Liquefaction potential of selected reclaimed areas of Dhaka city based on cone penetration test

Abstract

The purpose of this research is to estimate the earthquake induced liquefaction potential of selected reclaimed areas of Dhaka city based on both Cone Penetration Test (CPT) and Standard Penetration Test (SPT). The Cone Penetration Test (CPT) is an in situ testing method used to determine the Geotechnical Engineering properties of soils delineating soil stratigraphy. CPT is a method of assessing subsurface stratigraphy associated with soft materials, discontinuous lenses, organic materials (peat), potentially liquefiable materials (silt, sands and granule gravel) and landslides. Different parameters like cone tip resistance, local friction, friction ratio and pore water pressure have been found directly from CPT. CPT data have been collected from ten selected reclaimed areas of greater Dhaka city. The filling depth of the reclaimed areas varies from 1.5 to 13.5 m from the existing ground level (EGL). For the liquefaction analyses, the values of peak ground acceleration, amax and the magnitude, M have been taken as 0.15g and 7.5, respectively. The range of SPT-N, Cone tip resistance (MPa), local friction (kPa) and friction ratio varies between 1~42, 0.17~18.58, 0~273.2 and 0~9.34 respectively of the ten selected sites. Liquefaction potential has been estimated based on both CPT and SPT data. It has been observed that in reclaimed areas of Dhaka city especially for the locations reclaimed by dredged soil up to a filling depth of 1.5 to 4.5m there is high probability of liquefaction occurrence. In most of the cases, liquefaction zone for CPT have been observed in two different depth zones. Liquefaction zone for CPT of Bramangaon, Ashian City, Badda, Banasree, Gabtoli, Kawran Bazar, Purbachal, United City, Uttara and Kamrangir Char are 1.5 ~10 m and 18~22.5m, 1.8~3.9 m and 12.9~14.4 m, 4.5 ~5.5 m and 8~9.5m, 0.7 ~4.8 m and 14.4~15.3 m, 0.6 ~5.4 m, 11.4 ~12.3 m, 1.5 ~5.0 m and 15~15.6 m, 3.0~4.5 m. and 10.5~12.0 m, 2.7 ~4.8 m and 8.7~12.3 m, and 1.5 ~6 m and 7.5~12 m respectively. The range of obtained values of Overconsolidation ratio (OCR), Preconsolidation stress (kPa), Coefficient of lateral earth pressure (K0) and Angle of internal friction (ϕ). varies between 0.08~61.33, 2.69~463, 0.107~5.45 and 21~45 respectively for the ten selected sites. Different correlations between CPT, SPT and others parameters have also been developed.