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The aim of this study is to propose a new detection method for determining the damage locations in pile foundations based on deep learning using acoustic emission data. First, the damage location is simulated using a back propagation neural network deep learning model with an acoustic emission data set acquired from pile hit experiments. In particular, the damage location is identified using two parameters: the pile location (PL) and the distance from the pile cap (DS). This study investigates the influences of various acoustic emission parameters, numbers of sensors, sensor installation locations, and the time difference on the prediction accuracy of PL and DS. In addition, correlations between the damage location and acoustic emission parameters are investigated. Second, the damage step condition is determined using a classification model with an acoustic emission data set acquired from uniaxial compressive strength experiments. Finally, a new damage detection and evaluation method for pile foundations is proposed. This new method is capable of continuously detecting and evaluating the damage of pile foundations in service.

Steel shots are suitable for abrasive waterjet rock cutting and recycling because of the high hardness and magnetic properties of steel. This study evaluated the rock-cutting performance and recycling characteristics of steel shot waterjet. The rock-cutting responses of steel shot and garnet were compared at the same waterjet conditions. The used steel shot was collected and the particle-size changes were evaluated before reuse, and its cutting performance was re-evaluated. Overall, the steel shot waterjet yielded improvements in performance in the range of 30–50% compared with the garnet waterjet. Moreover, the recycled steel shot yielded a 50% reduction in cutting performance. Rust was observed on the surface of the used steel shot, the used steel shots were partially destroyed, and the debris on the abrasive surface needed to be removed by drying. The reusable steel shot left on the 80th sieve converged to 60% in each recycling run. The results of this study can be used to reduce the cost of abrasive waterjet and industrial waste.

The acoustic emission (AE) technique has been widely used to monitor damage for concrete structures in underground space. To analyze the damage status successfully, it is important to understand the characteristics of AE parameters during failure for concrete-based-underground structures. The AE parameters are related to the target material characteristics (i.e., sand content ratio) and failure steps (i.e., stress levels) of concrete specimens. In this study, the concrete specimens were prepared with different sand content ratio. Uniaxial compressive tests were performed for the specimens with AE monitoring to investigate the characteristics of AE parameters in the time domain (i.e., count, energy, and amplitude) and frequency domain (i.e., initial frequency and peak frequency). The experimental results were analyzed with the sand content ratio and failure step (1–4) in order to determine the suitable AE parameter as a monitoring index. The most suitable parameter was shown as the cumulative energy parameter of AE with high sensitivity.

Understanding exact rock conditions has a significant impact on the success of tunnel construction. Various methods such as Q-systems and rock mass rating (RMR) have been used to estimate the condition of jointed rock mass in fields. However, the evaluation of rock mass characteristics can diverge because of the subjective views of observers. Many researchers that work on the relationship between rock mass classification methods and its physical variables have tried to solve this problem; nevertheless, the accuracy of their studies has become a subject of controversy. Thus, in this study, we tried to evaluate rock mass classification in terms of RMR from the electrical resistivity that is readily affected by the characteristics of jointed rock mass. The relationship between the RMR parameters and the electrical resistivity was deducted using the formula of electrical resistivity analyzed for jointed rock mass. The correlation analyses were performed based on real data (4,689 sets) in order to obtain the degree of correlation among RMR parameters. The results show that some parameters are strongly correlated while other parameters are not. Stochastic analyses show that the theoretical relationship between RMR value and electrical resistivity can be improved by probabilistically removing the irrelevant (low possibility) relation among RMR parameters. Finally, a field test was performed to verify the suggested probabilistic RMR estimation using electrical resistivity.

