Indoor Simulation Test Research Articles

Construction and experimental verification of wave velocity model for source location in goaf overlying rock strata

The geological structure of the goaf overlying rock is complex, a consequence of coal mining that has modified the original stratified structure of the sedimentary strata. To enhance the accuracy of microseismic source location in such intricate geological formations, a wave velocity model for the “three zones” goaf was constructed based on natural divisions within the strata using Snell's law and assuming a homogeneous medium. The model took into account the effects of rock deformation and fracture development, enabling the derivation of formulas for microseismic wave propagation path and travel time calculation. Additionally, the concept of equivalent wave velocity was defined. An indoor simulation test using similar materials was conducted to establish a geological model of the goaf. By comparing the errors between the theoretical and measured values of equivalent wave velocity, assessing the locating effects before and after implementing the wave velocity model of the goaf, and verifying the feasibility of the model, it was demonstrated that establishing a wave velocity model based on the characteristics of the strata structure was crucial for improving the accuracy of the microseismic source location. Notably, as the propagation path of microseismic waves in the goaf increased, the equivalent wave velocity decreased. The wave velocity structure in the goaf exhibited nonuniformity, with the relative error between the theoretical and measured values of equivalent wave velocity being limited to 10 %. The incorporation of this established wave velocity model into the location method resulted in a substantial 58.57 % increase in locating accuracy.

Analysis of the research progress on the deposition and drift of spray droplets by plant protection UAVs

Plant protection unmanned aerial vehicles (UAVs), which are highly adapted to terrain and capable of efficient low-altitude spraying, will be extensively used in agricultural production. In this paper, single or several independent factors influencing the deposition characteristics of droplets sprayed by plant protection UAVs, as well as the experimental methods and related mathematical analysis models used to study droplet deposition and drift, are systematically investigated. A research method based on farmland environmental factors is proposed to simulate the deposition and drift characteristics of spray droplets. Moreover, the impacts of multiple factors on the droplet deposition characteristics are further studied by using an indoor simulation test system for the spraying flow field of plant protection UAVs to simulate the plant protection UAVs spraying flow field, temperature, humidity and natural wind. By integrating the operation parameters, environmental conditions, crop canopy characteristics and rotor airflow, the main effects and interactive effects of the factors influencing the deposition of spray droplets can be explored. A mathematical model that can reflect the internal relations of multiple factors and evaluate and analyze the droplet deposition characteristics is established. A scientific and effective method for determining the optimal spray droplet deposition is also proposed. In addition, this research method can provide a necessary scientific basis for the formulation of operating standards for plant protection UAVs, inspection and evaluation of operating tools at the same scale, and the improvement and upgrading of spraying systems.

The influence of tunnel insulation measures on the temperature spatiotemporal variation of frozen soil during artificial ground freezing

Artificial ground freezing (AGF) has been widely used in the construction of subway connection channels to reinforce the soil around the tunnel, especially the water-rich soft soil, to ensure the stability of the tunnel and the overlying buildings. However, the direct contact between the frozen soil curtain and the tunnel segment would cause the loss of cooling capacity, which is not conducive to ensuring the freezing effect. The indoor freezing and thawing model of silty soft soil was established to explore the influence of tunnel insulation measures with different thermal conductivity on the temperature spatiotemporal variation of frozen soil curtain through indoor simulation tests. The effects of thermal insulation materials with different thermal conductivity on the stable temperature and development speed of frozen soil curtains were also compared. The results indicated that the interface of tunnel segments has a significant impact on the freezing speed and stable temperature of frozen soil during the freezing process, as well as the thawing time during the natural thawing process. Compared with steel segment tunnel, the use of thermal insulation coating with low thermal conductivity increased the temperature of the soil at the same distance by 5.88% to 42.5%, and prolonged the freezing time of the soil far from the tunnel by 38.8%. On the contrary, the insulation foam with higher thermal conductivity not only reduced the temperature of frozen soil by 13.8% at most, but also shortened the freezing time by 42.1% at most, which can significantly improve the construction efficiency. For the natural thawing process, the thermal insulation coating would reduce the thawing time of frozen soil by more than 30%, while the thermal insulation foam can increase the thawing time of frozen soil far away from the tunnel by at least 23%, which was more conducive to extending the allowable duration of frozen soil excavation. The results can provide a reference for the selection of segment insulation measures in the AGF construction of subway cross channels in silty soft soil.

