Evaluation Of Underground Space Resources And Development Suitability In Yan'an City

Mountainous cities are affected by the topography and landscape and face pressures such as lack of available land on the surface,traffic congestion and dense population.Therefore,the exploitation of underground space is the main strategic objective of current development.This paper firstly summarized the engineering geological profile of the study area using a large amount of engineering geological and hydrogeological data obtained from the exploration of the project"Proposal for the Development and Use of Underground Space in the Main Urban Area of Yan’an City".Afterwards,in-situ experiments and indoor tests were carried out to measure the indicators and parameters required for this study.After that,combined with the specification,this paper elaborated the method of classifying the underground space envelope rock category in the study area and drew a geological profile of the study area.Subsequently,this paper discussed the basic geological conditions and limiting conditions that need to be considered in the process of 3D geological modeling.The basic geological conditions were topography and geomorphology,stratigraphic lithology and tectonics,geological hazards,hydrogeological conditions and human engineering activities;the constraints were heritage protection areas and existing engineering facilities in the city.According to the above conditions,the resource description was made based on the 3D geological model for different depths of underground land levels.Finally,this paper evaluated the suitability of underground space development in Yan’an City,and made recommendations on the layout of lateral space,vertical space and three key areas of Yan’an City for space development.The results show that the underground geotechnical conditions in the main sections of Yan’an City are good,with fewer and less hazardous geological hazards and hydrological conditions suitable for underground engineering construction.The area of suitable land in the shallow layer 0-10m is about 234.79 km~2,accounting for 62.33%of the assessment area;the suitable land in the sub-middle layer 10-20m is concentrated in the Chuan Gulch and most of the Liangxiang Mountains,with an area of about 57.61km~2,accounting for 15.30%of the whole area;the suitable sites for the middle layer of20-30m are mainly located in the northwest and south Sichuan valleys,covering an area of about 10.41 km~2,accounting for 2.76%of the area of the assessment area.Finally,based on the above results of the assessment of the suitability of the underground space for development,this paper proposes a"lateral hill+vertical underground"and the layout of underground space development in key areas.For lateral space,the middle and upper reaches of the Yan River are suitable for the construction of large span engineering facilities;for vertical space,suitable excavation areas are mainly located in Chuangu and parts of Yan’an New Area;for underground space in key areas,underground facilities such as underground pipelines and underground street crossings are to be laid out in the shallow layer 0-10m,and underground shopping malls and supporting facilities for tourist areas are to be laid out in the northwestern area of higher intensity;the sub-middle layer 10-20m The main focus is on the construction of the metro and corresponding supporting facilities and the construction of underground tunnels through the river;the middle level 20-30m is reserved for logistics tracks and underground road space;below 30m is reserved for special engineering and other long-term underground development space.