【作者】 谭代明；

【导师】 漆泰岳；

【作者基本信息】 西南交通大学 ， 桥梁与隧道工程， 2009， 博士

【摘要】 随着我国高速铁路、高速公路、海底隧道工程的建设,地质灾害一直都是威胁隧道与地下工程施工安全的主要灾害。在这些地质灾害中,地下水是影响隧道修建速度和威胁工程施工安全最主要因素之一,如:岩溶溶洞、暗河、岩溶陷落柱、岩溶淤泥带和富水断层破碎带等不良地质结构体,都会给隧道与地下工程的修建和运营带来困难和危害。显然,要避免这些地质灾害的发生,隧道地质灾害超前预报就显得尤为重要。目前,超前地质预报的方法不少,这些方法在应用中各有所长。但是在施工中,探测掌子面前方的水体病害方面,尚是一个待攻克的难题。瞬变电磁法是对充水充泥的不良地质体进行超前地质预报的新方法。瞬变电磁法对低阻充水断层、充泥充水溶洞、充水充泥破碎带等不良地质体反应灵敏。但是瞬变电磁解释技术的相对滞后,复杂的数值算法,正、反演计算需要大量的机时和内存等因素,严重制约着瞬变电磁法的发展。因此,研究二、三维模型的瞬变电磁响应具有重要的理论和现实意义。目前电磁法勘探中常用的数值模拟方法主要有:有限差分法、有限单元法、边界单元法和积分方程法等。有限差分法和有限单元法在时间域里更为方便。本文应用有限元软件ANSYS和时域有限差分编程方法对瞬变电磁场进行数值模拟,比较了两种计算方法的优劣。采用数值模拟的方法对瞬变电磁法超前地质预报进行了数值模拟分析,比较了地面半空间和地下全空间瞬变电磁传播特性。通过改变低阻异常体埋深、半径和电阻率及高阻围岩的电阻率,得到了各参数的变化对结果的敏感程度。分析研究了影响地质体响应异常的影响因素及响应异常随影响因素的变化规律。通过数据库系统的开发,将数值模拟结果作为样本集存储到数据库中。利用开发的数据库系统管理平台将数值模拟计算结果转换为隧道瞬变电磁法标准样本库。通过管理系统实现了对数据库的管理和维护,同时可将实际工程应用结果直接转换为系统中的标准样本库。在数据比较中对同一模型下不同时间门所对于的数据赋予不同的权值,得到与实测数据最接近的模拟结果,从而形成数据库反演专家系统。利用MATLAB软件,设计和开发了一个改进的BP神经网络反演系统。该系统避免了复杂的电磁场计算,只需经过学习训练就能够解决复杂的实际问题,而且具有记忆功能,从而使瞬变电磁法的反演工作具有延续性和可继承性。针对常规线性反演方法所存在的缺陷,提出了基于最小二乘支持向量机网络非线性反演方法。以数值模拟所得到的对应20个时间点结果值作为输入数据,该结果值所对应模型的地电参数作为输出数据。通过在MATLAB中加载LSSVM函数,形成LSSVM瞬变电磁反演专家系统。根据物理模拟相似准则,选择盐水和石墨作为实验材料模拟高阻围岩和低阻水体。研究了接收和发射线圈的电性参数对瞬变电磁信号的影响规律,根据这种影响规律,利用漆包线并采用间绕的方法绕制了实验中的接收和发射线圈,将野外使用的PROTEM47型瞬变电磁仪系统中的发射机和接收机应用于实验中,将石墨块、接收和发射线圈置于盐水槽中,通过改变石墨块大小、位置以及电阻率,来观察瞬变电磁信号受各参数的影响规律。将三种反演专家系统应用于实际工程中,同时根据全空间视电阻率公式,采用VC编程的方法,将实际工程探测所得到的时间——响应曲线转化为深度——视电阻率曲线,将掌子面测线数据转化为深度——视电阻率断面图,对比两种计算方法的结果,说明反演专家系统在瞬变电磁反演中的可行性。更多还原