Effect of Soil Configuration on Alfalfa Growth under Drought Stress

This paper aims to compare the effect of different soil configurations on plant growth under long-term drought to provide a theoretical basis for soil reclamation and vegetation restoration in the contiguous area between Shanxi, Shaanxi, and Inner Mongolia, China. With the widely distributed montmorillonite-enriched sandstone in this area as the soil structure ameliorator and the sandy soil as the test soil, indoor simulation and soil column tests were conducted to study the water holding capabilities of different reconstructed soils configurations. The drought stress test of alfalfa on these soils explored the correlation between the growth of alfalfa and soil water in various configurations. The soil–water characteristic curve and soil texture were analyzed to determine plant survival. The results showed that the addition of montmorillonite-enriched sandstone with high water holding capacity and water diffusion rates could increase the water content of the sandy soil. The treatments with 20 and 30 cm montmorillonite-enriched sandstone at the depths of 20–40 cm and 20–50 cm demonstrated the longest survival time (60 days and 59 days), the highest germination (34% and 35%), and the highest water holding capacity (22.6% and 27.3%), indicating that soils with higher water holding capacity and lower diffusion rates could be used as a reservoir, in combination with other soil materials with high water content, and that the addition of the montmorillonite-enriched sandstone layer at 20–30 cm in the sandy soil is the optimal choice for topsoil reclamation in open-mining areas.

Numerical Simulation of Bearing Characteristics of Bored Piles in Mudstone Based on Zoning Assignment of Soil around Piles

This study conducts a field indoor simulation test, SEM observation, and penetration test to determine the bearing capacity of the dynamic driving pile in the mudstone foundation. It comprehensively analyzes the variation laws of structure and strength of mudstone around piles after piling. Indeed, the strength of mudstone structure is significantly reduced from outside to inside. Therefore, the numerical simulation of piles in mudstone should consider the actual characteristics of soil damage around piles. The strength of mudstone after pile driving damage is measured, and the scatter diagram depicting the relationship between mudstone strength and pile side distance is produced. Then, the best-fitting curve of the relationship between the strength ratio and the distance ratio of the simulated pile driving test is established by the nonlinear fitting of multiple curves. A numerical simulation method is proposed to consider the damaged area and parameters surrounding the pile. The range of soil damage caused by pile driving in the mudstone foundation is determined to be two times that of the pile diameter. The disturbance area is divided into four parts on average, and the width of each part is 0.5d. The simulation results are compared to the conventional approach of uniform parameter assignment to prove the rationality of the method.

Calibration-free pH long-time measurement method based on electrode potential drift dynamic compensation-applying self-adaptive dynamic optimization exponential smoothing method

The long-term in-situ accurate measurement of pH value is an urgent need for environmental water quality monitoring without calibration of pH electrodes. The nonlinearity and potential drift of pH electrode is the main problem which restricts long-term continuous monitoring. The characteristic rules including electrode potential, zero value, electrode slope coefficient, and electrode potential drift for pH electrode are analyzed in detail under the condition of long-term continuous use. The exponential smoothing potential drift prediction model with self-adaptive dynamic optimization smoothing order and smoothing coefficient is established. Combining electrode potential drift threshold judgment and Nernst equation, calibration-free dynamic calculation mathematical model of pH long-term monitoring is established. Indoor simulation and field test indicate that the measurement absolute error caused by electrode drift is within 0.01 pH and the specified measurement error for pH monitoring instrument is always within 0.1 pH. The proposed method is very suitable for the terminal of pH detector with the advantages of good portability for the MCU chip, small samples, high-precision and fast running speed. Furthermore, the life of pH electrode can be prolonged significantly. It is also proved that the proposed method has a good application prospect.

