Sedimentation model tests were carried out on four clays in China for investigating the sedimentation behavior of slurries. The sedimentary process can be divided into fluid state and consolidation state. The consolidation state of slurries can be divided into Non-Terzahi soil and Terzaghi soil. The void ratio responsible for the intersect point of fluid state and consolidation state is determined as 8.6 times the void ratio at liquid limit based on the difference of settling type which can be divide into Consolidation settling and Zone settling with the initial void ratio increase. According to the relationship between the stable void ratio (at the end of consolidation) and the initial void ratio, the suggested value of void ratio at the transition point from Non-Terzaghi soil to Terzaghi soil is 2.8 times its value at liquid limit.

Oedometer tests were carried out using modified oedometer apparatuses on three different kinds of dredged slurries. Test results show that the compressibility of dredged slurries is influenced by initial water content when the initial water content is lower than upper limit water content. When the initial water content is higher than the upper limit water content, the compressibility is irrelevant with the initial water content. Result also shows that the upper limit water content is about three times their liquid limit. The compression curves of samples at the initial water content exceeding the upper limit water content overlap to a single curve. This compression curve is named as Top Compression Line (TCL) when it locates above the other compression curves of the same soil. At last, a normalized equation is obtained to normalize TCL of different soils.

This paper presents the experimental investigation into the effect of salinity on the strength behavior of cement-stabilized dredged clays as fills at high initial water contents. One source of dredged clay was dredged from Baima Lake of China. Specimens were prepared having different porewater salinities by blending the air-dried clays with NaCl solution at different salt concentrations. The prepared saline dredged clay specimens were thereafter adjusted to different initial water contents and blended with cement with different amounts. Unconfined compression tests were performed on cement-stabilized dredged clay specimens after 28-day curing. All tested specimens show strain softening behavior where the axial strain corresponding to the peak stress varies with amount of cement. Stress-strain curve for the specimen with lower salinity lies above on that of higher one. Initial water content has a negative effect on the strength of cement-treated clays while cement has a positive effect on the development of strength for cement-treated dredged clays due to the pozzolanic reactions. The presence of salt has an adverse influence on the obtaining of strength for cement-treated dredged clays because salt can inhibit cement from generating C-S-H and C-A-H. Unconfined compressive strength almost linearly decreases with the increasing salinity. A quantitative expression was presented to calculate the unconfined compressive strength for cement-treated saline dredged clays concerning the effects for initial water content, porewater salinity and amount of cement.

Clogging will inevitably occur while using vacuum preloading method to process super-soft soils with high water content. How to quantitatively evaluate the effect of clogging on the consolidation behavior is a key issue to be solved. Based on NALSC (negative axisymmetric large-strain consolidation) model, considering the “internal clogging” and the “external clogging”, a calculation method by using parameter “clogging rate” to reflect clogging problem is proposed for single-well consolidation theory. Effects of clogging rate and clogging occurred time on U_s (degree of consolidation defined by strain) and U_p (degree of consolidation defined by stress) are investigated. Differences of the effect of clogging on consolidation degree are determined between large-strain and small-strain consolidation theory. The results show that, the larger the clogging rate, the smaller the degree of consolidation of the soil at the same consolidation time. Effect of clogging on U_p is greater than U_s. The earlier the clogging occurs, the smaller the degree of consolidation at the same clogging rate. Influences on the degree of consolidation for large-strain and small-strain theory are the same. Consolidation rate of soil is determined to a certain extent by the “generalized clogging parameter μ”. The “external clogging” has a greater influence on the degree of consolidation than the “internal clogging” at the same clogging rate.

A series of studies have confirmed that vacuum preloading can effectively accelerate the consolidation process of soft soil. In recent years, further improvement in the efficiency of this method is still the continuing goal of scholars. This paper reviews the recent improvements in the vacuum preloading techniques as well as their practical applications in China. The advantages and disadvantages of each method are discussed. It is found that replacing or eliminating one or more components of the vacuum preloading system, such as sand-free, membrane-free, horizontal drain, multiple-step, and air booster vacuum preloading methods, achieved similar soil improvement effects to those of the traditional vacuum preloading method. Vacuum preloading combined with other soil improvement methods could improve the soil with the lower average water content and the higher average shear strength.

It is suggested to use wheat straw as both vertical and horizontal drainage materials when using vacuum consolidation method to process dredged slurry in this paper. To verify the feasibility of this proposal, compression and hydrulic conductivity test on wheat straw and vacuum consolidation tests on slurry using wheat straw as drainage materials were conducted. The results show that the compression process of wheat straw is composed of instantaneous settlement and creep. The density of wheat straw changes from 20 kg/m³ to 200 kg/m³ as vertical stress varies from 5 kPa to 100 kPa. The creep rate increases to maximum when vertical stress reaches 60 kPa and then decreases with as vertical stress further increases. The hydrulic conductivity coefficient of wheat straw is changed between 10⁴ cm/s and 10¹ cm/s, which decreases linearly as density increases in semi-logarithmic coordinates (hydraulic conductivity in log scale). In vacuum consolidation tests, the settlement, water content, and undrained shear strength of slurry proceeded by vacuum consolidation with wheat straw as drainage materials are similar to those obtained by using PVD and sand as drainage materials. All the results obtained by this paper show that it is feasibility to use wheat straw as vertical and horizontal drainage materials in vacuum consolidation.