Dry Side Research Articles

Coupling effect of cyclic wet-dry environment and compaction state on desiccation cracking and mechanical behavior of low and high plastic clays

This study investigates the complex interplay between wetting–drying (W-D) cycles and initial compaction states on desiccation cracking and the mechanical behavior of different clayey soils. Natural CH, CL, and ML soils, distinguished by their chemical composition and plasticity, are subjected to a meticulously designed experimental program. The specimens are remolded at various initial compaction states, including the optimum moisture content (wopt) having maximum dry density (γdmax), and wet and dry sides of the compaction curve having identical initial dry density (γd0). Subsequently, they undergo multiple W-D cycles, systematically documented through cinematography. Mechanical response is assessed after different W-D cycles. It is observed that desiccation cracking within both CL and CH initiates after the first W-D cycle, intensifying rapidly after the second cycle and reaching an optimal cracking state after the third cycle. The crack analyses indicate a transition from surface cracking to deeper-seated cracks with an increase in W-D cycles. CH soil, characterized by a 2:1-layered clay mineral with a high propensity for swelling and shrinkage, exhibits elevated desiccation cracking at high w0 for identical γd0. Notably, CH soil exhibits maximum cracking at the wopt and γdmax. In contrast, CL soil, characterized by a 1:1-layered clay mineral, displays an inverse response across all compaction states, and ML soil, characterized by a scarcity of clay mineral, shows insignificant cracks. This disparity in behavior is closely attributed to clay mineralogy and microstructure, which define the underlying mechanism responsible for the generation of internal stresses in the soil structure induced by moisture fluctuations causing desiccation cracking. Stiffness and unconfined compressive strength (qu) of CH and CL increase and compressibility decreases as w0 increases after undergoing W-D cycles due to the volume shrinkage response of specimens. Meanwhile, for a particular compaction state, strength decreases while compressibility increases with increasing W-D cycles.

Full optimal geometric exploration of M-cycle indirect evaporative dewpoint cooler using a substantial experiment-oriented AI algorithm

The most interesting feature of Maisotsenko indirect evaporative cooler (MIEC) is sub wet bulb supply temperature via water vaporization while adding zero humidity to the final product air. However, for a given thermal/fluid condition, achieving sub wet-bulb temperature while maximizing supply air mass flow is only possible within a unique range of geometric factors. Besides, the influence of each geometric factor on the performance of the cooler changes as any other geometric parameter varies. If only five values are considered for each parameter, 625 geometric combinations are possible. Artificial Intelligence seems the only helpful tool to handle such cumbersome and complex situations. Hence, in this research, first, an experimentally validated analytical model is employed to train a machine learning (ML) model considering geometric parameters of the cooler. Then, the ML model is employed to generate all possible geometric combinations of the cooler. It is noted that the inlet air thermal conditions, dry side airflow, and wet-to-dry side airflow ratio are fixed on certain values, making the absolute results valid only for these thermal/fluid conditions. For different ambient air or fluid flow conditions, the optimal geometry will vary, requiring the ML model to be re-run. However, the general trends of the curve may still serve as a guide. According to the results, the impact level of each parameter significantly depends on the values of other parameters as well. For example, while a larger channel length leads to a colder supply temperature, the extent of its impact depends on the channel gap and channel height. When the wet and dry channel gaps are at their minimum (0.5 mm), increasing the channel length from 0.05 to 0.25 m results in a supply temperature reduction from 25 °C to around 13 °C (for a channel height of 0.4 m) and from 16 °C to around 11 °C (for a channel height of 1.2 m). This represents a reduction of about 50 % in the first case and approximately 31 % in the second case. However, when the dry/wet side gap is larger (4.5 mm), increasing the channel length from 0.05 to 0.25 m causes the supply temperature to decrease from around 35 °C to about 26 °C (for a channel height of 0.4 m) and from 30 °C to around 18 °C (for a channel height of 1.2 m). This results in a reduction of approximately 25 % in the first case and about 40 % in the second case. For industrial consulting contact the corresponding author.

