Interpretation Of The Strength Characteristics Of Intact Clay Using Full-flow Penetrometers

Various submarine structures such as submarine pipelines and foundations are widely used in the exploitation and practice of Marine oil and gas resources.The design of submarine structures requires accurate undrained shear strength and softening parameters of marine clay.Full-flow Ball and T-bar penetrometers have been widely used to measure the strength characteristics of marine clay in situ.During the process of Ball and T-bar penetration into clay,the soil will soften and the shear strength will decrease.The bearing capacity measured by Ball and T-bar is lower than that of intact soil,thus the undrained shear strength calculated based on traditional method will be underestimated and the softening properties of seabed clay cannot be obtained..In order to accurately estimate shear strength of the intact submarine soft clay,this paper studied the bearing capacity factors during the process of Ball and T-bar penetration from the soil surface using RITSS(remeshing and Interpolation Technique with Small Strain)large deformation finite element method with considering the soil strain softening effect and the softening effect of interface between the penetrometers and clay.The first part of this paper studied the softening effect during the first penetration process of Ball and T-bar with deep embedments.The effects of the interface roughness and softening parameters on bearing capacity factors were investigated through parametric analyses,and the method for predicting the undrained shear strength and softening parameters of intact clay was put forward.Finally,the prediction method proposed in this paper was verified by the laboratory tests,centrifuge tests and field tests.The second part of this paper simulated the continuous penetration process of Shaft-Ball and T-bar from the surface of homogeneous clay.The effects of the soil weight,interface roughness and soil softening properties on bearing capacity were studied.Finally,based on the results from many parametric analyses,the methods for caiculating the bearing capacity factors of Shaft-Ball and T-bar in uniform clay were proposed and verified.The third part of this paper simulated the continuous penetration process of Shaft-Ball and T-bar from the surface of normally consolidated clay.The effects of interface roughness,soil heterogeneity coefficient,soil weight and softening parameters on the bearing capacity factors of Shaft-Ball and T-bar were studied by parametric analyses.The computional methods for bearing capacity factors of Ball and T-bar with softening effect were put forward and verified.