Compaction Levels Research Articles

Characterization of porosities and optimization of mix design of pervious concrete using image analysis

Although pervious reduces surface runoff and replenishes groundwater resources, industrial applications are hindered by uncertainty in properties during mass productions. Most experimental studies correlated design parameters to performance parameters predominantly analysing porosity measured from water replacement method. This explains only a fraction of porosity and leads to inappropriate correlations between the influencing parameters. This study quantified porosity using a novel image analysis. 480 samples of pervious concrete were cast varying aggregate to cement ratio and compaction levels and performance parameters such as, wet-density, compressive strength, apparent, actual and effective porosities were assessed. The developed novel image analysis method facilitates accurate computation of porosity and actual, apparent and effective porosities was analysed quantified and optimised. An optimum A/C ratio was observed as 4.0 corresponding to 30 blows of compaction and a resultant actual porosity of approximately 0.2. Further the study establishes relationships between different types of porosities and their performance implications.

Assessment of different agricultural soil compaction levels using shallow seismic geophysical methods

A well-developed soil structure is crucial for a fertile soil and rules its influence on the ecosystem. Slight variations in the way soil components are organized and connected can greatly impact the soil mechanical and hydraulic characteristics. However, these features are challenging to measure at a scale that is relevant for agricultural management. In this study, we assess the capability of two seismic geophysical methods, i.e. Seismic Refraction Tomography and Multichannel Analysis of Surface Waves, to monitor the effects of compaction on agricultural bare soil. The purpose is to highlight the different mechanical response caused both by soil plastic deformation and soil water distribution due to increasing compaction. Results demonstrate that both geophysical techniques provide sufficient information to capture the effects of soil compaction and distinguish its significance, while traditional direct measurements, being punctual, lack sufficient spatial coverage. P-wave velocities carry a strong imprint of soil compaction, provided by seismic refraction, incorporating the information given by the multiphase medium in its entirety. On the other hand, S-wave velocity derived from Surface Waves discriminates the effect of solid matrix structure. This work, moreover, aims to pave the way for seismic methods to spatially characterize compaction at field scale, illustrating its potential and suggesting possible developments.

Coupled geomechanical analysis of irreversible compaction impact on CO2 storage in a depleted reservoir

The utilization of depleted gas reservoirs for carbon storage offers substantial advantages. However, it raises concerns related to the geomechanical effects of historic gas extraction on the CO2 sequestration operation. In this study, a coupled thermo-hydro-mechanical investigation is conducted on a multi-layered sedimentary system that includes sealed bounding faults. Our simulations exhibit various levels of reservoir compaction during gas extraction under different pre-consolidation conditions of the sediments, highlighting the pivotal role of reservoir compaction in geomechanical analysis. The results demonstrate the occurrence of strain-hardening compaction behavior in the reservoir during post-yield depletion. This compaction is accompanied by a significant reduction in porosity and permeability, as well as irreversible surface subsidence. Hysteresis in the stress state is induced by the aforementioned irreversible reservoir compaction through two primary mechanisms: poro-elastoplastic stressing and differential compaction on each side of the sealing fault. These mechanisms alter the magnitude and orientation of stress inside and outside the depleted reservoir. Moreover, caprock compaction is impeded and delayed by the irreversible reservoir compaction owing to poro-elastoplastic stressing. This implies that conventional methods relying on the poro-elasticity theory alone may overestimate pressure required to fracture the caprock by approximately 2 MPa. When considering the combined effect of poro-elastoplastic stressing and differential compaction, neglecting irreversible reservoir compaction may lead to underestimation of the critical pressure for inducing fault slip by up to 4.9 MPa. Additionally, regardless of whether plastic void compaction is considered, we recommend increased attention be focused on the sub-vertical faults to mitigate the risk of significant slip that potentially could also lead to upward CO2 leakage. In scenarios where a slip event occurs in a fault during reservoir depletion, the results show that a subsequent CO2 injection operation tends to stabilize the faults. Nevertheless, it is crucial to consider that fault stability could deteriorate rapidly over time, potentially leading to a second slip event during carbon sequestration.

