Karst Development Mechanism and Characteristics Based on Comprehensive Exploration Along Jinan Metro, China
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sustainability Article Karst Development Mechanism and Characteristics Based on Comprehensive Exploration along Jinan Metro, China Shangqu Sun 1,2, Liping Li 1,2,*, Jing Wang 1,2, Shaoshuai Shi 1,2 , Shuguang Song 3, Zhongdong Fang 1,2, Xingzhi Ba 1,2 and Hao Jin 1,2 1 Research Center of Geotechnical and Structural Engineering, Shandong University, Jinan 250061, China; [email protected] (S.Sun); [email protected] (J.W.); [email protected] (S.Shi); [email protected] (Z.F.); [email protected] (X.B.); [email protected] (H.J.) 2 School of Qilu Transportation, Shandong University, Jinan 250061, China 3 School of Transportation Engineering, Shandong Jianzhu University, Jinan 250101, China; [email protected] * Correspondence: [email protected] Received: 28 August 2018; Accepted: 19 September 2018; Published: 21 September 2018 Abstract: Jinan is the capital of Shandong Province and is famous for its spring water. Water conservation has become the consensus of Jinan citizens and the government and the community. The construction of metro engineering in Jinan has lagged behind other cities of the same scale for a long time. The key issue is the protection of spring water. When metro lines are constructed in Jinan karst area, the water-inrushing, quicksand, and piping hazards can easily occur, which can change the groundwater seepage environment and reduce spring discharge. Therefore, we try to reveal the development conditions, mechanism, and mode of karst area in Jinan. In addition, we propose the comprehensive optimizing method of “shallow-deep” and “region-target” suitable for exploration of karst areas along Jinan metro, and systematically study the development characteristics of the karst areas along Jinan metro, thus providing the basis for the shield tunnel to go through karst areas safely and protecting the springs in Jinan. Keywords: Jinan metro; water conservation; karst exploration; development mechanism; shield tunnel 1. Introduction With the rapid development of cities and urban population, traffic congestion has become one of the greatest problems in most cities in China. However, metro construction makes full use of underground space and reduces congestion on the ground. Therefore, metro construction has become the main form of urban infrastructure and traffic in China in the 21st century [1–7]. Until now, 53 cities have won the approval of rail transit planning, with a total length of about 8600 km. By the end of 2020, a total of 177 rail lines will be in construction, with a total operating distance of about 6100 km. Due to the complex urban geological conditions, a large number of metro tunnels run through karst geological areas. The existence of karst caves along the planning metro line can have great effect on the safety of tunnel design, construction, and operation [8]. Although several research on shield tunnelling in soft soils and sand and gravels have been conducted by many scholars [9–15], shield tunnel excavation in karst regions is rarely discussed. Limestone geology is widely distributed throughout China. Moreover, seven primary karst areas can be concluded in China, each of which has its own characteristics. The common karst types include subterranean river-type caves, sink hole-type caves, through caves, phreatic caves along river valleys, Sustainability 2018, 10, 3383; doi:10.3390/su10103383 www.mdpi.com/journal/sustainability Sustainability 2018, 10, x 3383 FOR PEER REVIEW 22 ofof 2121 valleys, vadose caves, and tufa caves [16]. During the metro construction in karst areas, caves that vadose caves, and tufa caves [16]. During the metro construction in karst areas, caves that have have developed or are developing are often encountered, which pose great difficulties in tunneling developed or are developing are often encountered, which pose great difficulties in tunneling by shield by shield machine. As most of the karst caves are in non-filled, semi-filled, or rich muddy water-filled, amachine. number Asof hazards most of theincluding karst caves sink areholes, in non-filled, karst collapse, semi-filled, and water or rich inrush muddy can water-filled,easily occur ain number metro tunnelof hazards projects including when they sink pass holes, through karst collapse, karst areas and [17,18]. water inrush can easily occur in metro tunnel projectsJinan when City they is located pass through in Eastern karst China areas and [17 ,is18 famous]. for its springs with complex groundwater network.Jinan Jinan City isoverlooks located inthe Eastern Mount China Tai to and the issouth famous and for across its springs the Yellow with complexRiver to groundwaterthe north, as indicatednetwork. in Jinan Figure