Wet Cycles Research Articles

Critical slowing down characteristics of acoustic emission for fracture instability of sandstone down-slope rock bridge under cyclic wetting and drying

Down-slope rock bridge in slopes and dangerous rock masses are often affected by cyclic wetting and drying, leading to severe geological disasters. In order to investigate the deterioration mechanism, deformation failure mode and instability precursor information of sandstone down-slope rock bridge under different cyclic wetting and drying, uniaxial compression tests combined with acoustic emission (AE) tests were conducted. The failure of the specimen experienced four stages. As the number of the cyclic wetting and drying increased, the specimen’s uniaxial compressive strength and elastic modulus decreased, and the failure mode transitioned from tensile to shear. Utilizing the critical slowing down theory, the variance and autocorrelation coefficient curves of AE multi-parameters were analyzed. The abrupt change of RA value, RA/AF value, and b value at the crack damage stress point and the abrupt change of the peak frequency lagging behind the crack damage stress point can be used as the precursors of instability. The instability precursor identified based on the peak frequency variance is closer to the specimen’s peak stress point and can be used for short-term failure prediction. The autocorrelation coefficient curve of AE multi-parameters aligned with the variance curve, indicating that with an increased number of cyclic wetting and drying, the instability precursor appeared earlier, leading to a larger failure prediction time interval.

Effect of Wet-Dry Cycling on the Microstructure of Various Weathering Grade Sandstone

This study investigated the effect of rock-water interaction on microstructural properties of various weathering grade sandstone. Sandstone samples were acquired from the Sor-Range coal mine area, Pakistan, and were investigated using a tabletop scanning electron microscope (SEM). The characteristics of microstructures from micrographs were obtained using ImageJ software. According to the findings an increase in wet and dry cycles significantly affects the microstructures (pore spaces and microcracks). The porosity and microcracks density of sandstone increases with the number of wet and dry cycles. Furthermore, the length of microcracks increases as the weathering grade increases. As variation in rock macroscopic mechanical characteristics is directly associated with the deterioration of microstructures. Therefore, analyzing the effect of water-rock interaction in various weathering grades of rock can offer a more accurate reference index for assessing the stability of geotechnical structures.

Improved mechanical response of Nano-SiO2 powder cemented soil under the coupling effect of dry and wet cycles and seawater corrosion

Improved mechanical response of Nano-SiO2 powder cemented soil under the coupling effect of dry and wet cycles and seawater corrosion

Experimental study on the effect of water-induced deterioration on shear properties of bolted rock joints

The investigation into the impact of dry and wet cycles as well as prolonged immersion on the shear properties of bolted rock joints can facilitate comprehension of the mechanism behind shear damage in anchorage rock slopes located within dam sites, which is crucial for conducting long-term stability analyses of such slopes and ensuring safe operation of hydropower plants. In this study, the sandstone from the Three Gorges reservoir area was collected and utilized to made into bolted rock joint specimens, which underwent 12 cycles of wetting and drying as well as 180 days of immersion before undergoing direct shear tests to investigate the degradation of their mechanical properties. The test results indicate that both treatments for water deterioration can significantly reduce the peak shear strength of bolted sandstone joints. The shear deformation characteristics of bolts also vary with the decrease in rock mass strength. As the number of wet and dry cycles, as well as immersion time, increases, the plastic hinge length of the bolt gradually extends. The surface roughness of the joint has an impact on the fracture mode of the bolt. In a flat joint, the fracture section of the bolt exhibits a certain inclination angle, indicating a damage mode where positive and shear stresses act in concert; whereas in a rough joint, the fracture section of the anchor rod shows almost zero inclination angle and is damaged under positive stress. Finally, an attempt was made to apply the conclusions of this paper to engineering by conducting a time-varying reliability analysis of the generalized anchored slope model. The results obtained have significant guidance for evaluating the long-term stability of anchored slopes in hydropower projects.

