Influence Of Soil Moisture Content Research Articles

Nitrous Oxide Emissions during Cultivation and Fallow Periods from Rice Paddy Soil under Urea Fertilization

Rice cultivation serves as a significant anthropogenic source of methane (CH4) and nitrous oxide (N2O). Although N2O emissions remain relatively small compared to CH4 emissions, they are remarkably affected by nitrogen-fertilized soil conditions during rice cultivation. While numerous studies have investigated nitrous oxide emissions in response to nitrogen fertilization, existing research assessing nitrous oxide emissions based on nitrogen fertilizer levels has often been limited to cultivation periods. Therefore, there is a need for comprehensive analyses covering the entire year, including the dry periods, to address nitrous oxide emissions as an important source throughout the entire agricultural cycle. In this case study, we investigated the characteristics of N2O emissions in a central region of South Korea, where a single rice-cropping cycle occurs annually over a span of three whole years, from May 2020 to May 2023. We investigated the impact of variations in temperature and soil moisture on N2O emissions during rice cultivation and fallow periods. In this context, we attempted to discover the complex dynamics of N2O emissions by comparing longer fallow periods with the rice cultivation periods and extended non-dry periods with irrigated periods. We discovered that the greater contribution of cumulative N2O emissions during the fallow period made a much greater contribution (up to approximately 90%) to the whole-year N2O emissions than those during the rice cultivation period. During the fallow period from rice harvest to rice planting in the following year, variations in N2O emissions were associated with high-flux events after rainy periods on dry soils. This highlights the considerable influence of soil moisture content and weather conditions on N2O emissions during the fallow period. This affects high emission events, which in turn significantly impact the cumulative emissions over the entire period. We underscore that assessing N2O emissions solely based on the rice cultivation period would underestimate annual emissions. To prevent underestimation of N2O emissions, periodic gas collection throughout a year covering both rice cultivation and fallow phases is required in alignment with the monitoring of different temperature and soil moisture conditions. We captured statistical differences in cumulative N2O emissions due to nitrogen fertilization treatments across the three years. However, no significant difference was observed in the three-year average emissions among the different (one, one-and-a-half, and double) nitrogen fertilization treatments, with the exception of the control treatment (no fertilization). Based on the findings, we recommend at least three whole-year evaluations to ensure the estimation accuracy of N2O emissions under different nitrogen fertilization conditions. The findings from this study could help prepare the further revision or refinement of N2O emission factors from rice cultivation in the national greenhouse gas inventories defined by the inter-governmental panel on climate change (IPCC).

Cyclic stress–strain characteristics of red clay treated with permeable water-soluble polyurethane

Red clay, a globally distributed type of chemical weathering soil, is commonly utilized as a road base in road infrastructure. However, due to its susceptibility to water and vibrations, it is prone to settlement and formation of potholes during operation, consequently leading to damage in the pavement structure. This paper employs a dynamic triaxial apparatus to simulate realistic traffic loads and investigates the dynamic properties of red clays treated with permeable water-soluble polyurethane (PSP). Additionally, a series of microscopic tests are conducted to elucidate the microstructural mechanisms of using PSP for improving red clay, as well as the microscopic deformation mechanisms of the PSP-treated red clay (PSP clay) under cyclic loading. The results provide detailed insights into the influence of soil moisture content and PSP content on key parameters, including the resilient modulus, damping ratio, permanent deformation, and strength of PSP clay after repeated loading. Moreover, the overall performance of PSP clay is evaluated under varying loading amplitudes and confining pressures. These results are complemented and interpreted in conjunction with the findings from the microscopic tests. The findings reveal that the inclusion of PSP improves the strength of the soil skeleton by enveloping and interlocking with the clay particles. Furthermore, it is observed that the engineering properties of high-moisture-content red clay soils can be significantly improved with low levels of PSP. Under specific conditions, repeated loading further compact the PSP clays, thereby enhancing their mechanical properties. The experimental findings presented in this study are of utmost importance for the improvement and application of red clays through the utilization of rapid solutions, such as PSP.

