• Geomechanics and Engineering
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• 제18권4호
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• pp.417-426
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• 2019

Gangue filling in the goaf is an effective measure to control the surface subsidence. However, due to the obvious deformation of gangue compression, the filling effect deserves to be further studied. To this end, the deformation of coal gangue filling in the goaf is analyzed by theoretical analysis, large-scale crushed rock compression test, and field investigation. Through the compression test of crushed rock, the deformation behaviour characteristics and energy dissipation characteristics is obtained and analysed. The influencing factors of gangue filling and predicted amount of main deformation are summarized. Besides, the predicted equation and filling subsidence coefficients of gangue are obtained. The gangue filling effect was monitored by the movement observation of surface rock. Gangue filling can support the roof of the goaf, effectively control the surface subsidence with little influence on the ground villages. The premeter and equations of the main deformation in the gangue filling are verified, and the subsidence coefficient is further reduced by adding cemented material or fine sand. This paper provides a practical and theoretical reference for further development of gangue filling.

• 대한건축학회논문집:구조계
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• 제34권7호
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• pp.19-26
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• 2018

This study tested 25 lightweight aggregate concrete (LWAC) mixtures using the expanded bottom ash and dredged soil granules to examine the compressive strength gain of such concrete with different ages. The test parameters investigated were water-to-cement ratios and the natural sand content for the replacement of lightweight fine aggregate. The compressive strength gain rate in the basic equation specified in fib model code was experimentally determined in each mixture and then empirically formulated as a function of the water-to-cement ratio and oven-dried density of concrete. When compared with 28-day compressive strength, the tested LWAC mixtures exhibited relatively low gain ratios (0.49~0.82) at an age of 3 days whereas the gain ratios (1.16~1.41) at 91 days were higher than that (1.05~1.15) of the conventional normal-weight concrete. Thus, the fib model equations tend to overestimate the early strength gain of LWAC but underestimate the long-term strength gain. The proposed equations are in good agreement with the measured compressive strength development of LWAC at different ages, indicating that the mean and standard deviation of the normalized root mean square errors determined in each mixture are 0.101 and 0.053, respectively.

• 한국수처리학회지
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• 제26권6호
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• pp.43-51
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• 2018

In order to systematically and scientifically manage the organic and heavy metals against sediment at Daecheon Port, this study conducted particle composition, organic materials and heavy metals irradiation studies of sediments. Analysis of the grain size composition of sediments in the target study area showed the distribution characteristics of the mix of sand, silt and clay. That is, Station C (Stn. C) showed superior by fine-grained sediment, Station A and B (Stn. A and B) showed superior by coarse-grained sediment. The organic matter(COD, TOC, and IL) of Stn. C was appeared to be heavily polluted more than Stn. A and B. These data for the spatial properties in sediment showed that organic matter was related positively to the sediment silt-clay content. Also, in the case of heavy metals contamination in surface sediments, Stn. C was higher than Stn. A and B. Particularly, at the Stn. C, high organic matter concentration and C/N ratio value( >10) indicated that the sediment was composed highly of land-derived organic matter. From these results, it considered that the correlation analysis among to silt-clay, organic matter and heavy metal was found to have a good interrelationship.

• Structural Engineering and Mechanics
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• 제77권1호
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• pp.103-114
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• 2021

Ultra high strength concrete (UHSC) originally proposed by Richards and Cheyrezy (1995) composed of cement, silica fume, quartz sand, quartz powder, steel fibers, superplasticizer etc. Later, other ingredients such as fly ash, GGBS, metakaoline, copper slag, fine aggregate of different sizes have been added to original UHSC. In the present investigation, the combined effect of coarse aggregate (6mm - 10mm) and steel fibers (0.50%, 1.0% and 1.5%) has been studied on UHSC mixes to evaluate mechanical and fracture properties. Compressive strength, split tensile strength and modulus of elasticity were determined for the three UHSC mixes. Size dependent fracture energy was evaluated by using RILEM work of fracture and size independent fracture energy was evaluated by using (i) RILEM work of fracture with tail correction to load - deflection plot (ii) boundary effect method. The constitutive relationship between the residual stress carrying capacity (σ) and the corresponding crack opening (w) has been constructed in an inverse manner based on the concept of a non-linear hinge from the load-crack mouth opening plots of notched three-point bend beams. It was found that (i) the size independent fracture energy obtained by using above two approaches yielded similar value and (ii) tensile stress increases with the increase of % of fibers. These two fracture properties will be very much useful for the analysis of cracked concrete structural components.

• Geomechanics and Engineering
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• 제30권3호
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• pp.219-231
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• 2022

Geotechnical materials such as silt, fine sand, or coarse granular soils may be unstable under undrained shearing or during rainfall infiltration starting an unsaturated state. Some researches are available describing the instability of coarse granular soils in drained or undrained conditions. However, there is a need to investigate the instability mechanism of unsaturated silty soil considering the effect of degree of compaction and net confining stress under partially and fully drained conditions. The specimens in the current study are compacted at 65%, 75%, & 85% degree of compaction, confined at pressures of 60, 80 & 120 kPa, and tested in partially and fully drained conditions. The tests have been performed in two steps. In Step-I, the specimens were sheared in constant water content conditions (a type of partially drained test) to the maximum shear stress. In Step-II, shearing was carried in constant suction conditions (a type of fully undrained test) by keeping shear stress constant. At the start of Step-II, PWP was increased in steps to decrease matric suction (which was then kept constant) and start water infiltration. The test results showed that soil instability is affected much by variation in the degree of compaction and confining stresses. It is also observed that loose and medium dense soils are vulnerable to pre-failure instability i.e., instability occurs before reaching the failure state, whereas, instability in dense soils instigates together with the failure i.e., failure line (FL) and instability line (IL) are found to be unique.