Plant mucilage increases pull‐out resistance of root analogues from soil

AbstractThe interface between plants' roots and soil is strongly affected by rhizodeposits, especially mucilage, that change mechanical and hydrological behaviour. In addition to impacts to aggregation, water capture and root penetration, rhizodeposits may also affect the pull‐out resistance of plant roots. Due to the complex architecture of plant roots and an inability to restrict rhizodeposit production, this study used a simplified system of wooden skewers to simulate roots and chia seed mucilage as a model to simulate rhizodeposit compounds. Pull‐out tests were then carried out to measure the impacts of mucilage, and one (WD1) or two (WD2) cycles of wetting and drying of soils. Using a mechanical test frame, the maximum pull‐out resistance (Fmax) and pull‐out displacement (dL) were recorded, allowing for pull‐out energy (E), average pull‐out force () and bond strength (τmax) to be calculated. The results showed that all pull‐out parameters of the samples with added rhizodeposit compounds tended to decrease between WD1 and WD2, but they were still significantly greater than without the added mucilage. The model rhizodeposit increased all pull‐out parameters by a minimum of 30%. With an additional wet–dry cycle, the mucilage tended to cause a decline in pull‐out parameters relative to a single wet‐dry cycle. This suggests mucilages could enhance the mechanical resistance of roots to pull‐out, but resistance decreases over time with cycles of wetting and drying. To conclude, an important role of mucilage is pull‐out resistance, which has relevance to plant anchorage and root reinforcement of soils.

Study of the damage mechanism on mechanical properties of super absorbent polymer-improved geopolymers under dry–wet cycling

Study of the damage mechanism on mechanical properties of super absorbent polymer-improved geopolymers under dry–wet cycling

Analysis of the Mechanical Properties of Cured Sludge by Alkaline Excitation of Phosphogypsum

Engineering slag is a green building material that meets the requirements of contemporary sustainable development, and the solidification technology of residue is particularly important in the practical engineering of resource utilization and environmental protection. In order to reuse the waste soil and industrial waste and reduce the construction cost, the stabilization effect of adding different contents of calcium oxide, blast furnace slag and phosphogypsum to the waste soil of a township road reconstruction project was studied. The unconfined compressive strength test of calcium oxide further clarified the solidification mechanism of residual soil and helped us to obtain the optimal curing ratio. The dry and wet cycle test simulated the influence of temperature and humidity changes on the appearance, quality, strength and water resistance in actual engineering. The experimental results show that the unconfined compressive strength of the sample reaches 1.273 MPa after 7 days of curing when the mixture of 4% calcium oxide (ratio to 100% plain soil) and 16% blast furnace slag (ratio to 100% plain soil) is mixed. When the three materials were mixed, the unconfined compressive strength of 4% calcium oxide (the ratio of 35% phosphogypsum and 65% plain soil) and 16% blast furnace slag (the ratio of 35% phosphogypsum and 65% plain soil) reached 1.670 MPa and 3.107 MPa at 7 and 28 days, respectively. The curing age has a significant promoting effect on the stability of loess. The dry and wet cycle test results conclude that the specimens have good durability and stability. The results of microstructure analysis shows that a large number of ettringite and C-S-H gel were formed in the gelling system, which not only makes the original soil more stable, but also acts as a part of filling pores, and the two work together to support the soil and improve the strength.

Under Sulfate Dry–Wet Cycling: Exploring the Symmetry of the Mechanical Performance Trend and Grey Prediction of Lightweight Aggregate Concrete with Silica Powder Content

