Dry Layer Research Articles

The water vapor distribution profile in dry soil layer during evaporating with high spatial resolution monitored by distributed fibre-optic sensing technology

The dry soil layer (DSL) typically forms on the surface of sandy soils during the evaporation process, with water in the DSL moving solely as vapor. Understanding the DSL thickness and its water vapor distribution is crucial for accurately estimating soil water flux, improving evaporation mechanisms, and enhancing ecological conservation efforts. This study employed distributed fibre-optic sensing (DFOS) technology to achieve high spatial resolution measurements (up to 1 mm) of the water vapor distribution within the DSL. We measured soil water vapor profiles in a sand column subjected to evaporation over 24 days using a 60 cm long relative humidity sensing probe and an optical frequency domain reflection (OFDR) interrogator. We effectively captured the downward migration of the evaporating surface from the sand surface and quantified the inhibitory effect of DSL thickness on evaporation using a logarithmic function. Additionally, we identified a linear distribution of water vapor with depth in the DSL. Our findings offer novel insights into the role of DSL in the hydrological behaviour of unsaturated soils and demonstrate the potential of our approach for investigating dynamic changes in in-situ DSLs, particularly in arid and semi-arid regions.

Insight into the seismic response of gravity retaining walls

An extensive study of gravity walls subjected to strong seismic excitation is presented, exploring the role of parameters such as the width of wall, the type of excitation (idealised wavelets or recorded accelerograms), the peak ground acceleration (PGA), the dominant period (TP) of the wavelets, the accelerogram’s polarity and the coefficient of friction of the wall–soil interface. The retaining and foundation soil consists of dry sand layers modeled by a refined constitutive model. Appropriate interface elements, allowing separation and sliding, model the wall–soil interface. Results are presented mainly in terms of time-histories and dimensionless soil pressure distributions. Both horizontal and vertical seismic soil pressures are explored and compared with the classical Mononobe-Okabe–type and Rankine–type pseudostatic analytical solutions. It is shown that reduced acceleration coefficients must be input in such solutions to obtain reasonable results.

Field investigation of soil moisture profile in the seedbeds of clayey paddy fields composed of large clods (aggregates)

ABSTRACT Unstable germination and emergence of upland crops in clayey paddy fields is a pressing issue. As tillage leads to the formation of large clods measuring a few centimeters, the soil moisture content in the seedbed markedly decreases, potentially inhibiting germination of seeds. Although the effect of the clod size on the soil moisture profile was confirmed experimentally, the validity of this effect has not been tested in the field. In this study, we aimed to clarify the effect of clod size on the moisture profile and water balance in the seedbeds of clayey paddy field. We developed an apparatus for measuring soil moisture content in the soil layer with clods. This apparatus used a laser displacement sensor and large transparent plate horizontally fixed above the soil surface. Temporal changes in the soil moisture profile (0–10 cm depth) and evaporation rate of clayey paddy fields with different clod sizes were monitored during the sowing period of soybeans. We found that the larger the mean clod diameter (MCD), the greater the decrease in soil moisture content near the soil surface. In addition, soil moisture loss at the sowing depth (5 cm) was positively correlated with MCD. In terms of the water balance, the estimated upward water flux at a depth of 5 cm was less than 1 mm d−1 across all the plots and periods. By contrast, the estimated ratio of the apparent to molecular diffusion coefficient of water vapor in the dry soil layer of clayey paddy field with an MCD of 2.5 and 1.8 cm were 5.1 and 2.0, respectively. These results suggest that more significant soil moisture loss causing reduction of germination and emergence rate can occur in a clayey paddy field with large clods, likely owing to the increased enhancement of water vapor movement. To increase the germination and emergence rate, therefore, a numerical model that can evaluate the moisture profile of soil layer with clods should be developed and the sowing depth should be optimized based on the MCD.

