| The utilization of offshore oil has become an important means of energy production in the future because of the increasing demand for oil resources.The utilization of offshore oil must be carried out on offshore oil platforms,which usually adopt large diameter steel pipe pile foundation.The large diameter steel pipe pile would happen pile-sliding phenomenon and soil plug effect in the process of construction,due to the structural characteristics of large diameter steel pipe pile.The pile side friction and pile end resistance of large-diameter steel pipe pile foundation would be influenced by pile-sliding and soil plug effect,and the bearing characteristics of the large diameter steel pipe pile foundation would be changed.There are few studies on influence of pile-sliding and soil plug on bearing characteristics of large diameter steel pipe pile presently.In order to provide reference for the design and construction of large diameter steel pipe pile,the bearing characteristics of large diameter steel pipe pile under the influence of pile-sliding and soil plug effect were studied.Based on Liwan oil platform in South China sea,the resistance of penetration resistance was analyzed and the pile-sliding interval of steel pipe pile was calculated according to the static equilibrium equation and the energy equation.The pile side friction was divided into three different influence regions based on the characteristics of soil resistance distribution after the occurrence of pile-sliding,and different reduction coefficients were used for pile side friction in different affected areas.The calculation method of pile-sliding interval and the division of pile side friction influence region were verified by the actual data.Then the forced state of a micro soil plug unit was analyzed,the calculation formula of soil plug height was derived combining Terzaghi foundation bearing capacity formula,through ABAQUS to establish large diameter steel pipe pile soil plug effect numerical model,and the rationality of calculation formula of soil plug height was verified by engineering measured data.The load-bearing characteristics of large diameter steel pipe pile numerical model was established,the large diameter steel pipe piles considered pile-sliding and soil plug effect applied horizontal load and vertical load,analyzed of steel pipe piles under different working conditions of horizontal displacement of pile,soil pressure,bending moment of pile,pile top displacement and settlement of pile,end resistance and friction resistance of pile.The main conclusions are as follows:(1)The pile side friction would be influenced by pile-sliding.According to the slip section of large diameter steel pipe pile and the distribution characteristics of soil resistance after slip pile,the pile side friction is divided into three influence areas:complete impact area,incomplete impact area,no impact area.The soil in the complete impact area was area most seriously affected by pile-sliding.The side friction of pile was the same as that at the end of pile-sliding.The soil in the incompletely affected area was affected to some extent by pile-sliding.At the end of the pile-sliding,The side friction of pile still existed.As the piling process progresses,the friction provided by the soil around the pile gradually decreases to a very small value.The soil in the non-affected area was basically not affected by pile-sliding,the side friction of piles was ignored by pile-sliding,and the value of the side friction of piles didn’t change.(2)There was a soil plug in the pile body of the large diameter steel pipe pile foundation because of soil plug effect,the increased pile side friction could be reflected by the height of the plug.When steel pipe pile entered the sand layer from the clay layer,the height of soil plug and the growth rate of soil plug would be decreased comparing with entering cohesive soil,and the reaction force of pile bottom would be increased.The larger the pipe diameter of steel pipe pile was,the less obvious the influence of soil layer property on the height of soil plug would be.(3)Under the action of horizontal load,the horizontal displacement of the pile body,the horizontal displacement of the pile top and the soil pressure on the side wall of the steel pipe pile would be increased by pile-sliding.The horizontal displacement of the pile body,the horizontal displacement of the pile top and the soil pressure on the side wall of the steel pipe pile would be decreased by the soil plug effect.The reason was that the pile-sliding would reduce the horizontal side friction of steel pipe pile,which lead to the decrease of the horizontal bearing capacity of steel pipe pile.The soil plug effect would increase the pile end friction resistance of steel pipe pile,thus increasing the horizontal bearing capacity of steel pipe pile.(4)Under the action of vertical load,the pile side friction and pile end resistance would be reduced and the pile body settlement would be increased by pile-sliding.The pile side friction and pile end resistance would be increased and the pile body settlement would be reduced by soil plug effect.The reason was pile-sliding would reduce the vertical pile side friction,thus reducing the vertical bearing capacity of large-diameter steel pipe pile foundation.The soil plug effect would increase the end resistance of the pile and provide the inner friction of the pile,thus increasing the vertical bearing capacity of large diameter steel pipe pile foundation.(5)Under the action of horizontal load or vertical load,the bearing capacity of steel pipe pile only considered the influence of pile-sliding was the worst one.The bearing capacity of steel pipe pile only considered soil plug effect was the best one.The bearing capacity of steel pipe pile considering the effect of pile-sliding and soil plug effect was better than that considered the effect of pile-sliding,but weaker than that considered the influence of soil plug effect.The influence of pile-sliding on bearing characteristics of large diameter steel pipe pile was higher than soil plug effect. |
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