• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.1431-1437
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• 2008

The small-strain shear modulus ($G_{max}$) of uncemented sand is affected by the the mean principal stress and void ratio, and it has been known that the cementation and aging also affect to $G_{max}$ of sand. For extensive understanding about the effect of cementation on the $G_{max}$ of sand, a series of bender element tests was conducted on the cemented specimens prepared in a large calibration chamber by pluviation of the sand-gypsum mixture. It was observed from the experimental results that the $G_{max}$ of cemented sand is higher above 10 times than value of uncemented one, and it increases exponentially with the gypsum content increases. Whereas, the increase of the vertical stress from 50kPa to 200kPa and the relative density from 40% to 80% result in 20~30% and 2 times increase of $G_{max}$, respectively. It means that the gypsum content, that is cementation level, is the most influential factor on the $G_{max}$ of cemented sand. In addition, the effect of relative density on $G_{max}$ was more apparent on cemented sand than uncemented one.

• Journal of the Korean Geotechnical Society
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• v.24 no.2
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• pp.87-97
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• 2008

Behaviors of cemented engineered soils, composed of rigid sand particle and soft rubber particle, are investigated under $K_o$ condition. The uncemented and cemented specimens are prepared with various sand volume fractions to estimate the effect of the cementation in mixtures. The vertical deformation and elastic wave velocities with vertical stress are measured. The bender elements and PZT sensors are used to measure elastic wave velocities. After cementation, the slope of vertical strain shows bilinear and is similar to that of uncemented specimen after decementation. Normalized vertical strains can be divided into capillary force, cementation, and decementation region. The first deflection of the shear wave in near field matches the first arrival of the primary wave. The elastic wave velocities dramatically increase due to cementation hardening under the fixed vertical stress, and are almost identical with additional stress. After decementation, the elastic wave velocities increase with increase in the vertical stress. The effect of cementation hinders the typical rubber-like, sand-like, and transition behaviors observed in uncemented specimens. Different mechanism can be expected in decementation of the rigid-soft particle mixtures due to the sand fraction. a shape change of individual particles in low sand fraction specimens; a fabric change between particles in high sand fraction specimens. This study suggests that behaviors of cemented engineered soils, composed of rigid-soft particles, are distinguished due to the cementation and decementation from those of uncemented specimens.

• Journal of the Korean Geotechnical Society
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• v.24 no.11
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• pp.91-100
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• 2008

This study proposes the equations evaluating the shear strength of cemented sand by analytical interpretation based on Mohr-Coulomb failure criteria, and verifies them using the results of triaxial and unconfined compression tests. The internal friction angle of cemented sand is identical to that of uncemented one regardless of the stress level, while the cohesion intercept of cemented sand is constant before the breakage of cementation bonds. Therefore, the shear strength of cemented sand can be represented as a summation of the shear strength of uncemented sand and the unconfined compressive strength of cemented sand. In addition, the cohesion intercept of cemented specimen can be expressed as a function of unconfined compressive strength and friction angle. In the transition zone, assuming a constant shear strength, the equations to evaluate shear strength and cohesion intercept of cemented sand are also represented. It is observed that the predicted values using these solutions agree well with the experimental results. The experimental results also show a linear relationship between the unconfined compressive strength and the breaking point of cementation bonds.

• Journal of the Korean Geotechnical Society
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• v.22 no.4
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• pp.85-94
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• 2006

Triaxial tests at isotropic confining pressure of 200 kPa were carried out to show the undrained shear behavior of artificially cemented sands, which were cemented by gypsum, and the influences of relative density and DOC (degree of cementation) were investigated from the results. The yield strength, the elastic secant modulus at yield point and the peak frictional angle of cemented sands increased abruptly compared to uncemented sands, and it was checked that cementation exerts more influence on the behavior of sand than the relative density. But after breakage of the cementation bonds, the relative density was more important factor on the behavior of sand than the cementation. Because the compressibility md the excess pore pressure of cemented sands were reduced due to the cementation bonds, the effective stress path of cemented sands was going toward to the total stress path of uncemented sands. The cementation of sand restricted the dialtion of sand at the pre-yield condition, but induced more dilation in the post-yield condition.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.2C
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• pp.51-58
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• 2009

In this study, the small strain shear moduli ($G_{max}$) of uncemented and gypsum-cemented sands are evaluated by performing a series of bender element tests on the specimens reconstituted in the calibration chamber. It is observed from the experimental results that $G_{max}$ of crushed-sands is about 35~50% smaller than that of natural sands. The increase in gypsum content is observed to result in an exponential increase of $G_{max}$ value. It is also shown that the relative density has more significant effect on $G_{max}$ of cemented sand, whereas the vertical effective stress has more significant influence on $G_{max}$ of uncemented one. A prediction equation for cemented sand is expressed as a function of gypsum content as well as void ratio and vertical effective stress.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.331-340
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• 2009

