【作者】 徐浩；

【导师】 刘江平；

【作者基本信息】 中国地质大学 ， 地球探测与信息技术， 2021， 博士

【摘要】 土石坝是我国水利工程中最广泛的坝体类型之一,其安全性是各类水利工程正常运行的重要保障。土石坝防渗结构主要由大坝面板与坝体两部分组成,面板介质为混凝土,坝体由土料与石料按照一定的级配碾压堆筑而成。我国目前现有的土石坝大部分修建于上个世纪中后期,由于历史原因,大量土石坝存在工程标准偏低、建设质量较差、老化失修严重、工程管理落后、配套设施不全等一系列问题,经过几十年的运行后,许多土石坝都存在面板脱空开裂、坝体渗漏等隐患,对水利工程的正常运行造成较大的影响。因此及时准确地探明大坝面板与坝体病害,可为大坝渗漏隐患的综合处理提供依据,最大程度地降低渗漏隐患造成的损失。本文在当前土石坝病害探测研究基础上,针对大坝病害探测中存在的问题,开展土石坝病害地球物理波场研究,建立了离散随机介质土石坝模型,实现了土石坝三维地震波场模拟,阐明了土石坝坝体渗漏形成过程中渗漏区域含水量变化对渗漏波场的影响,揭示了渗漏隐患识别的有效地震属性,总结出混凝土面板不同脱空情况下雷达波场与瞬时属性特征,形成了有效的土石坝隐患探测技术,取得的主要研究成果如下:(1)基于常规随机介质理论,提出了能有效体现土石坝介质中土料与石料弹性介质差异且具有一定土石比的离散随机介质建模方法,分析了自相关长度、粗糙度因子以及局部窗口尺度等随机参数对离散随机介质模型建立的影响,阐述了不同随机参数与土石介质粒径大小的相关性。(2)实现了均匀介质、常规随机介质、离散随机介质地震波场数值模拟,对比分析了三种介质波场的差异性,分析了随机介质中散射波对有效波场识别的影响,总结了随机参数、土石比例变化与散射波强弱的对应关系。结果显示随着自相关长度增加,散射波能量强度逐渐增大,随着模型中石含量增加,波场的散射逐渐减少,散射波能量逐渐减弱,离散随机介质的波场特征逐渐趋向于均匀介质。(3)根据土石坝外部形态与边界条件特点,采用倾斜AEA自由边界、M-PML与C-PML吸收边界,分区域处理坝体不同部位边界,实现土石坝三维地震波场模拟。模拟结果显示在坝体上游存在面板的情况下,坝体上游检波点接收到的面波到达时间变短,随着坝坡坡比的增加,基岩界面反射横波在上游坝顶产生的绕射能量逐渐减弱。离散随机土石坝波场中面波产生的散射对整体波场影响较大,在面波到达时间之前的反射波同相轴基本不受其影响,坝体介质中随着土料含量增加,石料颗粒的散射效应更突出,波场中散射波能量更强。(4)通过对比分析不同激发点、不同平面、不同分量含渗漏隐患的三维地震波场记录,对比了纵波、转换波、横波对渗漏隐患的识别能力。基岩界面反射纵波与渗漏纵波反射叠加后,通过纵波信息很难识别出渗漏隐患,而基岩界面的横波反射与渗漏横波反射波场叠加之后呈现能量增强,频率降低的特征,故横波信息对渗漏的识别能力要强于纵波。(5)通过对离散随机土石坝渗漏区域不同含水量渗漏模型的地震波场对比分析显示,随着渗漏区域含水量的降低,渗漏反射波场能量逐渐减弱,当渗漏位于坝底时,只有渗漏区域含水量达到25%以上,才能从地震记录中有效地识别出渗漏异常;而当渗漏区域位于距离坝底5m处时,只有当渗漏区域含水量达到10%以上时,才能有效的识别出渗漏异常。(6)当土石坝内部存在渗漏隐患时,坝体地震属性中渗漏反射区域振幅与频率都会发生变化,渗漏反射同相轴呈现强能量、低频率特征。随着渗漏区域含水量降低,瞬时振幅中渗漏反射同相轴能量逐渐减弱,瞬时频率中渗漏反射低频同相轴连续性变差。瞬时振幅与瞬时频率主要体现强能量反射同相轴,对弱能量的反射波场敏感度不高;瞬时相位不受振幅能量的影响,可突出弱能量反射同相轴;小波变换抗干扰能量较强,可一定程度的压制地震记录中的散射波场。当渗漏区域含水量较低,渗漏反射能量较弱时,可利用瞬时相位来进行渗漏隐患识别;在地震记录信噪比不高时,可通过小波变换的频率切片来分析地震记录中的渗漏反射信息。(7)开展了无钢筋、单层与双层钢筋面板脱空模型雷达波场模拟,阐述了存在不同类型钢筋情况下面板脱空雷达波场响应特征,揭示了脱空反射同相轴的“下拉”现象,给出了能定量识别面板脱空厚度的条件。当面板内部存在钢筋时,脱空反射同相轴连续性变差,随着面板内部钢筋层数的增加,钢筋间距的减小,脱空反射波形态与反射同相轴“下拉”现象逐渐消失。当雷达数据信噪比较低,从雷达剖面图无法识别脱空存在的情况下,可借助瞬时属性来识别脱空隐患。本文主要的创新之处为:(1)基于随机介质理论,提出了能有效体现土石坝介质特点的离散随机介质建模方法,分析了建模过程中随机参数对模型非均匀性的影响,为建立与实际更为接近的土石坝模型提供了理论基础;(2)根据土石坝外部形态特点,分区域对坝顶、坝坡、坝底自由边界或吸收边界进行处理,实现了土石坝三维地震波场模拟,分析了土石坝坝体渗漏隐患形成过程中渗漏区域含水量变化对地震波场的影响;(3)基于地质雷达理论模拟与实测数据,分析了土石坝面板内部钢筋对脱空识别的影响因素,给出了能定量识别脱空厚度的条件,弥补了地震探测分辨率的不足。更多还原

【Abstract】 Earth-rock dams are one of the most widely used types of dams in China’s hydraulic engineering,and their safety is an important guarantee for the normal operation of all types of hydraulic engineering.The earth-rock dam containment structure consists of two parts,the panel and the dam body,the panel medium is concrete and the dam body is made of soil and stone in accordance with a certain gradation of rolling and stacking.Most of the existing earth-rock dams in China were built during the middle and end of the last century.Due to historical reasons,a large number of earth-rock dams have a series of problems such as low engineering standards,poor construction quality,serious aging and dilapidation,backward engineering management and incomplete supporting facilities,etc.After decades of operation,many earth and rock dams have hidden problems such as panel cracking and dam leakage,which have a negative impact on the normal operation of hydraulic engineering.Therefore,the timely and accurate detection of dam panel and body damage can provide the basis for comprehensive treatment of potential dam leakage and thus reduce the damage caused by potential leakage to the greatest extent.On the basis of current research on earth-rock dam damage detection,this paper conducts research on the geophysical waves of earth-rock dam damage to address the problems in dam damage detection,establishes a discrete random media earth and rock dam model,realizes the simulation of three-dimensional seismic wave field of earth and rock dams,clarifies the influence of water content changes on the leakage wave field during the formation of earth and rock dam leakage.It also reveals the effective seismic attributes for leakage hazard identification,summarizes