＜正＞1.引言可控源音频大地电磁（controlled-source audio-frequency magnetotelluric, CSAMT）法采用人工源发射电磁波,与大地电磁法相比,抗干扰能力更强、信噪比更高,广泛应用于固体矿产资源勘探领域（李勇,2017）。目前CSAMT法勘探多采用一维、二维技术,对三维地质体的解释结果可能会带来误差,因此,开展CSAMT法在复杂地质环境下的三维数值模拟研究尤为必要。

＜正＞大地电磁法是一种以天然交变电磁场为场源从而研究地壳和上地幔构造的地球物理探测方法。研究大地对天然电磁场的频率响应,可获得地下不同深度介质电阻率分布的信息[1]。现阶段大地电磁三维正演多是建立在平坦地形模型[2]的基础上,这种方法对于带地形模型的模拟不可避免地存在了近似与误差,因此运用非结构化四面体单元对带地形模型进行剖分并进行有限元正演对于野外真实模型的正演具有重要意义。

近年来,随着我国经济快速发展,加快了高速公路、城市地铁、矿井隧道等基础设施的扩充和修建。在隧道挖掘过程中,常遇到陷落柱、断层等导水构造,尤其是在大倾角的陡倾富水断层处十分容易发生突水灾害事故,严重威胁着隧道施工和安全生产。近几十年来,我国因突水事故造成伤亡人数愈万人,同时造成巨大的经济损失。然而,准确预测隧道掌子面前方的陷落柱、富水断层等灾害构造依然是亟需解决的难题。直流电阻率法具有设备轻便、抗干扰能力强以及对高导电率含水构造反应灵敏等优点,其利用隧道掌子面后方布置的三极剖面观测到的视电阻率极小值对应的偏移距来预测隧道迎头掌子面前方异常的距离,在隧道超前探突水灾害的预测防治中应用较广并取得不少成果。隧道超前探现阶段已有的经验预测模型均建立在电阻率各向同性的简单模型基础之上,而实际井下煤矿开采、地下隧道掘进过程中,煤层本身具有明显的电阻率各向异性,同时隧道前方陷落柱、断层等富水构造往往由于岩石破裂和节理发育亦表现出电阻率各向异性。诸多研究表明,电阻率各向异性对电阻率法勘探数据解释会产生难以预料的偏差,然而由于井下全空间电阻率各向异性三维模拟的复杂性,目前电阻率法隧道超前探还没有考虑介质的电阻率各向异性,煤矿开采、隧道挖掘等掌子面前方异常体电阻率各向异性问题的研究有助于防治可能的突水、涌水事故。本文实现了非结构网格隧道超前探电阻率各向异性的三维有限元正演模拟,在此基础上,计算获得隧道掌子面前方电阻率各向异性立方体和陡倾断层低阻模型的单极-偶极（三极）视电阻率剖面曲线,第一次建立起隧道超前探电阻率各向异性异常介质的预测模型。目前已存在的经验预测模型的准确性及可靠性很难评价,原因是这些模型均基于介质各向同性化或简单物理实验为基础。考虑到实际隧道掌子面前方异常介质电阻率的大小未知且方向分布复杂,本文利用蒙特卡罗法的随机特点来模拟隧道掌子面前方的异常电阻率分布不确定的问题,将立方体和陡倾断层异常三维非结构化网格单元的电阻率值在保持与围岩相比是低阻的条件下进行随机处理,陡倾断层的各向异性系数也是随机变化,以模拟隧道掌子面前方任意复杂的低阻特征的含水异常结构。基于10000个随机模型的三维数值模拟结果表明,在陷落柱立方体异常的预测模型中,有94.30%的预测结果误差在15%以内。在垂向断层异常的预测模型中,有85.36%的预测结果误差在10%以内。此外,利用本文基于垂向断层提出的预测公式去模拟75°陡倾的随机断层,有93.17%的预测结果误差在15%以内。和其他已有的经验预测模型相比,现存经验模型的预测结果与异常的实际距离分布误差很大,而本文提出的预测模型结果均呈现很好的正态分布特性,绝大多数的各向异性随机异常的预测距离与它们的实际距离非常接近,误差很小,这验证了本文预测模型的准确性和可靠性。蒙特卡罗法为隧道超前探精度和可靠性的定量评价提供了一种新的方法。以上传统的隧道超前探电阻率法将点电极源布置在紧邻掌子面、最靠近前方异常体的位置,是通过点电极源激发产生稳定电流场与前方低阻体耦合产生异常响应,并被掌子面后方布置的三极视电阻率剖面观测到用来推测前方低阻异常体位置。其最大问题是后方观测到的异常响应较小,造成传统点电极源隧道超前探电阻率法的探测深度小。尽管有学者提出通过改变激励点电极源或收发装置的组合形式,可在一定程度上增大探测深度,但终究因为掌子面前方的不可入性,探测效果有限。本文利用隧道掌子面掘进过程需要打先导钻孔的特点,将先导孔钻杆视为长电极源,从而可在离掌子面前方异常体更近处激发电流场并相互耦合,产生更强的异常信号。据此本文基于全空间长电极源电阻率三维数值模拟,首次提出了全空间长电极源装置的理论公式,并对长电极源超前探模型进行了测试,验证了该算法的准确性和精度。在传统底板观测形式条件下基于超前探断层模型大量模拟了长电极源的视电阻率响应规律,然后提取极小值位置,利用多元线性回归方法,第一次提出了隧道超前探长电极源的预测模型。该预测模型方程的R平方等于0.992,且有91.60%的预测结果与断层实际距离误差均较小,表明隧道超前探长电极源预测模型是准确可靠的。最后,通过超前探断层模型三维有限元数值模拟,在同等条件下将长电极源超前探预测模型与点电极源超前探预测模型进行比较,结果表明点电极源超前探预测模型仅对短距离异常位置的估计很准确,而长电极源超前探预测模型对短距离和远距离的异常位置估计均很准确。隧道超前探长电极源比点电极源的探测深度大。长电极源预测模型定量地给出了估计掌子面前方含水异常位置的方法,该方法增大了超前探的探测深度,对提高施工效率和保障隧道安全掘进具有重要意义。

