Non-plastic Silt Research Articles

Accelerated carbonation of non-plastic soils mixed with hydrated lime: index properties influencing binder formation rate and mechanical improvement

Chemical stabilization—the mixing of additives like cement, lime, or fly-ash with soil to improve its mechanical properties—conventionally relies on hydration reactions to generate a binder. Accelerated soil carbonation is a nascent alternative method, whereby carbon dioxide is intentionally introduced in soil mixed with alkali additives to generate a carbonate binder and sequester carbon dioxide. Non-plastic sand and silt specimens mixed with hydrated lime were carbonated for varying amounts of time at different water contents and densities to evaluate the index properties influencing the rate of carbonation and degree of mechanical improvement. It was demonstrated that volumetric air and water contents primarily govern the rate of binder formation and that mechanical properties are influenced by the carbonate binder content and density. Under optimum conditions, soil specimens could be fully carbonated within 3 to 24 hours and unconfined compressive strengths as great as 3 to 4 MPa were achieved. The degree of strength improvement is comparable to cement-stabilized materials with similar dependence on soil type, density, and binder content. If techniques are developed that enable carbonation at scale, the sequestration of carbon dioxide would offset emissions associated with production of chemical additives used for chemical stabilization.

Accelerated surface carbonation of non-plastic silt mixed with hydrated lime

Chemical stabilization via hydration reactions with cement or lime is a universally applied method to improve the mechanical properties of shallow soils. Accelerated soil carbonation is a nascent approach intended to bypass this reaction. Carbon dioxide gas is deliberately introduced at high concentrations to react with the alkali additives and precipitate a carbonate binder that permanently sequesters carbon dioxide in the process. A large soil box experiment was performed to examine the efficacy of an accelerated surface carbonation approach, which has the potential to be applied over large areas. High concentrations of carbon dioxide gas were introduced at grade beneath a seal to facilitate vertical penetration into lime-mixed silt. The real-time progression of accelerated soil carbonation was captured with a gas flowmeter and a distributed array of embedded thermocouples and bender elements for the first time. Post-carbonation measurements of binder content and California Bearing Ratio (CBR) verified the degree of carbonation and associated mechanical improvement. Synthesis of real-time monitoring data and post-carbonation measurements indicate carbonation progressed top-down 150 to 200 mm below grade within 5 h, resulting in a substantial increase in strength and stiffness. Potential challenges and benefits associated with adoption of accelerated surface carbonation are discussed.

Energy-Based Assessment of Liquefaction Behavior of a Non-Plastic Silt Based on Cyclic Triaxial Tests

Earthquakes cause cyclic shear deformations in soil and build-up of excessive pore water pressure as a result of undrained loading, accompanied with rearrangement of soil particles and degradation in stiffness of the soil due to decrease in effective stresses. During loading, the onset of soil liquefaction is defined as a stress state in which the excess pore water pressure is equalized to the total stress. From this point of view, assessment of the pore water pressure development pattern under cyclic loading has been one of the most salient research topics in geotechnical and earthquake engineering. In this study, results of a series of cyclic triaxial tests on non-plastic silt specimens consolidated under 100 kPa effective isotropic consolidation pressure were used to question the modelling ability of pore pressure development models previously proposed for sands. Tests were performed on specimens of 6 different initial relative densities (Dr) ranging between 30-80% and 10 different cyclic stress ratios (CSR). The key parameters of pore water pressure development and shear deformation in the energy-based model used are relative density, cyclic stress ratio and number of cycles. The results revealed that, these energy-based models have a strong potential in evaluation of pore water pressure development pattern of non-plastic silts. Test results also show that the increase in relative density and decrease in CSR causes a ladderlike behavior among pore water pressure and cyclic shear strain, which is relevantly rendered by energy-based models.

