When constructing on clay and gyttja soils, low-carbon ground improvement methods such as preloading should be preferred over carbon-intensive solutions (e.g., piles or deep mixing with lime-cement binder). The design of preloading requires knowledge about the compressibility and consolidation properties of subsoil, but site-specific oedometer tests may be scarce or even lacking, especially in the early design phases. Hence, this paper presents two extensive databases based on oedometer tests performed on Finnish clay and gyttja soils, with a special emphasis on consolidation rate and creep properties. The FI-CLAY-oedo/14/282 database contains 282 oedometer test-specific data entries, such as initial hydraulic conductivity and maximum creep coefficient. The second database, FI-CLAY-cv/8/774, contains 774 load increment-specific data entries (e.g., coefficient of consolidation) from 232 oedometer tests. The analysis of these databases provided three main results: (i) statistics for bias factors, which quantify the differences between determination methods (log time vs. square root time method and oedometer vs. falling head test), (ii) transformation models (and their transformation uncertainty) to predict creep coefficient from index or consolidation properties, and (iii) typical value distributions for various consolidation rate and creep properties, in a form of histograms and fitted lognormal distributions. All the results are given with statistical information, which allows their straightforward utilization as input data for probabilistic assessment (reliability-based design). It is concluded that the consolidation properties of clay and gyttja soils are indeed characterized by significant uncertainty. Hence, such results are recommended to be used as existing (prior) knowledge when determining design parameters, either by supporting engineering judgement or via a more systematic framework such as Bayesian statistics.

In order to understand the influence of sand content on the secondary consolidation behavior of sand-fine mixtures, a series of one-dimensional creep tests were conducted. These tests used mixtures with sand contents of 0%, 16.67%, 28.57%, 50%, and 60% and were run for 3,000 min. As the sand content increases, the structure of the mixtures transitions from being fine-supported to sand-supported. This results in changes in the time at the end of primary consolidation (TEOP), the proportion of secondary consolidation deformation in the total deformation (PCT), and the coefficient of secondary consolidation. These parameters decrease before the sand content reaches 28.57% and increases after this point. The sand-fine mixtures with a sand content of 28.57% exhibit the minimum TEOP, PCT, and coefficient of secondary consolidation. When the sand content is less than 28.57%, bound water (especially weakly bound water) significantly impacts the secondary consolidation behavior of the sand-fine mixtures. However, when the sand content exceeds 28.57%, the secondary consolidation deformation of the mixtures is primarily governed by particle crushing in the sand grains.

The current study examined the creep behavior of clay in terms of particle sliding using samples containing montmorillonite and kaolinite by modeling all interparticle forces using the discrete element method. The effects of the stress level, pore fluid chemistry, fabric structure and mineral compositions of clay on creep behavior have been studied. The results show that creep mechanisms emerged as a result of clay particle slippage at their points of contact and deformation of the particles themselves. It was also observed that interparticle physicochemical interactions affected the creep behavior of clay minerals. Generally, the rate of secondary consolidation declined with an increase in loading due to densification of the soil. Additionally, a stronger DDL repulsive force led to the neutralization of applied stress at higher compressions, resulting in sooner completion of primary consolidation and initiation of creep.

The calculation of the settlement after the soft foundation treatment is directly related to the unloading time of the soft foundation treatment. In order to study the post-construction settlement characteristics of soft foundation treatment under secondary consolidation, the numerical models of soft foundation without consideration of secondary consolidation and under secondary consolidation were established by MC (Mohr-Coulomb) constitutive and SSC(soft soil creep) constitutive construction, respectively, and the influencing factors of secondary consolidation were proposed. and the existing settlement calculation formula was modified, and the results showed that: (1) The secondary consolidation has a significant effect on the sedimentation rate, and the sub-consolidation is only about 0.5 times of the non-secondary consolidation sedimentation rate, and it is recommended that the sub-consolidation impact factor should be 0.5-0.8. (2) The sedimentation rate calculated by the method proposed in this paper is similar to the measured data and has good applicability.