Abrasive waterjets are being increasingly used in civil engineering for rock and concrete cutting, particularly for the demolition or repair of old structures. The energy of an abrasive waterjet is primarily provided by the accelerated abrasive. The momentum transfer during mixing and acceleration determines the abrasive velocity, which affects the cutting performance. Meanwhile, the geometry of the focus at which mixing occurs influences the momentum transfer efficiency. In this study, the effects of the focus geometry on the optimum abrasive flow rate (AFR) and momentum transfer characteristics in hard rock cutting were investigated. Experiments were conducted using granite specimens to test the AFR under different focus geometry conditions such as diameter and length. The results show that the focus geometry significantly affects the maximum cutting depth and optimum AFR. The maximum cutting energy was analyzed based on the cutting efficiency of a single abrasive particle. In addition, the momentum transfer parameter (MTP) was evaluated from the empirical relationship between the maximum energy and the cutting depth for granitic rocks. Accordingly, a model for estimating the MTP based on the AFR was developed. It is expected that the results of this study can be employed for the optimization of waterjet rock cutting.

Rock cutting with an abrasive waterjet system has been attempted in mining and construction fields. In abrasive waterjet cutting, the overall operating cost depends on the cost of the consumed abrasive. For this reason, it is important to identify an optimum abrasive feed rate for cost and performance efficiency. In this study, the concept of the abrasive/water ratio in volume (i.e., mixing rate of the abrasive and water amount) was introduced to explore the optimum feed rate for the cutting performance according to the water flow rate. Rock cutting tests were performed on intact granite specimens at different abrasive/water ratios. The test results were analyzed based on the effect of the abrasive feed rate in a constant water flow rate condition and on the effect of the water flow rate in a constant abrasive feed rate condition, respectively. In addition, the ratio of the abrasive particle size to the abrasive–water mixture flow space (i.e., mixing tube size) was considered and analyzed to determine the optimum abrasive/water ratio. Under the conditions given in this study, the optimum abrasive/water ratio ranges from 0.08 to 0.20 and tends to increase with an increase in the average particle size, particle size uniformity of the abrasive, and mixing tube size. In the performance analysis of rock cutting, a higher water flow rate causes a better cutting efficiency; meanwhile, the optimum abrasive feed rate achieves the maximum cutting performance. These findings can help to estimate the amount of abrasive required for efficient rock cutting.

Elastic wave based technology (e.g., acoustic emission or micro seismic sensors) has been widely used to monitor the stability of underground structures or rock failure. To achieve successful measurement, it is important to select an appropriate coupling material for the installation of sensors that are embedded in holes bored into the wall of a structure. The characteristics of the coupling material are related to its wave propagation ability (i.e., wave velocity and damping ratio), setting ability in the borehole (i.e., bleeding), and its workability (i.e., viscosity) in relation to being able to fill the holes tightly with the sensors. In this study, micro cement, Portland cement, and gypsum were the materials considered to couple with sensors in the borehole. Laboratory tests were performed to evaluate the characteristics of the coupling material according to the water-cement ratio (w/c, range 0.5–2.0). The test results show that the propagation ability and setting ability tend to decrease with increasing w/c ratio; on the other hand, workability benefits from an increasing w/c ratio. In addition, the characteristics of the coupling materials were analyzed to suggest a material with an optimized w/c ratio appropriate for a target test-bed site. The most suitable coupling recipe was found to be micro cement with a w/c ratio of 1.0. This study provides information about coupling material characteristics that should be useful for determining a suitable coupling recipe for field applications.

Acoustic emission (AE) monitoring has gained significant interest as a promising method for monitoring of changes in structural integrity and durability. Long-term AE monitoring needs to detect and distinguish crack signals from ambient noise (or dummy) signals; however, it is still a daunting task which currently limits field implementation of the AE method. Herein, we explore the feasibility of using convolutional neural network (CNN) models to detect AE crack signals from ambient signals. The trained models are validated both with noise-embedded synthesized signals and with upscaled physical model experiments simulating earthquake loading to a scaled model foundation by using a large-scale shaking table. The 2D CNN model trained the laboratory-synthesized signal sets effectively captured the crack and crack-free signals in all cases including the upscaled physical model experiments. This study presents a simple but robust CNN model for pre-filtering of crack signals and a novel training method for enhanced accuracy, which can be applied for real-time structural health monitoring of concrete-based structures.

