Stress And Deformation Rule And Optimization Of Supporting Structure Of Soil And Rock Mixed Deep Foundation Pit

In the soil foundation pit engineering,the design theory of the retaining structure is relatively mature,but in the soil and rock mixed stratum,the study on the calculation method of the soil-rock mixing foundation pit retaining structure design in the rock-based foundation pit engineering Still less.In view of the fact that the current existing theories cannot meet the needs of the design,construction safety,and economic efficiency of the soil-rock mixed foundation pit engineering,this paper uses the typical transfer station of Metro Line 3 and Metro Line 4 in Xuzhou area-South The deep foundation pit engineering of the Sanhuan Station is the research background,and the numerical calculation of the force and deformation of the foundation pit retaining structure under different parameter combinations has been carried out;based on the distributed optical fiber testing technology,the field measurement research of the entire process of foundation pit support and excavation has been carried out Work to obtain the law of interaction between the rock slope and the supporting structure and the law of force and deformation during the excavation and support of a soil-rock mixed foundation pit,and initially proposed that it is suitable for the rock-based subway foundation pit in Xuzhou area Design calculation method of engineering envelope.First of all,comparing the classical earth pressure theory and the rock mass lateral pressure calculation theory recommended by the code,with the deep foundation pit of the South Third Ring Station as the research background,the size and distribution characteristics of the rock and soil pressure in the deep foundation pit of the South Third Ring Station are calculated and analyzed.At the same time,the Lizheng deep foundation pit calculation software was used,and the deepest section of the foundation pit was selected as a typical section.The excavation and support conditions of the foundation pit were simulated and calculated,and the foundation pit retaining structure under various working conditions-drilling was obtained.The force and deformation laws of cast-in-place piles lay the foundation for the follow-up field survey research of cast-in-place piles.Through comparative analysis,it is found that under different theoretical calculation methods,the force of the retaining structure is very different.The rationality of the design of the retaining structure of the soil-rock mixed foundation pit similar to the South Third Ring Station using the earth pressure theory is obviously insufficient.Second,using ANSYS finite element analysis software,taking the deep foundation pit project of the Nansanhuan station in the interchange section of Xuzhou Metro Line 3 and Metro Line 4 as a typical example,the various factors affecting the deformation of the foundation pit in the case of soil-rock mixed strata are analyzed.Numerical simulation research is carried out.The simulation research results show that the thickness of soil layer,the rigidity of the retaining pile,and the support scheme have obvious effects on the deformation of the foundation pit;while the concrete strength grade of the cast-in-place pile and the thickness of the rock layer have little influence on the deformation of the foundation pit.Numerical simulation of the entire construction conditions of the deepest section of the deep foundation pit excavation at the Nansanhuan Station in the interchange section of Xuzhou Metro Line 3 and Metro Line 4 has been carried out.The simulation results show that during the entire excavation and support process of the foundation pit,In the initial stage of excavation of the foundation pit,the displacement of the pile body is large at the upper end and gradually decreases downward.With the excavation of the foundation pit,the uplift of the foundation increases and the uplift depth continues to move downward.After the support is applied,the displacement of the pile body is Decreasing trend,the position of maximum deformation of the foundation pit also continuously moves to the bottom of the foundation pit,and the deformation of the pile body is in the shape of an upper and lower outer drum.On the whole,the deformation of the foundation pit is not large.During the entire excavation and support process of the foundation pit,the deformation law of the enclosure structure is in good agreement with the field measurement results.Third,conducted field test research on the whole process of support and excavation of the deep foundation pit project of Xuzhou Metro Line 3 and Line 4-South Third Ring Station.Based on the distributed optical fiber test technology of OFDR test,carried out 6 bored and filled enclosure piles,3 concrete crown beams,and 4 concrete crown beam cross braces were used for distributed fiber optic structural strain field monitoring and analysis,and different openings for bored bored piles,crown beams,and cross braces were obtained.The force and deformation characteristics of the excavation stage,and the force and deformation of different enclosure structures are closely related to the state of excavation and support of the foundation pit.In the early stage of excavation of the foundation pit—before the construction of the first cross brace of the concrete crown beam,as the excavation progresses,the foundation pit is deformed into the pit,and the largest deformation occurs at the top of the pile.The full section of the pile is under compression,and the strain of the pile increases.The amount is 30～60×10-6,the measured value is small,and the inward displacement of the pile top is 2～4mm.The first cross bracing of the concrete crown beam is applied—the compressive strain of the retaining pile gradually increases with the excavation at the bottom of the foundation pit,and the strain in the middle of the retaining pile reaches the maximum value.The measured value of the compressive strain is about 250～390×10-6,the pile is in full-section compression;the first concrete cross brace gradually increases with the excavation of the foundation pit,the maximum compressive strain increment is about 250～400×10-6,the measured value is small,the horizontal The support force is within the safe force range,and the change in the force of the crown beam is also small.Field measurement studies have found that in rock foundation pit engineering,the application of the second and third steel supports has little effect on the force and deformation of the retaining piles.Preliminary analysis suggests that steel supports do not play an important role in the retaining structure system.Finally,comprehensive numerical calculations and on-site measurement research results are based on distributed optical fiber test data,combined with third-party monitoring data(deep displacement monitoring of retaining piles,steel stress,and soil pressure monitoring data),and rock-based foundation pits In the project,because the retaining pile and the rock mass in the rock slope are embedded with each other,the rock mass in a certain area is also under compression due to the reinforcement of the pile,and the pile is deformed together.The influence of the bored pile is proposed.It is assumed that it is more reasonable to design and calculate the enclosure structure according to the reinforcement affected area in the rock foundation pit engineering.Combined with the analysis of the actual measurement data of the rock foundation pit project of the South Third Ring Station,and according to the actual construction situation on the site,it is recommended to cancel the second and third steel supports similar to the South Third Station foundation pit project and replace it with the second concrete support + crown beam For the supporting mode of the bracing structure,the spacing of the bracing can refer to the first concrete brace,which is taken as 7～10m.The surrounding pile influence area and its load model proposed based on the foundation pit project of the South Third Ring Station can provide a reference for the subsequent design and construction of the foundation pit engineering of subway lines 4,5 and 6 in Xuzhou area.The paper has 120 figure,24 table,and 70 reference.