Abstract: Two sets of model tests using the conventional vacuum preloading(CVP) method and the air-booster vacuum preloading(AVP) method, were implemented to strengthen the ultra-soft dredger fills and compare their reinforcement effect. The microstructure characteristics of ultra-soft dredger fills after two methods of reinforcement were investigated using scanning electron microscope(SEM) and mercury intrusion porosimetry(MIP), respectively. A comparative analysis was performed with respect to variables microstructure characteristics of ultra-soft dredger fills, and quantitative analysis was conducted by Image-Pro Plus graphics processing technology under the two reinforcement methods. The model test results show that the reinforcement effect of AVP method is better than that of CVP method. The microstructural characteristics of soil reinforced by two methods were analyzed from three aspects: the morphology of soil skeleton particles, the contact form of soil skeleton particles and the pore space between soil skeleton particles. Compared with CVP method, the microstructure quantitative analysis results indicate that the number of pores, flattening degree K and shape coefficient ff of soil are larger, whereas the porosity and fractal dimension D of soil are smaller after reinforcement in AVP method. However, the directional probabilistic entropy Hm has no obvious change rule, and the peak of the aperture distribution increment is on the left, indicating a greater number of small pores by using AVP method. Furthermore, it is proved that the reinforcement effect of the AVP method is superior to that of CVP method from the microscopic aspect.

Key words: air-booster vacuum preloading, ultra-soft dredger fills, model test, microstructure, quantitative analysis, scanning electron microscope(SEM), mercury intrusion porosimetry(MIP)