Abstract: Municipal sludge was modified by water glass, quick lime and flocculent fiber. The consolidated undrained triaxial tests were carried out for studying mechanical strength and failure characteristics of modified sludge composites. Three ratios of modifier were set as 5%, 10% and 15%. After 5 days maintenance, compared with pure sludge, the failure strength of three modified sludge composites were increased by 1.25-1.426, 1.12-1.33 and 1.20-1.50. After 10 days maintenance, the hardening speed of 5% and 10% modifier superior to that of 15%, the failure strength of three modified sludge composites were increased by 1.33-1.45, 1.154-1.35 and 1.56-1.67 respectively. When principal stress difference reached 20 kPa after 10 days maintenance, initial tangent modulus have great mutations. Moreover, strain of modified sludge composites with 10% and 15% modifier have obvious 3%-5% delay period. The internal friction angle of 5% and 10% modifier are larger than that of 15%, whereas their cohesion much less than that of 15%. Based on stress-strain hyperbola proposed by Konde, the ultimate value of principal stress difference was adopted as the normalized factor. Meanwhile, the normalized stress-strain relationship of modified sludge was established under consolidated undrained triaxial tests

Key words: modified sludge, time effect, normalized relationship, consolidated undrained triaxial tests, shear strength