• Journal of the Korean GEO-environmental Society
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• v.25 no.8
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• pp.13-19
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• 2024

In this study, to reinforce the surface layer of weathered soil slopes where erosion and collapse of surface layer occur, compression strength tests were conducted by mixing carbon fiber and eco-friendly stabilizer (E.S.B.) To determine the optimal mixing ratio of E.S.B. and carbon fiber, E.S.B. was set at conditions of 10%, 20%, and 30%, and carbon fiber at 0.3%, 0.6%, 0.9%, and 1.2%. Additionally, to analyze the changes in compressive strength according to dry density and curing period, 85% and 95% of the maximum dry unit weight were applied, and curing periods were set to 3 days, 7 days, and 28 days. The standard strength for surface layer reinforcement of slopes is proposed as 4 MPa at 7 days and 6 MPa at 28 days according to ACI 230.1R-09 (2009). The compression test results showed that the unconfined compressive strength of E.S.B. reinforced soil met the standard strength at an E.S.B. mixing ratio of 10% or more for 95% compaction. Moreover, when carbon fiber was mixed with E.S.B. reinforced soil, a ductile fracture pattern was observed after the yield point due to compressive strength, indicating that the mixture could compensate for post-yield failure. It was analyzed that the maximum strength is exhibited at a carbon fiber mixing ratio of 0.6%. The unconfined compressive strength of carbon fiber reinforced soil increases by approximately 54-70% compared to the condition without carbon fiber.

• Journal of The Korean Society of Agricultural Engineers
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• v.55 no.3
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• pp.129-140
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• 2013

Bottom Ash is industrial by-product from a thermoelectric power plant. An immense quantities of bottom ash have increased each year, but most of them is reclaimed in ash landfill. In this study, in order to raise recycling rate of Bottom Ash, it is suggested to cure Bottom Ash (BA) mixtures mixed with cement, lime, Fly Ash (FA), and oyster shell (OS). Mixtures of 5~20 % mixing ratio had been cured for 1, 3, 7, 14, and 28 days using sealed curing and air-dry curing method. Unconfined compressive strength test was conducted to determine strength and deformation modulus ($E_{50}$) change for mixtures as mixing ratio and curing day, water contents of mixtures were measured after test. As a result, strength and $E_{50}$ were increased as mixing ratio and curing days, but values and tendencies of them appeared in different as kind of mixture, mixing ratio, curing method, and curing days. The results showed the addition of cement, lime, Fly Ash, and oyster soil in Bottom Ash could improved strength and $E_{50}$ and enlarge its field of being used.

• Journal of the Korean GEO-environmental Society
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• v.6 no.4
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• pp.5-12
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• 2005

In this study, the geotechnical applicability of permeable barriers that could filter the leachate from a landfill was evaluated. Specimens were cast from sand, loess and bentonite according to the specific weight ratios of them. A series of experiments are performed to determine the unconfined compressive strength and permeability of various mixing ratio of bentonite, loess, and sand. From the laboratory test, optimum mixing ratio that satisfied the regulations of unconfined compressive strength($5kgf/cm^2$) and coefficient of permeability ($10^{-3}{\sim}10^{-4}cm/sec$) in landfill was found when the weight ratio of sand and loess was 8:2 with 2% of bentonite. Using the laboratory test data and in situ test results, the applicability of the wall will be tested for various conditions.

• Computers and Concrete
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• v.8 no.2
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• pp.207-227
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• 2011

In flexural strength design of unconfined reinforced concrete (RC) members, the concrete compressive stress-strain curve is scaled down from the uni-axial stress-strain curve such that the maximum concrete stress adopted in design is less than the uni-axial strength to account for the strain gradient effect. It has been found that the use of this smaller maximum concrete stress will underestimate the flexural strength of unconfined RC members although the safety factors for materials are taken as unity. Herein, in order to investigate the effect of strain gradient on the maximum concrete stress that can be developed in unconfined flexural RC members, several pairs of plain concrete (PC) and RC inverted T-shaped specimens were fabricated and tested under concentric and eccentric loads. From the test results, the maximum concrete stress developed in the eccentric specimens under strain gradient is determined by the modified concrete stress-strain curve obtained from the counterpart concentric specimens based on axial load and moment equilibriums. Based on that, a pair of equivalent rectangular concrete stress block parameters for the purpose of flexural strength design of unconfined RC members is determined.

