Research On Micro-Structure Of Inorganic Chemical Modification Subgrade Fill

Our country’s highway mileage has reached first in the world. In the construction of highway, the design of the subgrade directly controls over the quality of the highway. Highway construction needs a lot of subgrade filling, and there is a clear national standard requirement for its performance index. With the development of science and the improvement of environmental awareness, soil stabilizer has been more and more widely used for subgrade filling.In this paper, a special class of silt in high grade highway in a coastal area in Jiangsu Province was studied. Relying on the National Natural Science Foundation of China "Research on Designing Theory of Inorganic Curing Agent for Embankment Filling basedon The Principle of Computational Material Science ", NaOH, Na2Si2O3 and Ca(OH)2 were selected as inorganic modifier. The macro-mechanical properties and micro-structure of the modified soil were studied, respectively. The main research contents and conclusions are as follows:(1) Macro mechanical propertiesUsing NaOH, Na2Si2O3 and Ca(OH)2 as inorganic modifier, four groups of contrast tests were set for comparing research, respectively. In standard curing condition, California bearing ratio test and consolidation undrained test were conducted to the modified soil. By compared experiments, it was found that inorganic modifier can effectively improve the road performance and shear strength index of the subgrade filling. The inorganic modifier used in this paper can effectively improve the strength of the studied soil.(2) Micro structure studyX-ray diffraction (XRD) analysis and Computerized Tomography were conducted to study the micro structure of the four groups of soil samples, respectively. By XRD spectrum analysis, it was found that the major constituents of the soil are quartz, kaolinite, potassium feldspar, plagioclase, mica and calcite. The inorganic modifier mainly reacts with kaolinite, potassium feldspar, plagioclase and mica and a small amount of calcite and CSH are generated. By CT scan test, the internal images of soil were acquired. Image enhancement and image segmentation were conducted to the images. After processing, the average grey value, pore geometry characteristics and the fractal dimension of the images were counted, respectively. Their values correspond to the micro-structure change of the modified soil samples. Three parameters show a reciprocal association with the macro mechanical properties of the soil samples and the average grey value has obvious linear relationship with the CBR values of the soil samples.(3) Particles flow numerical simulationBased on the principle of discrete element simulation, according to the grain distribution of the four soil samples, particle models were generated with the CT images. Using consolidated undrained tests indoor as reference object, biaxial test simulation were don·e to the particle models and particle mesoscopic parameters were calibrated. Comparing the simulation results with the consolidated undrained test, the results of numerical simulation were close to laboratory test results. The average grey values of the CT images have obvious linear relationship with the particle contact stiffness, which shows mesoscopic parameters of the CT images have certain reference function for the mesoscopic parameters calibration of particle flow model. Using the same particle models and mesoscopic parameters, CBR test particle models were founded after setting the servo-mechanism and loading system. The injection curve after simulation had a very good correspondence with laboratory test results, and the calculated CBR values were close to laboratory test results, which shows CBR values of soil samples calculated by numerical simulation is feasible. On this basis, mesoscopic mechanics of the models after loaded were analysed, and the relationship between friction coefficients, compressive strength and the contact stiffness with CBR values of the modes were studied.