• Proceedings of the Korean Geotechical Society Conference
• /
• 1991.10a
• /
• pp.332-347
• /
• 1991

Accurate prediction of future settlement is essential for the settlement control of soft soil by pre-loading method. To predict future settlement in clayey soft soils, several methods like Asaoka method, Hyperbolic Method and Hoshino method are currently being used. These methods predict the future sett1ement by mathmatical treatment of the measured settlement data on the basis of consolidtion theory and empiricism. But the correlation coefficient between the measured and the predicted settlement was relatively low (0.8~0.9). Also, the prediction of future settlemet for the design load is very difficult. In this article, the measured field settlement data was treated as the the field consolidation test. Hence, condolidation coefficient(Cv) and compression index(Cc) was evaluated from the field settlement data. Cv and Cc values from field data was used to calculate the degree of consolidation and settlement at desired time. By this method, the correlation coefficent between the measured and the predicted settlement was significantly increased(0.97~0.99). Also the settlement by the design load after the improvement of soft soil could be predicted reasonably. This method is quite rational and sound but it requires thousands of calculation steps. Today, by the aid of low priced personal computers above mentioned technique could be used much acre economically and effectively than conventional methods. This article presented the mechanisms and capacities of this method and demonstrated the enhanced correlation coefficient when applied to actual field settlement data.

• Geomechanics and Engineering
• /
• v.15 no.5
• /
• pp.1113-1124
• /
• 2018

Geological dynamic hazards during deep coal mining are caused by the failure of a composite system consisting of the rock and coal layers, whereas the joint in coal affects the stability of the composite system. In this paper, the compression test simulations for the rock-coal combined body with single joint in coal were conducted using $PFC^{2D}$ software and especially the effects of joint length and joint angle on strength and failure characteristics in a rock-coal combined body were analyzed. The joint length and joint angle exhibit a deterioration effect on the strength and affect the failure modes. The deterioration effect of joint length of L on the strength can be neglected with a tiny variation at ${\alpha}$ of $0^{\circ}$ or $90^{\circ}$ between the loading direction and joint direction. While, the deterioration effect of L on strength are relatively large at ${\alpha}$ between $30^{\circ}$ and $60^{\circ}$. And the peak stress and peak strain decrease with the increase of L. Additionally, the deterioration effect of ${\alpha}$ on the strength becomes larger with the increase of L. With the increase of ${\alpha}$, the peak stress and peak strain first decrease and then increase, presenting "V-shaped" curves. And the peak stress and peak strain at ${\alpha}$ of $45^{\circ}$ are the smallest. Moreover, the failure mainly occurs within the coal and no apparent failure is observed for rock. At ${\alpha}$ between $30^{\circ}$ and $60^{\circ}$, the secondary shear cracks generated in or close to the joint tips, cause the structural instability failure of the combined body. Therefore, their failure models present as a shear failure along partial joint plane direction and partially cutting across the coal body or a shear failure along the joint plane direction. However, at ${\alpha}$ of $60^{\circ}$ and L of 10 mm, the "V-shaped" shear cracks cutting across the coal body cause its final failure. While crack nucleations at ${\alpha}$ of $0^{\circ}$ or $90^{\circ}$ are randomly distributed in the coal, the failure mode shows a V-shaped shear failure cutting across the coal body.

• Magazine of the Korea Concrete Institute
• /
• v.11 no.2
• /
• pp.187-196
• /
• 1999

An experimental investigation was conducted to study the structural behavior of concrete columns confined with welded grids. The full-scale columns with different volumetric ratio, spacing and arrangement of welded reinforcement grids were tested under simulated seismic loading. The columns were subjected to constant axial compression of approximately 20% or 40% of their capacities accompanied by incrementally increasing lateral deformation reversals. The results indicate that the welded reinforcement grid can be used effectively as confinement reinforcement provided that the steel used, have sufficient ductility and the welding process employed does not alter the strength and elongation characteristics of steel. The grids improved the structural performance of columns, which developed lateral drift ratios in excess of 3% with the spacing and volumetric ratio of transverse reinforcement similar to those required by the ACI 318-95 Building Code. Drift capacity further increased when grids with larger number of cells were used. Furthermore, the use of grids reduced congesting of reinforcement while the dimensional accuracy provided perfect support to longitudinal reinforcement.

