| In the National 13th Five-Year Plan,in order to meet the scientific layout of the petrochemical industry and the need for safe and environmentally friendly intensive development,many petrochemical bases have been built on the reclamation land area near the coast,pile foundations are often used in the superstructure,in such deep soft soil foundations.Taking the second-stage ground treatment project of a petrochemical base in Zhoushan as an example,the petrochemical base is built on a 47-square-kilometer reclamation land foundation,and the foundation for dredging is pretreated by plastic drainage board and preloading method.Prefabricated pipe piles and bored piles.With the additional load on the upper part of the soft soil foundation,the foundation soil will produce long-term and continuous consolidation settlement,which will inevitably cause negative frictional resistance on the pile side,affect the bearing capacity of the pile foundation,and increase the investment in foundation treatment engineering.It is of great significance to analyze the post-construction settlement of the deep soft soil foundation and the negative frictional resistance of the pile on the construction design of the foundation and the reliability of the superstructure.In this paper,the distribution characteristics of pile foundation negative friction resistance are studied by field monitoring test in zhoushan petrochemical base,3d finite element numerical simulation is further carried out,and the main factors affecting pile foundation negative friction resistance are comprehensively analyzed.The research results provide technical support for the design and construction of foundation treatment engineering and superstructure.Based on the field monitoring test,the main results of this paper are as follows:(1)The neutral point of the negative frictional resistance of the pile foundation is significantly affected by the holding layer.After the first stage is stabilized,the neutral point depth ratio ln/l0 of the end-supporting pile is 0.65,0.81(ln is the neutral point depth,and l0 is the lower limit depth of the settlement of the pile surrounding soil layer),the neutral point depth ratio of the friction pile is 0.43,0.45.After the second stage of loading,the neutral point depth ratio of the end bearing pile is 0.91,0.81,which is close to 1;the neutral point depth ratio of the friction pile is 6.5,0.5.(2)The pile pull-down load caused by the consolidation settlement of the foundation gradually increases with the consolidation time,but the increase gradually decreases.By taking different data analysis starting point comparisons,the earlier the pile foundation construction time,the larger the consolidation settlement of the soft soil foundation,the larger the pull-down load caused by the pile-soil interaction,and the greater the axial force of the pile body.With the increase of the preloading time of the pile,after the pile foundation is constructed,the smaller the pile pull-down load,the smaller the settlement value of the foundation soil.(3)The plastic drainage board and surcharge preloading treatment scheme on the soft soil foundation has obvious effects.The treatment scheme can not only accelerate the drainage of the drainage plate treatment range,but also promote the consolidation of the silty clay layer below the reinforcement zone.After the final stage of loading,the settlement value of the upper part of the soft soil foundation is 0.76m～0.88m.At the same time,the three-dimensional finite element numerical simulation analysis shows that the settlement value of the upper part of the soft soil foundation is about 1.01m before the pile foundation construction and the drainage board.(4)Through the back-axis of the pile body,the distribution law of the pile side friction coefficient along the depth is obtained,and the measured parameters are provided for the pile foundation design.After the completion of the second-stage stacking,the pile-pile,negative friction coefficient is 0.32～0.4(prime fill),0.23～0.28(silt silty clay),0.4～0.26(silty clay).For the cast-in-place pile,the negative friction coefficient is 0.4～0.35(prime fill),0.21～0.18(muddy silty clay),0.41～0.20(silty clay).(5)Improve the workmanship of steel reinforced concrete and ensure the survival rate.For prefabricated pipe piles,the steel bar is buried in the process of pipe pile length production,and the cushion layer is used to improve the ability of the steel bar and the signal wire joint to adapt to deformation,and the ultra-long part of the steel wire signal line is used to draw the rod in the shape of the pile end.For the fixed side of the pile end,the survival rate of the steel bar is up to 99%.For bored piles,when the steel cage is lowered,the steel bar is buried,and the steel rods are fixed by spot welding rods and steel cages,the signal wires are protected by PVC hoses with embedded steel wires,and the signal lines are taken along the outer side of the steel cages.And other measures,the steel meter survival rate reached 98%.Figure[164]table[17]reference[23]. |
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