| With the acceleration of urbanization process, the Urban Heat Island effect of major cities and corresponding environmental issues are more and more significant. Due to Urban Heat Island effect, soil temperature and soil moisture are changed, and result in the variation of soil strength, soil deformation and cracking. Obviously, the safety of geotechnical structures is influenced by the variation of soil strength; and soil deformation may influence the stability of foundation. On the basis of field observation, laboratory tests and mathematical and physical theories, a series of numerical models is established. There model were used in the simulation and quantitative analysis of the variation of soil engineering properties and corresponding disasters in Urban Heat Island, and the following results are obtained:（1） On the basis of monitoring data of two observation sites in urban-and rural regions of Nanjing city, the spatial-and temporal variations of soil temperature and moisture of urban-and rural regions were analyzed. The result shows that the average Urban Heat Island Intensity and Urban Dry Island Intensity of the city are2.02℃and-7.2%, respectively.（2） A simplified model for the prediction of underground temperature is proposed, which is based on surface maximum-and minimum air temperatures. The model was used to simulate the variation of underground temperature field under the urban concrete surface and rural bare soil surface, and the simulated temperatures coincide with the field measured data. The deviation between simulated-and measured temperatures and the causes were discussed. Combined with the data of soil moisture, the Urban Heat Island, surface type and rainfall infiltration have major impacts on the underground temperature-and moisture fields.（3） A series tests were conducted to investigate the influence of soil density, moisture and temperature on the strength of Xiashu clay soil. The result shows that clay samples with low water content and low density show a thermal consolidation characteristic; while the samples with high water content or high density have a thermal softening characteristic. The temperature field of a slope in summer heat weather was simulated. Using the field temperature data and strength-temperature relation of the soil, the safety factor of the slope was calculated to analyze the influence of Urban Heat Island on the stability of geotechnical structures. Furthermore, a model of retaining wall was built, in which the variations of soil temperature and moisture were considered. Numerical simulation indicates that the Urban Heat Island environment has a negative impact on the safety of geotechnical structures, as the soil temperature increases and soil moisture fluctuates dramatically in urban area.（4） In the light of the characteristics of soil crack and corresponding requirement of modeling, the discrete element method was investigated and improved, and the elastic properties and failure modes of close-packed discrete element model was derived in the thesis. Using the derived conversion formula, a discrete element model can be built, which may perform similar elastic properties and failure modes as real material, and consequently has the ability to simulate the generation and development of soil cracks. Based on the theoretical research, a program "MatDEM" was developed to simulate and analyze the stress status, energy change and some phenomenon during crack propagation. Combined with experimental studies, a discrete element model of multi-field simulation of soil cracking is proposed.（5） In order to quantify the temperature effect on the shape of soil cracks, a set of methods is proposed to identify and quantify crack images, on the basis of image processing technologies. The quantification of soil cracks is divided into three steps, image segmentation, crack identification and measurement, and includes a series of image processing methods. Based on these methods, the software "Crack Image Analysis System"（CIAS） was developed. With the application of the software, various geometric parameters of crack can be measured automatically, including crack length, width, direction; clod area and perimeter; node number, crack number, surface crack ratio and fractal dimension of crack network; etc. Finally, the influence of temperature on the crack pattern is quantified and analyzed using the software. The result indicates that temperature has a significant impact on the crack pattern.（6） The influences of Urban Heat Island Effect on the engineering properties of soil are usually ignored. However, the thesis shows that soil engineering properties and the stability of geotechnical structures are influenced by Urban Heat Island effect. The research conclusions and methods provide a theoretical basis and new way to quantitatively investigate the variation of soil engineering properties and disaster effects in urban heat environment.The research in this dissertation was supported by the State Key Program of National Natural Science of China （40730739）, Academic Star Award of PhD. Student by Ministry of Education and the College Graduate Student Innovation Program of Jiangsu Province （CX09B011Z）... |
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