Influence of temperature and soil moisture on the toxic potential of clothianidin to collembolan Folsomia candida in a tropical field soil.

Climate change can alter the toxic effects of pesticides on soil invertebrates. However, the nature and magnitude of the influence of climatic factors on clothianidin impacts in tropical soils are still unknown. The influence of increasing atmospheric temperature and the reduction in soil moisture on the toxicity and risk of clothianidin (seed dressing formulation Inside FS®) were assessed through chronic toxicity tests with collembolans Folsomia candida in a tropical field soil (Entisol). The risk of clothianidin for collembolans was estimated using the Toxicity-Exposure Ratio (TER) approach. Organisms were exposed to increasing clothianidin concentrations at 20, 25 and 27 °C in combination with two soil moisture conditions (30 and 60% of the maximum water holding capacity-WHC). The effect of temperature and soil moisture content on clothianidin toxicity was verified through the number of F. candida juveniles generated after 28 days of exposure to the spiked soil. The toxicities estimated at 25 °C (EC50_30%WHC = 0.014 mg kg-1; EC50_60%WHC = 0.010 mg kg-1) and 27 °C (EC50_30%WHC = 0.006 mg kg-1; EC50_60%WHC = 0.007 mg kg-1) were 2.9-3.0-fold (25 °C) and 4.3-6.7-fold (27 °C) higher than those found at 20 °C (EC50_30%WHC = 0.040 mg kg-1; EC50_60%WHC = 0.030 mg kg-1), indicating that clothianidin toxicity increases with temperature. No clear influence of soil moisture content on clothianidin toxicity could be observed once the EC50 values estimated at 30% and 60% WHC, within the same temperature, did not significantly differ. A significant risk was detected in all temperatures and soil moisture scenarios studied, and the TER values indicate that the risk can increase with increasing temperatures. Our results revealed that temperature could overlap with soil moisture in regulating clothianidin toxicity and reinforce the importance of including climatic factors in the prospective risk assessment of pesticides.

Role of climatic factors in the toxicity of fipronil toward earthworms in two tropical soils: effects of increased temperature and reduced soil moisture content.

The aim of this study was to assess the effect of temperature on the toxicity of fipronil toward earthworms (Eisenia andrei) in two Brazilian soils (Entisol and Oxisol) with contrasting textures. In the case of Entisol, the influence of soil moisture content on toxicity was also investigated. Earthworms were exposed for 56days to soils spiked with increasing concentrations of fipronil (8.95, 19.48, 38.22, 155.61, and 237.81mgkg-1 for Entisol; 12.99, 27.94, 48.42, 204.67, and 374.29mgkg-1 for Oxisol) under scenarios with different combinations of temperature (20, 25 and 27°C) and soil moisture content (60 and 30% of water holding capacity (WHC) for Entisol and 60% WHC for Oxisol). The number of juveniles produced was taken as the endpoint, and a risk assessment was performed based on the hazard quotient (HQ). In Entisol, at 60% WHC the fipronil toxicity decreased at 27°C compared with the other temperatures tested (EC50 = 52.58, 48.48, and 110mgkg-1 for 20, 25, and 27°C, respectively). In the case of Oxisol at 60% WHC, the fipronil toxicity increased at 27°C compared with other temperatures (EC50 = 277.57, 312.87, and 39.89mgkg-1 at 20, 25, and 27°C, respectively). An increase in fipronil toxicity was also observed with a decrease in soil moisture content in Entisol at 27°C (EC50 = 27.95 and 110mgkg-1 for 30% and 60% WHC, respectively). The risk of fipronil was only significant at 27°C in Entisol and Oxisol with water contents of 30% and 60% WHC, respectively, revealing that higher temperatures are able to increase the risk of fipronil toxicity toward earthworms depending on soil type and soil moisture content. The results reported herein show that soil properties associated with climatic shifts could enhance the ecotoxicological effects and risk of fipronil for earthworms, depending on the type of soil.