In order to improve the mechanical properties and durability of lightweight aggregate concrete in extreme environments, this study utilized Inner Mongolia pumice as the coarse aggregate to formulate pumice lightweight aggregate concrete (P-LWAC) with a silica powder content of 0%, 2%, 4%, 6%, 8%, and 10%. Under sulfate dry–wet cycling conditions, this study mainly conducted a mass loss rate test, compressive strength test, NMR test, and SEM test to investigate the improvement effect of silica powder content on the corrosion resistance performance of P-LWAC. In addition, using grey prediction theory, the relationship between pore characteristic parameters and compressive strength was elucidated, and a grey prediction model GM (1,3) was established to predict the compressive strength of P-LWAC after cycling. Research indicates that under sulfate corrosion conditions, as the cycle times and silica powder content increased, the corrosion resistance of P-LWAC showed a trend of first increasing and then decreasing. At 60 cycles, P-LWAC with a content of 6% exhibited the lowest mass loss rate and the highest relative dynamic elastic modulus, compressive strength, and corrosion resistance coefficient. From the perspective of data distribution, various durability indicators showed a clear mirror symmetry towards both sides with a silica powder content of 6% as the symmetrical center. The addition of silica fume reduced the porosity and permeability of P-LWAC, enhanced the saturation degree of bound fluid, and facilitated internal structural development from harmful pores towards less harmful and harmless pores, a feature most prominent at the 6% silica fume mixing ratio. In addition, a bound fluid saturation and pore size of 0.02~0.05 μm/% exerted the most significant influence on the compressive strength of P-LWAC subjected to 90 dry–wet cycles. Based on these two factors, grey prediction model GM (1,3) was established. This model can accurately evaluate the durability of P-LWAC, improving the efficiency of curing decision-making and construction of concrete materials.

A meso‐damage‐based constitutive model for yellow sandstone under dry–wet cycles

AbstractThe mechanical properties of rocks weaken under dry–wet cycles. This weakening may significantly modify the safety reserve of underground caverns or reservoir bank slopes. However, meso‐damage has not been carefully studied based on micromechanical observations and analyses. Therefore, in this study, meso‐damage of a yellow sandstone is investigated and a meso‐damage‐based constitutive model for dry–wet cycles is proposed. First, computed tomography scanning and uniaxial compression tests were conducted on yellow sandstones under different dry–wet cycles. Second, the evolution of rock mesostructures and the damage mechanism subjected to dry–wet cycles were simulated using the discrete element method with Particle Flow Code in 2 Dimensions (PFC2D) software. Third, a constitutive model was proposed based on the meso‐statistical theory and damage mechanics. Finally, this constitutive model was verified with the experimental results to check its prediction capability. It is found that the radius and number of pore throats in the sandstone increase gradually with the number of dry–wet cycles, and the pore structure connectivity is also improved. The contact force of sandstone interparticle cementation decreases approximately linearly and the continuity of the particle contact network is continuously broken. The meso‐deformation and strength parameters show similar declining patterns to the modulus of elasticity and peak strength of the rock sample, respectively. This meso‐damage‐based constitutive model can describe well the rock deformation in the initial pressure density stage and the damage stage under the coupling effect of dry–wet cycles and loads.

Experimental study on damage of slope under drying and wetting cycle based on DC electric method.

In order to investigate the seepage law and crack development characteristics of dump slopes, as well as the impact on slope stability during drying and wetting cycles, a simulation test slope system was constructed in a rainfall environment, specifically designed to mimic the engineering conditions of dump slope. The apparent resistivity response formula for the seepage and crack development processes was derived based on the three-phase medium theory of rock-soil bodies and Maxwell's conductivity formula. The geoelectric field characteristics pertaining to slope damage and the corresponding patterns of alteration were comprehensively investigated. The results demonstrate a negative correlation between resistivity and slope water content, with resistivity increasing as cracks develop and decreasing with water infiltration. The progression of crack formation in a rainfall environment on a dump slope can be categorized into three stages: The initial phase involves the saturation of the slope as water content increases. Subsequently, the second phase entails the initiation and expansion of capillary zones, along with the formation of dominant waterways. Lastly, the third phase encompasses the formation and expansion of cracks within the dumping site. The occurrence of sudden changes and abnormal fluctuations in apparent resistivity within a saturated slope signifies the presence of cracks and weak surfaces, leading to gradual and irreversible damage. This phenomenon serves as an indicator of slope damage and can be utilized for the early prediction of slope instability.

