Research On Properties Of Ecological Composite Solidified Soil Based On Box-Behnken Design Method

With the development of urban underground projects,a large amount of excavated soil has been accumulated,resulting in a waste of soil resources.How to dispose of these excavated earthwork without causing damage to the ecological environment is a major problem that needs to be solved urgently.In order to re-use these soil resources,the soil needs to be reinforced.Usually a single curing agent can not make the soil meet the needs of the project,so this paper adopts the Box-Behnken method,using a variety of curing agents to modify the Suzhou soil,through unconfined compressive strength test combined with microstructure analysis to explore Curing mechanism.The main tasks of this paper are as follows:（1）Mix different amounts of cement,lime,fly ash,and biological enzymes for silt,clay,and sand,and prepare unconfined compressive strength on the basis of compaction test.According to the strength,determine the four curing agents in different Single mixing range in soil;（2）Based on the determination of the single mixing range,the Box-Behnken design method is adopted,with cement,lime,fly ash,and biological enzymes as single factors,and three soils at different ages（3d,7d,14d,28d）)Unconfined compressive strength as the response value,arrange the test plan;（3）According to the test data,establish the strength prediction model at different ages,analyze the influence of four single factors on the strength and the interaction effect between the two factors,and obtain the optimal ratio of various solidifying agents in the soil;（4）Prepare and maintain the microscopic specimens of different ages（7d,14d,28d）on the basis of the optimal ratio,use the scanning electron microscope（SEM）to obtain the microstructure,and use the Image-Pro Plus image processing software to analyze SEM images were processed and analyzed to determine the apparent void ratio,fractal dimension and the proportion of different particle sizes of stabilized soil,and XRD was used to test the mineral composition of the solidified soil.The main research results are as follows:（1）When the cement content is 9%,the 7d strength of silt,clay,and sand respectively reaches the maximum value,which is 2.67MPa,3.04MPa,and 2.97MPa.（2）When compounding,the best mixing ratio in the silt is cement6.35%,lime 10.34%,fly ash 15.11%,biological enzyme 3‰,and on this basis,the 3d,7d,14d,28d strengths are respectively 3.31 MPa,4.13MPa,4.73MPa,6.45MPa;the best mixing ratio in clay is cement 5.78%,lime 8.36%,fly ash 14.78%,biological enzyme2.1‰,on this basis 3d,7d,14d,28d strength Respectively 4.78MPa,5.38MPa,6.81MPa,7.71MPa;the best mixing ratio in sand is cement 6.73%,lime 8.48%,fly ash 17.97%,biological enzyme 2‰,on this basis 3d,7d,The strengths of 14d and 28d are 3.23MPa,4.09MPa,4.97MPa,6.04MPa respectively（3）As the curing age increases,the fractal dimension of soil particles and pores is between 2.3-2.5,and the proportion of small particles decreases.Small particles gradually transform into medium and large particles;while the proportion of small and micro pores increases,while the large and medium pores decrease.Through the XRD diffraction pattern,it can be seen that the content of AFt and Ca（OH）₂increases with age.