(1. Nanjing Institute of Geology and Mineral Resources, Nanjing 210016; 2. China Geo University, Wuhan 430074; 3. Jiangxi Geological Environment Monitoring Station, Jiujiang 3300 12)

Based on the preliminary study on the evaluation method of geological environment quality of urban construction land in Jiujiang city, a set of evaluation methods and index system of geological environment quality of urban construction land are put forward, so as to make objective and reasonable evaluation of geological environment of different cities, provide corresponding decision support for urban planning, construction and management, optimize the allocation of urban construction and geological resources and environment to the maximum extent, and realize the goal of safe, reasonable and economic urban construction.

Keywords: urban construction land; Evaluation method; jiujiang

Jiujiang City, Jiangxi Province is located in the south bank of the middle and lower reaches of the Yangtze River, bounded by the Yangtze River and adjacent to Hubei and Anhui. It is a famous cultural and tourist city in the south of the Yangtze River with a history of more than 2,200 years. It is a collection of famous mountains (Lushan Mountain), famous rivers (Yangtze River) and famous lakes (Poyang Lake). The overall terrain is high in the south and low in the north, from the middle and low mountains of Lushan Mountain to hills, ridges and alluvial plains. Surface water bodies mainly include the Yangtze River, Poyang Lake, Husai Lake and Qili Lake. With the rapid development of social economy and the acceleration of urbanization, Jiujiang urban construction land resources are increasingly scarce, and the geological environment quality of the original construction land is also more complicated. Therefore, it is proposed to establish a set of evaluation methods and index system for geological environment quality of urban construction land, and make an objective and reasonable evaluation of urban geological environment, so as to provide corresponding decision support for urban planning, construction and management, maximize the optimal allocation of urban construction and geological resources and environment, and realize the safety guarantee of urban construction.

1 Determination of evaluation method

1. 1 workflow

See figure 1 for the research steps of the evaluation method of geological environment quality of urban construction land.

1.2 analysis of evaluation index system

The main influencing factors for evaluating the geological environment quality of urban construction land are: (1) meteorological factors such as temperature, rainfall, evaporation, pressure zone, climate zoning and wind. (2) Hydrological information such as surface water area, basin area, surface runoff, hydraulic characteristics, water level and water pollution, such as pollutant composition, pollution source, pollution route, pollution degree, pollution scope and pollution development trend; (3) Terrain, such as type, surface elevation, ground slope, terrain cutting density, etc. (4) Landforms, such as micro-landforms, geomorphic units and general landforms. (5) Formation lithology, such as Quaternary sedimentary thickness and rock genetic type. (six) geological structures such as faults, folds, joints and cracks; (7) Seismic intensity, dynamic peak acceleration, historical seismic activity, etc. (8) Hydrogeology, such as groundwater occurrence type, aquifer burial condition, water level burial depth, single well water inflow, groundwater type, salinity, corrosivity grade, groundwater exploitation status, water level fluctuation, groundwater recharge, runoff and discharge, etc. (9) Engineering geology, such as regional crustal stability, buried depth of bedrock, lithology of main bearing stratum, bearing capacity, geotechnical engineering geological division, unfavorable geology, special rock and soil, etc. Groundwater environmental problems mainly include water resources shortage, unreasonable utilization, water quality deterioration, backward management and other factors; Geological disasters mainly include ground subsidence, ground fissures, ground collapse, collapse, landslide, debris flow, salt water intrusion, slope instability, port erosion and accumulation, sand liquefaction, loess collapse, soil erosion and other geological factors; Mine environmental geological problems; Radioactive pollution, the collapse of rivers and coasts, and the erosion and deposition changes of estuaries and coasts.

Figure 1 Flowchart of Geological Environment Quality Assessment of Urban Construction Land

In practical work, it is almost impossible to establish a model containing all geological environment factors to evaluate the quality of geological environment. Because, on the one hand, the parameters of some factors are difficult to obtain; On the other hand, too many parameters have complex coordination or interaction. Therefore, it is necessary to find out the main factors affecting the geological environment and abandon the secondary factors according to the specific analysis of specific problems in the evaluation. Therefore, according to the sensitivity of geological environment factors to the influence of geological environment, they are generally divided into sensitive factors, important factors and general factors. Based on the investigation of geological environment conditions in Jiujiang City and the analysis of the actual situation, it is considered that the sensitive factors are mainly terrain slope, geological disasters, existing resources and river erosion (table 1).

Table 1 Sensitive factors and their evaluation criteria

Important factors mainly involve topography, engineering geology, hydrogeology, land use, geological disasters, river erosion and the impact of human activities on the environment (Table 2).

Table 2 Important factors and their evaluation grades

Note: δ indicates the highest flood level.