Optimization analysis and Field application of gas-liquid cyclone separator based on CFX

At present, large and cumbersome gravity sedimentation separators are generally used in the separation of liquid and gas in the wellbore during emergency blowout or circulating degassing in drilling, and innovation and improvement are urgently needed. In this paper, CFX commercial simulation software is used to analyze the cut-in cyclone separator, and the axial inlet type cyclone separator with different length ratios of cylinder-cone section in swirling flow section under different flow channel structures, and carried out indoor simulation and field test verification. The results show that the axial inlet type cyclone separator is more suitable for gas-liquid separation than the cut-in cyclone separator, and the separation can be well improved by increasing the length-diameter ratio of the cyclone section under the cut-in cyclone separator structure. Finally, the experimental separation efficiency reached 99%, and the field test separation efficiency reached more than 98%. This greatly improves the separation efficiency of liquid and gas during the drilling process, and also plays a certain role in promoting the separation of gas and liquid in the entire oil and gas industry.

Damage Mechanism of Asphalt Concrete Pavement under Different Immersion Environments

With the construction of road infrastructure in China, the rapid development of expressways has provided great convenience for human travel and cargo transportation. Asphalt concrete pavement is widely used in highway construction because of its characteristics of good flatness, high strength, and convenient maintenance. But the water damage of asphalt concrete pavement is the main factor affecting the stability of highway subgrade and flatness of pavement, as well as the main cause of deformation and collapse of pavement. In view of the water damage problem of asphalt concrete pavement, this paper investigates the overall condition and water damage situation of asphalt concrete pavement with different immersed states and carries out indoor simulation test of asphalt concrete samples without water, dry and wet cycle, and saturated water. The quality, loss rate and Marshall stability of the samples under different times of cyclic rolling were obtained through the statistics of cyclic rolling pressure of the samples. The influencing factors of water loss, water resistance and failure forms of highway under different impregnation environments were analyzed, and the prevention measures of water loss of asphalt concrete were put forward. The test results show that the mass loss rate of the sample is water-free, dry-wet cycle, and water-saturated, and the Marshall stability of the sample is water-free, dry-wet cycle, and water-saturated from high to low. Under the action of rolling and friction forces, the fine aggregates in the asphalt concrete are worn off, which leads to the expansion of cracks on the surface of the sample and the formation of fissure network. Small holes appear on the surface of water-saturated sample, and the coarse aggregate is broken and disintegrated under pore water pressure. Traffic flow (cyclic rolling times) and immersion state have become the main factors of asphalt concrete pavement failure. This study has specific and important theoretical guiding significance for reducing and preventing water damage of asphalt concrete pavement of expressway, delaying road service life, and enhancing road safety.

Changes in litter traits induced by vegetation restoration accelerate litter decomposition in Robinia pseudoacacia plantations

AbstractThe chemical traits of litter are among the most critical factors that affect its decomposition. During vegetation restoration of planted forests, increasing age of the planted species and succession of the understory species may lead to significant changes in litter traits. However, it is unclear how these changes occur and how they affect litter decomposition. Therefore, we studied the decomposition of litter from four Robinia pseudoacacia plantations in the Loess Plateau in China with stand ages of 10–43 years using an indoor simulation test. We measured changes in litter substrate quality and chemical diversity, structural properties of the litter microbial community, activity of litter enzymes, and mixed decomposition effects during vegetation restoration. Their relationships to changes in litter decomposition rate were analyzed using structural equation modeling. Improvements in substrate quality of forest litter induced by vegetation restoration drove changes in fungal community composition during late decomposition (day 358), which in turn increased the activity of lignin‐decomposing enzymes and ultimately accelerated litter decomposition. At the same time, decreases in the chemical diversity of forest litter induced by vegetation restoration reduced the diversity of litter fungi during middle and late decomposition (days 182 and 358). This caused significant negative mixed decomposition effects, thereby inhibiting litter decomposition. However, improvements in litter substrate quality dominated the changes in litter decomposition rate, and the decomposition rate of R. pseudoacacia plantation litter thus increased over the course of vegetation restoration.

