Study On Load Capacity Of Structure Considering The Function Of Soil In Underground Engineering

In the last few years,with development of economy and enhancement of urbanization level,the quite great quantity large and middle scale cities have had the development strength of underground.At the same time,our country green space construction also have had the quite big development.It is reported that city afforested rate have achieved about 30% in our country.The everage green areas of per person have reached 6.49m2.But there are great distence to the target which proposed by the United Nations.In order to save the land,raise the green space use factor,increase the city domain,reduce environmental pollution,and full display social and economic benefits of urban center ,the pattern that underground space and the greenspace compound development has become the new spot of city sustainale development.From on century 50's,many developed countries know the superiority and potential of underground space in expansion spatial content and improve the environment quality.A spatial concept of ground,upsid spatial and underground spatial coordinated development has formed.Many developed cities have had many success example in compound development.Our country has also obtained huge results. From the city existing afforestation situation,we can see that the variety of plantspl is unitary;herb and short woody plants are majority,but few big woods.Many seasonal plants,but few evengreen plants;Some squares only decrated by colored ponds and potted plants.The majority is the flinty ground.The afforestation rate is extremely low. Some grounds only plant the lawn and the flowers or plant the bushes,tree afforestation has not carried on resonable matching.All of them have the derect relations with upside earth.Because the big woody plant needs deeper plant earth.And the earth deepth affects the structure and the construction work directly. Theory and practice proof that the earth thickness of the sod,the bush and the tree need is 0.4m,0.5m and 1.2m,the corresponding loads are about 5.18KN/m2,6.86KN/m2 and 15.892KN/m2,It is 5 times of general public buildings or loads .The differerce of the different plant loads are very big.This brings many difficulty for the structure value.The engineers often depend on the experence to estimate or define the numerical value according to some parameters.Some underground projects are the air defense works.In order to satisfy the the request of protenction resisting force rank of the air defence works ,the earth thickness of structure roof does not have to be smaller than 0.6~1.2m.Some need to achieve10m.Even achieve several meters and need to pack the earth in the protection structure space.In these place the artificial light soil are prohibited. So the project cost enhance greatly.In view of this kind of situation,the rearch become necessary whether resolve thickness of soil layer from structure angle.From using natural caverns to constructing underground rooms,human beings know the operational factor of underground space through survey,experience and inference.The people start to realized that underground structure only withstand the weight on the caves in arches from thinking on the underground structure withstanding all the weight of rock mass at first.Promjlyfakonkv theory and Takaaki theory was establised.People realized that the majority of the rock mass weights can pass to the lower beds of the hole room through the side wall of the hole room.Namely realized the bearing capacity of soil itself.In present design,the earth and the plant load are treated as extrior additional load fuction in the structure's top.In fact,soil body itself has certain supporting capacity.In certain scope ,this is advantageous to the stucture.Therefore,to research the influnce factor abuot earth and the strcture affect mutually is the effective method to solve soil depth question .Disscution how the earth and the structure affect together.The paper has carried on the numerical analysis and the experimental study to the underground strctureal model.We considered the structure rigidity,soil texture,structure board thickness,upside load,and soil depth etc.We analysed the influnce of each kind of factor to the structure distortion and the supporting capacity when the earth and the non-earth function.We obtain the basic regularity of soil participate in function in underground structure and put forward the referential proposal for the underground project design.The main research was carried out as followings:1.The paper discussed the development condition of underground stucture and green space comprehensive development and the background of the question,in the same time ,we elaborated the topic research goal and research direction.2.In the basis of analysis of the elastoplasticity theory and construction model combing the predecessor success experience,we select elastoplasticity construction model which based on Drucker-Prager Submits criterion to simulate soil body.Underground construction concrete according to elastic computation ,dose not consider the steel bar's function.3.We discussed the finite element analysis processor when the earth and the structure affect mutually,summarized the nonliner equation to solve and determined the unit type of the earth and structure analysis.Both the earth and the underground structure use the solide 45unit.This unit can meanwhile use to the elastic material and the elastoplasticityp material.4.Under the simulation elastic condition ,the influnce of structure rigidity,soil texture,stucture span,structure board thickness and the soil depth factor change for the structure when there have soil or no-soil function.We determined the structure board thickness,structure span,soil depth for sensitive factor. 5.In front foundation,we simulation analysised the mutural function of the earth and stucture in the elastoplasticity state.through comparisionin elastic and elastoplasticity results,furder determined the influnce change rule of various factors when the soil participate in function.6.For really simulating the earth and the structure contact situation,stucture stressful condition.determined the structure and the earth share the load computational procedure,provides the reference for the design.7.We researched the stuctural behavior of soil participate in function in underground structure,collected the test result and the analytical datas,compared the experiment and the theory value,and examinated theoretical analysis result.8.Draw the conclution according to the theory and the test result.Main conclution:1.In the paper,the finite element analysis code of ANSYS is adopted,the analysis of elastic elastoplasticity elastoplasticity contact and experiment are carried on.The massive analyses and the experimental result indicated that the soil participate in function in underground structure is fact.2.In the same deep,the same load condition,increase with the structure rigidity ,the load of the structure increase,structural stiffness on the lower part of the structure less impact.3.In the same deapth,the same load condition,the bigger that the structure area is,the bigger load proportion is.4.In the same load condition,increase with the deapth,the load of the structure reduces.When earth depth in 2~10 meters scopes,the share proportion is 0.39~0.515.5.When buring deep is small,the load undertakes together by the earth and the structure;when the buring deep is big,there are two kind of functions.one is come from arch,another is come from the earth and structure.The load undertakes together by two parts.6.When the earth buring depth is big,the calculation according to this theory is smaller than the one according to the traditional theory。If the result was considered in the design ,the structural design may even more to tend to Iresonably,the thickness of board and the amount of steel will be reduced,then the project consteuction cost will be reduced。Insufficient:This topic preliminary research the underground project considering the function of soil,and discovere the change rule of the function about soil-structure ,determined the corrispanding parameter。But there also has certain distance to the practical application.Accoding to aboved conclusion, we should study in following aspects:1.The influence of the consolidation process of backfilled earth.2.The influence of soil moister.3. The influence of frozen earth.The main innovation spot in the paper:1. Proposed the load question of plants in the underground space compound development from the structure angles.2. Proposed that the soil participate in function in underground structure existence. In the structure stress process, the upside soil layer participate the structure function and share the load, studied the load capacity contribution of the earth to the underground structure.3. The finite element modeling has established by element software. Has carried on the simulation analysis to many kind of factors, and carried on the model experiment It is confirmed that the results of theoretical analysis result is feasible. 4. With massive computation, comparison, analysis and experiment, the load share proportion was obtained , and the reference was provided for the structural design.5. The computational procedure of load proportion of every part was produced, and provided the convenience for the structural design.This topic research confirmed that soil participate in function in the underground structure is true,and gave the share proportion .This achievement provided one kind of new theory basis for the underground structure and the accident examing.It will reduce the steel bar in the project greatly. It will save the project construction cost.Especially may solve the load and the planter earth question in underground spatial and the green space development project .It will have the good soial efficiency and the economic efficiency in the present urbanization synthesis construction.