Moisture Content Sensor Research Articles

Conceptual and Applied Aspects of Water Retention Tests on Tailings Using Columns

The water retention capacity of porous materials is crucial in various geotechnical and environmental engineering applications such as slope stability analysis, landfill management, and mining operations. Filtered tailings stacks are considered an alternative to traditional tailings dams. Nevertheless, the mechanical behaviour and stability of the material under different water content conditions are of concern because these stacks can reach considerable heights. The water behaviour in these structures is poorly understood, particularly the effects of the water content on the stability and potential for liquefaction of the stacks. This study aims to investigate the water retention and flow characteristics of compacted iron ore tailings in high columns to better understand their hydromechanical behaviour. The research used 5 m high columns filled with iron ore tailings from the Quadrilátero Ferrífero region in Minas Gerais, Brazil. The columns were prepared in layers, compacted, and instrumented with moisture content sensors and suction sensors to monitor the water movement during various stages of saturation, drainage, infiltration, and evaporation. The sensors provided consistent data and revealed that the tailings exhibited high drainage capacity. The moisture content and suction profiles were effectively established over time and revealed the dynamic water retention behaviour. The comparison of the data with the theoretical soil water retention curve (SWRC) demonstrated a good correlation which indicates that there was no hysteresis in the material response. The study concludes that the column setup effectively captures the water retention and flow characteristics of compacted tailings and provides valuable insights for the hydromechanical analysis of filtered tailings stacks. These findings can significantly help improve numerical models, calibrate material parameters, and contribute to the safer and more efficient management of tailings storage facilities.

State-of-the-Art Review of Moisture Content Sensor Deployment in Mass Timber Construction

State-of-the-Art Review of Moisture Content Sensor Deployment in Mass Timber Construction

Soil Moisture Content Sensor: Utilizing Bacterial Cells as Living Sensors

Soil moisture affects water and heat exchange between soil and air, weather and climate, and plant growth. Therefore, controlling and predicting soil moisture is vital for irrigation, nutrient supply, absorption, and crop productivity. Soil microbial fuel cell (SMFC) is a recent technology that generates electricity from soil microorganisms and chemicals. SMFC can be used to sense soil moisture and treat polluted soil. In this study, we designed a low-cost, portable, and easy-to-install SMFC for soil moisture sensing, and it was tested at four moisture levels: 40%, 60%, 80%, and 100% soil water holding capacity (SWHC). The SMFC worked best at 60 - 80% SWHC, which is suitable moisture for many plants. The results suggest that the proposed SMFC can be a potential soil moisture sensor.

Designing a Cylindrical Capacitive Based Sensor for Monitoring the Table Salt’s Moisture Content during Iodization

Coaxial cylinder capacitive moisture sensor for determination of moisture content of table salts has been fabricated. The CMS method for determination of moisture content of table salts overcomes the effect of evaporation of iodine in table salt which results from heating in the oven drying method. The CMS overcomes the polarization effect result from the resistive methods of moisture content determination and it is non expensive to construct and it has high accuracy since measurements involves programming system in interpretation of the results. In this research, moisture content sensor based on capacitive principal created using two coaxial cylinders with height 5.207 cm, and different diameters of 4.303 cm and 1.198 cm embedded inside one another. The input signal of the CMS system was provided by the AC signal from the sensor capacitor, the capacitance of the sensor capacitor is directly proportional to the moisture content of the salt sample placed between the two coaxial cylinders of the sensor capacitor. The moisture content was obtained from the model m=6.6145×10-4c+4.54044 for calibration of the CMS by using the OVD as a reference method for determination of moisture content in the table salts. The model was then validated by constructing the comparison plot of OVD and CMS moisture contents. The comparison graph of OVD and CMS MC against test had conceding error bars between OVD and CMS MC. The coefficient of determination of 0.94 was obtained and the correlation plot was a linear relation expressed as y=0.971x+0.773. The model was then validated by solving for moisture content from measured values of capacitance.

