• Journal of the Korean Geotechnical Society
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• v.29 no.11
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• pp.5-15
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• 2013

The end bearing capacity of rock-socketed drilled shafts under axial loading is investigated by Hoek-cell tests and a numerical analysis. From the test results, it was found that the ultimate end bearing capacity ($q_{max}$) was influenced by pile diameter, rock mass modulus and the spacing of discontinuity. A new ultimate end bearing capacity method is proposed by taking end bearing capacity influence factors, including rock mass discontinuity, based on field data. Through comparisons with other field data, the proposed $q_{max}$ method represents a definite improvement in the prediction of ultimate end bearing capacity of rock-socketed drilled shafts.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.11
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• pp.5551-5557
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• 2012

Sedimentary rocks dug up in construction fields are mostly stockpiled for landfill disposal, leading to an increase in construction costs and construction inefficiency. After screening, some of the sandstone can be used as aggregate; however, most of the shale ends up as industrial waste in practice. In this study, to stabilize the demand and develop resources for alternative aggregates of concrete, the potential use of shale, which is widely distributed in the Daegu-Kyeongbuk region, as a concrete aggregate was evaluated. Red and black shale exported from a Daegu excavation site was selected for use in the experiments and evaluated by comparing with hornfels, which is widely used as a coarse aggregate and is a type of andesite and metamorphosed sedimentary rock. The physical properties of the aggregate were evaluated in accordance with the test methods of KS F 2527 "crushed concrete aggregate," and the compressive strength against the shale aggregate replacement ratio was measured. The compressive strength of the concrete after 28 days was 30.8 MPa when the black shale replaced 100% of the aggregate in the concrete and 31.1 MPa when the red shale replaced 100% of the aggregate in the concrete. Compared with the compressive strength of 37.5 MPa for concrete prepared by using plain aggregate, using shale as a substitute for the aggregate produced an average compressive strength that was 82% of normal concrete.

• Journal of the Korea Concrete Institute
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• v.17 no.1 s.85
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• pp.69-76
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• 2005

In this study, the high qualify recycled fine aggregate manufacturing system by the drying specific gravity separation method was evaluated. For the evaluation of the performance of the recycled aggregate, the engineering properties and durability of recycled aggregate has been tested. From the test results, the quality of recycled fing aggregates was improved by high quality recycled fine aggregate manufacturing system and satisfied with the quality standards of KS and JASS 5. Also, compressive and tensile strengths of recycled concrete show no critical difference caused by recycled fine aggregate replacement ratio. However, durability such as carbonation depth chloride ion penetration depth and drying shrinkage shows more deterioration than the concrete without recycled fine aggregate

• The Journal of Engineering Geology
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• v.23 no.3
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• pp.247-256
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• 2013

The carbonate sands of the Sabkha layer in the Middle East have very low shear strength. Therefore, instant settlement and time-dependent secondary settlement occur when inner voids are exposed, as in the case of particle crushing. We analyzed settlement of the Sabkha layer under a large-scale foundation by hydrotesting, and compared the field test results with the results of laboratory tests. With ongoing particle crushing, we observed the following stress-strain behaviors: strain-hardening (Sabkha GL-1.5 m), strain-perfect (Sabkha GL-7.0 m), and strain-softening (Sabkha GL-7.5 m). General shear failure occurred most frequently in dense sand and firm ground. Although the stress-strain behavior of Sabkha layer carbonate sand that of strain-softening, the particle crushing strength was low compared with the strain-hardening and strain-perfect behaviors. The stress-strain behaviors differ between carbonate sand and quartz sand. If the relative density of quartz sand is increased, the shear strength is also increased. Continuous secondary compression settlement occurred during the hydrotests, after the dissipation of porewater pressure. Particle crushing strength is relatively low in the Sabkha layer and its stress-strain behavior is strain-softening or strain-perfect. The particle crushing effect is dominant factor affecting foundation settlement in the Sabkha layer.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.8 no.2
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• pp.89-98
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• 1988

This research evaluated factors on cement-based solidification process designed for hazardous sludge produced from electroplating industry. Four factors of sand/cement ratio, water/cement ratio, amount of wet sludge and amount of a precipitator, were investigated in terms of leachability and compressive strength of the solidified materials. Results of triplicate tests and statistical analysis indicated that sand/cement ratio(S/C) had the greatest effect on leaching of Cr(VI) from the solidified materials while water/cement ratio(W/C) on Zn and compressive strength. Cr(VI) was fixed better than Zn by portland cement. An experimental modeing was developed to estimate leached metal concentration and compressive strength at a given condition. Proper mixing criteria were also suggested for the use of the solidified mixture as construction materials. In solidification of 30g dry sludge, optimal condition was studied for S/C ratio, W/C ratio and the weight of precipitator which were 1, 1.5 and 1.075g respectively.