Effect of non-plastic marine silt on physical and mechanical properties of Konarak carbonate sand

Effect of non-plastic marine silt on physical and mechanical properties of Konarak carbonate sand

Flow Failure Assessment for Dams and Embankments

A procedure is proposed to assess whether a liquefied strength should be applied to a zone of non-plastic silt, silty sand, and/or clean sand in a static or seismic stability analysis to assess the flow failure potential of dams and slopes. The procedure consists of the following five main steps to assess flow failure potential: (1) assess static liquefaction potential of segments along a potential failure surface, (2) assess seismic liquefaction potential by calculating the factor of safety against liquefaction (FoSLiquefaction) for any amplitude of shaking in each segment; (3) if liquefaction is not triggered in any of these segments, assess the magnitude of shear-induced pore-water pressures due to seismic or vibratory events of any amplitude; (4) assign a liquefied strength to segment(s) that experience seismic liquefaction, i.e., FoSLiquefaction < 1 or significant pore-water pressure generation, i.e., total pore-water pressure ratio ≥ 0.7; and (5) conduct a post-triggering stability analysis to assess flow failure potential. This procedure is illustrated using the 1971 seismic permanent deformations of Upper San Fernando Dam and 2015 Fundão tailings dam failure.

Dissipated Energy and Pore Pressure Generation Patterns in Sands and Non-Plastic Silts Subjected to Cyclic Loadings

The factors that influence dissipated energy and pore pressure generation patterns with respect to the cycle ratio and dissipated energy ratio were analyzed using the results of cyclic triaxial and cyclic direct simple shear tests. These analyses revealed several interesting differences in pore pressure generation patterns when related to cycle ratio than to dissipated energy ratio. Soils with different pore pressure generation patterns when plotted against the cycle ratio were found to have nearly identical pore pressure generation patterns when plotted against the dissipated energy ratio. The differences exist as the result of the fundamental differences between cycle ratio and dissipated energy ratio. The fundamental difference is that pore pressure generation is directly linked to the process of energy dissipation; it is not inherently linked to cycles of loading. Therefore, to achieve an understanding of the pore pressure response of a soil that is independent of the specifics of the applied loading, one needs to evaluate it in terms of energy dissipation, not in terms of cycles of loading, especially irregular loadings.

Monotonic and cyclic behaviour of sand-silt mixtures through the equivalent state parameter

This paper presents the results of a laboratory investigation into the effect of non-plastic fines on the monotonic and cyclic behaviour of sand-silt mixtures. For this purpose, drained and undrained triaxial monotonic and undrained stresscontrolled cyclic triaxial tests were performed on clean sand and its mixtures with non-plastic silt. The Critical State theory known as a characteristic state of soil behaviour and the equivalent state concept were used to the interpretation of the laboratory tests results. By estimating parameter b, which recognizes that different percentages of fines contribute differently to the strength of the sand and consequently the equivalent intergranular void ratio, (eg)eq, a single Critical State Line, CSL, is determined in the (eg)eq-log(p΄) plane, and a single liquefaction resistance curve at the CRR15-(eg)eq, independently of fines content, fc, based on the monotonic and cyclic tests results, respectively. It is shown that parameter b depends on the fines content, fc, and on the loading type of the laboratory test conducted, while (eg)eq proves to be a suitable parameter for the estimation of the monotonic behavior and undrained critical state strength as well as the liquefaction resistance of granular mixtures up to the threshold fines content value, fcth, independently of their fines content. The effectiveness of state parameter, ψ, and equivalent state parameter, (ψg)eq, in the estimation of the undrained critical state strength and liquefaction resistance of sand-silt mixtures is confirmed.

