Deep cavity detection using propagation of seismic waves in homogenous half-space and layered soil media
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ORIGINAL PAPER
Deep cavity detection using propagation of seismic waves in homogenous half‑space and layered soil media Sohrab Mirassi1 · Hossein Rahnema2 Received: 30 March 2020 / Accepted: 20 July 2020 © Springer Nature Switzerland AG 2020
Abstract Understanding of subsurface anomalies has always been of interest to the geotechnical and geological engineers. Identification of dimensions and the location of these anomalies are still controversial at deeper depths due to a reduction in the resolution and the accuracy of recorded data. In this paper, the propagation mechanisms of the longitudinal (P), Rayleigh (R) and shear (S) waves are compared to investigate the ability of P waves in cavity detection in half-space and layered soil media. The results obtained from the analysis of the propagated P waves from the cavity show that the location of the cavity can be revealed in homogeneous half-space media. Hence, filtering methods and large amplitude clipping of the direct P and R waves are used to detect diffracted waves and provide a more precise illustration of propagated waves, especially in 3D view. The diffracted waves from the cavity appear as a symmetrical arc in the wave-field in which the peak point indicates the location of the cavity. However, the shape (slope) of the three curved paths corresponding to the diffracted waves from the boundary between two layers is not symmetric and gradually turns to a linear form as the distance increases. Furthermore, it is difficult to detect deep cavity using Rayleigh waves in layered soil media. For this purpose, seismic sources with low frequencies or passive methods should be used. Keywords Cavity · Rayleigh waves · P waves · Diffracted waves · Scattered waves · Finite element method (FEM)
Introduction Subsurface anomalies such as cavities, sinkholes, weak subsurface layers, faults, tunnels, etc. may cause threats to humans (Chai et al. 2014; Shaaban et al. 2013). The sinkhole phenomenon has a particular importance, which is generally caused by factors such as groundwater level dropping and karst. Damages were appeared by sinkholes in various parts of the world, especially in the plains of Iran, e.g., in Surmagh plain (50 m in diameter and 16 m in depth), in Safashahr plain (50 m in width and 20 m in depth), in Kaboudarahang plain, Hamedan and the recently in Fassa plain (20 m in width and 100 m in depth) (Rahnema and Mirasi 2012; Rahnema and Mirassi 2016). Considering the numerous hazards of subsurface anomalies to humans, it * Sohrab Mirassi [email protected] 1
Department of Civil Engineering, Shahrekord Branch, Islamic Azad University, Shahrekord, Iran
Department of Civil and Environmental Engineering, Shiraz University of Technology, Shiraz, Iran
2
is essential to identify their dimensions, depths, and locations (Karray et al. 2009). The accurate identification of this phenomenon can play an effective role in controlling, eliminating and preventing its potential risks. Due to the development and capability of seismic methods in terms of geotec
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