Wu Shaoyuan

In the foreseeable future, Xiamen Metro will be completed and opened to traffic. When you get off at Xiamen North Station and head to Zhenhai Road, you won't have to suffer through about 2 hours of travel anymore; and for office workers who live in Jimei but work in Lianbinli, they won't have to endure the torment of traffic problems anymore... That's right, the metro will change the lives of Xiamen people, making travel convenient and fast, but the premise is that we must have a thorough understanding of Xiamen's urban geological conditions to ensure the metro construction.

Xiamen's geological conditions are relatively complex. Regarding metro construction, it is necessary to conduct professional assessment of Xiamen's geological conditions and geological disaster situations before determining the best route. In the early site selection and feasibility study of Xiamen Metro, a large number of basic geological survey results from the Xiamen Urban Geological Project provided preliminary basic geological data, and the urban 3D geological information management and service system developed based on the MapGIS platform also enabled construction personnel to have a clear understanding of the engineering geological structure characteristics, optimizing the rail transit survey plan.

Actually, it's not just in rail transit construction, but also in many aspects related to urban planning, urban construction, and citizens' lives in Xiamen, the Xiamen urban geological survey including the urban 3D system is the strong supporting force behind it.

Nine Topics and Six Special Projects, Laying the Foundation for "Excellent Grade"

At the end of 2008, in order to implement the "State Council Decision on Strengthening Geological Work," Xiamen City took the lead in conducting the "Xiamen Urban Geological Survey" work within Fujian Province. By the end of 2010, the China Geological Survey and Xiamen City cooperated to further expand the breadth and depth of urban geological survey work, covering the entire 1573 km² land area of the city and 340 km² of nearby sea areas.

As the project undertaking party, our institute (Xiamen Geological Engineering Survey Institute) set up nine topics including basic geological survey, engineering geological survey, hydrogeological survey, coastal zone survey, ecological geochemical survey, geological disaster survey, mineral resources survey, geothermal resources survey, and urban geological comprehensive database and information management service system construction, as well as six special projects including Quaternary sediment characteristics and paleoenvironmental evolution in Xiamen City, major fault zones and crustal stability evaluation, engineering geological problems survey and evaluation of sand soil liquefaction, engineering geological problems survey and evaluation of soft soil seismic subsidence, underground space resources and adaptability evaluation, and engineering geological problems and stability analysis and evaluation in large-scale reclamation areas in the East Sea based on the overall project goals and task requirements, considering the content of investigation, research, and informatization work and professional characteristics.

The project focuses on Xiamen's urban development strategy, addressing resource, security, and environmental issues facing Xiamen's social and economic sustainable development. Based on fully utilizing and integrating existing geological data and results, it comprehensively investigates urban geological resources and geological environments by comprehensively applying geological, remote sensing, geophysical, geochemical, drilling, and information technology and methods. The established 3D visualization urban geological information management service system realizes integrated management and visualization of city-wide geoscience data, providing a decision-making platform for urban planning, construction, and management.

In June 2013, the Nanjing Geological Survey Center of China Geological Survey organized an expert group to review the project results, which were comprehensively rated as "excellent grade."

Innovative Results with Unique Xiamen "Factors"

In the process of conducting the Xiamen urban geological survey project, we fully considered Xiamen's urban topography, landforms, and island characteristics, achieving innovative results with unique Xiamen "factors."

First, Xiamen is an island bay city. Around this special situation, coastal zone geological surveys were conducted (Figure 2). The basic engineering geological conditions, submarine topography and landforms, geological environment, sediment chemical characteristics, and dynamic changes in coastal erosion and deposition and shoreline changes in the coastal zone were basically clarified. Coastal zone engineering geological and geological disaster surveys were conducted, the stability of the coastal zone was evaluated, and suggestions for measures to maintain coastal zone stability were proposed.

Secondly, the rivers and bays in the Xiamen area are well-developed, with alluvial, flood, and marine sand layers and silt layers. Based on this characteristic, a relatively systematic study was conducted on the distribution and engineering geological properties of soft soil, sand soil, residual soil, and artificial fill soil in the Xiamen area, and zoning was conducted for the degree of seismic subsidence and liquefaction of soft soil and sand soil, and analysis and evaluation were conducted on the main engineering geological problems caused by special soils.

Again, considering the small and complexly changing geomorphological units in the Xiamen area, the interlaced development of terrestrial and marine sediments, and the uneven and greatly varying distribution of strata, the project adopted the newly developed "multi-source geological data coupling automatic modeling technology under geological zoning map constraints," which effectively solved the model construction problems and achieved ideal results.

First Construction of Bay City 3D System

As the saying goes, "A craftsman who wants to do his work well must first sharpen his tools." Xiamen is striving to build a unique bay city style, and for the first time nationwide, it has constructed a 3D geological information management and service system for bay cities. The system can effectively collect Xiamen's geological disaster points over the years and record in detail the geological disaster situation of each point. It can analyze based on geological disaster maps, comprehensive geological maps, engineering geological maps, hydrogeological maps, and topographic maps in the information database, enabling early detection of these problems and helping urban decision-makers effectively avoid urban disasters and scientifically and reasonably conduct urban planning.

This system consists of two main parts: database and 3D information management and service system. The database is established using the large commercial relational database software Oracle, which is the cornerstone for the smooth progress of the entire project; the 3D information management and service system is further divided into data management and maintenance subsystem, data analysis and evaluation subsystem, and data sharing and social service subsystem.

