Change In Void Ratio Research Articles

Effects of cement content and curing period on strength enhancement of cemented calcareous sand

Cement treatment is a promising and effective method to enhance strength of calcareous sand in regions where offshore foundations and coastal facilities are localized. In treatment, the added cement content and curing period influence the strength of cemented calcareous sand. In order to regulate the loading resistance of cemented calcareous sand, effects of cement content and curing period on strength enhancement are investigated experimentally. First, cemented specimens with 5%, 7.5%, and 10% cement contents and 1–28 days curing period are prepared. Then, unconfined compression test is conducted to measure strength. Nuclear magnetic resonance test is also performed to analyze microstructure change during hydration reaction. An empirical equation of strength is derived, considering the effects of cement content and curing period. This equation shows higher accuracy than existing empirical models. In addition, the microstructure change in hydration process is quantified by pore volume evolution. Void ratio is used to characterize the pore volume evolution. Hence, the dependence of strength on cement content and curing period is quantitatively explained by the change in void ratio. This sheds light on hydration reaction in cement treatment by cement content and curing period and the regulation of strength enhancement in cemented calcareous sand. Highlights Empirical equation on strength with effects of cement content and curing period Pore volume evolution by hydration reaction in cement treatment Characterization of microstructure change by void ratio Microscopic mechanism of strength enhancement for cemented calcareous sand

Microscopic investigation of internal erosion in binary mixtures via the coupled LBM-DEM method

The flow of small particles in porous media is of interest in many branches of science. In geotechnical engineering, this phenomenon usually occurs in graded granular materials and is termed as internal erosion. In this work, graded granular materials are simplified as binary mixtures under vertical compression, and water flows perpendicular to the vertical direction. We use the coupled Lattice Boltzmann method (LBM) and discrete element method (DEM) to investigate the initiation of internal erosion under different stress levels and hydraulic gradients. Suffusion was observed as the fine particles are transported by the seepage flow. The change of void ratio due to water flow and vertical compression demonstrates three patterns: erosion, stability, and compaction. Particles with low engagement in force transmission are more prone to erosion, while the hydraulic gradient is an external disturbance factor. The ballistic, caging, and diffusive regimes are observed in the initial process of internal erosion.

Cyclic Bi-Axial Tests on Assembly of Metal Rods Under Constant-Volume Condition to Study Re-Liquefaction Behavior

As a part of fundamental studies on re-liquefaction behavior of sandy soils, cyclic bi-axial tests on assembly of aluminum rods having circular cross section were conducted under constant-volume condition, while focusing on the effects of strain amplitude during the previous liquefaction stage. By conducting image analyses on the specimen photos, possible changes in the local void conditions were evaluated and discussed. As a result, with increase in the maximum double amplitude vertical strain from 2.0 to 7.5% during the previous liquefaction stage, decrease in the re-liquefaction resistance was observed, which was consistent with results from past relevant studies on sands. Formation of locally loosened zone was observed during the liquefaction stage up to the double amplitude vertical strain of 7.5%, which may have affected the decrease in the subsequent re-liquefaction resistance. These zones were partly re-formed during the re-liquefaction stage. By the liquefaction history that was followed by re-consolidation, homogenization was observed in terms of the change of local void ratio. In addition to overall densification, such change may be regarded as one of the factors that would cause increase in the re-liquefaction resistance, as observed in the tests with liquefaction stages up to the double amplitude vertical strain of 2.0 and 5.0%.

