuitable as geoelectric models of conductive surrounding rocks because they are based on regular local targets. We also propose a calculation and analysis scheme based on numerical simulations of the subsurface transient electromagnetic fields. In the modeling of the electromagnetic fields, the forward modeling simulations are performed by using the finite-difference time-domain method and the discrete image method, which combines the Gaver–Stehfest inverse Laplace transform with the Prony method to solve the initial electromagnetic fields. The precision in the iterative computations is ensured by using the transmission boundary conditions. For the response analysis, we customize geoelectric models consisting of near-borehole targets and conductive wall rocks and implement forward modeling simulations. The observed electric fields are converted into induced electromotive force responses using multicomponent observation devices. By comparing the transient electric fields and multicomponent responses under different conditions, we suggest that the multicomponent-induced electromotive force responses are related to the horizontal and vertical gradient variations of the transient electric field at different times. The characteristics of the response are determined by the varying the subsurface transient electromagnetic fields, i.e., diffusion, attenuation and distortion, under different conditions as well as the electromagnetic fields at the observation positions. The calculation and analysis scheme of the response consider the surrounding rocks and the anomalous field of the local targets. It therefore can account for the geological data better than conventional transient field response analysis of local targets.     

Forward modelling and imaging of ground‐penetrating radar in tunnel ahead geological prospecting

Adverse geologies are often encountered during tunnel construction, which could seriously endanger the construction. To ensure the safety, it is essential to detect adverse geologies and their water‐bearing situation ahead the tunnel face. Ground‐penetrating radar is a suitable instrument, but the accurate interpretation of its detection results is difficult. In this paper, at first, an improved back projection imaging algorithm is proposed, which can make reflection waves closer to the real geological boundaries with few artificial clutters. And then, forward modelling of ground‐penetrating radar is carried out for typical adverse geologies, such as karst caves, faults, fractured rock masses, fracture network, and water‐bearing body. Their corresponding response features are obtained, accumulating experience for geological interpretation. The above two methods provide the basis for target identification and geological interpretation. In the last part, the application of the above two methods in several engineering cases are given, and their effectiveness is verified.     

基于自适应有限元的复电阻率法2.5维复杂构造电磁场模拟

复电阻率法在矿产、油气勘探调查中发挥着重要作用.为了认识复杂构造的复电阻率法电磁场的变化规律,本文基于自适应有限元方法,采用非结构化网格,引入Cole-Cole模型,实现了电偶源2.5D复电阻率法电磁场正演,可以模拟复杂地形和地电结构,正演结果更符合野外实际地质情况.通过将本文的计算结果与半空间模型解析解、层状介质和起伏模型结果进行对比,验证了本文算法的正确性.最后,基于复杂地电模型,通过正演模拟,系统分析了地形、激电参数、复杂构造对复电阻率法电磁场的影响特征.     

瞬变电磁隧道超前预报成像技术

为解决隧道掌子面前含水带病害快速有效探测问题,尝试把对含水带结构反映敏感的瞬变电磁法引入到隧道掌子面前进行工作.文中介绍了瞬变电磁超前预报的工作装置形式;通过对掌子面特定环境的分析,提出引用“浮动薄板”理论,以二次电导微分参数为特征量建立隧道超前预报成像系统.推导出以等效导电薄板为虚拟像源的磁场响应与电导之间的非线性关系式. 通过引入辅助函数,采用遗传算法求得电导参数.最终以二次电导微分参数绘制成像剖面.对地电模型进行数值模拟和对应用实例进行了成像,结果表明成像方法对隧道掌子面前方水体病害预报效果明显.     

起伏地形下各向异性的2D大地电磁无网格法数值模拟

作为一种基于节点的计算方法,无网格法具有构造高阶导数方便,自适应分析便利的优点,特别适合复杂地质构造的数值模拟.本文针对实际地球物理勘探中存在的起伏地形和各向异性的地电结构,提出用无网格法来模拟大地电磁响应,采用复合二次径向基函数构造了形函数,推导了大地电磁无网格法等价线性方程组,研究了系数矩阵的压缩存储方法以及大型稀疏复线性方程组快速求解算法,实现了起伏地形下各向异性的2D大地电磁高精度数值模拟.基于层状模型验证了算法的正确性,计算结果表明:无论是TM模式还是TE模式,计算相对误差均小于1%;通过对地垒和地堑模型的模拟,得出了起伏地形对视电阻率和相位的影响规律;对起伏地形下含有不同各向异性系数异常体的模型进行了数值模拟,为开展复杂地质结构的电磁场特征研究以及地形校正奠定了理论基础.随着计算科学的快速发展,无网格法必将成为新的高精度电磁场数值模拟方法.     

LINE CURRENT FILTERING OF FIXED-LOOP TRANSIENT ELECTROMAGNETIC DATA1

The VLF filtering technique of Karous and Hjelt has been applied to fixed-loop step-response transient electromagnetic data. This allows the data measured in each channel to be converted to an equivalent current-density pseudosection. For a conductive half-space, the maximum value of the equivalent current density starts near the transmitter loop and migrates outwards as a function of delay time. The rate of migration tends to increase as a function of delay time, with the increase being faster for a surficial conductive layer than it is for a half-space. Theoretical and field examples show that the currents tend to be more persistent in the relatively conductive areas, so that a pseudosection which is the average of the current densities at all delay times will highlight the more conductive zones. In resistive ground, it is not so critical to average the pseudosections as a particular delay time may give a better idea of the conductivity structure. For example, the latest possible delay time will reveal the most conductive features.     