The Turkana Jet Diurnal Cycle in Observations and Reanalysis

Abstract The Turkana jet is an equatorial low-level jet (LLJ) in East Africa. The jet influences both flooding and droughts, and powers Africa’s largest wind farm. Much of what we know about the jet, including the characteristics of its diurnal cycle, derives from reanalysis simulations that are not constrained by radiosonde observations in the region. Here, we report the characteristics of the Turkana jet with data from a field campaign during March–April 2021: The Radiosonde Investigation for the Turkana Jet (RIFTJet). The southeasterly jet forms on average at 380 m above the surface, with mean speeds of 15.0 m s−1. The strongest low-level winds are during the night and early morning from 0300 to 0600 LT (>16 m s−1). The average wind profile retains a characteristic low-level jet structure throughout the day, with the low-level wind maximum weakening to a minimum of 10.9 m s−1 at 1500 LT. There is significant shear, of up to 1.5 m s−1 (100 m)−1 maintained through the 1000 m above the wind maximum. The diurnal cycle of the jet is associated with the nocturnal strengthening and lowering of elevated subsidence inversions, which form above the jet. Reanalysis simulations (ERA5 and MERRA-2) do not capture the daytime persistence of the jet and underestimate the speed of the jet throughout the diurnal cycle. The largest absolute errors of over 4.5 m s−1 (−35%) occur at 0900 LT. The reanalyses also fail to simulate the elevated subsidence inversions above the jet and associated dry layer in the lower troposphere.

Grass (Poa annua L.) cover for eight years as an effective strategy for recovering soil moisture

Deep soil desiccation has become a major obstacle to restoring vegetation in the Loess Plateau region of China. The restoration of deep soil water plays an important role in ecosystem health. In the present study, we compared the effects on moisture variations in deep dry soil of grass cover and clean tillage treatments based on in-situ soil column monitoring for eight years. The results showed that the dry soil layers could temporarily disappear and reappear again with rainfall under clean tillage. However, grass cover effectively increased the deep soil moisture. Grass primarily consumed soil moisture from the shallow layer (0–2 m), and the total amount of water consumed during the whole growth period was less than the annual rainfall in dry years. The average soil desiccation index decreased by 24.20 % and the deep soil water moisture (2–10 m) recovered from 7.5 % to 12.8 % after eight years, with an annual average recovery of 0.66 %. Thus, it would take half a year to recover to the stable field capacity and 14 years to reach the field capacity. Recovery of the soil moisture also depended on the rainfall supply. We found that precipitation had an obvious lagged effect of approximately two years on the supply of deep soil moisture. Our findings contribute to understanding how to alleviate dry soil layer, with potentially helpful implications for the ecological health in arid and semiarid regions.

Sustainable forest development in the face of global warming: Optimizing Robinia pseudoacacia L. stands to alleviate soil moisture depletion

To foster sustainable forest development amid global warming, it is imperative to enhance the quality of existing forest stands while avoiding excessive depletion of soil moisture. This study established 24 Robinia pseudoacacia L. standard plots (40 × 40 m2) in the Caijiachuan watershed, located in the gully region of the Loess Plateau, Shanxi Province, China, to monitor soil moisture content from 2007 to 2021. Additionally, the study examined the influence of 19 ecological factors, including climate, topography, and stand characteristics, on soil moisture. The findings indicated a sustained decline in soil moisture storage across the 0–200 cm soil profile, with significant depletion at 0–140 cm. The soil moisture content at depths of 80–200 cm was critically low, resulting in a “dry soil layer” during years with low precipitation. Climatic factors (average annual temperature and annual precipitation) and stand factors (uniform angle index, stand density, litter thickness, and Simpson diversity index of the shrubs) emerged as dominant factors impacting soil moisture variations. An increase in average annual temperature due to global warming, compounded by suboptimal stand density, primarily drove soil moisture depletion. Using a multivariate optimization equation to model the relationship between dominant factors and soil moisture storage, this study recommends a dynamic stand management strategy. This strategy involves selective thinning or replanting of Robinia pseudoacacia L. trees, targeting a gradual reduction in optimal stand density from 1500 to 1000 plants·ha−1 over the next two decades. Additionally, transitioning stand spatial arrangements from uniform or clustered to random distributions, maintaining ideal litter thickness (2.43–2.47 cm), and enhancing shrub diversity are advisable. Such measures can alleviate soil moisture deficits in Robinia pseudoacacia L. stands attributable to global warming, thereby promoting the Loess Plateau's sustainable forestry advancement.