Degradation mechanisms of concrete cold joint surfaces under sulfate cycles and varying pouring intervals

In concrete structures, particularly in arid and saline environments, the cold joint surface often serves as a primary entry point for erosion damage, thus dictating the lower limit of structural durability. This study investigates the erosion and damage mechanisms of cold joint concrete under such conditions, focusing on specimens with varying pouring intervals (0.25 d, 0.5 d, 1 d, 7 d, and 28 d). These specimens underwent 0, 30, 90, and 150 sulfate dry‒wet cycles, with their degradation assessed through compression‒shear tests. The findings reveal a logarithmic relationship between the cold joint surface adhesion and the pouring interval, and similarly, there is a logarithmic relationship between the internal friction angle and the pouring interval. Shorter intervals correspond to a higher rate of decrease in both adhesion and internal friction angle, while longer intervals result in lower, eventually stabilizing, values of these properties. Scanning Electron Microscopy analysis indicates that inherent defects in the cold joint surface expedite sulfate penetration into the concrete. As the number of sulfate cycles increases, ettringite formation in the cracks leads to their expansion and interconnection, diminishing the shear resistance of the cold joint surface. The study shows that the pouring interval significantly influences corrosion resistance, with its effects becoming more pronounced after a threshold of sulfate cycles (approximately 90). Shear strength is found to be more susceptible to sulfate erosion compared to compressive strength, with a faster degradation rate. After 80 to 110 erosion cycles, the adhesion corrosion resistance drops to 75%, while the compressive strength remains above this threshold.

Effects of hydrological dynamics in controlling phosphorus bioavailability in intermittent rivers and implications for estuaries

Several studies on intermittent rivers and ephemeral streams (IRES) have focused on the ecology of populations and communities, and very few explored the biogeochemistry and bioavailability of key elements, such as phosphorus (P) and nitrogen (N). In this study, we aimed to explore the role of environmental seasonality on P bioavailability in an intermittent river in Northeastern Brazil and the implications for nutrient dynamics to downstream ecosystems, such as the estuaries. The study was performed at the Cruxati River, located in the Litoral Hydrographic Basin on the coast of Ceará State, Brazil. We sampled riverine sediments during three hydroperiods (i.e., dry, rewetting, and flow) according to the theoretical model for research in intermittent rivers. We performed a geochemical fractionation of different P forms and determined the physicochemical parameters, particle size distribution, mineralogy, and total organic carbon of the sediments. Mean values were compared using the Kruskal–Wallis non-parametric statistical test (p-value < 0.05) and by discriminant function analysis. We observed that the predominant fractions of P were associated with Fe-oxides, silicates, and refractory organic matter, but there were no statistical differences among these fractions for all hydroperiods. The exchangeable-P form was higher in the dry and flow periods than in the rewetting period. On the opposite side, P associated with humic acids and carbonates was lower in the dry and flow periods but higher in the rewetting period. We concluded that seasonality influences the bioavailability of P in intermittent rivers, being strongly influenced by the organic fraction, including the humic acid fraction and the refractory organic matter, which are important sources of P in the aquatic system. Furthermore, the IRES may act as a source or a sink of nutrients throughout the cycles of wetting and drying, which may release P from the sediments to the aquatic environment. Hence, IRES plays an important role in transporting nutrients to estuaries and maintaining their ecosystem services.

Effects of different aging methods on the ability of biochar to adsorb heavy metal cadmium and its physical and chemical properties.

The aging process can affect the physical and chemical properties as well as adsorption capacity of biochar. This study focuses on the heavy metal cadmium (Cd) as the research object, and artificially ages biochar prepared from rice straw and corn straw through accelerated freeze-thaw cycles, alternating dry wet cycles, and ultraviolet light treatment, in order to evaluate the effects of different aging conditions on the physical and chemical properties of the two different types of biochar and on their adsorption capacities for Cd. After aging, the pH of rice and corn biochar decreased to varying degrees, respectively. The surface structure was ruptured, the average pore diameter was decreased, and the specific surface area was increased by 27.3%, 21.9%, and 9.8% (rice) and 95.4%, 27.7%, and 13.4% (corn). Ultraviolet light aging has the most significant impact on the elemental content of biochar, and the C content was decreased by 12.4% (rice) and 9.3% (corn). The O content was increased by 11.2% (rice) and 44.1% (corn), and the numbers of O/C, H/C, (O + N)/C, and oxygen-containing functional groups were increased. These results demonstrate that the aging process reduces the degree of aromatization of biochar, while enhancing its polarity and Cd adsorption capacity. Rice straw biochar (RSB) has a greater ability to adsorb Cd than corn straw biochar (CSB). In addition, ultraviolet light aging is particularly effective in increasing heavy metal adsorption.

