Numerical Analysis Of The Ultimate Bearing Capacity Of Spud Foundation For Offshore Jack-up Drilling Platform

With the growth of the national economy and the increase of requirement for energy,the exploration and exploitation activities of off shore oil and gas resources have become increasingly active.In order to study the penetration resistance of jack-up drilling platform in the process of piling,the sea bed was regarded as isotropic,elastic-plastic medium satisfying the Mohr-Coulomb yielding criteria.The interface between the pile and soil around was considered as master-slave intersection obeying the Coulomb law of friction.Using nonlinear finite element method,numerical calculations of ultimate bearing capacity?UBC?on single-and double-layered formulations were carried out on ABAQUS platform through pre-embedment method and continuous penetration method.The results were compared with those of the existing engineering calculation methods.The following conclusions are achieved:?1?In the clay,the penetration resistance of the pile shoe goes up with the increase of penetrating depth,the soil cohesion and the pile shoe's diameter.The calculated results are in compliance with those from Skempton?non-backfill?formula.The elastic modulus of the soil has significant influence on the resistance of pile penetration.In the sand,the penetration resistance of the pile shoe also increases with the penetration depth and the internal friction angle of the sand.The calculation result is close to the Terzaghi formula.When the angle of dilatancy is smaller,its influence on the bearing capacity of foundation should not be ignored.?2?For hard-soft clays,if the relative thickness H/B of overlying strata is 1.0,the smaller the strength ratio?Sut/Sub?of upper and lower layer is,the bigger the UBC will be;the Brown and Meyerhof formula can be used to calculate the UBC only when Sut/Sub>3.0.The scope of application of the method of projection area is 4.0<S_ut/S_ub<6.0.When S_ut/S_ub=3.0,the UBC of double layered foundation will gradually increase with the thickness of the overlying strata.Only when H/B<1.0,the UBC by Brown&Meyerhof formula and projection area method are reasonable.?3?For soft-hard clays,the UBC increases with the strength of upper clay,the thickness of the upper clay and the penetration depth.The calculated results have little error with those obtained by Meyerhof formula within a certain range.?4?For sand-clay foundations,when the strengths of upper and lower layer keep constant,the UBC increases with the thickness of the overlying sand.The results are close to those obtained by Brown&Meyerhof formula and projection area method.When the thickness of the upper sand is constant,the UBC increases with the strength of lower soil,and then tends to level off.When the strength of the lower soil is larger,the Brown&Meyerhof formula and the projection area method are no longer applicable.?5?There may be punch-through phenomenon in hard-soft foundation.The higher the strength ratio for overlying to underlying strata and the smaller the relative thickness of overlying stratum were,the greater the possibility for punch-through would be.?6?The ALE remeshing technique was used to simulate the behavior of the pile in the process of continuous penetration in single-layered soil.It is found that the change trend of dynamic bearing capacity is the same as that of the static bearing capacity,but with larger value.