• The Journal of Engineering Geology
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• v.29 no.1
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• pp.23-35
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• 2019

Landslides occur due to heavy rainfall in the summer season. Some of water may infiltrate into the ground; it causes a high saturation condition capable of causing a landslide. Soil properties are crucial in estimating slope stability and debris flow occurrence. The main study areas are Gwanaksan, Suraksan and Bukhansan (Mountain) in Seoul. A total of 44 soil samples were taken from the study area; and a series of geotechnical tests were performed. Physical and mechanical properties were obtained and compared based on region. As a result, among well-graded soils, they are classified as a clayey sand. Coarse-grained and fine-grained contents are approximately 95% and 5%, respectively, with very low amount of clay content. Density, liquid limit and dry unit weight are ranged in $2.62{\sim}2.67g/cm^3$, 27.93~38.15% and $1.092{\sim}1.814g/cm^3$. Cohesion and internal friction angle are 4 kPa and $35^{\circ}$ regardless of mountain area. Coefficient of permeability is varied between $3.07{\times}10^{-3}{\sim}4.61{\times}10^{-2}cm/sec$; it means that it results in great seepage. Permeability is inversely proportional to the uniformity coefficient and is proportional to the effective particle size. In the formal case, there was a difference by mountain area, while in the latter, the tendency was almost similar.

• Journal of the Korean Geosynthetics Society
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• v.18 no.4
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• pp.1-13
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• 2019

The purpose of this study is to examine the effect of soft ground improvement by dynamic replacement with utilizing crushed rock. In order to understand the ground improvement effect when applying dynamic replacement method with crushed rock, the laboratory test and field test were performed. The internal friction angle and apparent cohesion were derived through direct shear test. The dynamic replacement characteristics were identified by analyzing the weight, drop, and number of blows needed for dynamic replacement. Through the field plate bearing test and density test, the bearing capacity and settlement of the improved ground were measured, and the numerical analysis were conducted to analyze the behavior of the improved ground. In this study, it proposes modified soil experimental coefficient(C_DR) to 0.3~0.5 in the dynamic replacement method with crushed rock. Also when applying the dynamic replacement method using crushed rock, the particle size range is less than 100 mm, D₉₀ is less than 80 mm and D₁₅ is more than 30 mm.

• Journal of the Korean Geotechnical Society
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• v.39 no.12
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• pp.37-46
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• 2023

Dynamic soil properties are essential factors for predicting the detailed behavior of the ground. However, there are limitations to gathering soil samples and performing additional experiments. In this study, we used an artificial neural network (ANN) to predict dynamic soil properties based on static soil properties. The selected static soil properties were soil cohesion, internal friction angle, porosity, specific gravity, and uniaxial compressive strength, whereas the compressional and shear wave velocities were determined for the dynamic soil properties. The Levenberg-Marquardt and Bayesian regularization methods were used to enhance the reliability of the ANN results, and the reliability associated with each optimization method was compared. The accuracy of the ANN model was represented by the coefficient of determination, which was greater than 0.9 in the training and testing phases, indicating that the proposed ANN model exhibits high reliability. Further, the reliability of the output values was verified with new input data, and the results showed high accuracy.

• Korean Journal of Agricultural Science
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• v.19 no.1
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• pp.65-78
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• 1992

The paper describes the comparison between observed and predicted stress-strain characteristics of marine silty clay in Dangjin district. For prediction, the hyperbolic model which is applied the parameters acquiring by physical and triaxial compression test was adopted, and the obtained results were summarized as follows: 1. The Young's modulus were increased with decreasing of moisture contents and increasing of dry density. 2. The most affective factor to hyperbolic model is lateral stress and dry density. and than cohesion and internal friction angle. 3. The comparision between the statistical and hyperbolic values of maximum deviator stress have few accordance. and the statisticals is lower than the hyperbolics. 4. Without. much labor and tiresome procedures, effective computer program was made and applied, but technical procedure for prevents test errors of parameter calculation is importants.

• The Journal of Engineering Geology
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• v.14 no.2
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• pp.199-210
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• 2004

In this study, the physical and mechanical properties of the weathered shale soils distributed in the Hwasun area have been measured in the laboratory. The physical and mechanical properties of the weathered shale soils in the study area as follows: the specific gravity is 2.66 to 2.68, the liquid limit is 36.39 to 36.92(%), the plastic limit is 18.53 to 19.48(%), the plasticity index is 17.44 to 17.86 and soil classification is CL. The maximum dry unit weight and optimum moisture content as calculated by compaction test is 22.5 to 23% and 1.58 to $1.61t/\textrm{m}^3$, respectively. The result of direct shear testing show that cohesion in saturated and unsaturated conditions increases according to the increase of dry unit weight. Internal friction angle in an unsaturated condition increases with an increase of dry unit weight, but in a saturated condition, it increases after decreasing. When compares with engineering characteristics of tile weathered shale soils in the Daegu area (Kim et al., 1995), specific gravity is found to be similar, but the liquid and plastic limit of soil samples in this study area is slightly higher than those of soil samples in the Daegu area.

