Characteristics of undrained shear strength in shallow soils in deep water Gulf of Mexico

Shallow foundations are used when designing subsea structures on the seafloor of deep water Gulf of Mexico. In order to design these subsea shallow foundations it is important to understand the behavior of the undrained shear strength of the shallow soils (i.e. upper ten to twenty feet of soil). The objective of this research is to analyze a database of soil data from deep water Gulf of Mexico originally produced by Cheon (2011) with a focus on shallow soils. The purpose of this analysis is to gain a better understanding of the soil and how it will be usable with regards to shallow foundation design. The methodology of this analysis involves studying raw data collected from different measurements taken to aid in the creation of design profiles of undrained shear strength versus depth. Within the existing database there are 18 locations with a high resolution of point data from in-situ tests (Halibut Vane) and non in-situ tests (Minivane and Torvane) that provide the clearest picture of undrained shear strength in the shallow region. The data shows that the design profiles originally created for these locations for deep foundations are generally not representative of the strength in the shallow region. They also show that in-situ test data show more variability than non in-situ data. There are also 25 Cone Penetration Tests in the existing database that show very high resolution data in the shallow region. These Cone Penetration Tests also indicate a crust that appears to be about 1 ft thick and exists along the edge of the continental shelf. Recommended future activities to build upon this work include re-evaluating the design profiles at these 43 locations at which high resolution studies have been performed in the shallow region, collecting these design profiles as well as any new design profiles and organizing them into a new database focused on shallow soils, generating a new generic profile base on the data within the new database, and creating a model that uses spatial variability analysis to calculate undrained shear strengths at new locations based on the data in the database.