Abstract: The muddy-clayey soils was mixed with powdered fly ash in different proportion and was tested for its permeability, consolidation, direct shear, and triaxial shear strengths, respectively. The mechanism of the consolidation of soft-soil foundations powdered fly ash are studied in detail, and the change of engineering mechanical properties of the clayey soil mixed with the fly ash is elucidated in detail. The test result shows that using powdered fly ash to consolidate soft-soil foundations is inexpensive and effective.