scholarly journals Study on Hygroscopic Swelling and Dehumidification Cracking Characteristics of Expansive Soil under Acid Rain and Cyclic Drying-Wetting

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Jin Chang ◽  
Jie Xiao ◽  
Jian-Qing Jiang ◽  
Rui Zhang ◽  
Xi-Long Kuang ◽  
...  
Keyword(s):  
Acid Rain ◽  
Crack Width ◽  
Digital Camera ◽  
Expansive Soil ◽  
Crack Development ◽  
High Definition ◽  
Ph Values ◽  
Swelling Rate ◽  
Cracking Characteristics ◽  
Average Crack

In this study, to reveal the swelling and cracking characteristics of expansive soil subjected to cyclic drying-wetting of acid rain, the effects of acid rain and cyclic drying-wetting on the swelling deformation of expansive soil were studied by using the load-free swelling rate test. Afterward, a high-definition digital camera was used to capture the crack development images of the sample during the dehumidification process under cyclic drying-wetting of acid rain. Furthermore, the changes of the microstructure and mineral composition of the expansive soil after cyclic drying-wetting of acid rain were analyzed by using the scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. Finally, the effect mechanisms of acid rain and cyclic drying-wetting on the swelling deformation and crack development of the expansive soil were discussed. The results indicate that acid rain has a positive effect on the swelling deformation and crack development of the expansive soil. The effect is greater with a stronger acidity of rainfall. Moreover, the combined action of acid rain and cyclic drying-wetting can promote the swelling deformation and crack development of the sample more notably. The swelling rate of the sample increased most significantly during the first two-time cyclic drying-wetting. The measured swelling rates at pH = 3 and 5 are 23.7% and 20.6%, respectively, which are higher than the swelling rates of 19.0% at pH = 7. The humidity of samples is 17–18% after the first-time drying-wetting cycle. The crack area ratios (Mf) of the samples with pH values of 5 and 3 are, respectively, increased by 11.0% and 69.1%; the average crack width of the sample increases by 32.3% and 93.3%, respectively, compared with pH values of 7. After the fourth-time drying-wetting cycle, Mf and the average crack width of the samples under the rainwater environment of three pH values increase greatly, but the difference of Mf among them became unapparent. In addition, the microscopic test results show that acid rain can corrode the binding materials (e.g., SiO2, Al2O3, K2O, MgO, and CaO) in the expansive soil. The erosion of the binding minerals weakens the structural connection strength, resulting in continuous increases in both size and number of microvoids. Under the superimposed influence of cyclic drying-wetting, the above changes are even more dramatic. Macroscopically, the swelling deformation of expansive soil increases and the cracks develop rapidly.

scholarly journals Intercalation and calcination as methods to reduce expansive soil properties

2021 ◽  
Vol 18 (1) ◽  
pp. 36
Author(s):  
Ristiya Adi Wiratama ◽  
Eko Hanudin ◽  
Benito Heru Purwanto
Keyword(s):  
Crack Width ◽  
Expansive Soil ◽  
Treatment Method ◽  
Exchange Capacity ◽  
Expansive Clay ◽  
Average Crack ◽  
Interlayer Structure ◽  
The Stability ◽  
Swelling Volume ◽  
Calcination Treatment

The expansive ability of soil causes a series of problems in various sectors. The dominance of smectite clay minerals significantly affects expansive ability because they have an unstable interlayer structure. Cation intercalation and calcination is a treatment method that can increase the stability of the clay interlayer structure. This research investigated the effects of intercalation cations and calcination treatment on the swelling ability and cracking properties in the clay from vertisols; the cations used for intercalation were aluminum and iron. The intercalation tested doses were based on the equivalent weight of 0x, 0.5x, and 1x cation exchange capacity (CEC) clay value. The calcination treatments used were 200°C, 300°C, and no calcination. Each treatment interaction was repeated three times. Parameters observed were the total area, average crack width, average lump area, total number of lumps, moisture content, swelling volume, and pH after treatment. The results showed that each treatment had a significant effect. Clay with an Al intercalation dose of 1x CEC without calcination treatment had the highest total area after drying, which was 41.035 cm<sup>2</sup>; the lowest average crack width was 0.153 cm, and the smallest swelling volume was 3.6 cm<sup>3</sup>. In contrast, the clay without intercalation and calcination treatments had a swelling volume up to 10 cm<sup>3</sup> on the 7<sup>th</sup> day. The clay with an Al intercalation dose of 1x CEC with 200°C calcination exhibited the best results in reducing the expansive clay ability and can be used as a guideline for further testing to reduce the soil’s expansive ability.

scholarly journals Desorption of metals from Cetraria islandica (L.) Ach. Lichen using solutions simulating acid rain