Coupling elasto-plastic behaviour of unsaturated soils with piecewise linear large-strain consolidation

Slurried soils or tailings are often deposited in layers that undergo complex stress paths in terms of desiccation and loading, as a given layer may undergo variable degrees of desiccation before burial by subsequent layers, which has implications for geotechnical stability and geo-environmental performance. Proper analysis therefore requires not only an effective coupling of unsaturated flow with large-strain consolidation, but also inclusion of hysteresis effects. This paper presents the development and testing of a coupled unsaturated flow–large-strain consolidation model, UNSATCON, initially formulated for only monotonic dewatering, to include such effects. UNSATCON operates by a novel numerical algorithm that ensures mass conservation and handles the saturated/unsaturated transition smoothly. Differently from conventional integration schemes commonly embedded in finite-element formulations, this algorithm, tracking the void ratio change explicitly for large deformation, is shown to be applicable for most constitutive models of unsaturated soils under one-dimensional or isotropic stress conditions. Three constitutive models are implemented: a modified state surface model and the original and a minor variant of the Glasgow coupled model (GCM). The numerical model is evaluated using a recently published experimental study on multilayer deposition of thickened gold tailings. The model adequately reproduces the essential features of the dewatering processes, including the irrecoverable deformation induced by desiccation, the interlayer water exchange governed by deformation and deformation-dependent hysteretic retention behaviour. All three implemented constitutive models can reasonably simulate these experimental observations, despite some trivial discrepancies in magnitude. Point-level inspection, however, reveals some fundamental differences that may have important practical implications. For example, the additional plastic strain that occurs in GCM type models over multiple wetting–drying cycles may explain observed trends in increased strength in the simulated experiment.

Water-retention properties and microstructure changes of a bentonite pellet upon wetting/drying; application to radioactive waste disposal

Like bricks of compacted bentonite/sand mixtures, mixtures made up of pellets and powder of bentonite are considered as a possible material to make the sealing plugs used to fill up galleries and ensure long-term watertightness in deep radioactive waste disposal. Pellets/bentonite mixtures have a low permeability, high swelling capacity, good radionuclide retention capability and operational advantages in terms of placement in the galleries. Following a previous in-depth characterisation of bentonite pellets/powder mixture conducted by the same group, an investigation of the water-retention properties and microstructure changes of a bentonite pellet subjected to wetting/drying cycles under free swelling conditions was carried out by means of mercury intrusion porosimetry (MIP) and X-ray microtomography. A complete description of the changes in water content, void ratio and degree of saturation of the pellet was provided. Data showed that the free swelling of the pellet is due to the combined effect of both crack propagation at the macro scale, and the swelling of bentonite grains, governed by hydration mechanisms along the smectite faces at the nano scale. Significant development of a crack network is observed between 38 and 9 MPa. For suctions below 9 MPa, there is a significant decrease of the platelet thickness and an increase in the disorder of the platelet assembly, resulting in the average MIP entrance pore radius increasing to 0·4 μm within the expanded bentonite grains.

Evolution of the soil water retention curve based on plastic volumetric strain

The water retention behaviour of soil can be defined as the relationship between the degree of saturation (or water content) and suction at a constant temperature, which characterises the hydraulic behaviour of unsaturated soils, normally represented as the soil water retention curve (SWRC). The SWRC is commonly measured at nominal net stress by initially saturating a soil specimen and then subjecting it to drying and wetting paths, resulting in major drying and wetting curves. However, there is evidence that during these major drying and wetting paths and initial saturation, soil can undergo volumetric deformation with changes in void ratio, sometimes plastically. Therefore, for coupling the SWRC with mechanical behaviour, the dependency of SWRC on other state variables such as void ratio has been proposed. In this paper, an approach to defining SWRC for a particular plastic volumetric strain is presented within the generalised MPK model. The SWRC evolves as soil is subjected to wet/dry cycles, eventually approaching drying and wetting curves relevant to an environmentally-stabilised state. The performance of this model is demonstrated by the simulation of the loading/unloading/drying/wetting paths followed in a laboratory experiment. In addition, the evolution of the commonly-considered major drying and wetting curves is simulated, highlighting key features of the environmentally-stabilised line..

A new theory for membrane efficiency coefficient of compacted clay

A new method for calculation the membrane efficiency coefficient w of compacted clay is proposed in this paper. The influence of fixed negative charge on the surface of clay minerals is considered. What’s more, the change of porosity during deformation is considered. Based on the chemical potential of specimens, the true ion concentration in pore-water is obtained. Based on the true ion concentration in pore water, the disjoining pressure considering fixed negative charge inside soils and the change of void ratio is proposed. A new calculation method for the membrane efficiency coefficient of compacted clay is established. The test data of w considering different porosity are calculated and the calculated results are compared with the traditional calculation methods. The new calculation methods of w provide a more physical-based theory for environmental geotechnical engineering.

