• Computers and Concrete
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• v.26 no.3
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• pp.227-237
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• 2020

Strain rate investigations are needed to calibrate strain-rate-dependent material models and numerical codes. An appropriate material model, which considers the rate effects, need to be used for proper numerical modeling. The plastic concrete cut-off wall is a special underground structure that acts as a barrier to stop or reduce the groundwater flow. These structures might be subjected to different dynamic loads, especially earthquake. Deformability of a structure subjected to dynamic loads is a principal issue which need to be undertaken during the design phase of these structures. The characterization of plastic concrete behavior under different strain rates is essential for proper designing of cut-off walls subjected to dynamic loads. The Cowper-Symonds model, as one of the most commonly applied material models, complies well with the behavior of a plastic concretes in low to moderate strain rates and will be useful in explicit dynamics simulations. This paper aims to present the results of an experimental study on mechanical responses of one of the most useful types of plastic concrete and Cowper-Symonds constant determination procedures in a wide range of strain rate from 0.0005 to 107 (1/s). For this purpose, SHPB, uniaxial, and triaxial compression tests were done on plastic concrete samples. Based on the results of quasi-static and dynamic tests, the dynamic increase factors (DIF) of this material in different strain rates and stress state conditions were determined for calibration of the Cowper - Symonds material models.

• Journal of The Korean Society of Agricultural Engineers
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• v.51 no.6
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• pp.69-76
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• 2009

Soils exhibit creep behavior in which deformation and movement proceed under a state of constant stress or load. In Korea, weathered soil is abundant and occupies around one-third of the country. Weathered soil is visually described as a sandy or gravelley soil, but the behavior is quite different from the behavior of usual sand and gravel. In particular, the permeability of weathered soil is similar to sand, but the durability of settlement is similar to clay. Therefore analysis of time-dependent behavior of weathered soil is very important. In this study, Creep tests with weathered soils were carried out under constant principal stress differences of various stress levels which were experimentally obtained by triaxial compression test. The results of these tests showed the creep behavior for which the deformation increased with time, and the results are consistent with phenomenological model by creep equation of Singh-Mitchell.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.75-81
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• 2003

To investigate the reinforcing effect of subsurface layers of marine dredged clay(DMC) mixed with the micro-fiber(MF), a series of laboratory tests were performed on the DMC specimens with and without MF through uniaxial and triaxial compression tests. For the test programme, the elapsed time after dredging of marine clay, mixing rate and length of MF, and curing time of the composite were chosen as the important factors affecting the strength behaviour. The strength of the DMC mixed with MF and waste lime(WL) used for the admixture was found to be enhanced with the increasing content and length of MF, and with decreasing water content of DMC. MF and WL were applied as materials for trafficability improvement of the very soft reclaimed ground by DMC.

• Magazine of the Korean Society of Agricultural Engineers
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• v.40 no.5
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• pp.37-42
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• 1998

This study was performed to evaluate the characteristics of volume change is unsaturated clayed soil. The medium-plastic clay was selected and compacted by 50% of Proctor standard compaction energy at 6% higher moisture content than its OMC. A series of isotropic compression tests and triaxial shear tests were performed. The results of the study are summarized as follows. At each matric suction, when the matric suction was increased, the yield stress was increased and slope of volume change was decreased. The more net mean stress was, the less the quantity of volume change was. In shear test, the volumetric strain was much rapidly changed in large matric than in low matric suctions. But the effect of matric suction to volume change disappeared under high net mean stress. At lower deviator stress the more matric suction was, the higher volume change was. But As the matric suction was increasing, the behavior of the unsaturated clayey soil was similar to that of saturated clayey soil. Volume change in the unsaturated clayey soil can be represented as a unique plane in three-dimensional space, which is the axes of net mean stress, matric suction and void ratio.

• Geotechnical Engineering
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• v.8 no.2
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• pp.81-96
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• 1992

This paper dealt with the influence of experimental error generated inevitably during performing experiments on the granular soil behaviour analysis selecting Lade's Single Work-Hardening constitutive model. Several isotropic compression-expansion tests and a series of drained conventional triaxial tests with various confining pressures for Baekma river sands were performed and the values of parameters for the above model were determined using computer program developed for this study based on regression analysis. By finding the range of the upper and lower bound for deviator stress and volumetric strain versus axial strain dependant on the increase and decrease of the standard deviation from mean value of parameters, sensitivities of all the parameters were examined. Practical use of program to determine the parameters and capability to predict the behaviour of granular soil by Lade's Single Work -Hardening model verified.

