Clay sedimentation has been widely analyzed for its application in a variety of geotechnical constructions such as mine tailing, artificial islands, dredging, and reclamation. Chemical flocculants such as aluminum sulfate (Al₂(SO₄)₃), ferric chloride (FeCl₃), and ferric sulfate (Fe(SO₄)₃), have been adopted to accelerate the settling behaviors of clays. As an alternative clay flocculant with natural origin, this study investigated the settling of xanthan gum-treated kaolinite suspension in deionized water. The sedimentation of kaolinite in solutions of xanthan gum biopolymer (0%, 0.1%, 0.5%, 1.0%, and 2.0% in a clay mass) was measured until the sediment height was stabilized. Kaolinite was aggregated by xanthan gum via a direct electrical interaction between the negatively charged xanthan gum molecules and positively charged edge surface and via hydrogen bonding with kaolinite particles. The results revealed that the xanthan gum initially bound kaolinite aggregates, thereby forming larger floc sizes. Owing to their greater floc size, the aggregated kaolinite flocs induced by xanthan gum settled faster than the untreated kaolinite. Additionally, X-ray computed tomography images collected at various depths from the bottom demonstrated that the xanthan gum-induced aggregation resulted in denser sediment deposition. The findings of this study could inspire further efforts to accelerate the settling of kaolinite clays by adding xanthan gum.

Soil erosion can cause scouring and failures of underwater structures, therefore, various soil improvement techniques are used to increase the soil erosion resistance. The microbially induced calcium carbonate precipitation (MICP) method is proposed to increase the erosion resistance, however, there are only limited experimental and numerical studies on the use of MICP treatment for improvement of surface erosion resistance. Therefore, this study investigates the improvement in surface erosion resistance of sands by MICP through laboratory experiments and numerical modeling. The surface erosion behaviors of coarse sands with various calcium carbonate contents were first investigated via the erosion function apparatus (EFA). The test results showed that MICP treatment increased the overall erosion resistance, and the contribution of the precipitated calcium carbonate to the erosion resistance and critical shear stress was quantified in relation to the calcium carbonate contents. Further, these surface erosion processes occurring in the EFA test were simulated through the coupled computational fluid dynamics (CFD) and discrete element method (DEM) with the cohesion bonding model to reflect the mineral precipitation effect. The simulation results were compared with the experimental results, and the developed CFD-DEM model with the cohesion bonding model well predicted the critical shear stress of MICP-treated sand. This work demonstrates that the MICP treatment is effective in improving soil erosion resistance, and the coupled CFD-DEM with a bonding model is a useful and promising tool to analyze the soil erosion behavior for MICP-treated sand at a particle scale.

This study investigated the effect of water retention characteristics between aged and fresh Municipal Solid Waste (MSW) on the stability of the landfill. A series of transient numerical modeling for the slope of an MSW landfill was performed considering the variation of water retention characteristics due to leachate circulation. Four different scenarios were considered in this analysis depending on how to obtain hydraulic conductivity and the aging degree of materials. Unsaturated hydraulic properties of the MSW used for the modeling were evaluated through modified hanging column tests. Different water retention properties and various landfill conditions, such as subgrade stiffness, leachate injection frequency, and gas and leachate collection system, were considered to investigate the pore water distribution and slope stability. The stability analyses related to the factor of safety showed that unsaturated properties under those varied conditions significantly impacted the slope stability, where the factor of safety decreased, ranging between 9.4 and 22%. The aged materials resulted in a higher factor of safety than fresh materials; however, after 1000 days, the factor of safety decreased by around 10.6% due to pore pressure buildup. The analysis results indicated that using fresh materials yielded higher factor of safety values. The landfill subgrade was found to have a significant impact on the factor of safety, which resulted in an average of 34% lower factor of safety in soft subgrades. The results also revealed that a failed leachate collection system (e.g., clogging) could result in landfill failure (factor of safety < 1) after around 298 days, while the leachate recirculation frequency has no critical impact on stability. In addition, the accumulation of gas pressure within the waste body resulted in factor of safety reductions as high as 24%. It is essential to consider factors related to the unsaturated hydraulic properties in designing a landfill to prevent landfill instability.