Effect of Water Content and Degree of Compaction of Clay Subgrade Soil on the Interface Shear Strength Using Geogrid

Pavement performance in clay soil roads can be enhanced with the help of the geogrid concept by increasing lateral confinement, bearing capacity, and overall rigidity of the pavement. Also, geogrid is useful in minimizing vertical and lateral pavement deformations. In this study, 65 tests are performed without and with two types of geogrid, and the aim behind it is to investigate the effect of the moisture content and degree of compaction of clay soil on the interface shear strength. The number of materials used to conduct this study, included subbase granular (type B), clay subgrade soil, the Biaxial and SS2 geogrid which is used as a reinforcing material. Testing the direct shear is conducted by a large-scale direct shear manufactured device contains an upper box with side lengths of (20×20×10) cm, and a lower box with side lengths of (20×25×10) cm. Results show that for all tests the normal applied stresses are 25, 50, 75 and 100 kPa, the shear stress displacement curves for all cases follow similar trends and they are affected by normal stress, density and water content of subgrade soil and type of geogrid. Also, it is obvious that the shear stress increases by increasing the normal applied stress and degree of compaction of clay subgrade soil reaching its maximum value at 95% degree of compaction while it decreases by increasing the water content of subgrade soil. The maximum value of shear strength is observed when water content is equal to 8% (dry side) and finally, the Biaxial geogrid BX1100 (G1) is more efficient in reinforcing clay-subbase interface as compared with SS2 geogrid (G2).

Initiation of a Supercell by Convectively Generated Gravity Waves in the Simulated Kaiyuan Tornadic Event of 3 July 2019

Abstract An EF4-rated supercell tornado occurred on 3 July 2019 in Kaiyuan, China, causing heavy casualties. A three-level nested-grid high-resolution numerical simulation is used to investigate the initiation of the tornadic supercell. Automatic weather station (AWS) data, FY-4A visible satellite data, and Doppler radar data are used to verify the model simulation. The most important aspects of the simulated pre-supercell mesoscale convective system (MCS) and the initiation of the supercell agree with observations. Detailed investigation of the model results reveals that the initial cells form first above a convective boundary layer (CBL) on the dry side of a surface dryline. Above the CBL is a moist layer in terms of relative humidity and the layer is stable. Convectively generated gravity waves (GWs) emanating from the MCS and propagating southward along the stable layer above the CBL provide localized forcing for the actual triggering of initial cells at specific locations. The associated perturbation potential temperature and vertical velocity patterns confirm that the GWs trigger a series of cloud bands. The additional lifting by the updraft of a horizontal convective roll in the CBL underneath the GW updraft works together to promote faster growth of the initial cell that later becomes the supercell. Examination of the Scorer parameter profiles shows favorable conditions for vertical trapping of GWs along the wave guide in the stable layer, preventing the radiation of wave energy to the upper levels.

Climate and topography control variation in the tropical dry forest-rainforest ecotone.

Ecotones are the transition zones between ecosystems and can exhibit steep gradients in ecosystem properties controlling flows of energy and organisms between them. Ecotones are understood to be sensitive to climate and environmental changes, but the potential for spatiotemporal dynamics of ecotones to act as indicators of such changes is limited by methodological and logistical constraints. Here, we use a novel combination of satellite remote sensing and analyses of spatial synchrony to identify the tropical dry forest-rainforest ecotone in Area de Conservación Guanacaste, Costa Rica. We further examine how climate and topography influence the spatiotemporal dynamics of the ecotone, showing that ecotone is most prevalent at mid-elevations where the topography leads to moisture accumulation and that climatic moisture availability influences up and downslope interannual variation in ecotone location. We found some evidence for long-term (22 year) trends toward upslope or downslope ecotone shifts, but stronger evidence that regional climate mediates topographic controls on ecotone properties. Our findings suggest the ecotone boundary on the dry forest side may be less resilient to future precipitation reductions and that if drought frequency increases, ecotone reductions are more likely to occur along the dry forest boundary.