Hydromechanics – Slope Monitoring in Rainy Season

Rainfall and soil response are necessary to be monitored to have slope characteristics in detecting landslide occurrence. Even though much research has been carried out worldwide for rainfall monitoring, less research has been conducted in Indonesia for slope monitoring. Therefore, this research was conducted to observe the suction, soil moisture content, and rainfall in a silty sand slope. An automatic rain gauge was set on the ground to measure precipitation. Tensiometer and soil moisture content sensors were installed at depths of 0.5 m; 1 m; and 1.5 m from the slope surface. The monitoring was conducted during the peak rainy season from December 2022 to January 2023. The rainfall amount is about 436.6 mm, and the 6 hours of rainfall events contribute a relatively sizeable rainfall amount (about 31%) to the total. The safety factor of the slope is estimated to decrease by 39%-40% due to the rainfall.

Effects of changes in soil properties caused by progressive infiltration of rainwater on rainfall-induced landslides

Slope failure is associated with changes in pore water pressure induced by rainfall, this paper further attempt to bridge knowledge gaps that exist in understanding the relationship between mechanism of rainfall-induced regional-scale widespread shallow landslides in cohesive soils and change in pore water pressure. We designed in situ slope experiments with pre-designed vertical profiles at the toe of the slope, and used pore water pressure, conductivity, and moisture content sensors to capture the changing characteristics of soil properties during slope failure. The experiment finds that failure occurred first where internal material was continuously taken out of the slope, even before the maximum static pore water pressure is reached. However, the slope remains stable when the pore water pressure near the failure surface reached the maximum static pore water pressure that could be provided by rainfall. Instead, slope failure during subsequent rainfall periods, even if the pore pressure is then lower. Meanwhile, the soluble minerals in the soil continuously dissolve and migrate, causing the electrical conductivity before slope failure is approximately 1.38 times that after failure, on average. Here, we estimate that the changes in soil properties caused by progressive water infiltration only may have decreased test slope stability by an average of approximately 33.0%. Therefore, we suggest that the early attenuation of soil strength caused by the gradual changes in soil properties makes a significant contribution to soil failure caused by pore water pressure. This was verified in the case of the 7.25 Tianshui group-occurring landslides. Finally, by using an automatic laser particle size analyzer, scanning electron microscope, X-ray diffraction, ion chromatography, and quadruple direct shear instrument to analogize the changes in soil properties exposed to different leaching environments on loess platform, we further show that the early attenuation soil strength is caused by deteriorate in soil properties in the processes of successive years of rainfall, where the content of cemented minerals tends to decrease, fine particles tend to be lost, and pore structure tends to take the form of single macro-pores, which are more likely distributed around mineral particles >10 μm. Our results provide a new perspective on the widespread shallow landslides caused by changes in pore water pressure in a region and their associated gradual deteriorations in soil properties.

Embeddable Soil Moisture Content Sensor Based on Open-End Microwave Coaxial Cable Resonator

In this paper, we propose and demonstrate a novel corrosion-resistant, embeddable open-end coaxial cable soil moisture sensor. This microwave resonator is constructed using two reflectors along the coaxial line. The first reflector is a metal post at the signal input end, short-circuiting the inner conductor to the outer conductor. The second reflector comprises a welded metal plate parallel to the open-end of the coaxial line, maintaining a fixed gap. A moisture-sensitive Polyvinyl Alcohol (PVA) film is inserted into this gap. The resonance frequency of the open-end coaxial cable resonator is highly dependent on the fringe capacitance, which varies with soil moisture levels. As such, tracking resonance frequency changes allows for correlation with soil moisture fluctuations. We provide a detailed discussion of the embeddable open-end microwave coaxial cable resonator (EOE-MCCR) mathematical model and a proof of concept for soil moisture measurement. The demonstration experiments investigate soil moisture content ranging from 4% to 24%. The prototype device exhibits a soil moisture measurement sensitivity of 0.76MHz/% for soil moisture between 4% and 10%, and 1.44MHz/% for soil moisture between 10% and 24%. The soil moisture sensor presented here is robust, easy to manufacture, chemically resistant, low-cost, and suitable for long-term applications and potential industrial uses. This innovative sensor is ideal for sensing applications in harsh environments, advancing the field of chemical trace sensing.