In database construction, the system uses MapGIS K9 as the basic platform, employs the data center architecture, and uses the database tools provided by the system for data entry to obtain original data and basic data; it uses the analysis and modeling tools provided by the analysis and evaluation subsystem for modeling and analysis to obtain result data, establishing a multi-source, heterogeneous, massive urban geological database with different hierarchical structures of original data, basic data, and model data for Xiamen City, achieving cluster management and data sharing services for urban geological data.

In terms of 3D, the latest MapGIS DCS and IGServer platform architecture are adopted. Based on the construction of Xiamen's geological data warehouse, by developing a professional workflow function library for urban geological multi-professional query, analysis, calculation, and evaluation, a functional warehouse containing urban geological 2D and 3D visualization expression, data retrieval services, GIS spatial analysis of geological environment data, thematic map generation, professional evaluation and analysis, 3D geological modeling and analysis was constructed, and an evaluation and auxiliary decision support platform for Xiamen urban geology was provided through C/S or B/S mode.

Numerous Technologies "Join" the 3D System

Underground space is the key direction for future urban development. Geological conditions have a significant impact on the development and utilization of underground space. We used the multi-source geological data coupling automatic modeling technology under geological zoning map constraints to establish a 3D geological structure model, analyzing the impact of geological structures on underground space development more comprehensively, intuitively, and from multiple perspectives. Combined with urban underground cadastral surveys, this technology played an important role. The figure below shows a professional 3D geological model constructed based on multi-method integration and data coupling, reflecting basic geology, Quaternary sediment structure, bedrock structure, and engineering geological structure. It should be particularly noted that through more than 4,000 bedrock boreholes and other geological exploration data throughout the city, we constructed Xiamen's bedrock geological model. Different colored blocks represent rocks of different periods, origins, and compositions, such as the red area representing granite bodies formed 100 million years ago.

In addition, the system also adopted the elastic expansion technology of geological data based on object description. The advantage of this technology is that staff can arbitrarily expand geoscience data specialties, organizing different thematic data according to different existence modes in a professional tree structure for management. The addition of the 2D and 3D integrated management technology based on the data center changed the previous situation where 2D and 3D data were processed separately, making 2D and 3D data equally treated at the levels of data models, data management, data visualization, and data integration, truly realizing deep-level application of 2D and 3D spatial data.

Serving "Beautiful Xiamen," Continuous Follow-up Efforts

Xiamen City formulated the "Beautiful Xiamen Strategic Plan" last July, making new strategic plans for development to maximize the fundamental interests of Xiamen people. What is particularly exciting is that the application of project results including the 3D system has gradually emerged in the "Beautiful Xiamen Strategy."

In addition to the previously mentioned urban geological survey results providing preliminary basic geological data for Xiamen rail transit project feasibility studies and test section surveys, in Xiamen's comprehensive preparation work to create a "China Hot Spring Capital," the project's geothermal resource survey results were also extensively used - the identified recoverable geothermal flow volume is greater than 30,000 m³/day, which is the hardware condition for applying for "China Hot Spring Capital"; furthermore, with urban development, Xiamen plans to build a second airport between Dadeng and Xiaodeng islands, requiring a large amount of earth and stone materials for backfilling. Through the database and geological model constructed by the project, targeted preliminary work was provided for the investigation of earth and stone material sources for Xiamen's new airport land creation.

Overall, the connection between Xiamen City's urban development and the 3D geological information management and service system is very close. Not only the few examples mentioned above, but also in serving urban security, land use management, geothermal resource exploration and development, and the general public, it has extensive application value. Next, Xiamen's urban geological survey work will continue to focus on the following aspects to build a strong foundation and assist "Beautiful Xiamen."

First, continue to fully utilize the resources of the 3D system platform to produce geological science popularization promotional videos, increase the publicity of geological knowledge and geoscience results to the general public, and build the completed geological exhibition hall into a youth geological science education base for our city.

Second, with appropriate financial support from the government, gradually supplement, improve, and update database materials and 3D models year by year.

Third, based on urban geological surveys, expand the project to conduct island geological surveys, providing basic geological data for island protection and resource development and utilization.

Fourth, fully utilize the project's geothermal resource results to complete Xiamen's application for "Hot Spring Capital," adding a new business card to the construction of "Beautiful Xiamen."

Message to GIS Platform: Faster and More Accurate

Today, the development of many fields can no longer be separated from GIS technology. Especially in the field of urban geology, with urban development and further advancement of urban geological work, the development of digital cities and virtual cities will inevitably put higher demands on urban geological informatization work. Urban geological information systems will develop towards networked system architecture and distributed storage, and 3D GIS technology is crucial for underground modeling. Therefore, it is hoped that GIS software, especially domestic GIS software, can seize opportunities, with GIS platforms having faster processing speeds, more accurate 3D models, richer presentation forms, and more evaluation and analysis methods, better playing the role of auxiliary decision-making in urban planning, construction, and other aspects.

Author Introduction:

Wu Shaoyuan, Director of the Geological Environment Survey Institute of Xiamen Geological Engineering Survey Institute, Fujian Province, mainly engaged in hydrogeological and environmental geological surveys, geological disaster prevention and control, and mineral resource surveys.