Flexible pavement longitudinal joint quality evaluation using non-destructive testing

Longitudinal joint construction quality is critical to the life of flexible pavements. Maintaining deteriorated longitudinal joints has become a challenge for many highway agencies. Improving the joint's quality through better compaction during construction can help achieve flexible pavements with longer service lives and less maintenance. Current quality control (QC) and quality assurance (QA) plans provide limited coverage. Consequently, the risk of missing areas with poor joint compaction is significant. A density profiling system (DPS) is a non-destructive alternative to conventional destructive evaluation methods. It can provide quick and continuous real-time coverage of the compaction during construction in dielectrics. The paper presents several case studies comparing various types of longitudinal joints and demonstrating the use of DPS to evaluate the joint's compaction quality. The paper shows that dielectric measurements can provide valuable insight into the ability of various construction techniques to achieve adequate levels of compaction at the longitudinal joint. The paper proposes a dielectric-based longitudinal joint quality index (LJQI) to evaluate the relative compaction of the joint during construction. It also shows that adopting DPS for assessing the compaction of longitudinal joints can minimize the risk of agencies accepting poorly constructed joints, identify locations of poor quality during construction, and achieve better-performing flexible pavements.

Numerical Analysis of Soil Deformation in Earth Dams Using a Stiffness Variation Technique

Small earth dams have been used since ancient times and are often the main source of water in semi-arid regions. In this particular type of engineering work, soils saturated by water present changes in their mechanical properties (especially in the first filling), which usually cause a simultaneous loss of stiffness and shear strength. In this context, the software UNSTRUCT presents itself as a very useful tool, as it allows calculating the final state of stress x strain for a plane strain state, using the Finite Element Method, both for saturated and unsaturated embankments, considering an elastic model and the effect of suction (and its variation), through a stiffness variation technique. The present research used UNSTRUCT to assess the behavior of the embankment of a hypothetical earth dam, varying the features of its typical cross-section: homogeneity; internal drainage structures; geometry along a longitudinal profile; and the influence of the compaction level. The results showed that the soil responded better to strains for the scenario of better compaction along the dry branch of the compaction curve, as well as with the use of a vertical drainage element. It was also observed that the strains were higher when greater sections considered, which, in a real situation, would cause distortions along the longitudinal profile of the dam. The software UNSTRUCT proved to be efficient in obtaining and visualizing the modeling results, also making it possible to analyze the development of failure over time after the dam was filled. With UNSTRUCT, a more realistic analysis of the behavior of the hypothetical dam – considering factors that are specific to unsaturated soils – was possible. Worth mentioning also that the software allowed the appraisal of multiple changes in the dam’s geometry and parameters.

Comparative Measurement of Horizontal Penetrometry with a Focus on the Degree of Soil Compaction in Real Work Conditions

Potential soil production is closely related to the physical and mechanical properties. The aim of this paper was to evaluate the effect of different levels of soil compaction created by tractor chassis. The total area of the experimental plot was 13.22 ha. Up until 2019, a conventional tillage system had been used. The measurements were carried out with an innovative measuring device that allows for the continuous measurement of the horizontal penetrometry for comparative measurements while driving, which was designed at the Slovak University of Agriculture in Nitra. The measuring device measured the soil resistance in the tire track (On-track) and out of track (Off-track) as well as in three (50 s) sequences within one tractor pass. Three lines were chosen, where in each a pair of combinations was made. The results were subjected, in addition to graphical evaluation, to single factor ANOVA analysis. When comparing individual passes (PH1 to PH6), the statistical analysis showed that the results of the horizontal resistance measurements proved to be statistically significant (p < 0.05) with respect to the weight, number of passes, and tire underinflation. The highest compaction was caused by the first pass, while the higher weight of the tractor during the next pass had a smaller effect. Underinflating the tires ensured a reduction in compaction. Reducing the tractor tire pressure to 0.15 MPa resulted in a reduction in soil compaction of up to 16%.