General factors include: uniformity of foundation soil, corrosiveness of groundwater, etc. In addition, the evaluation criteria are specified in the table.

1.3 Determination of the method for determining the weight of evaluation factors

In the evaluation of geological environment quality, it is often necessary to select multiple environmental factors and environmental factors to participate in the evaluation. When these evaluation factors are integrated, the value to measure the weight of each variable is called "weight". The degree of "importance" reflected by the weight itself is obviously uncertain. The process of obtaining weight is the process of analyzing the "importance" of different evaluation factors. Reasonable determination of the weight coefficient of each participating factor is one of the key links in the evaluation of geological environment quality of urban construction land. The methods to determine the weight coefficient include empirical method, statistical method (arithmetic average statistics and weighted average statistics), regression analysis and analytic hierarchy process. In this evaluation, the method of "expert-analytic hierarchy process" is selected according to the actual situation, and the weight of evaluation factors is finally determined. It roughly goes through the following steps:

(1) Clarify the problem

This paper analyzes the main influencing factors of multi-objective comprehensive evaluation of urban construction land, their mutual relations and restrictive factors, and classifies the influencing factors, each of which is regarded as a level. Generally speaking, it includes the highest layer A (target layer), the middle layer B (criterion layer 1, criterion layer 2 ...) and the lowest layer C (candidate layer), and establishes the hierarchical structure of the evaluation problem.

(2) constructing a judgment matrix

There are several influencing factors Xl, X2, …, Xn, and their weights are M 1, M2, …, Mn. If the factors in the same layer are compared with each other, the ratio can form an n×n order matrix A:

Compilation of geological survey results in East China: 1999~2005

The weights of the impact factors of the evaluation matrix are determined according to Table 3. The scale in the table is determined according to the research of psychologists, and the ultimate ability of people to distinguish information registration is 7 2. For example, when the I factor is as important as the J factor, the scale is1; When the I factor is slightly more important than the J factor, the scale is 3, and the intermediate factor can be scaled as 2.

Table 3 Scale values of relative importance evaluation factors

(3) Calculate the weight of influencing factors of comparative evaluation of judgment matrix.

The essence is to calculate the eigenvector of each judgment matrix. Assuming that there is a normal vector w of the same order and AW = λ w, the maximum eigenvalue λmax obtained by solving this characteristic equation and its corresponding eigenvector W, after normalization, W represents the weight of each evaluation influence factor in this layer respectively. These steps include two aspects:

(1) normalization

Compilation of geological survey results in East China: 1999~2005

Where wi represents the eigenvector of the judgment matrix.

(2) Calculate the maximum eigenvalue (λmax) of the judgment matrix.

Calculate and compare the eigenvalue λ to get the maximum eigenvalue λmax of the judgment matrix, which is to check the consistency of the matrix. In order to prevent the constructed judgment matrix from deviating too much from the consistency, leading to some problems, the test formulas CI = (λ max-n)/(n- 1) and C.R = CI/R.I are defined, where C.R is the consistency index and R.I is the average random consistency index (for the matrix of order 1-9, The greater the value of C.R, the worse the complete consistency of the judgment matrix. Generally, it is only required that c.r is not more than 0. 1, and it is considered acceptable to judge the consistency of the matrix, otherwise the matrix must be reconstructed until it is satisfactory.

Table 4 value of R.I in analytic hierarchy process

Through the above analytic hierarchy process, the weight of each evaluation factor in Jiujiang City is finally obtained, as shown in Table 5.

Table 5 Weight determined by Jiujiang City

Determination of affiliation of 1.4

The determination of membership relationship is the process of establishing fuzzy matrix, which is the basis of fuzzy clustering evaluation. There are many methods to determine the membership function, such as rectangular distribution membership function, R distribution membership function, normal distribution membership function, Cauchy distribution membership function, trapezoidal distribution membership function, semi-ring distribution membership function and so on.

In the practical work of geological environment evaluation, the membership function of trapezoidal distribution is the most widely used and has achieved good results. In this study, the membership function of trapezoidal distribution is selected to construct fuzzy matrix. The solution formula is as follows:

Compilation of geological survey results in East China: 1999~2005

1.5 determination of evaluation mathematical model

Through the test of practical work, when determining the geological environment quality grade of urban construction land in Jiujiang City, the sensitive factor of multi-objective decision-fuzzy clustering comprehensive evaluation method can get more practical results [1] [2]. The following introduces the specific process of fuzzy clustering evaluation.

(1) Based on the systematic analysis of the geological environment in the evaluation area, its constituent elements and environmental factors are qualitatively described and divided into sensitive factors, important factors and general factors.

(2) Dividing evaluation units.

(3) Select sensitive factors for evaluation. Test and evaluate all sensitive factors in the evaluation area one by one. If there are sensitive factors in the evaluation unit, the test fails, the unit will be judged as unsuitable or extremely unsuitable for urban land use, and the unit without sensitive factors will participate in the next evaluation.

