1. INTRODUCTION Facilities of few deepwater ports along the Indian coastline are being upgraded to provide efficient cargo handling ser- vices. A new port has recently been built at Gangavaram on the Indian east coast. It is desired to improve an area of about 220,000 m 2 at the port in order to build an ore stack-yard. Site investigation data revealed that soft marine clays exist up to 20m depth. Much of these marine clays are impregnated with seashell fragments. Previous investigation in this region was mostly done on remolded and reconstituted clay (e.g. Mohan and Bhandari 1977, Rao et al. 1996, Moses et al. 2003). The behavior of remolded clay however does not exactly follow that of undisturbed clay because of particle bonding and alignment, and particle arrangement owing to stress history effects (Wroth 1984). This paper investigates the data of conven- tional consolidated undrained triaxial tests on undisturbed marine clays containing seashell fragments. Figure 1 shows the seashell fragments observed in the sample. The effect of consolidation pressure on pore pressure response during undrained shear up to failure was studied. The laboratory test results are compared to the numerical findings leading to the proposal of a semi-empirical method that allows pore pressure changes to be determined because of the presence of seashells. 2. EXPERIMENTAL PROGRAM Nine isotropically consolidated undrained triaxial tests with pore pressure measurement (CIU) were conducted on 75mm diameter undisturbed clay samples. The water content, liquid and plastic limits of the clay were 52-, 78- and 26%, respec- tively. The clay had an average bulk unit weight of 15.4kN/ m 3 . The samples were obtained from piston samplers col- lected from 4.5- to 11.5m depth during the site investigation. The samples were extruded directly from the sampler and cut into 150mm length. Two saturated porous stones were then placed at the ends of each sample and the entire assembly mounted on the triaxial chamber. Saturation was achieved by applying a partial vacuum (< 25kPa) to the top of the sample and concurrently allowing deaired water to percolate through the bottom. The cell pressure and back pressure were then increased in steps using two independent A. Juneja 1 * and B. A. Mir 2 Behavior of marine clays containing seashell fragments under undrained triaxial loading ABSTRACT: Marine clays at Gangavaram port on east coast of India are known to contain seashells which affect the und- rained shear strength of the soft clays. This paper reports the results of consolidated undrained triaxial tests (CIU) on undis- turbed samples of marine clay collected from the site. The findings from the tests are then compared to the results of the common elasto-plastic soil model used in the back analysis. The results seem to suggest that the presence of seashell fragments influence the measured pore pressure response and the strength especially at low consolidation pressure when stiffness of the clay is less. KEYWORDS: Bulk modulus; critical state framework; marine clays; triaxial testing. *Corresponding Author 1 Assistant Professor, Department of Civil Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 40 0076 India, Email: ajuneja@ iitb.ac.in 2 Research Scholar (QIP), Department of Civil Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 40 0076 India, Email: p7mir@ civil.iitb.ac.in 565 International Journal of Geotechnical Engineering (2010) 4: (565-571) DOI 10.3328/IJGE.2010.04.04.565-571 J. Ross Publishing, Inc. © 2010 TECHNICAL NOTE