Abstract: To improve the waste slurry discarded from a pile foundation project in Shanghai, the curing agent (calcium lime) is used as an additive material. The deformation on the waste slurry surface with various additives is measured during settlement at rest. The vacuum preloading tests are conducted for the slurry flocculation. The variation in water discharge during vacuum preloading and the particle distribution in the slurry flocculation at various locations as the tests completed are then investigated. The changes in the size distributions of the pores in the waste slurry are also explored using MIP tests before and after the vacuum preloading tests. The hydration mechanism of the calcium lime on the improvement of waste slurry is illustrated using the scanning electron microscope image processing. It shows that the settlement rate on the waste slurry surface accelerated after adding calcium lime, and soil particles are joined together by lime hydrate crystals to form the skeletonized soil-flocculation aggregates with larger volume, looser structure, and enhanced permeability. Among the calcium lime contents of 0.2%, 0.5% and 0.8%, the surface settlement of the waste slurry with the content of 0.5% is fastest both during the settlement at rest and in the vacuum preloading test. Most of the pore sizes of waste slurry decrease from between 3,184 to 11,308 nm before improvement to between 681 to 3,244 nm after vacuum preloading with flocculation, indicating that the total pore volume decreased by 60% to 79%.

Key words: vacuum preloading with flocculation, construction waste slurry, calcium lime, enhanced permeability effect, scanning electron microscope, mercury intrusion test