Microbial Induced Calcite Precipitate Improvement of Aeolian Soil for Use as a Construction Material

An environmentally friendly and successful technique of soil improvement known as Microbial Induced Calcite Precipitation (MICP) has attracted the attention of geotechnical engineers. This study was conducted to modify the engineering behaviour of an aeolian soil bio-treated with Bacillus brevis (B. brevis) to evaluate its suitability for use in construction works. Stepped B. brevis suspension density (i.e., 0.5, 2.0, 4.0, 6.0 and 8.0 McFarland standards equivalent to 0, 1.50 × 108, 6.0 × 108, 1.20 × 109, 1.80 × 109 and 2.40 × 109 cells/ml, respectively) and cementation reagent (i.e., 0.25, 0.5, 0.75 and 1.0 M), respectively, were utilized to activate the MICP process. Compaction was conducted using British Standard light (BSL) (or standard Proctor) energy. Tests results indicate that the engineering behaviour of the bio-treated non-plastic aeolian silt soil improved. The maximum dry density (MDD) and the angle of internal friction values marginally increased, while cohesion and optimum moisture content (OMC) decreased with higher B. brevis suspension density and cementation reagent concentration. Peak angle of internal friction and minimum cohesion were recorded at 1.5 x 108 cells/ml. Highest unconfined compressive strength (UCS) value of 215.58 kN/m2 was obtained for specimen treated with 25 % B. brevis (6.0 × 109 cells/ml): 75 % cementation reagent (0.75 M) mix ratio. The results recorded show that the improved aeolian soil could be used in engineering works.

Cyclic and Monotonic Behavior of Non-plastic Silts with the Presence of Initial Static Shear Stress Using Strain Energy Approach: A Case Study for a Tailings Dam

Cyclic and Monotonic Behavior of Non-plastic Silts with the Presence of Initial Static Shear Stress Using Strain Energy Approach: A Case Study for a Tailings Dam

Liquefaction susceptibility of clayey sands under saturated and partially saturated conditions

Experiences from previous earthquake events have indicated that sands containing non-plastic (silt) or plastic (clay) fines are susceptible to liquefaction. These experiences underline the need for improving the fundamental understanding of the seismic behaviour of silty and clayey sands and for developing appropriate methods to evaluate their liquefaction potential. This paper presents an attempt to elucidate the integrated effects of fines (non-plastic silt and plastic clay) inclusion and degree of saturation on the cyclic behaviour and liquefaction resistance of sands based on systematic experiments. One of the notable findings of the study is that, apart from the familiar mode of cyclic mobility, clayey sand can also undergo flow-type failure under either fully or partially saturated conditions. The unified correlation between the cyclic resistance ratio and the state parameter (ψ), established earlier for clean and silty sand in the framework of critical state soil mechanics, is found to work for clayey sand as well. Furthermore, it is shown that the impact of saturation on the cyclic strength of clean and clayey sands can be reasonably characterised using the compression wave velocity normalised by the shear wave velocity.

Experimental investigations on the effect of density, grain size, and fines content on ejecta-induced settlement

The occurrence of sand boils or ejecta following earthquakes can cause considerable ground settlement. This study aims to investigate how soil properties influence ejecta-induced settlement by conducting experimental tests that simulate the sand boil process. Three materials, namely coarse C306 sand, fine C778 sand, and non-plastic silt, were used to examine the effects of grain size, fines content, and density on the amount of sand boil and resulting settlement. The test results indicate that loose specimens with low density experience more ejecta-induced settlement, while specimens with higher amounts of coarse grains or fines exhibit less settlement even at similar void ratios or relative densities. However, the amount of ejecta produced is directly proportional to the duration of high pore water pressure (H-PWP), which is influenced by both PWP supplies and dissipation. The differences in permeability and one-dimensional stiffness among materials explain the varying H-PWP duration across the tests. Therefore, when estimating the ejecta amount, it is crucial to account for the varying stiffness and permeability during liquefaction and post-liquefaction consolidation to accurately assess the H-PWP duration.