the characteristics of radar wave field and transient attributes under different void conditions of concrete panels,thus forming an effective earth-rock dam hazard detection technique.Key research results achieved are as follows:(1)Based on the conventional random media theory,the discrete random media modelling method is proposed to effectively reflect the difference between soil and stone elastic media in earth-stone dam media with a certain soil to stone ratio.Analysing the influence of stochastic parameters such as correlation length,roughness factor and partial window scale on the modelling of discrete random media,the correlation between different stochastic parameters and the particle size of soil and rock media is illustrated.(2)The numerical simulation of the seismic wave field in homogeneous medium,conventional random medium and discrete random medium is realized,the differences of the wave field in the three mediums are compared and analyzed,the influence of scattered waves on the identification of the effective wave field in random medium is analyzed,as well as the correspondence between the random parameters,the change of soil to stone ratio and the strength of scattered waves is summarized.The results show that as the autocorrelation length increases,the intensity of the scattered wave energy gradually increases,the scattering of the wave field gradually decreases as the stone content in the model increases,the scattered wave energy gradually weakens,and the wave field characteristics of the discrete random medium gradually converge to that of a homogeneous medium.(3)According to the characteristics of the external morphology and boundary conditions of the earth-rock dam,the tilted AEA free boundary,M-PML and C-PML absorption boundaries are used to handle the boundaries of different parts of the dam body in different regions to realize the 3D seismic wave field simulation of the earth-rock dam.The simulation results show that in the presence of panels upstream of the dam,the arrival time of the surface waves received at the upstream detection point of the dam becomes shorter,and as the slope ratio of the dam slope increases,the reflected transverse waves at the bedrock interface produce gradually weaker bypass energy at the top of the upstream dam.The scattering generated by the surface wave in the wave field of a discrete random earth and rock dam has a greater effect on the overall wave field.The in-phase axis of the reflected wave before the arrival time of the surface wave is largely unaffected by it,and the scattering effect of the stone particles in the dam medium becomes more prominent as the soil content increases,and the scattered wave energy in the wave field becomes stronger.(4)By comparing and analysing the 3D seismic wavefield records with different excitation points,different planes and different fractions of leakage hazards,the ability of the longitudinal,converted and transverse waves to identify the leakage hazards was compared.After the superimposition of the reflected longitudinal waves at the bedrock interface and the reflected longitudinal waves of leakage,it is difficult to identify the hidden leakage by the longitudinal wave information,while the superimposition of the reflected transverse wave at the bedrock interface and the reflected transverse wave of leakage shows an increase in energy and a decrease in frequency,which means that the transverse wave information is more capable of identifying leakage than the longitudinal wave.(5)A comparative analysis of the seismic wave fields of the leakage models with different water contents in the leakage area of a discrete random earth-rock dam shows that as the water content of the leakage area decreases,the energy of the leakage reflected wave field gradually decreases,and when the leakage is located at the bottom of the dam,only when the water content of the leakage area reaches more than 25% can the leakage anomaly be effectively identified from the seismic record;And when the leakage area is located at a distance of 5m from the bottom of the dam,leakage anomalies can only be effectively identified when the water content of the leakage area reaches more than 10%.