• The Journal of the Acoustical Society of Korea
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• v.26 no.1E
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• pp.33-38
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• 2007

Compressional wave velocity and shear wave velocity were measured for gassy sediments collected from Jinhae Bay, Korea. To distinguish inhomogeneities of gassy sediments, Computed Tomography (CT) was carried out for gassy sediment using CT Scanner. The cored sediments are composed of homogeneous and soft mud (greater than $8{\Phi}$ in mean grain size) containing clay content more than 50%. In depth interval of gassy sediments, compressional wave velocity is significantly decreased from 1480m/s to 1360m/s, indicating that the gas greatly affects compressional wave velocity due to a gas and/or degassing cracks. Shear wave velocity shows a slight increasing pattern from ${\sim}55\;m/s$ in the upper part of the core to ${\sim}58\;m/s$ at 320 cm depth, and then decreases to ${\sim}54\;m/s$ in the lower part of the core containing a small amount of gas. But shear wave velocity in the gassy sediments is slightly greater than that of non-gassy sediments in the upper part of the core. Thus, the Vp/Vs ratio is decreased (from 30 to 25) in gas charged zone. The Vp/Vs ratio is well correlated with shear wave velocity, but no correlation with compressional wave velocity. This suggests that low concentrations of gas have little affects on shear wave velocity. By CT images, the gas in the sediments is mostly concentrated around inner edge of core liner due to a long duration after sediment collection.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.472-481
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• 2009

Cementation phenomenon has a huge influence on geotechnical stiffness and strength under low confining pressure. The goal of this study is to evaluate the characteristics of stiffness according to the depth. The piezo disk elements are installed at each layer of the cell for the detection of the compressional waves. The change of compressional wave velocity is classified by three stages. The compressional wave velocities are shown different according to the depth. The compressional wave velocity is especially influenced by cementation, effective stress, and coordinate number. Furthermore, the electrical conductivity and cone tip resistance are measured according to the depth. The electrical conductivity and the cone tip resistance show the similar trend with the compressional wave velocity. This study shows that the cementation by salt is affected by the depth on the granular materials.

• Journal of the Korean Geotechnical Society
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• v.25 no.9
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• pp.57-66
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• 2009

In the preliminary investigation (Park et al., 2009), the use of compressional wave velocity and its measurement techniques were proposed as a new quality control measure for trackbed fills. The methodology follows exactly the same procedure as the density control, except the density being replaced by the compressional wave velocity involving consistently with resilient modulus of design stage. The specifications for the control also include field compaction water content of optimum moisture content ${\pm}2%$ as well as the compressional wave velocity. In this sequel paper, crosshole and resonant column tests were performed as well direct-arrival method and laboratory compressional wave measurements to verify the practical applicability of a methodology far the new quality control procedure based upon compressional wave velocity. The stress-modified crosshole results reasonably well agree with the direct-arrival values, and the resonant column test results also agree well with the field crosshole results. The compressional wave velocity turned out to be an excellent control measure for trackbed fills both in the theoretical and practical point of view.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.255-264
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• 2009

Soils containing vanishing materials lead changes in the microstructure of particulate media due to water inflow. Thus, dissolution renders some local unstability. As the moisture contents decease, the component of the vanished materials may affects on the cementation of paniculate materials. This cementation phenomenon has a huge influence on the stiffness, strength and stability under lower stress level. The goal of this study is to introduce the cementation effects on a compressional wave velocity, a shear wave velocity, and the resonant frequency of shear waves. The glass bead and salt water with different mole contents are used. Test results show that the changes of shear and compressional wave velocities consist of three stages. In the first region, compressional wave velocities increase and shear wave velocities decrease with a decreases in reducing water contents from 100% to 90~95%. In the second region, shear and compressional wave velocities become stable at 90~95% to 10% of the water contents. In the third region, shear and compressional wave velocities increases dramatically with a decrease in the water content due to the capillary force and cementation of salt. Furthermore, the resonant frequency of the shear waves shows similar phenomenon. Specimens prepared by glass beads and salt water are proved to be able to provide a meaningful insight in under structural behaviors of the cementation.

• Journal of the Korean Geotechnical Society
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• v.25 no.9
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• pp.45-55
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• 2009

The quality of railroad trackbed fills has been controlled by field measurements of density and bearing resistance of plate-load tests. The control measures are compatible with the design procedures whose design parameter is $k_{30}$ for both ordinary-speed railways and high-speed railways. However, one of fatal flaws of the design procedures is that there are no simple laboratory measurement procedures for the design parameters ($k_{30}$ or, $E_{v2}$ and $E_{v2}/E_{v1}$) in design stage. To overcome the defect, the compressional wave velocity was adopted as a control measure, in parallel with the advent of the new design procedure, and its measurement technique was proposed in the preliminary investigation. The key concept of the quality control procedure is that the target value for field compaction control is the compressional wave velocity determined at optimum moisture content using modified compaction test, and direct-arrival method is used for the field measurements during construction, which is simple and reliable enough for practice engineers to access. This direct-arrival method is well-suited for such a shallow and homogeneous fill lift in terms of applicability and cost effectiveness. The sensitivity of direct-arrival test results according to the compaction quality was demonstrated at a test site, and it was concluded that compressional wave velocity can be effectively used as quality control measure. The experimental background far the companion study (Park et al., 2009) was established through field and laboratory measurements of the compressional wave velocity.