2014 ◽  
Vol 66 (1) ◽  
pp. 273-284 ◽  
Author(s):  
Ana Cuculovic ◽  
Mirjana Pavlovic ◽  
Jelena Savovic ◽  
D.S. Veselinovic
Keyword(s):  
Detection Limit ◽  
Acid Rain ◽  
Metal Content ◽  
Strong Link ◽  
Ph Values ◽  
Metal Detection ◽  
Logarithmic Dependence ◽  
Solution Volume

Desorption of metals K, Al, Ca, Mg, Fe, Ba, Zn, Mn, Cu and Sr from Cetraria islandica (L.) with solutions whose composition was similar to that of acid rain, was investigated. Desorption of metals from the lichen was performed by five successive desorption processes. Solution mixtures containing H2SO4, HNO3 and H2SO4-HNO3 were used for desorption. Each solution had three different pH values: 4.61, 5.15 and 5.75, so that the desorptions were performed with nine different solutions successively five times, always using the same solution volume. The investigated metals can be divided into two groups. One group was comprised of K, Ca and Mg, which were desorbed in each of the five desorption processes at all pH values used. The second group included Al, Fe, Zn, Ba, Mn and Sr; these were not desorbed in each individual desorption and not at all pH values, whereas Cu was not desorbed at all under any circumstances. Using the logarithmic dependence of the metal content as a function of the desorption number, it was found that potassium builds two types of links and is connected with weaker links in lichen. Potassium is completely desorbed, 80% in the first desorption, and then gradually in the following desorptions. Other metals are linked with one weaker link (desorption 1-38%) and with one very strong link (desorption below the metal detection limit).

Test Stand for Analysis of Fatigue Crack Propagation under Bending with Torsion

2008 ◽  
Vol 144 ◽  
pp. 90-93 ◽  
Author(s):  
Grzegorz Gasiak ◽  
Grzegorz Robak
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Digital Camera ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Test Stand ◽  
Crack Development ◽  
Fatigue Crack Propagation Rate ◽  
Fatigue Crack Development

The paper presents a test stand for measurements of fatigue crack propagation. The stand includes a fatigue machine MZGS–100 and a device for registration of the crack length. The test stand is equipped with a stereoscopic microscope with fluent magnification of 7× – 67.5×. The microscope can be applied for observation of fatigue crack development. The microscope is also equipped with a digital camera, which enables continuous observation of fatigue crack development on the computer monitor and it is not necessary to stop the machine. The test results obtained at this stand can be used for determination of fatigue life and fatigue crack propagation rate.

Theoretical Analysis of Reinforced Beams of UHTCC

2018 ◽  
Vol 878 ◽  
pp. 18-22
Author(s):  
Hua Qiang Yu
Keyword(s):  
Crack Width ◽  
Approximate Formula ◽  
Crack Spacing ◽  
Cementitious Composite ◽  
Reinforcement Effect ◽  
Ordinary Concrete ◽  
High Toughness ◽  
Reinforced Beams ◽  
New Type ◽  
Average Crack

UHTCC (Ultra High Toughness Cementitious Composite) is a new type of material which is widely used in this study. It is a kind of cement-based material with very good toughness. It is effective to improve the performance of damaged reinforced concrete and improve its durability. UHTCC is widely used in the reinforcement of concrete structures. There is no clear and effective method for calculating it. There is an approximate formula for the crack width of ordinary concrete. The concept of an average crack spacing is used in the derivation of the formula. The limit of UHTCC for cracks can be measured by the concept of average crack spacing. According to the obtained crack width limit, the reinforcement effect of UHTCC can be shown.

scholarly journals Analysis of Factors Influencing Stability of Overlying Soil Layer on Thin Bedrock Based on Crack Development-Closure Test

2019 ◽  
Vol 2019 ◽  
pp. 1-20 ◽  
Author(s):  
Guangming Wu ◽  
Haibo Bai ◽  
Luyuan Wu ◽  
Shixin He ◽  
Bin Du
Keyword(s):  
Water Content ◽  
Layer Thickness ◽  
Crack Width ◽  
Soil Layer ◽  
Crack Development ◽  
Sand Content ◽  
Particle Composition ◽  
Thin Bedrock ◽  
The Stability ◽  
Seam Mining