【Abstract】 With the construction of high speed railway, highway and submarine tunnel, geologic disasters always play the main part in threatening the safety of tunnel and underground engineering construction. Among these geologic disasters, underground water is one of the main factors. For example, karst cave, underground river, karst sink hole, karst muddy belts, water-saturated fracture zone and so on, all these can bring about difficulty and harm to construction and operation of tunnel and underground engineering. By all appearance, tunnel geological hazard forecasting plays an important part in avoiding these geological hazards. Presently, there are many methods used in the field of tunnel geological hazard forecasting and these methods have their own advantage. But there is an unsolved problem in the exploration of unfavorable geology in tunnel filled with water for the advanced forecast of geology in tunnel construction.Transient Electromagnetic method (TEM) is a new method used to forecast the unfavorable geology filled with water or mud. The new method is sensitive to the unfavorable low resistively geologic bodies filled with water or mud such as faults, caves, zones of rock fracture and water-saturated fracture zones. Because of relative backwardness in explain technology, complex algorithm, a large amount of time and computer memory for the inversion and forward of calculation and other factors, all these severely restricted the development of TEM. It is theoretical and practical demand to study the transient electromagnetic response of two-dimensional and three-dimensional models. At present the numerical simulation of electromagnetic method of finite difference method, finite element method, boundary element law, integral equation method, and so on were commonly used in the exploration. The time domain finite difference and the finite element method are more convenient. This thesis adopts the finite element software ANSYS to analyze transient electromagnetic method for geological prediction. The spreading characteristics of the transient electromagnetic field in tunnels in whole-space and in earth in half-space were compared. The sensitivity characteristics of geoelectric parameters were investigated by changing the depth, radius, and resistivity of an anomalous body and the resistivity of surrounding rock. Influencing factors of the geological anomaly response and the law of the abnormal response changing with the factor were studied.The results of simulating were stored into database as sets of specimens by development of database system. The computed results were transformed into standard samples of transient electromagnetic methods in tunnels using a developed database system, management and maintenance of the database were realized. The results of engineering applications can be transformed into standard samples. The measured data were inputted and compared with the data in database while inversing. Data of the same model on different time were assigned matching weighting, the data in database closed to measured data were selected by comparing the weighing data, and thus the expert system of database for inversion was formed. An improved inversion system of BP neural network had been designed and developed by using MATLAB software. The system avoided complicated calculations of electromagnetic field and can be used to solve some practical problems through learning and training. It can also memorize and make the inversion a continuous process which depends not only on current event but also the previous event. A nonlinear inversion method based on LSSVM network was proposed by analyzing the conventional inversion methods and overcoming their defects. Results of simulating on twenty time were inputted and the geoelectric parameters corresponding the model were outputted. LSSVM expert system was formed by loading function of LSSVM into MATLAB software.Brine and graphite were picked out as the experimental material to simulate rock with high resistivity and water body with low resistivity according to similarity criterion of physical modeling. The response law of transient electromagnetic signal affected by the electrical parameters of receiving loops and transmitting loops were researched. The receiving loops and transmitting loops were designed by spaced winding with lacquered wire according to the displine. The transmitter and receiver in PROTEM47 transient electromagnetic system used countryside were used in experiment. The graphite, receiving loops and transmitting loops were put into a pool filled with brine, the response laws of transient electromagnetic signal were observed by changing the measurement, position and resistivity of a graphite.Three expert systems for inversion were applied into practical engineering. Basing on the formulation of apparent resistivity in whole space, the curves of time vs. response which were gotten from practical exploring were transformed into the curves of depth vs. apparent resistivity by VC program. The data which were gotten from measurement line on working face in tunnel were transformed into the section map of depth vs. apparent resistivity. The result shows that expert system for inversion is feasible.更多还原