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One of the most important soil parameters required in the analyses of the piles of oil platforms subjected to lateral earthquake loading is the shear wave velocity (V S ) of the soil. Since in-situ measurements of V S is part of the scope of work of a limited amount of platform sites, there is the need to develop site specific correlations to estimate V S based on basic soil properties. To cover this need a database with in-situ measurements of V s and basic soil properties of clay has been established. Data were collected from eleven offshore geotechnical investigations performed on behalf of PEMEX for the design and installation of fixed offshore platforms in the Bay of Campeche. The database was tailored to developed empirical correlations between the shear wave velocity and undrained shear strength, effective vertical stress, water content, void ratio, overconsolidation ratio and net cone resistance, using simple regression analyses and multiple regression analyses. Three of the most prominent empirical correlations developed using multiple regression analyses are recommended to provide a mean of determining the best estimate V S in clay, along with a three step procedure to perform site response analyses in the Bay of Campeche when in-situ measurements of V S at a site are not available.

Predictive equations for estimating normalized shear modulus and material damping ratio of sand are presented in this paper. The equations are based on a modified hyperbolic model and a statistical analysis of existing isotropically consolidated resonant column and strain-controlled cyclic direct simple shear test results for 252 specimens obtained from the Bay of Campeche. Two independent modified hyperbolic relationships are fitted to model stiffness (G/Gmax)-strain using two parameters and material damping ratio-strain curves using four parameters. Variables used in the equation for normalized shear modulus are: confining pressure; shear-strain amplitude; a reference strain, defined as the shear strain at which the shear modulus has reduced to 0.5Gmax, and a curvature parameter which controls the rate of modulus reduction, such as the model suggested by Darendeli (2001). The equation for damping ratio D, is expressed in terms of the reference strain, defined as the shear strain for a 50% increase in material damping ratio (i.e. D/Dmax = 0.5), a curvature parameter which controls the rate of material damping ratio increase, the minimum material damping ratio Dmin, and the maximum material damping ratio Dmax, similar to the equation suggested by Gonzalez and Romo (2011). It is found that the Bay of Campeche sand exhibit more linear response and lower damping ratio than other sands reported in the literature. The uncertainties associated with the predictive equations are quantified. A case study is provided to illustrate an application of the predictive equations to seismic response analysis and the importance of considering confining stress. The predictive equations of normalized shear modulus reduction G/Gmax and Damping ratio curves are easy to apply in practice, and are useful in the analysis of granular strata and offshore structures subjected to earthquake loading when site specific laboratory testing is not available.

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This study presents the influence of using predicted (calculated) normalized shear modulus (G/Gmax) and material damping ratio (D) curves on the design acceleration spectrum at the depth of maximum soil–pile interaction of a calcareous soil deposit in the Bay of Campeche.When comparing the predicted curves to the laboratory curves, it is concluded that due to limitations in the predicting models, the minimum confining pressure (σ’m) that must be used to get a good match with the laboratory curves is 150 kPa. After performing site response analyses for three shear wave velocity profiles and eight recorded acceleration time histories, the design acceleration spectrum was developed based on the envelope of the 24 calculated acceleration spectra. The acceleration amplitudes of the design spectrum in the short period range are slightly larger using the calculated curves than the laboratory curves. For periods longer than 0.27 seconds, the acceleration amplitudes of the design acceleration spectra are identical for practical purposes when both calculated and laboratory curves are used. Therefore, it is recommened to use the equations presented herein to calculate the curves of G/Gmax and D for calcareous soils in practice for preliminary and final seismic site response analyses. They can be especially useful in final evaluations of large or critical projects to calculate the curves when time and cost constraints make it impractical to perform direct experimental determinations of G/Gmax and D curves for each soil layer encountered in the soil deposit.