Compaction State Research Articles

Experiment on compaction of air-dried soil under drop shocks.

For the requirement in container nursery culture that growing media should be achieved the appropriate degree compaction, this paper presents an experiment on the compaction dynamics of air-dried soil under repetitive drop shocks, as a preliminary step toward the mechanization of this compaction method. The drop height used to adjust the shock intensity included 2 mm, 4 mm, 5 mm and 6 mm. And the overall packing density of soil in a vertically stratified cylinder vessel and the local packing density in each layer were taken as indicators of soil compaction states. The stretched exponential function derived from KWW law than the empirical inverse-logarithmic function has been found to be more suitable for expressing the temporal evolution of soil compaction, according to the results of curve-fitting to test values of the overall and local density. It is inherent in this experimental configuration that the drop shock intensity even at a constant drop height varies with drop times, owing to the interaction between the soil packing itself and drop shocks caused by the combination of the packing and the container. But the function t/τf(t,H) is manifested as a straight line on the drop times t with the line slope related to the drop height H, so the soil compaction dynamics caused by its drop shocks and that under the condition with actively controlled intensity actually share the common relaxation law. In addition, the soil's one-dimensional distribution of local packing density showed a slight positive gradient as similar as monodisperse particles did.

Effects of pyrolysis temperature, feedstock type and compaction on water retention of biochar amended soil

Recent studies on water retention behaviour of biochar amended soil rarely considers the effect of pyrolysis temperature and also feedstock type into account. It is well known that pyrolysis temperature and feedstock type influences the physical and chemical properties of biochar due to stagewise decomposition of structure and chemical bonds. Further, soil density, which is in a loose state (in agricultural applications) and dense (in geo-environmental engineering applications) can also influence water retention behaviour of biochar amended soils. The major objective of this study is to investigate the water retention properties of soil amended with three different biochars in both loose and dense state. The biochars, i.e. water hyacinth biochar (WHB), chicken manure biochar (CMB) and wood biochar (WB) were produced in-house at different pyrolysis temperature. After then, biochars at 5% and 10% (w/w%) were amended to the soil. Water retention behaviour (soil suction and gravimetric water content) was studied under drying and wetting cycle simulated by varying relative humidity (RH, 50–90%). Results show that 10% WHB produced at 300 °C were found to possess highest water retention. CMB is found to possess higher water retention than WB for 10% amendment ratio. In general, the addition of three biochars (at both 300 °C and 600 °C) at 10% (w/w) significantly improved the water retention at all suction ranges in both loose and dense compaction state as compared to that of the bare soil. The adsorption (wetting) and desorption (drying) capacity of biochar amended soils is constant at corresponding RH.

DNA length tunes the fluidity of DNA-based condensates

Living organisms typically store their genomic DNA in a condensed form. Mechanistically, DNA condensation can be driven by macromolecular crowding, multivalent cations, or positively charged proteins. At low DNA concentration, condensation triggers the conformational change of individual DNA molecules into a compacted state, with distinct morphologies. Above a critical DNA concentration, condensation goes along with phase separation into a DNA-dilute and a DNA-dense phase. The latter DNA-dense phase can have different material properties and has been reported to be rather liquid-like or solid-like depending on the characteristics of the DNA and the solvent composition. Here, we systematically assess the influence of DNA length on the properties of the resulting condensates. We show that short DNA molecules with sizes below 1 kb can form dynamic liquid-like assemblies when condensation is triggered by polyethylene glycol and magnesium ions, binding of linker histone H1, or nucleosome reconstitution in combination with linker histone H1. With increasing DNA length, molecules preferentially condense into less dynamic more solid-like assemblies, with phage λ-DNA with 48.5 kb forming mostly solid-like assemblies under the conditions assessed here. The transition from liquid-like to solid-like condensates appears to be gradual, with DNA molecules of roughly 1–10 kb forming condensates with intermediate properties. Titration experiments with linker histone H1 suggest that the fluidity of condensates depends on the net number of attractive interactions established by each DNA molecule. We conclude that DNA molecules that are much shorter than a typical human gene are able to undergo liquid-liquid phase separation, whereas longer DNA molecules phase separate by default into rather solid-like condensates. We speculate that the local distribution of condensing factors can modulate the effective length of chromosomal domains in the cell. We anticipate that the link between DNA length and fluidity established here will improve our understanding of biomolecular condensates involving DNA.