The Influence of Internal Erosion in Earthen Dams on the Potential Difference Response to Applied Voltage

Internal erosion is widely perceived as contributing to the failure of earthen dams. To reduce the failure risk, timely monitoring of internal erosion is an effective method in observing their internal structure evolution. A set of earthen dam model experiments were conducted. Under an applied voltage, the response potential differences (PD) at the slope of the dam models were collected before and after the impoundment of the upstream reservoir. The discrepancy among the four dam models, the influence of soil moisture content on PD, and the impact of internal erosion on PD were studied. The results show that it is acceptable to employ different dam models to simulate the development of internal erosion, although the discrepancy among the models is inevitable. The moisture content of the soil significantly affects the PD response to applied voltage. The PD increases with an increase in soil moisture content until the soil is saturated. The change in PD is correlated with the development of internal erosion. With the progression of internal erosion, the starting position for the steep increase in PD distribution continues to move toward the dam toe. In addition, the electrode stability is noted to have an effect on measured PD, which requires further studies to be clarified. This study sets the stage for the PD-based monitoring method in observing the evolution of internal erosion in earthen dams.

Influence of soil moisture content on the traction performance of a 78-kW agricultural tractor during plow tillage

The aim of this study was to analyze the traction performance of an agricultural tractor according to soil moisture content (SMC). A load measurement system was assembled using a wheel torquemeter, a proximity sensor, a six-component load cell, and a data acquisition system. The field experiments for plowing were conducted at two test sites (Fields A and B) that were divided into 9-m2 (3 m × 3 m) grids in which SMC was measured. The overall SMC was in the range of 20.0–50.0 % vol. To analyze tractor traction performance based on SMC, the data measured at Fields A and B were integrated. The SMC was divided into ranges of 20.0–25.0 % vol, 25.0–30.0 % vol, 30.0–35.0 % vol, 35.0–40.0 % vol, 40.0–45.0 % vol, and 45.0–50.0 % vol. Overall tractor traction performance parameters such as axle torque, slip, and traction increased with SMC. The traction coefficient gradually rose from 0.484 to 0.539 (a 111.4 % gain) as the SMC increased from 20.0 to 25.0% vol to 45.0–50.0 % vol. Additionally, the tractive efficiency was 0.748 at the SMC range of 20.0–25.0 % vol and 0.713 at the SMC range of 45.0–50.0 % vol. The tractive efficiency at the highest SMC level was 95.3 % based on lowest SMC level. The SMC influences various tractor traction performance factors such as traction coefficient and tractive efficiency. Therefore, it is necessary to consider SMC in the design of experiments intended to explore traction performance improvement.

Toxicity of imidacloprid to collembolans in two tropical soils under different soil moisture.

Shifts in precipitation regimes due to the predicted climate changes can alter the water content in tropical soils and, consequently, may influence the toxicity of pesticides to soil fauna. This study assessed the influence of soil moisture content on the toxicity of the insecticide imidacloprid to the collembolans Folsomia candida in two tropical soils and evaluated the risk of this active ingredient for this species in the soils tested through the toxicity exposure ratio approach. Acute and chronic toxicity tests with F. candida were performed using an Entisol and an Oxisol. The soils were spiked with increasing imidacloprid concentrations while simulating normal water availability (60% of the water holding capacity [WHC]) and water restriction (30 or 45% WHC) for the tests. In the Oxisol, the reduction of soil moisture content significantly increased the toxic effects of imidacloprid on F. candida's survival (LC50 at 45% WHC=23.8 vs. LC50 at 60% WHC>64mg kg-1) and reproduction (effective concentration causing reductions in species reproduction of 50% [EC50] at 45% WHC=0.32 vs. EC50 at 60% WHC=2.83mg kg-1), but in the Entisol no clear influence of the soil moisture on the toxicity of imidacloprid for collembolans was found. A significant risk for F. candida was observed in the Oxisol only when in water restriction, whereas in the Entisol it occurred regardless of soil moisture, suggesting that the imidacloprid hazard and risk for F. candida may be increased if soil moisture decreases due to climate changes, depending on the soil type.

