• The korean journal of orthodontics
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• v.20 no.2
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• pp.283-291
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• 1990

The purpose of this study was to measure and compare tensile and shear strength for 4 types of new direct-bonding brackets and same brackets after recycling and to evaluate the change of bracket slot width after recycling. Four types of new direct-bond brackets were bonded to recently extracted human premolar teeth and the tensile and shear strength was measured by Universal Testing Machine. The brackets were recycled by chemical process and the tensile and shear test was repeated. To evaluate the change of the bracket slot width, slot width was measured by the Topcon Universal Measuring Microscope before and after recycling. Following results were obtained: 1. There was no satistically significant difference between the tensile and shear strength of recycled brackets and those of new brackets. 2. In both new and recycled brackets, the tensile and shear strength of perforated base bracket was lower than those of photoetched, foilmesh and contou-lok mesh base brackets. (P<0.01) 3. There was no statistically significant difference in bonding strengths of control group bonded only once and two times. 4. There was no statistically significant difference in the change of the bracket slow width after recycling process. 5. Of the failure, the combination type (58%) in the tensile strength and the tooth adhesive interface (65%) in the shear strength was the most common type.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.257-264
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• 2001

This study presents the slope stability analysis results for the model slope test. The model slope was made of the soil reinforced by FPF(Fibrillated Polyprophylene Fiber). The shear strength properties of the soil reinforced by FPF fibers were evaluated through the direct shear tests. The model slope 1:1 and 1:1.5 were made and the load tests were performed. Back analysis using limit equilibrium method was carried out to evaluate the shear strength increase on the FPF reinforced slope. The factor of safety of the FPF reinforce slope increased about 23% over unreinforced slope.

• Journal of the Korean Geotechnical Society
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• v.22 no.4
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• pp.51-59
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• 2006

In this paper, the effect of variation of density and uniformity coefficient on shear strength was analyzed from the results of large scale shear test. In addition, the friction coefficient at critical state per vertical load was estimated using the equation proposed by Wood (1998). The test sample fur the test was obtained from the local quarry sites. Tests results show that the shear strength of $2.10g/cm^3$ is relatively larger than that of $1.85g/cm^3$ and uniformity coefficient (5.0) has larger shear strength than that in 10.0. In the meantime, the friction coefficient at critical state shows $1.0{\sim}1.6$ according to the test conditions.

• The Journal of Engineering Geology
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• v.31 no.4
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• pp.561-577
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• 2021

The ten standard roughness profiles suggested by Barton and Choubey (1977) were extended to make three-dimensional (3D) joint models whose profiles were identical at any cross section. Replicas of joint models were produced using plaster of Paris, and direct shear tests were performed to verify the joint roughness coefficients (JRC) of the standard roughness profiles. Joint shear strengths measured by direct shear tests were compared with those predicted by the shear failure criterion suggested by Barton (1973) based on JRC, joint compressive strength (JCS), and joint basic friction angle (𝜙_b). Shear strengths measured from joints of the first and fourth standard roughness profiles were close to predicted values; however, shear strengths measured from the other joint models were lower than predicted, the differences increasing as the roughness of joints increased. Back calculated values for JRC, JCS, and from the results of the direct shear tests show measured shear strengths were lower than predicted shear strengths because of the JRC values. New JRC were back calculated from the measured shear strength and named JRC_m. Values of JRC_m were lower than the JRC for the standard roughness profiles but show a strong linear relationship to JRC. Corrected JRC_m values for the standard roughness profiles are provided and revised relationships between JRC_m and JRC, and new shear strength criterion are suggested.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.287-298
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• 2003

The feasibility of using neural networks to model the complex relationship between piezocone measurements and the undrained shear strength of clays has been investigated. A three layered back propagation neural network model was developed based on actual undrained shear strengths, which were obtained from the isotrpoically and anisotrpoically consolidated triaxial compression test(CIUC and CAUC), and piezocone measurements compiled from various locations around the world. It was validated by comparing model predictions with measured values about new piezocone data, which were not previously employed during development of model. Performance of the neural network model was compared with conventional empirical method, direct correlation method, and theoretical method. It was found that the neural network model is not only capable of inferring a complex relationship between piezocone measurements and the undrained shear strength of clays but also gives a more precise and reliable undrained shear strength than theoretical and empirical approaches. Furthermore, neural network model has a possibility to be a generalized relationship between piezocone measurements and undrained shear strength over the various places and countries, while the present empirical correlations present the site specific relationship.

