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Soil cracking is a common natural phenomenon. The existence of soil cracks has significant effects on the engineering properties of clayey soil, and can cause significant problems in geotechnical, geological, and environmental aspects. Understanding of the potential mechanisms of soil cracking is essential in assessments of potential damages to earthen infrastructures. We review the past research efforts devoted to the experimental investigations and applications of fracture mechanics in soil cracking, attempting to provide a better understanding of the formation mechanism of desiccation cracking with a perspective of fracture mechanics. This review analyzes the influence of soil cracking on soil engineering properties and the significance of soil cracking phenomena. Past and current formulations of soil fracture criteria and their experimental investigation are discussed. This review reveals the factors that affect the mechanisms of soil fracture can be divided into two groups, namely soil intrinsic properties and test-related factors. The applications of fracture mechanics in soil cracking are also discussed with particular focus on soil fracture models that are separately based on linear elastic fracture mechanics (LEFM), elastic plastic fracture mechanics (EPFM), and numerical simulations of soil cracking based on fracture mechanics. Some challenges and prospects of the applications of fracture mechanics in soil cracking are presented. Fracture mechanics is a significant method to explain soil crack initiation and propagation. It is expected that researchers can gain better understanding of the range of fracture mechanics applications in soil cracking, and seek improvements and extensions of existing models through this review.

In order to improve the mechanical properties of dredged sludge, short polypropylene fibers were used as physical reinforcement, while cement and fly ash were used as chemical stabilizers. Different mass percentages of fiber (i.e., 0%, 0.05%, 0.1%, 0.2%, 0.4%, and 0.8%), cement (i.e., 15%, 20%, and 25%), and fly ash (i.e., 15% and 30%) were added to dredged sludge at two initial high water contents (i.e., 92% and 120%) and evaluated using physical experiments. The unconfined compression test was performed on samples after curing them for 28 days. The results show that inclusion of cement and fly ash can significantly increase the dry density and reduce the water content of dredged sludge after curing, consequently enhancing the unconfined compressive strength (UCS). It is found that chemical stabilization can increase the stiffness and brittleness of dredged sludge. However, excessively high fly ash fraction in the mix inhibits strength development in cement-stabilized dredged sludge. The inclusion of fiber decreases the initial stiffness and enhances the UCS, strain at failure, and residual strength of dredged sludge. The UCS increases with fiber content and then decreases slightly, with the optimal fiber content being 0.1%. Fiber reinforcement generates a distinct transition zone in the stress–strain curve, which enlarges with increasing fiber content. The contribution of fiber reinforcement to the strength of dredged sludge is more pronounced at relatively lower water content. The inclusion of fiber can temper the brittleness of chemical-stabilized dredged sludge with more ductile behavior by inducing a ‘bridging’ effect. This effect helps in reducing loading-induced cracking of the stabilized sludge.

Under the influence of climate warming, sea level rise and human activities, seawater intrusion has become a significant problem. Seawater intrusion salinates groundwater and impacts on ecological environment and society. It needs to be monitored to scale to environment in order to develop and implement preventive or remedial measures. In-situ large-scale monitoring of groundwater salinity is a key step in the prevention of seawater intrusion. However, current monitoring technologies are either too labor-intensive or excessively expensive when used in large-scale in-situ monitoring. Optical fiber techniques that are presently used in measurements of salinity are mostly limited to laboratory experiments. Herein, a fiber Bragg grating (FBG) salinity sensor for in-situ monitoring of groundwater salinity is proposed. The sensor is composed of a FBG coated with polyimide (PI) and an uncoated FBG for salinity sensing and temperature compensation. On the basis of feasibility test and analyses using water diffusion model, a mathematical matrix for calculating salinity and temperature is proposed and applied to salinity measurement in gravel aquifers. The results indicate that the sensitivity coefficients of FBG coated with lamellar polyimide, to water salinity and temperature, are −0.0358 nm/%, 0.0321 nm/°C, respectively. The uncoated FBG is only sensitive to temperature, and the sensitivity coefficient is 0.0095 nm/%. The results of gravel aquifer measurements show that the FBG salinity sensor has good repeatability and consistency with measurements obtained with an electronic salinity meter. The absolute and RMS errors of the salinity measurements are −0.16 to 0.21%, 0.1048%, respectively, and the absolute and RMS errors of temperature are −0.31 to 0.33 °C, 0.1917 °C, respectively. The FBG salinity sensor provides a new means for in-situ monitoring of seawater intrusion.

