Experimental study on the dynamic properties of low-cement sludge solidified soil under long-term cyclic loading.

The stabilization of waste sludge generated from various engineering projects to produce sludge solidified soil for use as subgrade fill is one of the effective approaches for the resource utilization of construction spoil. However, such solidified soils are typically characterized by relatively low stabilizer content and are subjected to long-term cyclic dynamic loading during their service life. In this study, typical sludge from the Ningbo region was used to prepare cement-stabilized soils with low cement content (4-7%). A series of dynamic triaxial tests under long-term cyclic loading were conducted to systematically investigate the evolution of dynamic strength, cumulative deformation, and initial dynamic elastic modulus. The test results revealed the following: (1) The cumulative deformation of the solidified soil exhibited either a "stable" or a "failure" pattern, with the transition governed by the critical dynamic load, which was strongly influenced by the cement content. (2) Increasing the cement content significantly enhanced the fatigue resistance of the solidified soil; when the content was increased from 4 to 6%, the fatigue life improved by up to 575%. (3) When the cement content exceeded 6%, the growth rates of both fatigue life and initial dynamic elastic modulus slowed markedly, indicating a clear phenomenon of diminishing marginal returns. This study identified 6-7% as the optimal economic range of cement content, achieving an optimal balance between dynamic stability and material cost. These findings provide critical design parameters and performance optimization references for the application of stabilized sludge in road engineering.