• Journal of the Korean Geosynthetics Society
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• v.17 no.4
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• pp.189-197
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• 2018

A sprayable waterproofing membrane which has relatively high adhesive property onto concrete enables faster construction with better waterproof performance compared with a conventional sheet membrane. However, the sprayable waterproofing membrane is a recently developed material and its performance and behavior with structures are not sufficiently reported. Therefore, in this study, the shear behavior of sprayable waterproofing membrane was numerically analyzed using the results of previous studies of composite shotcrete with sprayable waterproofing membrane. From the previous study, shear behavior of shotcrete with sprayable waterproofing membrane was different from shotcrete case and there was a limitation to express the behavior of the interface in general shear strength method. Therefore, in this study, the direct shear test was numerically simulated using two contact models, and then the best suitable method to express the shear behavior of the sprayable waterproofing membrane was suggested.

• Journal of the Society of Disaster Information
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• v.20 no.2
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• pp.270-283
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• 2024

Purpose: Considering the rising frequency of earthquakes in Korea, it is crucial to revise the rainfall thresholds for landslide triggering following earthquake events. This study was conducted to provide scientific justification and preliminary data for adjusting rainfall thresholds for landslide early warnings after earthquakes through soil physical experiments. Method: The study analyzed the change in soil shear strength by direct shear tests on disturbed and undisturbed samples collected from cut slopes. Also, The study analyzed the soil strength parameters of remolded soil samples subjected to drying and wetting conditions, focusing on the relationship between the degree of saturation after submergence and the strength parameters. Result: Compaction water content variation in direct shear tests showed that higher water content and saturation in disturbed samples led to a significant decrease in cohesion (over 50%) and a reduction in shear resistance angle (1~2°). Additionally, during the ring shear tests, the shear strength was observed to gradually decrease once water was supplied to the shear plane. The maximum shear strength decreased by approximately 65-75%, while the residual shear strength decreased by approximately 53-60%. Conclusion: Seismic activity amplifies landslide risk during subsequent rainfall, necessitating proactive mitigation strategies in earthquake-prone areas. This research is anticipated to provide scientific justification and preliminary data for reducing the rainfall threshold for landslide initiation in earthquake-susceptible regions.

• Tunnel and Underground Space
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• v.26 no.5
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• pp.384-395
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• 2016

Both the roughness measurement tests and the multi-stage shear tests were carried out on the 110 rock joint samples in order to investigate the influences of rock type, joint roughness and normal stress on the shear behaviour of rock joints. Test samples were composed of quartz porphyry, dacite, granite and gneiss, which were classified into three detailed groups according to their JRC values. Roughness parameters of rock joints were analyzed by roughness measurement tests, and shear characteristics were also investigated by multi-stage shear tests. Both peak shear strength and shear stiffness were increased as both joint roughness and normal stress were increased, whereas dilation angles showed lower values at the lower roughness and higher normal stress conditions. Besides, shear characteristics obtained from all tests of four different rock types with different rock strengths showed irrelevant details, therefore the influences of both joint roughness and normal stress on shear behaviors were found to be more considerable than the strength of intact rock. The results obtained from both multi-stage shear tests and direct shear tests were finally compared, where the dilation angles obtained from multi-stage shear tests were found to be valid only for the first normal stress conditions.

• Journal of the Korea Institute of Building Construction
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• v.12 no.5
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• pp.510-517
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• 2012

This study evaluated the recycling potential of in-site waste soil as pile back filling material (PBFM). We performed experiments to check workability, segregation resistance, bond strength, direct shear stress test, and dynamic load test using in-site waste soil in coastal areas. We found that PBFM showed better performance than general cement paste in terms of workability, segregation resistance, and bond strength. On the other hand, the structural performance of PBFM was slightly lower than that of general cement paste due to the skin friction force of pile by Pile Driving Analyzer and direct shear stress. However, because this type of performance degradation in terms of structure can be improved through the use of piles with larger diameter or by changing the type of pile, considering the economics and environment, we considered that recycling of PBFM has sufficient value.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.583-588
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• 2002

As environmental problem in course of construction has been a matter of interest, noise and vibration in the process of piling are considered as a serious problem. For this reason, the use of SIP method inserting pile as soon as boring and cement grouting is rapidly increasing for preventing vibration and noise. But a resonable bearing capacity formula for SIP method does not exit and even the standard specification for domestic condition isn't formed, though the lateral friction between cement paste and the ground does an important role and boring depth largely influences to the design bearing capacity, applying the SIP method . Therefore, the lateral friction was analyzed after the direct shear test worked with the lateral face of SIP and the soil.