Laboratory observations for examining estimates of soil dry surface layer thickness with parsimonious models

ABSTRACT Soil dry surface layer (DSL) thickness is often considered a key parameter for land surface resistance to gas exchange. Commonly used, simple models for DSL thickness are typically empirical in nature and based on limited observational evidence. Laboratory experiments were performed to test soil condition and boundary effects on DSL formation. DSL thickness was analyzed in soil columns with varying texture, initial water content, and potential evaporation rate. DSLs formed to greater depth in fine-textured compared to coarse-textured soils, when beginning from similar initial water content. Based on experiments, we compared a simple but physically-based mass balance DSL model to an empirical DSL model from the literature. The mass balance model performed better than the empirical relative-wetness-based model, and is similar in structure to the current DSL parameterization in the Community Land Model. Results suggest soil resistance parameterizations can be improved by employing simple, but texture-dependent, physically-based DSL formulations.

Pre-Support Method for Horizontal Overlapping Jet Grouting Columns for Very-Large Cross-Section Tunnels in Dry Silty Sand Strata: A Case Study

The Shangbai Tunnel on the Daxi Passenger Dedicated Line passes through unsaturated dry silty sand strata which is prone to sand leakage and gushing after disturbance, posing a significant threat to the safety and progress of construction work. Using the Shangbai Tunnel project as a case study, we conduct laboratory experiments to determine the physical and mechanical properties of dry silty sand layers and analyze the limitations of advanced large pipe shed pre-support and small pipe grouting pre-support structures. The objective is to evaluate the feasibility and reveal the mechanism of horizontal rotary jet grouting for column formation and pre-support. The physical and mechanical properties of the consolidated body of the overlapping columns are evaluated. Three pre-reinforcement schemes using overlapping columns for tunnels crossing different subsurface profiles are proposed. Experiments are conducted to assess the physical and mechanical properties of the overlapping columns, and on-site monitoring and analysis of the tunnel arch settlement and stress changes are performed. The results indicate that the proposed method for creating overlapping columns ensures the stability of the working face, controls arch settlement, and is cost-effective. Our study summarizes the findings from the data and information for the construction of similar projects.

Воздействие криогенных сред и струйного горения на эпоксидные интумесцентные композиции, предназначенные для защиты оборудования и строительных конструкций нефтегазового комплекса

The article discusses the studies of epoxy intumescent fire-protective coating of steel structures impacted by cryogenic media and jet fire, in accordance with the requirements of the methodology developed at the Orenburg branch of the Federal State Autonomous Educational Institution of Higher Education VNIIPO EMERCOM of Russia, and harmonized with the international standards ISO 22899-1:2021, ISO 20088-1:2016, and ISO 20088-3. The tests have been conducted with the epoxy fire- and cryogenic-protective intumescent composition «Plamkor-5» (produced by JSC Scientific and Production Holding «VMP», Yekaterinburg, Russia). According to the results of the test for resistance of a square-shaped sample with internal dimensions 1500×1500×500 mm and a central shelf made of 10 mm thick carbon steel coated with the fire-retardant composition «Plamkor-5» to cryogenic fluid spill, it has been established that the sample does not reach the critical temperature of minus 49 °C with an actual 22.37 mm dry layer thickness. The average sample temperature at the 60th minute of the test was minus 32.09 °C. The results of the test of a similar sample in order to determine the resistance of the fire-protective composition «Plamkor-5» to a jet fire with an actual 10,89 mm thickness of the protective dry layer have shown that the sample does not reach the critical temperature of 500 °С during 60-minute fire exposure, whereas the average temperature of the sample was only 37 % (184.84 ºС) of the temperature limit value. According to the results of the test for resistance of a steel column shape sample of I-section 25K2 coated with the fire-retardant composition «Plamkor-5» to spill under the pressure of the cryogenic liquid, it has been established that the sample does not reach the critical temperature of minus –49 °С with an actual 23.78 mm dry layer thickness, whereas the average temperature of the sample at the 60th minute of test was minus 48.38 °С. The obtained results are comparable with the effect of the best import analogs; therefore, «Plamkor-5»-based fire-protective coatings can be used for the design and development of fire protection of building structures, at the facilities of the oil and gas industry, in tunnel structures, and civil engineering.

