• Proceedings of the Korean Geotechical Society Conference
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• 2007.09a
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• pp.363-372
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• 2007

The residual settlement due to difference between predicted and observed settlement is one of the social problems during reclaiming construction in the soft ground having a deep depth such as Busan and Gwangyang province. Prediction error for the secondary compression settlement makes the construction much harder. To examine characteristics of the secondary compression settlement, the secondary compression index is the most important factor. In this study, various empirical methods for determining the secondary compression index are evaluated. And errors applied to the design case practically are also explained. The pre loading method is the only way to reduce the secondary compression settlement and reduction ratio of the secondary compression should be investigated correctly. Hence, research results on the reduction ratio of the secondary compression are analyzed in this paper. Moreover, decrement of the secondary compression index due to over consolidation ratio is examined closely by laboratory consolidation test using clay in the Gwangyang area.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.10a
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• pp.537-544
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• 2002

Deformations of clays continue beyond the end of primary consolidation: this is secondary consolidation. Mesri(1973) have shown that C $\_$a/' is related to the natural water content W$\_$n/. For clays, C $\_$a/' is approximately equal to 0.01 W $\_$n/. And the ratio C $\_$ae// C $\_$c/ is approximately equal to 0.04. In this study, coefficient of secondary compression was analyzed by the consolidation tests datas in the 3 sites. In conclusion, coefficient of secondary compression was similar to Mesri's suggestions.

• Journal of The Korean Society of Agricultural Engineers
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• v.65 no.6
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• pp.51-63
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• 2023

To improve the problem that the settlement curve of the consolidation theory of Terzaghi does not match well with the actual settlement curve, we included a secondary compression settlement and analyzed it by varying the beginning point and then obtained the following results. The current methods of calculating the compression index from the  log𝜎 curve and the coefficient of consolidation from the time-dependent settlement curve for each consolidation pressure proved that the final settlement amount will be consistent after a long time, but the actual settlement amount will always be smaller than the predicted settlement amount during the settlement progress stage. The consolidation factors estimated by the curve fitting with the condition that the secondary compression begins in the second half of the primary compression showed similar values to the consolidation factors estimated by the curve fitting for the primary compression only, and the settlement curves were in better agreement throughout the compression. It showed different values, showing low validity. It can be inferred that secondary compression acts from the point when a significant portion of the excess pore water pressure is dissipated, and the loading stress begins to have more influence on the skeletal structure of the soil. Analysis results show that secondary compression begins at the range of 91 % to 98 % on the average degree of primary consolidation.

• Geomechanics and Engineering
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• v.16 no.2
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• pp.125-140
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• 2018

Tianjin, which is located on the west shore of the Bohai Sea, is part of China's Circum-Bohai-Sea Region, where very weak clay is deposited. From the 1970s to the early $21^{st}$ century, Tianjin marine clay deposits have been the subject of numerous geotechnical investigations. Because of these deposits' geological complexity, great depositional thickness, high water content, large void ratio, excessive settlement, and low shear strength, the geotechnical properties of Tianjin marine clay need to be summarized and evaluated based on various in situ and laboratory tests so that Tianjin can safely and economically sustain more infrastructure in the coming decades. In this study, the properties of Tianjin marine clay, especially its consolidation properties, are summarized, evaluated and discussed. The focus is on establishing correlations between the geotechnical property indexes and mechanical parameters of Tianjin marine clay. These correlations include the correlations between the water content and the void ratio, the depth and the undrained shear strength, the liquid limit and the compression index, the tip resistance and the constrained modulus, the plasticity index and the ratio of undrained shear strength and the preconsolidation pressure. In addition, the primary consolidation properties of Tianjin marine clay, such as the intrinsic compression line (ICL), sedimentation compression line (SCL), compression index, $C_c$, coefficient of consolidation, $C_v$, and hydraulic conductivity change index, $C_{kv}$, are evaluated and discussed. A secondary consolidation property, i.e., the secondary compression index, $C_a$, is also investigated, and the results show that the ratio of $C_a/C_c$ for Tianjin marine clay can be used to calculate $C_a$ in secondary consolidation settlement predictions.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.235-242
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• 2004