Hurricane Katrina swept New Orleans, Louisiana, USA, in 2005, causing more than 1,000 fatalities and severe damage to the flood protection system. Recovery activities are complete, however, clarifying failure mechanisms and devising resilient and cost-effective retrofitting techniques for the flood protection system are still of utmost importance to enhance the general structural integrity of water retaining structures. This study presents extensive centrifuge test results to find various failure mechanisms and effective retrofitting techniques for a levee system. The result confirmed the rotational failure and translational failure mechanisms for the London Ave. Canal levee and 17^th St. Canal levee, respectively. In addition, it found that the floodwalls with fresh waterstop in their joints perform better than those with old/weathered waterstop by decreasing pore water pressure build-up in the levee. Structural caps placed on the top of the joints between I-walls could also prevent local failure by spreading the load to surrounding walls. At the same time, the self-sealing bentonite-sand mixture installed along the riverside of floodwalls could mitigate the failure of floodwalls by blocking the infiltration of seepage water into the gap formed between levee soils and floodwalls.

This study evaluated slope stability through a case study to determine the disaster risks associated with increased deforestation in structures, including schools and apartments, located in urban areas adjacent to slopes. The slope behind the ○○ High School in Gwangju, Korea, collapsed owing to heavy rain in August 2018. Historically, rainwater drained well around the slope during the rainy season. However, during the collapse, a large amount of seepage water flowed out of the slope surface and a shallow failure occurred along the saturated soil layer. To analyze the cause of the collapse, the images of the upper area of the slope, which could not be directly identified, were captured using unmanned aerial vehicles (UAVs). A digital elevation model of the slope was constructed through image analysis, making it possible to calculate the rainfall flow direction and the area, width, and length of logging areas. The change in the instability of the slope over time owing to rainfall lasting ten days before the collapse was analyzed through numerical analysis. Imaging techniques based on the UAV images were found to be effective in analyzing ground disaster risk maps in urban areas. Furthermore, the analysis was found to predict the failure before its actual occurrence.

In general, the design of structures and its construction processes are fundamentally dependent on their foundation and supporting ground. Thus, it is imperative to understand the behavior of the soil under certain stress and drainage conditions. As it is well known that certain characteristics and behaviors of soils with fines are highly dependent on water content, it is critical to accurately measure and identify the status of the soils in terms of water contents. Liquid limit is one of the important soil index properties to define such characteristics. However, liquid limit measurement can be affected by the proficiency of the operator. On the other hand, dynamic properties of soils are also necessary in many different applications and current testing methods often require special equipment in the laboratory, which is often expensive and sensitive to test conditions. In order to address these concerns and advance the state of the art, this study explores a novel method to determine the liquid limit of cohesive soil by employing video-based vibration analysis. In this research, the modal characteristics of cohesive soil columns are extracted from videos by utilizing phase-based motion estimation. By utilizing the proposed method that analyzes the optical flow in every pixel of the series of frames that effectively represents the motion of corresponding points of the soil specimen, the vibration characteristics of the entire soil specimen could be assessed in a non-contact and non-destructive manner. The experimental investigation results compared with the liquid limit determined by the standard method verify that the proposed method reliably and straightforwardly identifies the liquid limit of clay. It is envisioned that the proposed approach could be applied to measuring liquid limit of soil in practical field, entertaining its simple implementation that only requires a digital camera or even a smartphone without the need for special equipment that may be subject to the proficiency of the operator.

This study presents the prediction of the California bearing ratio (CBR) of coarse- and fine-grained soils using artificial intelligence technology. The group method of data handling (GMDH) algorithm, an artificial neural network-based model, was used in the prediction of the CBR values. In the design of the prediction models, various combinations of independent input variables for both coarse- and fine-grained soils have been used. The results obtained from the designed GMDH-type neural networks (GMDH-type NN) were compared with other regression models, such as linear, support vector, and multilayer perception regression methods. The performance of models was evaluated with a regression coefficient (R²), root-mean-square error (RMSE), and mean absolute error (MAE). The results showed that GMDH-type NN algorithm had higher performance than other regression methods in the prediction of CBR value for coarse- and fine-grained soils. The GMDH model had an R² of 0.938, RMSE of 1.87, and MAE of 1.48 for the input variables {G, S, and MDD} in coarse-grained soils. For fine-grained soils, it had an R² of 0.829, RMSE of 3.02, and MAE of 2.40, when using the input variables {LL, PI, MDD, and OMC}. The performance evaluations revealed that the GMDH-type NN models were effective in predicting CBR values of both coarse- and fine-grained soils.

