Department of Civil Engineering, Indian Institute of Science Bangalore
Forensic Investigation in Geotechnical Engineering
Investigation of Soil Compaction Homogeneity in the Finished BuildingForensic investigation in geotechnical engineering involves legalistic and scientific investigations of a structure to detect the causes as well as the process of distress in the structure, which are attributed by geotechnical origin. In this study application of GPR for forensic investigation of compaction problem is investigated. Improper compaction is the one of the main reason behind the settlement of floor or footing in made up ground. Routine quality assessment procedure of in-situ sampling and determination of optimum water content and dry density determination fails to provide compaction quality throughout the construction area. Compactness character of soil directly related to water content and density. Variation of water and density can be easily estimated using fast non-invasive technique of Ground Penetration Radar. A model study was carried out on the typical soil used in the study area to understand the GPR wave character on the soil sample. Models were constructed with different density and water content. It is observed that the loose soil has tendency to saturate, which reduces GPR wave amplitudes and signals strength. Strong GPR wave reflection is noticed for less saturated and high density section and distorted wave forms are noticed for loose saturated section. This wave form character has been used to assess compaction quality heterogeneity of soil fills below the floor slab. A detailed GPR survey was carried out at the field in a grid pattern on finished floor slab without disturbing existing setup. Non uniform compaction identified using GPR is well comparable with borehole and N-SPT values measured. GPR can be used deduct compaction heterogeneity/voids without removing casted floor slab and machine foundation.
GPR Survey in 90% Finished Building to Determine Compaction Quality
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