A Study On Comprehensive Detection Methods Of Surrounding Rock Loose Circle And Application

Underground cavernof hydropowerstationisan important part ofwater resources and hydropower projects, the stability of its surrounding rock affects the safe production of the entire hydropowerdirectly. Due to the joint action of rock damage caused by the excavation and stress redistribution from itself, broken annular regions appeared in the internal surrounding rock ofunderground caverns, which known as loose circle. Loose circle threatens the stability of underground caverns directly, therefore,it is necessary to monitor its range.In monitoring process, selecting accurate detection methods and scientific analysis methods is the key to get the range of loose circle and its variation law.Therefore, the study on detectionmethods and analysismethods has a positive significance in the monitoring of loose circle and the ensuringof surrounding rock stability.Through the study on comprehensive loose circle detection methods, the accuracy was improved. Applying this results in practice, combining with scientific analysis method,the variation with time and space of loose circle was revealed. The main contents and achievements are as follows:First, the factors such asaccuracy, economy and convenience of various loose circle detection methods were compared. Single hole sonic wave testing and borehole imaging were chosen as the selected methods after consideration.Two defects of sonic wave testing were also pointed out: the noise interference and the lack of horizontal continuity.Aiming at the problem of noiseinterference,adenoising processing based on wavelet transformwas used to improve the readability of preliminary. An assessment of denoising performancewith limited understanding of puresignal was put forward while studying. The optimal combination of denoising was selected by this assessment.Then, denoised test results were interpreted,the integrity ofrock masswasassessdin all directions by using amulticriteria assessment. Wave velocity curvesweredivided it into 5types, and for each type, the rock conditions it reflects were described.Based on the interpretation, analyzing the measured data of a hydropower station underground powerhouse as an example, the view that the reason of the extending loose circlewould be time-continued stress redistribution was pointed out,consolidation and monitoring should be keeping at a certain levelafter the end of the excavation was suggested.Last but not least, aiming at the problem of the lack of horizontal continuity, the profilesof underground cavern were taken as the object during the loose circle analysis.The adverse effects were suppressedby using this kind of analysistechnique.According to the study listed above, the defects of single hole sonic wave testingwere overcame effectively, These achievementswere used in a underground cavern project of an underground hydropower station and got a good effect,itsfeasibility,effectiveness and promotion value were verified.