• Geomechanics and Engineering
• /
• v.16 no.4
• /
• pp.375-384
• /
• 2018

Unconfined compressive strength (UCS) of high plasticity clayey soil mixed with 5 and 10 % of Portland cement and four chemical agents such as sodium hexametaphosphate, aluminum sulfate, sodium carbonate, and sodium silicate with 0, 5, 10, and 20% concentrations was comparatively evaluated. The individual and combined effects of the cement and chemical agents on the UCS of the soil mixture were investigated. The strength of the soil-cement mixture generally increases with increasing the cement content. However, if the chemical agent is added to the mixture, the strength of the cement-chemical agent-soil mixture tends to vary depending on the type and the amount of the chemical agent. At low concentrations of 5% of aluminum sulfate and 5% and 10% of sodium carbonate, the average UCS of the cement-chemical agent-soil mixture slightly increased compared to pure clay due to increasing the flocculation of the clay in the mixture. However, at high concentrations (20%) of all chemical agents, the UCS significantly decreased compared to the pure clay and clay-cement mixtures. In the case of high cement content, the rate of UCS reduction is the highest among all cement-chemical agent-soil mixtures, which is more than three times higher in comparison to the soil-chemical agent mixtures without cement. Therefore, in the mixture with high cement (> 10%), the reduction of the USC is very sensitive when the chemical agent is added.

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

• Journal of the Korean Geosynthetics Society
• /
• v.17 no.3
• /
• pp.9-18
• /
• 2018

The soil parameters important for the design of the soft ground are the compression index ($C_c$), the consolidation settlement and consolidation speed at the field. Compression index is obtained by laboratory consolidation test. In the laboratory consolidation test, sample disturbance always occurs. In order to correct the disturbance phenomena, the method of calculating the compression index proposed by Schmertmann (1955) is generally used. However, recent developments in sampling technology and Korean soil conditions are different from those proposed by Schmertmann. So it needs to be verified. In this study, each consolidation curve's cross void ratio is evaluated by doing consolidation test varying disturbance on high-plastic clay (CH), low-plastic clay (CL) and low-plastic silt (ML). The test results were $0.521e_0$ for low-plastic silt, $0.404e_0$ for low-plastic clay, and $0.458e_0$ for the high-plastic clay. This results were different from those of Schmertmann's suggested value of $0.42e_0$. Therefor we proposed a correction formula using the plastic index according to soil type. However, since the results of this study are limited test results, further studies on various korean soil are needed to suggest the compression index correction method according to the degree of plasticity index of soil.

• Geomechanics and Engineering
• /
• v.30 no.5
• /
• pp.461-469
• /
• 2022

One of the most important factors that should be considered for using any ground improvement technique is the stability of stabilized soil and the durability of the provided solution for getting the required engineering properties. Generally, most of the earth structures that are constructed on clayey soils are exposing movements due to the long periods of drying or wetting cycles. Over time, environmental changes may result in swells or settlements for these structures. In order to mitigate this problem, this research has been performed on mixtures of high plasticity clay with traditional additives such as lime, cement and non-traditional additives such as polypropylene fiber. The purpose of the research is to assess the most appropriate ground improvement technique by using commercially available additives for resisting the developed desiccation cracks during the drying process and resisting the volume changes that may result during wet/dry cycles as an attempt to simulate the changes of environmental conditions. The results show that the fiber-reinforced samples have the lowest volumetric deformation in comparision with cement and lime stabilized samples, and the optimum fiber content is identified as 0.38%. In addition, the desiccation cracks were not visible on the samples' surface for both unreinforced and chemically stabilized samples. Regarding cracks resistance resulting from the desiccation process, it is observed, that the resistance is connected with the fiber content and increases with the increase of the fiber inclusion, and the optimum content is between 1% and 1.5%.

• Journal of the Korean Geotechnical Society
• /
• v.27 no.5
• /
• pp.5-15
• /
• 2011

Recent increase of large scale construction near costal area has also increased the application of soft ground treatment. As a result, solidification with cement and lime which increases stability and durability of soils, is frequently used for surface layer stabilization in soft ground site. While stabilization of very soft clay with high plasticity and compressibility has widely been studied, studies on silty clay with low plasticity and compressibility are relatively rare. In this study, after stabilizing low plasticity silty clay of Songdo area with cement and lime under various water contents, mixing ratio, and curing time, uniaxial compression test and plate load test were performed. Strength properties from both tests were considerably consistent. And trackability of construction equipment on the treated surface layer of dredged land was estimated. Finally, optimum mixing condition for Songdo silty clay was proposed.

• Geomechanics and Engineering
• /
• v.10 no.6
• /
• pp.827-836
• /
• 2016

The rate of softening is an important factor to determine whether the failure occurs along localized shear band or in a more diffused manner. In this paper, strength loss and softening rate effect depending on sensitivity are investigated for weakly cemented clays, for both artificially cemented high plasticity San Francisco Bay Mud and low plasticity Yolo Loam. Destructuration and softening behavior for weakly cemented sensitive clays are demonstrated and discussed through multiple vane shear tests. Artificial sensitive clays are prepared in the laboratory for physical modeling or constitutive modeling using a small amount of cement (2 to 5%) with controlled initial water content and curing period. Through test results, shear band thickness is theoretically computed and the rate of softening is represented as a newly introduced parameter, ${\omega}_{80%}$. Consequently, it is found that the softening rate increases with sensitivity for weakly cemented sensitive clays. Increased softening rate represents faster strength loss to residual state and faster minimizing of shear band thickness. Uncemented clay has very low softening rate to 80% strength drop. Also, it is found that higher brittleness index ($I_b$) relatively shows faster softening rate. The result would be beneficial to study of physical modeling for sensitive clays in that artificially constructed high sensitivity (up to $S_t=23$) clay exhibits faster strain softening, which results in localized shear band failure once it is remolded.