Reservoir landslide, as one of the most serious geohazards, is worldwide distributed. To investigate its triggering factors and mechanisms that underlie its propagations, a real-time monitoring system based on Fiber Bragg Grating (FBG) technology was designed for the Majiagou landslide in the Three Gorges Reservoir (TGR) region. Through analyses of inclinometer data, it is found that there are two sliding surfaces existed in the Majiagou landslide and that the deeper sliding surface is the critical one. It accounts for nearly 80% of the deformation of the landslide. This information necessitated the recording of the displacement at the deeper sliding surface, together with the rainfall, water level, pore water pressure, temperature of the landslide using a real-time monitoring system. After analyzing the multi-parameter data in detail, it is found that observed deformation is mainly governed by reservoir water levels, while precipitation has some minor effects. The reservoir water level is the determining factor of landslide deformation when it exceeds 160 m or lower than 150 m. Whereas the reservoir water level varies from 150 m to 160 m, the fluctuation velocity plays a dominant role. The relationship between the variation of seepage field and kinematic evolution of Majiagou landslide is recognized. The average displacement rate of Majiagou landslide is within 0.1 mm/day, signifying that the landslide is still creeping presently. The results are significant with respect to stability evaluation and formulation of early warning plans for the reservoir landslide.

Although many methods of soil moisture measurement exist, there remains a lack of soil moisture sensor with small volume, high precision, excellent real-time performance and distributed monitoring capability. In this paper, a fiber Bragg grating (FBG)-based carbon fiber heated sensor (CFHS) that can overcome the deficiencies in soil moisture movement is proposed. The CFHS consists of a carbon fiber rod with a diameter of 5 mm, quasi-distributed FBG sensors on an optical fiber, a coating, two binding posts, and two electric cables. Laboratory calibration tests have been conducted to establish an empirical piece-wise relationship between the temperature characteristic value and soil moisture for sand, silt and clay. A laboratory validation test under normal gravity and a centrifuge test under overweight conditions, have been performed to verify the feasibility of this technique for soil moisture monitoring. The test results show that the CFHS can (i) accurately record soil moisture under normal gravitational and overweight conditions and (ii) track the evolution of capillary zones, and the generation and migration of moisture transition zones under centrifuge acceleration. During a response period of 5 min, the accuracy is 0.033 m3/m3 under 1 g condition, and 0.047 m3/m3 under overweight condition. With the advantages of small sensor size, low disturbance of soil mass and wide adaptability in physical model tests, the proposed method can achieve distributed soil moisture measurement at different scales and with high efficiency.

Evaporation of water from soils is a three-stage process that has great significance in stress development in exposed geotechnical structures, generation of dusts that can cause environmental pollution and respiratory ailments, and dereliction of land by generating drought conditions. In this study, the factors that influence water evaporation from soil have been divided into two categories: external, referring to atmospheric conditions and interior, covering surficial soil characteristics and water content conditions. Particularly, five different sets of laboratory based evaporation tests were performed using cylindrical (150 mm diameter and 7–28 mm height) samples of clayey soil mixed with quartzite sands (three grainsize ranges: 0.2–0.5 mm, 0.5–1.0 mm, and 2.0–3.0 mm) in weight proportions ranging from 0% to 50% to evaluate the effects of soil texture, mineralogy and initial compactive state on its free water evaporation process at room temperature (20–22 °C) and relative humidity (50 ± 2%) conditions. The evaporation tests were performed using mass loss measurements on soil samples to an accuracy of 0.01 g. Findings show that in the first stage of soil drying, water content decreases continuously with time while the ratio of actual to potential evaporation, Ea/Ep stays mostly stable. During the falling rate stage, both water content and Ea/Ep decrease significantly. However, the water content varies but not significantly due to the low value of residual evaporation rate in the residual evaporation stage. Soil with lower sand content starts the falling rate stage at higher water content: 32.52% at added sand proportions of 0% versus 21.87%, 20.65%, 20.45%, 20.26% and 18.34% at added sand proportions of 10%, 20%, 30%, 40%, and 50% respectively. Larger soil sample thicknesses accelerate water evaporation rate and extend the constant evaporation rate stage. Soil particle size was not found to have significant impact on evaporation rate on per unit weight of added soil basis. The evaporation rate increases in direct proportionality to increase in initial water content and dry density.

