Geotechnical Characterization Of Rio Caribe Soils
Authors: ullya J.P. , Sgambatti J. , Templetonb J.S. , McClelland Fugro , Perez F. , Laya E. 
Published: October 2008

The results of a geotechnical study for the proposed Rio Cariben offshore development are presented. The profile essentiallyconsists of firm to very hard clays, with a surface layer of calcareous sand. Back artalyses of spud can penetration at a site close to the site under study were used to evaluate engineering parameters for the carbonate sands. In addition, analyses of the resistance of the surface sandswas also evaluated based on the results of several in situ and laboratory tests.A discussion of the problems of evaluating liquefaction susceptibility in calcareous sands is presented, principally in terms of shortcomings of the offshore SPTprocedures employed,

INTRODUCTION

As part of the preliminary preparations for the engineering analysis, design and planning fm the development of the Rio Caribe offshore platform, a 500 fi (152 m) geotechnical boring was completed at the proposed location of the structure, Both in situ and laboratory test data were obtained for the purpose of character rizing the geotechnical parameters of thefoundation soils', The objective of the field and laboratory testing program was to provide information for evaluating the foundation bearing capacity for piles under axial and lateral loads for static, cyclic and dynamic loading.

The offshore geotechnical boring and laboratory testing program were performed by Fugro-McClelland under contract to LAGOVEN, S.A. The field work was supervised by INTEVEP, S,A, who also peformed corroboratorylaboratory testing.

The purpose of this paper is to review the data available From the field and laboratory testing program and to present the engineering parameters that were used for the static, cyclic and dynamic foundation analyses. The, data are taken from the various Fugro-McClelland field and laboratory reports produced for LAGOVEN and from the INTEVEP laboratory test results.

SOIL PROFILE

The simplified soil profile for the site is shown in Fig. 1. A surface calcareous sand exists to a depth of 9.1 m, after which the complete profile consists essentially of stiff to hard clays. Based on initial liquefaction analyses, the sand layeris to be consideredliquefiable to a depth of 15 ft (4.57 m) due to the expected ground accelerations at the site 2.

The variation of Atterberg Limits of the recovered samples is indicated in Fig. 2. The liquid (LL) and plastic (PL) limits are reasonably constant over the depth of the boringand give an average plasticity index (LL-PL) of around 40%.

Laboratory measurements of the submerged unit weight (y') are also presentedin Fig. 2, as is the smoothed trend used in the analyses performed,

STRENGTH PROFILE

The variation of the measured undrained shear strength in the cohesivesoils is indicated in Fig. 3. The measured shear strengthshave been obtained from several types of test and the scatter is that generally associated with offshore investigations. For the initial static analyses, the design profile indicated in Fig. 3 was used. For the subsequent dynamic and pseudo-dynamic analyses, the relationship from DSS and triaxial results (Eq. 1) has been used, Depending on the type of evaluation, this relationship ismodified to take into account the effects of rate of loading and cyclic degradation.