Tillage recommendation for commercial forest production: Should tillage be based on soil penetrability, bulk density or more complex, integrative properties?

Efficient soil tillage methods to create a favorable environment for commercial forest require proper evaluation of soil compaction with depth, by using operative indicators of physical quality for diverse soils. Our aim was to investigate the spatial variability of field-measured penetration resistance (PR), and then determine the relationships between penetrability and mechanical and hydrologic properties of Planosol, Nitisol, and Regosol used for eucalyptus production. Low, intermediate, and high compaction states were defined based on field PR spatial variability, and in those areas with distinct compaction states we determined bulk density, degree-of-compactness, macroporosity, water retention and availability, and least limiting water range. The soil compaction states are related to composition or capacity (mass/volume) properties, most consistently with soil bulk density and relative compaction. Whether using simple measurements such as penetrability and bulk density, or more complex, integrative properties (e.g. degree-of-compactness and least limiting water range), tillage recommendation would be the same. Namely, deep tillage for Nitisol, and shallower tillage for Planosol and Regosol. In practical terms, the first soil requires deep subsoiling, and second and third soil demand shallower subsoiling associated or not with ridging. In conclusion, mapping of soil compaction states based on PR data can be used for best management practices and tillage recommendation for forest installation.

Modelling a compressible packed bed flow-through washing and deacetylation reactor for corn stover pretreatment

The deacetylation process is a key step in the lignocellulosic biomass pretreatment process that currently is done in batch reactors. A flow-through diffuser type reactor is a promising approach to make the process more efficient and economically favorable. A washing step before deacetylation can further reduce chemical usage and increase the process efficiency. However, the highly compacted biomass particles can cause significant pressure-drop for fluid flow through the bed, which in the worst case can cause self-enhancing pressure-drop leading to reactor blocking. Detailed understanding of the fundamentals of flow through a compressible packed bed is necessary to scale up the washing and deacetylation process. This work closely examines the classical Kozeny Carman equation and proposes modifications to accurately predict the pressure-drop at different compaction states. A compressible packed bed model is further developed based on the interaction between solid mechanics and fluid dynamics. Experimental measurements of water flow through a packed bed of corn stover show good agreement with the developed model. Corn stover washing process scale up simulations show that smaller reactor diameter, higher friction lining material, lower process throughput, and higher process temperature is favorable in stabilizing the bed from extensive compression when the bed height is fixed.

Assessment of the possibility of using GPR to determine the working resistance force of tools for subsoil reclamation

The article presents a study on the determination of working resistance force of a tool that reclaims the topsoil based on GPR research. The experiment used a strain gauge force measurement system in a three-point linkage suspension system of the tool on a tractor with automatic registration of other operating parameters of the unit at a frequency of 10H. For the research with the use of GPR, a shielded antenna with a frequency of 800 MHz was used, allowing to obtain a wavelength of 0.12 m and a resolution of 0.03 m. The tests were carried out for several combinations of soil compaction, which was initially measured with the Eijkelkamp cone penetrometer. A large convergence of the results of the working resistance forces was found with the indications of the states of excessive compaction identified in the space of the echogram. It should be noted that the convergence of the measurement results increases with the degree of soil compaction. Therefore, it is possible to estimate the energy consumption of cultivation treatments on the basis of non-invasive GPR surveys and selective soil reclamation treatment with degraded subsoil.

