• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.1110-1116
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• 2010

Void ratios are one of the key parameters for exact calculation of settlement of soft groundse. In the study, shear wave velocities of a soft ground were used to measure the field void ratio using bender elements sensors. The bender-element probes were installed in situ at the depths of 3, 5 and 8m on a pre-loading site near Incheon, Korea. During 90 days after installation, the changes of shear wave velocity and ground surface settlement were measured. The field void ratio was estimated from measured shear wave velocities. The void ratio estimated by the shear wave velocity measured by bender elements agrees well with the measured values in the field.

• Journal of the Korean Geotechnical Society
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• v.18 no.6
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• pp.17-24
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• 2002

The objective of the present research is to evaluate the wave propagation velocity and attenuation characteristics of kaolin clay specimens using ultrasonic testing. Test specimens with known initial micro-fabric were prepared using a two-stage slurry consolidation technique. For a known state of stress conditions, initial void ratio, and micro-fabric, a series of experiments were conducted to evaluate the longitudinal wave propagation velocity and associated damping behavior. The effects of major variables involved in ultrasonic testing of cohesive soil were considered in this study. Ultrasonic velocity was not correlated to the microfabric structure under the given consolidated pressure whereas ultrasonic attenuation was affected by the microstructural properties of the specimen.

• Fisheries and Aquatic Sciences
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• v.11 no.2
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• pp.103-112
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• 2008

Compressional sound velocities of shelf sediments in the South Sea of Korea, were measured in situ and in the laboratory for six cores. In situ sound velocity was measured using the Acoustic Lance (frequency of 7.5-15 kHz), while laboratory velocity was measured by the pulse transmission technique (frequency of 1MHz). Physical properties were relatively uniform with sediment depth, suggesting little effect of sediment compaction and/or consolidation. Average in situ velocity at each core site ranged from 1,457 to 1,488 m/s, which was less than the laboratory velocity of 1,503 and 1,604m/s. In muddy sediments the laboratory velocity was 39-47 m/s higher than in situ velocity. In sandy sediments, the difference was greater by an average of 116 m/s. Although the velocity data were corrected by the velocity ratio method based on bottom water temperature, the laboratory velocity was still higher than the in situ velocity (11-21 m/s in muddy sediments and 91 m/s in sandy sediments). This discrepancy may be caused by sediment disturbance during core collection and/or by the pressure of Acoustic Lance insertion, but it was most likely due to the frequency difference between in situ and laboratory measurement systems. Thus, when correcting laboratory velocity to in situ velocity, it is important to consider both temperature and frequency.

• The Journal of Engineering Geology
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• v.26 no.3
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• pp.307-314
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• 2016

Shear characteristics of soils can be investigated using various types of shear stress measuring apparatus. Ring shear tests are often applied for examining the residual shear strength under the unlimited deformation. This paper presents drainage-consolidation-shear velocity dependent undrained shear strengths measured in terms of water leakage. A series of ring shear tests were performed under the constant normal stress (50 kPa) and controled shear velocity ranging from 0.01~1 mm/sec under the undrained condition. As a result, undrained shear strengths are dependent on shear velocity. It exhibits that straining hardening behavior is observed for the shear velocity lower than 0.1 mm/sec; however, the strain softening behavior is observed for the shear velocity higher than 0.1 mm/sec. Water leakage can cause the increase in shear stress irrespective of shear velocity. Shear stress increases with increasing amount of water leakage. It is due to the fact that the small grains and water flow out through the rubble edge in the ring shear box. Repetitive saturation and consolidation processes may minimize the error.

• Journal of the Korean Geotechnical Society
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• v.22 no.11
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• pp.47-54
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• 2006

Shear wave velocity of uncemented soil can be expressed as the function of effective stresses when capillary phenomena are negligible. However, the terms of effective stresses are divided into the direction of wave propagation and polarization because stress states are generally anisotropy. The shear wave velocities are affected by ${\alpha}$ parameters and ${\beta}$ exponents that are experimentally determined. The ${\beta}$ exponents are controlled by contact effects of particulate materials (sizes, shapes, and structures of particles) and the ${\alpha}$ parameters are changed by contact behaviors among particles, material properties of particles, and type of packing (i.e., void ratio and coordination number). In this study, consolidation tests are performed by using clay, mica and sand specimens. Shear wave velocities are measured during consolidation tests to investigate the stress-induced and inherent anisotropies by using bender elements. Results show the shear wave velocity depends on the stress-induced anisotropy for round particles. Furthermore, the shear wave velocity is dependent on particle alignment under the constant evvective stress. This study suggests that the shear wave velocity and the shear modulus should be carefully estimated and used for the design and construction of geotechnical structures.

