Compressibility and Permeability of Sand-Silt Tailings Mixtures

Microstructure showing the involvement of the fine and coarse grains in the soil skeleton is evaluated. Incremental loading tests using a stress-dependent permeameter are conducted on the mixtures of poorly graded sand and nonplastic fines originating from tailings. The results are compared with the published data of various tailings. It is shown that increasing the fines content from 0 to 100%, the involvement of the fine and coarse components of soil skeleton can be classified into four categories: no fines involvement (<10% fines), fines partially involved (10% —35% fines), increasing cushioning effect surrounding the coarse (35% — 40% fines), and constant cushioning effect (> 40% fines). At the same consolidation stress, the void ratio, e, rapidly decreases for fines less than 30%, then almost remains constant between 30% and 50% fines, and gradually increases for fines exceeding 50%. The hydraulic conductivity, k, decreases more than 20-fold as the fines content increases from 12% to 50%, then remains constant. k is proportional to [e3/(1+e)]A and inversely proportional to S2, where A is a factor describing the effect of particle angularity and S is the specific surface. Finally, the influence of fines content on the seepage-induced internal stability is discussed.

Responses of Laterally Loaded Single Piles Subjected to Various Loading Rates in a Poroelastic Soil

Groundwater table has an important role in soil–structure interaction problems. However, analysis of laterally loaded single piles has often been conducted by solely considering the mechanics of the soil skeleton or decoupling the interactive mechanics of the soil skeleton and the fluid flux; in other words, most analyses were performed without taking into consideration the coupling effect between the soil skeleton and the fluid flux. To improve our understanding of the hydromechanical coupling effect on laterally loaded single piles, a series of finite element study on laterally loaded single piles in saturated porous media was conducted. The effect of pile cap geometries, cap widths, cap embedment depths, and pile lengths, on the response of laterally loaded single piles was also studied. The loading condition of the pile was found to have a significant effect on the generation of excess pore-water pressure. The lateral displacement and bending moment computed at the maximum excess pore water pressure, which in turn, is equivalent to an undrained analysis, produced the minimum responses among all the other loading conditions. The effect of pile cap geometries was found to be much less significant than anticipated.

Effects of bio-chemo-mechanical processes on the properties of contaminated marine sediments

A detailed multi-scale investigation of the geotechnical, chemical and mineralogical properties was conducted on contaminated sediment samples collected within the Mar Piccolo, a marine basin in south of Italy. The basin is located close to one of the most important industrial sites in Europe also declared ‘at high risk of environmental crisis’ and prioritised for remediation activities. A multidisciplinary investigation campaign showed that the samples collected close to the seafloor are characterized by high values of both heavy metals and organic pollutants and by the presence of significant amount of organic matter. Several samples in the top layer exhibited peculiar geotechnical properties, in terms of plasticity and activity indexes, compressibility and hydraulic permeability. While the prime suspect for such unconventional behaviour was the chemo-mechanical coupling between soil skeleton and contaminants, it turned out that the biogeochemical degradation of organic matter and the presence of microfossils and diatoms is likely to affect significantly the micro to macro behaviour of polluted marine sediments.

COMPACTION OF LINEAR ELASTIC-CREEPING INHOMOGENEOUS SOILS

В данной работе рассмотрен процесс уплотнения линейных упругоползучих неоднородных грунтов. Областью изменения независимых переменных является прямоугольник, образованный прямыми х=±ℓ; y=0; y=h. Уплотнение этого прямоугольника безусловно определяется своей сжимаемостью. Сжимаемость основания зависит как от типа грунта, так и от характера нагрузки. При этом деформация сжатия грунтов в основном происходит вследствие сближения твердых частиц между собой и оценивается изменением коэффициента пористости при изменении сжимающих напряжений в скелете грунта. Определение этой зависимости обычно производится лабораторным путем в компрессионных приборах. In this paper, the process of compaction of linear elastic-creeping inhomogeneous soils is considered. The domain of change of independent variables is a rectangle formed by straight lines x = ±l; y = 0; y = h. the Compaction of this rectangle is unconditionally determined by its compressibility. Compressibility of the base depends on both the type of soil and the nature of the load. In this case, the deformation of soil compression mainly occurs due to the convergence of solid particles with each other and is estimated by changing the porosity coefficient when compressive stresses in the soil skeleton change. The determination of this dependence is usually made by laboratory means in compression devices.

USING WASTEPAPER SLUDGE ASH (WSA) AS A MATERIAL FOR SOIL STRENGTHENING FOR THE CONSTRUCTION OF LAYERS OF PAVEMENT

The article considers the possibility of using wastepaper sludge ash (WSA) as a soil reinforcement material for the construction of layers of road wear. Loamy sand, sandy loam, silty clay loam, silty clay were chosen as soils for strengthening. The maximum density of the soil skeleton at optimum humidity was established by the method of Proctor. Wastepaper sludge ash and Portland cement grade 400 were used separately for soil strengthening. Six compositions of strengthened soil for each type of soil were investigated according to the strength criterion of water-saturated samples at the age of seven, fourteen and twenty-eight days. The research results indicate that wastepaper sludge ash can be used to strengthen different types of soils with the achievement of following grades of stabilized soil: M10, M20, M40.

Physical bases of packing of frozen clods of soil in ground massifs in transport and hydraulic structures

The current regulatory documents for infrastructure construction indicate the use of only thawed, mainly sandy soils. When erecting embankments during the winter period, a limited number of applied frozen soils are allowed. In this case, the stability and strength of the soil massif decrease. The absence of thawed soils in the regions of Siberia and the Arctic requires an expansion of the types of soils used, one of which is frozen soils. We have developed the designs of the subgrade that allow using frozen soils, enclosed in geosynthetic cages or without them. Increasing the stability and strength of the embankment by creating a dense soil skeleton is one of the scientific issues, which is solved in this article by applying the theory of granular media. In practice, the formation of dense systems from frozen soils is based on two principles: the method of dense mixtures and the method of impregnation, where the main layer of frozen soil is impregnated from above with dry frozen soils. Almost by selection of the composition, you can achieve the maximum density.

A Novel Approach to the Analysis of the Soil Consolidation Problem by Using Non-Classical Rheological Schemes

The paper presents classical and non-classical rheological schemes used to formulate constitutive models of the one-dimensional consolidation problem. The authors paid special attention to the secondary consolidation effects in organic soils as well as the soil over-consolidation phenomenon. The systems of partial differential equations were formulated for every model and solved numerically to obtain settlement curves. Selected numerical results were compared with standard oedometer laboratory test data carried out by the authors on organic soil samples. Additionally, plasticity phenomenon and non-classical rheological elements were included in order to take into account soil over-consolidation behaviour in the one-dimensional settlement model. A new way of formulating constitutive equations for the soil skeleton and predicting the relationship between the effective stress and strain or void ratio was presented. Rheological structures provide a flexible tool for creating complex constitutive relationships of soil.