WITHDRAWN: Pullout Capacity of Piles in Unsaturated High Plasticity Clayey Soil: An Experimental Model Study

Unsaturated soils exhibit distinct physical and mechanical characteristics compared to dry or saturated soils. Ignoring the influence of unsaturation (matric suction) and assuming either dry or saturated conditions can lead to unreliable predictions of pile behavior in unsaturated soils. In this study, the pullout capacity of different physical model piles driven in an unsaturated Kaolinite-Bentonite matrix is investigated. A series of lab-scale pullout tests were carried out to examine the influence of matric suction, pile type, pile L/D ratio, and undrained cohesion (cu) of soil on the ultimate pullout capacity of model piles. Soil samples were prepared and compacted in a tank, and holes were created using a pile. Four model piles (solid and hollow stainless steel) were driven into the holes, ensuring proper spacing. Incremental loading was applied until the piles slipped out, with displacement measured by an LVDT. The pile pullout capacity increased with increased matric suction and undrained cohesion. The uplift capacity increased by 50 % to 136% as matric suction increased by 157.97% as the compaction state was changed from 0.95 γd(max) on the wet side of optimum moisture content (OMC) to 0.95 γd(max) on the dry side of OMC of the compaction curve. However, for the compaction state of 0.90 γd(max), the matric suction increased by 398.80%, leading to a 275% to 800 % increase in the uplift capacity. As the cohesion of the five samples increased from 17.84 kPa to 137.84 kPa, the uplift capacity of all the model piles increased. In Kaolinite-Bentonite mixes compacted on the dry side of OMC, hollow model piles resisted higher pull-out loads than solid model piles. The increase in uplift capacity was found to be in the range of 11.11% to 75% for different combinations of pile type and compaction density (matric suction). The results from the study imply a strong influence of matric suction, undrained cohesion, L/D ratio, and pile type on pullout capacity for piles driven in unsaturated Kaolinite-Bentonite mix.

Developing an experiment-based strong machine learning model for performance prediction and full analysis of Maisotsenko dewpoint evaporative air cooler

Among all direct and indirect water-based evaporative air coolers, Maisotsenko indirect evaporative cooler (MIEC) is the only one which can supply sub wet-bulb air temperature while adding no moisture to the product air. For any given MIEC, four thermal/fluid parameters including dry channel flow rate, wet-to-dry-side air flow ratio, ambient air temperature and ambient relative humidity impact the performance of the MIEC. Sub-wet bulb supply temperature while having maximum cooling capacity happen only for a specific range of the mentioned thermal/fluid parameters. For any ambient condition and dry side air flow, a magic value of air-flow-ratio can maximize the cooling capacity of the cooler. Thousands of data is required to provide a simultaneous multi-aspect analysis of each parameter (while other parameters vary as well) to identify all possible curve behaviors and secrets of this technology. That is why, for the first time in this research, a strong machine learning (ML) model, is developed for MIEC cooler using 625 validated analytical/experimental-based training data (full factorial design). This model is employed to generate around 3600 unseen data to fully clarify the impact of each parameter (on supply temperature, total cooling capacity, useful cooling capacity and wet-bulb effectiveness) while other parameters are variable too. This strategy makes it possible to see all hidden extremum or peak point where the performance of the cooler is maximized or minimized. Interesting results are found in this research. For any ambient condition, there is an extremum point of the air flow ratio at which the total cooling capacity is maximized. The results indicate that as the dry side air flow increases, this extremum value decreases. For instance, under an ambient condition of 18 °C and 9 % relative humidity, the extremum point of the air flow ratio is 0.45 when the dry side air flow is 0.8 L/s and 0.25 when the dry side air flow is 4.8 L/s. In real-world commercial cooler, this can be simply happened by appropriate re-adjusting the dry and wet side fan speeds.