Experimental analysis of zero-natural-frequency damper for transmission line large cross project based on NES

The operation experience of transmission line large cross project shows that the traditional anti-aeolian-vibration devices had poor adaptability to complex terrain and micro meteorological conditions, and they were difficult to meet the application requirements of super large cross project at this stage. A zero-natural-frequency damper was designed by introducing nonlinear energy sink in this paper, and the solid prototypes were processed. According to the actual design parameters of conductor using in a large cross project, the anti-vibration effect was tested by using the indoor simulation test span. The test results showed that the anti-vibration effect of the scheme based on the zero-natural-frequency damper could meet the needs of practical engineering. The installation of this damper could improve conductors’ and fittings’ adaptability to complex terrain and enhance the wind and anti-vibration ability of transmission line.

Indoor simulation test research on cumulative longitudinal displacement of rail based on force and displacement sensors data collection.

The train sometimes needs to brake frequently on the turnout, although the braking force does not exceed the limit resistance of fastener, cumulative displacement of rail occurs because of the long-term effect of the train brakes, thus, the relationship between the cumulative displacement of rail and the number of train braking actions should be explored. Aiming at the spring bar type III fastener, a 1:1 physical indoor simulation test was carried out, and an electromagnetic relay device was used to simulate the train load, force, and displacement sensors for data collection. Then a single load no more than the maximum resistance of fastener was applied to the rail end to explore the relationship between the number of loads and the rail cumulative deformation. The rail longitudinal cumulative displacement changes linearly in positive correlation with the number of load actions, and increases faster when the number of load actions is small. As the number of repeated loads increases, the above-mentioned relationship approximately and credibly obeys the power function distribution. Repeatedly applying load no more than the maximum longitudinal resistance of fastener to the rail, the existence of the rail cumulative displacement caused by frequent train braking can be demonstrated, and the relationship curve between the rail displacement and the number of loads can be obtained. Applying the fitting formula, the rail displacement after a specific number of loading times can be attained, and then referring to specific codes, we can determine whether it will exceed the safety limit.

Reflection Crack Analysis of Asphalt Overlay on Cement Concrete Pavement Based on XFEM

Based on the improved Paris formula, the reflection cracking characteristics of asphalt overlay on the cement concrete pavement are carefully scrutinized. The fatigue life is also predicted through the indoor simulation tests and establishing the two‐ and three‐dimensional extended finite‐element method (XFEM) models. Four fracture factors of the Paris formula in the asphalt mixture are appropriately calculated by fitting the N‐a curve of the indoor test, and their predicted values are then exploited in the numerical simulations. The obtained results show that the numerical model can successfully predict the results of the indoor simulation test. It indicates that the XFEM has apparent advantages in examining the reflection cracking of the asphalt overlay on the cement concrete pavement.

Investigation of Permanent Deformation Behavior of Steel Slag Asphalt Mixture under Indoor Simulation

Previous studies have indicated that steel slag can be used as a substitute for natural aggregates in asphalt mixture, while little attention has been paid to systematic investigation of the influences of various external environmental factors on deformation resistance of steel slag asphalt mixture. In order to understand the service behavior of steel slag asphalt mixture, its permanent deformation under different condition was investigated based on an indoor simulation test. The chemical composition, microscopic structure, surface texture, and volume stability of steel slag were firstly characterized. The uniaxial repeated loading test and standard wheel‐tracking test were applied to evaluate the effect of temperature, stress levels, and water damage on the permanent deformation of AC‐16 and AC‐20 steel slag asphalt mixtures. The results indicate that a higher content of alkaline oxide and high‐grade texture index existing in steel slag contribute to its strong absorptivity and adhesion of asphalt. The steel slag demonstrates fine volume stability due to its lower free‐CaO (f‐CaO) content, autoclave chalked ratio, and immersion expansion ratio. The permanent deformation of steel slag asphalt mixtures increases rapidly under higher stress and temperatures in contrast to lower increment at lower stress and temperatures. Asphalt mixtures at higher stress and higher temperatures and water condition exhibit larger rutting deformation and inferior rutting resistance. AC‐16 steel slag asphalt mixture has superior resistance to permanent deformation than AC‐20 asphalt mixture. Rutting factors show different degrees of impact in a decreasing order of temperature, water damage, and stress levels. The findings have significant implications for providing a theoretical basis for reusing steel slag in pavement construction and facilitating engineering application of steel slag asphalt mixture.

