Number Of Dry-wet Cycles Research Articles

Study on failure mechanism of red clay slope under dry and wet cycles

In order to study the failure characteristics and mechanism of red clay slope under dry-wet cycling conditions, a model slope similar to engineering slope was established. The test slope was monitored by testing elements, and the variation laws of moisture content, temperature, pore water pressure, soil pressure and displacement were analyzed respectively under the alternating conditions of dry-wet cycling. The failure characteristics and mechanism of slope are obtained. With the increase of dry-wet cycles, the overall water content of slope increases, pore water pressure decreases, lateral displacement increases, and vertical displacement remains unchanged to a certain extent. After five dry-wet cycles, the water content of the top and top of the slope is the largest, the water content of the bottom and foot of the slope is the smallest, the horizontal displacement of the slope is the largest, and the horizontal displacement of the top of the slope is the smallest. The range of temperature change increases with the number of dry-wet cycles, and tends to be stable after the third dry-wet cycle. The earth pressure is the largest at the top of the slope, followed by the foot of the slope and the smallest at the slope surface, and the first two dry-wet cycles have the greatest impact on the earth pressure. In the process of dry-wet cycling, the surface cracks of slope undergo the cyclic process of cracking, healing and re-cracking. The width and depth of cracks increase gradually. The surface failure characteristics represented by gully weathering and spalling gradually change into shallow failure characteristics represented by collapse and slump.

Experimental investigation on the mechanical behavior of red sandstone under the coupled effects of temperature and acidic etching

The red sandstone that commonly exists in nature is used to study the coupled effects of temperature and acidic etching on its mechanical properties. The dry-wet cycle is adopted to accelerate the corrosion process during the test, and the increase in the number of dry-wet cycle indicates the increase of the degree of corrosion. A series of uniaxial compression tests were carried out, and the influence of dry-wet cycle times on the physical and mechanical properties of red sandstones was analyzed. Besides, the crack propagation, phase composition, and the micromorphology of red sandstone were analyzed by means of acoustic emission (AE), X-ray diffraction (XRD), and scanning electron microscope (SEM). The results show that the physical and mechanical parameters of red sandstone such as the P-wave velocity and the uniaxial compressive strength have been deteriorated in different degrees considering coupled effects of temperature and acidic etching. With the increase of the number of dry-wet cycle times, the elastic deformation section of the axial stress-strain curve of the specimen becomes shorter and the softening characteristic is gradually obvious. The evolution of AE is a good evidence for the changes of internal structure of the specimen due to the coupled effects of temperature and acidic etching. The results of the XRD and the SEM indicate that the species of minerals increase and the microstructures of the specimen were changed with the increase in the number of dry-wet cycles.

Hydrogen Absorption Behavior of Pre-Rusted Steels under an NaCl Droplet

In this study, we investigated the hydrogen absorption behavior of pre-rusted steel in an NaCl droplet by measuring the hydrogen permeation current and corrosion potential. To prepare the pre-rusted steel, a 30-μL droplet of a 0.1-mol/dm3 NaCl solution was placed on the surface of steel and exposed to wet-dry cyclic conditions by changing the relative humidity (RH) repeatedly from 40% to 95% at a constant rate of 27.5%/h and 298 K. The hydrogen permeation current and corrosion potential of the pre-rusted steel were measured during the drying of an electrolyte droplet using an electrochemical hydrogen permeation test and the Kelvin probe (KP) technique, respectively. The corrosion potential of the pre-rusted steel shifted in the negative direction simultaneous with the evolution of the hydrogen permeation current during the drying of the droplet. The hydrogen permeation current increased with the number of wet-dry cycles in the early stages of the rusting process, which related to the negative shift in corrosion potential. As the whole surface of the steel was covered with iron rust in the later stages of the rusting process, the corrosion potential shifted in the positive direction and the hydrogen absorption current decreased gradually.

