土体变形破坏电磁辐射效应及前兆特征识别研究

Geological disasters and engineering problems such as collapse, landslide and ground subsidence are caused by soil failure, which can cause heavy losses. Recognition of disaster precursor is an important basis for preventing geological disasters. The characteristics and precursor of variation frequency of electromagnetic radiation (EMR) in different soil are studied under different loading condition. Then, we analyze the physical mechanics parameters, pre-crack and electrical parameters of soil effecting on variation frequency in electromagnetic radiation during the process of soil fracture. We study the relationship between soil damage and dominant characteristics frequency of EMR of soil under different stress level, and establish the coupling model of stress, EMR and energy for soil damage based on the dominant characteristics frequency of EMR. Then the generation mechanism of electromagnetic radiation in soil failure is discussed theoretically. After that, we study the haracteristics of variation frequency of EMR in the dynamic instability and evolution process of Side-slope, to establish the relationship between the dominant characteristics frequency of EMR and the risk degree of side-slope, and to propose a side-slope stability assessment method based on EMR variation monitoring. The results have important significance not only for theoretical and but also for practical significance in further revealing microscopic processes of the soil fracture and generation mechanism of electromagnetic radiation, and which can promote the application of electromagnetic radiation monitoring technique.

土体破坏失稳会带来崩塌、滑坡及地表塌陷等地质灾害与工程问题，造成惨重的损失。灾害前兆信息的准确识别是防治地质灾害的重要基础。本项目拟研究不同性质土体材料在不同加载条件下失稳破坏过程多频电磁辐射特征规律，分析土体性质、预制弱面、视电阻率及含水量对其变形破裂过程电磁辐射影响；研究确定土体破坏电磁辐射前兆特征规律及优势特征频率，并分析其与土体材料损伤的关系，建立基于电磁辐射的土体损伤力-电-能耦合模型；现场测试边坡动力失稳破坏过程的多频电磁辐射响应规律，建立多频电磁辐射信号与边坡稳定性及危险程度的关系，初步提出土体边坡稳定性评估的电磁辐射监测方法。项目的研究成果对进一步揭示土体材料损伤破坏的微观过程和电磁辐射产生机理，促进煤岩电磁辐射监测技术的发展和应用具有深远的理论意义和现实意义。

项目从岩体、土体试样损伤过程的电磁辐射、表面电位信号入手，研究了不同加载过程岩体、土体试样的电磁辐射、表面电位的规律及前兆特征，分析材料参数、含水量、加载速率等因素对电磁信号的影响，建立土体损伤过程的力-电模型。通过相似实验分析边坡孕育过程表面电位特性，现场测试分析了边坡稳态电磁辐射特征规律。. （1）岩体、土体试样在单轴压缩、劈裂、摩擦等加载过程中均有电磁辐射信号、表面电位信号产生，电磁信号的强度与试样力学性质成正比，较好地反映了岩体、土体损伤过程。从波谱特性分析，岩体在30kHz、300kHz、800 kHz、1000 kHz等频段响应明显，低频段的电磁辐射幅值高于中高段，高频电磁辐射信号在不同应力水平下，主频频率变化较大，低频电磁辐射信号的主频相对稳定。土体试样为重塑样，各向异性明显，300kHz、800 kHz电磁辐射传感器未采集到电磁辐射信号，其它频段电磁辐射主频幅值低于同频段岩体试样电磁辐射。土体电磁辐射信号的低频电磁辐射峰值主频相对岩质边坡体而言，更加稳定，高频电磁辐射峰值主频偏离方向相反，偏差接近。. （2）土体材料含水率的增加，对于其损伤过程产生的电磁辐射峰值主频频率影响较小，但其幅值呈下降的趋势。加载速率的增加，使得土体破坏峰值压力增加，其峰值主频幅值增加，通过数值模拟实验得到验证。. （3）表面电位相似模拟实验表明，人为扰动影响下，边坡表面电位波动显著，自然状态下，电位信号仅为人为扰动阶段的0.7% ~ 2.1%。在边坡的孕育发展过程中，表面电位信号呈现出“活跃-平静-活跃”交替式变化特征。. （4）建立了土体试样变形破坏低频电磁辐射力-电模型，在土体应力水平（0~0.7σmax） 条件下，低频电磁辐射幅值呈现先下降后增长的趋势，可应用于其稳定性的评价。现场岩体边坡稳态状态下，电磁辐射频谱呈多峰特性、双峰特性，峰值频段集中30~30kHz，多峰电磁辐射频谱的峰值较小，双峰电磁辐射频谱辐值高。