• The Journal of Engineering Geology
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• v.24 no.3
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• pp.397-409
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• 2014

The appearance of faults during tunnel construction is often difficult to predict in terms of strike, dip, scale, and strength, even though this information is essential in determining the strength of the surrounding rock mass. However, the strength and rock mass classification of fault zones are generally determined empirically on the construction site. In this study, 109 specimens were collected from fault of nine area throughout Korea, and direct shear tests were conducted and the particle distribution was analyzed to better characterize the fault zones. Six multiple regression models were established, using 97 of the specimens, to analyze the correlation between the shear strengths and weight rations of these fault materials. A verification of the six models, using the remaining 12 specimens, shows that in all of the models the coefficient of determination yielded $R^2{\geq}0.60$, with two models yielding $R^2{\geq}0.69$. These results provide useful information for determining the shear strength of fault materials in future studies.

• Tunnel and Underground Space
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• v.10 no.2
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• pp.196-210
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• 2000

This study was aimed to verify the validity of the flexural toughness evaluation method of steel fiber reinforced shotcrete(SFRS) currently being adopted by Korea Highway Corporation(KHC). Total 33 beam specimens using six different kinds of steel fiber products were prepared at tunnel construction sites and flexural toughness tests were executed at laboratory. Equivalent flexural strengths and toughness quotients were evaluated from the tests following the KHC guide iud these were compared with the quality grades determined under the guides proposed by ASTM, ITA and EFNARC. To discard the disadvantage that the toughness quotient could be influenced by flexural strength when following the KHC guide, a modification substituting the designed flexural strength for the flexural strength in the toughness quotient calculation formula was proposed to rate the quality of SFRS more adequately.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.6C
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• pp.287-294
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• 2009

Suction Drain Method is a relatively new technique to improve soft ground using vacuum pressure which can be directly applied to the soft ground through drains that the pore water pressure around them are decreased without changing total stress. This can accelerate volume changes and increase strength of the ground. This paper shows the results of field test of the suction drain method applied at dredged and reclaimed clay. To evaluate the improvement effects of soft ground by the suction drain method, this paper analyzed real-time field measurements to the results of the laboratory tests and numerical analysis. The comparisons of the settlement and shear strength between suction drain method and surcharge preloading method show possibilities for replacement of the preloading methods. The settlements by suction drain method were 2.3 times larger and undrained shear strength were 300%~400% higher than surcharge method. Moreover, the water content is decreased about 30% and the preconsolidation pressure is increased about $0.52kgf/cm^2$.

• Journal of the Korean Geotechnical Society
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• v.33 no.12
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• pp.35-44
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• 2017

A large amount of recycled aggregates was produced and crushed from old buildings and pavements. In this study, when these aggregates are re-used in subbase or subgrade materials in near construction sites, their engineering characteristics caused by crushing are investigated in terms of permeability and shear strength. Three different sizes of aggregates (31.5-45.0 mm, 19.0-31.5 mm, 9.5-19.0 mm) and their mixtures, a total of 7 types of aggregates were used in compaction tests (modified D and B methods). After compaction tests, aggregates were sieved and analyzed with four different breakage factors ($B_{15}$, $C_c$, $B_{10}$, $B_r$). The D compaction method gave 2.0-8.0 times more crushable than B compaction method. The breakage factors for the largest size aggregate was 1.4-3.0 times higher than those of the smallest size aggregate. For aggregates with 5.6-9.5 mm sizes, the samples were prepared with $B_{15}$ of 1, 3, 10, 20, 30, 50, 60, and 70 for permeability and direct shear tests. As $B_{15}$ increased, the hydraulic conductivity decreased up to 1/22 for $B_{15}=50$. As $B_{15}$ increased from 1 to 50, the peak friction angle increased from $46.1^{\circ}$ to $54.5^{\circ}$. On the other hand, the friction angle decreased after $B_{15}=60$.

• Tunnel and Underground Space
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• v.21 no.4
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• pp.320-327
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• 2011

In this study, for stemming effect in blast of the mortar block body, the crushed granite sand as fine aggregate, which is waste rock obtained at the ○○ limestone mine, was investigated to compare with stemming materials such as sea sand, river sand, clayed soil and water can be acquired easily at the field. The mortar block body was manufactured with the dimensions of 50 cm width, 50 cm length and 70 cm height. The direct shear and sieve separator test were performed, and the properties of friction resistance were analyzed by the extrusion test for five stemming materials. Axial strain of steel bar and ejection velocity of stemming materials due to the explosive shock pressure in blasthole with the stemming length of 10 cm and 20 cm in the mortar blast test were measured by the dynamic data acquisition system. Among stemming materials, axial strain showed the largest value at the crushed granite sand as fine aggregate, and the ejection velocity was the smallest value at the stemming of water. The results has shown correlate with harden unit weight in blasthole, particle size distribution, shear resistance, and extrusion strength of stemming materials. The ejection velocity of stemming material at the mouth of blasthole and the axial strain of steel bar in the inside of blasthole tend to be inversely proportional to each other, represent exponentially.