Hydraulic characteristics of a large rotation-angle baffle-drop shaft through synergetic discharge from dry and wet sides

To enhance the operational capacity and space utilization of baffle-drop shafts, this study improved the traditional baffle-drop shaft by expanding the wet-side space, incorporating large rotation-angle baffles, and installing overflow holes in the dividing wall. A three-dimensional turbulent model was developed using ANSYS Fluent to simulate the hydraulic characteristics of both traditional and new baffle-drop shafts across various flow rates. The simulation results demonstrated that the new shaft design allowed for discharge from both the wet and dry sides, significantly improving operational capacity, with the dry side capable of handling 40% of the inlet flow. Compared to the traditional shaft, the new design reduced shaft wall pressures and decreased the mean and standard deviation of pressure on typical baffles by 21% and 63%, respectively, therefore enhancing structural safety. Additionally, the new shaft achieved a 2%–12% higher energy dissipation rate than the traditional shaft across different flow rates. This study offers valuable insights for the design and optimization of drop shafts in deep tunnel drainage systems.

Effects of Remolding Water Content and Compaction Degree on the Dynamic Behavior of Compacted Clay Soils

The stable and safe operation of highway/railway lines is largely dependent on the dynamic behavior of subgrade fillings. Clay soils are widely used in subgrade construction and are compacted at different remolding water contents and compaction degrees, depending on the field conditions. As a result, their dynamic behaviors may vary, which have not been fully investigated until now. To clarify this aspect, a series of cyclic triaxial tests were carried out in this study with three typical remolding water contents (w = 19%, 24%, and 29%), corresponding to the optimum water content as well as its dry and wet sides, and two compaction degrees (Dc = 0.8 and 0.9), which were selected according to the field-testing data. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests were also conducted on typical samples to investigate the corresponding soil fabric variations. The findings indicate the following: (a) The soil fabric at the optimum remolding water content and its dry side was characterized by a clay aggregate assembly with a bimodal pore size distribution. In contrast, the soil fabric on the wet side of the optimum water content consisted of dispersed clay particles with a unimodal pore size distribution. (b) As the compaction degree increased, to ensure the optimum water content and its dry side, large pores were compressed to make them smaller, while small pores remained unchanged. Comparatively, all the pores on the wet side were compressed to make them smaller. (c) For each compaction degree, as the remolding water content increased, a non-monotonic changing pattern was identified for both the permanent strain and resilient modulus; the permanent strain first decreased and then increased, while, for the resilient modulus, an initial increasing trend and then a decreasing trend were identified. In addition, a larger changing rate of the permanent strain (resilient modulus) was observed on the dry side, indicating a larger effect of the remolding water content. (d) For each remolding water content, as the compaction degree increased, the permanent strain exhibited a decreasing trend, but an increasing trend was identified for the resilient modulus. Moreover, the rate of change in the permanent strain (resilient modulus) on the dry side of the optimum water content was larger than that on the wet side. In contrast, the minimum rate of change was identified at the optimum water content. The obtained results allowed for the effects of the remolding water content and compaction degree on the dynamic behavior to be analyzed, and they helped guide the construction and maintenance of the subgrade.

Laboratory studies of movement and microenvironment choices of engorged adult female Amblyomma maculatum (Acari: Ixodidae).