Heat transfer characteristics of gravelly soils with different compactness during unidirectional freezing process

During the construction of clay core rockfill dam in cold regions in winter, the heat transfer characteristics of gravelly soil are important to the anti-freezing control of the core. Laboratory experiment and field test data showed that the frost depth of gravelly soil in unconsolidated state was deeper than that in compacted state at the early period of soil freezing. With the increase of the freezing time, however, the frost depth of compacted soil is deeper than that of unconsolidated soil. Further study showed that this phenomenon was main caused by the change of thermophysical parameters between unconsolidated and compacted soil. Under the same soil temperature, the thermal conductivity of compacted soil was approximately 2.6 times of that of unconsolidated soil, and the volume heat capacity and phase change latent heat of compacted soil was approximately 1.7 times of that of unconsolidated soil. The different thermophysical parameters caused the differences of the heat transfer rate, temperature distribution and heat release by cooling between compacted soil and unconsolidated soil. This study provides a theoretical guidance for freezing process of soil with different compactness and anti-freezing technology of clay core rockfill dam in cold regions.

Mechanical performance and micro-structure of bentonite-fly ash and bentonite-sand mixes for landfill liner application

Abstract Low permeability (10−9 m/s) and adequate unconfined compressive strength (UCS = 200 kPa) forms the basis of using compacted bentonite (B) clay in landfill liner. However, B induces cracks or swells upon excessive drying and wetting events, respectively. To overcome failure of liner layer, B is amended with cohesionless sand (S), despite S being costly and ecologically unsustainable. In the recent past, fly ash (FA) a by-product from thermal power plants, has been explored as a suitable additive material in landfill liner, in line with the adoption of cleaner usage of waste material in construction. The objective of this study was to investigate the mechanical performance of both B-FA and B–S mixes along with the related changes in microstructure and physio-chemistry. 180 sets of UCS tests were conducted on 4 B-FA mixes (including class C and F) and B–S mixes at different compaction state and additive rate. Unlike B–S mixes, all B-FA mixes showed an increase in UCS with respect to B regardless of compaction state and additive rate. Detailed microstructure and physio-chemical characterization for B–FAs revealed the relative abundance in the formation of calcium aluminosilicate hydrate, and ettringite minerals after curing as compared to B–S mixes. In fact, Class C FA exhibited the largest UCS even at high moisture content, which can be attributed to higher formation of minerals upon curing. All B-FA mixes showed UCS greater than the minimum limit for liner application regardless of the compaction state. All B–S mixes did not adhere to the minimum UCS criterion at higher moisture content. FA additive at 50% showcased the highest increase in strength improvement factor (10 out of 12 cases), while for B–S mixes, this factor decreased with an increase in additive rate. Based on the measured data, two new linear relationships of UCS with pH and electrical conductivity (both indicative of reaction) of the mixes were observed. The relationship with respect to pH was more pronounced at higher moisture content as pH indicates the existence of CaO minerals.

Interpretation of undrained shear strength observed in confined triaxial compression tests on compacted clay

This paper presents an interpretation technique to quantify the effects of compaction state and matric suction on the undrained shear strength of compacted clay under confined undrained triaxial compression. This novel technique is based on the mathematical frameworks of the “stress history and normalized soil engineering property” (SHANSEP) method for saturated soil and the “Barcelona basic model” (BBM) for unsaturated soil. Test data of compacted Calgary till were analyzed and interpreted using the proposed technique. The interpretation technique is very useful in delineating the relative impacts of the factors on the behavioural trends in measured undrained shear strength. It was found that in addition to the initial compacted void ratio and suction, soil structure and failure mode exert significant influence on the undrained shear strength of compacted clay. This technique is attractive to engineering practitioners because the confined undrained compression tests (with no pore-air and pore-water pressure measurement) are much simpler and less time-consuming compared to rigorous laboratory tests on unsaturated soil.

Compaction and solid state sintering behavior of Cu-20%wt ZnO powders

Compaction and solid state sintering behavior of Cu-20%wt ZnO powders

Filter for penetration resistance correction in cultivated and compacted Histosols