Influence of wetting-drying cycles on the pore structure and mechanical properties of mudstone from Simian Mountain

The deterioration of mudstone induced by cyclic fluctuations in the groundwater level in subtropical regions affects the stability of underground construction. To investigate the evolution of the micropores and mechanical properties of mudstone under cyclic wetting-drying conditions, mudstone samples from Simian Mountain in southwest China are subjected to different numbers of wetting-drying cycles in the laboratory. The pore structure change induced by periodic wetting and drying process is evaluated through low-field nuclear magnetic resonance (NMR), a nondestructive detection method. The results from the experiments show that the porosities of the mudstone samples dramatically increase during cyclic wetting-drying. A significant linear relationship between the incremental in porosity and the number of wetting-drying cycles was established. The influence of wetting-drying cycles on the mechanical properties of mudstone is analyzed in terms of the pore structure. The increase in porosity leads to the decline of the uniaxial compressive strength (UCS) and elastic modulus of the mudstone samples. A quantitative equation is tentatively established to describe the relationship between the porosity and UCS of mudstone damages by wetting-drying cycles.

Corrosion Characteristics of Reinforced Concrete Under the Coupled Effects of Chloride Ingress and Static Loading: Laboratory Tests and Finite Element Analysis

The aim of this paper is to describe the coupled effects of chloride ingress and static loading on the evolution of corrosion of steel reinforcement in concrete. A new corrosion test was adopted to accelerate the non-uniform corrosion of the steel. Finite element analysis was used to investigate the influence of coupled chemo-mechanical processes on corrosion expansion stress of the concrete cover. As is shown by the results, the half-cell potentials of steel reinforcement in the reinforced concrete specimens decreased with increase in the number of wetting-drying cycles and the applied static loading, which cause the steel reinforcement to be more prone to corrosion attack. Owing to the coupled action of chloride ingress and static loading, non-uniform distribution of corrosion activity on the steel reinforcement increased significantly. The finite element simulations showed the existence of static loading increased the maximum stress on the concrete cover, which increases the susceptibility of concrete cover to corrosion-related expansion cracking. DOI: http://dx.doi.org/10.5755/j01.ms.24.2.17963

A modified shear strength reduction finite element method for soil slope under wetting-drying cycles

The shear strength reduction finite element method (SSRFEM) is a powerful tool for slope stability analysis. The factor of safety (FOS) of the slope can be easily calculated only through reducing effective cohesion (c') and tangent of effective friction angle (tanφ') in equal proportion. However, this method may not be applicable to soil slope under wetting-drying cycles (WDCs), because the influence of WDCs on c' and tanφ' may be different. To research the method of estimating FOS of soil slopes under WDCs, this paper presents an experimental study firstly to investigate the effects of WDCs on the parameters of shear strength and stiffness. Twelve silty clay samples were subjected to different number of WDCs and then tested with triaxial test equipment. The test results show that WDCs have a degradation effect on shear strength (σ1 – σ3)f, secant modulus of elasticity (Es) and c' while little influence on φ'. Hence, conventional SSRFEM which reduces c' and tanφ' equal proportion cannot be adopted to compute the FOS of slope under conditions of WDCs. The SSRFEM should be modified. In detail, c' is merely reduced among shear strength parameters, and elasticity modulus is reduced correspondingly. Besides, a new approach based on sudden substantial changes in the displacement of marked nodes is proposed to identify the slope failure in SSRFEM. Finally, the modified SSRFEM is applied to compute the FOS of a slope example.

Concrete Strength and Deformation Property under Sea Water Erosion Environment

In order to effectively assess the concrete strength and deformation property under sea water erosion environment, concrete stress and strain curve was researched with the number of wet and dry cycle of 0 times, 10 times , 20 times, 30 times, 40 times, 50 times and 60 times based on the large-scale static and dynamic stiffness servo test set. The stress - strain curves of concrete was tested for the lateral pressure 10.8MPa, 14.4MPa, and 18.8MPa at different dry-wet cycles, The failure modes and superficial cracking characteristics of specimens are reported at different dry-wet cycles. Concrete elastic modulus and compressive strength were researched. Based on concrete mechanical theory , the classic Kufer-Gerstle strength criteria of concrete was used, a large number of test samples of multivariate data were nonlinear regressed, a biaxial concrete strength criterion was established taking into account the stress ratio and the number of dry-wet cycles.

Concrete Strength and Deformation Property under Sea Water Erosion Environment

In order to effectively assess the concrete strength and deformation property under sea water erosion environment, concrete stress and strain curve was researched with the number of wet and dry cycle of 0 times, 10 times , 20 times, 30 times, 40 times, 50 times and 60 times based on the large-scale static and dynamic stiffness servo test set. The stress - strain curves of concrete was tested for the lateral pressure 10.8MPa, 14.4MPa, and 18.8MPa at different dry-wet cycles, The failure modes and superficial cracking characteristics of specimens are reported at different dry-wet cycles. Concrete elastic modulus and compressive strength were researched. Based on concrete mechanical theory , the classic Kufer-Gerstle strength criteria of concrete was used, a large number of test samples of multivariate data were nonlinear regressed, a biaxial concrete strength criterion was established taking into account the stress ratio and the number of dry-wet cycles.

