Instrumentation and technology support of the acoustic monitoring in the vicinity of shafts

Abstract

The paper presents the hardware and technology support for geophysical examination over the structure and conditions in the vicinity of shafts in a potassium salt mine. The details of multichannel linear observation design, acoustic data processing, and interpretation approaches to the detection of the potentially permeable zones are discussed.Safety of underground mine workings depends on many geological and engineering aspects, including conditions in shafts. Mine shafts operate continuously, which calls for specific precaution and prevention. We are focusing on the safety of shafts in water-soluble mineral formations, such as the 80-years-long operating mines at the Upper Kama Potassium Salts Deposit.The construction technology and design of shafts imply vicinity of the shafts being watertight, yet water entries appear regularly at the level of aquifers during the life of mines. The method of controlling water ingresses is plugging-back oriented to dampproofing of the 1.5-2-m vicinity outside the shaft tubbing. Reliable plugging-back condition monitoring and the dampproofing quality control are required in this case [1].The annulus condition monitoring uses nondestructive geophysical examination techniques [2]. Acoustic measurements are obviously most effective for the tubbing quality control. If a control object is largely velocity-heterogeneous, the classic acoustic measurement schemes and one-channel echosounding interpretation appear noninformative.Based on the most intelligent geophysical technique-seismic survey, a dedicated hardware and technology complex has been developed for the acoustic measurement implementation in the near zone of shaft vicinity, including a multichannel data acquisition system, adaptable processing graph and a collection of interpretative algorithms.Applicability of the classic seismic survey approaches in the acoustic frequency range depends on the "quasi-layered" structure of a shaft in plan-the tubbing, cement column, and the rock mass. This model is characterized with variable physical and geometrical parameters of its components. In the condition of the velocity and structure heterogeneity of the monitored geological and engineering objects in a mine, the acoustic measurements are the most informative within the common depth point technique (CDP). The frequency of the measurements, effective spatial processing of the recorded wave field, and the dynamic correlation of reflected waves contribute to that [3].Major advantage of CPD is the spreads of sources and receivers and their shifting in the course of data acquisition [4]. During the field seismic survey within the acoustic frequency range, numerical rating of the recording system parameters are aligned with the minimum and maximal depths of the target interval, frequencies of the reflected waves, and with the required resolution and performance capacity of the hardware used [5].