Chemical dust suppressants generally require more than one application to exposed ground surfaces to maintain the soil wetness level required to reduce dust emissions under the combined action of wind, high ambient temperature, low relative humidity, and vehicular traffic. A quantitative methodology is herein formulated for estimation of the cost-effectiveness of dust suppression with chemical agents within a specified construction duration. This is applied to the 3 polymers: sodium carboxymethyl cellulose (CMC A), polyacrylamide (PAM B) and polyethylene oxide (PEO A) used on 2 base soils (sodium montmorillonite (Na-montmorillonite) and kaolinite (K)). Polymer aqueous concentrations ranging from 0.5 g/L to 10 g/L, with distilled water as control, were used to perform desiccation tests at 25 °C and 30% relative humidity. The results show that liquid loss kinetics alone which indicated CMC A at 8 g/L and 4 g/L aqueous concentrations for Na-montmorillonite during 891 h and kaolinite during 696 h, respectively, may not provide complete information on the potential cost-effectiveness of dust suppressants over multiple applications in the field. It identifies water and PAM B at

The effects of wetting-drying (W-D) cycles on the desiccation-induced cracking of a fat clay (CH) as well as the role of soil suction in the evolution of soil strength, were investigated. Cylindrical block soil samples (50 mm in diameter and 100 mm in height) compacted to a dry density of 1.3 Mg/m3, were subjected to 3 stages of drying at a temperature of 22 ± 2 °C, the first of which had an initial water content of 25%. Three parallel samples were retrieved and tested for unconfined compressive strength (UCS) and surface fracture characteristics at moisture content levels ranging from 13% to 25%. Analyses of images of crack patterns obtained using stereological software, indicate that the pattern of increases in UCS with decreasing moisture content induced by drying, is strongly affected by the intensity of cracks on the samples. Desiccation cracking only occurred in the 2nd and 3rd stages of soil drying. During the first stage of drying, the stress-strain curve of the soil exhibited increase in slope with decreasing water content. This implies the domination of suction at the initial stages. The number of crack segments observed on samples, increases with W-D cycles, thus decreasing soil brittleness. However, increase in W-D cycles does not significantly affect the soil water retention characteristics. These findings illustrate the significant role played by soil suction in strengthening soils against the degradation effects of cracks during the early stages of drying. As drying proceeds, the proliferation of cracks eventually reduces soil strength as soil suction is overcome. Therefore, in developing structures on clayey soils that will be subjected to seasonal changes in moisture content, assessments of the balance of the effects of suction and soil desiccation cracking should be made.

Dredged sludge has poor mechanical properties and its safe disposal is highly risky. Fiber has been considered as an effective additive for soil reinforcement because of its cost effectiveness, easy adaptability, and reproducibility. The main objective of this research is to investigate the effects of polypropylene fiber on hydro-mechanical behavior of dredged sludge. A series of compression and direct shear tests were performed on dredged sludge samples with different percentage contents of polypropylene fiber 0%, 0.05%, 0.1%, 0.2%, 0.4%, and 0.8% by weight of dredged sludge and the direct shear tests were performed at vertical stresses of 50, 100, 200 and 400 kPa. The test results indicate that inclusion of fiber improves shear strength of sludge with increasing compression, void ratio, consolidation coefficient and hydraulic conductivity. The optimum fiber content for these improvements was found to be 0.1%. Presumably the post-consolidation moisture content of sludge after consolidation is minimal at this fiber content, although the shear strength continues to increase with fiber content even after consolidation. The shear strength of samples with the fiber contents of 0.8% is 1.48, 1.58, 1.42, 1.27 times that of the non-reinforced samples under respective consolidation pressures of 50, 100, 200 and 400 kPa, and the reinforcement efficiency is most significant under a pressure of 100 kPa. The strain hardening tendency is more pronounced with the increase of fiber content in the late shear failure process. The results of this study indicate that the mechanism of fiber reinforcement for the consolidation test is “bridging” as different from the shear strength test, which is “friction”. This realization should impact upon the failure patterns of fiber reinforced materials.

On the basis of textural and hydro-mechanical characteristics, bentonite has been proven to be an effective buffer/backfill material for long-term containment of high-level radioactive waste (HLW) in deep geological repositories. Herein, the results of experiments performed to investigate the swelling equilibrium limit (SEL) of bentonite under various boundary conditions are presented. A special apparatus was employed to simulate various stress–strain boundary conditions, including constant volume (CV), constant vertical stress (CVS), and constant stiffness (CS). Bentonite samples were prepared with various initial dry densities ranging from 1.5 to 1.7 g/cm3 and vertically stressed to different levels. During wetting, they were subjected to different boundary conditions before the swelling strain or swelling pressure reached equilibrium. Test results indicate that stress–strain boundary conditions have significant effects on the measured swelling strain and swelling pressure of the tested bentonite. More specifically, the relationship between the sequence of swelling pressure under different boundary conditions is CV > CS > CVS, while the relationship between the sequence of swelling strain is CVS > CS > CV. In addition, the characteristics of SEL curves are governed by the initial dry density and vertical stress with the effect of dry density being more significant. Based on these results, several SEL curves were developed to index the effects of boundary conditions on swelling potential of bentonite. They can be used to evaluate the final stress and volume states of bentonite during fluid infiltration under the range of boundary conditions possible in HLW repositories.

