Construction Of Evaluation Index System Of Xi ’an Urban Underground Space Development And Application Demonstration

As the only megacity in Northwest China with a population of over 10 million and a GDP of over one trillion yuan,Xi’an has the demand and economic foundation for large-scale underground space development.However,the current situation of underground space development has problems such as fragmented development,single utilization form,low utilization rate,poor overall planning operability,and imperfect evaluation index system.In order to identify the key limiting factors of underground space development in Xi’an,correctly examine the exploitable intensity of underground space,identify priority development areas,improve resource utilization rate,and realize the rational layout of underground space,this paper comprehensively considers the geological environmental conditions and social and economic status quo of Xi’an.A relatively complete evaluation index system and evaluation process for Xi’an’s underground space resource and environment carrying capacity,development suitability and resource quality were established,and an application demonstration of the underground space evaluation index system was completed in the main urban area of Xi’an based on Arc GIS.The main research contents and conclusions are as follows:(1)The key limiting factors of urban underground space development in Xi’an are:active faults,ground cracks,existing structures,ecological environment,food security,cultural protection units and special land.The influence area of the key limiting factors in the main urban area of Xi’an is about 68.7km~2,accounting for about 7.71%of the main urban area.(2)In view of the lack of evaluation results on the carrying capacity of underground space resources and environment in Xi’an,this paper comprehensively considers the bearing background and bearing state,and selects 14 indexes from the geological environment,groundwater resources and mineral resources,including peak acceleration of ground motion,vulnerability to geological disasters and distribution density of ground fractures.An index system suitable for the evaluation of Xi’an urban underground space resources and environment carrying capacity is established.The application demonstration shows that the background carrying capacity of resources and environment in the main urban area is mainly affected by the density of ground fractures,the exploitable modulus of groundwater and the accumulated ground settlement.The underground space development intensity of most areas in the main urban area has not reached the natural bearing limit.The proportion of strong,strong,medium,weak and weak bearing capacity is as follows:67.73%,20.15%,9.89%,1.98%,0.25%.(3)In view of the problem that only geological factors are considered in the suitability evaluation index system for underground space development in Xi’an,this paper innovatively and comprehensively considers geological conditions,ecological environment,construction technology and underground space demand,and establishes an evaluation index system for the suitability of underground space development in Xi’an,which consists of 16 indexes such as soil type,formation uniformity and groundwater depth.The application demonstration shows that the development suitability of underground space in the main urban area is mainly affected by soil type,population density,groundwater richness and accumulated ground settlement.The areas with poor development suitability are all affected by development limitation factors,and the proportion of good,good,medium and poor suitability is 4.37%,44.30%,43.62%and7.71%,respectively.(4)In view of the lack of evaluation index system for the quality of underground space resources in Xi’an and the lack of consideration of ecological and social benefits in the current potential benefits of underground space development,this paper establishes an index system for the evaluation of urban underground space development benefits in Xi’an,which is composed of eight indexes,including POI density,benchmark land price and location conditions,from the comprehensive consideration of economic,social and ecological benefits.Combined with the results of comprehensive evaluation of geological conditions in the suitability evaluation,the quality evaluation of underground space resources in the main urban area of Xi’an is completed.The application demonstration shows that the potential benefits of the development of the inland space in the main urban area are mainly affected by location conditions,benchmark land price and congestion alleviation.The areas with good resource quality are concentrated in the areas with dense subway lines,and the proportion of good,good,medium and poor resource quality are 3.20%,13.84%,54.56%and 28.40%,respectively.