Numerical Investigation on the Effect of Cementing Properties on the Thermal and Mechanical Stability of Geothermal Wells

In this paper, a two-dimensional (2-D) Finite Element (FE) analysis of a geothermal well was performed with respect to five different cross-sections corresponding to the design specifications for the geothermal well that is currently constructed in Pohang, South Korea. Among the essential components (such as ground formation, casing, and cementing) of a geothermal well, the thermal and mechanical stability of the cementing component was discussed based on a series of parametric studies with consideration of the thermal conductivity and Young’s modulus of the cementing component. With increasing number of casing layers, the cementing component experiences less stress concentration. In addition, the lower thermal conductivity of the cementing material is advantageous for effectively controlling radial displacement. Consequently, it should be noted in geothermal well cementing construction that long-term strength degradation of the cementing might cause the severe structural instability of an entire geothermal well

Machine Learning-Based Approach for Seismic Damage Prediction Method of Building Structures Considering Soil-Structure Interaction

Conventional seismic performance evaluation methods for building structures with soil–structure interaction effects are inefficient for regional seismic damage assessment as a predisaster management system. Therefore, this study presented the framework to develop an artificial neural network-based model, which can rapidly predict seismic responses with soil–structure interaction effects and determine the seismic performance levels. To train, validate and test the model, 11 input parameters were selected as main parameters, and the seismic responses with the soil–structure interaction were generated using a multistep analysis process proposed in this study. The artificial neural network model generated reliable seismic responses with the soil–structure interaction effects, and it rapidly extended the seismic response database using a simple structure and soil information. This data generation method with high accuracy and speed can be utilized as a regional seismic assessment tool for safe and sustainable structures against natural disasters

Stochastic modeling of kaolinite transport through a sand filter

Accurately modeling the transport of clay particles through coarse-grained porous media is essential to engineering applications ranging from filtration and drainage, groundwater flow modeling, to contaminant transport. However, predicting the retention and clogging behavior of clay particles within a coarse-grained soil matrix is extremely challenging because clay particles can aggregate and form clusters with a variety of fabrics depending on the prevailing geochemistry of the pore fluid (i.e., pH and ionic strength). The work performed in this study developed a stochastic model to investigate the uncertainty of clay particle transport in porous media using random sampling at a given grain-size distribution to account for inherent uncertainty of the size of clay clusters being transported. Results demonstrated that the model proposed in this work can evaluate upper and lower boundaries of retention profiles of clay particles in a sand medium at given mean and standard deviation of grain-size distributions. In addition, the deterministic approach (using median sizes of sand and clay particles in the simulation) underestimated the mass of retained particles at small size ratios of clay particle size/sand particle size when compared with the stochastic prediction, which would result in nonconservative design.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Impact of clay particle reattachment on suffusion of sand-clay mixtures

The detached clay particles directly filtrated through the sand-clay mixture lead to suffusion; however, if the detached clay particles are subjected to reattachment, the degree of suffusion may be less significant. This study investigates the impact of clay particle reattachment on suffusion of sand-clay mixtures through laboratory soil-column experiments. The observed breakthrough curves (BTCs) of kaolinite, illite, and montmorillonite for 5 different column lengths (3 in, 6 in, 9 in, 12 in, and 18 in; 1 in = 2.54 cm) indicated that a higher breakthrough concentration was observed as the column length (L) decreased for kaolinite and illite, whereas a reverse trend was observed for montmorillonite. In addition, the increase in the fraction of filtrated clay particles (Me) with an increase in L (Me = 10.42% for L = 3 in and Me = 3.59% for L = 18 in) for the sand-illite mixture indicated that the reattachment effect became more significant as the travel length of detached clay particles increased. The observed BTCs, retention profiles after injection, and fraction of filtrated clay presented herein suggest the need to incorporate the reattachment effect when assessing the suffusion of clay-containing soils

Impact of Particle Sizes, Mineralogy and Pore Fluid Chemistry on the Plasticity of Clayey Soils

The current classification of clayey soils does not entail information of pore fluid chemistry and particle size less than 75 µm. However, the pore fluid chemistry and particle size (at given mineralogy) are critical in the plasticity of clayey soils because of their impact on negative charge density. Therefore, this study extensively discusses the description of clay with respect to mineralogy, particle sizes, and pore fluid chemistry based on liquid and plastic limits of kaolinite, illite, and bentonite, and estimates undrained shear strength from the observed liquid limits. The liquid limits and undrained shear strength estimated from the observed liquid limits as a function of mineralogy (clay type), particle size, and ionic concentration reveal the need of incorporating pore fluid chemistry and particle size into the fines classification system. Furthermore, multiple linear regression models developed in this study demonstrate the importance of particle size and ionic concentration in predicting the liquid limit of clayey soils. This study also discusses the need for a comprehensive understanding of fines classification for proper interpretation of natural phenomena and engineering applications for fine-grained sediments