Contaminant sorption reactions in soils are generally heterogeneous, multi-steps solid–liquid reactions that compliment transport processes. For contaminant barrier materials, reaction heterogeneity is promoted by variability in the mineralogy and grain size distribution of materials required in mix proportions to satisfy various design functions. The adsorption/desorption of contaminants in barrier systems is necessary for performance assessments. In this paper, the sorption/desorption rates of Pb 2+ and Cd 2+ on Na-montmorillonite ((OH) 4 Si 8 Al 4 O 20 nH 2 ONa) and kaolinite ((OH) 8 Si 4 Al 4 O 10 ) were investigated by varying nature of aqueous contaminants and clay. Heavy metals including Pb 2+ and Cd 2+ were adsorbed/desorbed on the clays at pH levels of 2, 3, 4, and 7 for 48 h. Sorption/desorption of these heavy metals was found to be influenced by point of zero charge, cation exchange capacity, particle size, pH of the system, complexation of metals, and hydrated ionic radius of metals. As a result, Elovich equation was found to adequately explain the kinetics of Pb 2+ and Cd 2+ on two clay minerals with the squared correlation coefficients ( R 2 ) that range from 0.70 to 0.99. At pH 2, removal rate were 36.3% for Pb 2+ and 64.5% for Cd 2+ from Na-montmorillonite while 67.1% for Pb 2+ and 75.0% Cd 2+ from kaolinite, respectively. The results obtained from the Elovich equation could be useful for assessing the sorption equilibrium for the metals potentially attained in soil barrier systems.

A series of desiccation tests were performed to investigate the effects of both interfacial friction and layer thickness on desiccation cracking behavior of soil. Nine groups of slurry specimens with different interfacial roughness and layer thicknesses were prepared and dried under a constant temperature of 30 °C. During drying, the change in water content was recorded and the dynamic process of soil cracking was monitored with a digital camera at different time intervals. Using digital image processing technique, the propagation characteristics of desiccation cracks on soil sample surfaces were quantitatively described with a series of geometric parameters. The results show that the initiation and propagation of cracks occur at relatively high water content ranging from 10% to 40% during drying. For the same soil layer thickness, the larger the interfacial roughness, the faster the propagation velocity of soil cracks. However, the influence of interfacial friction on soil cracking decreases with increase in soil layer thickness. Besides, there is a negative linear relationship between soil layer thickness and peak propagation velocity of soil cracks. During drying, the critical water content (wf, refers to the water content when the propagation of soil cracks tends to stabilize) decreases with increase in interfacial roughness under the same soil layer thickness. The final morphology of the desiccation crack network on each soil sample is significantly influenced by both the interfacial friction and soil layer thickness. The intensity of soil cracking increases with increase in interfacial roughness or decrease in soil layer thickness. These results also confirm that the effects of interfacial friction and layer thickness on soil desiccation cracking are coupled. Generally, the interface friction effect is more pronounced for thinner soil layers.

Water infiltration in soil is a complex process that still requires appreciation of interactions among three phases (soil particles, water and air) to enable accurate estimation of water transport rates. To simulate this process, the Green&ndash, Ampt (GA) model and the Modified Green-Ampt (MGA) model introduced in the paper &ldquo, A new method to estimate soil water infiltration based on a modified Green&ndash, Ampt model&rdquo, have been widely used. The GA model is based on the hypothesis that the advance of the wetting front in soil under matric suction can be treated as a rectangular piston flow that is instantaneously transformed after passage of the infiltration front, and the MGA model does not contain the influence of pore size change. This cannot accurately reflect the soil moisture change process from unsaturation to saturation. Due to soil stratification and other inhomogeneity, predictions produced with these models often differ widely from observations. To quickly obtain the soil moisture distribution after passage of the wetting front for horizontal infiltration, an improved modified Green&ndash, Ampt (IMGA) model is presented, which estimates the soil moisture profile along a horizontal column in a piecewise manner with three functions. A logarithmic function is used to describe the gradual soil saturation process in the transmission zone, and two linear functions are used to represent the wetting zone. The algorithm of the IMGA model for estimating the water infiltration rate and cumulative infiltration is configured. To verify the effectiveness of IMGA model, a lab model test was performed, and a numerical model was built to solve the horizontal one-dimensional Richards equation using the finite&ndash, element method. The results show that the IMGA model is more accurate than the GA and MGA models. The horizontal soil moisture profiles obtained by the IMGA model are closer to the measured data than the numerical simulation results. The relative errors of the MGA and IMGA models decrease with an increase in infiltration time, whereas that of the GA model first decreases and then increases with infiltration time. The primary novelty of this study is nonlinear description of soil moisture content distribution, and derivation of unit transfer coefficient.