Microenvironmental factors affect ovipositional choices and behavior in ticks. In this study, engorged female Amblyomma maculatum Koch were released in an observation arena covered with garden soil. The arena was evenly split into wet and dry sides, each containing 5 different types of structures (totaling 10). Upon release, observations at particular time points were made over 2 days as to speed, distance, actual paths traveled, and ultimate site selection, presumably for oviposition. In addition, time-lapse videography was utilized to record the track of each individual tick. This scenario was replicated 3 times with different cohorts of ticks (n = 5 per replicate). Of the total 15 ticks released in the arena, all attained a final site selection by 24 h. These final sites were 7/15 (47%) edge of arena; 2/15 (13%) under bark; 2/15 (13%) open soil; 2/15 (13%) at or near release point; 1/15 (7%) tunnel with animal fur; and 1/15 (7%) tunnel with chicken feathers. At final site selection, 11/15 (73%) subsequently burrowed into the soil, 3 of which were completely buried. Time-lapse videography revealed that most ticks (80%) explored the arena in a "looping back" fashion. Overall, engorged Gulf Coast ticks moved at an average speed of 0.09 mm/s, and the total distance traversed by the ticks averaged 2.37 m.

Micro-destructive assessment of subgrade compaction quality using ultrasonic pulse velocity

The ultrasonic pulse velocity (UPV) correlates significantly with the density and pore size of subgrade filling materials. This research conducts numerous Proctor and UPV tests to examine how moisture and rock content affect compaction quality. The study measures the changes in UPV across dry density and compaction characteristics. The compacted specimens exhibit distinct microstructures and mechanical properties along the dry and wet sides of the compaction curve, primarily influenced by internal water molecules. The maximum dry density exhibits a positive correlation with the rock content, while the optimal moisture content demonstrates an inverse relationship. As the rock content increases, the relative error of UPV measurement rises. The UPV follows a hump-shaped pattern with the initial moisture content. Three intelligent models are established to forecast dry density. The measure of UPV and PSO-BP-NN model quickly assesses compaction quality.

Influence of desiccation during freeze-thaw cycles on volumetric shrinkage and tensile strength of compacted clayey soils

Tensile strength is a crucial mechanical property that governs the initiation and propagation of soil tensile cracks. With the global prevalence of warming effects and extreme climatic events, the recurrent freeze-thaw (F-T) cycles intensify the complex evolutions of soil pore structure and tensile strength in regions with widespread seasonal freezing or permafrost active layers. This study investigates the combined influence of F-T cycles and desiccation on the tensile strength of clayey soils. Specimens with varying compaction water contents (14.5%, 16.5%, and 18.5%) and dry densities (1.5 Mg/m3, 1.6 Mg/m3, and 1.7 Mg/m3) were prepared and subjected to cyclic F-T actions. A direct tensile test apparatus was utilized to measure tensile strength (σt) along the desiccation path. Additionally, the changes in void ratio (e) and suction (s) during F-T cycles were analyzed to understand the mechanism behind the changes in σt. Experimental results reveal that as the number of F-T cycles (N) increases, water content (w) declines at a decreasing rate and eventually stabilizes. With increasing N, the tensile displacement at failure and σt show a pattern of initially decreasing and subsequently rising, with the inflection point typically around 1.5%–2.0% lower than the compaction water content (w0). Under a few F-T cycles, soils compacted at the optimum water content and on the wet side exhibit higher void ratio and lower suction and σt compared with dry-side compacted soils. However, this trend reverses with further increasing N. In addition, σt increases as compaction dry density (ρd0) rises within all water content ranges, primarily attributed to the significant interparticle cohesion controlled by a dense pore structure. The variation of σt under F-T and associated desiccation is linked with the microstructural evolution characterized by aggregates, interaggregate pores and water-bridges. It is recommended to compact soils both on the dry side of the optimum water content and at the maximum dry density to enhance the freeze-thaw resistance of earth-works in seasonally frozen regions.

