• Journal of the Korean GEO-environmental Society
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• v.19 no.12
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• pp.47-58
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• 2018

Duncan & Chang(1970) proposed the Duncan-Chang model that a linear relation of transformed stress-strain plots was reconstituted from a nonlinear relation of stress-strain curve of triaxial compression test using hyperbolic theory so as to estimate an initial tangent modulus and ultimate deviator stress for the soil specimen. Although the transformed stress-strain plots show a linear relationship theoretically, they actually show a nonlinearity at both low and high values of strain of the test. This phenomenon indicates that the stress-strain curve is not a complete form of a hyperbola. So, if linear regression analyses for the transformed stress-strain plot are performed over a full range of strain of a test, error in the estimation of their linear equations is unavoidable depending on ranges of strain with non-linearity. In order to reduce such an error, a modified regression analysis method is proposed in this study, in which linear regression analyses for transformed stress-strain plots are performed over the entire range of strain except the range the non-linearity is shown around starting and ending of the test, and then the initial tangent modulus and ultimate deviator stresses are calculated. Isotropically consolidated-drained triaxial compression tests were performed on compacted weathered soil with a modified Proctor density to obtain their model parameters. The modified regression analyses for transformed stress-strain plots were performed and analyzed results are compared with results estimated by 2 points method (Duncan et al., 1980). As a result of analyses, initial tangent moduli are about 4.0% higher and ultimate deviator stresses are about 2.9% lower than those values estimated by Duncan's 2 points method.

• Geomechanics and Engineering
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• v.34 no.4
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• pp.449-459
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• 2023

The design and development of underground nuclear waste repositories should cover the performance evaluation of the different components such as the construction materials because the long term stability will depend on their response to the surrounding conditions. In South Korea, Gyeonju bentonite has been proposed as a candidate to be used as buffer and backfilling material, especially in the form of blocks to speed up the construction process. In this study, various cylindrical samples were prepared with different dry density and water content, and their physical and mechanical properties were analyzed and correlated with X-ray CT observations. The main objective was to characterize the samples and establish correlations for non-destructive estimation of physical and mechanical properties through the utilization of X-ray CT images. The results showed that the Uniaxial Compression Strength and the P-wave velocity have an increasing relationship with the dry density. Also, a higher water content increased the values of the measure parameters, especially for the P-wave velocity. The X-ray CT analysis indicated a clear relation between the mean CT value and the dry density, Uniaxial Compression Strength, and P-wave velocity. The effect of the higher water content was also captured by the mean CT value. Also, the relationship between the mean CT value and the dry density was used to plot CT dry densities using CT images only. Moreover, the histograms also provided information about the samples heterogeneity through the histograms' full width at half maximum values. Finally, the particle size and heterogeneity were also analyzed using the Madogram function. This function identified small particles in uniform samples and large particles in some samples as a result of poor mixing during preparation. Also, the μ_max value correlated with the heterogeneity, and higher values represented samples with larger ranges of CT values or particle densities. These image-based tools have been shown to be useful on the non-destructive characterization of bentonite samples, and the establishment of correlations to obtain physical and mechanical parameters solely from CT images.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.6
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• pp.451-464
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• 2014

This study used numerical methods to investigates investigate the exhaust gas recirculation (EGR) effect under the condition of boost pressure condition on a homogeneous charge compression ignition (HCCI) combustion engine using numerical methods. The detailed chemical-kinetic mechanisms and thermodynamic parameters for n-heptane, iso-octane, and PRF50 from the Lawrence Livermore National Laboratory (LLNL) are were used for this study. The combustion phase affects the efficiency and power. To exclude these effects, this study decided to maintain a 50 burn point (CA50) at 5 CA after top dead center aTDC. The results showed that the EGR increased, but the low temperature heat release (LTHR), negative temperature coefficient (NTC), and high temperature heat release (HTHR) were weakened due by theto effect of the O2 reduction. The combined EGR and boost pressure enhanced the autoignition reactivity, Hhence, the LTHR, NTC, and HTHR were enhanced, and the heat-release rate was increased. also In addition, EGR decraeased the indicated mean effective pressure (IMEP), but the combined EGR and boost pressure increased the IMEP. As a results, combining the ed EGR and boost pressure was effective to at increase increasing the IMEP and maintaining the a low PRR.