Evaluation of the atmospheric corrosion resistance of AISI A-36 steel painted with coatings based on epoxy and poly(urethane) resins using semi-accelerated testing

The influence of temperature, humidity, salinity, and the number of wet-dry cycles in the atmospheric corrosion resistance of the AISI A-36 steel, painted with coatings based on epoxy and poly(urethane) resins was studied. The aim of this work is to present an alternative to the accelerated and field tests developing a semi-accelerated test for evaluating the resistance and durability of a protection system that is applied to a specific environment for one year. The samples were exposed in a corrosion cyclic test chamber for 2000 h with fixed parameters of temperature, relative moisture of air, salinity, and a number of dry-wet cycles. Mass loss of substrate in the scratch area was measured after each 250 h of testing. The second stage of research was the sensibility analysis of the corrosion rate with the change of the reference test parameters. The third stage was the testing of the samples using the cyclic test for 750 h, and the transfer of samples to a marine atmosphere exposure for one year. The mass loss was measured after each 60-day period of testing. Material characterization involved scanning electron microscopy, X-ray diffraction, energy dispersive spectroscopy, Fourier transform infrared spectroscopy, and X-ray fluorescence spectroscopy. After polynomial adjustment of the mass loss function associated with the sensibility analysis of the parameter alteration, the estimated life span of the samples ranged from 30 to 38 months.

Scanning Kelvin Probe Measurements near Salt Particles on Zinc and Iron in High Humidity

During the atmospheric corrosion process, the surface potential on zinc or steel samples in the presence of a single particle of sodium chloride (NaCl) or potassium chloride (KCl) was studied using a scanning Kelvin probe (SKP) technique, With the initiation and propagation of the atmospheric corrosion, the surface potential varied from flat to valley and then to volcano shape when the relative humidity (RH) was higher than that of the over-saturated solution of the salt (RHoss). These nonuniform potential distributions could be attributed to the local corrosion reactions and to the differential oxygen aeration under the solution droplet formed by the deliquescence of the salt particle. Continual measurements of surface potential during wet-dry cycles indicated that the potential difference between the peak and valley (the electromotive force of the corrosion cell) increased with an increasing number of wet-dry cycles. Based on the above observations, a model was proposed for describing the variations in the surface potential during the atmospheric corrosion process induced by a single deposited salt particle.

Soil Structure Degradation and Mellowing of Compacted Soils by Saline-Sodic Solutions

Aggregates are formed by joining of structural units of different sizes in a hierarchical order. During wetting, the aggregates may either disintegrate completely (slaking) or remain intact with only loosening at the points of weakness (mellowing). This study investigated the effect of saline-sodic solutions with sodium adsorption ratio (SAR) of 5 and 20 and electrical conductivity (EC) of 0.1 to 4 dS m -1 after a number of wetting-drying cycles on soil mellowing. A Vertic Palexeralf with a coefficient of linear extensibility (COLE) value of 0.15 and a Typic Haploxeralf with COLE of 0.05 were studied. Using a Ca solution, the degree of aggregation in both soils was improved about two times in >50 and 20- to 50-μm aggregates compared with the original soils. The values for the Vertic Palexeralf were three times those of the Typic Haploxeralf. In contrast, sodic solutions led to the collapse of aggregates. Mellowing ratios of aggregates changed after 10 wetting-drying cycles and were 0.6 to 0.7 for SAR 5 and 0.8 to 1 for SAR 20 for the Vertic Palexeralf ; for the Typic Haploxeralf they were 0.7 to 0.8 and 0.9 to 1.2 for SARs 5 and 20, respectively. Mellowing ratios between 0.9 and 1 were obtained for the Vertic Paleoxeralf minicores using solutions of SAR 20 and EC 0.1 dS m -1 . The mellowing ratio was 0.2 when a solution of SAR 5 and EC 4 dS m -1 was used. In soils where aggregates collapsed without hierarchical breakdown, mellowing ratios were always higher, indicating structural degradation.