From the test results, it is suggested that the incorporation of fly ash has a strengthening effect on E50 of lime-treated sediments, but has a weakening effect on E50 of cement-treated sediments. This is to say, the addition of fly ash increases E50 of lime-treated sediments, but decreases E50 of cement-treated sediments. For example, E50 of SD3L at 90 days is increased from 96.2 MPa to 152.9 MPa by addition of 3% fly ash, whereas E50 of SD3C at 90 days is decreased from 95.2 MPa to 75.6 MPa. Furthermore, the lime-fly ash-treated sediments have a higher E50 than cement-fly ash-treated sediments except SD6C3CV. This is well consistent with the UCS development of lime-/cement-fly ash-treated sediments.