Evolution of Small Strain Soil Stiffness during Freeze-Thaw Cycle: Transition from Capillarity to Cementation Examined Using Magnetic and Piezo Crystal Sensors

Freeze-thaw cycles caused by seasonal temperature fluctuations significantly affect the geotechnical engineering properties. This study investigated the crucial role of water distribution patterns in the characterization of elastic wave properties for the fine F-110 sand during a freeze-thaw cycle. Sand specimens with four different water distribution patterns were prepared, namely homogeneously-mixed, evaporation-driven, vertically-, and horizontally-layered specimens. The P- and S-wave signatures of the specimens were monitored using piezo crystal sensors. Results indicated the criticality of water distribution patterns in the determination of small-strain soil properties even though the specimens had identical global water saturation. The nuclear magnetic resonance-based water volume depth profiles indicated that the evaporation-driven specimens had more heterogeneous pore-invasive ice-bonding layers at a high water saturation region; by contrast, the drying process facilitated uniform meniscuses around the particle contacts near the air percolation threshold. Elastic wave measurements for laboratory-prepared specimens might over/underestimate the small-strain soil stiffness of sediments in nature, wherein the drying processes prevailed to control the water saturation. This study highlighted a clear transition from capillary-controlled to cementation-controlled elastic wave properties during temperature oscillations

Numerical Investigation on the Effect of Cementing Properties on the Thermal and Mechanical Stability of Geothermal Wells

In this paper, a two-dimensional (2-D) Finite Element (FE) analysis of a geothermal well was performed with respect to five different cross-sections corresponding to the design specifications for the geothermal well that is currently constructed in Pohang, South Korea. Among the essential components (such as ground formation, casing, and cementing) of a geothermal well, the thermal and mechanical stability of the cementing component was discussed based on a series of parametric studies with consideration of the thermal conductivity and Young’s modulus of the cementing component. With increasing number of casing layers, the cementing component experiences less stress concentration. In addition, the lower thermal conductivity of the cementing material is advantageous for effectively controlling radial displacement. Consequently, it should be noted in geothermal well cementing construction that long-term strength degradation of the cementing might cause the severe structural instability of an entire geothermal well

Sequential backward feature selection for optimizing permanent strain model of unbound aggregates

This study proposes a novel framework for identifying the optimal feature set required to predict the permanent strain of unbound aggregates. An experimental database consisting of 16 input features is preprocessed and the performance of 10 machine learning models is evaluated. The best-performing model is then paired with a sequential backward selection algorithm to determine the optimal feature set for predicting the permanent strain. Finally, the selected features are used to predict the permanent strain, and the performance is compared with those obtained from the principal components analysis. Six features are selected as the optimal feature set. Furthermore, the selected features accurately predict permanent strain with a root mean square error value of 0.014, which is smaller than those obtained from principal components analysis. Thus, the feature selection approach for machine learning models effectively predicts the permanent strain of unbound aggregates using a limited set of input features

Impact of Particle Size Distribution of Colloidal Particles on Contaminant Transport in Porous Media

The presence of retained colloidal particles causes the retardation of contaminant transport when the contaminant is favorably adsorbed to colloidal particles. Although the particle size distribution affects the retention behavior of colloidal particles, the impact of particle size distribution on contaminant transport has not been reported to date. This study investigates the impact of the particle size distribution of the colloidal particles on contaminant transport through numerical simulation by representing the particle size distribution as a lognormal distribution function. In addition, the bed efficiency and contaminant saturation of simulated breakthrough curves were calculated, and a contaminant transport model with the Langmuir isotherm for the reaction between the contaminant–sand and contaminant–colloidal particle was introduced and validated with experimental data. The simulated breakthrough curves, bed efficiency, and contaminant saturation indicated that an increase in the mean and standard deviation of the particle size distribution causes the retardation of contaminant transport

Applicability Evaluation of Energy Slabs Installed in an Underground Parking Lot

A floor slab of buildings can be used as a ground heat exchanger by equipping heat exchange pipes with a horizontal layout, namely energy slabs. The thermal performance of conventional energy slabs is relatively low due to the interference with the ambient air temperature. This fatal drawback can be overcome by installing energy slabs in an underground parking lot, where the influence of ambient air is not significant. This study experimentally investigated the applicability of two types of energy slabs (floor type and wall type), which were constructed on the basement slab in an underground parking lot. In particular, an aerogel-type thermal insulation layer was fabricated in each energy slab to isolate it from the ambient air along with enhancing the structural stability against automobiles. In the thermal performance tests, the constructed energy slabs showed a thermal performance 265% higher than the conventional energy slabs. Moreover, the aerogel-type thermal insulation layer effectively prevented surface condensation. However, the thermal stress of 2350 kPa was induced by the cooling operation in the energy slabs, which means the energy slab should possess sufficient tensile strength to secure the structural integrity of the parking lot basement