Generative Convective Parametrization of a Dry Atmospheric Boundary Layer

AbstractTurbulence parametrizations will remain a necessary building block in kilometer‐scale Earth system models. In convective boundary layers, where the mean vertical gradients of conserved properties such as potential temperature and moisture are approximately zero, the standard ansatz which relates turbulent fluxes to mean vertical gradients via an eddy diffusivity has to be extended by mass‐flux parametrizations for the typically asymmetric up‐ and downdrafts in the atmospheric boundary layer. We present a parametrization for a dry and transiently growing convective boundary layer based on a generative adversarial network. The training and test data are obtained from three‐dimensional high‐resolution direct numerical simulations. The model incorporates the physics of self‐similar layer growth following from the classical mixed layer theory of Deardorff by a renormalization. This enhances the training data base of the generative machine learning algorithm and thus significantly improves the predicted statistics of the synthetically generated turbulence fields at different heights inside the boundary layer, above the surface layer. Differently to stochastic parametrizations, our model is able to predict the highly non‐Gaussian and transient statistics of buoyancy fluctuations, vertical velocity, and buoyancy flux at different heights thus also capturing the fastest thermals penetrating into the stabilized top region. The results of our generative algorithm agree with standard two‐equation mass‐flux schemes. The present parametrization provides additionally the granule‐type horizontal organization of the turbulent convection which cannot be obtained in any of the other model closures. Our proof of concept‐study also paves the way to efficient data‐driven convective parametrizations in other natural flows.

New insights into the parameterization of the dry surface layer and its hydrogeochemical mechanism: An experimental study

Knowledge of the parameterization of the dry surface layer (DSL) is essential for evaluating near-surface water flow and water balance in arid and semi-arid areas. Existing studies have parameterized DSL thickness and vapor flow as functions of the soil moisture content (SMC) in the surface layer to predict soil evaporation. However, hydrochemical processes related to DSL development have been ignored, including changes in hydrochemistry, the underlying hydrochemical mechanism, and the role of dissolved substances in the DSL development. Herein, we performed a series of soil evaporation experiments for 260 days and explored the factors influencing DSL development (e.g., soil texture, atmospheric temperature, SMC, solutes). Evaporation experiments were performed using silty loess, sandy loess, and fine sand with a 60-cm water table. Results showed that the cumulative evaporation of silty loess, sandy loess, and fine sand over the experimental period were 1,391.52, 460.10, and 185.53 mm, respectively, which determined by the maximum height of liquid flow continuity. The content of total dissolved solids (TDS) and major ions at the surface soil were significantly higher than the values at deep depths of 5‒55 cm, which largely depend on evaporative water loss. Evolutionary trends of chemical facies in sand media along the liquid water migration were from HCO3-Ca type to SO4·Cl-Na type. This was attributed to mineral dissolution at a depth of 5–55 cm and their transport with liquid water, resulting in the precipitation of salt crystals at the surface soil. Furthermore, a consolidated DSL with a thickness of 3.0–3.5 cm in the sandy loess and a loose DSL with a thickness of 1.5–2.0 cm in fine sand were observed at the end of the experiments. The accumulation of solutes at the surface leads to a reduction in effective porosity and the aggregation of soil particles during continuous drying, which facilitates the consolidation of DSL in sandy loess. This overestimated the DSL thickness, resulting in a difference between the experimental and predicted evaporation rates by Fick's law. Overall, these results highlight the limitations of considering DSL thickness as a function of SMC only, providing new insights into hydrochemical processes and dissolved solutes involving DSL parameterization during continuous soil drying.