Early Warning on Mass Imbalance and Clean-in-Place Strategy for Rotor of Rotating Packed Bed

Rotating packed bed is a new high-gravity gas-liquid mass-transfer equipment. The gas-liquid phase chemically reacts to the wire mesh packing of the rotor, and solid products easily adhere to the wire mesh packing, resulting in rotor vibration caused by rotor mass imbalance, thereby causing damage to bearings and seals. Such a fact hinders the long-cycle operation and large-scale process of the rotating packed bed. Research institutions and scholars all around the world have done a lot of work on mechanical balance. But the current mechanical balance is only temporary balance, and it does not fundamentally solve the problem of vibration and mass transfer efficiency degradation caused by the mass imbalance of the reaction product adhering to the rotating packed bed rotor. According to this situation, the strategy of early warning on mass imbalance and clean-in-place for rotating packed bed rotor is proposed. Firstly, the relationship of pressure, flow rate, and the void ratio of packing is established by numerical simulation. And the change of the rotor void ratio in the rotating packed bed can be calculated from the flow velocity or pressure change. Secondly, a dual-electromagnetic rotating packing bed based on ultrasonic cleaning is designed. Once the adhesion exceeds the threshold of early warning, the electromagnetic clutch controls the current rotating packed bed to stop working and the spare rotating packed bed to start to work. Two rotating packed bed structures complement each other to reduce the rate of the shutdown and avoid damage to bearings and seals.

Utilization of Depolymerized Recycled Polyethylene Terephthalate in Improving Poorly Graded Soil

This study introduced recycled plastic waste as a soil stabilizer and encouraged using it as an alternative material in the improvement of poorly graded soil. The water bottles’ plastic waste was depolymerized and recycled to produce a powder material then used this material as a soil stabilizer. Different percentages (0.0, 0.5, 1.0, 1.5, 2.0%) of the depolymerized recycled polyethylene terephthalate (DRPET) (by dry weight of soil) have been chosen to evaluate its effects on the properties and behavior of poorly graded sandy soil. These effects studied through a series of laboratory tests including scanning electron microscopy. Also, the applicability of DRPET in inundation conditions has been studied using confined compression tests. It was found that untreated and treated poorly graded soil show the same shape of compaction curves, and DRPET filled the pore spaces and affected the compaction characteristics of the soil. The soil treated with 1.5 and 2.0% DRPET exhibited brittle behavior, and the addition of DRPET increased the angle of internal friction and reduced the maximum vertical contractive displacement of the soil. DRPET coated the surface of particles and increased the resistance between soil particles and, therefore, increased the time lag during compression. Finally, under confined compression, poorly graded soil treated with DRPET exhibited small changes in void ratio and slightly influenced by inundation in water.

A coupled hydro-mechanical-biodegradation model for municipal solid waste in leachate recirculation

The weight of Municipal solid waste (MSW) leads to a decrease of void ratio in landfill with depth and the biodegradation of MSW also results in decrease of void ratio with time. The spatial and temporal changes of void ratio of MSW have significant effects on its hydraulic properties and consequently influence the leachate recirculation process. In this paper, an advanced coupled hydro-mechanical-biodegradation (H-M-B) model is proposed to analyze the full coupling process for leachate recirculation taking into account the effect of initial density profile and its change due to biodegradation. A new solver is presented using the finite volume method based on the OpenFOAM platform to implement the coupled H-M-B model. The volume change caused by effective stress, degree of saturation and degradation, and the effect of void ratio change on hydraulic properties, can be taken into account in the coupled H-M-B model. The results calculated by the coupled H-M-B model illustrate the effect of void ratio on hydraulic properties, and the effect of compressibility, initial density and biodegradation on leachate recirculation. This study will contribute to the understanding of the leachate recirculation process and enhance the design of MSW landfills.

