| Since jack-up drilling platform spud shoes were first introduced into the offshore drilling industry in 1951,mobile jack-up drilling platforms have been widely used in offshore oil and gas development.In the past few decades,many engineers and scholars have conducted in-depth research on the risks that may occur during the installation of jack-up drilling platforms.However,there are still many factors not considered in the bearing capacity calculation method in the ISO standard,such as the formation of artificial hard layers and the influence of soil plugs on the penetration resistance of spudcans.Based on this,this paper proposes a large-size rectangular spudcan,designs a rectangular spudcan penetration centrifuge test system,conducts the penetration test of a single layer of clay after consolidation and the puncture test of the upper hard sticky lower soft clay layer,and has achieved innovative results as follows:(1)A large-scale rectangular spudcan centrifuge test system was established.Most of the existing research focuses on circular spudcans.The circular spudcan has a good axisymmetric structure,and a single-sided plexiglass model box can be used for centrifuge tests.The experimental research in this paper is a large-sized rectangular spudcan.The prototype is HYSY944 large-size rectangular spudcan.The long and short sides of the large-size rectangular spudcan are different,so the original test device is no longer applicable.Considering the influence of the boundary effect in the spudcan penetration process,the test device used in this paper is a double-sided plexiglass model box,and the spudcan is a 1/4 rectangular spudcan.Observe the difference of soil backflow between the long and short sides of the rectangular spudcan in the kaolin clay and silty clay penetration tests,and analyze the influence of parameters such as soil sensitivity on the formation of cavities and the mechanism of soil backflow.(2)Propose a calculation method for the bearing capacity of rectangular spudcans and a prediction method for the bearing capacity of discontinuous consolidation.Most of the existing pile can penetration bearing capacity calculations are based on circular foundations or strip foundations.There is no unified solution for large-size rectangular spudcans.The size and shape of large-sized rectangular spudcans vary greatly.There is no such solution in ISO Regarding the guidance and suggestions on the bearing capacity of large-size rectangular spudcans penetrated into clay,only the equivalent area method can equate irregular spudcans to circular spudcans,but the penetration depth of largesized rectangular spudcans in soft clay is much deeper.Shallow,the effectiveness of its equivalent area method needs to be verified.The spudcan ballasting process is usually carried out in stages,and there is an observation period during the ballasting process.During the observation period,the dissipation of excess pore pressure in the soil around the spudcan will lead to soil consolidation and increase the peak bearing capacity of the soil.There is a risk of puncture through the upper hard soil layer.ISO does not give specific recommendations and guidance.Aiming at the temporary incrustation that may be formed during the suspension of ballasting,the influence of load size and consolidation time on the bearing capacity of soft clay is studied through experiments,the existence of the temporary incrustation is determined according to the test,and the formation conditions of the temporary incrustation are discussed.Single-layer clay bearing capacity prediction formula and single-layer soil bearing capacity prediction method considering discontinuous consolidation.(3)Revise the formula for predicting the bearing capacity of rectangular spudcans in soft clay at the top.When the spudcan penetrate into the upper hard and sticky lower soft eggshell stratum,there will be a great puncture risk.Combined with different working conditions,the large-scale rectangular spudcan penetrate the upper hard and lower soft stratum.The soil penetration bearing capacity in ISO does not consider the influence of the soil plug at the bottom of the spudcan.Combined with the test results of the centrifuge,the test results are compared with the guidance and suggestion formula in the ISO standard,and the analysis of the large-size rectangular spudcan penetration is hard at the top and soft at the bottom.The influence of soil plugs in the formation on the bearing capacity,the mechanism of pile-soil interaction in the process of spudcan penetration,and the prediction method of the bearing capacity of rectangular spudcans in the upper hard clay and lower soft clay layers are proposed,which will further improve the engineering of rectangular spudcans.Applications provide theoretical support. |