Molecular dynamics of structural effects of reactive carbonyl species derivate of lipid peroxidation on bovine serum albumin

BackgroundSerum albumin is the most abundant protein in the Mammalia blood plasma at where plays a decisive role in the transport wide variety of hydrophobic ligands. BSA undergoes oxidative modifications like the carbonylation by the reactive carbonyl species (RCSs) 4-hydroxy-2-nonenal (HNE), 4 hydroxy-2-hexenal (HHE), malondialdehyde (MDA) and 4-oxo-2-nonenal (ONE), among others. The structural and functional changes induced by protein carbonylation have been associated with the advancement of neurodegenerative, cardiovascular, metabolic and cancer diseases. MethodsTo elucidate structural effects of protein carbonylation with RCSs on BSA, parameters for six new non-standard amino acids were designated and molecular dynamics simulations of its mono‑carbonylated-BSA systems were conducted in the AMBER force field. Trajectories were evaluated by RMSD, RMSF, PCA, RoG and SASA analysis. ResultsAn increase in the conformational instability for all proteins modified with local changes were observed, without significant changes on the BSA global three-dimensional folding. A more relaxed compaction level and major solvent accessible surface area for modified systems was found. Four regions of high molecular fluctuation were identified in all modified systems, being the subdomains IA and IIIB those with the most remarkable local conformational changes. Regarding essential modes of domain movements, it was evidenced that the most representatives were those related to IA subdomain, while IIIB subdomain presented discrete changes. ConclusionsRCSs induces local structural changes on mono‑carbonylated BSA. Also, this study extends our knowledge on how carbonylation by RCSs induce structural effects on proteins.

Studying Structure and Functions of Nucleosomes with Atomic Force Microscopy.

Chromatin is an epigenetic platform for implementation of DNA-dependent processes. Nucleosome, as a basic level of chromatin compaction, largely determines its properties and structure. In the study of nucleosomes structure and functions physicochemical tools are actively used, such as magnetic and optical "tweezers", "DNA curtains", nuclear magnetic resonance, X-ray crystallography, and cryogenic electron microscopy, as well as optical methods based on Förster resonance energy transfer. Despite the fact that these approaches make it possible to determine a wide range of structural and functional characteristics of chromatin and nucleosomes with high spatial and time resolution, atomic force microscopy (AFM) complements the capabilities of these methods. The results of structural studies of nucleosome focusing on the AFM method development are presented in this review. The possibilities of AFM are considered in the context of application of other physicochemical approaches.

Alfalfa Responses to Intensive Soil Compaction: Effects on Plant and Root Growth, Phytohormones and Internal Gene Expression.

The perennial legume alfalfa (Medicago sativa L.) is of high value in providing cheap and high-nutritive forages. Due to a lack of tillage during the production period, the soil in which alfalfa grows prunes to become compacted through highly mechanized agriculture. Compaction deteriorates the soil's structure and fertility, leading to compromised alfalfa development and productivity. However, the way alfalfa responses to different levels of soil compaction and the underlying molecular mechanism are still unclear. In this study, we systematically evaluated the effects of gradient compacted soil on the growth of different cultivars of alfalfa, especially the root system architecture, phytohormones and internal gene expression profile alterations. The results showed that alfalfa growth was facilitated by moderate soil compaction, but drastically inhibited when compaction was intensified. The inhibition effect was universal across different cultivars, but with different severity. Transcriptomic and physiological studies revealed that the expression of a set of genes regulating the biosynthesis of lignin and flavonoids was significantly repressed in compaction treated alfalfa roots, and this might have resulted in a modified secondary cell wall and xylem vessel formation. Phytohormones, like ABA, are supposed to play pivotal roles in the regulation of the overall responses. These findings provide directions for the improvement of field soil management in alfalfa production and the molecular breeding of alfalfa germplasm with better soil compaction resilience.

DNA damage and repair in the nucleosome: insights from computational methods.

