| With the continuous development of city construction,and expanding population,cities can use of decreasingly scarce land resources,so high-rise and super high-rise building,deep excavation technology to develop,the technical problems also emerge in endlessly,the cause of all kinds of potential quality mainly divided into three kinds,the first may be representative of the problem;Second,it is possible that the contractor;The third is the adverse natural disasters caused by foundation pit collapse.For the design of deep foundation pit,for different geological conditions and the surrounding site usage,supporting form generally adopt cantilever pile,inner support(steel support or concrete support),anchor rod,anchor cable,anchor pipe such as slope,soil nailing wall,natural put several combinations,in order to satisfy the requirement of stability of deep foundation pit,to adjust measures to local conditions,designed to meet the requirements of the safety and reliability and economical efficiency.To meet the requirements of economy,appropriate chooses pile's support plan;To meet the requirements of safety and convenience construction site should adopt the scheme of pure cantilever pile,but pure cantilever foundation pit construction cost is too high,millions of construction costs.Based on Hefei cross-border electricity project of deep foundation pit project,combined with the geological survey report and design scheme,theoretical analysis is given priority to with ansys,combination principle is deep foundation pit for calculation of the stiffness reduction after displacement,internal force,settlement of surrounding conditions.After analysis due to compression of pile lateral stiffness reduction theory,the possible dangers timely notify the design institutes,make contingency plans in advance,in case of a foundation pit collapse.Combined with the third party monitoring,contact theory and practical comprehensive analysis,it is concluded that the most close to the actual analysis,in order to make the most effective contingency plans.After pile stiffness reduction are studied in this paper,for safety and stability of foundation pit,the horizontal displacement and internal force and surrounding ground settlement line,use ansys15.0 finite element analysis software for a project of deep foundation pit,numerical analysis to study the design consideration for reasons beyond the actual level of displacement and internal force and surrounding ground settlementwhether meet the specification requirements,to determine whether safety and reasonable.For damaged piles,adopt the method of stiffness reduction numerical simulation that by ANSYS finite element calculation,it is easy to draw two piles(normal pile,pile after the stiffness reduction),under the condition of stiffness reduction coefficient is 0.7,see the three kinds of working condition of the excavation of foundation pit in three layer(first excavation 1.5 meters,1.5 meters,the second excavation excavation for the third time 2.75 meters)of the foundation pit near the top of the vertical settlement and stress of pile,pile top horizontal displacement of the changes.Through analysis,the result of the normal stiffness of the pile is fully meet the requirements of the specification,but after the stiffness reduction of pile,the maximum horizontal displacement of 40.4 mm,30 mm,and maximum allowable displacement displacement beyond specification stipulated ratio is about 26%,so this type of engineering safety hidden trouble of the pile.Also,the stiffness reduction after the vertical settlement and stress of pile is larger,the construction unit or design units should be timely prepare contingency plans in advance.Contingency planning section is described below. |
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