| Geological environment restricts the development of society and economy,and human activities also exert important influence on geological environment.The construction of a modern city with the development of large-scale human activities,which caused environmental engineering geological problems increasingly serious and complicated,such as landfill pollution,fountains blocked,etc.At present,there is still a lack of accepted standards on how to evaluate environmental engineering geology problems.Using geology,hydrogeology,environmental geology,engineering geology,disaster geology,GIS technology and mathematical geology theory,the paper establishes a"primary-secondary problems comprehensive evaluation method",and constructs 5levels of environmental engineering geological problems evaluation model based on the characteristic of Jinan city.This method takes into consideration the factors of primary and secondary environmental engineering geological problems in Jinan,highlighting the reaction of human activities to the geological environment.In this paper,the safety of environmental engineering geology in Jinan is divided into four grades,and the typical problems such as the impact of the subway construction,urbanization and the landfill pollution on groundwater are simulated and predicted in Jinan.At the same time,according to the characteristics of the problems and the difficulty of management,the prevention and control division is carried out and the concrete countermeasures are put forward.The research results have certain theoretical significance and engineering value.(1)The influence of engineering construction on spring water has been taken as the evaluation factor for secondary environmental engineering problems,and a new evaluation system of environmental engineering geological problems has been set up.The primary environmental engineering geological problems in Jinan city are developing,such as collapses,landslidses,debris flows,karst collapses,loess collapsibility and silt(sand)soil liquefaction.The secondary environmental engineering geological problems in this area include unstable slope deformation,mining subsidence and associated fractures,garbage pollution and the impact of engineering construction on spring water gushing.(2)The primary environmental engineering geological problems in Jinan city are evaluated based on the fuzzy comprehensive analysis method of AHP.The risk of primary environmental engineering geological problems in Jinan is divided into four categories:high,low,minor and small.The high risk area is about 310.73km~2,accounting for about3.88%of the city's total area.It is mainly located in the middle of Changqing,the urban areas and the southern of Zhangqiu District.It is the recharge and conservation area of Jinan spring water.This area belongs to the middle and low mountain area.The terrain slope is about 30 degrees.The geological disasters such as collapses,landslides and debris flows are relatively developed.The earthquake intensity is 6 degrees and the peak acceleration of earthquake motion is 0.05g.There are some soft soil in this area,and no collapsible loess and liquefied sandy soil are distributed.(3)Based on the AHP fuzzy comprehensive analysis method,the risk of secondary environmental engineering geological problems in Jinan city are also divided into four grade:high,middle,minor and small.The high risk area is about 175.41km~2,accounting for about 2.20%of the city's area.It is mainly located in the northwest of Suncun town in Licheng District,Shengjing,Bucun,Guanzhuang and eastern Puji of Zhangqiu District and drainage area of Baotu Spring,Pearl Spring,Heihu Spring,etc.The mineral resources such as iron ore,coal mine,clay mine and bauxite are abundant in this area,and mining activities are frequent,resulting in a large area of mined out area and presumed mined out area.The risk of landfill pollution to the groundwater is large-medium.The spring water has a strong control over the engineering geological environment.(4)The paper takes the destruction of groundwater runoff channel,the influence of ground hardening on spring water recharge and groundwater potential pollution as the constraint factors,and defines the restricted zoning of spring water to engineering geological environment.It is divided into 4 divisions:restricted,middle,weak and no.The?restrictive areas are located near the drainage area of the four spring groups.The?moderate constraints areas are mainly distributed in the middle of Pingyin County,Shizhong,Lixia and Licheng District and the eastern part of the Zhangqiu District.The?weak constraints areas are mainly distributed in the southeast of Changqing,the southern of Licheng and Zhangqiu District.The non restrictive areas are mainly distributed in Shanghe,Jiyang,Tianqiao,northern of Licheng and Zhangqiu District,west of Changqing District and Pingyin County.