• Tunnel and Underground Space
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• v.33 no.3
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• pp.109-125
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• 2023

Disposal repository for high-level radioactive waste secures its safety by means of engineered and natural barriers. The performance of these barriers should be tested and verified through various aspects in terms of short and/or long-term. KAERI has been conducting various in-situ demonstrations in KURT (KAERI Underground Research Tunnel). After completing previous experiment, a conceptual design of an improved in-situ experiment, i.e. K-COIN (KURT experiment of THMC COupled and INteraction), was established and detailed planning for the experiment is underway. Preliminary characterizations were conducted in KURT for siting a K-COIN test site. 15 boreholes with a depth of about 20 m were drilled in three research galleries in KURT and intact rock specimens were prepared for laboratory tests. Using the specimens, physical measurements, uniaxial compression, indirect tension, and triaxial compression tests were conducted. As a result, specific gravity, porosity, elastic wave velocities, uniaxial compressive strength, Young's modulus, Poisson's ratio, Brazilian tensile strength, cohesion, and internal friction angle were estimated. Statistical analyses revealed that there did not exist meaningful differences in intact rock properties according to the drilled sites and the depth. Judging from the uniaxial compressive strength, which is one of the most important properties, all the specimens were classified as very strong rock so that mechanical safety was secured in all the regions.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.6C
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• pp.305-314
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• 2012

This paper presents the quantitative damage assessment of granite taken from KAERI Underground Research Tunnel using acoustic emission (AE). The results determined showed the crack initiation and crack damage stress occurred at 48%, 72% of uniaxial compressive strength (UCS) and until the applied stress level was reached the crack damage stress, the damage degree was 0.06. When the applied stress exceeded 80%, 90% of UCS, the damage degree were 0.34, 0.06 and which were similar to those obtained from axial deformation modulus. The simply regression analysis was used to interpret the relationship of the two damage assessment techniques and the two were highly correlated ($R^2$=0.90). Therefore, damage degree based on the AE energy and mohr-coulomb failure criterion were adopted to predict the mechanical properties. As results, the axial deformation modulus, rock strength, internal friction angle, and cohesion of KURT rock were reduced 6%, 12%, 7%, and 3% until the applied stress was 70% of UCS. But when the applied stress reached 90% of UCS, the results were more reduced 69%, 72%, 62%, and 24%, respectively.

• Journal of the Korean Geotechnical Society
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• v.39 no.9
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• pp.13-24
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• 2023

To investigate the stability of temporary retaining walls during excavation, it is essential to develop reverse analysis technologies capable of precisely evaluating the properties of the ground and a learning model that can assess stability by analyzing real-time data. In this study, we targeted excavation sites where the C.I.P method was applied. We developed a Deep Neural Network (DNN) model capable of evaluating the stability of the retaining wall, and estimated the physical properties of the ground being excavated using a Differential Evolution Algorithm. We performed reverse analysis on a model composed of a two-layer ground for the applicability analysis of the Differential Evolution Algorithm. The results from this analysis allowed us to predict the properties of the ground, such as the elastic modulus, cohesion, and internal friction angle, with an accuracy of 97%. We analyzed 30,000 cases to construct the training data for the DNN model. We proposed stability evaluation grades for each assessment factor, including anchor axial force, uneven subsidence, wall displacement, and structural stability of the wall, and trained the data based on these factors. The application analysis of the trained DNN model showed that the model could predict the stability of the retaining wall with an average accuracy of over 94%, considering factors such as the axial force of the anchor, uneven subsidence, displacement of the wall, and structural stability of the wall.

• Journal of the Korean GEO-environmental Society
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• v.12 no.7
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• pp.57-65
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• 2011

Numerical simulations by three-dimensional Particle Flow Code($PFC^{3D}$, Itasca) considering distinct element method (DEM) were carried out for prediction of triaxial compression test with sand material. The effect of scale conditions for numerical model and distinct material on final prediction results was analyzed by numerical models under various scale conditions, and following observations were made from the numerical experiments. It is very useful to model the initial material condition without any porosity conversion from 2-D to 3-D DEM. Numerical experiments have shown that in all cases considered, 3D distinct element modeling could provide good agreement on stress-strain behavior, volume change and strength properties with laboratory testing results. It was important thing to assess reasonable scale ratio of numerical model and distinct elements for saving calculation time and securing calculation efficiency under condition with accuracy and appropriateness as numerical laboratory. As results of DEM simulations under various scale conditions, most of results show that shear strength properties as cohesion and internal friction angle are similar in condition of $D_{mod}/D_{gmax}$ < 10. It shows that 3-D distinct element method could be used as efficient tool to assess strength properties by numerical laboratory technique.

• Journal of the Korean Geotechnical Society
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• v.16 no.1
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• pp.131-143
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• 2000

Several theoretical analyses are performed to predict the vertical load on embankment piles with cap beams. The piles are installed in a row in soft ground below the embankment and the cap beams are placed perpendicular to the longitudinal axis of the embankment. Two failure mechanisms such as the soil arching failure and the punching shear failure are investigated according to the failure pattern in embankment on soft ground supported by piles with cap beams. The soil arching can be developed when the space between cap beams is narrow and/or the embankment is high enough. In the investigation of the soil arching failure, the stability in the crown of the arch is compared with that above the cap beams. The factors affecting the load transfer in the embankment fill by soil arching are the space between cap beams, the width of cap beams and the soil parameters of the embankment fill. The portion of the embankment load carried by cap beams decreases with increment of the space between cap beams, while it increases with the embankment height, the width of cap beams, the internal friction angle and cohesion of the embankment fill. Thus, the factors affecting load transfer in embankment should be appropriately decided in order to maximize the effect of embankment load transfer by piles.