Land use/land cover changes and bare soil surface temperature monitoring in southeast Brazil

The land surface temperature (LST) provides important information about energy exchange processes, which are influenced by land use/land cover (LULC). Thus, our objective was to evaluate LST patterns driven by LULC changes, detected over a time series of Landsat images. The study area of 2990 km2 is located in the Piracicaba region, state of São Paulo, Brazil. We acquired Landsat images from 1985 to 2019, in dry and moist seasons. Six LULC classes (agriculture, bare soil, straw, forest, water, and pasture) were identified by maximum-likelihood supervised classification every five years and then LST was estimated using the inversion of Planck’s function in the thermal band. Spectral indices representing vegetation, water, bare soil, and straw were calculated and correlated to LST in specific years. Bare soil images and their respective LST in both seasons were used annually to approach the influence of bare soil areas on the LST, considering soil class, time and rainfall. LULC alterations over 1985–2015 were an important factor on the LST change, which varied on average from 21.46 °C to 41.31 °C in the moist season and 17.05 °C to 31.67 °C in the dry one. Water bodies and vegetation had the lowest LST values, whereas bare soil and straw had the highest ones. The correlation between LST and spectral indices somewhat agreed with such patterns. Arenosols presented the highest LST mean values in both seasons and differed from Acrisols in the dry season, which is probably related to their texture and mineralogical composition. In the moist season, LST was negatively correlated to rainfall, suggesting the influence of soil moisture content on its surface temperature. In the dry season, the LST of bare soil areas increased by an average of 0.13 °C per year, indicating a warming trend. In general, LST increased in the studied period, probably due to the increase of anthropic activity, such as the expansion of agricultural areas. These findings can assist future studies on the influence of soils and land use on climate alterations.

Above-Ground Biomass Retrieval over Tropical Forests: A Novel GNSS-R Approach with CyGNSS

An assessment of the National Aeronautics and Space Administration NASA’s Cyclone Global Navigation Satellite System (CyGNSS) mission for biomass studies is presented in this work on rain, coniferous, dry, and moist tropical forests. The main objective is to investigate the capability of Global Navigation Satellite Systems Reflectometry (GNSS-R) for biomass retrieval over dense forest canopies from a space-borne platform. The potential advantage of CyGNSS, as compared to monostatic Synthetic Aperture Radar (SAR) missions, relies on the increasing signal attenuation by the vegetation cover, which gradually reduces the coherent scattering component σ coh , 0 . This term can only be collected in a bistatic radar geometry. This point motivates the study of the relationship between several observables derived from Delay Doppler Maps (DDMs) with Above-Ground Biomass (AGB). This assessment is performed at different elevation angles θ e as a function of Canopy Height (CH). The selected biomass products are obtained from data collected by the Geoscience Laser Altimeter System (GLAS) instrument on-board the Ice, Cloud, and land Elevation Satellite (ICESat-1). An analysis based on the first derivative of the experimentally derived polynomial fitting functions shows that the sensitivity requirements of the Trailing Edge TE and the reflectivity Γ reduce with increasing biomass up to ~ 350 and ~ 250 ton/ha over the Congo and Amazon rainforests, respectively. The empirical relationship between TE and Γ with AGB is further evaluated at optimum angular ranges using Soil Moisture Active Passive (SMAP)-derived Vegetation Optical Depth ( VOD ), and the Polarization Index ( PI ). Additionally, the potential influence of Soil Moisture Content (SMC) is investigated over forests with low AGB.

