Simulation Analysis And Strategy Study On The Impact Of Underground Space Construction On The Benefits Of Low Impact Development Facilities

The concept of the sponge city was born in response to the need to effectively alleviate serious urban flooding,and the importance of its development has been established by construction standard documents and technical guidelines issued by the state and relevant authorities,which have promoted and implemented a series of planning and design projects.However,the impact of underground space construction and utilisation,which aims at intensive three-dimensional development,is often overlooked in sponge city practice today,and few studies have been conducted to verify the relationship between the impacts.Therefore,this study starts with the study of the benefits of sponge city practice,using a series of scientific research methods such as comparative research,synthesis and simulation,to verify and explore the specific impact of underground space construction on the benefits of low-impact development facilities,the main mechanism of action and the optimisation strategy to ensure the synergy of multiple effects,in order to explore the balance between ecological and environmental benefits and urban intensive development.This paper aims to provide a theoretical reference and practical reference for research and planning design in the field of sponge cities and underground space.This paper presents the following research in the vein of problem formulation,method construction,example validation and strategy proposal:Firstly,we analyse the background of the study,sort out and summarise relevant studies on sponge city construction,low-impact development facilities and underground space construction at home and abroad,and uncover the lack of consideration and exploration from the perspective of underground space in current sponge city research,so as to define the scope of the research object and put forward the main issues and the significance of the purpose.Secondly,the mechanism of the effect of underground space on the benefits of lowimpact development facilities and the four influencing factors are explored and selected in the light of previous research in the field of sponge cities and underground space,and the Delphi method is applied to complete the screening of conventional benefit factors based on relevant theoretical analysis.Afterwards,the study compares and discusses the appropriate benefit measurement and quantification methods and simulation models and principles for this study,and designs simulation experimental scenarios for different scenarios and determines comparison ideas,so as to complete the construction of an analysis method for the relationship between the benefits of underground space construction on low-impact development facilities and lay the foundation for the subsequent empirical study.Furthermore,the established analysis method was introduced into the practical design project of the Haichuang Building in Kunshan City.Based on the analysis of the realistic conditions in terms of rainfall hydrology,topography and layout structure of the base site,the generalisation of the site area,the construction of the SWMM model and the design of the simulation scenarios were completed.The model was run to simulate the rainfall and drainage conditions in the study area,and a series of simulations with different rainfall return periods(P=1a,P=2a,P=5a,P=10a,P=20a)were carried out.It was verified and found that: the large-scale development and construction of underground space has a negative impact on the benefits of low-impact development facilities,with a decreasing trend as the proportion of underground space increases;changes in the type of sub-bedding will affect the benefits of low-impact development facilities to varying degrees,specifically grass and permeable paving materials are much better than the results of hard paving;increasing the slope of the underground space cover layer will have a negative impact on the benefits of low-impact development facilities,with a decreasing trend as the proportion of underground space increases.The benefits of low-impact development facilities are negatively inhibited by increasing the slope of the underground space cover layer,with a decreasing trend as the slope of the underground space cover layer increases;the thickness of the underground space cover has a positive relationship with the benefits of low-impact development facilities,with an increasing trend as the thickness of the underground space cover increases.However,the construction of the underground space development limits the thickness of the top slab layer,which inhibits the LID facilities from achieving better results.In addition,all scenarios show that as the rainfall return period increases,the overall degree of change in both stormwater runoff control and pollutant reduction decreases,with a corresponding increase in the level of stormwater resource utilisation.Finally,based on the experimental findings,the real-life contradictory problems of the case are comprehensively sorted out and summarised,and targeted spatial optimisation strategies are proposed in terms of spatial layout and functional design,as well as benefit enhancement measures from the level of LID facility improvement and information monitoring and management,with a view to ensuring the synergistic development and construction of sponge cities and underground spaces,while enhancing the benefits of both and alleviating the contradictions.