The water-blocking properties of the clay layer at the bottom of the Cenozoic overburden in China are an important factor influencing the safety of thin bedrock coal seam mining. Clay has remolding properties that are unlike the nonreversible characteristics of cracks in brittle rock, and failure cracks in clay can reclose or continue to expand under the influence of different external factors. In this work, the soil layer on top of thin bedrock is the research object, and the influences of the particle composition, water content, soil layer thickness, and crack width on the crack development-closure state of soil layer are analyzed by the orthogonal test method. Visual analysis shows that the order of influence of each factor on the stability of soil layer is the crack width, particle composition, soil layer thickness, and water content. The stability of soil layer decreases with increasing crack width and sand content and decreasing soil layer thickness; in addition, soil layer stability decreases first and then increases with increasing water content. Further variance analysis shows that the crack width and particle composition are key factors that impact the stability of soil layer and that the soil layer thickness has some influence, while the water content has little effect on the stability of soil layer. In addition, the crack will reclose when the sand content in soil is less than 50% and the crack width is less than or equal to 1.0 mm, and the soil layer is prone to further failure when the sand content in soil is more than 50% and the crack width is greater than or equal to 3.0 mm; when the soil layer thickness is 15.0 cm, its stability is better than when the soil layer thickness is 10.0 cm or 5.0 cm.

scholarly journals A Comparison of Crop Parameters Estimation Using Images from UAV-Mounted Snapshot Hyperspectral Sensor and High-Definition Digital Camera

2018 ◽  
Vol 10 (7) ◽  
pp. 1138 ◽  
Author(s):  
Jibo Yue ◽  
Haikuan Feng ◽  
Xiuliang Jin ◽  
Huanhuan Yuan ◽  
Zhenhai Li ◽  
...  
Keyword(s):  
Digital Camera ◽  
Parameters Estimation ◽  
Growth Stages ◽  
Least Squares Regression ◽  
High Definition ◽  
Area Index ◽  
Near Surface ◽  
Crop Height ◽  
Crop Parameters ◽  
Hyperspectral Sensor

Timely and accurate estimates of crop parameters are crucial for agriculture management. Unmanned aerial vehicles (UAVs) carrying sophisticated cameras are very pertinent for this work because they can obtain remote-sensing images with higher temporal, spatial, and ground resolution than satellites. In this study, we evaluated (i) the performance of crop parameters estimates using a near-surface spectroscopy (350~2500 nm, 3 nm at 700 nm, 8.5 nm at 1400 nm, 6.5 nm at 2100 nm), a UAV-mounted snapshot hyperspectral sensor (450~950 nm, 8 nm at 532 nm) and a high-definition digital camera (Visible, R, G, B); (ii) the crop surface models (CSMs), RGB-based vegetation indices (VIs), hyperspectral-based VIs, and methods combined therefrom to make multi-temporal estimates of crop parameters and to map the parameters. The estimated leaf area index (LAI) and above-ground biomass (AGB) are obtained by using linear and exponential equations, random forest (RF) regression, and partial least squares regression (PLSR) to combine the UAV based spectral VIs and crop heights (from the CSMs). The results show that: (i) spectral VIs correlate strongly with LAI and AGB over single growing stages when crop height correlates positively with AGB over multiple growth stages; (ii) the correlation between the VIs multiplying crop height and AGB is greater than that between a single VI and crop height; (iii) the AGB estimate from the UAV-mounted snapshot hyperspectral sensor and high-definition digital camera is similar to the results from the ground spectrometer when using the combined methods (i.e., using VIs multiplying crop height, RF and PLSR to combine VIs and crop heights); and (iv) the spectral performance of the sensors is crucial in LAI estimates (the wheat LAI cannot be accurately estimated over multiple growing stages when using only crop height). The LAI estimates ranked from best to worst are ground spectrometer, UAV snapshot hyperspectral sensor, and UAV high-definition digital camera.

The vertical gradient of bark pH of twigs and macrolichens in a Picea abies canopy not affected by acid rain

2001 ◽  
Vol 33 (4) ◽  
pp. 353-359 ◽  
Author(s):  
Thale Kermit ◽  
Yngvar Gauslaa
Keyword(s):  
Picea Abies ◽  
Species Composition ◽  
Acid Rain ◽  
Vertical Gradient ◽  
Small Scale ◽  
High Ph ◽  
Ph Values ◽  
Constant Ph ◽  
Horizontal Variation ◽  
Cyanobacterial Lichens

AbstractThe pH of 192 thin, even-aged twigs from 4 height levels of 12 randomly selected trees within a boreal Picea abies canopy naturally exposed to rainfall with a high pH (>5·2) was measured. The largest variation in bark pH was due to the height above the ground. However, a highly significant horizontal variation between trees was also found, apparently due to small-scale soil variations. The biomass of alectorioid lichens increased with increasing height above die ground to at least 12 m, a height interval with fairly constant pH values. The uppermost twigs had an unusually high pH and an abnormal species composition for P. abies, with dominance of the foliose Melanelia exasperatula. The canopy hosted several cyanobacterial lichens, but these were scattered and had low biomass, restricted to lower branches of the trees with the highest bark pH.

scholarly journals Seabed video and still images from the northern Weddell Sea and the western flanks of the Powell Basin