GNSS-Reflectometry and Remote Sensing of Soil Moisture: A Review of Measurement Techniques, Methods, and Applications

The understanding of land surface-atmosphere energy exchange is extremely important for predicting climate change and weather impacts, particularly the influence of soil moisture content (SMC) on hydrometeorological and ecological processes, which are also linked to human activities. Unfortunately, traditional measurement methods are expensive and cumbersome over large areas, whereas measurements from satellite active and passive microwave sensors have shown advantages for SMC monitoring. Since the launch of the first passive microwave satellite in 1978, more and more progresses have been made in monitoring SMC from satellites, e.g., the Soil Moisture Active and Passive (SMAP) and Soil Moisture and Ocean Salinity (SMOS) missions in the last decade. Recently, new methods using signals of opportunity have been emerging, highlighting the Global Navigation Satellite Systems-Reflectometry (GNSS-R), which has wide applications in Earth’s surface remote sensing due to its numerous advantages (e.g., revisiting time, global coverage, low cost, all-weather measurements, and near real-time) when compared to the conventional observations. In this paper, a detailed review on the current SMC measurement techniques, retrieval approaches, products, and applications is presented, particularly the new and promising GNSS-R technique. Recent advances, future prospects and challenges are given and discussed.

Research on Influence of Soil Moisture Content of Farmland on Infiltration Model Parameters

In order to study the influence of the initial moisture content on the parameters of the infiltration model using an indoor soil column test method, and the relationship between the initial moisture content and each model parameter was analyzed by using the Green-Ampt model, the Kostiakov model, and the Horton model. The results show that there is a certain relationship between the initial water content and the parameters of the infiltration model. Based on comprehensive considerations, the Kostiakov model is the best surface irrigation infiltration model, and the Kostiakov model has the best effect when the observation time is not less than 80 minutes to simulate the soil infiltration process.

Influence of soil moisture content and soil and water conservation measures on time to runoff initiation under different rainfall intensities

Time to runoff initiation (TRI) is an important factor related to water infiltration, runoff generation, and hillslope erosion. This study assesses TRI values for six different plots and investigates the effects of rainfall intensity, surface soil moisture content at depths of 0–5 cm, soil and water conservation measures (longitudinal ridges, cross ridges, grass, forest, and flat field under fruit trees), and vegetation on TRI for bare soil, longitudinal ridges under maize, cross ridges under peanut crops, grass, forest, and flat field under fruit trees. Results showed that bare soil exhibited the shortest TRI, followed by the longitudinal ridges under maize and cross ridges under peanut crops. The remaining three plots did not generate runoff. The first principal component affecting TRI was soil moisture content, which contributed 69.87%, 64.88%, and 85.73% to the TRI of bare soil, longitudinal ridges under maize, and cross ridges under peanut crops, respectively. The second major component of these three plots were combined rainfall intensity, comprehensive rainfall and vegetation factors, and vegetation factors, which contributed 27.98%, 33.73%, and 14.27%, respectively. Maximum load factor was generated during runoff with maximum rainfall intensity (0.969), stalk diameter (0.985), and maize height (0.864). In conclusion, soil moisture content are the main factors influencing TRI, and soil and water conservation measures provided key benefits for improving the time to runoff initiation and reduction of runoff erosion in the farmlands.

Virtual Modelling and Laboratory Research of Parameters of Planting Unit’s Working Parts

Abstract Research relevance is determined by the need of agricultural producers of Nizhny Novgorod Region to increase the profitability of sugar beet cultivation and to reduce seed losses at sowing. Another important factor is optimal energy efficiency of sowing machines, which can be achieved by reducing the draft force input required to operate the working parts. Leading approach to the research of this issue is to conduct a multifactorial laboratory experiment, taking into account several factors that have the greatest influence on the process of interaction of working parts with the soil. Virtual simulation methods were applied with use of Computer-Aided Engineering (CAE) FlowVision®(TESIS Group) engineering analysis system, allowing creation of close-to-real controlled conditions. Relationships between the lift angle and the span angle of a duckfoot opener were identified; influence of soil moisture content, speed of working parts and their working depth on draft force input and quality of the formed seedbed was determined with justification of their optimal combination. Presented technology and the planting unit assure the technological process quality, they are of practical value for agricultural and engineering companies, as well as for research institutes for design of modern agricultural machinery.