＜正＞高密度电法可以高效地获得大量地电观测数据,使得地下精细结构的电阻率三维反演成像成为可能,并迅速成为该领域国内外学者关注的前沿课题。然而目前电阻率三维反演及其应用多基于平坦地形,实际勘探中地形影响不可避免,其对电阻率反演结果可能造成难于预料的偏差。已有结果表明:做地形改正只能是近似的,地下结构稍复杂,这种改正误差就很大。只有将地形同时带入反演算法中,才能精确消除地形影响及其对反演结果的偏差。但是

During tunnel excavation, water hazards in faults, especially steep water rich faults, pose a serious threat to safe construction in some complex mountains, which leads to low economic growth and development in these areas. Direct current resistivity method, which has high resolution and sensitivity to the low resistivity body is widely used to predict the water-bearing structures in the front of tunnel face. The current prediction models are based on the resistivity isotropic medium, however, the resistivity of water bearing fault is often anisotropic due to rock fracture. The prediction model neglecting the anisotropy is obviously inaccurate, which brings potential threats to safe construction. We develop a three-dimensional resistivity modeling for anisotropic media using unstructured finite element method. The algorithm is proved to be accurate by comparison of numerical results and analytical solutions for a whole-space model. Another classical anisotropic model also demonstrated the reliability of our code from a physical point of view. Then we propose a prediction equation to predict the position of a vertical fault with anisotropic resistivity in the front of tunnel face by the finite element simulations. The parallel Monte Carlo method is used to test and evaluate the quality of our prediction equation by simulations of 10000 random vertical fault models, results counted by the histogram showed 85.36% of the results are predicted within 10% of the error. Besides, 93.17% of the results are predicted within 15% of the error using the equation for random faults with 75 degree dip angle, which shows that our prediction model can effectively forecast steeply dipping water-rich faults or fracture zones.

防渗墙广泛应用于堤坝防渗处理,为确保其抗渗能力,需对墙体底界进行检测。为提高对防渗墙底界的判定能力,提出了动态高密度视电阻率测试方法。构建了防渗墙物理模型,并在模型两侧分别布置了高密度电法测试系统和钻孔,通过测试钻孔注入盐水前后的动态电性参数,发现视电阻率及其变化率对受注水影响的地质体敏感,初步确定注水后的地质体视电阻率变化率约为15%时可作为模型底界判定的依据。工程实践进一步证实了研究方法的有效性和可靠性。

Water inrush during tunnel excavation severally threatens the mining safety as blind water-bearing structures may develop in front of the working face. The transient electromagnetic method (TEM) has been widely applied in the advanced detection of tunnel water-bearing structures. However, the metal interference of both supports and tools in the tunnel has become a bottleneck that reduces the forecast accuracy of this method. In this paper, we analyse the effect of metal interference on TEM data and propose a novel set of an observation and correction method under metal interference based on the ratio of anomalous and background apparent resistivity. Flume model experiments both with and without metal interference are carried out, showing that this interference can affect TEM measurements significantly and result in false anomalies, and that our proposed method can remove this ambient noise caused by metal interference appropriately. The practical application further proves that this method can effectively reduce low-resistivity interference introduced by the support and other metal tools inside the tunnel. By applying this correction method, the location of water-rich anomalies can be detected more precisely during the excavation process of the same tunnel, which is of high application value of reducing exploration difficulty and tunneling risk.