AbstractThe objective of this study was to design, using field data, a filter to correct the soil penetration resistance (PR) values by considering all the effects (penetration friction component [PFC], varying penetration rate, and shocks) that bias PR interpretation. The data used were collected in cultivated peatlands of Montérégie (Canada) known for their advanced state of compaction. Penetration resistance (standard measurements) and cone resistance (CR) measurements (successive measurements per 10‐cm layer) were carried out on four peatlands (five stations per peatland). The filter components, a multi‐resolution analysis (AMR), a polynomial model, and a quantification and removal of PFC were identified and were used to design the filter and tested by cross‐validation. Our study showed that PFC exists (p value < 5%) and does not depend on the peatland on which the measurements are made. An average filter has therefore been designed for the entire site and its effectiveness has been demonstrated. An application to the data collected in 10 fields on the site made it possible to identify the main soil density profiles existing in Montérégie and to quantify the average PFC characterizing these soils. We noticed that, on average, PFC represents between 18.6 and 41% of the PR value. The combined results of the statistical and physical analyses of the filter made it possible to recommend degrees 2 (D2), 3 (D3), and 5 (D5) of the polynomial model to adjust density profiles of cultivated Histosols when there are no, one, or two compact layers.

Effects of compaction and suction on the hydromechanical properties of a dam core clay

The paper presents an experimental study of the hydromechanical behavior of a compacted clay used in the design of the core of the Boughrara dam (western Algeria). The influence of compaction energy level (CEL) is explored using three different energies: Standard Proctor energy (SP), reduced Proctor energy (SP-20 blows) and enhanced Proctor energy (SP+ 20 blows). The resulting compaction curves are supplemented by measurements of suction, which is a very important parameter in the behavior of compacted unsaturated soils. In addition to the compaction curves, elastic modulus and immediate bearing capacity ratio (IBCR) are measured, and related to suction and compaction energy level (CEL). Mechanical compaction paths following the SP curve and drying-wetting paths starting from SPO are compared. Mechanical properties such as E-modulus and IBCR are related to the two independent major parameters γd and Sr. Measuring these mechanical properties in the field allows to evaluate the compaction state regardless of the CEL. The results are compared with those of the literature.

Influence of soil microstructure on air permeability in compacted clay

This paper describes an experimental study aimed at evaluating the influence of soil microstructure on air permeability in compacted clay. Air permeability measurements, estimated using the gas pressure decay method, were carried out for a wide range of compaction states. The evolution of the air permeability during wetting and drying paths was also evaluated. The experimental results show that, for an increase in the as-compacted degree of saturation, air permeability may either increase or decrease depending on the as-compacted dry density. Air permeability increases with increasing the degree of saturation in loose specimens, whereas the opposite trend is observed for dense specimens. Microstructural analysis, carried out using mercury intrusion porosimetry (MIP) tests, shows a strong dependency of the air permeability on the as-compacted soil microstructure. This behaviour is also noticed in specimens that experienced a large variation in the degree of saturation during wetting and drying. Microstructural data indicate that air permeability is mainly controlled by large pores that display high connectivity. The degree of saturation plays a dual role in soil microstructure which, in turn, affects the air permeability. Denser specimens (dry density ≥ 1·5 Mg/m3) show a reduction in keff due to the expansion of the clay aggregates with increasing the as-compacted degree of saturation. The increase in the as-compacted degree of saturation in loose samples (dry density ≤1·3 Mg/m3) produces an enhancement in the proportion of macro pores, thus increasing keff, as a consequence of modifications in the pore size distribution. A threshold value has been identified, above which further increase in degree of saturation causes a reduction in the proportion of macro pores, and therefore in keff. A new proposal for estimating the air permeability is proposed in this paper based on the determination of a pore size parameter obtained from MIP data. The proposed approach seems capable of describing the evolution of air permeability for the whole spectrum of compaction states, including specimens subjected to wetting and drying paths.