Detecting and monitoring the damage locations of in-service reinforced concrete (RC) structures is difficult as they exhibit more complex geometries and consist of composite materials. In this study, a new method for detecting the source location of acoustic emission (AE) signals in RC structures using machine learning was introduced and tested on an in-service RC column. An impulse response test was conducted using an AE testing system to gather data regarding the source locations. Meanwhile, the source locations on the test column were generated through manual hits. The corresponding AE data were collected using a AE data acquisition system. The significant AE parameters were determined using neighborhood component analysis for feature selection to obtain a dataset for machine learning. Further, a support vector machine classifier was adopted to classify the source locations of the columns for three sensor groups. Furthermore, the source locations were predicted using feedforward backpropagation neural networks. This study validated the detectability of AE signals in RC columns and proposed a novel detection method, which can be employed to perform continuous nondestructive tests on in-service RC columns.

Using a transparent fracture replica with aperture size and water-cement ratio (w/c), the factors affecting the penetration behavior of rock grouting were investigated through laboratory experiments. In addition, the waterproof efficiency was estimated by the reduction of water outflow through the fractures after the grout curing process. Penetration behavior shows that grout penetration patterns present similarly radial forms in all experimental cases; however, velocity of grout penetration showed clear differences according to the aperture sizes and watercement ratio. It can be seen that the waterproof efficiency increased as the aperture size and w/c decreased. During grout injection or curing processes, air bubbles formed and bleeding occurred, both of which affected the waterproof ability of the grouting. These two phenomena can significantly prevent the successful performance of rock grouting in field-scale underground spaces, especially at deep depth conditions. Our research can provide a foundation for improving and optimizing the innovative techniques of rock grouting.

Prediction of penetration rate of tunnel boring machine (TBM) is important in tunneling design; however, the effect of machine specifications of the TBM on penetration rate remains poorly identified. This study defined a representative machine factor (MF) composed of thrust force, number of cutters, and TBM diameter, and its correlations with penetration rates, using the previously reported field data. In addition, the correlations between the machine factors and the unconfined compressive strength (UCS) of rocks were examined. The stronger relationship between penetration depth and MF than between penetration rate and MF was found. Finally, the generalized prediction-model to penetration depth per revolution was suggested. The presented findings provide insights into the roles of machine factors in TBM performance.

Acoustic emission (AE) has garnered significant interest as a promising way to detect the early-stage development of internal cracks and damage in underground and geotechnical structures, associated with natural disasters. Meanwhile, AE source localization techniques that can identify the damage location in a piled-raft foundation (PRF) are premature because of its complex geometry, although the PRF is a widely used deep foundation type for high-rise buildings. In this study, we propose an integrated approach to localize AE sources in the PRF by using the modified Akaike information criterion (AIC) method and examine its accuracy to mark with pile zones. We performed a series of experiments on a scaled PRF model at a ratio of 1:50, composed of one raft and 25 piles. The results demonstrate that the combined approach with the modified AIC method and the Simplex method can localize the AE source zones with good accuracy, greater than 95% on average. The suggested two-stage AIC picker shows accurate onset time determination, and hence, it significantly improves the accuracy, particularly effective for the signals with low signal-to-noise ratios. The approach exploiting the two-stage AIC picker can be readily used for automated real-time AE monitoring to detect crack generation and its location in buried foundations that cannot be inspected visually.

Undrained shear strength is a fundamental parameter for estimating the stability of soft soils. This study explores the relationship between undrained shear strength, void ratio, and shear wave velocity for saturated and normally consolidated clay specimens. The undrained shear strength void ratio-shear wave velocity relationship was correlated to empirically determined parameters of selected marine clay specimens. To verify the proposed relationship between undrained shear strength and shear wave velocity, in situ flat dilatometer tests were used for determining the undrained shear strength, and downhole tests were used to assess the shear wave velocity on a natural soil deposit at various depths. The undrained shear strength estimated from the in situ shear wave velocities was compared to the undrained shear strength obtained in the field. The results show that the inferred undrained shear strength yield similar values and follow the same trends as the in situ undrained shear strength data. This...

