| As the urbanization process continues to increase,various underground projects have emerged,resulting in a large number of complex and diverse foundation pit works.In order to meet various foundation pit support requirements,the support methods of foundation pit projects are also Keeping up with the times and constantly innovating.As a new type of support form,the drilled bite pile has the advantages of large overall rigidity,good water stopping,convenient operation,economical and environmental protection,and has a good application prospect.Occlusal piles were first introduced and used in the southeastern coastal areas of China,and there are many successful cases,but there are not many application cases in the northwest loess area of Lanzhou,etc.,and in some specific projects in this area,like the foundation pit project of Lanzhou near the Yellow River channel The application of occlusal piles has great value in application.Due to the strong regional characteristics of the foundation pit project,many experiences in the southeast coastal area cannot be fully copied.Therefore,the study of the use of occlusal piles in the foundation pit project in Lanzhou is of great significance.Provide cases and references for the use of occlusal piles in Lanzhou and other northwest regions.In this paper,the method of combining theoretical analysis,numerical simulation and on-site monitoring is used for research.The supporting form and deformation theory of deep foundation pit and the design theory and construction method related to occlusal pile were studied.Taking the foundation pit support of the main tower of a Yellow River Bridge in Lanzhou City,Gansu Province as the research background,the deep foundation pit was first rationalized The design scheme of the foundation pit was verified,and then the horizontal displacement change law of the supporting pile and the settlement deformation law of the soil behind the pile were obtained according to the monitoring data of the project,and then the supporting structure of the foundation pit was used by the finite element software ABAQUS Create a numerical model,analyze the displacement of the supporting structure and the surrounding soil around the foundation pit during the excavation process,and compare it with the measured data to verify the feasibility of the model.Based on this model,the degree of influence of the bite pile on the support effect ofthe bite pile under different bite amounts,concrete strength of the plain concrete pile,the diameter of the bite pile and the embedded depth of the pile body is studied,and various The influence weights of the factors and corresponding suggestions are given to provide reference for the design and construction of similar projects in this area in the future.The study results are as fellow:(1)Occlusal piles are used better in the cantilever excavation foundation pit project closer to the Yellow River,and their support and water stop can meet the design requirements of the foundation pit.(2)The pile diameter factor has a significant influence on the performance of the occluded pile.During the increase of the pile diameter from 800 mm to 1200 mm,the maximum horizontal displacement of the pile body is reduced by 38.97% and the gradient reduction is basically average,and the soil settlement is reduced.At about 10%,the increase in pile diameter can significantly reduce the relevant deformation of the foundation pit.In the design of occluded piles,the pile diameter should be a key factor to improve the performance of the supporting pile body.(3)The amount of bite has a certain influence on the performance of the bite pile.With the increase of the bite amount,the deformation of the pile body gradually decreases,but when the bite amount increases to 250 mm,the reduction of the deformation of the foundation pit is very weak.With the increase of the bite amount,the decrease of the maximum horizontal displacement of the pile body was reduced from 21% to 3%.The recommended value of the angle bite amount based on the actual construction and engineering safety is 250 mm.(4)The concrete strength of plain concrete piles has a limited effect on the performance of occlusal piles,and the increase of concrete strength of plain piles has a limited contribution to the reduction of foundation pit deformation.In the process of increasing the strength of each gradient of concrete,the maximum horizontal displacement of the pile and the average decrease in soil settlement are about 3%,and the benefit is not proportional to the increase in economic cost.Therefore,the influence of this factor may not be considered in the design,but in actual In the project,the concrete strength of the plain concrete pile cannot be set too low.If the strength difference between the two piles is too large,shear failure is easy to occur.It is reasonable to select C15 according to the actual engineering experience.(5)The embedding depth of the pile body has a general influence on the performance of the occluded pile.When the embedding depth of this project increases from 5m to 9m,the maximum horizontal displacement of the shape body decreases by 25% and from 9m to 13 m only decreases by 10 %,The decrease in soil settlement has been reduced from 20% to 4.9%,so increasing the embedded depth of the pile within a certain range has a positive contribution to controlling the deformation of the foundation pit,but excessively increasing the depth has a general benefit and results in resources waste.(6)It can be known from engineering practice that it is suitable for cantilever excavation in the 6-10 m deep foundation pit project.According to the engineering experience of this paper,the design of occlusal piles for similar foundation excavation projects by cantilever excavation by the river at high water level in Lanzhou Recommended values of factors: bite amount is250 mm,pile diameter is 1100 mm or 1200 mm,strength of plain pile concrete is C15,and embedded depth of pile body is H(depth of foundation pit). |
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