Correlations for Estimating Coefficients for the Prediction of Maximum and Minimum Index Void Ratios for Mixtures of Sand and Non-Plastic Silt

One common method of estimating emax and emin for mixtures of sand and silt requires that the values of several empirical constants be determined. These empirical constants are the filling coefficients, a, and embedment coefficients, b, which can be determined either via lab testing or correlations. The study reported here developed simple correlations for estimating the filling and embedment coefficients using readily obtained laboratory data. These models were found to be excellent in producing filling and embedment coefficients that accurately predicted values of the index void ratios for sand and silt mixtures, with most R2 values being 0.94 or greater.

Mechanical properties of a high plasticity clay mixed with sand and low-plastic silt

It is of fundamental importance in geotechnical engineering practice to have a comprehensive understanding of how the mechanical properties of widespread alluvial soils are affected with varying concentration of sand, silt, and clay particles. Moreover, among the available methods of chemical and mechanical stabilization of high plasticity cohesive soils, mixing this soil with sand and/or non-plastic silt still brings a cost-effective and environment friendly solution. In this study, clay-sand and clay-silt mixtures were prepared by adding sand and silt to the clay samples in different proportions to explore geotechnical properties of sand-clay and silt–clay mixtures and develop empirical correlations for Atterberg’s limits, compaction properties, unconfined compression strength, and consolidation characteristics for these soil mixtures. It was observed that for additive contents of up to 50%, the liquid limit and plasticity index of high plasticity clay sample decreased by 36% and 55% (with silt) and 47% and 58% (with sand), respectively. The reduction in undrained shear strength determined from unconfined compressive strength tests was about 37% with silt and 59% with sand contents. The compression index decreased by almost 13% with silt and 39% with sand. Likewise, it was also observed that the coefficient of consolidation increased with addition of silt and sand by 57% and 87%, respectively. As the increase in silt and sand content transformed the soil into a compact mass which ultimately should lead to a decreased total settlement as well as the rate of settlement of such soils. The statistical models proposed in this study have high coefficient of determination which depicts the reliability of these models in predicting the mechanical properties of sand-silt–clay mixtures.

Investigation on the Behavior of Bridge Piers Considering Rocking Isolation Constructed on Non-plastic Silts and Sands Using 1g Shaking Table Tests

Occurred damages on the bridge piers during earthquakes lead to significant financial losses worldwide every year and can cause social problems by disrupting traffic flow and transportation services. Rocking isolation of foundations is one of the damage reduction approaches to avoid structural damage on piers by transferring plastic hinges from piers to underlying soil media. The behavior of rocking foundations on non-plastic silts has not been investigated well until now in the literature. In this research, the characteristic seismic behavior of a bridge pier considering rocking isolation is evaluated using small-scale physical modeling tests. To this aim, eight shaking table tests (with sinusoidal excitations) are conducted where both sandy and silty materials are employed as the soil media. In addition to the effects of the underlying soil, the effects of the critical contact area ratio of the foundation and frequency of input motions are evaluated. Achieved results indicate that the considered bridge pier shows the same behavior trend for underlying silty soil and sandy one. However, because of the frequency-dependent behavior of non-plastic silty soil, the pier attracts lower accelerations and higher moments. Therefore, the achieved results show that the proposed design approaches of rocking foundations that are mostly extracted based on experimental studies on sands (or rarely on clay) can lead to non-conservative designs in silty soils.

Three-dimensional stress–strain and strength behavior of silt–clay transition soils

The effect of silt content on the mechanical behavior of silt–clay transition soils under 3D stress conditions is presented. Undrained true triaxial tests with constant b values were performed on normally consolidated specimens of silt–clay transition soils created from the same base clay and nonplastic silt, however, with systematically varying gradations. With increasing amount of nonplastic silt, the cohesive soils exhibit less contractive tendencies, stiffer stress–strain response, and larger shear strength. The magnitude of intermediate principal stress, as indicated by the b value, also strongly influences the stress–strain relations, pore pressure behavior, and both total and effective failure surfaces. Although the transition soils exhibit overall clay-like behavior, more pronounced frictional characteristics, as indicated by the shapes of the failure and plastic potential surfaces, were exhibited with increasing silt content.

