The Effects of Mineral Wool Fly Ash on Cohesive Soil Strength Behaviour

This research work represents updated results of cohesive soil strength improvement with mineral wool fly ash. In the investigations, these materials were used: Portland cement CEM I 42.5 R, fly ash obtained from a mineral wool production process, sand and clay. Mixtures were prepared as follows: dry mixing of Portland cement and fly ash; dry mixing of sand and clay; adding water into Portland cement and fly ash; adding sand and clay mixture into already prepared Portland cement and fly ash suspension. The content of fly ash replacing Portland cement varied from 0% to 40%, and the content of sand mixture varied from 20% to 60%. After 24 hours, investigated samples were taken out from cylinder forms and kept in a desiccator with a humidity of 90% and at 20 °C temperature. Uniaxial compressive strength of the samples was determined after 548 days and compared to previous research results obtained after 7, 28 and 183 days. The most predictable compressive strength is for samples, which composition is 100% cement and 0% fly ash. In these samples, the highest compressive strength was obtained, comparing them to the other investigated samples. Compressive strength change is minimal for samples with a 10–30% amount of fly ash. The most significant decrease in compressive strength was obtained for samples with a 40% fly ash after 183 days. Nonetheless, the compressive strength of these samples increased after 548 days and is almost the same as for samples with 100% Portland cement.

Review on Soil Improvement by Using Various Chemical Additives for Foundation

This work aimed to study the most effective chemical additives to increase the strength of the clay soil. The problem statement is to improve the soil strength to avoid failure in the ground. The chemical additives that be used are lime, cement, and fly ash. These chemical additives were commonly used to stabilize the soil and make the shear strength of the soil increase. The data taken was from the previous research, where the data was compared to get the most effective chemical additives to improve the soil stability and soil strength. The percentage of the chemical additive used in the soil mixture was 8% to 10%. The data from previous research was chosen based on the rate used of the chemical additive and the research was taken from Science Directed website only. Data were collected through 30 previous studies using clay and chemical additives such as cement, lime, and fly ash. The data for Plastic Limit, Liquid Limit, Plasticity Index, Optimum Moisture Content, Maximum Dry Density, and Unconfined Compressive Strength was taken by referring to the previous study. Then the data was listed in Microsoft Excel to generate the graph for comparison. All the data obtained are then compared to get which chemicals can increase the strength of the soil. The result of this study shows that the cement was the most effective chemical additive to improve the soil strength and to stabilize the soil than the lime and fly ash.

Root reinforcement: continuum framework for constitutive modelling

The mechanical contribution of plant roots to soil strength has typically been studied at the ultimate limit state only. Since many geotechnical problems are related to serviceability, such as deformation of infrastructure, a new constitutive modelling framework is introduced. The rooted soil is treated as a composite material with separate constitutive relationships for soil and roots, and a comprehensive stress-strain relationship for the root constituent is presented. The model is compared to direct shear experiments on field soil reinforced with gorse, grass and willow roots, as well as an existing root reinforcement model based on Winkler-spring supported beam theory. The results show that both the newly developed model and the beam-type model yield good predictions for the evolution of root-reinforced shear strength as a function of increasing shear displacements. Both successfully capture the large deformations required to reach peak reinforcement, the reduction in reinforcement due to root breakage and the presence of significant reinforcement even after very large deformations, associated with root slippage. Since both fibre and beam models only require physically meaningful input parameters, they can be useful tools to study the mobilisation of rooted soil strength and simulate the response of rooted soil in continuum-based numerical simulations.

An iterative algorithm for random upper bound kinematical analysis

A new approach for stochastic upper bound kinematical analyses is described. The study proposes an iterative algorithm that uses the Vanmarcke spatial averaging and kinematical failure mechanisms. The iterative procedure ensures the consistency between failure geometry and covariance matrix, which influences the quality of the results. The proposed algorithm can be applied to bearing capacity evaluation or slope stability problems. The iterative algorithm is used in the study to analyse the three-dimensional undrained bearing capacity of shallow foundations and the bearing capacity of the foundation for two-layered soil, in both cases, the soil strength spatial variability is included. Moreover, the obtained results are compared with those provided by the algorithm, based on the constant covariance matrix. The study shows that both approaches provide similar results for a variety of foundation shapes and scale of fluctuation values. Therefore, the simplified algorithm can be used for purposes that require high computational efficiency and for practical applications. The achieved efficiency using a constant covariance matrix for one realisation of a three-dimensional bearing capacity problem that includes the soil strength spatial variability results in about 0.5 seconds for a standard notebook. The numerical example presented in the study indicates the importance of the iterative algorithm for further development of the failure mechanism application in probabilistic analyses. Moreover, because the iterative algorithm is based on the upper bound theorem, it could be utilised as a reference for other methods for spatially variable soil.

Analysis of Influencing Factors and Mechanism of Strength of Cement-Modified Silty Sand

The unconfined compressive strength of cement-modified silty sand in Jilin Province was investigated in this study. For this purpose, various tests were conducted, including the screening test, compaction test, CBR test, X-ray fluorescence detection, and unconfined compressive strength test. Effects of compaction degree, soil quality, water quality, cement content, and curing age were considered. The results show that CBR value is positively correlated with compactness. Two kinds of different water qualities have little effect on unconfined compressive strength of cement-improved soil; with the increase in cement content, the unconfined compressive strength increases, and the power function equation established by the two is significantly correlated. The logarithmic relationship between cement-soil strength and curing age is approximately linear. Through regression analysis, the comprehensive characterization parameters of cement-soil strength, such as water-cement ratio, cement content, and curing age, are put forward. The unconfined compressive strength of cement-modified silty sand has a good power function relationship with the comprehensive characterization parameters, and the fitting degree between the strength prediction formula and the existing research and test data exceeds 90%, which verifies the effectiveness of the comprehensive characterization parameters.

Influence of stress history on undrained cyclic shear strength evolution

Offshore infrastructure often interacts cyclically with the seabed over the operational life of a project. Previous research on the evolution of soil’s undrained strength under long term, large-amplitude cyclic loading has focused on contractile clays and demonstrated that this cyclic interaction can lead to the initial generation and later dissipation of positive excess pore pressure in the soil. This process generally leads to an initial strength reduction, with subsequent densification and soil strength gains that can have consequences on the performance of seabed infrastructure during its design life. In this paper, new experimental data from T-bar penetrometer testing in reconstituted kaolin and Gulf of Mexico clays is presented. The data illustrate how the stress history, quantified via the overconsolidation ratio, affects soil strength changes during large-amplitude cyclic loading. The experiments explore both long-term continuous loading cycles and episodic loading with packets of undrained cycles followed by quiescent consolidation periods. A critical state-based framework is used to interpret the experimental data and provide predictions of the long-term steady-state strength of both soils as a function of the initial in situ state of the soil.