T-Bar Penetration Response and Parameter Interpretation in Layered Soft–Stiff–Soft Clays: Insights from the LDFE Analysis

Soils with interbedded soft/stiff layers are commonly encountered in marine sediments, which has been verified to have a significant effect on the bearing capacity of marine foundations and seabed safety. T-bar penetrometers are increasingly being used in seabed geotechnical investigations and show high potential for interpreting the parameters of layered soils. Based on the large deformation finite-element (LDFE) analysis method, this paper presents a detailed investigation of the process of T-bar penetration through soft–stiff–soft clay layers. Computational efficiency is enhanced through techniques such as the mass scaling method, pre-embedding, and applying overburden pressure. The thickness of stiff layers and their strength ratios to adjacent soils determine the variation trend of the penetration resistance curve, thereby affecting the identification of layer strength and thickness. Trapped soil is observed when the T-bar penetrates from an interbedded stiff layer into the underlying soft layer. The study found that the strength of the bottom layer soil had a more pronounced effect on the T-bar penetration resistance within the interbedded stiff soil layer. By systematically modeling T-bar penetration with varying interbedded layer thicknesses and strength ratios, a series of characteristic penetration resistance curves were generated. Based on the distinct inflection points observed in these curves, two distinct explanatory frameworks were developed to quantitatively interpret key parameters of the interbedded stiff layer, including its surface location, thickness, and undrained shear strength.