• Journal of the Korea Concrete Institute
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• v.22 no.4
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• pp.535-546
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• 2010

Recently, the probability of collision accident between vehicles or vessels and infrastructures are increasing at alarming rate. Particularly, collision impact load can be detrimental to sub-structures such as piers and columns. The damaged pier from an impact load of a vehicle or a vessel can lead to member damages, which make the member more vulnerable to impact load due to other accidents which. In extreme case, may cause structural collapse. Therefore, in this study, the vehicle impact load on concrete compression member was considered to assess the quantitative design resistance capacity to improve, the existing design method and to setup the new damage assessment method. The case study was carried out using the LS-DYNA, an explicit finite element analysis program. The parameters for the case study were cross-section variation of pier, impact load angle, permanent axial load and axial load ratio, concrete strength, longitudinal and lateral rebar ratios, and slenderness ratio. Using the analysis results, the performance based resistance capacity evaluation method for impact load using satisfaction curve was developed using Bayesian probabilistic method, which can be applied to reinforced concrete column design for impact loads.

• Journal of the Korean GEO-environmental Society
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• v.14 no.11
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• pp.65-71
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• 2013

Despite of the various merits of soil pavement, it has not been widely adapted because portland cement was conventionally used as soil stabilizer to improve the mechanical properties such strength parameters. Recently, natural soil stabilizer(NSS) were developed and virtually adopted to several case of soil pavement construction under control of heavy metal pollution compared to cement-used cases. However, the application of natural soil stabilizer is not settled yet, and empirical design have been widely adopted. In this study, therefore, the strength parameter of soil-NSS mixture was estimated by some triaxial compression tests, CU-test. From the tests, the relationship between curing period and strength parameter such as internal friction and effective cohesion was examined. As a result, effective cohesion of dredged clay and granite soil increased as curing time is increased. However, internal friction is almost same result in all soil type used in this study.

• Tunnel and Underground Space
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• v.14 no.1
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• pp.69-77
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• 2004

Investigation of the time-dependent behavior of rock and the associated mechanisms are of key interest in long-term stability analysis of many engineering applications. In this study, creep tests were performed on Daejeon granite samples of 25.4mm diameter under uniaxial compression at varying stress levels. The effect of moisture was investigated by testing both air-dried and fully water-saturated samples. The creep behavior of Daejeon granite exhibited three distinctive stages of primary, secondary and tertiary creep. The ultimate strength of granite under a constant stress decreased considerably with time. Saturation and immersion of the test specimen in water markedly increased the total creep strain as well as the secondary creep rate. The experimental creep curves are fitted to Burger's model as well as two other empirical models suggested by previous researchers. A number of the parameters determined for each model are dependent on stress and influenced by the presence of water. Based on the experimental results, an empirical relation between the applied stress and the time-dependent strain is established separately for each air-dried and fully water-saturated Daejeon granite.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1115-1123
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• 2008