Influence of GFRP Confinement of Reinforced Concrete Columns Exposed to Sodium Chloride on Microstructure and Hydration Products

This paper explores the effect of sodium chloride (NaCl) on microstructure and hydration products of cylindrical column concrete and compares the results after covering it with Glass Fiber Reinforced Polymer (GFRP). 20 short RC columns were prepared with a single concrete mixture. The specimens have cured in different concentration of NaCl (0, 5%, 10%, 15%), some specimens cured directly in solution and other specimens exposed to wet and dry cycle. These specimens were tested, a first group after 28 days of curing, second group after 56 days, while the third group was repaired by GFRP after 28 day then returned to the cured environment and tested after56 day. In order to determine the main crystalline phase composition of concrete specimens and for phase identification of a crystalline material, scanning electron microscopy (SEM) morphology of microstructure concrete and X-ray diffraction (XRD) have been used. The results revealed denser microstructure with the concentration of NaCl crystalline, existence of binding chloride as free halite, chemical pound as a Friedel’s salt or Physical binding held to the surface of hydration products. In addition, the corrosive compounds were observed, and the hydration product phase decreased due to concentration of curing environment. Furthermore, the results from the samples that were covered with GFRP showed that the value of the hydration products didn't change when compared with the samples that were tested after 28 days, moreover, the voids were found in them when compared with the samples exposed to the environment damage without covering it with GFRP.

Multiscale study of the strength deterioration and microstructure changes in loess during dry‒wet and freeze‒thaw cycles

ABSTRACT To study the influence of climate and the environment on the stability of loess slopes in Yan’an, China, the macromechanical deterioration and changes in its internal structure were explored by simulating its behavior during drying, wetting, freezing and thawing under natural conditions. A triaxial apparatus was used to conduct multiple shear tests to obtain stress‒strain relationships and shear strength parameters of the soil under different cycle modes, and the results were applied to analyze the macromechanical changes of the loess samples with increasing numbers of cycles. The results of the stress‒strain curves and the trends of the shear strength parameters showed that when a sample experienced coupled dry‒wet and freeze‒thaw cycles, its shear strength was considerably lower than that under a single type of cycle. Additionally, dry‒wet cycles had a stronger negative effect than freeze‒thaw cycles on soil strength. Microscopic tests showed that the contact mode of particles tended to be unstable due to the effects of dry‒wet and freeze‒thaw cycles, resulting in the reduction of soil cementation. The results of this multiscale research provide a reference for future work on geological disaster prevention and engineering control in areas where loess is present.

Degradation mechanism and life prediction of cemented tailings backfill under dry–wet cycles and salt erosion

In this paper, the effects of drywet cycling and salt erosion on the unconfined compressive strength (UCS), relative dynamic elastic modulus and mass of cemented tailings backfill (CTB) were investigated, and the mechanism for CTB deterioration was explored with scanning electron microscopy-energy dispersive spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The reliability lifespan of CTB was predicted with the Wiener stochastic process. The results showed that with the increases in the number of drywet cycles, the damage to the CTB deepened continuously, including skin peeling, corner damage, and aggregate exposure; the UCS, relative dynamic elastic modulus and mass of CTB immersed in a sodium chloride solution, a sodium sulfate solution, and a solution of both first increased and then decreased; and the UCS, relative dynamic elastic modulus and mass of CTB immersed in a magnesium chloride solution, a magnesium sulfate solution, and a solution of both showed a decreasing trend. Cl- inhibited the erosion of CTB by SO42- but did not inhibit erosion by Mg2+. Cl- and SO42- invaded the CTB to produce calcium hydroxide, gypsum, Friedel's salt, ettringite, C-S-H and other products. The reliable lifetime predicted with the relative dynamic elastic modulus used as the degradation index was the longest, followed by the UCS, and the lifetime predicted with the mass was the shortest.