(5)First of all,the factors affecting the primary and secondary environmental engineering geological problems are evaluated respectively based on AHP and fuzzy comprehensive evaluation method.Secondly,the secondary environmental engineering geological problems and the primary problems are determined as equal weights.Finally,the Nemerow index method is used to evaluate the two second level indexes comprehensively.These above form a primary-secondary problems comprehensive evaluation method.Based on MAPGIS technology,the safety of environmental engineering geology in Jinan from low to high is divided into four grades:A,B,C and D.Safety A class area is about 159.36km~2,accounting for about 1.95%of the city's total area.It is the lowest level of safety,and is not suitable for the construction of major projects.This area is mainly distributed in west Baotu spring of Lixia District,south Guodian town,Suncun town of Licheng District,Shengjing,Bucun,Mingshui,Shuangshan of Zhangqiu District.After analysis and comparison,the evaluation results accord better with the geological environment condition of Jinan city,and provides the scientific basis for the protection of geological environment.(6)In order to prevent the construction of underground space to destroy the runoff channel of springs,the hydrogeological conceptual model of Jinan spring area is established.According to the GMS numerical model of karst water in Jinan spring area,the influence of construction of Jinan Metro loop line,M line and R line on spring water level is optimized.The results show that when the depth of M1 is 18-35m,the depth of M2 25-40m,the depth of M3 16-40m,the depth of M4 12-40m,the depth of R1 35m,the depth of R2 18-25m and the depth of loop line 25-40m,the influence on the spring water level is rather weak.After the completion of the whole subway,the construction has little effect on the spring water level of the Baotu Spring area,the maximum value is only0.03m.(7)With the social and economic development,the built-up area of Jinan city is becoming larger and larger,and the mathematical model about the correlation between the flow of springs in Jinan and the built-up area,groundwater exploitation and precipitation is established.The study shows that the ground hardening of urban expansion has an important influence on the recharge of karst water,and directly reduces the spring flow.Through calculation,due to urban expansion,groundwater recharge of karst groundwater has decreased by 27,700 m~3/d,and over the past 50 years,the engineering construction activities of Jinan have a significant impact on the spring water flow.(8)Jinan karst water has shown a trend of water quality deterioration since the 1980s.On the basis of groundwater flow model,the MT3D module is used to simulate the pollutant transport process of historical garbage sites in the southern mountains.The prediction results show that the pollution plume of nitrate,sulfate,chloroform in the next10 years,20 years,30 years,40 years,50 years is gradually expanded.This may cause potential pollution risk to downstream water and groundwater of the urban area.The ways of pollution includes three types:the point source-surface flow stage infiltration,surface source-rainfall intermittent infiltration and point source-mining leakage infiltration.The way of karst water pollution in the west of Jinan is the first type.The karst water pollution in the southern mountain area is the second type and the third kind of karst water pollution is in the east part of the city.(9)According to the characteristics of complex diversity of environmental engineering geological problems in Jinan city and the degree of difficulty to control,the whole zone is divided into key control areas,sub key control areas,general control areas,and no need to take measures areas.In view of regional stability,geological disaster,bad soil,unstable slope,goaf collapse and ground crack and so on,the reasonable and feasible prevention and control measures are put forward.For typical problems,in spring protection,pollution channel should be cut off and seepage control and monitoring should be strengthen in the restrictive area.The depth of foundation and hardened area should be controled in the middle restricted area.In major project,the subway construction should adopt the shield method construction,the recharge,the reasonable embedment depth and the design of the sponge city.In garbage pollution,it is necessary to delineate the protected area,to increase the recovery,to eliminate the landfill in the bare area of the limestone,to establish the filtrate standard for implement.To sum up,the paper takes the spring constraints to engineering construction into the secondary environmental engineering problems,and establishes a new evaluation system of environmental engineering geological problems.A"primary-secondary comprehensive evaluation method"was established to evaluate the safety of environmental engineering geology in Jinan.In theory,a relatively complete evaluation index system and mature evaluation method for environmental engineering geology have been initially formed,which can enrich the research theory of environmental engineering geology.In practice,through the engineering geological environmental safety division,typical of environmental engineering geological problems simulation and prediction,control zoning division and specific measures formulated,the practicability of the paper is further highlighted.The results can be used for guiding the planning and construction,the disaster prevention and reduction,and the environmental protection of Jinan city. |
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