Cellular DNA is constantly exposed to endogenous or exogenous factors that can induce lesions. Several types of lesions have been described that can result from UV/ionizing irradiations, oxidative stress, or free radicals, among others. In order to overcome the deleterious effects of such damages, i.e., mutagenicity or cytotoxicity, cells possess a highly complex DNA repair machinery, involving repair enzymes targeting specific types of lesions through dedicated cellular pathways. In addition, DNA is highly compacted in the nucleus, the first level of compaction consisting of ~ 147 DNA base pairs wrapped around a core of histones, the so-called nucleosome core particle. In this complex environment, the DNA structure is highly constrained, and fine-tuned mechanisms involving remodeling processes are required to expose the DNA to repair enzymes and to facilitate the damage removal. However, these nucleosome-specific mechanisms remain poorly understood, and computational methods emerged only recently as powerful tools to investigate DNA damages in such complex systems as the nucleosome. In this mini-review, we summarize the latest advances brought out by computational approaches in the field, opening new exciting perspectives for the study of DNA damage and repair in the nucleosome context.

An overview of green roof acoustic performance

This comprehensive review provides an in-depth examination of the acoustic performance of green roofs within urban and built environments over the past 15 years. Green roofs, characterized by their vegetative cover and substrate layers, offer a multifaceted solution to address challenges associated with urban noise pollution. The objective of this review is to synthesize existing literature, emphasizing key studies and methodologies employed to assess the noise reduction and sound isolation capabilities of green roofs. Factors influencing green roof acoustic performance, such as plant species selection in the plant layer, soil distribution, moisture content, and compaction level in the vegetation layer, as well as the overall roof design in terms of shapes and building configuration, are discussed in detail. Additionally, the impact of overall roof design, including shapes and building configuration, is explored. The relevant sound absorption coefficient and insertion loss values, drawn from the existing literature, will be reported. By systematically analyzing empirical findings, this overview offers valuable insights into the potential of green roofs as sustainable components for noise mitigation in building construction, contributing to the development of more resilient and harmonious urban landscapes.

Soil disturbance caused by timber harvesting in a natural forest, West Sumatera Indonesia

Logging operations in natural forests generally use bulldozers. Bulldozers skid logs from the stump site to the landing site. The bulldozer maneuvers in the felling area cause skid trails and soil compaction. Soil compaction is one of the negative impacts of logging operations. The research aim is to analyze the level of soil compaction in various bulldozer skidding intensities after logging operations. The research occurred at a natural forest area in Siberut West Sumatera, Indonesia. The results of the study showed that there was a relationship between skidding intensity and the level of soil bulk density. The more a bulldozer moves at the same skid trail, the higher the soil bulk density. The range of soil bulk density is from 0.82 g cm−3 to 1.31 g cm−3. The bulk density increases markedly after the bulldozer’s first, second, and third passes. After the fourth pass, the bulk density is relatively constant. The porosity of the soil decreases with the increase of the bulk density. On skid trails where the soil is very compact, seeds that fall on skid trails will have difficulty growing well. Requires planting on primary skid trails. Soil damage in the form of soil compaction by bulldozers needs serious attention in the Reduce Impact Logging technique.

Performance of seedlings and yield of soybean genotypes under soil compaction

AbstractThe identification of soybean genotypes tolerant to soil compaction makes it possible to reduce productivity loss under stress conditions. Added to this, the prior selection of these genotypes will result in greater assertiveness in the positioning of cultivars in the field. Thus, the objective was to evaluate the susceptibility of soybean genotypes to compaction in greenhouse and field conditions; verify which characteristics of seedlings under high resistance to root penetration are correlated with crop production in compacted soil; and to validate the substrate mechanical impedance method for evaluating the susceptibility of plant genotypes to soil compaction. Seeds of 20 genotypes were sown in a substrate mechanical impedance system under controlled conditions. The characteristics evaluated were total root length, total root surface area, mean root diameter, total root volume, taproot length, shoot length, root dry matter and seedling shoot dry matter. In the field experiment, half of the planting area was compacted, constituting two treatments, soil with and without compaction. The percentage of seedling emergence, initial plant height, stem diameter, number of nodes, internode length, number of lateral branches, shoot dry matter, final plant height, absolute and relative growth rate, number of pods, weight of 100 seeds and grain yield. In addition, the number of days between soybean sowing until plant flowering and grain harvest was recorded according to genotype and soil compaction level. In a controlled environment, genotypes tolerant to soil compaction show greater plasticity of root characteristics and smaller alterations in the shoot of seedlings. In the field, these genotypes show smaller reductions in growth rate, height, number of pods and grain yield. The shoot dry matter and the root dry matter of soybean seedlings in a mechanical impedance system present a positive and negative correlation, respectively, with soybean yield in compacted soil, indicating that the genetically determined susceptibility to soil compaction stress was similar throughout ontogenesis. The substrate mechanical impedance system used to evaluate the performance of soybean seedlings under stress, facilitates the decision‐making in breeding programs focused on identifying genotypes expressing soil compaction tolerance.