Experimental Study on the Deformation and Failure Characteristics of Anchor under Graded Loading and Corrosion

During the entire life cycle of rock and soil anchors, owing to the influence of adverse factors such as the working environment, load change, and anchor performance degradation, the working load of the anchor will continue to increase and the mechanical properties will continue to deteriorate, which significantly affects the safety and stability of rock and soil anchors. Therefore, this study focuses on the deformation and failure characteristics of anchors under loading and corrosion conditions by means of indoor simulation tests under laboratory conditions. The results indicate the following. (1) There are obvious cracks on the surfaces of specimens 2# and 10#. In the two groups of specimens, the corroded bolt surface exhibited a corrosion phenomenon. This indicates that the corrosion environment conditions cause a certain degree of damage to the anchored rock mass. (2) Under the same gradient load condition, three observable cracks were found in the 10# anchorage specimens and one observable crack was found in the 2# anchorage specimens. Therefore, it is clear that the damage degree of the anchor increases with an increase in the corrosion time. (3) Under the condition of corrosion environment, the strain in the lower part of the specimen is generally greater than that in the upper part of the specimen, and the failure of this group of specimens in the loading process is mostly splitting failure, which is basically generated along the trend of the strain nephogram, and shear failure occurs with the extension and diffusion of cracks.

Relationships between soil properties and the accumulation of heavy metals in different Brassica campestris L. growth stages in a Karst mountainous area

The speciation and activity of heavy metals in farmland were changed with the different soil properties and flooded environment, especially in the complex and rainy environment in soil of Guizhou Province. The objective of this study was to explore the concentrations of a variety of heavy metal activity and the speciation of those heavy metals in rhizosphere soil at different growth stages of Brassica campestris L. in a Karst mountainous area. Tessier's five-stage sequential extraction procedure, the potential ecological risk index, a Bayesian network, accumulation factors, translocation factors and a laboratory simulation experiment were applied in this study. The results showed that (1) no heavy metal concentrations (except the Cd concentration) exceeded the limits of the soil environmental quality risk control standards for soil contamination of agricultural land in China (GB15618-2018). (2) The orders of the accumulation factor and translocation factor values were Zn > Cd > Cu > Pb > Cr and Cd > Cu > Zn > Pb > Cr, respectively. The order of the heavy metal contents of different tissues during the whole growth period was roots > leaves > stems. (3) The indoor simulation test exhibited that the dry-wet alternation and flooding can reduce Cd activity in soil. (4) Redox potential (Eh), rather than pH or organic matter, was the main factor impacting the total content and chemical speciation of heavy metals in the soil, based on a dynamic Bayesian network. Based on the results, we suggest that the activity of heavy metals should be improved by using dry-wet alternation, whereas the proportions of ion-exchangeable forms of heavy metals are relatively low in the study area (except for Cd). Several measures may be taken to enhance soil acidity and reduce the Cd activity during Brassica campestris L. cultivation.

Simulation of Polarization Image Based on Intensity Image

Due to the limitation of industrial and civil fields of the polarization camera, we have developed a scheme for synthesizing polarization image based on intensity image and simulation technology. A whole process polarization or intensity transfer model from the incident solar light to the point at which the camera enters the pupil is set up based on 6SV. The indoor simulation test system of the target surface reflectivity is formed. The simulated polarization image is compared with the image directly obtained by the polarization camera under the same condition. Compared with the image from the polarization camera, we get the same trend of contrast information, while the target characteristic information is obviously improved for the intensity image and the error rate of the improved contrast does not exceed 12%.