(4) For units without sensitive factors, select important factors for fuzzy clustering comprehensive evaluation.

(5) Synthesize the evaluation results of sensitive factors and important factors, merge the evaluation units at the same level, and prepare the evaluation chart.

The evaluation process is shown in Figure 2.

After evaluating the sensitive factors, the mathematical method of weighted average is selected to evaluate the important factors comprehensively by fuzzy clustering. Its analytical formula is, where the sum of weight coefficients is the membership degree of the actual contribution of rij evaluation factors. This model considers the contribution of various factors to the final result. It has been proved by many practices that this method is an effective evaluation model for geological environment evaluation with many influencing factors. In this study, the weighted average model is selected for fuzzy clustering comprehensive evaluation. The specific evaluation process is as follows:

Fuzzy cluster analysis involves four factors (Y 1, Y2, Y3, Y4),

The evaluation results are divided into five grades (Ⅰ, Ⅱ, Ⅲ, Ⅳ, Ⅴ).

The fuzzy matrix is:

Compilation of geological survey results in East China: 1999~2005

Assume that the weights of the four participating factors are:

A=(A 1 A2 A3 A4)

Then the result of fuzzy clustering evaluation is: b = a R.

Fig. 2 Flow chart of fuzzy clustering comprehensive evaluation method

Compilation of geological survey results in East China: 1999~2005

Calculated B = (B=(b 1b2b3b4b5 B5).

Result judgment:

If max (b1b2b3b4b5) = b1,the evaluation unit is Grade I;

If Max (B 1B2B3 B4 B5) = B2, the evaluation unit is Grade II;

If Max (B 1B2B3 B4 B5) = B3, the evaluation unit is Grade III;

If Max (B 1B2B3 B4 B5) = B4, the evaluation unit is Grade IV;

If max (b 1b2b4b5) = b5, the evaluation unit is rated as ⅴ.

2 Evaluation results and analysis

In this evaluation and calculation of geological environment quality of construction land in Jiujiang City, due to a lot of data, the whole calculation process is complicated. We mainly calculate it through the compiled calculation program CityGeology, and sort out the results in a unified way.

The zoning map of geological environment quality evaluation of urban construction land is formed on MapGIS platform to reflect the differences of urban construction geological environment in the planning area. See Table 6 for the final evaluation results, classification and explanation.

Table 6 Classification and explanation of geological environment quality evaluation results of urban construction land in Jiujiang City

3 Conclusion

The sensitive factor-fuzzy cluster comprehensive evaluation method is used to evaluate the geological environment quality of construction land in Jiujiang city, and satisfactory results are obtained. The mathematical model can reflect the quality evaluation of construction land, and it is a good theoretical method and means to solve the problem of quality evaluation of urban construction land.

refer to

Emily Xu Jiawei. Suitability evaluation of urban construction land in Changchun. Economic geography, 1992, 19(6), 10 1 ~ 104.

[2] Chen Guihua, Xu Zhuili. Study on quality evaluation of urban construction land. Natural resources,1995,5 (4): 22 ~ 30

Study on evaluation of geological environment quality of urban development land

Su Jingwen 1, Liu Hongying 1, Shen Manting 1, Liang Hecheng 2, Li Donghong 3, Zhou Jianwei 2, Long Xunlian 3.

(1. Nanjing Institute of Geology and Mineral Resources, Nanjing 210016; 2. China Geo University, Wuhan 430074; 3. Jiangxi Geological Environment Comprehensive Monitoring Station, Jiujiang 3300 12)

Abstract: Through the experimental study on the evaluation of geological environment quality of urban development land in Jiujiang City, this paper tries to establish a set of evaluation methods and index system. Therefore, the geological environment of different types of cities can be objectively evaluated. This study will provide decision support for urban planning, urban construction and urban management in terms of geological environment information, and maximize the optimal allocation of urban construction and geological environment. Achieve the goal of safe, reasonable and economical urban construction.

In this study, the mathematical model of fuzzy cluster evaluation is adopted. In this model, we choose four sensitive factors and eleven important factors. These factors are the main factors affecting the geological environment of urban development land. Sensitive factors will directly deny the applicability of construction. Determine the weight of important factors with "expert analytic hierarchy process"

Because of the large amount of data, we use the program CityGeology to calculate these data. Then the zoning map of urban construction suitability is formed on the MapGIS platform.

Practice has proved that the fuzzy clustering evaluation method can achieve satisfactory results. This result can reflect the geological environment quality of urban development land. It is a good theoretical method and means to solve the problem of geological environment quality evaluation of urban development land.

Keywords: urban development land; Evaluation method; jiujiang