The Fuyong sludge landfill site is located in the middle of the extension area of Shenzen International Airport

where it is going to build the T4 terminal. There is a great amount of solidified sludge soil landfilled in this site

which is a difficult problem for airport foundation improvement. In order to find out the geotechnical engineering properties of the solidified sludge soil

experiments including component analysis，microstructure observation，laboratory soil tests and in-situ tests were performed in this study. The results showed that the solidified sludge soil contained flake clay mineral particles

unshaped hydrated calcium silicate (CSH)

needle like ettringite and loose structure organic matters; there were a lot of voids between the soil particals including macrovoid(1~6 μm) and microvoid; the solidified sludge soil had characters of low density

low soil particle density

high water content

high void ratio

high liquid limit and high plastic limit; the vane shear strength of the soil was 13.8~23.7 kPa and its strength increased greatly with the increase of the consolidation stress; the characteristic value of foundation bearing capacity was 78.9 kPa and the deformation modulus was 4.1 MPa

but the compression coefficient of the remolded soil was 3.073 MPa-1.