To quickly and effectively detect the hidden hazards of dams,this study proposed the microtremor B-mode ultrasound technology based on linear arrays.Most of the (earth) dams also act as highways,and the vibration signals generated from running vehicles propagate along dams.Therefore,this study proposed deploying linear arrays along the dams,with the vibration propagation direction consistent with the signal receiving direction.In this way,abundant vibration sources can be provided for detecting hidden hazards of the dams.The results of this study show that the data on multiple exploration points can be simultaneously acquired using the multi-channel acquisition technique based on linear arrays,thus improving the efficiency of field data acquisition.Moreover,the influence of source differences can be avoided,and the lateral resolution and the accuracy of exploration results can be improved.The technology proposed in this study was applied to the pre-flood safety inspection of a dam in Jiujiang,Jiangxi Province.Three low-velocity hidden hazards were identified in this dam and were presumed to be the weak layers of the dam foundation and the loose media of the dam body.Practices have proved that this technology effectively counteracts the deficiencies (i.e.,low efficiency and lateral resolution) of the previous microtremor exploration.Moreover,this technology allows scanning at a spacing of 1 m or 0.5 m,thus improving the lateral resolution.This study will provide efficient and accurate guidance for dam safety management.
Ministry of Water Resources,PRC. Bulletin of first national census for water[Z]. Beijing: China Water and Power Press, 2013.
Cardarelli E, Cercato M, De Donno G.Characterization of an earth-filled dam through the combined use of electrical resistivity tomography,P- and SH-wave seismic tomography and surface wave data[J]. Journal of Applied Geophysics, 2014, 106:87-95.
Liu Y Q, Xu H M, Hu J J. Application of comprehensive geophysical exploration technique to detecting hidden defects of reservoir dams[J]. Chinese Journal of Engineering Geophysics, 2019, 16(4):546-551.
Okada H. The microtremor survey method[C]// Tulsa:Society of Exploration Geophysicists Geophysical Monographs Series,translated by Koya Suto,Society of Exploration Geophysicists, 2003.
Okada H. Theory of efficient array observations of microtremors with special reference to the SPAC method[J]. Exploration Geophysics, 2006, 37(1):73-85.
Xu P F, Shi W, Ling S Q, et al. Mapping spherically weathered “Boulders” using 2D microtremor profiling method:a case study along subway line 7 in Shenzhen[J]. Chinese Journal of Geophysics, 2012, 55(6):2120-2128.
Wang F, Okeke A C U, Kogure T, et al. Assessing the internal structure of landslide dams subject to possible piping erosion by means of microtremor chain array and self-potential surveys[J]. Engineering Geology, 2018, 234:11-26.
Huang G M, Xu P F, Li C A, et al. Application of 2D microtremor section survey method in covered karst area,taking Yongan Dahu Basin,Fujian Province as example[J]. Journal of China Coal Society, 2019, 44(2):536-544.
Xie P, Wang Q L, Li J G, et al. Application of SPAC method on stratification of stratigraphic structure in Jianghan Plain[J]. China Earthquake Engineering Journal, 2019, 41(3):718-723.
Singh A P, Sairam B, Pancholi V, et al. Delineation of thickness of intrabasaltic rocks beneath the Deccan Volcanic province of western India through microtremor analysis[J]. Soil Dynamics and Earthquake Engineering, 2020, 138:106348.
Aki K. Space and time spectra of stationary stochastic waves,with special reference to microtremor[J]. Bulletin of the Earthquake Research Institute, 1957, 35:415-456.
Ling S, Okada H. An extended use of the spatial autocorrelation method for the estimation of the geological structures using microtremors[C]// Nagoya:Proceeding of the 89th SEGJ Conference,Society of Exploration Geophysicists of Japan, 1993:44-48.
Ohori M, Nobata A, Wakamatsu K. A comparison of ESAC and FK methods of estimating phase velocity using arbitrarily shaped microtremor arrays[J]. Bulletin of the Seismological Society of America, 2002, 92(6):2323-2332.
Liu Y Z, Mei R W, Ye P, et al. Data acquisition and processing system of WD intelligent natural source surface wave and its application test[J]. Geophysical and Geochemical Exploration, 2016, 40(5):1007-1015.