Comparison of In-Situ Vane, Cone Penetrometer, and Laboratory Test Results for Gulf of Mexico Deepwater Clays

Abstract

Site investigations were recently performed offshore at three prospective plat-form sites in water depths between 400 and 500 m in the Gulf of Mexico. Soil conditions at the sites generally range from very soft clays near the seafloor to very stiff clays at 120- to 150-m penetration. Analyses of stress history indicate the soils at these locations are generally normally consolidated. Laboratory tests were performed on recovered specimens to deter-mine the undrained shear strength. Standard laboratory miniature vane shear tests and unconsolidated-undrained triaxial tests were performed in addition to consolidated-undrained tests using stress history and normalized soil engineering properties (SHANSEP) procedures. Tests performed in the field included in-situ vane and cone penetrometer. Cone factors Nk were computed using in-situ vane shear strengths as the reference strength. This paper compares the results of consolidated-undrained (SHANSEP) laboratory and in-situ tests to determine a relationship that may be used to correlate these results. The effects of soil strength and plasticity are examined and used to correlate shear strength with the liquidity index. A comparison is also made between peak and residual in-situ vane strengths. This paper further describes how a combination of these in-situ and laboratory tests can be used to characterize a deepwater site for foundation design. Recommendations for future site investigations are also discussed.

Characterization and finite element analysis of lime and polymer treated ultra-soft clay soils using the electrical resistivity and miniature penetrometer methods

“…Several methods such as Vane Shear Test (VST), Cone Penetration Test (CPT) and T-Bar method are being used for the downhole testing. The vane shear test has been used widely in offshore site investigations, especially in the Gulf of Mexico (Johnson et al, 1988;Young et al, 1988) while T-bar can be considered as a modified cone penetration device and both have been used for soft soil characterization (Teh and Houlsby, 1991).…”

Non-destructive experimental testing and modeling of electrical impedance behavior of untreated and treated ultra-soft clayey soils

“…Thus, the effect of the intermediate principal stress is ignored compared to other tests such as triaxial compression test (Xiao et al, 2016a, b). The VST has been widely used in offshore site investigations, especially in the Gulf of Mexico (Johnson et al, 1988;Young et al, 1988), while T-bar can be considered as a modified cone penetration device, and both have been used for soft soil characterization (Teh and Houlsby, 1991). However, these methods may face extreme challenges in characterizing the top surface soil of the seabed, since the undrained shear strength of such kind of soil may reach 0.01 kPa (Vipulanandan and Raheem, 2015).…”