Feasibility Analysis Of Natural Foundation With Sand Pebble Layer For High-rise Buildings

With the acceleration of the process of urban modernization in my country,more and more high-rise buildings appear,and the superstructure has become more diverse and complex.Compared with multi-storey buildings,high-rise buildings have a larger load on the upper structure and a greater pressure on the foundation.It is difficult for ordinary natural foundations to meet the design requirements.Therefore,most high-rise buildings mainly adopt pile foundations,Piled raft foundation,etc.Pile foundations have become the most used foundation form for high-rise buildings in our country,and a phenomenon of "piling every high-rise building must be driven" has gradually appeared.From the current construction technology and safety,the pile foundation is undoubtedly the most suitable.However,based on the requirements of the general design principles,economic rationality should be considered when selecting the basic scheme,and the geological conditions,technical and economic aspects of the specific project should be studied and analyzed in combination with the local geotechnical engineering conditions.A technology feasible,economical and reasonable shallow foundation form is preferred,to avoid blindly adopting pile foundation for obtaining greater economic benefits and better social benefits.Based on the sand and gravel soil existing in the shallow part of Jiujiang area,it has important academic value and practical guiding significance to further explore the feasibility of using it as the natural foundation of high-rise buildings in Jiujiang area in theory,and fully taps the foundation bearing potential of sand and gravel soil from many aspects,hoping to provide theoretical and technical basis and suggestions for taking non-pile foundation projects and to overcome the situation of "pile driving in every high-rise building".The specific work contents are as follows:(1)Through the collection and analysis of a large number of high-rise building foundation design selection documents and engineering data,the foundation selection conditions of high-rise buildings are analyzed,and it is found that insufficient bearing capacity of sand and pebble foundations is the biggest obstacle restricting the use of natural foundations for high-rise buildings.The root cause of insufficient bearing capacity is the improper method of bearing capacity value.Most of them use the original code experience value or the experience value in the engineering geology manual as the so-called local experience,and no field loading test confirmation has been carried out.(2)Through the analysis of Jiujiang geotechnical engineering conditions,there are relatively thick sandy gravel soil layers in the shallow part of some areas,and the engineering geological conditions are good.However,according to the statistical analysis of the foundation bearing capacity based on the geotechnical engineering survey data,compared with other provinces and cities,it is found that the bearing capacity of the sand and gravel soil layer is lower.The analysis of field loading test results proves the existence of this problem.The characteristic value of the foundation bearing capacity thus obtained is greatly improved by testing,which can reach an increase of more than 180%.(3)From the perspective of foundation bearing theory and the characteristics of high-rise buildings with podiums,it is found that under certain circumstances,the podium has a positive effect on the foundation bearing capacity of the supporting layer of the main building.Therefore,the suppression of the podium should be considered when correcting the bearing capacity of the foundation,and the value of the foundation embedding depth should be proposed for the depth correction of high-rise buildings with podiums.(4)Based on the fact that most of supporting structures of foundation pit still exist underground after the building is built,it is found that it has a certain restraint around the foundation of the building,and the role of the supporting structure can be considered in the design of the foundation.Therefore,starting from the mechanism of supporting structure,combined with the theory of foundation bearing capacity,its influence and contribution to foundation bearing capacity is analyzed in order to further increase the possibility of using sandy gravel soil natural foundation for high-rise buildings.(5)Use the MIDAS/GTS NX finite element software to further analyze the influence of the supporting structure on the bearing performance of the foundation.The research results show that the reinforced concrete row-pile supporting structure has a positive effect on the bearing capacity of the foundation.The central settlement of the raft foundation is reduced by 5.72% after considering the role of the supporting structure.The central settlement of the two sides are respectively reduced by 13.84%and 8.94%,and the corner settlement reduced by 14.88%,after considering the role of the supporting structure.(6)The fact that some high-rise buildings in Jiujiang have successfully adopted raft-shaped foundations in sand and gravel soil natural foundations in recent years also fully proves that the use of sand and gravel soil as natural foundations of high-rise buildings is feasible,which is useful for reducing project costs,shortening construction period and decreasing the impact of the surrounding environment,which has played a positive effect,and also confirmed that the theoretical and technical results in this paper are practical.