2021 ◽  
Vol 13 (2) ◽  
pp. 609-615
Author(s):  
Autun Purser ◽  
Simon Dreutter ◽  
Huw Griffiths ◽  
Laura Hehemann ◽  
Kerstin Jerosch ◽  
...  
Keyword(s):  
Digital Camera ◽  
Weddell Sea ◽  
Video Data ◽  
High Definition ◽  
Short Baseline ◽  
Still Images ◽  
Still Image ◽  
Topographic Complexity ◽  
Camera Systems ◽  
Quality Video

Abstract. Research vessels equipped with fibre optic and copper-cored coaxial cables support the live onboard inspection of high-bandwidth marine data in real time. This allows for towed still-image and video sleds to be equipped with latest-generation higher-resolution digital camera systems and additional sensors. During RV Polarstern expedition PS118 in February–April 2019, the recently developed Ocean Floor Observation and Bathymetry System (OFOBS) of the Alfred Wegener Institute was used to collect still-image and video data from the seafloor at a total of 11 predominantly ice-covered locations in the northern Weddell Sea and Powell Basin. Still images of 26-megapixel resolution and HD (high-definition) quality video data were recorded throughout each deployment. In addition to downward-facing video and still-image cameras, the OFOBS also mounted side-scanning and forward-facing acoustic systems, which facilitated safe deployment in areas of high topographic complexity, such as above the steep flanks of the Powell Basin and the rapidly shallowing, iceberg-scoured Nachtigaller Shoal. To localise collected data, the OFOBS system was equipped with a Posidonia transponder for ultra-short baseline triangulation of OFOBS positions. All images are available from: https://doi.org/10.1594/PANGAEA.911904 (Purser et al., 2020).

scholarly journals Mechanical Behavior and Constitutive Model for Loess Samples under Simulated Acid Rain Conditions

2021 ◽  
Author(s):  
xia ye ◽  
Enlong Liu ◽  
Baofeng Di ◽  
yayang yu
Keyword(s):  
Mechanical Properties ◽  
Acid Rain ◽  
Mechanical Model ◽  
Ph Value ◽  
Simulated Acid Rain ◽  
Test Results ◽  
Hardening Model ◽  
Ph Values ◽  
Scanning Electron ◽  
Peak Value

Abstract In this paper, the sulfuric acid solution is diluted to pH 5.0, 4.0 and 3.0 to simulate the acid rain condition, and the triaxial compressional tests and scanning electron microscope are carried out to study the mechanical properties and evolution of the microstructure of the saturated loess samples. The results demonstrate that acid rain increases the porosity of loess samples, and the pore distribution is not uniform, so that the mechanical properties of loess samples change. With the decrease of pH value, the peak value of the deviatoric stress and the volumetric contraction of loess samples decreases, which causes the strength of soil to decrease. Furthermore, the framework of the chemical-mechanical model for loess under the action of acid rain is established, in which the loess is considered as porous medium material, and the variable of acid rain at different pH values through the degree of chemical reaction is taken into account in the double-hardening model, and the model is also verified by the triaxial test results finally.

scholarly journals Experimental Study on Cracking Behaviour and Strength Properties of an Expansive Soil under Cyclic Wetting and Drying

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Tao Li ◽  
Yanqing He ◽  
Guokun Liu ◽  
Binru Li ◽  
Rui Hou
Keyword(s):  
Shear Strength ◽  
Expansive Soils ◽  
Expansive Soil ◽  
Strength Properties ◽  
Rate Of Change ◽  
Crack Development ◽  
Structural Morphology ◽  
Limit Value ◽  
Strength Change ◽  
Length Direction

Expansive soil is characterized by its unique structural morphology and drastic volume change. With infrastructure increasingly constructed in expansive soil areas, engineering problems caused by the properties of expansive soils have attracted more attention. Cyclic wetting-drying and shear testing were accordingly conducted on an expansive soil from Chengdu area in China. Crack development and shear strength change were analyzed using the Mohr–Coulomb equation for shear strength by fitting the experimental data. The results show the following: (1) With the increase in wetting-drying cycles, the crack ratio increases, the shear strength decreases, and the shear strength parameters gradually decrease at the same rate of change. The applied vertical load reduces the weakening effect of the wetting-drying cycles on the soil structure and strength by restraining the expansion and contraction deformation. (2) By analyzing the number of wetting-drying cycles and the crack images, the crack development (length, direction, etc.) of the expansive soil can be predicted and described. (3) There is a specific linear correlation between the crack ratio and strength that approached a limit value with ongoing wetting-drying cycles. The strength of the expansive soil can therefore be obtained based on crack development, improving the ability of designers to account for the behaviour of expansive soils.

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