Research on the Strength Damage and Permeability Characteristics of Cemented Paste Backfill under Chlorine Salt Erosion and Dry–Wet Cycles

Cement paste backfill (CPB) suffers serious damage and deterioration under the dual erosion conditions of the dry–wet cycle caused by the high chloride salt concentration in mine water and the fluctuation of mine water level. In order to discuss the mechanical properties and permeability characteristics of CPB under erosion, this study designs an immersion experiment for CPB under chloride salt and dry–wet cycle conditions. Through a uniaxial compressive strength (UCS) test, the change law for the mechanical parameters of the CPB was investigated, the strength constitutive equation of the CPB was constructed and the deterioration process of the CPB was analyzed. The penetration test was used to investigate the diffusion characteristics of the packing under chloride salt and dry–wet cycle conditions. The results showed that the strength and Young’s modulus of the CPB initially increased and then rapidly decreased, with maximum decrease rates of 32.2% and 38.2%, respectively. The CPB structure exhibits an initial undamaged stage, an initial damaged stage, a damaged development stage, a damaged destruction stage and a residual damaged stage. The chloride ion penetration depth gradually increased with the number of dry–wet cycles, with a maximum diffusion depth of 20.5 mm. The maximum apparent diffusion coefficient of chloride ion was 18.99 × 10−10 m2/s, and the maximum concentration was 0.303 mol/L. Under the double erosion conditions of chloride salt and dry–wet cycle, the CPB structure was severely damaged.

3D Morphology Characteristics of Concrete Interfaces under Seawater Dry–Wet Cycles

3D Morphology Characteristics of Concrete Interfaces under Seawater Dry–Wet Cycles

Response of granite residual soil slopes under dry–wet cycles

Granite residual soil is widely distributed in the southern coastal areas of China, and the slopes of granite residual soil are prone to instability and failure under the alternating action of rainfall and drying, which will cause great disasters to human society. In order to study the response mechanism of granite residual soil slopes under the alternating action of rainfall–drying–static–rainfall (RDSR), this study conducted indoor scaling model tests to analyze the response during dry and wet cycles. This study presented the response process of the slope under the influence of dry and wet cycles and discussed the change laws of slope deformation, water content, and matric suction. The results show that, under the alternating action of rainfall–drying–static–rainfall, 1) the network cracks on the slope form a dominant channel for rainwater seepage, which is the main reason for the rapid decline in soil anti-sliding ability within a short time; 2) at a rainfall intensity of 1.7–2.4 mm/min, the erosion effect of rain on the slope is obviously stronger than that of osmotic erosion, and the surface erosion failure of the granite residual soil slope tends to occur without an obvious sliding surface; 3) after the loss of matric suction over a certain period, the phenomenon of channeling and loss failure on the slope serve as a sufficient condition for slope instability failure but is not a necessary condition. The above research results are expected to provide the basis and reference for preventing and controlling landslide hazards in granite residual soil slopes under similar conditions.

At-rest lateral earth pressure of compacted expansive soils: Experimental investigations and prediction approach

This paper presents experimental studies on a compacted expansive soil, from Nanyang, China for investigating the at-rest lateral earth pressure σL of expansive soils. The key studies include (i) relationships between the σL and the vertical stress σV during soaking and consolidation, (ii) the influences of initial dry density ρd0 and moisture content w0 on the vertical and lateral swelling pressures at no swelling strain (i.e. σV0 and σL0), and (iii) evolution of the σL during five long-term wetting-drying cycles. Experimental results demonstrated that the post-soaking σL-σV relationships are piecewise linear and their slopes in the passive state (σL > σV) and active state (σL < σV) are similar to that of the consolidation σL-σV relationships in the normal- and over-consolidated states, respectively. The soaking σL-σV relationships converge to the consolidation σL-σV relationships at a threshold σV where the interparticle swelling is restrained. The σL0 and σV0 increase monotonically with ρd0; however, they show increasing-then-decreasing trends with the w0. The extent of compaction-induced swelling anisotropy, which is evaluated by σL0/σV0, reduces with an increase in the compaction energy and molding water content. The σL reduces over moisture cycles and the stress relaxation in the σL during soaking is observed. An approach was developed to predict the at-rest soaking σL-σV relationships, which requires conventional consolidation and shear strength properties and one measurement of the σL-σV relationships during soaking. The proposed approach was validated using the results of three different expansive soils available in the literature.