• Proceedings of the Korean Geotechical Society Conference
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• 1997.10a
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• pp.261-266
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• 1997

• The Journal of the Acoustical Society of Korea
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• v.25 no.2E
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• pp.49-55
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• 2006

Compressional wave velocity (Vp), shear wave velocity (Vs), elastic and physical properties, and electrical resistivity for two core sediments obtained from Southeastern Yellow Sea Mud (SEYSM) were measured and computed. The sediments consist of homogeneous mud (mostly silt and clay) with shells and shell fragments. As a result, the mean grain size is uniform ($7.5-8.5{\Phi}$ throughout the core sediments. However, physical properties such as wet bulk density and porosity show slightly increasing and decreasing patterns with depth, compared to the mean grain size. The compressional (about 1475 m/s in average) and shear wave (about 60 m/s in average) velocities with depth accurately reflect the pattern of wet bulk density and porosity. Electrical resistivity is more closely correlated with compressional wave velocity than physical properties. The computed Vp/Vs and Poisson's ratios are relatively higher (more than 10) and lower (approximately 0.002) than Hamilton's (1979) data, respectively, suggesting the typical characteristics of soft and fully water-saturated marine sediments. Thus, the Vp/Vs ratio in soft and unconsolidated sediments is not likely sufficient to examine lithology and sediment properties. Relationships between the elastic constant and physical properties are correlated well. The elastic constants (Poisson's ratio, bulk modulus, shear modulus) given in this paper can be used to characterize soft marine sediments saturated with seawater.

• 한국해양학회지
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• v.23 no.3
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• pp.146-157
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• 1988

Properties of porosity, compressional wave velocity, velocity anisotropy, electrical resistivity, and resistivity anisotropy are measured and calculated for two DSDP clay-rich hemipelagic sequences in the northwestern Pacific. Velocity and resistivity increase with burial depth at the expense of decreasing porosity. Profiles of velocity anisotropy and resistivity anisotropy show almost the same trend. Horizontally developed low aspect ratio pores may generate velocity and resistivity anisotropy. The preferred orientation of clay minerals is also believed to be responsible for the observed anisotropy.

• Geophysics and Geophysical Exploration
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• v.9 no.3
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• pp.193-206
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• 2006

Among various borehole seismic testing techniques for determining body wave velocity, crosshole seismic method has been known as one of the most suitable technique for evaluating reliably geotechnical dynamic properties. In this study, to perform successfully the crosshole seismic test for rock as well as soil layers regardless of the groundwater level, multi-purposed spring-loaded source which impact horizontally a subsurface ground in vertical borehole was developed and applied at major facility sites in Korea. The geotechnical dynamic properties were evaluated by determining efficiently the body wave velocities such as shear wave velocity and compressional wave velocity from the horizontally impacted crosshole seismic tests at study sites, and were provided as the fundamental parameters for the seismic performance evaluation and seismic design of the target facilities.

• Journal of the korean society of oceanography
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• v.38 no.4
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• pp.166-172
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• 2003

Multi­Sensor Core Logger (MSCL) is a useful system for logging the physical properties (compressional wave velocity, wet bulk density, fractional porosity, magnetic susceptibility and/or natural gamma radiation) of marine sediments through scanning of whole cores in a nondestructive fashion. But MSCL has a number of problems that can lead to spurious results depending on the various factors such as core slumping, gas expansion, mechanical stretching, and the thickness variation of core liner and sediment. For the verification of MSCL data, compressional wave velocity, wet bulk density, and porosity were measured on discrete samples by Hamilton Frame and Gravimetric method, respectively. Acoustic impedance was also calculated. Physical property data (velocity, wet bulk density, and impedance) logged by MSCL were slightly larger than those of discrete sample, and porosity is reverse. Average difference between MSCL and discrete sample at both sites is relatively small such as 22­24 m/s in velocity, $0.02­-0.08\;g/\textrm{cm}^3$ in wet bulk density, and 2.5­2.7% in porosity. The values also show systematic variation with sediment depth. A variety of factors are probably responsible for the differences including instrument error, various measurement method, sediment disturbance, and accuracy of calibration. Therefore, MSCL can be effectively used to collect physical property data with high resolution and quality, if the calibration is accurately completed.