A Non-Destructive Measurement of Trunk Moisture Content in Living Trees Based on Multi-Sensory Data Fusion

Water plays an important role in various physiological activities of living trees. Measuring trunk moisture content (MC) in real-time without damage has important guiding significance for transpiration research in forest ecosystems. However, existing standing tree MC detection methods are either too cumbersome to install or cause different degrees of damage. Here, we propose a novel Internet of Things (IoT) monitoring system that includes wireless acoustic emission sensor nodes (WASNs) and underground soil MC sensor nodes to efficiently detect and diagnose the MC level of living tree trunks. After the characteristic parameters were collected by the two sensors, a feature selection and multi-sensory global fusion method for MC diagnosis was designed and developed and several statistical parameters were selected as the input variables to predict the heartwood MC level with a support vector machine (SVM) model. Moreover, to achieve the highest prediction accuracy, an improved sparrow search algorithm (ISSA) is applied to ensure the most suitable parameter combinations in a two-objective optimization model. Extensive experiments result in a fusion of the environment, and AE signals show that the proposed mechanism has better diagnostic performance than state-of-the-art methods and is more adaptable to the fluctuation of working conditions.

Evaluation of the Collapse Potential Magnitude of Untreated and Treated Collapsible Gypseous Soil — A New Procedure

Many researches have been conducted to study the collapse potential of collapsible soils using collapse tests; single-oedometer tests, and double-oedometer tests. The radical rearranging of particles in response to a significant volume loss from wetting under loading is the definition of collapse. The main goal of this study is to create a method for recognition of gypseous soil that is susceptible to collapse. The suggested procedure depends on using a sample larger than that used in conventional collapse tests and the saturation of sample is done by flowing water from the bottom to the top of the sample. The new idea for the modified collapse test was made because of the limitations of conventional tests including the small size of sample that may not give a suitable collapse. In addition, the saturation process of the sample may not saturate all the particles. Also, the behavior of collapsible gypseous soil was investigated on soil improved with different Magnesium Oxide percentages (0, 5, 10, and 15%) and carbonated Magnesium Oxide with variable carbonation times (0, 1, 3, and 24 hours). The soil was prepared at two relative densities of 35 and 75 percent relative density. The collapse potential was investigated using a modified Rowe cell with soil moisture content sensors. The results illustrated that the size of the sample affects the collapsibility, the collapse potential increased from 15.8% to 22.3% and the collapse severity is changed from (severe trouble) to (very severe trouble) for the natural untreated gypseous soil using the conversional tests and modified test, respectively. The collapse potential increased by about 40% for the soil treated with different percentages of “Magnesium Oxide”. For the modified test, the collapse potential decreased by about 93% when using 10 percent of Magnesium Oxide then the sample was carbonated for 3 hours as compared with untreated soil.

Decision Support System and Fuzzy Logic Controller for Capillary Irrigation System

Purpose: Different irrigation systems exist and they all possess various degrees of benefits in enhancing food sufficiency. In this study however, the enhancement of capillary irrigation system through an integrated fuzzy logic controller with Decision Support System (DSS) to ensure improvement in water saving for irrigation thereby improving crop yield towards food security was examined and achieved.
 Methodology: An integrated fuzzy logic controller with Decision Support System (DSS) for capillary irrigation system was adopted for the enhancement of water saving for irrigation. By using this method, the challenges of irrigation management which is prevalent with capillary irrigation system is minimised using the fuzzy logic controller. An Internet of things (IoT) based weather station for computation of potential evapotranspiration (PET), for measuring rainfall and a VH400 moisture content sensor for monitoring the volumetric water content of soil, were some facilities used to control the water level depth (WLD) autonomously through a fuzzy controller simulated in MATLAB and implemented on Arduino Mega.
 Findings: The soil moisture content (SMC) depicts that fuzzy controlled water level depth (WLD) is able to compensate reduction of water in crop medium that took place due to plant water uptake which changes daily. The result proves that dynamics of water supply depth has substantial effects on the water absorption flow rate, wetting pattern, soil water content and cumulative infiltration which are proportional to the water supply depth decrement. 
 Unique Contribution to Practice: An integrated fuzzy logic controller with Decision Support System (DSS) is a new technique proposed for managing capillary irrigation system as it offers enhanced water saving capacity (irrigation volume) based on crop demand.

