Application Of Variable Weight Model For Quality Evaluation Of Urban Engineering Geological Environment:

A new evaluation model was introduced to urban engineering geological environment quality. Geological environment is extremely sensitive to engineering construction, which cannot be predicted under present conditions. Quality evaluation of engineering geological environment is general implemented by constructing the reasonable assessment index system and determining these indexes'weights. Those traditional methods for quality evaluation of urban engineering geological environment can not reflect the effect of each index internal differences on urban engineering geological environment, which result in the final evaluation results lost their objectivities and justices. Once the index weights have been determined, they would never change with the index value variations. In this paper, the variable weight theory was introduced into the assessment system of urban engineering geological environment quality.Quality variable weight comprehensive evaluation for urban engineering geological mainly includes five steps:(1) Based on the characteristics of urban engineering geological environment and the evaluation requirements, the index system for quality evaluation of urban engineering geological environment was constructed, then classifications of the evaluation index was put forth.(2) According to the index system for quality evaluation of urban engineering geological environment, constant weights, also called "basic weights", were obtained.(3) According to the collected evaluation indexes data, those index images were obtained by vectorization processing of MAPGIS graphic processing module.The new spatial features and new relative attribute of grid date graph layer of every index was achieved by extracting information, assignment, buffer analysis and DTM process, while coordinate system, projection mode, study regional boundary were all unified. The database of evaluation index was established, and the data was standardized, then the index images were divided into many grids.(4) Based on the features of urban engineering geological environment and the evaluation precision requirements, the segmented strong penalty-incentive state variable weight function adjusted the constant weight, and the variable weights for every index of basic assessment unit were calculated.(5) Grid punctate units and vector surface units were coupled, the basic unit comprehension valuation values were calculated by association of MATLAB and the variable weight evaluation model. Merged the same quality grades of urban engineering geological environment, and then the comprehension evaluation zone map were finished.The variable weight comprehensive evaluation model applied to quality evaluation for urban engineering geological environment of Zhengzhou, and obtained the following knowledge and progress:1. Based on the analysis of engineering geological environment, topography and geomorphology, hydrogeology conditions, engineering geological problems, geological hazards and human influence were selected as the first level evaluation indexes of engineering geological environment quality. Topography, slope, ground elevation, groundwater depth, distance from surface water bodies, foundation bearing stratum thickness, foundation rock and soil uniformity, foundation bearing capacity, collapsible loess, liquefaction of sandy soil, mucky soil thickness, distance from activity fault, geological hazard, groundwater drawdown funnel and human engineering activity were selected as the second-level indexes, and then evaluation system for urban engineering geological environment quality was established. Classification of the evaluation index was adopted by fuzzy mathematics, and the constant weights were calculated by analytical hierarchy process.2. Urban engineering geological evaluation quality is a level-division and multiple index comprehensive evaluation system. Every index not only influences urban engineering geological environment quality, and every index internal different grades also impact its integrity. During the assessment process, the final comprehensive evaluation values reduce obviously, if one index value is worse, although its weight value is extremely low, but single index value is very high, the final evaluation values could not always increase obviously. Based on aforementioned characteristics, penalty-incentive state variable weight function was established. The function include three stages:primary penalty stage, intense penalty stage and ultra-intense stage, punished index worse values, inspired index excellent values, and index qualified values no punish no inspire. For qualitative indexes, the function adjusted its weight from one to five for each, while quantitative indexes, their weights changed with their values variations.3. Spotty unit and planar vector unit of MAPGIS were combined in this paper. Index data vector and basic evaluation unit were separated during quality evaluation process, easy to calculate. The complicated calculation was solved by using MATLAB programming, which MAPGIS and EXCEL hardly to implement under present conditions.4. The constant weight and the variable weight methods were respectively applied to assess urban engineering geological environment depth8-9m quality in main urban area of Zhengzhou. The analysis indicates that the discreteness of the variable weight comprehensive evaluation result is better than that of constant weight result, which easily distinguishes the quality grades of urban engineering geological environment. Two methods of evaluation result trends are consistent, different grades comprehensive evaluation areas of urban engineering geological environment quality from more to less in order are the third grade, the second grade, the fourth grade, the fifth grade, the first grade. Because index difference of urban engineering geological environment quality, the variable weight method using state variable function punished index worse values, inspired index excellent values, so evaluation areas of two methods are different. Different grade comprehensive evaluation changing areas of two methods from more to less orderly is the third grade, the first grade, the fourth grade, the second grade and the fifth grade. The analysis of two methods and field survey indicate the variable weight method significantly improves the reliability of quality evaluation grades urban engineering geological environment, therefore, the variable weight method avoids the defects of the constant weight distribution for urban engineering geological environment quality. More importantly, the variable weight method emphasizes punishing those indexes'worse values and encouraging those indexes'excellent values, no punishing and no encouraging qualified indexes, and this method fully reflects the influence of every index internal different grades on the comprehensive evaluation results of urban engineering geological environment quality.