• Advances in Computational Design
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• v.5 no.2
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• pp.195-207
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• 2020

The present study focuses on the application of artificial neural network (ANN) and Multiple linear Regression (MLR) analysis for developing a model to predict the unconfined compressive strength (UCS) and split tensile strength (STS) of the fiber reinforced clay stabilized with grass ash, fly ash and lime. Unconfined compressive strength and Split tensile strength are the nonlinear functions and becomes difficult for developing a predicting model. Artificial neural networks are the efficient tools for predicting models possessing non linearity and are used in the present study along with regression analysis for predicting both UCS and STS. The data required for the model was obtained by systematic experiments performed on only Kaolin clay, clay mixed with varying percentages of fly ash, grass ash, polypropylene fibers and lime as between 10-20%, 1-4%, 0-1.5% and 0-8% respectively. Further, the optimum values of the various stabilizing materials were determined from the experiments. The effect of stabilization is observed by performing compaction tests, split tensile tests and unconfined compression tests. ANN models are trained using the inputs and targets obtained from the experiments. Performance of ANN and Regression analysis is checked with statistical error of correlation coefficient (R) and both the methods predict the UCS and STS values quite well; but it is observed that ANN can predict both the values of UCS as well as STS simultaneously whereas MLR predicts the values separately. It is also observed that only STS values can be predicted efficiently by MLR.

• Magazine of the Korean Society of Agricultural Engineers
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• v.28 no.4
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• pp.66-76
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• 1986

This study was attempted to investigate the effects of delayed compaction on the unconfined compressive strengh and dry density of Soil-cement mixtures. Soil-cement construction is a time-consuming procedure. Time-delay is known as a detrimental factor to lower the quality of soil-cement layer. A laboratory test was performed using coarse and fine weathered granite soils. The soils were mixed with 7% cement at optimum moisture content and excess moisture content in part. Socondary additives such as lime, gypsum-plaster, flyash and sugar were tried to counteract the detri-mental effect of delayed compaction. The specimens were compacted by Harvard Miniature Compaction Apparatus at 0,1,2,4,6 hors after mixing. Two kinds of compactive efforts(9 kgf and 18 kgf tamper) were applied. The results were summarized as follows: 1.With the increase of time delay, the decrease rate of dry density of the specimen compacted by 9 kgf tamper was steeper than that of the specimen compacted by 18kgf tamper. In the same manner, soil-B had steeper decreasing rate of dry density than soil-A. 2.Based on the results of delayed compaction tests, the dry density and unconfined compressive sterngth were rapidly decreased in the early 2 hours delay, while those were slowly decreased during the time delay of 2 to 6 hours. 3.The dry density and unconfined compressive strength were increased by addition of 3% excess water to the optimum moisture content during the time delay of 2 to 6 hours. 4.Without time delay in compaction, the dry densities of soil-A were increased by adding secondary additives such as lime, gypsum-plaster, flyash and sugar, on the other hand, those of soil-B were decreased except for the case of sugar. 5.The use of secondary additives like lime, gypsum-plaster, flyash and sugar could reduce the decrease of unconfined compressive strength due to delayed compaction. Among them, lime was the most effective. 6.From the above mentioned results, several recommendations could be suggested in order to compensate for losses of unconfined compressive strenght and densit v due to delayed compaction. They are a) to use coarse-grained granite soil rather than fined-grained one, b) to add about 3% excess compaction moisture content, c) to increase compactive effort to a certain degree, and d) to use secondary additives like line gypsum-plaster, flyash, and sugar in proper quantity depending on the soil types.