The role of soil moisture-temperature coupling for the 2018 Northern European heatwave in a subseasonal forecast

This study investigates the predictability of the 2018 Northern Europe heatwave using the GloSea5 forecast model from the perspective of land-atmosphere interactions. We focus on an inverse relationship wherein soil drying leads to increased temperatures and the model's ability to simulate this hypersensitivity in the soil moisture-temperature coupling on the dry side of a breakpoint defined as the soil moisture threshold below which land feedbacks nonlinearly amplify extreme heat. When evaluating forecast model performance in predicting this heatwave, we compare deterministic forecast scores (Hit Rate (HR) and True Skill Score (TSS)) for whether model Surface Soil Moisture (SSM) falls within the hypersensitive regime. GloSea5 exhibits enhanced prediction skill for the extreme heat event when the modelled soil moisture is within the hypersensitive regime. To understand the skill of the heatwave forecast for hit and missed cases of capturing SSM below the breakpoint, we first evaluate the climatological model performance for the water- and energy-limited processes, and then perform a comparison classified by whether SSM verifies on the dry side of the wilting point. The composite analysis demonstrates that the reproducibility of the breakpoint is tied to an improvement in climatological land coupling processes, mainly for classification in the water-limited coupling regime. Therefore, the results suggest that the process-based connection between soil moisture and temperature is a potential source for improving heatwave forecasts on subseasonal to seasonal (S2S) time scales.

Flow through and Volume Change Behavior of a Compacted Expansive Soil Amended with Natural Biopolymers

Natural biopolymers offer a sustainable alternative for improving soil behavior due to their inert nature, small dosage requirement, and applicability under ambient temperatures. This research evaluates the efficacy of natural biopolymers for ameliorating an expansive soil by using a 0.5% dosage of cationic chitosan, charge-neutral guar gum, and anionic xanthan gum during compaction. The results of laboratory investigations indicate that the flow through and volume change properties of the expansive soil were affected variably. The dual porosity, characterized by low air entry due to inter-aggregate pores (AEV1 of 4 kPa) and high air entry due to the clay matrix (AEV2 of 200 kPa) of the soil, was healed using chitosan and guar gum (AEV of 200 kPa) but was enhanced by the xanthan gum (AEV1 of 100 kPa and AEV2 of 200 kPa). The s-shaped swell–shrink path of the soil comprised structural (e from 1.23 to 1.11), normal (e from 1.11 to 0.6), and residual stages (e ranged from 0.6–0.43). This shape was converted into a j-shaped path through amendment using chitosan and guar gum, showing no structural volume change, with e from about 1.25 to 0.5, but was reverted to a more pronounced form by xanthan gum, with e from 1.5 to 1.32, 1.32 to 0.49, and 0.49 to 0.34 in the three stages, respectively. The consolidation behavior of the soil was largely unaffected by the addition of biopolymers such that the saturated hydraulic conductivity decreased from 10−9 m/s to 10−12 m/s over a void ratio decrease from 1.1 to 0.6. At a seating stress of 5 kPa, the swelling potential (7.8%) of the soil slightly decreased to 6.9% due to the addition of chitosan but increased to 9.4% and 12.2% with guar gum and xanthan gum, respectively. The use of chitosan and guar gum will allow the compaction of the investigated expansive soil on the dry side of optimum.

Micro-scale investigations on the mechanical properties of expansive soil subjected to freeze-thaw cycles

Freeze-thaw (FT) cycle is one of the most important factors contributing to the deterioration of expansive soil properties in seasonal frozen regions. In this study, a multiscale approach was used to investigate the impact of FT cycles on the volume deformation, mechanical properties and microstructure of expansive soil with different initial compaction states. FT cycle, unconfined compression, scanning electron microscopy and mercury intrusion porosimetry tests were carried out. The test results indicated that the volume deformation of the frozen expansive soil showed a completely opposite trend and varied in magnitude with different initial compaction states. The failure strength and elastic modulus of the expansive soil sample decreased significantly with increasing number of FT cycles. Under the impact of FT cycles, the porosity of the expansive soil increased significantly and the proportion of macropores grew. The growth of macropores and the generation of microcracks in the expansive soil were the main causes of FT damage. Besides, the FT damage variable was defined by the failure strength and had a good linear relationship with the soil porosity. In addition, the strength of loose and dense soil samples decreased significantly after FT cycles. It is found that an optimal compaction state may exist at around 95% compaction and the water content can be controlled on the dry side of the optimum water content, where FT cycles have minimal effect on the soil strength and microstructure. The study can provide guidelines for selecting the appropriate initial compaction and water content for the expansive soil projects in seasonal frozen regions.