Three-dimensional resistivity characterization of a coastal area: Application of Grounded Electrical-Source Airborne Transient Electromagnetic (GREATEM) survey data from Kujukuri Beach,Japan

An airborne electromagnetic (AEM) survey using the Grounded Electrical-Source Airborne Transient Electromagnetic (GREATEM) system was conducted over the Kujukuri coastal plain in southeast Japan to assess the system's ability to accurately describe the geological structure beneath shallow seawater. To obtain high-quality data with an optimized signal-to-noise ratio, a series of data processing techniques were used to obtain the final transient response curves from the field survey data. These steps included movement correction, coordinate transformation, the removal of local noise, data stacking, and signal portion extraction.We performed numerical forward modeling to generate a three-dimensional (3D) resistivity structure model from the GREATEM data. This model was developed from an initial one-dimensional (1D) resistivity structure that was also inverted from the GREATEM field survey data. We modified a 3D electromagnetic forward-modeling scheme based on a finite-difference staggered-grid method and used it to calculate the response of the 3D resistivity model along each survey line. We verified the model by examining the fit of the magnetic-transient responses between field data and the 3D forward-model computed data, the latter of which were convolved with the measured system responses of the corresponding data set.The inverted 3D resistivity structures showed that the GREATEM system has the capability to map resistivity structures as far as 800 m offshore and as deep as 300–350 m underground in coastal areas of relatively shallow seawater depth (5–10 m).     

CSAMT全区电阻率法数值模拟及应用探讨

常规的可控源电磁法理论在计算视电阻率公式上,多半采用其电磁场的渐近特征,难以直接反映全区视电阻率的值,及直观地显现地下介质的地质构造.文中采用水平偶极子激发的电磁场,提出了电场的全区精确表达式,直接计算出大地电阻率.利用汉克尔数值滤波算法和逆样条插值算法对水平层状电磁场进行正演计算,并与计算的卡尼亚视电阻率的对比和野外试验结果表明：该方法的结果在远区等价卡尼亚电阻率,在近区和过渡带则明显地改善了卡尼亚电阻率的非波场区场畸变,从而能更好地接近基底的真电阻率,更形象地反映了地下介质的垂向电性变化.     

从瞬变电磁场到波场的优化算法

在波场的正变换中,保证瞬变电磁场的计算精度的同时,应用两步最优化算法,成功地控制和减少了积分系数个数和离散数字积分的采样点个数,解决了在波场反变换式中,由于积分系数过多而产生的欠定方程组的问题,同时改善了第一类算子方程的不适定性.在波场反变换中,将正则化算法用于逆变换过程的计算中,通过采用偏差原理和Newton迭代格式选出最优的正则化参数,使得反变换所得到的波场稳定、可靠.通过对数值计算结果与已知波场函数对比,证明了该方法的有效性和实用性.     

电磁测深数据地形影响的快速校正

地形起伏会对电磁法的数据产生一定影响,尤其会影响浅部地层电性结果的准确性.本文通过对地形影响基本规律、经典比值校正原理的分析,认为可以用实测标准电阻率替代数值模拟中均匀半空间电阻率,提出一种新的地形影响快速校正方法,即采用小极矩直流电阻率法获得无地形影响的表层电阻率值,作为地形校正的标准电阻率,以此构造一个新的校正公式.分别对CSAMT和TEM仿真和实际测量资料进行地形校正处理,效果较好.说明新的比值校正公式,是一种快速、有效和实用的校正算法.     

The tunnel seismic advance prediction method with wide illumination and a high signal-to-noise ratio

Tunnel seismic prediction is widely used in the field of tunnel seismic advance detection. The illumination of the target and the signal-to-noise ratio of the data are two key factors affecting the precision of data interpretation. Current seismic prospecting has shortcomings on sites: (1) The lighting shots are solely towards one side of the tunnel wall, (2) the geophones are placed far away from the tunnel face and (3) the surface waves from the tunnel wall dominate over the reflection waves, lowering the signal-to-noise ratio of the data at the tunnel wall. This paper proposes a tunnel symmetrical geometry to tackle the above challenges. The arrangement is to place 12 sources uniformly on each side of the tunnel wall and six geophones on the tunnel wall and face. Results of simulated data and measured data show that the proposed method enables (1) broad illumination of the target body, (2) the enhancement of illumination energy of the target body, and (3) higher data signal-to-noise ratio. The proposed symmetrical geometry method provides better interpretation in terms of broader coverage, higher quality and greater distance of investigation.     

坑道直流电阻率超前聚焦探测新方法研究

研究和提出了一种坑道直流电阻率超前聚焦探测新方法.该方法通过在掌子面上设立不同功能的环状电极组,使一次场电流具有像探照灯一样的聚焦功能,可有效探测坑道掘进前方不良地质体的存在,达到超前预报的目的.本文首先介绍了直流电阻率超前聚焦探测的基本原理,并给出了两种聚焦观测方式.为了验证所提方法的可行性,通过轴对称电性介质二维异常电位有限元数值模拟方法,对聚焦观测条件下几例坑道模型进行了模拟计算.结果表明,该方法对异常反映明显,可进行即时解释,建议在坑道超前预报中逐步推广使用.