• Geomechanics and Engineering
• /
• v.36 no.6
• /
• pp.589-599
• /
• 2024

Dispersion occurs when clay soil disperses under specific conditions and is rapidly washed away. While there are numerous methods for rectifying it, they are neither cost nor time-effective. The current study used metakaolin and zeolite to improve heavily dispersive clay soil either separately or in combination at 0%, 2%, 4%, 6%, and 8% of the soil weight. After 7 days of curing, the samples were tested to determine the extent of change in the dispersion potential, as well as the improvement of the geotechnical properties of the soil. The results indicated that the addition of 2% zeolite with 6% to 8% metakaolin decreased the dispersion potential considerably. Double hydrometry test findings revealed that the dispersion potential decreased by almost 70% and entered the non-dispersive group; the crumb test also revealed this. Atterberg limits testing indicated a decrease in the plasticity index which reduced the flexibility of the samples. The greatest decrease in PI (67.5%) was achieved with the addition of 8% zeolite plus 8% metakaolin to the soil. The results of density tests revealed that a decrease in the optimal moisture content increased the maximum dry density of soil. This increase in density was a response to the high reactivity of metakaolin with calcium hydroxide and the formation of calcium hydroxide hydrate gel. This eventually caused an increase in the unconfined compressive strength, the greatest increase in strength of about 1.8-fold was observed with a combination of 2% zeolite and 6% metakaolin compared to the unmodified sample.

• Geomechanics and Engineering
• /
• v.24 no.2
• /
• pp.115-127
• /
• 2021

This paper investigates the effects of soaking on a lime stabilized high plasticity clay and evaluates the implications for pavement design. In this context, the soil was stabilized by 4%, 6% and 9% hydrated lime. The soil was pulverized in two different gradations so that representative field gradations could be simulated. Both soil pulverization levels passed the relevant field gradation criteria. Curing durations were chosen as 7 days, 28 days and 56 days. Two groups of samples were prepared and were tested in unconfined compression test apparatus to measure the strength and secant modulus at failure values. One of the groups was tested immediately after curing. The other group of samples were first cured and then subjected to soaking for ten days before testing. Visual observations were made on the samples during the soaking period. The results showed the superiority of fine soil pulverization over coarse soil pulverization for unsoaked conditions in terms of strength and modulus values. Soaking of the samples affected the unconfined compressive strength and modulus values based on lime content, curing duration and soil pulverization level. In soaked samples, fine soil pulverization resulted in higher strength and modulus values compared to coarse soil pulverization. However, even with fine soil pulverization, effects of soaking on modulus values were more significant. A new term named as "Soaking Influence Factor (SIF)" was defined to compare the reduction in strength and modulus due to soaking. The data was compared with the relevant design guidelines and an attempt was made to include Soaking Influence Factors for strength and modulus (SIFS and SIFM) into pavement design processes. Two equations which correlated secant modulus at failure to unconfined compressive strength were proposed based on the samples subjected to soaking. The results of this study showed that in order to decrease the diverse effects of soaking for lime stabilized soils, soil pulverization level should be kept as fine as possible in the field. Importance of proper drainage precautions in the pavements is highlighted for better performance of the pavements.

• Geomechanics and Engineering
• /
• v.29 no.6
• /
• pp.683-696
• /
• 2022

Dams are inevitably planned to be built on thick overburden with high permeability and deformability. The connection part between concrete cut-off wall in overburden and earth core in dam body is not only a key part of the anti-seepage system, but also a weak position. Large uneven settlement will be aroused at the concoction part. However, the interaction behavior and the scope of the connection part cannot be determined effectively. In this paper, numerical analysis of a high earth core dam built on thick overburden was carried out with large deformation FE method. The mechanical behavior of the connection part was detail studied. It can be drawn that there is little differences in dam integral deformation for different analysis method, but big differences were found at the connection part. The large deformation analysis method can reasonably describe the process that concrete wall penetrates into soil. The high plasticity clay has stronger ability to adapt to large uneven deformation which can reduce stress level, and stress state of concrete wall is also improved. The scope of high plasticity clay zone in the connection part can be determined according to stress level of soils and penetration depth of concrete wall.

• Journal of Industrial Technology
• /
• v.25 no.A
• /
• pp.57-65
• /
• 2005

In this paper, for the highly plastic marine soft clay distributed in west and southern coast of Korean peninsula of Kwangyang and Busan New Port areas, correlation between compression index and other indices representing geotechnical engineering properties such as liquid limit, void ratio and natural water content were analyzed. Appropriate empirical equations of being able to estimate the compressibility of clays in the specific areas were proposed and compared with other existing empirical ones. For analyses of the data and test results, data for marine clays were used from areas of the South Container Port of the Busan New Port, East Breakwater, Passenger Quay, Jungma Reclamation and Reclamation Containment in the 3rd stage in Kwangyang. In order to find the best regression model by using the commercially available software, MS EXCEL 2000, results obtained from the simple linear regression analysis, using the values of liquid limit, initial void ratio and natural water content as independent variables, were compared with the existing empirical equations. Multiple linear regression was also performed to find the best fit regression curves for compression index and other soil properties by combining those independent variables. On the other hands, another software of SPSS for non-linear regression was used to analyze the correlations between compression index and other soil properties.