| With the acceleration of urbanization in China,the number of high-rise buildings is also growing rapidly.The traditional pile foundation construction method has low mechanization degree and large pollution,and is greatly affected by the formation conditions.In order to meet the requirements of high-rise buildings with higher bearing capacity of foundations,in response to the call of national energy conservation and environmental protection and industrialization of buildings,prestressed high-strength concrete pipes Piles will be the focus of promotion.In the process of constructing prestressed pipe piles by traditional hammering method and static pressure method,it is easy to cause damage to the pile body when encountering hard stratum and boulder,which is not conducive to structural bearing and even lead to pile deflection;In the process of drilling holes by the hole pile method,it is easy to produce collapse holes and affect the driving of the pipe piles.In response to these problems,large diameter Drilling with PHC pipe cased piles(DPC pipe piles) effectively overcomes the adverse effects of conventional construction methods.The large-diameter drilling-and-pipe pile construction steps are highly integrated,and the drilling is carried out at the same time as dumping and sinking.The construction speed is fast and the degree of mechanization is high,which is in line with the national trend of energy conservation and emission reduction.As a new type of pipe pile construction method,the large-diameter drilling and pipe pile construction method needs to further clarify its vertical bearing capacity and load transfermechanism,and ensuring its safe bearing capacity is a major premise for gradually promoting it to the market.At the same time,large-diameter drilling and pipe piles generally need to be filled with concrete to seal the bottom and increase the rigidity of the pile.The volume of the cavity is large,and the price difference of concrete of different strength grades is large,in different geological conditions and loading conditions.The length of the core and the strength of the concrete used for core filling will directly affect the economic rationality of large diameter drilling and pipe piles.Therefore,in the study of the vertical compressive bearing capacity of large diameter Drilling and pipe piles,it is necessary to conduct an in-depth analysis of the necessity of using different strength concrete cores.This research project relies on the Guangzhou Institute of Building Science to carry out the indoor compression test and the on-site static load test of the cored piles.The vertical bearing capacity of the core-filled large diameter while drilling piles is studied,and the numerical analysis is combined.The main conclusions drawn are as follows:1.Under normal circumstances,the strength grades of large-diameter pipe pile pile concrete and core-filled concrete are quite different.In the calculation of the design value of the compressive bearing capacity of the cored pile,the deformation coordination mechanism of the pile and the core should be considered.It is advisable to calculate the vertical compressive bearing capacity of the pile body part by calculating the elastic strain value corresponding to the axial compressive strength design value of the core part of the concrete to correct the compressive bearing capacity of the cored pile The calculation formula of the value is generally smaller than the measured value,and the correction formula is reasonable and reliable.After the finite element simulation analysis,according to the strength grade of the core-filled concrete in the numerical model,the vertical compressive bearing capacity of the pile body with the C30~C80 concrete filled in the outer diameter of 1000 mm pipe pile cavity is obtained.2.In the two test piles that were drilled by the Guangzhou Institute of Building Researchusing large-diameter drilling and pipework methods,the vertical ultimate bearing capacity was measured to reach 20571 kN and 15100 kN,respectively.Compared with the prestressed concrete hollow piles driven by traditional construction methods under the same geological conditions,the vertical ultimate bearing capacity of single piles has increased by more than 40% on average,which is close to the single pile of post-grouting piles under the same formation conditions.Standard value of ultimate bearing capacity.Before entering the large-diameter drilling-and-drilling piles,the calculation formula for the ultimate bearing capacity of the post-grouting piles in the Technical Code for Building Piles can be used to approximate the prediction of the large-diameter drilling in the same formation.Vertical ultimate bearing capacity of a single pile of pipe piles.3.When the quality of the pipe pile construction is good,the single pile will lose its utilization value because the settlement is too large before the pile body is damaged by pressure.In order to make the engineering design economically reasonable and make full use of the high vertical bearing capacity of the core-filled large-diameter while drilling piles,the vertical ultimate bearing capacity of the single pile and the compressive bearing capacity of the pile can be compared by comparing the piles after entering the soil.The characteristic value is used to determine the strength level of the cored concrete.For large diameter drilled pipe piles with a diameter of 1000 mm.(1)When estimating the vertical ultimate bearing capacity of single pile N?10000 kN,only a small amount of C30 concrete should be used to seal the pile bottom,and there is no need to set the core to fill the core;(2)When 10000 kN<N?13000 kN The C30 concrete core can be set up by the length of the core.After the core is shared and the load is shared,the cored pile structure is in the elastic deformation and the structure is safe.(3)When N>13000 kN,the vertical limit bearing of the single pile can be different according to the following.The concrete strength grade table that should be used for the core part under the force standard value is used to set the concrete core with different strength grades,so that the vertical ultimate bearing capacity of the single pile is less than the compressive bearing capacity of the pile of the cored pile..4.The effect of grouting on the pile side will affect the tangential stiffness of the pile-soil interface to a large extent.The better the grouting effect,the greater the tangential stiffness of the pile-soil interface,and the vertical ultimate bearing capacity of the single pile The tangential stiffness of the pile-soil interface increases and increases.When the tangential stiffness is small,the pile is prone to "sudden drop" damage.As the tangential stiffness increases,the single pile failure form gradually changes from "sudden drop type" to "slowly change type" and finally reaches a stable state.To ensure the good quality of the concrete sediment layer at the bottom of the pile also has a great effect on improving the vertical ultimate bearing capacity of the single pile.When the test pile is filled with C40 concrete,the good concrete sediment layer can make the vertical ultimate bearing of the single pile.The force is increased by about 2000 kN. |
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