Modeling for critical state line of granular soil with evolution of grain size distribution due to particle breakage

Determination of the critical state line (CSL) is important to characterize engineering properties of granular soils. Grain size distribution (GSD) has a significant influence on the location of CSL. The influence of particle breakage on the CSL is mainly attributed to the change in GSD due to particle breakage. However, GSD has not been properly considered in modeling the CSL with influence of particle breakage. This study aims to propose a quantitative model to determine the CSL considering the effect of GSD. We hypothesize that the change of critical state void ratio with respect to GSD is caused by the same mechanism that influences of the change of minimum void ratio with respect to GSD. Consequently, the particle packing model for minimum void ratio proposed by Chang et al. (2017) is extended to predict critical state void ratio. The developed model is validated by experimental results of CSLs for several types of granular materials. Then the evolution of GSD due to particle breakage is incorporated into the model. The model is further evaluated using the experimental results on rockfill material, which illustrates the applicability of the model in predicting CSL for granular material with particle breakage.

Coupled Effect of Wet-Dry Cycles and Rainfall on Highway Slope Made of Yazoo Clay

Expansive Yazoo clay soil is susceptible to volumetric deformation and is dominant in central Mississippi and other neighboring southern states of the United States. Recurring shrink-swell behavior causes a significant problem to infrastructures in the area. Although Yazoo clay causes a significant problem in the deep southern states, limited study has been conducted on the behavior of Yazoo clay, especially in the presence of rainfall. The objective of this current study is to investigate the coupled effect of changes in void ratio due to wet-dry cycles and rainfall on the stability of highway slopes made of Yazoo clay. The finite element method in Plaxis 2D by Bentley System (https://www.plaxis.com/) has been utilized to investigate the coupled effect of changes in mechanical properties and rainfall using flow-deformation and stability analysis. Reconstituted expansive clay soil samples were used for the laboratory experiment. The reconstituted Yazoo clay samples were subjected to 3, 5, and 7 wetting and drying cycles in an enclosed chamber for a 24-h period. The axial deformation of the samples and the change in void ratios at each number of the cycle was closely monitored. The strength change at each wet and dry cycle was also investigated and used for slope stability analysis in the presence of rainfall. The test results indicate that the void ratio increases with the increasing number of wet-dry cycles. A continuous increment in void ratios from 0.99 in an undisturbed state with no wet-dry cycle to 1.49 at the 7th wet-dry cycle, indicating a 48.9% increase, as the wetting and drying cycle increases was recorded; in turn, decreasing the cohesion of the soil by 77%. The factor of safety considering the effect of two total rainfall periods of Rv = 126.2 mm (2 h) and Rv = 271.7 mm (3 days) reduced from 1.7 to 1.2 and 1.68 to 1.02, considering the effect of the 7th wet-dry cycle at the topsoil. The changes in the void ratio due to the wetting and drying cycle of Yazoo clay soil reduces the shear strength to a fully softened condition, increasing the possibility of slope failure. This condition further worsens in the presence of a perched water condition due to the infiltration of rain water.

Macro and micro investigation of gravel content on simple shear behavior of sand-gravel mixture

The gravel content (GC) may influence the mechanical properties of sand-gravel mixture (SGM) used in earth structures and may compromise the stability of such structures. The purpose of this paper is to present a macro and micro study on the effect of GC on simple shear behavior of SGM using experimental and numerical approaches. Firstly a series of large-scale simple shear tests on SGM with different gravel contents under different normal stresses were conducted. The test results demonstrate that GC affects the shear strength and friction angle of SGM according to the change of void ratio at macro-scale. The variations of dilatancy and initial modulus with GC were also discussed. Then a 3D discrete element model was established for numerical simulations, in which the grading distributions of particles had similar shapes with the simple shear tests, but the particle size was 5 times scaled. The Herts-Mindlin model was used for contact, and the rolling resistance was taken into account. The numerical results showed a fairly good agreement with the experimental results. After that the micro mechanism of gravel content effect was investigated according to the analysis of micro force chain topology and contact force distributions. In summary, the experimental and numerical investigations provide valuable insights into the gravel content effect of SGM at both macro- and micro- scales.