Efficiency of The Spaw Model in Estimation of Saturated Hydraulic Conductivity in Calcareous Soils

The measurement of soil hydraulic properties is tedious, time-consuming, and costly. An alternative approach is to formulate models that utilize the physical and chemical properties of the soil as input variables to predict soil saturated hydraulic conductivity (Ks). However, the previous studies have not paid attention to the calcium carbonate content in their models; it can lead to reducing the size and number of the pores in the soil which, in turn, can lead to reduction Ks . Here we evaluated the ability of the Soil, Plant, Atmosphere, and Water (SPAW) model to predict Ks under different states of compaction for calcareous soils with wide-ranging textures sampled along a precipitation gradient in northwestern Iraqi Kurdistan. The results revealed that the best match occurred under loose to normal state of compaction for these soils. Among the soil properties, sand content was high significantly correlated with Ks followed by CaCO3, clay, organic matter content, silt and Electrical conductivity. A pedotransfer function (PTF) was proposed using these data and its results were compared to these from the SPAW model. Root mean square error (RMSE) and coefficient of variation (CV) for the comparison between measured Ks values and those predicted by the SPAW model were very high 2.7×10-4 cm s−1 and 166% respectively, that due to the values of Ks predicted by the SPAW model are overestimated for calcareous soils, for these reasons the accuracy of the SPAW model was improved via calibration. The RMSE and CV of the calibrated SPAW model were dropped to 9.8×10-5 cm s−1 and 61.2%, respectively. Additionally, the accuracy of our best PTF that constructed from sand, clay, and CaCO3 was slightly higher than the calibrated SPAW model. Therefore, it is recommended to use the calibrated SPAW model for predicting Ks in calcareous soils.

Two-Stage Sector Partition Path Planning Method for Automated Fiber Placement on Complex Surfaces

Automated fiber placement (AFP) is an advanced composite manufacturing technology which is widely used in the production of complex shaped aircraft components. However, on the surface with large curvature, the fiber compaction performance is poor, and the direction deviation and the geodesic curvature of the path increase sharply with the offset distance, resulting in various placement defects. To solve this problem, the influence of the surface curvature on the path performance is studied, and a two-stage sector partition path planning method for AFP on complex surface is proposed in this paper. The constraints of the direction deviation, turning radius and the compaction state of the fiber are comprehensively considered in this method. By analyzing the compaction feature, the distance between the roller and the surface is used to evaluate the compaction condition and an initial partition criterion is established according to the normal curvature of the surface along the roller axis. Then, the quantitative relationship between path performance and offset distance is derived, and the precise sector is determined under the constraints of placement direction and turning radius. The path performance constraints are fully considered in the path generation process, so the iterative process of evaluation–modification is effectively avoided. Simulations and experiments are then carried out on the winglet surface and the results show that compared with the parallel method, the proposed method can significantly improve the direction deviation, turning radius and compaction quality of the placement paths at the cost of gaps/overlaps. Satisfactory placement paths can be obtained with reasonable constraints on the complex surface.

A prediction model for the gas permeability of geomaterials

Geomaterials involved in deep geological repositories, geosequestration of greenhouse gases, oil and gas exploration and so on are subjected to moderate temperatures in response to the natural geothermal gradient, as well as an imposed thermal flux. In such instances, the influence of temperature on the gas permeability characteristics of geomaterials needs to be evaluated in view of assessing their long-term performance. The present study describes a simplified gas permeability apparatus developed for evaluating the gas permeability characteristics of geomaterials over a range of compaction states and temperatures, based on the principle of pressure decay. Further, the study proposes a prediction model for estimating the gas permeability characteristics of a variety of geomaterials in terms of their soil–water characteristics, by considering the effect of temperature. The efficacy of the proposed model has been established by validating it using the experimental results of the present study, as well as those available in the literature.

Probing the Conformational State of mRNPs Using smFISH and SIM.

mRNAs and lncRNAs assemble with RNA-binding proteins (RBPs) to form ribonucleoprotein complexes (RNPs ). The assembly of RNPs initiates co-transcriptionally, and their composition and organization is thought to change during the different steps of an RNP life cycle. Modulation of RNP structural organization has been implicated in the regulation of different aspects of RNA metabolism, including establishing interactions between the 5' and 3' ends in regulating mRNA translation and turnover. In this chapter, we describe a single-molecule microscopy approach that combines fluorescent RNA in situ hybridization (smFISH) and structured illumination microscopy (SIM ) and allows to measure different aspects of RNP organization in cells, including distances between different regions within individual mRNAs, as well as the overall compaction state of RNAs in different subcellular compartments and environmental conditions. Moreover, we describe a detailed workflow required for image registration and analysis that allows determining distances at sub-diffraction resolution.