SOIL MOISTURE ON EMERGENCE AND INITIAL DEVELOPMENT OF Bidens pilosa

<p>Some species are used as cover crops, so they can produce and release products from their secondary metabolism. When these products are released in the environment, they are exposed to direct or indirect influences. Thus, this trial aimed to evaluate the influence of soil moisture content in plant decomposition, possibly caused by allelochemicals release. The influence of soil field capacity was evaluated by the decomposition of black oats (<em>Avena strigosa</em> Schreb), turnip (<em>Vicia villosa</em> Roth) and hairy vetch (<em>Raphanus sativus</em> L.) residues, with 70 and 50% of water availability and the control. Pots (1.0 kg) were filled with sterilized and unsterilized soil, plus 30 g of plant residue, which remained in decomposition for four weeks before the experiment start. After that, five seeds of beggartick (<em>Bidens pilosa </em>L.) were sowed and seedling emergence was daily evaluated for 10 d. The emergence speed index and emergence speed were calculated. Five seedlings were transplanted at the 8th d and evaluated during 30 d, to obtain the initial development of plants, and to determine fresh and dry mass. Greatest growth inhibition of the weed tested occurred with 70% available water for plant emergence and with 50% for initial plant development.</p>

Influence of soil moisture content on assessment of bulk density with combined frequency domain reflectometry and visible and near infrared spectroscopy under semi field conditions

The potential of combining frequency domain reflectometry (FDR) and visible and near infrared spectroscopy (vis-NIRS) was shown to successfully assess soil bulk density (BD). However, the accuracy of both sensing tools was reported to be influenced by the soil moisture content (MC). The aim of the paper is to evaluate the influence of soil MC level on accuracy of BD assessment under semi field conditions by the combination of FDR and vis-NIRS data. Measurements of volumetric moisture content (θv) in the field and gravimetric moisture content (ω) in the laboratory using a FDR and a vis-NIRS (350–2500nm) techniques were conducted in five arable fields of different soil texture classes in Silsoe, Bedfordshire, UK. In order to account for different MC levels, three measurement campaigns were carried out during the period from July 2011 to October 2012, where a total of 300 soil samples were used, representing three natural MC levels of low (L1), medium (L2) and high (L3). L1, L2 and L3 datasets were subjected to artificial neural network (ANN) analysis to predict ω and θv based on fusion of vis-NIRS spectra and FDR output voltage, and subsequently the predicted values were substituted into a model to assess BD.Results showed that MC has large influence on both the vis-NIRS and FDR sensors for measuring ω and θv, respectively. The accuracy of BD assessment improved with soil MC increase, with root mean square error of prediction (RMSEp) values of 0.079, 0.072 and 0.061 g cm−3, for average ω of 0.106 (L1), 0.197 (L2) and 0.28 (L3) gg−1, respectively. The accuracy of θv measurement with the FDR depended on ensuring good contact with the soil, which is not the case for dry soil conditions, at which accuracy of θv measurement and BD assessment was deteriorated. It is recommended to set an optimal MC range (depending of soil texture), over which precise soil BD estimation can be certain.

畑土壌の土壌水分の運動に関する研究(第1報) : 土壌水分応力におよぼす土壌水分の影響

畑土壌の土壌水分の運動に関する研究(第1報) : 土壌水分応力におよぼす土壌水分の影響

Effect of soil moisture on trace elements concentrations using portable x-ray fluorescence spectrometer