As one of the non-destructive testing (NDT) methods, acoustic emission (AE) can be widely applied to the field of engineering and applied science owing to its advantageous characteristics. In particular, the AE method is effectively applied to monitor concrete structures in civil engineering. For this technology to be employed in a monitoring system, it is necessary to investigate the propagation characteristics of the AE in structures. Hence, this study investigates the characteristics of AE in concrete structures to evaluate the field applicability of AE monitoring systems. To achieve this goal, experiments employing an AE system are conducted for concrete structures 20 &times, 0.2 &times, 1.2 m in length, width, and height, respectively, to explore the AE parameters according to the impact energy. Among all AE parameters, absolute energy is determined to be most sensitive factor with respect to the impact energy. In addition, the attenuation effect of the AE wave is quantitatively evaluated according to the wave propagation distance. Moreover, the concept of effective distance is newly suggested based on the experimental results. The effective distance is shown to increase as the impact energy increases, although the increased effective distance is limited because the damaged AE signal is of high frequency. This study helps improve the field applicability of AE monitoring systems by suggesting suitable AE sensor spacing, which contributes to promote the practice of technology.

Source location technology has been broadly used for structure monitoring. Source location (damage detection) of the structure is a challenging task due to the complex underground conditions. The basic assumption in many currently available techniques is that the velocity of wave, which is generated by structural damage and propagates in the structure, is considered in the constant value to estimate the source location. If the wave velocity is assumed to be a fixed velocity in the target structure, significant error can occur for detecting the damage location. In this study, laboratory tests were performed to analyze the accuracy of the source location according to the wave velocities. This study proposes a velocity model with the receiver distance, with which we verify the accuracy of the source location. Our results from the proposed velocity model produce an erorr rate of only 4%, which is significantly lower than the error rate of the original source location with a varied velocity. This velocity model achieves a high degree of reliability in damage monitoring.

The rock fracturing during waterjet cutting is very complicated because rock is inhomogeneous and anisotropic, compared with artificial materials (e.g., metal or glass). Thus, it is very important to verify the effects of roc k properties on waterjet rock cutting performance. Properties affecting the rock cutting efficiency have been variously described in the literature, depending on the experimental conditions (e.g., water pressure, abrasive feed rate, or standoff distance) and rock-types studied. In this study, a rock-property-related literature review was performed to determine the key properties important for waterjet rock cutting. Porosity, uniaxial compressive strength, and hardness of the rock were determined to be the key properties affecting waterjet rock cutting. The results of this analysis can provide the basic knowledge to determine the cutting efficiency of waterjet rock cutting technology fo r rock excavation-related construction.Keywords: High pressure waterjet, Abrasive waterjet, Rock property, Rock cutting

Abrasive waterjets are widely used in the fields of civil and mechanical engineering for cutting a great variety of hard materials including rocks, metals, and other materials. Cutting depth is an important index to estimate operating time and cost, but it is very difficult to predict because there are a number of influential variables (e.g., energy, geometry, material, and nozzle system parameters). In this study, the cutting depth is correlated to the maximum kinetic energy expressed in terms of energy (i.e., water pressure, water flow rate, abrasive feed rate, and traverse speed), geometry (i.e., standoff distance), material (i.e., α and β), and nozzle system parameters (i.e., nozzle size, shape, and jet diffusion level). The maximum kinetic energy cutting depth model is verified with experimental test data that are obtained using one type of hard granite specimen for various parameters. The results show a unique curve for a specific rock type in a power function between cutting depth and maximum kinetic energy. The cutting depth model developed here can be very useful for estimating the process time when cutting rock using an abrasive waterjet.

Weathering is the breaking/cutting down process of rocks due to physical and chemical processes in natural as well as artificial environment including CO2 injection for storage in the sediment, or natural resource recovery process. This study suggests an alternative method to estimate the degree of weathering for granites. A series of laboratory and field experiments are performed to measure electrical resistivities on various rock samples experienced different degrees of weathering and their residual soils under different saturation conditions. It is found that the normalized electrical resistivity increases with a decrease in water absorption and the saturation. Simple boundaries are suggested to identify the weathering degree of granites, based on limited data. Field test results for three sites confirm that the suggested method could be estimated well the degree of weathering of granites compared with the other methods suggested previously. Although further research is required, this study suggests that an electrical resistivity could be an effective approach to estimate the degree of weathering of granites compared with the other methods suggested previously.

