Abstract:

The soft clay with low strength and high compressibility is widely distributed in the coastal area of China. The engineering characteristics evaluation of soft clay is crucial for engineering construction. Piezocone penetration test (CPTU) is one of the most commonly used in-situ testing methods, which has slight disturbance on soil. However, the mechanical properties of the soil requires interpretation of CPTU test results, which is site-specific. This paper presents a study conducted in the Taizhou coastal area to investigate the strength characteristics of deep soft clay through CPTU and laboratory tests. Based on the direct shear test (consolidated quick shear) results of reconsolidated Taizhou soft clay, the relationship between the normalized strength and overconsolidation ratio (OCR) of Taizhou soft clay was obtained, where the empirical coefficients a and b of the stress history and normalized soil engineering properties (SHANSEP) method were determined to be 0.226 and 0.761, respectively. The cone factor N _kt of Taizhou soft clay were calibrated from 10.23 to 16.88, with a total mean value of 14.08. Utilizing the SHANSEP formula and the undrained shear strength s_u obtained by N _kt method, a continuous section of the in-situ OCR of Taizhou soft clay was derived. The interpretation empirical coefficient k of different strata OCR were calibrated from 0.315 to 0.570, a value of k = 0.33 was recommended for interpreting the OCR of Taizhou soft clay.

Key words: soft clay, piezocone penetration test, overconsolidation ratio (OCR), joint calibration