Field experiment on the attenuation rule of main frequency for mining blasting vibration in the karst area
The study area is located within the Gudan lead-zinc mining region of Rong'an county,Guangxi.This area falls under the subtropical monsoon climate zone,experiencing four distinct seasons with abundant rainfall.It is characterized by a karst landscape of peak-cluster valleys,with undulating topography and a relative elevation difference of about 300 m.The study area is located in the gently flexural fold structure of rock strata from Siding to Tunqiu in a nearly north-south direction.The secondary small-scale fold structures are developed in a normal way,but fault structures are well developed,consisting of two main groups in north-south and north-east directions.The overlying soil layer mainly consists of clay soil,while the underlying bedrock is made up of sandstone,quartz sandstone,dolomite and gray rock.Karst is well developed primarily in exposed form,followed by buried type.The distribution trend of karst is in accordance with the fault structure of the area.Karst development is subject to lithology,and slows down with the increase of depth.Many surface collapses have occurred on a large scale in the study area.Karst fissure water is the primary groundwater,mainly existing in the limestone of Donggangling Formation(D2d)of the Middle Devonian.Groundwater is recharged by atmospheric precipitation and replenished vertically through surface weathering fissures,karst caves,funnels and sinkholes.The karst fissures well developed at the shallow part serve as conduits for groundwater recharge and karst formation.This paper presents an analysis of the relationship between the main frequency for mining blasting vibration and various influencing factors in the karst area.The attenuation patterns of the main frequency of blasting vibration in collapse areas,backfilled areas,and non-collapse areas have been investigated,with the aim of providing suggestions for the prevention and control of surface subsidence in the karst mining area.The field data on blasting vibration were collected with the use of the engineering exploration detector of SWS-type multi-wavelength digital image and the ABEM Terrafo Mark6 seismometer.To determine the main frequency of blasting vibration at different measurement points under different conditions,the collected data were analyzed by WinWave software from Guilin University of Technology,supplemented by Matlab software.This facilitated the establishment of the relationship between the main frequency for mining blasting vibration and the influencing factors of mining in the karst area.The results indicate that the properties of the rock and soil have a significant effect on the main frequency of blasting vibration,which can be manifested that the looser the structure is,the larger the porosity becomes,and the smaller the compactness is,and thus the faster the attenuation of the main frequency and vibration energy of blasting vibration will be.In addition,the main vibration frequency f tends to decrease with the increase of epicentral distance R in the outer subsidence area and the subsidence backfill area.However,the main vibration frequency shows a fluctuation and a slight upward trend within the subsidence area.Furthermore,the frequency formula of blasting vibration was verified that this formula is of high reference value for testing mining blasting vibration in karst collapse areas.In collapse and non-collapse areas,the main frequency of blasting vibration decreased with the increase of epicenter distance and dosage of explosive.Under the same vibration load,the attenuation rate of the main frequency of blasting vibration in the collapse is significantly higher that than that in the non-collapse area.The impact of explosive dosage on the attenuation rate of the main frequency of blasting vibration is greater in the collapse area compared to the non-collapse area.
karst areablasting vibrationmain vibration frequencytransmission speedFourier transformattenua-tion law
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