## 3 Test Results and Analysis
### Improved Mechanisms  
SEM tests were carried out on granite residual soil amended with fly ash at 0%-20% admixture. The gold-spraying treatment instrument was an SBC-12 ion sputtering instrument from Langfang Zhongyi Technology Co., which located in Hebei Province, China, and the soil section was tested using a JSM-7800F field emission scanning electron microscope from Japan Electron Optical Laboratory.  
Figure 15 shows the SEM images of the granite residual soil at 500\(\times\) and 2000\(\times\). As observed from the 500\(\times\) image, granite residual soil particles are represented by the areas in the picture with high brightness and light color, while granite residual soil pores are represented by the areas with low brightness and dark color. The image illustrates how the vegetal soil particles are loosely skeletal and unevenly massive. Fly ash particles are shown by the round, spherical material in the picture. The SEM image of the modified soil clearly shows the presence of fly ash particles, which are clearly visible and dispersed throughout the soil interstitials inside the fly ash-doped soil samples. With fewer and more dispersed fly ash particles, the fly ash-improved soil with 5% and 10% fly ash content  
Figure 14: Relationship of the permeability coefficient with fly ash dose.  
produces less cementitious material and has a higher porosity than fly ash dosages of 15% enhanced the soil. With a total of 15% fly ash in granite residual soil, fly ash particles plug soil pores and produce a gelatinous substance; the cementitious material indicated in the figure is easily observable, and the SEM diagrams show how part of the gelatinous substance is wrapped around the fly ash particles. The soil particles are bound together by fly ash particles and the gelatinous substance. A total of 20% of the dosed fly ash specimen in the fly ash particles was too much; this is evident from the image, which shows that some of the fly ash particles emerged in a condition of \"aggregation,\" meaning that they were not completely filled in the granite residual soil but rather were next to one another. In this condition, the structural qualities of the granite residual soil are diminished, and its net content also declines, weakening the soil body's skeleton and strength.  
From the 2000\(\times\) SEM image, it can be found that the surface of the plain soil specimen is smoother, flatter and more porous. There were visible fly ash particles in the pores of the enhanced granite residual soil mixed with fly ash, and the improved soil with fly ash dosages of 5% and 10% still had visible pores. Fly ash dosages of 15% and 20% enhanced the soil, clearly reduced the number of pores and mostly revealed fly ash particles and a gelatinous substance. The hydration process between the fly ash and the water adhering to  
Figure 15: SEM images of granite residual soil with different fly ash dosages at 500\(\times\) and 2000\(\times\).  
the surface of the soil particles, or partially enclosed in the fly ash, produces this gelling substance, which takes the form of a net or floc structure. The internal pores of the granite residual soil were plugged by the produced gelatinous substance and fly ash particles, creating a more tortuous hydraulic infiltration channel. This confirms the results of the infiltration test reported in the previous section, namely that the seepage resistance of granite residual soils can be successfully increased by the addition of fly ash.