Soil Compaction and Productivity Evolution in a Harvested and Grazed Mediterranean Scots Pine (Pinus sylvestris L.) Forest

The effects of machinery and livestock on forest soil compaction have mostly been studied at short-term and local scales. A better understanding of the long-term effects of compaction in mature stands at the management scale is needed, especially in hot and dry climates. This study aims to analyze (1) soil compaction in a Mediterranean Scots pine (Pinus sylvestris L.) forest subjected to mechanized logging and grazing for more than 50 years and (2) forest productivity trends during these 50 years of disturbance. Soil penetration resistance (0–10 cm and 10–20 cm) and soil moisture (0–12 cm) were measured in 181 randomly selected points affected by “high machinery traffic”, “high cattle traffic” or “low traffic”. Decennial forest inventory data on density, timber volume, and recruitment were collected and analyzed over the five decades preceding soil measurements. Soil penetration resistance exceeded 2500 kPa at a significant portion of the sampled points, although the highest levels of compaction tended to be concentrated in the subsurface layer of the high-traffic areas. Cattle and machinery caused significant compaction in these areas and increased penetration resistance in the range of 350–450 kPa. However, despite the long period of disturbance and the increase in penetration resistance observed, no signs of productivity decline were detected in the forest.

Suppression of Carbon Dioxide Emissions from Soil Amended with Autoclaved Lightweight Aerated Concrete Under Different Compaction and Moisture Conditions

Carbon dioxide (CO2) emissions has been highlighted worldwide as a contributor to the greenhouse effect. Soil physical characteristics such as bulk density and moisture content can influence the emissions of greenhouse gasses (GHGs) from soil. Soil conditioners applied to soil can also affect the terrestrial CO2 emissions. Autoclaved lightweight aerated concrete (ALC) is in use at present as a soil conditioner or calcium silicate fertilizer, it is a type of porous material made from industrial waste. In this study, we determined the effect of ALC (Inenica, Clion Co., Ltd, Japan) on CO2 emissions from paddy soil with considering soil compaction and moisture content. Laboratory experiments were conducted using soils with and without ALC (0 and 5%), under two levels of compaction (compacted and non-compacted), and two soil moisture contents (60% and 100% water holding capacity: WHC) in 200 mL glass vials. All treatments with triplicates were incubated at 25° C for 21 days under aerobic conditions. Emissions of CO2 were determined at 0, 1, 3, 7, 14, and 21 days using gas chromatography with the thermal conductivity detector. The addition of ALC significantly decreased CO2 emissions from soil at the early stages of incubation. Emissions of CO2 were significantly lower at 100% WHC than at 60% WHC. Non-compacted treatments showed significantly higher emissions of CO2 than compacted treatments during the incubation time period. This is possibly due to improved soil aeration and porosity, which enhanced the activity of soil microorganisms responsible for the decomposition of organic matter. The interactions between moisture content with ALC addition and compaction on cumulative CO2 emissions were statistically significant (p<0.05). The effect of ALC addition on CO2 suppression was more effective at compacted and 100% WHC (51% reduction compared with control). Our study suggested that precise dosage of ALC application (5%) can effectively reduce CO2 emissions from soil, under 100% WHC and compaction conditions than 60% WHC and non-compaction conditions.
 