Drying Kinetics and Quality Attributes of Solar-Dried Red Peppers: A Comparative Study with Traditional and Industrial Methods

Red pepper is a valuable ingredient known for its abundance of vitamins and antioxidants. But, it usually needs to be dried for longer preservation. Hence, this research is aimed at examining the drying kinetics and quality attributes of dried red peppers utilizing various solar drying methods, in comparison with traditional open sun drying (OSD) and industrial laboratory thin layer dryers (LTLD). Analysis parameters employed include determining moisture content, measuring color properties, evaluating antioxidant capacity, analyzing capsaicinoid content, and assessing microbial presence. The drying process took place in a sunny environment with fluctuations in temperature and relative humidity as evidence of the dynamic conditions experienced within the solar dryers. It was observed that the logarithmic model was the most accurate in predicting moisture ratio over time, estimating a drying time of 25 hours to achieve 10% moisture content. The result demonstrated that direct solar dryers (DSD), indirect solar dryers (ISD), and mix mode solar dryers (MMSD) methods showed moderate changes in color parameters, with average ΔL∗, Δa∗, and Δb∗ values of -5.08, -23.71, and -13.62, respectively. The average overall color difference (ΔE) for these methods was 27.96. In addition, after comparing it to the LTLD method, which showed the highest content of phenolic compounds at 47.89%, MMSD displayed a slightly lower content of 44.71%. Similarly, MMSD exhibited higher levels of DPPH radical scavenging activity and ferric reducing power, measuring at 44.22% and 1163.75 μmol Fe2+/L, respectively. The capsaicin content remained relatively consistent across all drying methods, with MMSD, DSD, and LTLD demonstrating similar levels of approximately 31 mg/g. Although MMSD had slightly higher mold and yeast counts compared to LTLD, ISD, and DSD, it remained lower than OSD (less than 0.56 log10cfu/g). Furthermore, MMSD showed a lower total microbial count in comparison to other drying methods. These findings suggest that MMSD shows promise as a drying technique for preserving the phenolic compounds and antioxidant activity of the dried product.

In situ study of the effect of endogenous and exogenous agents on color stability, hardness, and surface roughness of an elastomer for facial prostheses.

To evaluate in situ the influence of sweat, oil, sunscreen, and disinfectant solution on the color stability, hardness, and roughness of elastomer for facial prostheses. Standardized and intrinsically pigmented specimens remained in contact with human skin from the same person for 30days, considering exposures (n=36 per group), absent of exposition (Control, C); sweat and oiliness contact (SO); sweat and oiliness associated with sunscreen (SOS); 0.12% chlorhexidine digluconate immersion (CD0.12%); and all agents exposed (SOSCD). The main variables were color change (CIELab and National Standard Bureau system, NBS), Shore A hardness, and surface roughness, measured at baseline and 30days. Qualitative analyses were performed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The data were analyzed by Kruskal-Wallis tests (color) and two-way ANOVA (hardness and roughness) with Sidak post-test (α=0.05). CD0.12% (1.54±0.49) and SOSCD (2.10±1.03) had similar effects and caused the smallest color changes, considered mild and noticeable (NBS), respectively. SOS promoted the greatest color change (6.99±1.43, NBS: large) and hardness (17.97±0.56); SOS promoted intermediate roughness (3.48±1.05) between SOSCD (2.25±0.53), and two similar groups: C (4.46±0.95), and CD0.12% (4.39±1.26). The qualitative analysis showed an irregular, dense, dry, and whitish layer on the surface of the specimens exposed to sunscreen, which was reduced when in contact with 0.12% chlorhexidine digluconate. Endogenous and exogenous factors are capable of altering elastomer properties. The 0.12% chlorhexidine digluconate minimized the changes caused by sweat, oil, and sunscreen.