Novel multifunctional negative stiffness mechanical metamaterial structure: Tailored functions of multi-stable and compressive mono-stable

Negative stiffness (NS) mechanical metamaterials have excellent application prospect in a broad range of fields such as energy trapping, repeated energy absorption and so on. Although various kinds of NS mechanical metamaterials have been proposed, one configuration cannot simultaneously achieve multi-stability and mono-stability. This paper presented a novel multifunctional NS mechanical metamaterial structure, which possessed tailored functions of multi-stable and compressive mono-stable state without geometrical parameters adjustment. The novel multifunctional NS mechanical metamaterial structure with a conical shape consisted of both soft and hard material part and was fabricated by additive manufacturing technology. NS behaviors were achieved by the instability of the soft counterpart. Mechanical performance of this novel multifunctional NS mechanical metamaterial structure under axial compression was experimentally and numerically investigated. Influences of geometrical parameters tailoring stable state were systematically investigated and the ratio of offset distance, tilt angle, slenderness were found the key factors. Effective methods to make sure the tri-layer metamaterial structure achieving multi-stable after unloading from completely compacted state were proposed.

Porosity, Pore Structure, and Fluid Distribution in the Sediments Entering the Northern Hikurangi Margin, New Zealand

AbstractHosting both tsunami earthquakes and slow slip events at shallow depth, the northern Hikurangi margin has motivated strong research efforts over the last two decades to better understand the relation between fluid pressure and fault mechanical behavior. Recently, IODP Expeditions 372 and 375 drilled, cored, and logged the basin entering this subduction zone providing a unique opportunity to characterize initial hydrogeological and petrophysical properties that drive seismic hazards along the margin. We inventory bound and interstitial fluid contents and assess the compaction state of the heterogeneous incoming sequence by correcting shipboard total connected porosity from the bound water content that typically characterizes clay‐rich sediments. By combining mercury injection capillary pressure, nuclear magnetic resonance, and nitrogen gas adsorption, we further document the evolution of pore structure with increasing depth. We also compare porosity data at the logging and sample scales. Both logging and laboratory data evidence contrasted porosity, pore structure, and fluid distribution across the entering section. Shallow macroporous siliciclastic units show very low bound water content and undergo compaction‐induced dewatering as they are normally consolidated during burial. In contrast, mesoporous volcaniclastic Hikurangi Plateau facies are characterized by high potential for bound water release from smectite, zeolite, and opal dehydration at greater depths. They mostly exhibit very low permeability except potentially in uncemented highly porous intervals where the décollement may initiate. Macroporous to mesoporous pelagic carbonates sandwiched in between exhibit mixed behavior and may also host the future décollement, similarly to the southern part of the margin.

A novel carbon thermal reduction approach to prepare recorded purity β-Ti3O5 compacts from titanium dioxide and phenolic resin

β-phase titanium pentoxide (β-Ti3O5) has great potential applications in sensors, electrodes and laser devices, due to its unique phase-transforming behaviors. However, just this reversible phase transition behaviors between λ and β phases made its high purity preparation be challenging, and the high energy consumption of present industrialized method also limited the high-level applications of β-Ti3O5. In this work, a novel carbothermal reduction method has been acquired to produce highly pure β-Ti3O5 compacts from titanium dioxide “wrapped” by phenolic resin served as carbon source. Their phase and microstructure evolutions during the whole reaction process were systematically characterized under the assistance of Rietveld refinement and SEM images. The highly active pyrolytic carbon of phenolic resin could deposit on the surface of TiO2 and this compacted state could promote the generated CO to accelerate the reaction process and decrease the addition of reductant, simultaneously. The reduction sequences were TiO2→ Ti4O7→ Ti3O5→ Ti2O3. The weight ratio of phenolic to precursor of 9.0% could achieve the pure β-Ti3O5 as high as 98.06% under the calcination temperature of 1250 °C for 4 h. This work provided a novel and industrialized route to prepare β-Ti3O5 for applications in sensor and electrode in electrochemical reactions.