• Tunnel and Underground Space
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• v.13 no.5
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• pp.362-372
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• 2003

Since the occurrence of Portland cement, a great number of concrete structures were constructed. But the concrete structures have their own life times, which inevitably demand repairing treatments, especially on their surface parts. Currently many various methods have been developed and are being applied fer this purpose. In this study, a newly developed method using pneumatic chipping machine and anchor pin was adopted far repair of old concrete structure and the mechanical characteristics of cementing plane between existing and new concrete were tested. Comparing the removal methods for the decrepit part of existing concrete using pneumatic chipping machine and hydraulic breaker, the peak cohesion was higher when using chipping machine at the cementing plane. On the other hand, the residual cohesion was higher for the case of breaker. Step shaped chipping on the cementing plane was effective in increasing peak cohesion, which results 14% increase in the case of 30 mm step height and 22% in 50 mm height when compared with planar chipping plane. The use of anchor pin increased the residual cohesion, which restricted shear slip on the cementing plane after peak shear stress and the tensile strength of 32% compared with that of non-anchored case. According to the combined effect of step shaped chipping of 30 mm and anchor pin with an interval of 15 cm, the peak cohesion reached up to 77% and the residual cohesion showed 180% of the ones of the fresh concrete, respectively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.10
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• pp.539-550
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• 2017

The purpose of this study was to investigate the differences in family cohesion and family adaptability between college students and their parents to identify the factors that affect family cohesion and family adaptability using a descriptive research study design. The subjects of this study were 197 college students and their parents. The data were analyzed using descriptive statistics, the t-test, ANOVA, correlation and multiple regression analysis by SPSS for Windows (ver. 22.0). The mean of the family function index of the subjects was $7.42{\pm}2.28$ on the scale of 1 to 10, and that of the normal family functional group was 65.48%. There was no significant difference in family cohesion between the college students and their parents, and family adaptability was significantly different in discipline(t=-3.100, p<.01) and role(t=.212, p<.05). The factors affecting the family adaptability of the students were the sharing of family activities, emotional intimacy and attending family events, which showed a combined explanatory power of 45.9%. The factors affecting the family cohesion of the parents were housework assignment, emotional intimacy and attending family events, which showed a combined explanatory power of 51.4%. Family emotional intimacy and attending family events, as well as the sharing of family activities, were found to be important to the family adaptability of the college students and housework assignment was found to be important to the family cohesion of the parents.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.1252-1258
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• 2005

The coarse grained materials which is produced in the domestic stony mountains are used as principle materials in the construction sites such as dams, ports, pavement structures and etc. Despite using of various fields like this, There is few apparatuses to experiment these materials in the country. some design parameters of the structures until these days was used from the result of former research abroad. Hereupon, We have developed the large scale direct shear test apparatus and we conduct research in order to get a shear strength of the coarse grained materials from the domestic stony mountains in Kyuong-gi, Choong-chung and Kyoung-sang province. As results of the test, it was revealed that the internal friction was ranging from $38.6^{\circ}$ to $44.5^{\circ}$ and the cohesion was from $1.1kg/cm^2$ to $1.7kg/cm^2$ depending on the local rock conditions.

• Journal of the Korean Geosynthetics Society
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• v.13 no.4
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• pp.69-75
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• 2014

The shear strength characteristics of an unsaturated earth material are highly important not only for evaluating the seepage characteristics but also the stability of levee for a lifelong. In this study, unsaturated strength characteristics of Nak-dong river sand and clay that frequently used for the levee construction in southern province of Korea were analyzed using unsaturated triaxial compressive test. The strength characteristics due to the variation of matric suction were analyzed using multi-stage compression technique and the results were directly compared with the non-linear formulation for the apparent cohesion ($C_{max}$), and the friction component ${\varphi}^b$ were determined and evaluated from the test for the application of linear Mohr-Coulomb failure criteria. Cohesion and friction characteristics of the unsaturated levee material under various suction phases were also explored during this study.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.9 no.3
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• pp.76-81
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• 2006

The reinforcement of soil shear strength by nylon net as substitute materials simulating a fine root system was evaluated by soil strength parameters(apparent cohesion(c) and internal friction angle(tan${\phi}$), using simple shear tester which clearly depicts shear deformation and controls soil suction. And the results of shear test by using bamboo as a substitute materials simulating a main root system and using nylon net as a substitute materials simulating a fine root system were compared. The reinforcement of soil strength by nylon net are expressed by apparent cohesion more than internal friction angle. In addition the increment of apparent cohesion by nylon net reached a peak in suction 60 $cmH_2O$. Different from with bamboo, the possibility of the change on internal friction angle(tan${\phi}$) caused by the soil water condition was shown in shear strain 20% condition. These results show that the mechanism of reinforcement by substitute materials simulating root system may be different in the condition of various soil water content.

