Model Test And Numerical Analysis Of Large Axial Force Pile Foundation Underpinning Of Xianyang Airport

Pile foundation underpinning technology as the core construction technology for the development of underground space of existing buildings,it is mainly used in the construction of buildings or structures such as reinforcement,correction,addition,extension and displacement of buildings or structures.It is the rapid rise in recent decades that underpinning buildings or piers for more underground space.Especially in recent years,the construction of the domestic subway,which greatly promoted the development of pile-based technology,and gradually become a solution to the construction of urban subway construction through the underground structure of the technical problems such as an important means.Therefore,the connection behavior of pile foundation and the connection performance of underpinning girder joints,especially the internal force and force mechanism of old and new concrete in the underpinning system,are still needed.Based on the background of the large axial force pile foundation replacement project of XianYang International Airport,this paper carries out the numerical analysis of the 1:6 and 1:4(1/2)node model test and the integral model of the cast-in-place and the contact model,and completed the following:(1)Summarizes the concept of Underpinning,characteristics typical of pile foundation engineering change at home and abroad,discusses the research status of pile foundation connectivity between the nodes of the old and new interface change,it illustrates the necessity of research and proposed urgent key issue to be solved urgently.(2)Discussion on pile foundation underpinning the bond-slip mechanism interface node and the main factors affecting shear capacity of the old and new concrete,consider node will underpinning accordance with the "space-pull-pressure arch" force model for analysis;Discusses the advantages and disadvantages and applicability of the calculation methods of the old and new concrete interface shear capacity at home and abroad,and existing research results and a few comments based on consideration of the effects of linear superposition of the various roles at the interface of old and new interface shear capacity.Based on the existing research results and several suggestions,proposed formula of shear capacity of pile foundation underpinning node interface of old and new,all-inclusive.(3)The 1: 6 and 1: 4(1/2)node model tests were carried out.The failure modes of the joints were all broken,and there was no shear or punching of the joint surface,show that the interface roughening + embedding steel + interface glue + drilling bar tensioning the new type of connection is reasonable and feasible;The experimental study shows that the force model of the coupling node is in accordance with the force model of the "space-pull-pressure arch";The theoretical results of bearing capacity are in good agreement with the experimental results,which indicates that the theoretical formula proposed in this paper has certain reference value.(4)The numerical analysis shows that the load-bearing cloud of the underpinting beam under the action of ultimate failure load shows the shape of the "space-pull-pressure arch";The ultimate load of the theoretical calculation is given by the numerical analysis of the entrainment model of the entrainment node and the new and old interface contact model.The experimental model is less error-prone than the initial slip bearing capacity and the ultimate failure bearing capacity of the contact model.The results show that the experimental model can achieve the bearing capacity of the cast-in-place model,and the accuracy of the theoretical calculation is further verified.