Increasing effect of biocrusts on evaporation is evidenced by simulating evaporation and diffusion experiments and water stable isotope analysis

Evaporation, one of the main components of the water and energy balance between soil and atmosphere, plays a key role in hydrological processes particularly in semi-arid and arid climate regions. As critical living organism communities inhabiting the soil-atmosphere boundary, biocrusts are capable of modifying near-surface soil properties and structure in drylands. However, the roles of biocrusts in mediating soil evaporation still remain greatly controversial, and the literature yet lacks in a systematic assessment. In this study, evaporation experiments were conducted under simulated isothermal and non-isothermal conditions for bare soil and three types of biocrusts (cyanobacterial, moss, and their mixture) sampled from a semi-arid climate region of the Chinese Loess Plateau. During the evaporation, soil temperature and moisture were measured at depths 2, 5, 10, and 15 cm for those biocrusts and bare soil. Their water vapor diffusion process and stable isotopic composition were also analyzed in the laboratory. We found that the measured evaporation yielded 4.9%, 17.5%, and 31.6% higher average evaporation rate for cyanobacterial, cyano-moss, and moss crusts, respectively, when compared to the bare soil. In comparison to bare soil, all types of biocrusts markedly reduced the rate of temperature rise, prolonged the duration of wetting time, and delayed the formation of dry surface layer. The largest regulating effects on soil temperature and moisture were found in the moss crusts instead of cyanobacterial or cyano-moss crusts. The increasing evaporation in biocrusts was attributed to their higher fine particle content, lower bulk density, and greater water holding capacity. Moreover, the water vapor diffusion rate and diffusivity of biocrusts were 18.2% and 16.4% higher than those of bare soil, respectively, which is attributable to the increased total porosity and better soil structure. Additionally, the isotopic composition of soil water (0–50 cm) in bare soil and moss crusts was distributed below the local meteoric water line. The mean δ18O and δ2H in soil water gradually decreased with increasing soil depth, and the moss crusts were more isotopically enriched than bare soil. Based on the enhanced soil evaporation rate, improved vapor diffusivity, and enriched isotopic composition of biocrusts in contrast to bare soil, we conclude that biocrusts exacerbate vapor transport and evaporative loss, and consequently they are crucial surface cover in rebalancing surface ecohydrological and biochemical processes in global drylands. These findings improve our understanding of the complexity of dryland hydrology, and a full consideration should be given in future biocrust studies.

Physicochemical and Rheological Characterization of a Novel Manna Exudate from Alhagi pseudalhagi (Iranian Tarangabin)

Tarangabin manna (TM) is a resinous substance having a yellowish sticky character with a reasonably sweet taste. It is largely collected in Iran and Afghanistan. This study for the first time presents a comprehensive investigation of the techno-functional, rheological, and interfacial characteristics of water-soluble components for TM. The composition analysis revealed protein, moisture, fat, ash, and carbohydrate contents of 1.58, 2.98, 0.51, 2.04, and 92.90%, respectively. The effects of TM concentration on the physicochemical, structural, rheological, interfacial, emulsion, and foaming ability and stability were evaluated. X-ray diffraction analysis showed an amorphous structure for the purified sample and a crystalline structure for the raw sample. TM solutions exhibited Newtonian behavior, with the apparent viscosity decreasing as temperature increased, fitting well with the Arrhenius model. The TM solutions exhibited weak viscoelastic properties, primarily demonstrating a dominant viscous character. The surface tension and interfacial tension of the TM solution prepared at a concentration of 50% were measured at 45.23 mN/m and 7.74 mN/m, respectively. The contact angle of the dry thin layer of TM was determined to be 31.74°. Remarkably, the TM solution at a concentration of 50% exhibited the highest foaming ability (76.80%), foaming stability (91.92%), and emulsifying activity index (24.53%). The findings, coupled with TM appropriate foaming ability and stability, sweetness, and characteristic flavor, suggest that TM holds potential as a special food ingredient.

Dynamic modeling of minimum mass of pore-gas for triggering landslide in stable gentle soil slope

This paper presents a dynamic modeling method to test and examine the minimum mass of pressurized pore-gas for triggering landslides in stable gentle soil slopes. A stable gentle soil slope model is constructed with a dry cement powder core, a saturated clay middle layer, and a dry sand upper layer. The test injects H2O2 solution into the cement core to produce new pore-gas. The model test includes three identical H2O2 injections. The small mass of generated oxygen gas (0.07% of slope soil mass and landslide body) from the first injection can build sufficient pore-gas pressure to cause soil upheaval and slide. Meanwhile, despite the first injection causing leak paths in the clay layer, the generated small mass of gas from the second and third injections can further trigger the landslide. A dynamic theoretical analysis of the slope failure is carried out and the required minimum pore-gas pressure for the landslide is calculated. The mass and pressure of generated gas in the model test are also estimated based on the calibration test for oxygen generation from H2O2 solution in cement powder. The results indicate that the minimum mass of the generated gas for triggering the landslide is 2 ppm to 0.07% of the landslide body. Furthermore, the small mass of gas can provide sufficient pressure to cause soil upheaval and soil sliding in dynamic analysis.