• The Journal of Engineering Geology
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• v.24 no.1
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• pp.111-122
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• 2014

For accurate laboratory evaluations of soil deposits, it is essential that the samples are undisturbed. An artificial ground-freezing system is the one of the most effective methods for obtaining undisturbed samples from sand deposits. The objective of this study is to estimate the shear strengths and the characteristics of elastic waves of frozen-thawed and unfrozen specimens through the undrained triaxial compression test. For the experiments, Jumunjin standard sands are used to prepare frozen and unfrozen specimens with similar relative densities (60% and 80%). The water pluviation method is used to simulate the fully saturated condition under the groundwater table. When thawing the frozen specimens, the temperature is measured every minute. After the specimens are completely thawed, undrained triaxial compression tests are conducted using the same procedures as for the unfrozen specimens. During the triaxial tests (saturation, consolidation, and shear phase), compressional and shear waves are measured. The results show that the freeze-thaw process has minor effects on the peak deviatoric stress and shear strength values, and that the process does not affect the internal friction angle. The compressional wave velocity increases with increasing B-value to 1800 m/s in the saturation phase, but tends to remain constant in the process of consolidation and shearing. The shear wave velocity decreases with increasing B-value in the process of saturation, but changes velocity in accordance with the change in effective stress in the processes of consolidation and shearing. The compressional wave velocity has similar values regardless of the freeze-thaw process, but values of shear wave velocity are slighly lower in frozen-thawed specimens than in unfrozen specimens. This study is a preliminary experiment for estimating the shear strength and characteristics of elastic wave velocity in undisturbed frozen specimens that have been obtained using the artificial ground-freezing method.

• Economic and Environmental Geology
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• v.29 no.6
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• pp.739-744
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• 1996

'Kite' is a newly developed single-channel seismic imaging system capable of producing high resolution three dimensional images of subbottom geology in one traverse of a survey region. The system consists of a horizontally towed hydrophone array and active source. The hydrophone array is towed axis perpendicular to ship direction and the airgun source at the end of the hydrophone array is excited at timed intervals during the progression. The construction of the three dimensional subbottom image was made simply by using conventional multichannel seismic reflection data processing techniques. Common source shot (CSS) gathers of the hydrophone traces are evaluated using Dix's equation for average interval velocity of each subbottom layer. From the interval velocity profile and the normal consolidation stress condition, values of shear modulus, porosity, and shear velocity are deduced from the chosen values of physical constants. The system has been successfully tested at several locations on the North Atlantic continental shelf.

• Tunnel and Underground Space
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• v.22 no.1
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• pp.69-76
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• 2012

Theoretical backgrounds on the experimental methods of explosive welding, explosive forming and shock consolidation of powders are introduced. Explosive welding experiments of titanium (Ti) and stainless steel (SUS 304) plate were carried out. It was revealed that a series of waves of metal jet are generated in the contact surface between both materials; and that the optimal collision velocity and collision angle is about 2,100~2,800 m/s and $15{\sim}20^{\circ}$, respectively. Also, explosive forming experiments of Al plate were performed and compared to a conventional press forming method. The results confirmed that the shock-loaded Al plate has a larger curvature deformation than those made using conventional press forming. For shock consolidation of powders, the propagation behaviors of a detonation wave and underwater shock wave generated by explosion of an explosive are investigated by means of numerical calculation. The results revealed that the generation and convergence of reflected waves occur at the wall and center position of water column, and also the peak pressure of the converged reflected waves was 20 GPa which exceeds the detonation pressure. As results from the consolidation experiments of metal/ceramic powders ($Fe_{11.2}La_2O_3Co_{0.7}Si_{1.1}$), shock-consolidated $Fe_{11.2}La_2O_3Co_{0.7}Si_{1.1}$ bulk without cracks was successfully obtained by adapting the suggested water container and strong bonding between powder particles was confirmed through microscopic observations.

• Journal of the Korean Geotechnical Society
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• v.25 no.5
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• pp.5-16
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• 2009

Preconsolidation stress is one of the important design parameters in soft soils because the behavior of saturated soft soils changes dramatically at the preconsolidation stress. For the estimation of preconsolidation stress, the global vertical settlement without considering micro strain behavior has been considered. The purpose of this study is to propose and verify a new method called the "shear wave velocity method" for determination of the preconsolidation stress reflecting on particle behavior at the small-strain. In this study, the undisturbed soft soils obtained at Busan, Incheon and Gwangyang in Korea were used. The oedometer cell incoporated with the bender elements is used for the consolidation tests under the $K_0$ condition. The preconsolidation stress determined by the proposed method is compared with that estimated by Casagrande (e-log p'), Sridharan (log (1+e)-log p'), and Onitsuka (In(1+e)-log p') methods. This study suggests that the shear wave velocity method may determine simply the preconsolidation stress with considering the small-strain behavior.

• Journal of the Korean GEO-environmental Society
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• v.16 no.5
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• pp.55-66
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• 2015

Big tidal differences, which range from 3.0 m to 8.0 m, exist with regional locations at south and west shores of Korea. Under this ocean circumstance, since a large scour may occur due to multi-directional tidal current and transverse stress of the wind, the scour surrounding the wind turbine structure can make instability of the system due to unexpected system vibration. The hydraulic resistance capacity of soils consolidated under different pressures are evaluated by Erosion Function Apparatus (EFA) under unidirectional and bi-directional flows in this study. It was found that the flow direction change affects significantly on the sour rate and critical shear stress, regardless of soil types while the consolidation pressure affects mainly cohesive soil. Among geotechnical parameters, the undrained shear strength can be well-correlated with the hydraulic resistance capacity, regardless soil type while the shear wave velocity shows the proportional relationships with the hydraulic resistance capacities of fine grained soil and coarse grained soil, respectively.