When constructing projects such as road embankments, bridge approaches, dikes or buildings on soft, compressible soils, significant settlements may occur due to the consolidation of these soils under the superimposed loads. The compressibility of the soil skeleton of a soft clay is influenced by such factors as structure and fabric, stress path, temperature and loading rate. Although it is possible to determine appropriate relations and the corresponding material parameters in the laboratory, it is well known that sample disturbance due to stress release, temperature change and moisture content change can have a profound effect on the compressibility of a clay. The early research of Tezaghi and Casagrande has had a lasting influence on our interpretation of consolidation data. The 24 hour, incremental load, oedometer test has become, more or less, the standard procedure for determining the one-dimensional, stress-strain behavior of clays. An important notion relates to the interpretation of the data is the ore-consolidation pressure ${\sigma}_p$, which is located approximately at the break in the slope on the curve. From a practical point of view, this pressure is usually viewed as corresponding to the maximum past effective stress supported by the soil. Researchers have shown, however, that the value of ${\sigma}_p$ depends on the test procedure. furthermore, owing to sampling disturbance, the results of the laboratory consolidation test must be corrected to better capture the in-situ compressibility characteristics. The corrections apply, strictly speaking, to soils where the relation between strain and effective stress is time independent. An important assumption in Terzaghi's one-dimensional theory of consolidation is that the soil skeleton behaves elastically. On the other hand, Buisman recognized that creep deformations in settlement analysis can be important. this has led to extensions to Terzaghi's theory by various investigators, including the applicant and coworkers. The main object of this study is to suggestion the modified compression index value to predict settlements by back calculating the $C_c$ from different numerical models, which are giving best prediction settlements for multi layers including very thick soft clay.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.48 no.5
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• pp.88-98
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• 2011

Recently, according as the importance of GIS(geography information system) database security is embossed, much researches had been achieved about GIS network security. But most such researches are weak against sourceful illegal reproductions and distributions of GIS vector data map. In this paper, we proposed an efficient layer unit contents based partial encryption technique in the vector map compression domain to prevent illegal distributions and unauthorized accesses. This method achieves a partial encryption about each central coordinate and directional parameters of a MCA(minimum coding attribute) that is created at the vector map compression processing in the vector space. First, the position encryption is applied as permutating randomly the center coordinate of each record that is minimum unit of vector map shape. And second, the direction encryption that changing shapes of vector map topography is applied as encrypting the direction of vertices's coordinates of each record. In experimental results, we confirmed that our proposed method can encipher the large volumed vector map data effectively in low computational complexity. Also, we could minimize the decline of compression efficiency that occurred by conventional contents based encryption schemes using AES or DES algorithms.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.4
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• pp.75-82
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• 2021

The objective of this study is to examine the loss of prestressing stress in the developed prestressing reinforcing units using steel bar and pipe (SP). The main parameters were the reinforcing bar type, the magnitude of prestressed force, and prestressing method. The test results showed that the loss of prestressing stress for SP was highest in the initial prestressing step, which was higher for the compression introduction typed specimens than tension introduction typed specimens. The loss of prestressing stress of SP made with P800 was 1.6% for the compression introduction typed specimen with 0.8f_y, which was lowest than the other specimens. Meanwhile, the relaxation of SP with the respect to the time ranged between 0.4 and 1.9%, irrespective of SP material type, the magnitude of prestressed force, and prestressing method. These values were less than 2.5%, which is the maximum value for the relaxation of prestressed reinforcing steel bars in design codes. Consequently, considering the loss of stress developed in the initial prestressing step, the developed SP material type, prestressing introduction method, and magnitude are recommended to be P800, compression introduction type, and 0.8f_y.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.2
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• pp.617-624
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• 2021

Concrete-filled steel tubular columns can improve the strength and deformation capacity of structures, thereby enabling the development of efficient structures. The Korean design standard (KDS41) regarding concrete-filled steel tubular structures, established by the architectural institute of Korea in 2005, was revised in 2009 and 2016. The objective was to understand the compressive strengths and deformation capacity of stub columns for concrete-filled square steel tubes under uniaxial compression and validate the KDS41's standard code for necessary corrections. Experiments were conducted on 26 specimens with parameters, such as the width-thickness ratio of cold-formed square tubes. The following values of the stub columns for concrete-filled square steel tubes were obtained: compressive strengths, relationship between the axial load and axial displacement, and failure modes. An analysis of these results enabled an understanding of the concrete-filled effect and the influence of the wide-thickness ratio. The compressive strengths of filled concrete saw a 9% increase compared to a state of uniaxial stress, which must be noted in a future edition of KDS41. After benchmarking the results regarding square steel tubes generated by cold forming to the guidelines provided by the KDS41, the KDS41's value of 2.26 for the limiting width-to-thickness ratio for the compact section was found to be inflated. With a safety concern, this paper proposes a more conservative value of 1.35.