Road performance of tourmaline/rubber powder modified asphalt mixture

To study the effects of tourmaline type and content on the road performance of rubber powder modified asphalt mixture, different types of tourmaline rubber powder modified asphalt mixtures were prepared by adding tourmaline powder instead of equal weight mineral filler into the mixtures. Based on indoor simulation test, the high temperature stability, low temperature crack resistance and water stability of rubber powder modified asphalt mixture under different tourmaline type and content were systematically analyzed. The results show that with the increase of tourmaline powder content, the road performance of asphalt mixtures show an overall growth trend. The 60 °C of rutting test dynamic stability, the -10 °C of bending test flexural-tensile strain, immersion residual Marshall stability and freeze-thaw splitting tensile strength ratio of rubber powder modified asphalt mixtures with tourmaline powder increase by 12.5-19.6%, 7.5-12%, 1.8-4.7% and 1.7-4.3%, respectively.

A Highly Integrated BOTDA/XFG Sensor on a Single Fiber for Simultaneous Multi-Parameter Monitoring of Slopes.

A highly integrated sensing technology, combining a stimulated Brillouin scattering-based distributed sensor with XFG (fiber Bragg grating (FBG) and long-period fiber grating (LPFG)) sensors on a single fiber, is proposed for the simultaneous measurement of fully distributed and multiple discrete dynamic strains/temperatures. A multiparameter monitoring scheme for slope safety is developed using this integrated sensing technology. An indoor simulation test is carried out to verify its ability to simultaneously monitor a slope’s surface displacement, an anchor reinforcement’s axial force, and rockfall vibration. The experimental results show that distributed static strain and discrete dynamic strain can be well-measured simultaneously with little interference. The results also demonstrate the XFG sensors’ capability for multi-type and multipoint multiplexing. In addition, the proposed hybrid sensor system has potential for the monitoring of multiple slope parameters simultaneously.

Noise reduction characteristics of asphalt pavement based on indoor simulation tests

Abstract Low noise asphalt pavement mitigates the impact of traffic noise on the ecological environment and surrounding population to a certain extent. To explore the noise reduction characteristics of different asphalt pavements, an indoor simulation device for pavement noise reduction is developed in this paper, based on the principle of pavement noise reduction. The device simulates the process of noise reflection and interference on the surface and inside of the pavement, which consumes the sound energy to achieve the noise reduction effect. The mechanical performance of six different types of asphalt mixtures is first tested. The noise reduction performance of the asphalt mixtures is then studied using the self-made noise testing device and Kundt’s tube method to verify the accuracy of the device. The influence of surface texture on pavement noise is also analyzed, and test results show that the six types of asphalt mixtures used in this study all meet mechanical performance requirements. A strong correlation is also observed between the noise testing device and the traditional Kundt’s tube method. The noise testing device is found to accurately measure the noise reduction characteristics of asphalt mixtures. For noise of different sound pressure levels, the same type of asphalt mixture displays different noise reduction capabilities. The better the noise reduction performance, the lower the sensitivity to sound wave changes, and the more stable the noise reduction effect. Excessive air void content does not significantly improve the pavement noise reduction performance, and it is recommended that the pavement air void content is maintained within the range of 17%–24%. The density of the asphalt mixture is found to be negatively correlated with the noise reduction performance, while the air void content and the mean texture depth is positively correlated with noise reduction. The results of grey relational analysis show that air void content is the most important factor affecting the noise reduction characteristics of asphalt pavement, followed by mean texture depth. Aggregate particle size is also found to exert a significant influence on noise reduction characteristics, and the influence degree of 9.5 mm particles is found to be the greatest, with 1.18 mm and 2.36 mm particles also showing a high degree of influence. Reasonable control of aggregate particle size should therefore be carried out in the design of low noise asphalt pavement.

Prediction model for carbonation depth of concrete subjected to freezing-thawing cycles

Through the indoor simulation test of the concrete durability under the coupling effect of freezing-thawing and carbonation, the variation regularity of concrete neutralization depth under freezing-thawing and carbonation was obtained. Based on concrete carbonation mechanism, the relationship between the air diffusion coefficient and porosity in concrete was analyzed and the calculation method of porosity in Portland cement concrete and fly ash cement concrete was investigated, considering the influence of the freezing-thawing damage on the concrete diffusion coefficient. Finally, a prediction model of carbonation depth of concrete under freezing-thawing circumstance was established. The results obtained using this prediction model agreed well with the experimental test results, and provided a theoretical reference and basis for the concrete durability analysis under multi-factor environments.