Lower Atmospheric Ducts over the South China Sea Related to the Monsoon, Atmospheric, and Ocean Conditions Based on ECMWF Reanalysis Data

Abstract Atmospheric ducting is a highly refractive propagation condition that frequently occurs at sea and significantly impacts radar and communication equipment. This paper analyzes the spatiotemporal distribution of lower atmospheric ducts (LAD) in the South China Sea (SCS) and the variation of their occurrence rate with the monsoon by using reanalysis data from the ECMWF from 1980 to 2022. Additionally, the study discusses the relationship between ducting occurrences and atmospheric and oceanic conditions. The results indicate that wind dynamics in the SCS significantly impact ducting incidents. During the high-incidence period of LAD, humidity-gradient-constructed ducts are the primary mechanism. Before the onset of the monsoon, the mountains in the western part of Luzon Island obstruct the easterly wind, resulting in high temperatures and strong evaporation along the western coast of the mountains. Meanwhile, low temperatures and humidity prevail in the eastern part of the mountains, and they lead to a stratified atmosphere characterized by dry and cold upper layers and warm and humid lower layers in the western part of Luzon Island, which causes a distinct decrease in humidity with height. After the onset of the monsoon, the air from the Indochina Peninsula to the ocean is dry and cold, but the high-altitude area blocks it. This weakens the horizontal mobility of the low-level humid atmosphere over the sea, resulting in atmospheric stratification in the eastern coastal area of the Indochina Peninsula. This stratification leads to dry and cold upper layers and warm and humid lower layers. Significance Statement Atmospheric ducting is a superrefractive propagation condition that frequently occurs at sea and has a significant impact on radar and communication equipment and is related to large-scale or medium- and small-scale atmospheric stratification. The distribution of land and sea around the South China Sea (SCS) and the monsoon are important factors affecting the existence of atmospheric ducts in this region. Many scholars have studied the mechanism of atmospheric ducts in local areas based on observation data (or reanalysis data). The literature on the atmospheric ducts in the SCS mainly focuses on the spatial and temporal statistical distribution of seasons, months, and days, and gives the spatial and temporal distribution characteristics of the region within the statistical time, emphasizing the important influence of the monsoon on the duct, but there is no relevant research on the reasons for the existence of the specific relationship and its temporal and spatial distribution characteristics. The manuscript analyzes the temporal and spatial distribution of lower atmospheric ducts in the SCS and the variation of their occurrence rate with the monsoon, quantifies the contributions of temperature, humidity, and air pressure to the ducting occurrence, meanwhile discussing the ducting occurrence relation with atmospheric and oceanic conditions. In the end, we demonstrate that the development of high-incidence areas for SCS ducts prior to and following the onset of monsoon season is connected to factors such as wind patterns, seawater evaporation, and topography. Furthermore, unstable vertical transport of water vapor in both the atmosphere and oceanic conditions plays a crucial role in facilitating the creation of humidity-type ducts.

Impact of mix proportions on particle bed 3D printed concrete properties

Additive manufacturing of concrete using particle-bed printing by selective binder activation is examined. This technique consists of spreading of a dry powder layer onto the build platform, selective liquid deposition to form a geometry on the layer, and repetition until complete. This enables the manufacturing of complex structural elements and eliminates the need of support structures during fabrication. A commercial liquid-jet 3D printer was modified and used along with a dry mixture of sand, cement, and a specially formulated aqueous solvent. The influence of the proportions of the dry powders, water/cement ratio, type and gradation of sand, type of cements, and additives on the strength and dimensional inaccuracy is examined. The results indicate that the CSA cement with round grain silica sand provides the best mechanical performance and surface quality. The use of a sand/cement ratio of 2.0, printed water/cement ratio of 0.151, and sand fineness modulus of 2.751 produced the best mechanical strength and dimensional accuracy. The results can be used to guide the design for this innovative 3D printing approach for concrete structural elements.