A New Osmotic Oedometer with Electrical Resistivity Technique for Monitoring Water Exchanges

This article presents a new osmotic oedometer that is able to measure changes in the degree of saturation (Sr) during suction-controlled drying-wetting and oedometric tests. A circular four-electrode cell made of polyvinyl chloride was developed. The geometric factor of the cell was determined by numerical simulation and validated by calibration tests. A total of 29 samples was statically compacted in the oedometric cell at different moisture contents and dry densities. Based on these measurements, the normalized electrical resistivity was defined and correlated with the Sr. After that, three suction-controlled drying-wetting and oedometric tests were performed on the samples statically compacted at the water content of 21 % and dry density of 1.62 g/cm3, which corresponds to the standard Proctor optimum conditions. The results show (i) the potential of the new oedometer for the study of the hydromechanical behavior of unsaturated soils, (ii) the ability of the electrical resistivity technique to estimate the variation of the Sr in unsaturated oedometric tests, with a relative error smaller than 5 %, and (iii) the coupled effect of vertical stress and suction on the change in void ratio (e) and Sr shown in the (e - suction pressure [s] - vertical total stress [σv]) and (Sr - s - σv) state surfaces.

Fully coupled elastoplastic hydro‐mechanical analysis of unsaturated porous media using a meshfree method

SummaryThis paper presents the first application of an advanced meshfree method, ie, the edge‐based smoothed point interpolation method (ESPIM), in simulation of the coupled hydro‐mechanical behaviour of unsaturated porous media. In the proposed technique, the problem domain is spatially discretised using a triangular background mesh, and the polynomial point interpolation method combined with a simple node selection scheme is adopted for creating nodal shape functions. Smoothing domains are formed on top of the background mesh, and a constant smoothed strain, created by applying the smoothing operation over the smoothing domains, is assigned to each smoothing domain. The deformation and flow models are developed based on the equilibrium equation of the mixture, and linear momentum and mass balance equations of the fluid phases, respectively. The effective stress approach is followed to account for the coupling between the flow and deformation models. Further coupling among the phases is captured through a hysteretic soil water retention model that evolves with changes in void ratio. An advanced elastoplastic constitutive model within the context of the bounding surface plasticity theory is employed for predicting the nonlinear behaviour of soil skeleton. Time discretisation is performed by adopting a three‐point discretisation method with growing time steps to avoid temporal instabilities. A modified Newton‐Raphson framework is designed for dealing with nonlinearities of the discretised system of equations. The performance of the numerical model is examined through a number of numerical examples. The state‐of‐the‐art computational scheme developed is useful for simulation of geotechnical engineering problems involving unsaturated soils.

Laboratory Tests for the Consolidation Property of Dredger Fill in the Shenzhen Area

In order to analyze the special engineering properties of the super soft dredger fill, experimental studies had been done on the physical-mechanical properties of that in Shenzhen, especially for its consolidation properties. The test results indicated that the super soft dredger fill had the properties of high water content, high void ratio and high clay content; When the confining pressure applied to the sample was less than 200kPa, the change of deformation and void ratio of it was more obvious; When the confining pressure applied to the sample was less than 80kPa, the chang of permeability coefficient of that was more significant.

Deformation of the aquifer system under groundwater level fluctuations and its implication for land subsidence control in the Tianjin coastal region.