• Journal of the Korean Geotechnical Society
• /
• v.17 no.6
• /
• pp.47-51
• /
• 2001

There are two strategies to cope with the troubles in landfill site after closure. The first method is active in a way that the wastes are dug up and the recyclable materials are reutilized, meanwhile the materials not recyclable are incinerated in order to minimize the volume of residues to be disposed of. The second method is rather passive and defensive in a way that the source of contamination, that is, buried wastes are not treated. Instead, the transport of leaking leachate and gases generated from the wastes are intercepted and controlled. In this study, as a passive way of the efficient leachate blocking process, applicabilities of geocrete and soluble sodium silicate as a substitute to control leachate leaking from landfill sidewall were investigated. In case of compression test, the strength of mixture I (Geocrete:Sodium silicate=1:3.9 v/v) and mixture II (Geocrete:Sodium silicate=1:2.5 v/v), even after 7 days' curing was higher than the minimum allowance to tolerate the loading(5 kg/$\textrm{cm}^2$). Soaking in the acid fur 4 days and 7 days respectively, the compressive strength of the specimens reduced seriously. The toxicity of geocrete is not detected through the bioassay test, once it was mixed with sodium silicate and the complex was formed. The hydraulic conductivity of the mixtures even after 7 days' curing was lower than the threshold limit $(1.0\times10_{-7}cm/s)$.

• Journal of the Korea Concrete Institute
• /
• v.24 no.1
• /
• pp.25-35
• /
• 2012

For a member subjected to direct shear forces, forces are transferred across interface concrete area and resisted by shear transfer capacity. Shear-friction equations in recent concrete structural design provisions are derived from experimental test results where shear-friction capacity is defined as a function of steel reinforcement area contained in the interface. This empirical equation gave too conservative values for concrete members with large amounts of reinforcement. This paper presents a method to evaluate shear transfer strengths and to define ultimate conditions which result in crushing of concrete struts after yielding of longitudinal reinforcement perpendicular to the interface concrete. This method is based on the bi-axial stress field theory where different constitutive laws are applied in various means to gain accurate shear strengths by considering softening effects of concrete struts based on the modified compression-field theory and the softened truss model. The validity of the proposed method is examined by applying to some selected test specimens in literatures and results are compared with recent design code provisions. A general agreement is observed between predicted and measured values at ultimate loading stages in initially uncracked normal-strength concrete test.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.39 no.4
• /
• pp.106-113
• /
• 1997

Dynamic loading of structures often causes excursions of stresses well into the inelastic range, and the influence of the geometric changes on the dynamic response is also significant in many cases. Therefore, both material and geometric nonlinearity effects should be considered in case that a dynamic load acts on the structure. A structure in a nuclear power plant is a structure of importance which puts emphasis on safety. A nuclear container is a pressure vessel subject to internal pressure and this structure is constructed by a reinforced concrete or a pre-stressed concrete. In this study, the material nonlinearity effect on the dynamic response is formulated by the elasto-viscoplastic model highly corresponding to the real behavior of the material. Also, the geometrically nonlinear behavior is taken into account using a total Lagrangian coordinate system, and the equilibrium equation of motion is numerically solved by a central difference scheme. The constitutive relation of concrete is modeled according to a Drucker-Prager yield criterion in compression. The reinforcing bars are modeled by a smeared layer at the location of reinforcements, and the steel layer model under Von Mises yield criteria is adopted to represent an elastic-plastic behavior. To investigate the dynamic response of a nuclear reinforced concrete containment structure, the steel-ratios of 0, 3, 5 and 10 percent, are considered. The results obtained from the analysis of an example were summarized as follows 1. As the steel-ratio increases, the amplitude and the period of the vertical displacements in apex of dome decreased. The Dynamic Magnification Factor(DMF) was some larger than that of the structure without steel. However, the regular trend was not found in the values of DMF. 2. The dynamic response of the vertical displacement and the radial displacement in the dome-wall junction were shown that the period of displacement in initial step decreased with the steel-ratio increases. Especially, the effect of the steel on the dynamic response of radial displacement disapeared almost. The values of DMF were 1.94, 2.5, 2.62 and 2.66, and the values increased with the steel-ratio. 3. The characteristics of the dynamic response of radial displacement in the mid-wall were similar to that of dome-wall junction. The values of DMF were 1.91, 2.11, 2.13 and 2.18, and the values increased with the steel-ratio. 4. The amplitude and the period of the hoop-stresses in the dome, the dome-wall junction, and the mid-wall were shown the decreased trend with the steel-ratio. The values of DMF were some larger than those of the structure without steel. However, the regular trend was not found in the values of DMF.

