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.

After the Hurricane Roxanne passage over the Bay of Campeche in 1995, a reassessment and requalification of the offshore infrastructure was required. In order to represent better the real behavior of the platforms under current, wind and wave forces for the reassessment, effects such as soil sampling, strain rate and aging on the soil properties were incorporated in the analysis. The use of static parameters of the soil is an assumption 'very conservative for the analysis of reassessment of existent structures and for better geotechnical characterization the effect of strain rate, sampling technique and aging are considered. The consideration of these effects on the properties of soil were evaluated in IS sites. The laboratory results for soils with strain rate of 10–4 % hour, which corresponds to the wave forces, show a mean value of increment of 35% in the shear resistance of the soil. The push sampling technique showed an increase of 20% in Su versus the wire line technique. For including aging effect, triaxial and direct shear testing is being carry out on samples of different sites of the Bay of Campeche. The reassessment of the offshore structures is optimum if the analysis includes the mentioned effects since the assumptions of the geotechnical characteristics are more realistic. Introduction Offshore facilities in the Bay of Campeche were subjected to hurricane storm loadings during the passage of hurricane Roxanne in 1995. The oceanographic conditions developed were similar to those predicted for a 100 year return period. Due to that event, a reassessment program of the offshore platforms in the Bay of Campeche was initiated. In some cases, the reassessment of the marine platforms involved analytical methods for evaluating the ultimate limit state of the structures. Analyses were carried out using an ultimate limit-state limit- equilibrium analytical model, which is based on plastic-hinge theory and limit equilibrium (Bea et al, 1997). The yield strength of structural elements, the elastic modulus of steel and the soil characteristics have to be defined by the user. The depth variation of the undrained shear strength (for cohesive soils) or the angle of internal friction (for cohesionless soils) are considered, along with the bias and coefficient of variation of the pile capacity subjected to axial and lateral loads. Bias is defined as the ratio between true and computed values. The uncertainties in the parameters considered in the geotechnical problems are thus identified and assessed. Sources of bias in pile capacities may be introduced by the procedure used to (Bea, 1983; Tang, 1988; Tang, Gilbert, 1990):perform the soil boring;sample;perform the testing (in situ, laboratory);define the pile -loads;analyze the individual pile and pile system performance; anddefine the age of the pile at the time that the capacity is to be evaluated. In this paper, only points 2, 3 and 7 are addressed for the Bay of Campeche conditions. It is important to notice that if each of the above sources introduced a bias of 10%, the total bias in the pile capacity would be equal to 2.

The present work reports requalification results of 33 platforms installed in the Bay of Campeche (BOC), Offshore Mexico, based on simplified and detailed ultimate strength analyses. These analyses have been carried out according with the Transitory Criteria (TC) developed for the BOC and the API RP 2A 20th edition. Taking into account that simplified structural analysis performed with a software called Template Offshore Platform Capacity Assessment Tools (TOPCAT) are quick and conservative as compared with sophisticated computer programs, PEMEX - IMP decided to use this software. In general terms, results obtained with TOPCAT agree well with those from the sophisticated software. Introduction As an offshore platforms becomes older it is more difficult to comply with modern codes, due to accumulated damages load increments, changes of service and so on. On the other hand codes are stricter than the ones used in the design of old platforms. A structure that does not comply with a code can not be replaced with a new one, because this implies time and cost, among other technical problems. Fortunately API issued Supplement 1, which is applicable to requalification of existing offshore platforms. As a result of the first non-linear ultimate strength analyses carried out for PEMEX according with Supplement 1, Petroleos Mexicanos (PEMEX) and Instituto Mexicano del Petroleo (IMP) developed the TC for design of new offshore platforms and requalification of existing structures in the BOC. API RP 2A Supplement 1 and the TC change the engineering practices, including the non-linear ultimate strength analysis as a compulsory task when assessing an existing structure that does not pass the design level analysis or does not have adequate deck height. This change requires reliable software for ultimate strength analysis. For planning and taking decisions purposes PEMEX needed some structural assessments in a short period of time, too short to carry out detailed structural analyses. Therefore, TOPCAT was used to assess nine platforms considering that this software gives quick and conservative results as compared with those from sophisticated software. Nine platforms were assessed in one week by a group of three structural engineers. With sophisticated software this nine structures could not be assessed in this time. For this reason and the results obtained with the simplified ultimate strength tools, PEMEX - IMP have carried out several analyses. However, TOPCAT itself can not replace the sophisticated computer programs. Requalification of 33 platforms was conducted, analyses were carried out with simplified and sophisticated tools and results of both tools are very close. TOPCAT has the capability to model damages on the structural members such as dents and out of straightness, as well as the capability to consider grout repair of week members. Based on the above mentioned if necessary one can recommend to grout repair structural members. In some cases, it is recommended to perform detailed analyses, because detailed analysis could be less expensive that grouting members.