A new rock excavation method using an abrasive injection waterjet system has been developed to enhance the efficiency and reduce the vibration of tunnel excavation. The abrasive feed rate is an important factor for the cutting performance and the economical efficiency of waterjet-based excavation. In this study, various experiments were performed to explore the effects of major process parameters for both the abrasive feed rate and the suction pressure occurring inside the mixing chamber when the abrasives are inhaled. Experimental results reveal that the abrasive feed rate is affected by geometry parameters (abrasive pipe height, length, and tortuosity), abrasive parameters (abrasive particle size), and jet energy parameters (water pressure and water flow rate). In addition, the relation between the cutting performance and the abrasive feed rate was discussed on the basis of the results of an experimental study. The cutting performance can be maximized when the abrasive feed rate is controlled appropriately via careful management of major process parameters.

Carbon dioxide (CO 2 ) can be geologically stored in unconsolidated sediments that have overlain impermeable layers that act as a cap rock. The migration of injected CO 2 can be monitored by analyzing the P- wave velocities of the hosting sediments. This study suggests a new empirical bulk modulus model for the CO 2 that considers the temperature and pressure effects (in the ranges of 5–35 °C and 4–22 MPa) of the storage site. Moreover, a P- wave velocity model of unconsolidated sediments containing CO 2 is developed and verified by experimental tests. Because of the model's simple formula, the suggested model can be readily applied to general numerical analyses and seismic exploration. The effects of temperature, pressure, CO 2 saturation, and effective stress on the P- wave velocities are also discussed on the basis of the proposed P- wave velocity model. The effects of temperature and pressure are more significant at shallow depths. Therefore, CO 2 saturation may be incorrectly estimated at shallow depths if the temperature and pressure of the storage site are not carefully considered.

Fluid-driven rock fracturing has been attempted in the fields of mining and civil engineering. This type of rock fracturing is initiated by applying high-pressure water to target rock. In this study, the fracturing characteristics of hard granite specimens were explored through experimental tests using a high-pressure water jet system. Various tests were performed to evaluate the effects of several geometric parameters: standoff distance, indentation depth, and free surface condition. The fracture depth, radius, volume, and angle were measured, and then analyzed to investigate the fracturing characteristics. In addition, we prepared a theoretical estimate of maximum shear stress via shear stress analysis using a crack-tip stress field model. In these experimental and theoretical studies, efficient rock fracturing was demonstrated with a combination of short standoff distance, deep indentation, and nearby free surfaces. Meanwhile, the fracture angle for infinite free surface boundary specimens was identified as a unique value regardless of the standoff distance and indentation depth.

Various methods, including the Q-system method, have been proposed to estimate the conditions of rocks in fields, and many researchers have quantitatively estimated the Q-values of the Q-system. Physical variables have been considered in various studies, but the accuracy of those studies has become a subject of controversy. This study investigates the conditions of a rock mass using electrical resistivity, which is strongly affected by the flow of water and the condition of the joints. The relationship between the parameters of the Q-system and the electrical resistivity was deducted using an electrical resistivity formula. The relationship between the Q-value and the electrical resistivity of the sandstone was obtained using an electrical resistivity formula as well. A correlation analysis was performed to verify the degree of correlation between the parameters of the Q-system and the electrical resistivity. This study also tried to establish stochastically the relationship between the parameters of the Q-system, possible to existing in reality, on the basis of field data.

The geomechanical and thermal responses of sediments can be significantly affected by the dissociation of gas hydrates via various emergent phenomena such as fluid volume expansion, free gas generation, gas migration, and sediment softening. This study explores the geomechanical and thermal responses of hydrate-bearing sediments subjected to thermal stimulation, using physical modeling with a geotechnical centrifuge that enables the simulation of near-seafloor sediment conditions. A water-saturated and CO2 hydrate-bearing sand column was prepared in a large cylindrical pressure vessel, and a linear stress gradient for a near-seafloor condition was created by increasing centrifugal acceleration. The hydrate-bearing sand column was subjected to thermal stimulation, and changes in temperature, pressure, compressional wave velocity (VP), shear wave velocity (VS), and electrical resistance were monitored at various locations across the column. It was found that VP and electrical resistance were good indicators...