• Geophysics and Geophysical Exploration
• /
• v.14 no.4
• /
• pp.324-334
• /
• 2011

Seismic wave velocity change has been monitored due to the accumulation of micro-cracks by uniaxial loads on the rock samples from Seokmo Island with stepwise increase in 5 stages. After the load was applied up to 95% of UCS, P- and S-wave velocities varied in ranges of 0.9 ~ 18.3% and 2.8 ~ 14.8% of fresh rock sample velocities, respectively. Unlike seismic velocity of the dry rock samples that showed overall decreases after the loading, velocity changes of saturated rock samples were much more complicated. These seemed to be due to the mixture of two contradictory mechanisms; i.e. accumulation of micro-crack causes an increase in porosity and a decrease in wave velocity, while saturation causes an increase in wave velocity. Most of tested rocks showed a trend of velocity increase with low axial load and then velocity decrease at later stages. Starting stage of velocity decrease differs from samples to samples. After the failure of rock occurred, noticeable increases of porosity and decreases of wave velocity have been observed. It showed overall trend that the more the quartz contents and the lower the silicate, the higher the Young's modulus.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.14 no.6
• /
• pp.1417-1431
• /
• 1994

In this study, shear strength characteristics of the Nak-Dong river sand in Taegu area are investigated by triaxial compression test, considering shear strain control velocity, relative density, and confining pressure. The results from Lade model and Modified Lade model are compared with the measured value in the laboratory test. The results by the change of shear strain control velocity, relative density, and confining pressure are as follows; 1) The stress limit, which can be Coulomb's law about the Nak-Dong river sand, have ranged 120~200 kpa at 0.08%/min and 120~150 kpa at 0.5%/min. These limits are smaller than that of the calcareous sand and the well-graded, quartz sand. 2) The parameters needed to Lade model and Modified Lade model are much affected by the strain control velocity and the relative density. Consequently, in the field, it is important to use parameters aptly after accurately understanding both the loading condition and subsoil condition. 3) Overall, the principal stress ratio obtained from constitutive model equations is not affected by the control velocity, but both the relative density and confining pressure affect the result of constitutive model equations. Consequently, the study on the various conditions about the relative density and confining pressure is needed to accurately predict the stress-strain behavior on the Nak-Dong river sand. 4) For the range of the used confining pressure in the study, the Lade model shows better agreements with the measured value than the Modified Lade model, comparing the measured value with the principal stress ratio at failure and the internal friction angle of failure envelope obtained from the Lade model and Modified Lade model.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.40 no.11
• /
• pp.927-933
• /
• 2016

In a solid propulsion system, the rocket nozzle is exposed to high temperature combustion gas. Hence, choosing an appropriate material that could demonstrate adequate performance at high temperature is important. As advanced materials, carbon/silicon carbide composites (C/SiC) have been studied with the aim of using them for the rocket nozzle throat. However, when compared with typical structural materials, C/SiC composites are relatively weak in terms of both strength and toughness, owing to their quasi-brittle behavior and oxidation at high temperatures. Therefore, it is important to evaluate the thermal and mechanical properties of this material before using it in this application. This study presents an experimental method to investigate the fracture behavior of C/SiC composite material manufactured using liquid silicon infiltration (LSI) method at elevated temperatures. In particular, the effects of major parameters, such as temperature, loading, oxidation conditions, and fiber direction on strength and fracture characteristics were investigated. Fractography analysis of the fractured specimens was performed using an SEM.

• Journal of Korean Society of Steel Construction
• /
• v.26 no.4
• /
• pp.361-373
• /
• 2014

As the height and beam span of buildings built in the construction market increase, increasingly higher quality is being required of the construction materials. In response to this trend, 800MPa tensile strength class steel was developed in domestic company. Currently, experiments applying flexural member, compression member, and connections are continuously conducted, but a design guideline for high strength steel has yet to be established. Among those construction materials, for the high strength steel beam-to-column connections, the evaluation of implementing ductile connections for the high strength steel beam-to-column connections is producing pessimistic results and the number of related researches is inadequate because of the high yield ratio, which is the characteristic of high strength steel. This study on implementation of ductile connections made of high strength steel was conducted using the connection detail as the variable, for the purpose of enhancing the deformation capacity of high strength steel beam-to-column connections. Cyclic loading test and nonlinear finite element analysis were conducted with full-scale mock-up connection models with the applied connection details. As a result, the structural performance of high-strength steel beam-to-column connection with presented detail was contented with demand of Special Moment Frames of KBC standard.