• Journal of the Korean Geotechnical Society
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• v.33 no.12
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• pp.127-139
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• 2017

Site investigation including boring and various in-situ borehole test (Pressuremeter test, Borehole shear test, Downhole test, Suspension PS logging, Density logging) and X-ray fluorescence analysis for rock core sample were performed to estimate geotechnical properties and weathering degree of weathered granite rock in Goyang. Deformation modulus, shear strength parameter and shear wave velocity estimated through in-situ borehole test had a tendency to increase with depth. And several chemical weathering indices evaluated by X-ray fluorescence analysis had a general tendency of reducing weathering degree in accordance with depth. Also, relationship between VR determined as a representative weathering index and the geotechnical properties was analyzed.

• Geomechanics and Engineering
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• v.20 no.2
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• pp.165-174
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• 2020

The enzyme-induced carbonate precipitation (EICP) method has been investigated to improve the hydro-mechanical properties of natural soil deposits. This study was conducted to explore the stiffness evolution during various stress scenarios. First, the optimal concentration of urea, CaCl₂, and urease for the maximum efficiency of calcite precipitation was identified. The results show that the optimal recipe is 0.5 g/L and 0.9 g/L of urease for 0.5 M CaCl₂ and 1 M CaCl₂ solutions with a urea-CaCl₂ molar ratio of 1.5. The shear stiffness of EICP-treated sands remains constant up to debonding stresses, and further loading induces the reduction of S-wave velocity. It was also found that the debonding stress at which stiffness loss occurs depends on the void ratio, not on cementation solution. Repeated loading-unloading deteriorates the bonding quality, thereby reducing the debonding stress. Scanning electron microscopy and X-ray images reveal that higher concentrations of CaCl₂ solution facilitate heterogeneous nucleation to form larger CaCO₃ nodules and 11-12 % of CaCO₃ forms at the interparticle contact as the main contributor to the evolution of shear stiffness.

• Journal of the Korean Geotechnical Society
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• v.26 no.12
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• pp.61-70
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• 2010

A series of shaking table tests were conducted to estimate the seismic performance of soft ground deposits improved by stone column. The amplification of acceleration, shear strain, and shear wave velocity were evaluated to compare the seismic response of unimproved ground deposits with that of improved ground deposits. From the test results, it was shown that the stone column can prevent large shear deformation in ground deposits. However, it was also found that the acceleration of improved ground deposits may be amplified more than that of unimproved ground deposits when it was subjected to short periodic seismic wave. The results suggest that it is necessary to perform the ground response analysis with model experiments for both unimproved and improved ground deposits to evaluate the effect of stone column on the seismic performance of improved ground deposits.

• Journal of the Korean Geotechnical Society
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• v.22 no.11
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• pp.37-45
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• 2006

Bender elements, composed of thin piezo-ceramics and elastic shims, have been used to measure shear wave velocities of specimens in laboratories. In a preliminary stage of their field applications, an in-house research of optimizing suitable bender elements and their geometrical arrangement has been carried out in a barrel of kaolinite-water mixture. Two types of measurement configuration, similar to cross-hole and in-hole seismic testing, have been implemented. prototype instrumented rods were penetrated into a soft clay layer in the west coast and excellent shear waves were recorded. Development of penetration device (mandrel) and associated instrumented rods are in progress for deeper investigation.

• Tunnel and Underground Space
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• v.31 no.6
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• pp.561-577
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• 2021

The compacted bentonite buffer in a geological repository for high-level radioactive waste disposal is saturated due to groundwater inflow. Saturation of the bentonite buffer results in bentonite swelling and bentonite penetration into the rock discontinuities present around the disposal hole. The penetrated bentonite is exposed to groundwater flow and can be eroded out of the repository, resulting in bentonite mass loss which can affect the physical integrity of the engineered barrier system. Hence, the evaluation of buffer-rock interactions and coupled behavior due to groundwater inflow and bentonite penetration is necessary to ensure long-term disposal safety. In this study, the effects of the bentonite penetration and swelling on the physical properties of jointed rock mass were evaluated using the quasi-static resonant column test. Jointed rock specimens with bentonite penetration were manufactured using Gyeongju bentonite and hollow cylindrical granite rock discs obtained from the KAERI underground research tunnel. The effects of vertical stress and saturation were assessed using the P-wave and S-wave velocities for intact rock, jointed rock and jointed rock with bentonite penetration specimens. The joint normal and joint shear stiffnesses of each joint condition were inferred from the wave velocity results assuming an equivalent continuum. The joint normal and joint shear stiffnesses obtained from this study can be used as input factors for future numerical analysis on the performance evaluation of geological waste disposal considering rock discontinuities.

• Journal of the Korean Geotechnical Society
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• v.22 no.12
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• pp.15-24
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• 2006

The evaluation of shear modulus is very important in various fields of civil engineering. Non-destructive seismic methods can be used to determine shear wave velocity ($V_s$) profile. Non-destructive seismic methods geneally consist of three steps: field testing, evaluation of dispersion curve, and determination of Vs profile by inversion process. Non-destructive seismic methods can be divided into two categories according to the number of receivers used for data reduction: two-channel tests and multi-channel tests. Two channel tests use apparent velocity dispersion curve and multi-channel tests use mode dispersion curves. Multi-channel tests using mode dispersion curve can reduce calculation time to determine soil profile and uncertainties in inversion process. So far, only multi-channel tests can determine mode dispersion curves but multi-channel test needs many receivers to determine reasonable mode dispersion curves. In this paper, HWAW (Harmonic Wavelet Analysis of Wave) method is applied to determine mode dispersion curves. HWAW method uses short test setup which consists of two receivers with a spacing of 1 to 3 m. Through numerical simulations and field application, it is shown that HWAW can determine resonable mode disperson curves.