overlooks 1. The structural the Mount unit Tai of tothe the northern south foothills and across of Mount the Yellow Tai, gradient River to from the north,south toas north, indicated is accelerative in Figure1. Thefor formation structural unitof spring of the wa northernter. After foothills the atmospheric of Mount Tai, rainfall gradient infiltrates from south into theto north, soluble is carbonate accelerative rocks, for formationthe water flows of spring from water. south Afterto north the along atmospheric the topographic rainfall infiltratestrend, gathers into inthe the soluble connecting carbonate area rocks, of the the monoclinic water flows structure from south and the to northnorthern along plain, the topographicand then crops trend, out gathers of the surface,in the connecting forming a area rising of thespring. monoclinic The comprehensiv structure ande conditions the northern of strata, plain, andgeological then crops structure out of and the hydrogeologysurface, forming lead a risingto concealed spring. karst The comprehensivecaves, which can conditions cause ground of strata, surface geological settlement structure and karst and collapse,hydrogeology water leadinrush, to concealedmud inrush, karst and caves, other which hazard cans. The cause metro ground lines surface under construction settlement and in Jinan karst willcollapse, inevitably water inrush,go through mud inrush,karst areas, and other which hazards. contain The rich metro groundwater lines under constructionand a large innumber Jinan will of concealedinevitably karst go through caves. karstKarst areas,caves whichwill threaten contain the rich safe groundwater construction and and a large stability number of shield of concealed tunnel, especiallykarst caves. when Karst considering caves will the threaten complexity the safe of constructiongroundwater andin Jinan stability spring of shieldareas and tunnel, the appeal especially for “protectingwhen considering the spring”. the complexity Therefore, of safe groundwater constructi inon Jinan is particularly spring areas important and the appeal in karst for areas “protecting where Jinanthe spring”. Metro runs Therefore, through. safe construction is particularly important in karst areas where Jinan Metro runs through. Figure 1. OverviewOverview of of Jinan Jinan city [19]. [19]. This paper mainly mainly focuses focuses on on the the karst karst areas areas where where R1 R1 and and R2 R2 lines lines of of Jinan Jinan Metro Metro go go through. through. The planning map of main metro lines is shownshown inin FigureFigure2 .2. AfterAfter revealingrevealing thethe conditionsconditions andand development mechanism mechanism of of karst karst area area in Jinan, we propose the comprehensive detection method of “shallow-deep” and “region-target” suitable for exploration of karst areas, and systematically studies thethe development scalescale andand characteristicscharacteristics of of karst karst areas areas along along Jinan Jinan metro, metro, thus thus providing providing the the basis basis for forthe the shield shield tunnel tunnel to go to throughgo through karst karst areas areas safely. safely. Sustainability 2018, 10, 3383 3 of 21 Sustainability 2018, 10, x FOR PEER REVIEW 3 of 21 FigureFigure 2.2. JinanJinan metrometro planplan mapmap [[19].19]. 2. Karst Development Conditions and Mechanism along the Jinan Metro 2. Karst Development Conditions and Mechanism along the Jinan Metro The karst development is mainly controlled by the solubility of rocks, geological structures The karst development is mainly controlled by the solubility of rocks, geological structures (including rock strata, faults, fissures, etc.), and groundwater [20–25]. Among them, the fluidity of (including rock strata, faults, fissures, etc.), and groundwater [20–25]. Among them, the fluidity of water is the most active factor. According to the special hydrogeological conditions in Jinan, the factors water is the most active factor. According to the special hydrogeological conditions in Jinan, the affecting karst development can be divided into four categories: topography, formation lithology, factors affecting karst development can be divided into four categories: topography, formation groundwater action, and geological structure. lithology, groundwater action, and geological structure. 2.1. Topography 2.1. Topography The terrain of Jinan is high in the south and low in the north, with small mountain ranges in the east andThe westterrain sides, of Jinan forming is high a unique in the semi-basinsouth and low landform. in the north, The southern with small part mountain of Jinan is ranges a hilly in area, the whileeast and the west northern sides, part forming is near a unique the Yellow semi-basin River. Thelandform. urban The area southern in Jinan ispart located of Jinan in theis