Portable X-ray fluorescence (PXRF) technology can offer rapid and cost-effective determination of the trace elements concentrations in soils. The aim of this study was to assess the influence of soil moisture content under different condition on PXRF measurement quality. For this purpose, PXRF was used to evaluate the soil elemental concentrations for Ca, Mg, Cd, Cr, Cu, Ni, Zn, P, Fe, Mn and Pb in 60 samples in a perimeter irrigated with treated wastewater (Cebala Borj Touil, North-east Tunisia). Scanning was conducted under four moisture conditions: in-situ , dried soil at 105°C, 40% moisture content soil and saturated soil. All were then compared relatively to dried sample scans. As expected, the relationship between dried vs both in-situ and 40% moisture content elements concentrations were linear. However, PXRF readings from saturated samples were significantly underestimated compared to the measurements on dry samples. Furthermore, soil moisture content caused a significant under-reporting of elemental concentrations compared to the scanning on dry samples. PXRF acted differently for each element following the moisture content of soil. In fact, attenuation coefficient σ of Cr, Fe and Mn were the most affected by saturation of soil samples, whilst Ca, Mg and Ni were more affected for 40% moisture content while Cd, Pb, Zn, Cu and P were affected for in-situ measurements . Correction equations enhanced the error produced by the water influence moisture content and corrected PXRF measurements.

A review of visual soil evaluation techniques for soil structure

AbstractSoil structure forms a key component of soil quality, and its assessment by semi‐quantitative visual soil evaluation (VSE) techniques can help scientists, advisors and farmers make decisions regarding sampling and soil management. VSE techniques require inexpensive equipment and generate immediate results that correlate well with quantitative measurements of physical and biochemical properties, highlighting their potential utility. We reviewed published VSE techniques and found that soils of certain textures present problems and a lack of research into the influence of soil moisture content on VSE criteria. Generally, profile methods evaluate process interactions at specific locations within a field, exploring both intrinsic aspects and anthropogenic impacts. Spade methods focus on anthropogenic characteristics, providing rapid synopses of soil structure over wider areas. Despite a focus on structural form, some methods include criteria related to stability and resiliency. Further work is needed to improve existing methods regarding texture influences, on‐farm sampling procedures and more holistic assessments of soil structure.

Erratum to: An Improved Heat Flux Theory and Mathematical Equation to Estimate Water Vapor Advection as an Alternative to Mechanistic Enhancement Factor

The current study extended the theory of heat flux which was normally used to estimate the mechanistic enhancement factor. The current improved heat flux theory included three additional phenomena that were excluded from the simplified heat flux equation. Those three phenomena were the sensible heat by liquid water movement, the sensible heat by water vapor movement, and the partial derivative of matric pressure head effects on relative humidity with respect to temperature. The first phenomenon was found to be an important factor in relatively wet porous media, whereas the third phenomenon was found important near-dry porous media condition. Moreover, mathematical descriptions derived to allow direct conversion of mechanistic enhancement factor to water vapor advection term. The study used basic mass balance equation, ideal gas law, and air advection to describe the water vapor advection mechanism. The water vapor advection equation was found to be able to describe the influence of soil moisture content and air pressure.

Direct shear behaviour of residual soil–geosynthetic interfaces – influence of soil moisture content, soil density and geosynthetic type

ABSTRACT: Soil–geosynthetic interface shear strength is an essential parameter for the design and stability analysis of geosynthetic-reinforced soil structures. Economic and environmental reasons have led to increasing use of locally available residual soils with a significant percentage of fines and lower draining capacity, when compared with the traditional good-quality backfill materials. This paper describes an extensive laboratory study carried out using a large-scale direct shear test device, in which the influence of soil moisture content, soil density and geosynthetic type on the direct shear behaviour of the soil–geosynthetic interface was evaluated. The study involved a locally available granite residual soil and four geosynthetics: two geogrids (one uniaxial and the other biaxial), one geocomposite reinforcement (high-strength geotextile) and one geotextile. Test results have revealed that the increase in soil moisture content can measurably reduce the soil–geosynthetic interface shear strength. Regardless of soil moisture content, soil density proved to have a remarkable influence on interface shear strength, particularly when geogrids were used. Among the different geosynthetics tested, the biaxial geogrid was found to be the most effective reinforcement for this particular type of soil, concerning the direct shear mechanism. For soil–geogrid interfaces, the coefficients of interaction ranged from 0.71 to 0.99. For soil–geotextile interfaces, the coefficients of interaction varied from 0.54 to 0.85.