(6)When there are leakage hazards inside the earth-rock dam,the amplitude and frequency of the leakage reflection region in the seismic attribute of the dam will change,and the leakage reflection homogeneous axis will show strong energy and low frequency characteristics.As the water content of the leakage area decreases,the energy of the leakage reflection homogeneous axis in the transient amplitude gradually decreases,and the continuity of the leakage reflection low-frequency homogeneous axis in the transient frequency deteriorates.The transient amplitude and transient frequency mainly reflect the strong energy reflection homogeneous axis,and are not sensitive to the weak energy reflection wave field;the transient phase is not affected by the amplitude energy,and can highlight the weak energy reflection homogeneous axis.The wavelet transform is more resistant to interference energy and can suppress the scattered wave field in the seismic record to some extent.When the water content of the leakage area is low and the leakage reflection energy is weak,the instantaneous phase can be used for leakage hazard identification;when the signal-to-noise ratio of the seismic record is not high,the frequency slicing of the wavelet transform can be used to analyse the leakage reflection information in the seismic record.(7)The radar wave field simulations of panel devoid without reinforcement,single-layer and double-layer reinforcement are carried out to illustrate the response characteristics of panel devoid radar wave field in the presence of different types of reinforcement,reveal the “pull-down” phenomenon of the reflected homogeneous axis of devoid,and give the conditions for quantitative identification of panel devoid thickness.When reinforcement is present inside the panel,the continuity of the reflected in-phase axis of the devoid becomes poor.As the number of layers of reinforcement inside the panel increases and the spacing between the reinforcement decreases,the“pull-down” phenomenon of the devoid reflection wave pattern and the reflected in-phase axis gradually disappears.When the signal-to-noise ratio of the radar data is low and the presence of voids cannot be identified from the radar profile,transient attribute can be used to identify the potential for voids.The main innovations of this paper are as following:(1)Based on the theory of random media,a discrete random media modeling method that can effectively reflect the characteristics of earth-rock dam media is proposed,and the influence of random parameters on the size of grain in the model building process is analyzed,which provides a theoretical basis for setting up an earth-rock dam model that is closer to the actual one.(2)According to the characteristics of the external morphology of earth and rock dams,the free boundary or absorption boundary of the top,slope and bottom of the dam are processed in different regions to realize the simulation of the three-dimensional seismic wave field of earth and rock dams,and the influence of the change of water content in the leakage area on the seismic wave field during the formation of the potential leakage of earth and rock dams is analyzed.(3)Based on theoretical simulations of geo-radar and actual measurement data,the factors influencing the identification of de-voiding by internal reinforcement in earth-rock dam panels are analysed,and the conditions that can quantitatively identify the thickness of de-voiding are given to make up for the lack of accuracy in seismic detection resolution.更多还原