• Geomechanics and Engineering
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• v.25 no.4
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• pp.317-330
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• 2021

This paper reports the results of advanced data analysis involving artificial neural networks for the prediction of the unconfined compressive strength of granite using only two non-destructive test indexes. A data-independent site-independent unbiased database comprising 182 datasets from non-destructive tests reported in the literature was compiled and used to train and develop artificial neural networks for the prediction of the unconfined compressive strength of granite. The results show that the optimum artificial network developed in this research predicts the unconfined compressive strength of weak to very strong granites (20.3-198.15 MPa) with less than ±20% deviation from the experimental data for 70% of the specimen and significantly outperforms a number of available models available in the literature. The results also raise interesting questions with regards to the suitability of the Pearson correlation coefficient in assessing the prediction accuracy of models.

• Geomechanics and Engineering
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• v.12 no.6
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• pp.935-948
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• 2017

An experimental program was conducted to investigate the effects of the static compaction pressure, cement content, water/cement ratio, and curing time on unconfined compressive strength (UCS) of the cement treated sand. UCS were conducted on samples prepared with 4 different cement/sand ratios and were compacted under the lowest and highest static pressures (8 MPa and 40 MPa). Each sample was cured for 7 and 28 days to observe the impact of curing time on UCS of cement treated samples. Results of the study showed the unconfined compressive strength of sand increased as the cement content (5% to 10%) of the cement-sand mixture and compaction pressure (8 MPa to 40 MPa) increased. UCS of sand soil increased 30% to 800% when cement content was increased from 2.5% to 10%. Impact of compaction pressure on UCS decreased with a reduction in cement contents. On the other hand, it was observed that as the water content the cement-sand mixture increased, the unconfined compressive strength showed tendency to decrease regardless of compaction pressure and cement content. When the curing time was extended from 7 days to 28 days, the unconfined compressive strengths of almost all the samples increased approximately by 2 or 3 times.

• Geomechanics and Engineering
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• v.4 no.2
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• pp.135-150
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• 2012

This paper presents the study of the effect of microorganism Bacillus pasteurii on the properties such as Atterbergs' limit and unconfined compressive strength of cohesive soils. The results of this study reveal that the liquid limit and plasticity index for all clay soils decreased and the unconfined compressive strength increased. Decrease in plasticity index is very high for Kuttanad clay followed by bentonite and laterite. The unconfined compressive strength increased for all the soils. The increase was high for Kuttanad soil and low for laterite soil. After 24 h of treatment the improvement in the soil properties is comparatively less. Besides the specific bacteria selected Bacillus pasteurii, other microorganisms may also be taking part in calcite precipitation thereby causing soil cementation. But the naturally present microorganisms alone cannot work on the calcite precipitation.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.519-523
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• 2009

In this study, the base mixing ratio was determinated to estimate the optimal mixing ratio of material with a change of mixing ratio of micro cement, sand, foaming agent, plasticizer by testing the unconfined compressive strength test. The unconfined compressive strength test was performed to grasp a engineering characteristics of with a change of micro cement, bubble. The results of test, the unconfined compressive strength increased with a micro cement's increase and bubble's decrease. In the future, it will be secured that is reliable datas from laboratory of various condition and in-situ tests to develop optimal lightweight foamed concrete.

• 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 Geosynthetics Society
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• v.18 no.4
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• pp.253-262
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• 2019

This paper described the evaluation results on unconfined compressive strength characteristics of CLSM with paper sludge ash, in order to develop a CLSM that can prevent sewer pipe damage. The flowability test and the unconfined compressive strength test were performed according to mix design condition of CLSM. The flowability test result showed that the water content, which can satisfy the flowability criteria, was 24% to 32% according to the mix design condition. The results of unconfined compressive strength test showed that the strength incremental ratio was high between 1 and 7 days of curing time, and the strength at this time was more than about 50% of the strength at 28 days of curing time. The strength of CLSM was greatly influenced by fly ash. However, it was analyzed that the mixture of paper sludge ash is required when the reference strength of CLSM is considered. Although the strength of the high cement ratio was higher than that of the low cement, a cement ratio of 5% would be a reasonable mix design condition of CLSM.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.489-494
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• 2010

A geo-composite soil (GCS) is a stabilized mixture of bottom ash, cement and dredged soil. Various samples with different mass ratios of mixtures were tested under curing time of 7 and 28 days to investigate physical properties and compressive strength. This paper focused on the effect of bottom ash on the strength characteristics of Busan marine dredged soil. Cement has been added as an additive constituent to enhance self-hardening of the blended mixture. The unconfined compressive strength of GCS increases with an increase in curing time due to pozzolanic reaction of the bottom ash. The strength after 28 days of curing is found to be approximately 1.3 to 2.0 times the strength after 7 days of curing, regardless of mixture conditions. The secant modulus of GCS is in the range of 55 to 134 times the unconfined compressive strength. The correlation of unconfined compressive strength with bottom ash content and initial void ratio are suggested.

• Geomechanics and Engineering
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• v.19 no.4
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• pp.307-314
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• 2019

Light construction waste (LCW) particles are pieces of light concrete or insulation wall with light quality and certain strength, containing rich isolated and disconnected pores. Mixing LCW particles with soil can be one of the alternative lightweight soils. It can lighten and stabilize the deep-thick soft soil in-situ. In this study, the unconfined compressive strength (UCS) and its mechanism of Construction Waste Stabilized Lightweight Soil (CWSLS) are investigated. According to the prescription design, totally 35 sets of specimens are tested for the index of dry density (DD) and unconfined compressive strength (UCS). The results show that the DD of CWSLS is mainly affected by LCW content, and it decreases obviously with the increase of LCW content, while increases slightly with the increase of cement content. The UCS of CWSLS first increases and then decreases with the increase of LCW content, existing a peak value. The UCS increases linearly with the increase of cement content, while the strength growth rate is dramatically affected by the different LCW contents. The UCS of CWSLS mainly comes from the skeleton impaction of LCW particles and the gelation of soil-cement composite slurry. According to the distribution of LCW particles and soil-cement composite slurry, CWSLS specimens are divided into three structures: "suspend-dense" structure, "framework-dense" structure and "framework-pore" structure.

• 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.

• Geomechanics and Engineering
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• v.7 no.3
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• pp.247-261
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• 2014

Analytical and numerical modeling of soft or problematic soils stabilized with lime and cement require a number of soil parameters which are usually obtained from expensive and time-consuming laboratory experiments. The high shear strength of lime and cement stabilized soils make it extremely difficult to obtain high quality laboratory data in some cases. In this study, an alternative method is proposed, which uses the unconfined compressive strength and estimating functions available in literature to evaluate the shear strength parameters of the treated materials. The estimated properties were applied in finite element model to determine which estimating function is more appropriate for lime and cement treated granular soils. The results show that at the mid-range strength of the stabilized soils, most of applied functions have a good compatibility with laboratory conditions. However, application of some functions at lower or higher strengths would lead to underestimation or overestimation of the unconfined compressive strength.