Slope Crack Propagation Law and Numerical Simulation of Expansive Soil under Wetting–Drying Cycles

This study investigated the crack propagation law of expansive soil slopes under drying–wetting conditions and the influence of cracks on slopes by conducting a large-scale indoor slope test subjected to drying–wetting cycles. The change in soil moisture content at different depths during the drying–wetting cycles was monitored using a moisture content sensor, and the variation in crack depths in the expansive soil during the drying process was measured using a crack depth detector. The cracks on the slope’s surface were processed using a self-made binarization program, and the crack evolution mechanism of the expansive soil during the drying process was analyzed. The rainfall-induced change in moisture content in the fractured soil was used to obtain the influence of moisture content change on expansive soils, and to analyze the dry–wet cycle failure mode of surface soil. The surface cracks of the soil were quantified by binary processing, and the area of the cracks and the area ratio of cracked soil to intact soil were calculated. Finally, by using PFC simulation software with the slope cracks and quantitative analysis results as parameters, it was confirmed that the greater the number of drying–wetting cycles, the greater the number of cracks, and the greater the damage to the slope.

Effect of Rainfall Intensity on Landslide Initiation: Flume Tests and Numerical Analysis

This paper seeks to investigate the effect of rainfall intensity on the occurrence of shallow landslides by means of a series of flume tests. Coarse-grained material was used to build a slope, and several rainfall events with an intensity of either 40 mm/h, 70 mm/h, or 100 mm/h were simulated to initiate slope failure. A set of pore water pressure and moisture content sensors was installed in the slope to monitor changes in the water conditions during each test. Different initial moisture contents of 5% and 10% of the soil mass were used to better understand the effect of moisture on slope stability during rainfall. It was found that the slope failed when intensities of 70 mm/h and 100 mm/h were used; however, no failure was observed with a rainfall intensity of 40 mm/h. The failure patterns were found to be similar, with progressive slides occurring as more water infiltrated the slope. A numerical procedure to estimate the factor of safety over the period of the rainfall event was proposed and validated against the laboratory data. The results of the numerical analysis yielded the failure time, which was close to the time observed in the flume tests.

Impedance spectroscopy method for testing moistened wheat crops

The authors presented the results of a study of the electrical and dielectric characteristics of wetted wheat grains by measuring their complex electrical resistance (impedance Z) in a wide frequency range (from 1 Hz to 100 MHz). The results of electrical impedance measurements of grains with surface or volumetric moisture content under different experimental conditions can provide useful information on the properties of the biological tissues of grain crops. These results can also be used to develop a new type of impedance sensor for testing grain quality and moisture content. The authors used well-dried wheat grains and grains saturated with moisture and saline as objects of research. A major problem in grain impedance measurements is the selection of a suitable electrode material to be placed on the end surfaces of the samples. The electrodes must ensure reliable contact with the grain and have a minimum transient resistance. The end surfaces of the pressed samples were reinforced with a protective dielectric ring to prevent transverse deformation. These contacts provided a transition resistance between 1-2 ohms. The authors have identified processes of accumulation of electric charges near the surface of metal electrodes at low frequencies and on internal grain structures, leading to an increase in the dielectric permittivity and dissipation factor. The behavior of the active and reactive components of the impedance at higher frequencies is determined by dielectric relaxation processes. The obtained impedance spectra were compared with the spectra of the most suitable equivalent electrical circuits. The radio components of the circuits provide information about the basic mechanisms of alternating electric current flow through the complex inhomogeneous structure of the grain. The authors found that moistening the grain with saline water enhances the process of accumulation of electric charges and affects the dispersion of the real and imaginary components of the impedance.