Monotonic and cyclic undrained behaviour and liquefaction resistance of pumiceous, non-plastic sandy silt

Experimental data related to the mechanical behaviour of crushable pumiceous soils are limited compared with those for hard-grained soils. The main focus of previous studies has been on pumiceous sands, whereas pumiceous silts have not been investigated to date. In this paper, several series of monotonic and cyclic triaxial tests were performed to investigate the undrained behaviour and liquefaction resistance of a natural volcanic-ash derived, non-plastic pumiceous silt from northern New Zealand. Particle crushing due to sample reconstitution and triaxial testing was analysed by quantifying the changes in grain-size parameters and pumice contents. The main results can be summarized as follows. (1) The pumiceous silt showed a contractive response, even at medium to high relative densities, leading to high flow liquefaction susceptibility. (2) When subjected to cyclic undrained loading, the silt exhibited similar trends in terms of excess pore water pressure and axial strain accumulation to those established for hard-grained soils as opposed to those for pumiceous sands. (3) The liquefaction resistance of both medium-dense and dense samples was within the lower range compared to published cyclic resistance curves of both hard-grained soils and pumiceous sands. (4) The material did not undergo significant particle crushing after testing. Result (4) was considered to be the main factor that contributed to the fact that, in general, the cyclic undrained behaviour of the pumiceous silt was close to the trends established for those of hard-grained soils.

Liquefaction Susceptibility and Cyclic Response of Intact Nonplastic and Plastic Silts

Liquefaction Susceptibility and Cyclic Response of Intact Nonplastic and Plastic Silts

Mechanics of the instability of sand and non-plastic silt mixture using equivalent intergranular void ratio

Mechanics of the instability of sand and non-plastic silt mixture using equivalent intergranular void ratio

Ice-Water Phase Change Studies in Plastic and Non-Plastic Silts

This article presents experimental results and analysis of change in freezing characteristics of clays and silts with change in pH and moisture content in the pore structures. The plastic and non-plastic silts and clays in the cold regions undergo significant changes in thermal properties causing non-equilibrium thermal conditions which can lead to frost-heave, thaw-weakening, thawing-induced landslides, and mass wasting events. In geotechnical engineering, particularly in cold regions, a soil’s thermal properties play a large role in the design, functionality, and longevity of an earthen structure. The thermal properties of the soil will also govern the porous media phase changes influencing thermal hysteresis and heat capacity in soils. These variables will change with seasonal freeze–thaw cycles, which can lead to changes in a soil’s structure, fabric, density, moisture content, and strength over time. With global warming causing the temperatures to gradually rise over time, the rapidly varying seasonal freeze–thaw cycles are now becoming an issue in areas where the designs have relied heavily on the permafrost. This research study investigates the fundamental changes to freezing and thawing characteristics of plastic and non-plastic silts with changes in frost penetration rates (cooling rate); moisture content (liquid limit, plastic limit, and optimum moisture content); pH (2–7); and soil type with different percentages of fines content and specific surface area.

On seismic protection of wind turbine foundations founded on liquefiable soils

Wind turbine structures can be susceptible to damage from earthquake loading due to large overturning moments at the foundation level. As the wind energy market expands to seismically active parts of the world, it becomes important to evaluate the seismic behaviour of these structures. Especially, earthquake-induced liquefaction can be important when wind farms are located on sites with marginal soil conditions such as loose, saturated sands or non-plastic silts. Reduction of stiffness during liquefaction can cause excessive foundation settlement and/or rotation. Thus, suitable mitigation methods should be investigated. This paper discusses the seismic behaviour of the wind turbine on liquefiable soil and the effectiveness of the stone column-based liquefaction mitigation method. Two geotechnical centrifuge tests were conducted with and without stone columns for a model wind turbine on a circular raft foundation. The results show that stone columns can significantly reduce both the settlement and rotation of the raft.