Physical and mechanical characteristics of pyroclastic soil for the construction of embankments

In the framework of wider research activity on the physical and mechanical behaviour of volcanic soils, this paper reports the results of some laboratory tests on this type of geomaterial. The background of this research is the need for a construction company to possibly use pyroclastic material excavated along a tunnel profile to build railway embankments included in the design of a new High-Speed Train Line near the city of Naples, Italy. However, according to the standards of the National Italian Railways Company, pyroclastic soils cannot be employed as construction materials unless they are supported by a specific testing program demonstrating their good performance. The pyroclastic soil, which is widespread in the project area, is the product of Mt. Vesuvius volcanic activity. It is a coarse-graded soil that includes a significant percentage of non-plastic fines. They should be placed under compact conditions. The experimental campaign was aimed at identifying some physical characteristics that can synthesize the homogeneity of the pyroclastic deposit in terms of shearing resistance. The preliminary results obtained in terms of grading curves, modified Proctor compaction curves, and stress-strain curves from conventional drained triaxial tests are presented and discussed in this paper. The latter were executed on fully saturated specimens after compacting the soil at the optimum water content and on the dry and wet sides of the Proctor curve. The overall initial outcomes of the experimental campaign indicated that this material has acceptable characteristics and is suitable for the construction of railway embankments.

Effects of Dry Density and Moisture Content on the Kaolin–Brass Interfacial Shear Adhesion

Kaolin clay, with its consistent properties, fine particle size, high surface area, and extensive historical use, stands out as a reliable choice for laboratory research. This study aims to assess the interface shear adhesion behaviour between compacted clay and a metallic surface. For this purpose, a new testing approach was developed. The proposed method is simple, requires neither advanced equipment nor specialised test procedures, and, thus, represents an improvement over existing practices in this field. The experimental program focuses on determining the interface shear adhesion strength between reconstituted kaolin clay and a metallic surface. The kaolin clay testing specimens were dynamically compacted at various energy levels and moisture contents. The results indicate that the optimum moisture content is 30%, which provides the highest density to the sample and divides the compaction curve into dry and wet sides. Furthermore, the results demonstrate that the interface shear adhesion strength increases with the clay’s dry density. Conversely, there is a significant decrease in strength as the moisture content specifically rises on the wet side of the compaction curve. The adhesion behaviour was also attributed to matric suction, where high suction enhanced interfacial adhesion, while low suction weakened bonding and diminished adhesion. Additionally, this study presents a unique three-dimensional contour graph illustrating the combined effects of dry density and moisture content on the interfacial adhesion.

Fire activity and deforestation in Remote Oceanian islands caused by anthropogenic and climate interactions.

Remote islands in the Pacific Ocean (Oceania) experienced dramatic environmental transformations after initial human settlement in the past 3,000 yr. Here, human causality of this environmental degradation has been unquestioned and viewed as evidence of the inherent destructive tendencies of human societies in both archaeological and popular discourse. We use charcoal and stable carbon isotopes from deep soil cores to reconstruct the dynamics of fire activity and deforestation across the Sigatoka River valley on the leeward (dry) side of Viti Levu, Fiji. Fires and pyrogenic patches of grassland predated human settlement by millennia, but the magnitude of fire activity and landscape transformation accelerated with the establishment and expansion of swidden agriculture. Regional comparisons with previous studies in Fiji and elsewhere in Remote Oceania settled between 3,200 and 2,900 yr BP reveal a similar pattern of pre- and post-settlement fire activity and landscape change. Pre-settlement fires generally corresponded to droughts, probably driven by El Niño, often correlating with drought-driven wildfires elsewhere in the region. Post-settlement, charcoal and C4 grasses increased dramatically, but nearly all major peaks in charcoal and grasses corresponded to increased El Niño activity. This indicates that fire activity and deforestation were a product of the interaction between swidden agriculture and climate rather than land use alone.