Development and application experiments of a grain yield monitoring system

An impact-type grain yield monitoring system was developed and tested in laboratory and field to meet the requirement of precision agriculture in China. The system consisted of a mass flow sensor, a clean elevator speed sensor, a ground speed sensor, a moisture content sensor, a controller area network-bus processor, a global navigation satellite system receiver, and an industrial personal computer. The system was used to collect yield data and create the grid map in a field of winter wheat from 2018 to 2019. Laboratory and field calibrations were implemented to verify the accuracy of the mass flow sensor and the moisture content sensor. The errors of time delay and parking were removed, and exponential smoothing was performed in the data preprocessing. A yield reconstruction method was proposed to calculate the yield data of the sampling points based on the empirical model between flow voltage and grain weight. The predicted errors of total yield in both years were less than 5%, which indicated that the accuracy of yield monitoring system was high. An averaging method was used to generate the yield grid map. The spatiotemporal variation of the two-year yield was analyzed. Hierarchical management for precision farming was studied according to spatial variability (CVS = 31%) in 2018. Results showed that the temporal variability was CVT = 34%, which confirmed that the yield increased by about 0.3 t compared with the previous year. Moreover, the variability of the grid map showed the distribution of the yield reduction area, which was related to the characteristics of the seeds and the regional properties of the soil. The results proved that the developed yield monitoring system can be used as a tool to provide a reference for precision agriculture and high-yield management of winter wheat.

Study on sliding stability of porous-concrete retaining wall model test subjected to rainfall infiltration

The common disadvantage of a conventional retaining wall is a heavy object as a block that is difficult to lift and handle conveniently. A drainage pipe is commonly used to displace water from the backfill. In areas with high annual rainfall, the soil could be saturated in a short time and added lateral load significantly. In this study, porous concrete was utilized as a retaining wall material with the advantages of the lighter weight of the block and additional drainage capability due to its high void ratio. A set of a laboratory-scale retaining walls using conventional and porous concrete walls was investigated through three different rainfall modes. To initiate the instability condition, a vertical load was applied then the lateral moving was recorded using LVDT sensors. Soil moisture content sensors recorded hydrologic responses of the saturation process. The loading test results showed that the porous concrete wall model was being displaced less than experienced by the conventional concrete wall. It shows that the porous concrete wall model can withstand the load as the additional lateral load from infiltrated rainwater dissipates rapidly. Therefore, the porous concrete wall has the advantage of being used as a Retaining Wall Material.

Capacitive Online Corn Moisture Content Sensor Considering Porosity Distributions: Modeling, Design, and Experiments

An online corn moisture content measurement device would be a key technology for providing accurate feedback information for industrial drying processes to enable the dynamic tracking and closed-loop control of the process. To overcome the problem of large measurement error caused by the characteristics of the corn flow state and the pore distribution when a parallel plate capacitor is applied to the online moisture content measurement process, in this study, we summarized the constraint conditions of the sensor’s structure parameters by mathematical modeling and calculated the optimal sensor design size. Moreover, the influence of porosity variation on moisture content measurement was studied by using the designed sensor. In addition, a mathematical model for calculating corn moisture content was obtained for the moisture content range of 14.7% to 26.4% w.b., temperature of 5 °C to 35 °C, and porosity of 38.4% to 44.6%. The results indicated that the fluctuation in the online moisture content measurement value was obviously reduced after the porosity compensation. The absolute error of the measured moisture content value was −0.62 to 0.67% w.b., and the average of absolute values of error was 0.32% w.b. The main results provide a theoretical basis and technical support for the development of intelligent industrial grain–drying equipment.

Dielectric Properties of Switchgrass and Corn Stover in the Radio Frequency Range

HighlightsDielectric permittivities of switchgrass and corn stover in the radio frequency range were calculated.Prediction models achieved R2 > 0.9, except for the switchgrass loss factor for the material in motion.The loss factors were different when static and in motion, but the dielectric constants were similar.Abstract. The dielectric properties of biological materials are relevant when developing moisture content sensors. However, little is known about the permittivities of switchgrass and corn stover in a wider frequency range. The goal of this research was to determine their dielectric constants and loss factors at different moisture contents across a frequency range of 5 Hz to 13 MHz and with the material static and in motion inside a sample container. The permittivity of these materials was calculated by measuring their admittance in a test fixture using an impedance analyzer at three different moisture levels (9.0% to 30.5%). Overall, the materials’ dielectric properties increased with moisture but decreased with frequency. Prediction models were developed using the data in a frequency range of 10 kHz to 5 MHz. Model coefficients of determination were higher than 0.90 in general, except for the model measuring the loss factor of switchgrass in motion. Additionally, the dielectric constant was not different with the materials static or in motion, but the loss factor values were distinct. This work can be used for the development of electrical moisture content sensors for switchgrass and corn stover. Keywords: Corn stover, Dielectric constant, Loss factor, Moisture content, Permittivity, Switchgrass.