This study demonstrates characteristics and mechanisms of deformation of an aquifer system in response to seasonal fluctuations of groundwater level when groundwater pumping has been strictly regulated after experiencing longtime land subsidence. Two boreholes with depth of 1226m (G2 site) and 905m (G3 site) were drilled at the Tianjin coastal region where severe land subsidence had occurred since the 1950s. Extensometer/piezometer groups installed at the G2 site illustrate synchronized variations of compaction and groundwater level since 2010 in the aquifer system between depth of 100-400m which contributes most groundwater pumpage. Monitored land subsidence demonstrates that the shallow aquifer has become the main contributor to the land subsidence, and inelastic compaction still occurred in the aquifers where groundwater level has recovered. Pre-consolidation stresses show that clayey soils in depth < 100m are under-consolidated, and deep clayey soils show the state of normal- to over-consolidation. The effects of the cyclic groundwater level oscillation on deformation were investigated using repeated loading and unloading tests. Void ratio changes in loading/unloading cycles illustrate that inelastic deformation rate decreases gradually and elastic deformation rate remains almost unchanged with increases of cyclic numbers. The deformation of soil samples from 100 to 400m is mostly elastic for loading stress in the over-consolidation stress range. These findings suggest that groundwater dewatering in the shallow (depth < 100m) aquifer will be the primary target to control land subsidence. Groundwater level fluctuations higher than pre-consolidation value in 100-400m only lead to elastic and recoverable deformation even small residual permanent deformation may continue for a long time. The results improve the understanding of deformation in complex urban aquifers affected by groundwater level fluctuations and highlight the importance of city planning management for controlling land subsidence in coastal cities.

Water retention of geosynthetics clay liners: Dependence on void ratio and temperature

The dependence of the geosynthetic clay liners (GCLs) soil-water characteristic curve (SWCC) on temperature and overburden stress are characterised experimentally. It is shown that changes in void ratio and temperature alter the relationship between suction and moisture content and new forms of existing SWCC equations are developed. To cover a wide suction range, the SWCCs are measured using axis-translation and dew point methods. Based on the available experimental data, both proposed SWCCs are shown to perform well in predicting the effects of void ratio on SWCC along the drying path when compared to the experimental results. It is found that the air-entry value increases as the net vertical stress increases for the experiments under the same temperature. In addition, elevation of temperature reduces retention capacity of the GCL.

Numerical simulation of nonlinear consolidation problems by models based on the network method

• Nonlinear consolidation models for any type of constitutive dependences and eliminating the most restrictive hypotheses. • Tabulated models are also designed and solved by the network method. • The network models are built from very simple rules, providing the almost exact solution of the problem. The nonlinear consolidation problem in saturated soils, for any type of constitutive dependences of the hydraulic permeability and the void ratio on the effective pressure, has been numerically simulated by the network method. Three different network models, based on logarithmic and/or potential constitutive dependences, called the Davis and Raymond, Juárez-Badillo and Cornetti and Battaglio models, as well as a fourth one with dependences in tabulated form, are solved. In addition, new network models that delete the two restrictive hypotheses assumed by these authors are presented. These hypotheses are the influence of the void ratio changes in the term of contraction of the governing equation and the influence of the thickness change of the volume element as consolidation progresses. Only a few rules based on elementary theory of circuits are required for the design of the models, whose solution is reliable with relatively small grids and computational times. After verifying the results of the network method with the solutions of the classic authors, the extended models have been used to address a real case of consolidation.

Investigation of Abrasion and Impact Resistance of Aggregates in Different Environments in Direh, Kermanshah, Iran

The abrasion and impact resistance of aggregates are important factors that should be taken into consideration during the production of concrete or asphalt that are subjected to abrasion and impact. The aim of this study was to examine the relationship between abrasion and impact resistance of aggregates related to the rivers, alluvial fans and taluses. In order to achieve this purpose, samples were collected from 3 rivers, 12 alluvial fans and 2 taluses located in Direh in Kermanshah province, Iran. The samples were studied in terms of changes in void ratio, cracks and weight loss induced by abrasion and impact. The lowest amount of weight loss due to abrasion and impact was observed in aggregates from rivers, with about 30% weight loss due to abrasion and 15% due to impact. The highest amount of weight loss was found among aggregates collected from taluses (45% for abrasion and 35% for impact). This results can be attributed to the degree of cracks and porosity in aggregates. It was also observed that the abrasion and impact resistance of aggregates in alluvial fans was dependent on the morphometric properties of alluvial fans catchment. Thus, a lower amount of weight loss caused by abrasion and impact was in aggregates taken from alluvial fans with larger catchments and longer main channel catchments.