• Journal of the Korean Geotechnical Society
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• v.40 no.3
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• pp.41-54
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• 2024

Regular monitoring plays a crucial role in ensuring the safety of geotechnical structures. Currently, nondestructive methods are employed to monitor such structures to minimize the impact, e.g., sensor-based accelerometers, displacement meters, image-based lasers, and drone imaging. These technologies can observe surface changes; however, they frequently suffer difficulties in terms of identifying changes in internal properties. To monitor changes in internal properties, in situ geotechnical investigations can be employed. A nondestructive test that can be used for this purpose is the spectral analysis of surface wave (SASW) test using geophones. The SASW test is a nondestructive method; however, due to the time required for data interpretation and the difficulty in analyzing the data, it is challenging to use the SASW test for monitoring applications that require frequent observations. However, it is possible to apply the first-step analysis, which yields the dispersion curve, for monitoring rather than the complete SASW analysis, which yields the shear wave velocity. Thus, this paper presents a fundamental study on the phase difference that derives the dispersion curve to utilize the SASW test for monitoring. The reliability of each phase difference interval is examined to determine the boundary to the subjected monitor. The study used phase difference data obtained using a geophone from a single-layered, homogeneous ground site to evaluate reliable boundaries. The findings of this study are expected to improve the utility of monitoring by identifying the ideal boundary for phase difference data.

• Geophysics and Geophysical Exploration
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• v.17 no.1
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• pp.11-20
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• 2014

To reveal shear-wave velocities ($v_s$) and site characterization of Wonju, Korea, Rayleigh waves were recorded at 78 sites of lower altitude using 12 to 24 4.5-Hz vertical geophones for 20 days during the period of February to September 2013. Dispersion curves of the Rayleigh waves obtained by the extended spatial autocorrelation method were inverted using the damped least-squares method to derive $v_s$ models. From these 1-D models, the average $v_s$ to a depth of 30 m ($v_s30$), $v_s$ of weathered rocks, depths to these basement rocks, and average $v_s$ of the overburden layer were derived to be $16.3{\pm}0.7m$, $576{\pm}8m/s$, $290{\pm}7m/s$, and $418{\pm}13m/s$, respectively, in the 95% confidence range. To determine adequate proxies for $v_s30$, we computed correlation coefficients of $v_s30$ with topographic slope (r = 0.46) and elevation (r = 0.43). An empirical linear relationship is presented as a combination of individually estimated $v_s30$ with weighting factors of 0.45, 0.45, and 0.1 for topographic slope, elevation, and mapped lithology, respectively. Due to a weak correlation between $v_s30$ obtained from inversion of dispersion curves and the proxy-based estimation (r = 0.50), however, the relatively large error range should be considered for applications of this relationship.

• Journal of the Korean Ceramic Society
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• v.40 no.6
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• pp.539-546
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• 2003

The GaN/sapphire layered structure is a potential candidate for high frequency devices due to high acoustic velocity of sapphire. Generally, the GaN thin films are epitaxially grown on c, a, and r-plane sapphire substrates. In this study, wave equations of GaN/sapphire structure were calculated according to crystallographic relationship between GaN layer and sapphire substrate. On each plane, the shear velocity was changed by the kH of GaN layer and propagation direction on sapphire substrate. We found electromechanical coupling constant of r-plane was better than the others. As a result, elastic stiffness and electromechanical coupling constant of materials are affected by a cut and an orientation of substrate. GaN/r-plane sapphire structure is more advantageous for high frequency SAW devices.

• Earthquakes and Structures
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• v.14 no.4
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• pp.313-322
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• 2018

The present study is dedicated to investigate the SH body-as well as Love-waves propagation effects in porous media with uncertain porosity and permeability. A unified formulation of the governing equations for one-dimensional (1-D) wave propagation in anisotropic porous layered media is presented deterministically. The uncertainties around the above two cited parameters are taken into account by random fields with the help of Monte Carlo Simulations (MCS). Random samples of the porosity and the permeability are generated according to the normal and lognormal distribution functions, respectively, with a mean value and a coefficient of variation for each one of the two parameters. After performing several thousands of samples, the mathematical expectation (mean) of the solution of the wave propagation equations in terms of amplification functions for SH waves and in terms of dispersion equation for Love-waves are obtained. The limits of the Love wave velocity in a porous soil layer overlaying a homogeneous half-space are obtained where it is found that random variations of porosity change the zeros of the wave equation. Also, the increase of uncertainties in the porosity (high coefficient of variation) decreases the mean amplification function amplitudes and shifts the fundamental frequencies. However, no effects are observed on both Love wave dispersion and amplification function for random variations of permeability. Lastly, the present approach is applied to a case study in the Adapazari town basin so that to estimate ground motion accelerations lacked in the fast-growing during the main shock of the damaging 1999 Kocaeli earthquake.