 Keywords: Aerobic, Autoclaved lightweight aerated concrete, Carbon dioxide, Compaction, Moisture content

Translocation of tropical peat surface to deeper soil horizons under compaction controls carbon emissions in the absence of groundwater

Compaction is recognized as an effective method for mitigating the risk of fires by enhancing soil moisture levels. This technique involves restricting peat pore spaces through compaction, facilitating improved capillary action for water retention and rehydration. The compaction of tropical peatlands, while beneficial for fire prevention, has the potential to influence biogeochemical processes and subsequent carbon emissions. The magnitude of compaction and groundwater level are strongly coupled in such environments, making it difficult to distinguish the control of physicochemical properties. Therefore, this study seeks to understand how peat compaction affects its properties, carbon emissions, and their relationship, with a focus on geophysical processes. Intact peat samples were collected from a secondary peat swamp forest and an oil palm plantation in Selangor, Peninsular Malaysia. Compaction treatments were applied to achieve three levels of volume reduction. CO2 and CH4 emissions were measured using an automated gas analyzer, and the physicochemical properties of the peat were determined. The results revealed that mechanical compaction significantly altered the physicochemical properties of the secondary forest peat, displaying an opposite pattern to the oil palm plantation, particularly regarding total nitrogen and sulfur. Moreover, the average reduction percentage ratio of CO2 emissions (from 275.4 to 182.0 mg m-2 hr-1; 33.9%) to CH4 uptakes (from -17.8 to -5.2 µg m-2 hr-1; 70.1%) (~1:2) indicated distinct stages of decomposition and translocation of less decomposed peat to deeper layers due to compaction, predominantly in secondary peat swamp forest samples. The oil palm plantation samples were unaffected by compaction in terms of physicochemical properties and carbon emissions, indicating the ineffectiveness of this approach for reducing fire risk in already drained systems. This study underscores the necessity of understanding the effects of compaction in the absence of groundwater to accurately evaluate the widespread application of this technique.

Logging Machinery Traffic Has Greatest Influence on Soil Chemical Properties in the Amazonian Rainy Season

Abstract In the forests of Amazonia each year, previously unentered stands are logged, which usually results in some degree of soil compaction. Consequently, the soil chemical properties in compacted areas are altered. The aim of this study was to determine how these changes may help or hinder site recovery in the context of seasonal variation and increased levels of compaction. To investigate these changes, an experiment was established in the Central Amazon. This consisted of tractor trails compacted at three incrementally increasing traffic intensities of one, three, and twelve machine cycles in the wet and dry seasons. Results revealed that elevated moisture in the wet season combined with heavy compaction from twelve machine cycles had the greatest impact on soil chemical properties. This was indicated by diminished total nitrogen, organic carbon, available phosphorus, cation exchange capacity, and elevated ammonium and Fe2+. Nevertheless, heavy compaction in the wet season led to lower Al3+ and higher base saturation, which could be beneficial for future site recovery. Study Implications: Annually, vast swathes of old-growth forest are logged for the first time in Amazonia. These areas require an extensive skid trail network to facilitate movement of logging machinery and subsequent log skidding. Skid trails always entail some level of soil compaction, especially in the heavily used primary skid trails. This compaction influences the soil chemical properties. Some impacts are only apparent in the wet season and may not be present in the dry season. Therefore, to reduce overall impacts to soil chemical properties, skid trail coverage should be planned to reduce the coverage of the logging site.

Decadal Trends in Surface Elevation and Tree Growth in Coastal Wetlands of Moreton Bay, Queensland, Australia

