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.
Highlights
Before commencement of any engineering construction, it is important to check soil profiles and soil characteristics in order to ensure that the site is acceptable for making such construction
This paper focuses on site characterization at five locations at Phuentsholing in Bhutan Himalayas using the Seismic refraction tomography (SRT) and multichannel analysis of surface waves (MASW) to assess the feasibility of engineering constructions and to classify the sites as per NEHRP site classification
Since no prior soil tests were done in the past and no information on the soil types was available for the sites, the velocity data were interpreted referring to Appendix B; Clause 3.2 of the IS: 1892-1979 [13]
Summary
Before commencement of any engineering construction, it is important to check soil profiles and soil characteristics in order to ensure that the site is acceptable for making such construction. In Bhutan Himalaya, the terrain poses difficulties in conducting conventional soil investigations using shell and auger, open-pit, etc These methods are noneconomic and take time to perform. Seismic refraction tomography (SRT) provides velocity structure and the required soil parameters without disturbing the natural ground condition [2, 5, 18, 25]. Seismic refraction methods have been used for civil engineering purposes in mountainous terrain [10, 14, 28] They have been used to locate faults and in determining the soil parameters [4, 16]. The multichannel analysis of surface waves (MASW) is a method used to estimate the shear wave velocity at a shallow depth and help to determine the elastic parameters of the soil [14, 30]. This paper focuses on site characterization at five locations at Phuentsholing in Bhutan Himalayas using the SRT and MASW to assess the feasibility of engineering constructions and to classify the sites as per NEHRP site classification
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