ESTIMATION OF BEDROCK USING GPR

Abstract

Ground Penetration Radar (GPR) and Multichannel Analysis of Surface Wave (MASW) are the methods to explore the bedrock anomalies and variation of bedrock with depth. In GPR system low frequency antenna of 80 MHz, 35 MHz, and 16 MHz were used, because electromagnetic wave penetrate higher depth in case of low frequency antenna, but provide low resolution images. GPR experiment were conducted at Mansa Devi landslide area Haridwar and Shurbhi land slide area Mussoorie to estimate the bedrock depth. A 24-channel land streamer system of Multichannel analysis of surface wave (MASW) was also carried out at Mansa Devi Land Slide area. Generally Shear wave velocity in bedrock is 760±60 m/s. Data collected by GPR is processed by software RADAN-7 and data collected by MASW is processed by SeisImager/2D. Both the result obtained by GPR and MASW were compared and results matched with error 10% or less. GPR experiments were also conducted at sites viz. convocation ground, Hospital ground Saraswati mandir ground ,and department of Earthquake Engineering ground in IIT Roorkee campus, due to same soil strata no soil layering were obtained in the processed images. At Mansa Devi site, loose soil layer of 2 m thickness was calculated below that a consistent hard soil strata was obtained. At Santura Devi temple bedrock was found at depth of 24 m. above the bedrock two soil layering of different thickness were also found at the depth of 10 m inclined layer was also observed. At Banglow ki kandi site Mussoorie the depth of bedrock was found at 27 m. Validation of GPR data has been done with SPT data at two location DEQ Ground and Seismic observatory Ground, followed by the GPR result with MASW result at Mansa Devi site. In this dissertation calibration of dielectric constant of soil also has been performed & presented.