摘要
水利学科前沿实验是"新工科"人才培养模式下实验教学的重要环节.为丰富前沿实验内容,将科研与教学紧密结合,设计了跨孔雷达检测水工防渗墙隐蔽病害的可视化实验系统.该系统由可视化水箱、可视化模型箱和跨孔雷达系统三部分组成.可视化水箱尺寸为1.2 m×1.0 m×1.5 m;可视化模型箱尺寸为0.6 m×0.2 m×1.0 m;跨孔雷达系统由网络分析仪和收发天线采集数据,由控制主机存储和显示数据.实验教学表明,该系统能够利用跨孔雷达有效检测出水工防渗墙内部隐蔽病害,具有较强的创新性和前沿性,有助于激发学生的创新思维,提高科研能力,达到以研促教、教研相长的目的.
Abstract
[Objective]A hydraulic antiseepage wall is an underground diaphragm wall built in an Earth and rockfill dam to prevent seepage.The quality of the wall directly affects the impermeable effect and structural safety.However,defects within the antiseepage wall are usually randomly distributed and relatively hidden,so it is crucial to timely and accurately capture the hidden defects within the wall.Crosshole ground penetrating radar(GPR)is an efficient geophysical method for detecting and locating inner defects in antiseepage walls without excavation.It involves inserting antennas into measurement pipes buried in the structure to conduct high-frequency electromagnetic signal(EMS)measurements.By analyzing and inverting the EMS data,an inference of the defect position,size,shape,and physical characteristics is achieved based on the differences in the electrical parameters of various media.Crosshole GPR has advantages such as high accuracy,high resolution,and sensitivity to water-containing materials,and it is not limited by penetration depth.[Methods]Herein,a teaching experiment was performed using crosshole GPR to detect concealed defects in an antiseepage wall.The experimental system comprises a visual water tank,a visual model box,and a stepped-frequency crosshole GPR system.The dimensions of the visual water tank and model box are 1.2 m×1.0 m×1.5 m and 0.6 m×0.2 m×1.0 m,respectively.The visual model box is placed inside the water tank,and the cavity between these two components is filled with water(permittivity of 78.28 and conductivity of 0.30 S/m)to simulate the surrounding backfill.The visual model box is filled with dimethyl malonate to simulate the concrete wall because the dielectric parameters of dimethyl malonate(permittivity of 15.88 and conductivity of 0.24 S/m)are similar to those of concrete wall.Two measurement pipes are placed vertically from the top to the bottom of the visual model box,enabling the antennas to move up and down in the pipes and facilitating the zero-offset profiling and multioffset gather.The stepped-frequency crosshole GPR system comprises a vector network analyzer(VNA),a pair of transmitting and receiving antennas,and a laptop.The VNA generates and collects electric signals(ESs).The transmitting antenna converts ES to EMSs,propagating through the medium between the antennas.Next,the receiving antenna receives EMSs and relays them back to the VNA.[Results]Four cases are well-designed to simulate the different defects in a hydraulic antiseepage wall,including voids full of air,water,mud,and uncompacted stone.Crosshole GPR data are collected for all the cases,and electronic parameter inversion is performed using computed tomography.The physical characteristics of the defects can be accurately revealed,indicating that the experimental system can use crosshole GPR to effectively detect concealed defects within the antiseepage wall.[Conclusions]Using this experimental system,GPR images are easily acquired and the electronic parameter inversion of the medium is achieved,enabling an inference of the defects.Meanwhile,this system inspires students'innovative thinking,enhancing their research capabilities and achieving the goal of promoting teaching through research and vice versa.
基金项目
国家本科教学工程项目(ZL2021260)
国家重点研发计划(2022YFB4703404)
国家自然科学基金(52079022)
大连理工大学教育教学改革项目(YB2023048)
NETL
NSTL
万方数据