Site Characterization of Existing and Abandoned Coal Ash Ponds Using Shear-Wave Velocity from Multichannel Analysis of Surface Waves

Abstract

Coal ash ponds or lagoons are surface impoundments constructed to store the unused coal ash generated from thermal power plants. In India, by the end of 2020 nearly 82,200 ha of land will be under ash ponds. Once the capacity of these ponds is reached, they are closed in compliance with the statutory regulations. Recent trends suggest that these lands could be reclaimed to accept light- to heavy-weight structures over them, which makes in situ characterization essential to ensure the safety of structures built over them. This paper presents the site characterization in terms of shear-wave velocity (Vs) of four hydraulically deposited coal ash lagoon sites (two existing and two abandoned) at two ash pond sites in India using the multichannel analysis of surface waves (MASW) technique. The ash is deposited using the wet slurry technique, and the age of deposition is found to have a significant effect on the shear-wave velocity of these deposits. An empirical correlation is presented between the mean Vs and depth (z) for all the sites considered. The measured Vs values were extrapolated using three different methods to obtain Vs,30 values, and the sites were classified as per the recommendations of the International Building Code. Standard penetration tests (SPTs) were conducted near the MASW testing locations at one of the abandoned ash ponds, and the SPT values (N values) had significant scatter. An empirical correlation is proposed between the mean Vs and N values obtained.