Near-surface seismic refraction tomography and MASW for site characterization in Phuentsholing, Bhutan Himalaya

Abstract

It is essential to understand the soil characteristics of the subsurface layers for any engineering construction. In difficult terrains like hilly areas, conventional methods of investigation are expensive and difficult to conduct. It calls for nondestructive testing methods to get reliable estimates of subsurface properties. In the present study, seismic refraction tomography (SRT) technique and multichannel analysis of surface waves (MASW) methods were carried out along five selected profiles in Phuentsholing region of Bhutan Himalaya. The profile length ranges from 37 to 81.5 m, and depth of imaging down to 10 m. While the SRT data imaged the P-wave velocity (Vp) structures, the MASW imaged the shear wave velocity (Vs) structures. The P-wave images provide a fair knowledge of geological layers, while the MASW images provide S-wave velocity structures (Vs). These results are useful to estimate soil parameters, like the density, Poisson’s ratio, Young’s modulus, shear modulus, N-value and the ultimate bearing capacity. The seismic images reveal the presence of sand, sandy clay, gravels and shale layers below the selected sites. Bhutan Himalayas being seismically vulnerable, the obtained results in terms of shear wave velocity were accustomed to categorize the sites as per NEHRP site classes, and a ground response analysis was performed to determine the reliable amplification factors. From the study, it is suggested that the engineering construction is feasible at all the sites except in one site, where an indication of saturated soil is observed which is vulnerable for liquefaction, and ground needs to be improved before construction at that site.

Shear Wave Velocity Applications in Geomechanics with Focus on Risk Assessment in Carbon Capture and Storage Projects

“…While providing accurate results, they are often time-consuming, labor-intensive, and expensive, thereby making them less feasible for large-scale assessments [159]. Geophysical methods, including seismic refraction [160], surface wave analysis [161,162], and seismic tomography [163] offer cost-effective and energy-efficient alternatives to traditional laboratory testing and borehole measurements. These methods have demonstrated their practical applications in characterizing Vs profiles and capturing variations in complex geological settings [164].…”

The Estimation of Shear Wave Velocity for Shallow Underground Structures in the Central Himalaya Region of Nepal

“…The dispersiveness of soils is determined mainly by the vertical variation on Vs [64,67]. The calculated Vs of the subsurface will be utilized to calculate density, Poisson's ratio, elastic moduli, and other geotechnical parameters of the material layer [68] which can be used for site classification. The calculated Vs30 geotechnical parameters will be used to calculate PGA value of the area leading to site-specific seismic hazard assessments of the area prior to any construction activities.…”

“…A dispersion image in the frequency-phase velocity domain is the most popularly used method in geotechnical engineering [74][75][76][77]. The application of MAM tests in shallow-to medium-depth soil/rock sites by using a Vs profile has also been evaluated by [41,[66][67][68]. Figure 7 depicts the seismograph, accessories, and cable layout performed in MASW/MAM survey during the research.…”

Multichannel Analysis of Surface Waves (MASW) to Estimate the Shear Wave Velocity for Engineering Characterization of Soils at Hawassa Town, Southern Ethiopia

“…where Vp is the compressional wave velocity which can be estimated from the measured Vs and Vs is the shear wave velocity measured from the field using MASW. The Gmax and E30 estimated from the measured Vs was used to characterize the investigated site [53]. For this purpose, G30max and E30 which are given in equation ( 4) [54] and 5 [55], respectively, were used to characterize the soil condition of the sites in the study area.…”