• Journal of the Korean GEO-environmental Society
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• v.16 no.12
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• pp.53-58
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• 2015

Engineers should take great care of characterizing the engineering properties of mudrock, because the uncemented mudrock can be considered as a hard rock in appearance. Therefore, the mudrock samples obtained from the cut slope in Gyeongki-do were tested to evaluate the strength characteristics of uncemented mudrock in this study. The performed tests are index properties, slake durability, and swelling tests for the classification of the mudrock for engineering practice. To evaluate the effect of water on the engineering properties of the uncemented mudrock, resonant column, triaxial compression and direct shear tests with various water contents were performed. With the increasing water contents, stiffness at very small to small strain region and the cohesion value of the strength parameters decrease. Based on the test results, engineers should take great care of evaluating the engineering properties of uncemented mudrock.

• Journal of Korean Tunnelling and Underground Space Association
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• v.14 no.1
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• pp.79-91
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• 2012

A curved fiber reinforced polymer (FRP) panel is produced with a certain width depending on allowances of manufacturing processes and facilities. An targeted arch-shaped structure could be built by sequential connection of series of the FRP panels. The connection manner between the FRP panels could be given by chemical treatment, mechanical treatment and hybrid method. Among those, the connection between the panels by chemical treatment is commonly adopted. Therefore, For an optimized design of the connected part between FRP pannels, a number of direct shear tests have been undertaken in terms of a number of parameters: surface treatment conditions, bonding materials, etc.. As results, surface grinding condition by sand paper or surface treatment by sand blasting appear properly acceptable methods, and epoxy and acryl resins are shown to be effective bonding materials for the purpose in this study.

• Journal of the Korean GEO-environmental Society
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• v.7 no.6
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• pp.67-73
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• 2006

In this study, basic physical tests and mechanical tests of crushed rock were performed in order to investigate the field application of crushed rock as substitute materials of sand that is commonly being used as foundation and backfill materials of sewer conduit. Particle-size distribution curve of crushed rock is similar to sand and also it is well-graded soil than common sand. Maximum dry unit weight in proctor compaction test for crushed rock is higher than the values of common sand. So we can estimate that the crushed rock has advantages in workability than sand for the backfill compaction after construction of sewer conduit. When we investigate the results of direct shear test and triaxial compression test on the crushed rock, it has a similar value of shear strength parameters to sand at the same stress state and as time goes by, it tends to increase the unconfined compression strength. But, because the strength reaches at the constant value after 6~7 days, we expect that it can absorb the lateral strain of flexible conduit well. All the above experimental results just proves that crushed rock can substitute for sand as backfill materials and foundation of sewer conduit.

• Journal of the Korean Geotechnical Society
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• v.15 no.2
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• pp.43-71
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• 1999

This research is an experimental work of developing a construction material using municipal wastewater sludge as liner and cover materials for waste disposal landfill. Weathered granite soil and flyash, produced as a by-product in the power plant, were used as the primary additives to improve geotechnical engineering properties of sludge. For secondary additives, bentonite and cement were mixed with sludge to decrease the permeability and to increase the shear strength, respectively. Various laboratory test required to evaluate the design criteria for liner and cover materials, were carried out by changing the mixing ratio of sludge with the additives. Basic soil properties such as specific gravity, grain size distribution, liquid and plastic limits were measured to analyze their effects on permeability, compaction, compressibility and shear strength properties of mixtures. Laboratory compaction tests were conducted to find the maximum dry densities and the optimum moisture contents of mixtures, and their effectiveness of compaction in field was consequently evaluated. Permeability tests of variable heads with compacted samples, and the stress-controlled consolidation tests with measuring permeabilities of samples during consolidation process were performed to obtain permeability, and to find the compressibility as well as consolidational coefficients of mixtures, respectively. To evaluate the long term stability of sludges, creep tests were also conducted in parallel with permeability tests of variable heads. On the other hand, for the compacted sludge decomposed for a month, permeability tests were carried out to investigate the effect of decomposition of organic matters in sludges on its permeability. Direct shear tests were performed to evaluate the shear strength parameters of mixed sludge with weathered granite, flyash and bentonite. For the mixture of sludge with cement, unconfined compression tests were carried out to find their strength with varying mixing ratio and curing time. On the other hand, CBR tests for compacted specimen were also conducted to evaluate the trafficability of mixtures. Various test results with mixtures were assessed to evaluate whether their properties meet the requirements as liner and cover materials in waste disposal landfill.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.6C
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• pp.221-229
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• 2011

A core zone of a fill dam is an important part of a dam for cutoff of water. Therefore, the material properties and behavior characteristics of a core zone are very important factors in an analysis of dam stability. However, the investigation on material properties of actual dam core is extremely rare so far. The material properties have been acquired or estimated by indirect methods like a surface wave surveying or empirical equation. In this research, in-situ and laboratory tests were conducted during dismantling an existing dam directly to investigate characteristics of the core zone in terms of the depth and transient variation of properties after construction of the dam. Dynamic material properties like shear wave velocity and shear modulus were measured and compared to other existing empirical correlations. In addition, aging characteristics of dynamic material properties were investigated by a series of laboratory tests.