| Underground space development as an important means to solve the problem of urban space shortage has become a widespread consensus.Due to its non-renewable and potentially destructive nature,the site selection of the early planning needs to be quite cautious.However,at present,the traditional underground space planning pays more attention to the macro factors such as economy and society,and pays less attention to the problems easily generated in the later construction stage,which leads to a series of follow-up problems such as excessive project cost and cracking of surrounding buildings.From the perspective of geotechnical engineering,it is one of the important means to improve the level of fine planning of urban underground space that the micro-engineering design basis has a reverse influence on the macro planning scheme.At present,there are the following logical breakpoints to support the refined site selection of underground space from engineering considerations: the relation between the scale of planning demand and the size of underground structure has not been established,leading to the failure of geotechnical engineering analysis to intervene in advance;The quantitative study of surface settlement distribution around foundation pit excavation is not perfect,which leads to the failure of geotechnical knowledge to be integrated into the process of fine planning and site selection.The traditional building damage evaluation system does not match with the underground space scheme,which leads to the failure to assess the impact degree of existing buildings(groups)under excavation disturbance in advance.In order to get through the working logic of site selection optimization of new urban underground space based on damage prediction of existing buildings and to provide site selection decision-making suggestions with mathematical basis from the perspective of geotechnical engineering,the following work was carried out in this study:1)Establish the relationship between the scale of planning requirements and the geometry of the project.By sorting out the prediction methods of underground space demand by regions and functions,the working logic of planning level before site selection is reviewed.The geometric dimension information of existing underground space cases in China is investigated,and the statistical analysis is carried out for three main types of urban underground space.The relationship between the scale of sub-functional buildings,the ratio of length and width,and the depth of development is established.It realizes the transition from demand prediction and function allocation at the planning level to the size refinement of conceptual scheme at the engineering level.2)Simplify the surface settlement distribution function around the foundation pit.Based on the research results of the surface settlement behind the wall of a two-dimensional foundation pit,the recommended values of the surface settlement curve behind the wall under various geological conditions are given.The settlement curves of any section behind the wall are obtained by using the plane strain ratio,and the settlement curves of each Angle section are obtained by using the key section.Based on this,a simplified spatial distribution function of surface settlement around foundation pit excavation is innovatively proposed.It provides the precondition for the subsequent damage evaluation of the building complex.3)Optimize the plan-oriented damage evaluation system of buildings(groups).This paper summarizes the technical system and experience of building damage evaluation at home and abroad,puts forward the building damage evaluation standard oriented to the problem of planning site selection,gives the damage prediction method matching with the plane settlement distribution function,and takes into account many factors to modify the damage risk rating.The overall damage evaluation method of buildings(groups)in the disturbed area is constructed from the perspectives of quantity and score,which provides reference for the optimization of site selection.4)Taking Qingliangshan area in Nanjing as an example,according to the new site selection optimization work path,detailed comparison and selection and suggestions are given for the new underground space scheme in this area.This paper constructs a practical new idea of optimizing the site selection of new underground space in city.It fully integrates the existing research results of planning and geotechnical research and makes targeted bidirectional expansion and extension,enabling the urban underground space planning based on the mathematical and physical basis from the engineering perspective.It provides an important reference for the multidisciplinary decisionmaking of urban layout. |