In this study, the ground settlement in backside of retaining wall and the behavior of the retaining wall were analyzed according to the method of groundwater drawdown due to excavation by using two-dimensional(2D) finite element analysis. Numerical analysis was performed by applying 1) fixed groundwater level, 2) constant groundwater drawdown, and 3) transient groundwater drawdown. In addition, the behavior of the retaining wall according to the initial groundwater level, ground conditions, and surcharge pressure in backside of retaining wall was evaluated. Based on the numerical analysis results, it was confirmed that when the groundwater level is at 0.1H from the ground surface (H: Excavation soil height), the wall displacement and ground settlement are not affected by the method of groundwater drawdown, regardless of soil conditions (dense or loose) and surcharge pressure. On the other hand, when the groundwater level is at 0.5H from the ground surface, the method of groundwater drawdown was found to have a significant effect on wall displacement and ground settlement. In this case, the difference in ground settlement presents by up to 4 times depending on the method of groundwater drawdown, and the surcharge load could increase the ground settlement by up to 1.5 times.

One major advantage of ground penetrating radar (GPR) over other field test methods is its ability to obtain subsurface images of roads in an efficient and non-intrusive manner. Not only can the strata of pavement structure be retrieved from the GPR scan images, but also various irregularities, such as cracks and internal cavities. This article introduces a deep learning-based approach, focusing on detecting subsurface cracks by recognizing their distinctive hyperbolic signatures in the GPR scan images. Given the limited road sections that contain target features, two data augmentation methods, i.e., feature insertion and generation, are implemented, resulting in 9,174 GPR scan images. One of the most popular real-time object detection models, You Only Learn One Representation (YOLOR), is trained for detecting the target features for two types of subsurface cracks: bottom cracks and full cracks from the GPR scan images. The former represents partial cracks initiated from the bottom of the asphalt layer or base layers, while the latter includes extended cracks that penetrate these layers. Our experiments show the test average precisions of 0.769, 0.803 and 0.735 for all cracks, bottom cracks, and full cracks, respectively. This demonstrates the practicality of deep learning-based methods in detecting subsurface cracks from GPR scan images.

This study analyzes the changes in the physical properties of grout by irradiating it with ultrasonic energy and assesses the injectability of the grout into deep rock fractures. The materials used in the research are OPC (Ordinary Portland Cement) and MC (Micro Cement), and are irradiated depending on the water/cement ratio. After irradiating the grout with ultrasonic energy, viscosity, compressive strength, and particle size are analyzed, and the results of the particle size analysis were applied to Nick Barton's theory to evaluate the injectability of the grout into deep rock fractures under those conditions. It was found that the viscosity of the grout decreased after ultrasonic wave irradiation, and the rate of viscosity reduction tended to decrease as the water/cement ratio increased. Additionally, an increase in compressive strength and a decrease in particle size were observed, indicating that the grout irradiated with ultrasonic energy was more effective for injection into rock fractures.

The liquefaction of soil occurs when a soil loses strength and stiffness because of applied stress, such as an earthquake or other changes in stress conditions that result in a loss of cohesion. Hence, a method for improving the strength of liquefiable soil needs to be developed. Many techniques have been presented for their possible applications to mitigate liquefiable soil. Recently, alternative methods using biopolymers (such as xanthan gum, guar gum, and gellan gum), nontraditional additives, have been introduced to stabilize fine-grained soils. However, no studies have been done on the use of carrageenan as a biopolymer for soil improvement. Due to of its rheological and chemical structure, carrageenan may have the potential for use as a biopolymer for soil improvement. This research aims to investigate the effect of adding carrageenan on the soil strength of treated liquefiable soil. The biopolymers used for comparison are carrageenan (as a novel biopolymer), xanthan gum, and guar gum. Then, sand samples were made in cylindrical molds (5 cm × 10 cm) by the dry mixing method. The amount of each biopolymer was 1%, 3%, and 5% of the total sample volume with a moisture content of 20%, and the samples were cured for seven days. In terms of observing the effect of temperature on the carrageenan-treated soil, several samples were prepared with dry sand that was heated in an oven at various temperatures (i.e., 20℃ to 75℃) before mixing. The samples were tested with the direct shear test, UCS test, and SEM test. It can increase the cohesion value of liquefiable soil by 22% to 60% compared to untreated soil. It also made the characteristics of the liquefiable increase by 60% to 92% from very loose sandy soil (i.e., ϕ=29°) to very dense sandy soil. Carrageenan was also shown to have a significant effect on the compressive strength and to exceed the liquefaction limit. Based on the results, carrageenan was found to have the potential for use as an alternative biopolymer.