Coastal wetlands surrounding urban environments provide many important ecosystem services including protection from coastal erosion, soil carbon sequestration and habitat for marine and terrestrial fauna. Their persistence with sea-level rise depends upon their capacity to increase their soil surface elevation at a rate comparable to the rate of sea-level rise. Both sediment and organic matter from plant growth contribute to gains in soil surface elevation, but the importance of these components varies among sites and with variation in climate over long time scales, for which monitoring is seldom available. Here, we analysed variation in surface elevation, surface accretion and mangrove tree growth over 15 years in Moreton Bay, Queensland, Australia, a period that spans variation in the El Niño/La Niña (ENSO) cycle, which strongly influences rainfall and sea level in the region. Piecewise structural equation models were used to assess the effects of biotic (tree growth, plant cover and bioturbation by invertebrates) and environmental factors on annual surface elevation increments throughout this period. Our model for mangroves identified that surface accretion and tree growth were both positively influenced by rainfall, but surface elevation was not, and thus, higher levels of compaction of the soil profile in high rainfall/high sea level years were inferred. In contrast, our saltmarsh model found that rainfall positively influenced surface accretion and elevation gains. Declines in surface elevation in the mangroves were influenced by the species composition of the mangrove, with higher levels of elevation loss occurring in mangrove forests dominated by Avicennia marina compared to those with a higher proportion of Rhizophora stylosa. Decadal-scale variation in ENSO affected mangrove tree growth, but surface elevation trends were more strongly influenced by variation in environmental conditions than by tree growth, although effects of biotic factors (mangrove species composition and bioturbation) on surface elevation trends were observed. Further research into tipping points with extreme ENSO events (either La Niña with high rainfall and high sea level or El Niño with low rainfall and low sea levels) will help clarify the future of mangrove and saltmarsh distribution within Moreton Bay.

A Two-Step Mechanism for Creating Stable, Condensed Chromatin with the Polycomb Complex PRC1.

The Drosophila PRC1 complex regulates gene expression by modifying histone proteins and chromatin architecture. Two PRC1 subunits, PSC and Ph, are most implicated in chromatin architecture. In vitro, PRC1 compacts chromatin and inhibits transcription and nucleosome remodeling. The long disordered C-terminal region of PSC (PSC-CTR) is important for these activities, while Ph has little effect. In cells, Ph is important for condensate formation, long-range chromatin interactions, and gene regulation, and its polymerizing sterile alpha motif (SAM) is implicated in these activities. In vitro, truncated Ph containing the SAM and two other conserved domains (mini-Ph) undergoes phase separation with chromatin, suggesting a mechanism for SAM-dependent condensate formation in vivo. How the distinct activities of PSC and Ph on chromatin function together in PRC1 is not known. To address this question, we analyzed structures formed with large chromatin templates and PRC1 in vitro. PRC1 bridges chromatin into extensive fibrillar networks. Ph, its SAM, and SAM polymerization activity have little effect on these structures. Instead, the PSC-CTR controls their growth, and is sufficient for their formation. To understand how phase separation driven by Ph SAM intersects with the chromatin bridging activity of the PSC-CTR, we used mini-Ph to form condensates with chromatin and then challenged them with PRC1 lacking Ph (PRC1ΔPh). PRC1ΔPh converts mini-Ph chromatin condensates into clusters of small non-fusing condensates and bridged fibers. These condensates retain a high level of chromatin compaction and do not intermix. Thus, phase separation of chromatin by mini-Ph, followed by the action of the PSC-CTR, creates a unique chromatin organization with regions of high nucleosome density and extraordinary stability. We discuss how this coordinated sequential activity of two proteins found in the same complex may occur and the possible implications of stable chromatin architectures in maintaining transcription states.

Effect of compaction and moisture content on the deformation characteristics of unsaturated sandy soils varying fines content

ABSTRACT This research explores how the dynamic behaviour under cyclic compression loading affects compaction characteristics. Three types of sand, varying in fines content, are compacted under different saturation ( S r ) and compaction ( D c ) levels. Suction-controlled drained cyclic loading tests are conducted to predict axial strain accumulation, with initial suction measured for each compacted state. The study seeks to understand the correlation between axial strain accumulation and initial suction across soil types. Findings indicate that initial soil suction, influenced by saturation, significantly impacts axial strain under cyclic loading. Lower saturation enhances particle bonding, increasing initial suction and reducing strain accumulation. Moreover, an increase in fines content results in greater strain accumulation. Despite that, sands with elevated fines (18.8%) can achieve similar soil performance through effective compaction with precise saturation control. This underscores the role of saturation in moisture regulation during compaction, particularly for sands with higher non-plastic fines content, in achieving effective compaction.