• Geomechanics and Engineering
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• 제30권4호
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• pp.393-399
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• 2022

The Segregation Potential (SP) is one of the most widely used predictors of frost heave in cold regions. Laboratory step-freezing tests determining a representative SP at the onset of the formation of the last ice lens (near the thermal steady state condition) can predict susceptibility to frost heave. Previous work has proposed empirical semi-log fitting for determination of the representative SP and applied it to several fine-grained soils, but considering only frost-susceptible soils. The presence of fines in coarse-grained soil affects frost susceptibility. Therefore, it is required to evaluate the applicability of the empirical semi-log fitting for both frost-susceptible and non-frost-susceptible soils with fines content. This paper reports laboratory frost heave tests for fines contents of 5%-70%. The frost susceptibility of soil mixtures composed of sand and silt was classified by the representative SP, and the suitability of the empirical semi-log fitting method was assessed. Combining semi-log fitting with simple laboratory frost heave testing using a temperature-controllable cell is shown to be suitable for both frost-susceptible and non-frost-susceptible soils. In addition, initially non-frost-susceptible soil became frost susceptible at a 10%-20% weight fraction of fines. This threshold fines content matched well with transitions in the engineering characteristics of both the unfrozen and frozen soil mixtures.

• 한국초전도ㆍ저온공학회논문지
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• 제11권4호
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• pp.8-11
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• 2009

This study introduced wastewater treatment method by High Gradient Magnetic Separation (HGMS). HGMS treatment was high efficient method for various industrial wastewaters. The system is currently research state, but we have surveyed commercialize the technology for industry. In rolling plate process, coolant wastewater was recycled by sedimentation and sand filter system. It needs several large reservoirs and long time to remove suspended solid (SS) like metal fines and iron oxide in hot rolling plate making process. If removing rate of suspended solid in rolling coolant wastewater is improved by using HGMS system, the productivity of working process can be increased and the area of reservoir can be reduced. We manufactured high temperature superconducting HGMS system that had a purpose to treatment of coolant wastewater in rolling plate process. We fabricated the prototypes of magnetic matrix filter consisting of stainless steel 430 mesh, which is a core component in the magnetic separation system, In our basic preliminary experiment using HGMS system, it has been clear that the fine paramagnetic particles in the coolant wastewater obtained from rolling plate process of POSCO can be separated with high efficiency.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2020년도 가을 학술논문 발표대회
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• pp.94-95
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• 2020

Oyster shells are characterized by coarse and coarse grains, but similar in strength to sand, and egg shells are fine grains but weak in strength. In terms of supply and demand of raw materials, oyster shells can be supplied only in limited periods and regions in winter and south coast of the year, but egg shells have the advantage of being able to supply and supply nationwide 365 days. This study aims to study the change in strength characteristics by mixing oyster shell powder and egg shell powder with the same particle size and mixing up to 150%. The conclusions of the flexural and compressive strength tests of mortar mixed with oyster shell powder and egg shell powder are as follows. The 7-day flexural and compressive strength with ESP added and the 3-day flexural and compressive strength with OSP added were similar, which is thought to be because the strength of OSP is higher than that of ESP.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2021년도 가을 학술논문 발표대회
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• pp.21-22
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• 2021

This study incorporates fine waste glass (GS) as a replacement for natural sand (NS) in ground granulated blast furnace slag (GGBS) based alkali activated mortar (AAm). Tests were conducted on the AAm to determine the mechanical properties, apparent porosity and the durability based on its resistance to Na2SO4 5% and H2SO4 2% concentrated solutions. The study revealed that increasing GS up to 100 wt%, increased strength and decreased porosity. The lower porosity attained with the incorporation of GS, improved the resistance of mortar to Na2SO4 and thus increasing durability. However, the durability of mortar to H2SO4 solution was negatively impacted with the further reduction of porosity observed with increasing GS above 50 wt.% believed to be caused by the stress induced as a result of expansive reaction products created when the mortar reacted with acid.

• Structural Engineering and Mechanics
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• 제84권2호
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• pp.167-180
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• 2022

A strategic structure when exposed to direct hit of conventional bomb/projectile are severely damaged because of large amounts of energy released by the impact and penetration of bomb. When massive concrete slabs suffer a direct hit, the energy released during impact and penetration process are able to easily break up large mass of concrete. When over stressed under such impact of bombs, the concrete structure fails showing brittle behavioural nature. This paper is intended to study and suggest the protective measures for structures used for strategic application by adopting a means to dissipate the large quantum of energy released. To quantitatively evaluate the force, displacement and energy in such scenario, a fine numerical model of the proposed layered structure of different combinations was built in ANSYS programme in which tri-nitrotoluene (TNT) explosive was detonated at penetration depth calculated for GP1000 Lbs bomb. The distinct blast mitigation effect of the proposed structure was demonstrated by adopting various layers/barriers created as protective measures for the strategic structure. The calculated result shows that the blast effect on the structure is potentially reduced due to provision of buster slab with sand cushioning provided as protective measure to the main structure. This concept of layered protective measures may be adopted for safeguarding strategic structures such as Domes, Tunnels and Underground Structures.