Simulation of Diurnal Evolution of Evaporation Zone during Soil Drying after Rainfall

To better understand processes involved in the evaporative drying of the soil, simulations on the dynamics of the evaporation zone, condensation zone, and dry surface layer (DSL) were conducted during a 10-day drying event under diurnal atmospheric conditions. Simulated water contents and soil temperatures matched well with the measured data in the lysimeter. Surface evaporation predominantly occurred during the early period each day, while subsurface evaporation dominated during the remaining part of the day. The evaporation zone presented a distinctly diurnal pattern, moving toward the deeper soil layer during the daytime and back toward the soil surface during the nighttime. The DSL and condensation zone, located immediately above and below the evaporation zone, respectively, also presented diurnal patterns following those of the evaporation zone. As soil drying progressed, both the position of the evaporation zone within the profile and the DSL width exhibited an overall increasing trend, reaching about 4.9 mm by the end of the study period. The occurrence of condensation zones was limited to the daytime when there was a downward surface temperature gradient present. Diurnal patterns observed in both evaporation zones and DSL could potentially be determined by quantifying changes in the near-surface profile’s soil water content, relative humidity, pressure head, and vapor density.

Comparative research on the pipe-soil frictional resistances of circular and rectangular pipe sections during trenchless pipe jacking.

Pipe jacking is a trenchless construction method to achieve forward tunneling and efficient construction of underground structure simultaneously without extensive surface excavation. In the process of pipe jacking construction, the jacking force provided by the hydraulic jacking equipment must overcome the frontal resistance of the cutter head and the frictional resistance between the pipe sections and formation at the same time. In particular, the pipe-soil frictional resistance increases with the increases of jacking distance, buried depth, pipe diameter and the complexity of jacking trajectory. Therefore, it is very important to correctly estimate jacking force in trenchless jacking engineering practice for the smooth implementation of pipe jacking, operation risk and comprehensive cost control. Firstly, the stress states of jacking circular and rectangular pipe sections in the soil are analyzed, and the key influencing factors of their pipe-soil frictional resistance are obtained respectively. Then, the pipe-soil frictional resistance of jacking the circular and rectangular pipe sections with the same external surface area in the dry sandy soil and coal granular layer are tested separately by using the self-developed multifunctional experimental apparatus during trenchless pipe jacking. The results show that the pipe-soil frictional resistances of jacking circular and rectangular pipe sections in the coal granular layer are always smaller than that in the sandy soil under the same experimental conditions, and the corresponding fitting calculation equation of pipe-soil frictional resistances are obtained respectively. Meanwhile, the modified calculation methods of the above pipe-soil frictional resistances are proposed respectively based on the relationship between the lateral pressure coefficient K and the buried depth of pipe section H. Moreover, the disturbed area of soil in the upper part of jacking circular pipe section presents an arc distribution, while the disturbed area of soil in the upper part of jacking rectangular pipe section presents a slightly concave distribution. Due to the different disturbance conditions of soil around the pipe section, the lateral pressure coefficient K should be corrected in the calculation equations of pipe-soil frictional resistance of jacking circular and rectangular pipe sections based on the discrete element numerical simulation analysis by EDEM software. Finally, the pipe-soil frictional resistances obtained by different methods in the sandy soil are compared and analyzed. The calculated values of the modified theoretical calculation method are very close to the experimental test values, while the other methods are smaller than the experimental test values, which makes the rationality of the modified theoretical calculation method of pipe-soil frictional resistance is verified, and some suggestions are also put forward for the value of some coefficients in the relevant empirical estimation equations. The above research achievements systematically compared the states of pipe-soil frictional resistances of jacking circular and rectangular pipe sections based on different research methods, especially for the correct evaluation of jacking force during trenchless pipe jacking, they could provide some valuable references and effective guidance for the subsequent research, engineering practice and further development of trenchless pipe jacking technology.