The rock cutting performance of an abrasive waterjet is affected by various parameters. In this study, rock cutting tests are conducted with different energy (i.e., water pressure, traverse speed, and abrasive feed rate), geometry (i.e., standoff distance), and material parameters [i.e., uniaxial compressive strength (UCS)]. In particular, experimental tests are carried out at a long standoff distance (up to 60 cm) to consider field application. The effective parameters of the rock cutting process are identified based on the relationships between the cutting performance indices (depth, width, and volume) and parameters. In addition, the cutting efficiency is analyzed with effective parameters as well as different pump types and the number of cutting passes considering the concept of kinetic jet energy. Efficiency analysis reveals that the cutting depth efficiency tends to increase with an increase in the water pressure and traverse speed and with a decrease in the standoff distance and UCS. Cutting volume efficiency strongly depends on standoff distance. High efficiency of cutting volume is obtained at a long standoff distance regardless of the pump type. The efficiency analysis provides a realistic way to optimize parameters for abrasive waterjet rock excavation.

The conventional blasting method generates serious blasting vibration and underbreak/overbreak in spite of its high efficiency for rock excavation. To overcome these disadvantages, this paper introduces an alternative excavation method that combines the conventional blasting process with the free surface on the perimeter of the tunnel face using waterjet cutting technology. This proposed excavation method has advantages of (1) reducing vibration and noise level; (2) minimizing underbreak and overbreak; and (3) maximizing excavation efficiency. To verify the effects of the proposed excavation method, field tests were performed with a smooth blasting method at the same excavation conditions. Test results show that the vibration is reduced by up to 55% and little underbreak/overbreak is generated compared with the smooth blasting method. In addition, the excavation efficiency of the proposed method is greater than that of the smooth blasting method. The proposed blasting method with a free surface using waterjet cutting can be applied to urban excavation construction as well as to underground structure construction.

Inserting a nozzle assembly into a removed cutting space during a continuous cutting operation is necessary in rock excavation using an abrasive waterjet. In this study, a combined two nozzle assembly is used to secure enough removal width. The shape of the cut space is affected by the geometric parameters (standoff distance, nozzle angle, and vertical distance between the nozzle tips) of the combined nozzle assembly. Abrasive waterjet cutting tests are performed with various geometric parameters for granite rock specimens. Optimized geometric parameters for the nozzle inserting process are determined and verified through the experimental tests.

Rock excavation (removal) tests are performed with effective parameters using an abrasive waterjet. For verification of the field rock excavation capabilities, the removal performance and level of efficiency are analyzed for hard granite rock in terms of the water pressure, exposure time of the jet, and the standoff distance. In particular, experimental tests are performed with a long standoff distance required condition in the real excavation field. The rock removal performance level changes according to the rock properties. In this study, various rock specimens are used and P-wave velocities are measured in order to determine the correlation between the removal performance and the P-wave velocity. As a result of the experimental study, the effect of waterjet parameters on rock removal is analyzed.

The electrical characteristics of soil-water mixtures reflect the soil type, ionic concentration, surface conduction, fluid saturation, porosity, and pore connectivity of the mixtures. Archie’s law commonly is used to analyze the electrical resistivity measurement results of soil-water mixtures. This paper explores the pore-fluid effect on Archie’s law. Experimental tests were performed on sand and clay specimens to measure the variation in their electrical resistivity at different porosities and for different electrical resistivities of the pore fluid. The results demonstrate that the sand specimens (i.e., low specific surface soil) have a unique Archie’s law curve; however, the clay specimens (i.e., high specific surface soil) have an inconsistent Archie’s law curve owing to the surface conduction induced by the double layer of clay particles. In particular, Archie’s law should be applied and analyzed cautiously when high specific surface soils are subjected to pore fluids with high electrical r...