• Journal of Korean Academy of Nursing
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• v.41 no.5
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• pp.642-651
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• 2011

Purpose: The purpose of this study was to explore the resilience of adult children of alcoholics (ACOA) who are college students, and examine factors contributing to their resilience. Methods: A total of 459 college students from a university in Incheon, participated in this study. Data were collected between April 6 to 30, 2010 using the Korean version of the Children of Alcoholics Screening Test (CAST-K), CAGE, Social Support, Self-Esteem, Family Adaptability and Cohesion, and Resilience measurements. Data were analyzed using the SPSS/WIN 18.0 program. Results: Overall, ACOA group showed lower scores of resilience, social support, self-esteem and family adaptability and cohesion compared to non-ACOA group. Resilience among the ACOA group showed significant relationships with self-esteem (r=.53, p<.001), social support (r=.43, p<.001), and family adaptability and cohesion (r=.25, p<.013). Multiple regression analysis showed that 45% of the variance for resilience in the ACOA group was accounted for by age, gender, social support, self-esteem, and religion. Conclusion: The results of the study show that self-esteem and social support are important determinants of resilience in ACOA, thus it is recommend that further resilience training programs for ACOA be developed to enhance their social support and self-esteem, and ultimately to increase their resilience.

• Geomechanics and Engineering
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• v.32 no.3
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• pp.271-291
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• 2023

Settlement estimation in cohesion materials is a crucial topic to tackle because of the complexity of the cohesion soil texture, which could be solved roughly by substituted solutions. The goal of this research was to implement recently developed machine learning features as effective methods to predict settlement (S_m) of shallow foundations over cohesion soil properties. These models include hybridized support vector regression (SVR), random forests (RF), and coot optimization algorithm (COM), and black widow optimization algorithm (BWOA). The results indicate that all created systems accurately simulated the S_m, with an R² of better than 0.979 and 0.9765 for the train and test data phases, respectively. This indicates extraordinary efficiency and a good correlation between the experimental and simulated S_m. The model's results outperformed those of ANFIS - PSO, and COM - RF findings were much outstanding to those of the literature. By analyzing established designs utilizing different analysis aspects, such as various error criteria, Taylor diagrams, uncertainty analyses, and error distribution, it was feasible to arrive at the final result that the recommended COM - RF was the outperformed approach in the forecasting process of S_m of shallow foundation, while other techniques were also reliable.

• Journal of the Korean GEO-environmental Society
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• v.18 no.2
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• pp.29-37
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• 2017

As the behavior of the debris flow due to the torrential rains in mountain is affected by shear strength and rheological properties of the fine fraction in the ground, the evaluation of both properties is necessary to estimate the behavior of the debris flow. The objective of this study is to evaluate the shear strength and rheological properties using the direct shear apparatus. The direct shear tests are conducted for two kinds of fine-grained soil specimens, which are in dry state and liquid limit state. From the direct shear tests, shear strengths are measured according to the normal stresses applied on the specimens to evaluate the cohesion and internal friction angle. In addition, reversal shear tests are performed for the fine-grained soil specimens in liquid limit state according to the shear rate to evaluate the residual shear strength. The results of direct shear tests show that the specimen at the liquid limit state has lower internal friction angle and higher cohesion compared to the dry stated, and the residual friction angle and cohesion at the residual state are lower than those at the peak state. In the result of reversal shear test, the residual shear strength is directly proportional to the shear rate and viscosity is calculated as $73.60Pa{\cdot}s$. This study demonstrates that the direct shear apparatus can be effectively used for the evaluation of the shear strength and rheological properties of the fine-grained soils related with the debris flow.

• Geomechanics and Engineering
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• v.31 no.5
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• pp.519-527
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• 2022

Shear failure in soil is the primary cause of most geotechnical structure failures or instability. Soil water content is a significant factor affecting soil shear strength. In this study, the shear strength of samples with different water contents was tested. The shear strength, cohesion, and internal friction angle decreased with increasing water content. Based on the variation of cohesion and internal friction angle, the water content zone was divided into a high-water content zone and low-water content zone with a threshold water content of 15.05%. Cohesion and internal friction angle have a good linear relationship with water content in both zones. Environmental Scanning Electron Microscopy (ESEM) test presented that the aggregates size of the compacted loess gradually increases with increasing water content. Meanwhile, the clay in the compacted loess forms a matric that envelops around the surface of the aggregates and fills the inter-aggregates pores. A quantitative analysis of bound water and free water under different water contents using a nuclear magnetic resonance (NMR) test was carried out. The threshold water content between bound water and free water was slightly below the plastic limit, which is consistent with the results of shear strength parameters. Combined with the T2 distributions obtained by NMR, one can define a T2 relaxation time of 1.58 ms as the boundary point for bound water distribution without free water. Finally, the effects of bound water and free water on shear strength parameters were analyzed using linear regression analysis.

• Geomechanics and Engineering
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• v.33 no.2
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• pp.133-140
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• 2023

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.