This study evaluates the relationship between cone tip resistance ($q_c$) and small-strain shear modulus ($G_{max}$) of cemented sand. For this purpose, a series of miniature cone penetration and bender element tests are performed in calibration chamber specimens with various gypsum contents. Experimental results show that both $q_c$ and $G_{max}$ of sand increase with increasing cementation level as well as relative density and vertical confining stress. However, the relative density and vertical confining stress has more significant influence on $G_{max}$ and $q_c$ of uncemented sand than those of cemented sand. It is observed that the $G_{max}/q_c$ ratio of cemented sand decreases with increasing relative density. This result means that state variables have more affect on $q_c$ than $G_{max}$ of cemented sand. Test results also show that the effect of vertical stress on $G_{max}-q_c$ relation is reduced by cementation effect.

• Journal of the Korean Geotechnical Society
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• v.34 no.2
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• pp.33-42
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• 2018

In this study, the EMI (electro-mechanical impedance) of a small piezoelectric sensor was applied for measuring a unit weight and cementation (strength) of sand. Three different sizes of uncemented Nakdong River sand were filled loosely or densely into a compaction mold. A piezoelectric sensor with 20 mm in diameter was installed within sand for impedance measurement. A small Nakdong River sand was mixed with cement ratios of 4, 8 12, 16% and then compacted into a specimen with 50 mm in diameter and 100 mm in height. The specimen consisted of 6 layers with a sensor at the third layer. The impedance signals for 3 days and unconfined compressive strength at the 3rd day were measured. As the unit weight of uncemented sand increased, the resonant frequency increased slightly from 102 to 105 kHz but a conductance at resonant frequency decreased. For cemented sands, as the curing time and cement ratio increased, the resonant frequency increased significantly from 129 to 266 kHz but the conductance at resonant frequency decreased. The unconfined compressive strength (UCS) of cemented sands was between 289 and 1,390 kPa for different cement ratios. The relationship of UCS and resonant frequency linearly increased but one with a conductance at resonant frequency was in inverse proportion.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.628-635
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• 2008

A series of cone penetration tests in large calibration chamber were performed to investigate the effect of cementation level, relative density and vertical confining stress on cone resistance. From the experimental results, it was observed that the cone resistance is increased with increasing gypsum content, relative density, and confining stress. The increasing ratio on cone resistance of cemented sand compared with that of uncemented sand, that is IR($q_c$), was increased with increasing gypsum content and relative density, whereas it was decreased as the vertical confining stress increases. It was also observed that the cementation of granular soil influences the behavior of ground at low level of confining stress and its effect is diminished with depth.

• Journal of the Korean Geotechnical Society
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• v.25 no.2
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• pp.67-77
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• 2009

In this study, the relations of cone tip resistances (qc) and DMT indices of cemented sand are analyzed from a series of calibration chamber tests. The experimental results show that, with increasing the cementation level, three DMT indices also increase. The CPT and DMT do not appear to properly reflect the cementation effect of sand, since the penetration induces the damage of cementation. Nevertheless, the DMT is more sensitive to deformation characteristics of cemented sand than CPT. It is also observed that the $E_D/q_c$ ratio of cemented sand is larger than that of uncemented sand. However, the $K_D-q_c/{\sigma}_v'$ relation is independant of cementation, unlike the result of previous study. In addition, this study evaluates the constrained modulus and cohesion intercept of cemented sand using the relation between cone resistance and dilatometer constrained modulus ($M_D$).

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3C
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• pp.181-190
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• 2006

The behavior of artificially cemented sands were investigated by undrained triaxial test of isotropically consolidated sample. The cementation were induced by gypsum that is generally used for the aitificial cementation of sands. The gypsum of 5~20%(sand weight) were included in the sand and cured in the mold under the overburden pressure 55kPa. The yielding strength and stiffness of cemented sand were increased as the degree of cementation. And the dilation of sand was restricted by the cementation bonds, but after breakage of the bonds, it was increased more abrupt than the uncemented sands. The effective stress path showed that the aspects of effective pore water pressure were changed as the degree of cementation and the relative density. The effective stress ratio of cemented sand in the phase transformation line and the failure line were changed by the cementation. Generally the behavior of cemented sand more influenced by the degree of cementation than the relative density.