• Geomechanics and Engineering
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• v.18 no.1
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• pp.21-27
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• 2019

Rockburst disasters pose serious threat to mining safety and underground excavation, especially in China, resulting in massive life-wealth loss and even compulsive closed-down of some coal mines. To investigate the mechanism of rockbursts that occur under a state of static forces, a stress model with sidewall as prototype was developed and verified by a group of laboratory experiments and numerical simulations. In this model, roadway sidewall was simplified as a square plate with axial compression and end (horizontal) restraints. The stress field was solved via the Airy stress function. To track the "closeness degree" of the stress state approaching the yield limit, an unbalanced force F was defined based on the Mohr-Coulomb yield criterion. The distribution of the unbalanced force in the plane model indicated that only the friction angle above a critical value could cause the first failure on the coal in the deeper of the sidewall, inducing the occurrence of rockbursts. The laboratory tests reproduced the rockburst process, which was similar to the prediction from the theoretical model, numerical simulation and some disaster scenes.

• Geotechnical Engineering
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• v.4 no.1
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• pp.17-28
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• 1988

Among several types of element tests to predict soil behalf.iota in a laboratory, the torsion shear apparatus, in which the directions of principal stresses could be rotated during shearing, wra explained. In this study, this torsion shear apparatus was improved so as to be used in tests on clay specimens . And some undrained torsion shear tests u.ere performed on remolded specimens of Ko-consolidated clay to investigate the influence of reorientation of the principal stress directions on the stress-strain behavior The soil behavior by the torsion shear apparatus without torque was compared It.ith that by the conventional triaxial compression tests . The stress path, provided by both vertical loads and torque during torsion shear tests, has much effect on the stress-strain behavior, the pore pressure and the effective principal stress ratio . The rotation angle of the principal stress and the b-value were gradually increased with increasing shear strain, but converged to the values at failure.

• Journal of the Korean GEO-environmental Society
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• v.7 no.6
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• pp.67-73
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• 2006

In this study, basic physical tests and mechanical tests of crushed rock were performed in order to investigate the field application of crushed rock as substitute materials of sand that is commonly being used as foundation and backfill materials of sewer conduit. Particle-size distribution curve of crushed rock is similar to sand and also it is well-graded soil than common sand. Maximum dry unit weight in proctor compaction test for crushed rock is higher than the values of common sand. So we can estimate that the crushed rock has advantages in workability than sand for the backfill compaction after construction of sewer conduit. When we investigate the results of direct shear test and triaxial compression test on the crushed rock, it has a similar value of shear strength parameters to sand at the same stress state and as time goes by, it tends to increase the unconfined compression strength. But, because the strength reaches at the constant value after 6~7 days, we expect that it can absorb the lateral strain of flexible conduit well. All the above experimental results just proves that crushed rock can substitute for sand as backfill materials and foundation of sewer conduit.

• Journal of the Korean Geotechnical Society
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• v.22 no.10
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• pp.55-67
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• 2006

Modern methods for designing IGM(Intermediate Geomaterial) socketed drilled shafts require knowledge of the compressive strength and modulus of the IGM. However, the weathered IGMs at many sites prohibit the recovery of samples of sufficient length and integrity to test cores in either unconfined or triaxial compression tests. Since rational design procedures usually require values of compressive strength, surrogate methods must be employed to estimate the compressive strength of the IGM. A surrogate method considered in this study was Texas cone penetrometer tests which were performed at several sites in North Central Texas. Correlations of Texas cone penetrometer tests and compressive strengths of cores from these formations are provided in the paper. In order to develop the relationships between Texas cone penetrations and side and base resistance of IGM socketed drilled shafts, three filed load tests were conducted in the same sites. Based on the field study and literature reviews, a design method for IGM socketed drilled shafts using Texas cone penetration test was proposed.

• Journal of the Korean Geotechnical Society
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• v.18 no.5
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• pp.169-178
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• 2002

The stress~strain characteristics of geosynthetics reinforced clayey soil were investigated by triaxial compression tests. All the tests were peformed either on unreinforced or reinforced soils under fully drained condition after having been consolidated isotropically or anisotropically to the required level of effective stresses by the small increment of 0.05kgf/$cm^2$. The anisotropically consolidated drained tests were performed to simulate the in-situ condition of reinforced soil structures such as reinforced soil wall, abutment and embankment which are generally in the anisotrpic state. From a series of tests it was ffund that the behavior of the anisotropically consolidated reinforced clayey soils was very different from stress~strain characteristics of consolidated reinferced clayey soils. It was found especially that the initial Young's moduli of anisotropically consolidated reinforced clayey soils were higher than those of isotropically consolidated reinforced clayey soils. It was found also that the reinforcement effect in anisotropically consolidated reinforced soils developed at a much lower level of axial strain(0.01%) compared with isotropically consolidated ones(about 1.0~5.0%).