Penetration Of Jack-up Spudcan Foundation In Spatially Varied Layered Clay

Offshore oil and gas exploitation plays an important role in future energy extraction.Jack-up platform is widely used in shallow seas below 150 m.Jack-ups is fixed on the seabed through spudcan foundation.During the installtion of jack-ups.The preloading loads is 2-3 times of the operating load,make sure spudcan penetrate to Predetermined depth.As the seabed soil has been deposited,weathered and consolidated for many years,it tends to be distributed in layers.Preloading in such layered clay often lead to punch-through damage of the spudcans which causes serious accidents.In the current research,the seabed soil is often simplified to homogeneous soil,while the spatial variability of the seabed soil is ignored.This paper controlles the compaction of soil to change the undrained shear strength,Prepared layered soil with certain spatial variability.The penetration test of the model spudcan is carried out in homogeneous soil and spatial variability soil.The load-displacement curve during the penetration process is obtained by a high-precision loading device;the failure mechanism of the soil is observed by PIV.It is found that the spatial variability of the soil has a significant effect on the penetration resistance and failure mechanism of the spudcan.In the spatially variable soil,soil deformation develops along the weak soil area.The failure mechanism is transformed from the shallow general shear failure and deep punching shear failure in homogeneous soil to multiple combinations of punching shear failure,local shear failure and back-flow mechanism in spatially variable soil.In this paper,a large-deformation stochastic finite element model of spatially variable soils is established by coupling Euler-Lagrangian method,and the model is verified by experiments in this paper.In the past research on the spatial variability of soils was usually carried out through traditional random fields which generates only by statistical characteristics of soil parameters,while conditioned random fields could consider both statistical characteristics of soil parameters and constraints of geological exploration data.In this paper,Markov Monte Carlo method is used to generate the conditioned random field of the undrained shear strength of the soil.It is found that the penetration resistance obtained in the conditional random field is closer to experimental results.At the same time,this paper also carried out a case study of jack-up punch-through.Based on the CPT data,the traditional random field model conded random field model of the undrained shear strength of the engineering site were generated.Monte Carlo simulation of spudcan penetration was carried out based on those random fields.It is found that the spatial variability of the undrained shear strength of the soil is reduced after the CPT data constraint is applied,and the homogeneity of the puncture position and puncture distance is close to the traditional random field,and their are closer to the measured value of the real value,but their standard deviation significantly reduced in conditioned random fields,and it shows that using condition random field can predict the penetration behavior of pile shoe foundation under preload more accurately...