ABA is required for differential cell wall acidification associated with root hydrotropic bending in tomato.

Hydrotropism is an important adaptation of plant roots to the uneven distribution of water, with current research mainly focused on Arabidopsis thaliana. To examine hydrotropism in tomato (Solanum lycopersicum) primary roots, we used RNA sequencing to determine gene expression of root tips (apical 5 mm) on dry and wet sides of hydrostimulated roots grown on agar plates. Hydrostimulation enhances cell division and expansion on the dry side compared with the wet side of the root tip. In hydrostimulated roots, the abscisic acid (ABA) biosynthesis gene ABA4 was induced more on the dry than the wet side of root tips. The ABA biosynthesis inhibitor Fluridone and the ABA-deficient mutant notabilis (not) significantly decreased hydrotropic curvature. Wild-type, but not the ABA biosynthesis mutant not, root tips showed asymmetric H+ efflux, with greater efflux on the dry than on the wet side of root tips. Thus, ABA mediates asymmetric H+ efflux, allowing the root to bend towards the wet side to take up more water.

Spatially coherent variability in modern orographic precipitation produces asymmetric paleo-glacier extents in flowline models: Olympic Mountains, USA

Abstract. Glaciers are sensitive to temporal climate variability. Glacier sensitivity to spatial variability in climate has been much less studied. The Olympic Mountains of Washington state, USA, experience a pronounced orographic precipitation gradient, with modern annual precipitation ranging between ∼6500 and ∼500 mm water equivalent. In the Quinault valley, on the wet side of the range, a glacier extended onto the coastal plain, reaching a maximum position during the Early Wisconsin glaciation. On the dry side of the range, in the Elwha valley, there is no evidence of a large paleo-glacier during the Wisconsin glaciation. We hypothesize that asymmetry in the past glacier extent was driven by spatial variability in precipitation. To evaluate this hypothesis, we constrain the past precipitation gradient and model the glacier extent. We explore variability in observed and modeled precipitation gradients over timescales from 6 h to ∼100 yr. Across three datasets, basin-averaged precipitation in the Elwha is 54 % of that in the Quinault. Our analysis overwhelmingly indicates spatially coherent variability in precipitation across the peninsula. We conclude that the past precipitation gradient was likely similar to the modern gradient. We use a one-dimensional glacier flowline model, driven by sea level summer temperature and annual precipitation to approximate the glacier extent in the Quinault and Elwha valleys. We find several equilibrium states for the Quinault glacier at the mapped maximum position within paleoclimate constraints for cooling and drying, relative to present-day conditions. Assuming stable precipitation gradients, we model the Elwha glacier extent for the climates of these equilibria. At the warm end of the paleoclimate constraint (July average sea level temperature of 10.5 ∘C), a small valley glacier occurs in the high headwaters of the Elwha valley. Yet, for the cooler end of the allowable paleoclimate (July average sea level temperature of 7 ∘C), the Elwha glacier advances to a narrow notch in the valley, thickens, and rapidly extends far beyond the likely true maximum extent. Therefore, we suggest that the Early Wisconsin period was more likely to have been relatively warm because our models of the glacial extent are consistent with the past record of glaciation in both the Quinault valley and Elwha valley for warm conditions but inconsistent for cooler conditions. Alternatively, spatially variable drivers of ablation, including differences in cloudiness, could have contributed to past asymmetry in the glacier extent. Future research to constrain past precipitation gradients and evaluate their impact on glacier dynamics is needed to better interpret the climatic significance of past glaciation and to predict the future response of glaciers to climate change.