The main characteristics of sludge are as follows: natural water content is higher than liquid limit, pore ratio is more than 1.0; dry density is small, only 0.8-0.9 g/cubic centimeter; compressibility is especially high, when pressure increases from 9.8 x 10 Pa to 19.6 x 10 pa, compressibility coefficient is A1-2 > 0.05, compression coefficient a1-3 > 0.1 when pressure increases from 9.8 x 10 Pa to 29.4 x 10 pa; strength is very low, often in Flow state is regarded as weak foundation. Silt can be subdivided into silt (pore ratio greater than 1.5) and muddy soil (pore ratio 1-1.5).
The natural structure change of silt is very sensitive, and the structure and its strength can be automatically restored after being destroyed, which is called thixotropy. Silt should not be used as natural foundation, because it will produce uneven settlement, which will cause cracks, inclination and affect the normal use of buildings. Artificial reinforcement measures must be taken when building on silt. If compacted and compacted, drainage by vertical sand wells will accelerate sludge consolidation. Sometimes, column foundation, rigid ring girder and settlement joints can be used to ensure the stability and safety of buildings.