• Journal of the Korean Geotechnical Society
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• v.27 no.8
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• pp.31-37
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• 2011

In order to evaluate the effect of matric suction on the strength and deformation characteristics, the unsaturated unconfined compression test is performed for the statical1y compacted silty sand. Specimens used were made under conditions with various initial degrees of saturation. The initial matric suction, matric suction at the peak shear strength and the volumetric deformation during the shear process were measured. From these results, it was found that the initial degree of saturation exerts the influence on the behaviors of suction, peak shear strength and the volumetric deformation. Furthermore, the suction stress($P_s$) which means the apparent cohesion due to matric suction in the unsaturated shear strength could be derived.

• Journal of the Korean GEO-environmental Society
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• v.16 no.2
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• pp.15-25
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• 2015

As the physical and mechanical properties of lightweight air-mixed soil change in the procedure of transportation of mix truck, it is necessary to assure whether the properties during construction satisfy those in design. In this study, variations of properties of mixed soil after transportation by mix truck are proved by field test. Lightweight air-mixed soil used field test the unit weight of $9.0{\pm}1.0kN/m^3$, the flow value of $190{\pm}20mm$ was produced. To analyze variations of properties of mixed soil the unit weight and flow value of the sample before and after transport was measured unconfined compressive strength tests were performed. Mixing time was 19~175 minutes diversified. As the test results, it is known that the density, the flow value and the unconfined compressive strength of lightweight air-mixed soil change by transportation, but these values satisfy the specifications of material of air-mixed soil. After transportation the average value of the unit weight and flow value change in the flow of the $(+)0.10kN/m^3$, 4.8 mm respectively, the average change in the unit weight and the flow value due to the mixing time was constant. And unconfined compressive strength of 28-day specimen increases from 20 to $150kN/m^2$. But, these values do not have some clear relationship with the transportation time within 175 minutes which is longest test time. Consequently, Within 175 minutes the changes of properties by transportation are too small to show some problems in the construction field.

• Journal of the Korean Geotechnical Society
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• v.36 no.2
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• pp.17-28
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• 2020

With respect to the tensile strength of volcanic rocks in Jeju Island, a comparative study was conducted using the existing research results and the test results performed in this study. In addition, the characteristics and effectiveness of the cohesion and internal friction angle estimated from the Brazilian tensile strength and unconfined compressive strength of Jeju volcanic rocks were investigated. As results, the Brazilian tensile strength of Jeju volcanic rocks was closely related to absorption, and decreased exponentially as the absorption increased. It was confirmed that the internal friction angle was closely related to the ratio of unconfined compressive strength to Brazilian tensile strength (σ_c / σ_t), and increased logarithmically as the ratio of σ_c / σ_t increased. In addition, the ratios of σ_c / σ_t of Jeju volcanic rocks were in the range of 5~20 depending on the magnitude of internal friction angle. In the case of cohesion, it was closely related to the absorption and Brazilian tensile strength. The cohesion exponentially decreased as the absorption increased, such as the relation between the Brazilian tensile strength and absorption. It was confirmed that there was a linear relation between the cohesion and Brazilian tensile strength.

• Computers and Concrete
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• v.7 no.2
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• pp.191-202
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• 2010

A laboratory investigation was conducted to characterize the constitutive property behavior of Cor-Tuf, an ultra-high-performance composite concrete. Mechanical property tests (hydrostatic compression, unconfined compression (UC), triaxial compression (TXC), unconfined direct pull (DP), uniaxial strain, and uniaxial-strain-load/constant-volumetric-strain tests) were performed on specimens prepared from concrete mixtures with and without steel fibers. From the UC and TXC test results, compression failure surfaces were developed for both sets of specimens. Both failure surfaces exhibited a continuous increase in maximum principal stress difference with increasing confining stress. The DP tests results determined the unconfined tensile strengths of the two mixtures. The tensile strength of each mixture was less than the generally assumed tensile strength for conventional strength concrete, which is 10 percent of the unconfined compressive strength. Both concretes behaved similarly, but Cor-Tuf with steel fibers exhibited slightly greater strength with increased confining pressure, and Cor-Tuf without steel fibers displayed slightly greater compressibility.