Fertilization and precise irrigation scheduling for mature avocado

Irrigation scheduling (IS) and fertilization are among the most important practices in the production of horticultural crops because they affect fruit quality and quantity directly. Thus, a 15-year-old avocado orchard (cv. ‘Simmonds’) was used to determine precise IS, based on monitoring soil moisture content (SMC), remote sensing technologies [Unmanned Aerial Vehicle (UAV)] under two fertilization levels using granular formulation 15-3-19. In October 2015, all trees were pruned (topped and hedged) to 3.05 m height and 2.44 m diameter. In December 2015, soil moisture (SM) sensors were installed at five (10, 30, 50, 70 and 90 cm) soil depths in six locations. Trees received two fertilizer treatments: F1-9.06 kg and F2-12.07 kg of 15-3-19/tree/year every three months. Precipitation and SM data were recorded daily for 21 months; SM data was corrected with a quadratic equation (y = -4.1881x2 + 3.6886x - 0.3083) generated specifically for the Coto soil series (Typic Hapludox). The SM values recorded were always greater than 41%, indicating that the avocado orchard was growing under water saturation conditions; thus, micro-irrigation was not needed. The UAV data at 5, 13 and 20 months after pruning (MAP) showed quick closure of the avocado canopy; acquiring a denser and more cylindrical shape (from 17.6 ± 2.65 m2 to 52.7 ± 6.10 m2), regardless of fertilizer level. Based on correlation of UAV and manual results, F2-treated trees indicated stronger correlation at 13 and 20 MAP (R2 >0.75) than F1-trees. Yield production (110 avocados per tree = 13,200 per hectare) and leaf nutrient content did not differ significantly with fertilizer level. For commercial avocado farmers the use of SMC sensors and UAV technology could be an advantage, albeit an expensive one. Soil moisture content sensors have been shown to be very effective in irrigation water conservation. In terms of fertilization, the results suggest not using more than 9.06 kg of 15-3-19/tree/year as this amount seems enough to satisfy avocado requirements, under the experiment’s conditions. Future evaluations will determine if it is possible to use less fertilizer and still maintain an optimal avocado production.

New Trend to Measure the Saturation Point and Suction in Granular Soil

There are many methods to measure the suction and saturation point of any soil and the most used is Tensiometer. The objective of this research is to investigate a new trend to measure the saturation point and suction by using soil moisture content sensors (SMCS) and compare the procedure with tensiometer for the granular soil. The soil in this study has been prepared at three relative densities (5%, 35% and 75%) used. The results show that the readings of SMCS become stable when the water content is more than 20% with different relative densities. The relative density did not affect the SMCS reading when approximately reaching the saturation point.

Construction of a large oedometer for MSW and non-conventional materials testing

The design, construction and evaluation of a large consolidometer for testing municipal solid waste (MSW) and other non-conventional materials is proposed. The apparatus features leachate recirculation and biogas production monitoring. Furthermore, it is equipped with moisture content sensors, suction and at-rest lateral earth pressure measuring capabilities. Fresh MSW samples were collected from a metropolitan centre landfill and were used to test performance and conduct MSW mechanical behaviour analyses. Values of vertical stress (σz) ranging from 10 to 1000 kPa were employed in the test, which lasted for approximately 1 year. The results show that the secondary compression index was affected by sample saturation and that biogas composition acted as an indicator of the MSW phase of decomposition. Lateral earth pressure at rest values increased with σz, although they decreased over time for the same loading stage. Values of primary compression and swelling indexes (cc and ce, respectively) are close to those reported in the literature for similar material.