MASW-Based Geophysical Testing and Bearing Capacity Assessment at Bridge Sites from Dolabari to Jamugurihat, Assam

This article describes the active MASW field investigation conducted at the proposed bridge sites over and alongside the Jia Bharali and Mara Bharali river flowing through Tezpur in Assam, India. For the four-laning of the existing road between Dolabari and Jamugurihat, Assam, construction of two major and two minor bridges are proposed. Due to presence of variability in the soil profile at the river bed and river banks, substantial difficulty was encountered while conducting the excavation and boring operations for the abutments and piers. Hence, in order to assess the subsurface stratigraphy, prior to the construction exercises, geophysical investigation using multichannel analysis of surface waves (MASW) was conducted. Active MASW survey, in a roll-along mode, wherever necessary, was undertaken to decipher the subsurface stratigraphy. Each of the site had variable length of experimentation, the longest being the major bridge over Jia Bharali river bed that was more than 1 km long. For each of the sites, specific configurations of field experimental setup, involving offset distance, inter-receiver spacing and overlap lengths (for roll-along survey), have been used to collect the raw wavefields. They are further processed for generating the dispersion image, which is subsequently subjected to image processing and automated dispersion curve extraction. Finally, through a suitable inversion analysis, the subsurface stratigraphy was identified. Vertical stacking is also adopted at certain sites for larger depth subsurface information. Based on the inferences from field experimentation, the bearing stratum for the respective bridge sites were identified. Furthermore, following the recommendations, available in the literature, the bearing capacity of different stratum was also assessed. This geophysical investigation proved extremely beneficial in visualizing the subsurface, identification of the bearing stratum over which the foundation for abutments and piers would be placed, and more so the planning and providing guidance to the excavation at different locations for piers and abutments.