• Journal of the Korean Geotechnical Society
• /
• v.28 no.12
• /
• pp.41-51
• /
• 2012

Soils are commonly unsaturated in the near surface. The stiffness of soils is affected by the amount of air and water. The objective of this study is to evaluate the porosity of the unsaturated soils by using the elastic waves including compressional and shear waves. The elastic waves are measured at different degrees of saturation by controlling the matric suction. Thus, the unsaturated soils are characterized at different levels of the matric suction. Shear and compressional waves are measured by using the bender elements and the piezo disk elements, respectively. Both transducers are installed on the walls of the rectangular cell. The unsaturated soils are prepared by using uniform size sands and silts. Test results show that both compressional and shear wave velocities change according to the matric suction. The elastic modulus, the shear modulus, and the Poisson's ratio are estimated based on the measured elastic wave velocities. In addition, the void ratio of the unsaturated soils estimated using elastic wave velocities matches well with the volume based void ratio. This study demonstrates that the elastic waves can be effectively used for the characterization of unsaturated soils.

• Journal of the Korean Geotechnical Society
• /
• v.15 no.3
• /
• pp.177-197
• /
• 1999

The measurement of sonic velocities is commonly used as an index of engineering properties of rock, but it is not widely appreciated that this velocity can change markedly with the degree of saturation of the sample. This paper records the nature of this variation as seen in samples of Korean granite. The ISRM method of testing suggested for this index can also create difficulties, especially if vaseline is used as a coupling agent, and invades the samples, and if the sample volume changes with degree of saturation. Careful measurements of the natural variation in sonic velocity that occur in a sample whose saturation is gradually increased may be a means of assessing the relic stresses within it.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.10 no.4 s.50
• /
• pp.1-13
• /
• 2006

Soil and rock dynamic properties such as shear wave velocity $(V_s)$, compressional wave velocity $(V_p)$ and corresponding Poisson's ratio (v) are very important geotechnical parameters in predicting deformational behavior of structures as well as practicing seismic design and performance evaluation. In an effort to measure the parameter efficiently and accurately, various bore-hole seismic testing techniques have been, thus, developed and used during past several decades. In this study, cross-hole seismic testing technique which is known as the most reliable seismic method was adopted for obtaining geotechnical dynamic properties. To perform successfully the cross-hole test for rock as well as soil layers regardless of the ground water level, spring-loaded source which impact laterally a subsurface ground in vertical bore-hole was developed and applied at three study areas, which contain four sites composed of two existing port sites and two new LNG storage facility sites. The geotechnical dynamic properties such as $V_s,\;V_p$ and v with depth from the soil surface to the engineering and seismic bedrock were efficiently determined from the laterally impacted cross-hole seismic tests at study sites, and were provided as the fundamental parameters for the seismic performance evaluation of the existing ports and the seismic design of the LNG storage facilities.

• 한국지구물리탐사학회:학술대회논문집
• /
• 2005.09a
• /
• pp.155-175
• /
• 2005

Soil and rock dynamic properties such as shear wave velocity (VS), compressional wave velocity (VP) and corresponding Poisson's ratio ( v ) are very important geotechnical parameters in predicting deformational behavior of structures as well as practicing seismic design and performance evaluation. In an effort to measure the parameter efficiently and accurately, various bore-hole seismic testing techniques have been, thus, developed and used during past several decades. In this study, cross-hole seismic testing technique which is known as the most reliable seismic method was adopted for obtaining geotechnical dynamic properties. To perform successfully the cross-hole test for rock as well as soil layers regardless of the ground water level, spring-loaded source which impact laterally a subsurface ground in vertical bore-hole was developed and applied at three study areas, which contain four sites composed of two existing port sites and two new LNG storage facility sites. The geotechnical dynamic properties such as VS, VP and v with depth were efficiently determined from the laterally impacted cross-hole seismic tests at study sites, and were provided as the fundamental parameters for the seismic performance evaluation of the existing ports and the seismic design of the LNG storage facilities.

• Earthquakes and Structures
• /
• v.9 no.4
• /
• pp.753-766
• /
• 2015

An investigation has been carried out for the propagation of torsional surface waves in an inhomogeneous prestressed layer over an inhomogeneous half space when the upper boundary plane is assumed to be rigid. The inhomogeneity in density, initial stress (tensile and compressional) and rigidity are taken as an arbitrary function of depth, where as for the elastic half space, the inhomogeneity in density and rigidity is hyperbolic function of depth. In the absence of heterogeneities of medium, the results obtained are in agreement with the same results obtained by other relevant researchers. Numerically, it is observed that the velocity of torsional wave changes remarkably with the presence of inhomogeneity parameter of the layer. Curves are compared with the corresponding curve of standard classical elastic case. The results may be useful to understand the nature of seismic wave propagation in geophysical applications.