• Journal of the Korean Geotechnical Society
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• v.19 no.1
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• pp.209-220
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• 2003

Modification of general Hoek and Brown criterion is carried out to estimate the shaft resistance of drilled shaft socketed into rock mass. Since the general Hoek-Brown criterion can consider the in-situ state of the rock mass, the proposed method, estimating the unit shaft resistance of drilled shafts based on the Hoek-Brown criterion, has increased flexibility compared to other methods exclusively considering uniaxial compressive strength of intact rocks. The proposed method can form the upper and lower bounds, and most culled data (from 21 pile load tests) from the literature can be found between these two bounds. A comparison between the estimated and observed unit shaft resistances shows quite a good correlation even with crude assumptions for the input parameters. The best-fit line drawn from this analysis shows that at the lower strength of intact rocks (up to 10MPa), Horvath and Kenney's equation shows a good correlation with the measured values, and fur strong rocks Rosenberg and Journeaux's equation provides a close estimation with colleted data. The results of parametric studies for GSI and confining stress show that the normalized unit shaft resistance increases with these two factors. In addition, coefficient of the equational form of the estimation can vary with GSI and confining stresses.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.5
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• pp.75-83
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• 2019

In order to fulfill the obligation to voluntarily reduce greenhouse gas emissions under the Paris Climate Agreement, the proportion of coal and nuclear power generation is reduced worldwide and national efforts are being made to spread renewable energy including solar power generation. Korea also intends to increase the proportion of renewable energy generation to 30~35% by 2040 by introducing laws and regulations. In addition, while the country is trying to apply solar power generation to sidewalks and roads, there is no research related to it in Korea. Therefore, as a precedent study to develop solar power generation roads, solar power generation concrete blocks applicable to sidewalks and plazas were developed and the applicability was evaluated by constructing them on the site. As a result of indoor experiment, compressive strength was measured by 25.5~35.7MPa and flexural strength was measured by 5.1~10.5MPa, which showed that all domestic standards were satisfied. However, the higher the unit cement amount, the lower the strength was measured according to the mixing of the broken fine aggregate. The absorption rate was 5.7%, which satisfied the domestic standard of 7% or less. As a result of the freeze-thawing test, the reduction rate of the compressive strength after 100 cycles was up to 6.3%. As a result of measuring the settlement amount after construction, the maximum of 2.498mm was measured and irregular settlement occurred in the overall area, which is because the resolution of the sand layer was poor during construction. Maintenance techniques of sidewalk concrete block and solar panel need to be established more efficiently through long-term operation in the further.

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.169-179
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• 2003

Undrained shear strength of clay deposit is one of the most important properties in the design of geotechnical structures. The use of piezocone test is rapidly growing due to its merit that can measure the in-situ undrained shear strength continuously with less error. The reliability of the shear strength from piezocone test depends upon the cone factor applied. Many researchers have suggested different ranges of values for the factors. This study performs to find out the validity of the suggested values in Korea and their charateristics related to the mechanical properties of clay. Piezocone tests were performed at the site of pilot project of ground improvement at Yangsan-Mulgeum Gyeongnam to investigate the charateristics of piezocone factors. The piezocone fators$(N_{kt}, N_{ke}, N_{\Delta u})$ based on the undrained shear strength from quick triaxial compression test are generally within the suggested range. And there appears considerable relations between undrained shear strength and $(N_{kt}, N_{ke}, N_{\Delta u})$ and between preconsolidation pressure and $(N_{kt}, N_{ke})$, while plasticity index, rigidity index and friction ratio do not show any relations with cone factors. The results also reveal that factor $(N_{\Delta u})$ shows higher reliability than factors $(N_{kt} and N_{ke})$, which show smaller standard deviation, breadth of change and scattering.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.3
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• pp.27-34
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• 2017

Recently, the importance of the industrial warehouse floor has been increasing due to the development of the distribution and logistics industry. In this present study, an early-hardening polymer floor mortar which can compensate for the limitation of conventional cement based floor mortar regarding fluidity and long curing time was developed. In order to achieve the early-hardening of mortar characteristic ultra rapid hardening cement was used as binder. Four types of mixture proportions in accordance with the vinyl acetate ethylene(VAE) polymer contents with range from 10% to 20% and the other proto proportion without VAE polymer were designed. Mechanical experiments including the fluidity test, compressive strength test, bending test, bond test, and abrasion test were conducted for all mixture proportions. From the flow test result, it was possible to achieve the high flow with 250 mm by controlling the amount of superplasticizer. The incorporation of VAE polymer was found to affect the compressive strength reduction, however, the flexural strength was higher than that of the proto mixture, and it was evaluated to increase the compressive strength / flexural strength ratio. Moreover, at least 2.6 times higher bond strength and more than 4 times higher abrasion resistance were secured. From the mechanical experiments results, the optimum mixing ratio of the VAE polymer was determined to be 10%. As a result of application and monitoring, it shows that it has excellent resistance to cracking, discoloration, impact, and scratch as well as bond performance compared to the cement based floor mortar.

• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.6
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• pp.533-542
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• 2014

In this study TBM disc cutter prediction models including Gehring, CSM and NTNU models were investigated and the characteristics of the models were examined. The influence of penetration, uniaxial compressive strength and abrasiveness index on the models was analyzed. The life of disc cutter linearly increases with penetration per revolution and decreases with increasing uniaxial compressive strength of rocks. As the abrasiveness index, CAI, increases, the life of disc cutter in Gehring and CSM model decreases. On the contrary, the life of disc cutter life in NTNU model decreases with increasing CLI. Also, comparisons of predicted disc life were made between models using actual job site data.