• The Journal of the Acoustical Society of Korea
• /
• v.13 no.2E
• /
• pp.76-82
• /
• 1994

The characteristics of bottom sediment may be able to vary within a few meters of depth in shallow water. Since bottom attenuation coefficient as well as sound velocity in the bottom layer is determined by the composition and characteristics of sediment itself, it is reasonable to assume that the bottom attenuation coefficient is accordingly variable with depth. In this study, we use a parabolic equation scheme to examine the effects of depth-varying compressional wave attenuation on acoustic wave propagation in the low frequency ranging from 100 to 805 Hz. The sea floor under consideration is sandy bottom where the water and the sediment depths are 40 meters and 10 meters, respectively. Depending on the assumption that attenuation coefficient is constant or depth-varying, the propagation loss difference is as large as 10dB within 15 km. The predicted propagation loss is very much comparable to the measured one when we employ a depth-varying attenuation coefficient.

• Tunnel and Underground Space
• /
• v.6 no.3
• /
• pp.239-244
• /
• 1996

Cracks have influence on the physical and mechanical and, more importantly, on the engineering properties of the rock. Physical properties including the volumetric deformation coefficient, electrical resistivity, seismic wave velocity, and the mechanical properties such as the elastic constants and strength of rock are affected significantly by the presence of cracks of various sizes. An experimental program was undertaken to investigate the effect of a finite line crack on the diffraction of the plane compressional wave. Horizontal and vertical components of displacement and acceleration curve were obtained using a single-source and multi-receivers system. A theoretical model from numerical analysis implementing the finite element method was compared with the measured data.

• The Journal of Engineering Geology
• /
• v.13 no.2
• /
• pp.257-266
• /
• 2003

Jurassic granites of three sites, Pocheon, Geochang and Habcheon, were tested to investigate the effect of microcracks on Physical and mechanical properties of the granites. Fifteen oriented core specimens were used for the physical property test. The test result shows that porosity is almost proportioned to water content. P-wave velocity is the highest in the direction of axis ‘H’, intersection of two major microcrack sets and the lowest in the axis ‘R’, normal to the rift plane. Compressional strength tests were carried out for each core specimen taken parallel with axes ‘R’, ‘G’ and ‘H’, measuring strains. The results revealed a strong correlation between microcrack orientation and other mechanical properties such as rock strength.

• Geomechanics and Engineering
• /
• v.30 no.3
• /
• pp.247-258
• /
• 2022

A field velocity resistivity probe (FVRP) can measure compressional waves, shear waves and electrical resistivity in boreholes. The objective of this study is to perform the soil classification through a machine learning technique through elastic wave velocity and electrical resistivity measured by FVRP. Field and laboratory tests are performed, and the measured values are used as input variables to classify silt sand, sand, silty clay, and clay-sand mixture layers. The accuracy of k-nearest neighbors (KNN), naive Bayes (NB), random forest (RF), and support vector machine (SVM), selected to perform classification and optimize the hyperparameters, is evaluated. The accuracies are calculated as 0.76, 0.91, 0.94, and 0.88 for KNN, NB, RF, and SVM algorithms, respectively. To increase the amount of data at each soil layer, the synthetic minority oversampling technique (SMOTE) and conditional tabular generative adversarial network (CTGAN) are applied to overcome imbalance in the dataset. The CTGAN provides improved accuracy in the KNN, NB, RF and SVM algorithms. The results demonstrate that the measured values by FVRP can classify soil layers through three kinds of data with machine learning algorithms.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.30 no.2C
• /
• pp.85-93
• /
• 2010

The shear stiffness has become an important design parameter to understand the soil behavior. In particular, the elastic moduli and void ratio has been considered as important parameters for the design of the geotechnical structures. The objective of this paper is the development of the penetration type Field Velocity and Resistivity Probe (FVRP) which is able to assess the elastic moduli and void ratio based on the elastic wave velocities and electrical resistivity. The elastic waves including the compressional and shear wave are measured by piezo disk elements and bender elements. And the electrical resistivity is measured by the resistivity probe, which is manufactured and installed at the tip of the FVRP. The penetration tests are carried out in calibration chamber and field. In the laboratory calibration chamber test, after the sand-clay slurry mixtures are prepared and consolidated. The FVRP is progressively penetrated and the data are measured at each 1 cm. The field experiment is also carried out in the southern part of Korea Peninsular. Data gathering is performed in the depth of 6~20 m at each 10 cm. The elastic moduli and void ratio are estimated based on the analytical and empirical solutions by using the elastic wave velocities and electrical resistivity measured in the chamber and field. The void ratios based on the elastic wave velocities and the electrical resistivity are similar to the volume based void ratio. This study suggests that the FVRP, which evaluates the elastic wave velocities and the electrical resistivity, may be a useful instrument for assessing the elastic moduli and void ratio in soft soils.