For this study, a Peliyagoda area located on a route was selected among many sections of a CKE(Colombo to Katunayake Expressway) route in Sri-Lanka. Its subground consists of a very weak and thick peat soil named amorphous or fibrous peat. All of data, obtained in the design process of soft ground treatment were analyzed to evaluate the settlement characteristics resulted from an embankment load and to present reasonable methods for estimation of secondary compression settlement. For these purposes, soil parameters were used obtainedby field and laboratory tests the settlement analyses were conducted base on the field monitoring results within 20 months. In addition, Reasonable methods were studied to estimate primary consolidation and secondary compression settlement.

• Journal of the Korean Geotechnical Society
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• v.24 no.8
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• pp.99-109
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• 2008

The standard consolidation tests using the incremental loading technique test (IL) were performed on remolded normal consolidation and undisturbed clay samples to find out the effects of plastic index and loading period on consolidation in this study. The remolded samples used were prepared by mixing Gunsan-Samangum clay with bentonite so that they may have plasticity indexes of 15, 30, 45, and 60%, respectively. The undisturbed clay samples were collected from Inchon, Kwangyang, and Uoolsan. The samples were tested at the condition of 4 different loading periods (1, 2, 4, and 8 days). Settlement, coefficient of consolidation, compression index, secondary compression index, and pore water pressure characteristics were investigated from the plastic index and loading period aspects, and the compression index, coefficient of consolidation, and secondary compression index were formulated in terms of the plastic index and loading. To verify the applicability of proposed equations, the settlements obtained from Terzaghi's theory, modified Cam-Clay model (elasto-plastic model), and the Sekiguchi model (elasto-viscoplastic mode) were compared with the test results. The comparison indicates that the Sekiguchi model incorporating the secondary consolidation characteristic well predicts the results.

• Journal of The Korean Society of Agricultural Engineers
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• v.66 no.2
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• pp.1-12
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• 2024

In order to integrate two consolidation theories of Terzaghi's consolidation theory and Mesri's secondary compression theory and to identify a model suitable for analyzing stress-strain behavior over time, numerical analysis on consolidation tests were conducted using a modified cam-clay model and a soft soil creep model and the following conclusions were obtained. The results of numerical analysis applying the theory that a linear proportional relationship is established between the void ratio at logarithmic scale and the permeability coefficient at logarithmic scale is better agreement with the result of oedometer test than the results of applying constant hydraulic conductivity. The modified cam-clay model is a model that does not include secondary compression, but the slope of the normal consolidation line corresponding to the compression index of the standard consolidation test includes secondary compression, so the actual settlement curve over time is lower than the predicted value through numerical analysis. It always gets smaller. Other previous studies that applied Terzaghi's consolidation theory to consolidation test analysis showed the same results and were cross-confirmed. The soft soil creep model, which includes secondary compression in the theory, showed good agreement in all sections including secondary compression in the consolidation test results. It was judged appropriate to use a soft soil creep model when performing numerical analysis of soft clay ground.

• Magazine of the Korean Society of Agricultural Engineers
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• v.45 no.5
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• pp.133-139
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• 2003

Dredged soil from sea has much higher water content than liquid limit of clay and even if small loads apply, it will suffer a great settlement. Therefore it is very difficult to perform a consolidation test with general consolidation apparatus because of high water content. In this study Rowe Cell Apparatus consolidation tests have been performed with 1 remolding clay of water content 56% and 4 slurry clays of a water content of 100%, 120%, 133% and 150%. From the test results the consolidation characteristics such as compression index, secondary compression index and consolidation coefficient have been investigated with a variation of water content of dredged soil. The equations to get consolidation constants such as a compression index, a consolidation coefficient have been proposed with the field water content.

• Geomechanics and Engineering
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• v.24 no.1
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• pp.43-55
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• 2021

Peatland is distributed in China widely, and organic matters in soil frequently induce problems in the construction and maintenance of highway engineering due to the high permeability and compressibility. In this paper, a selected site of Dali-Lijiang expressway was surveyed in China. A numerical model was built to predict the settlement of the foundation of the selected section employing the soft soil creep (SSC) model in PLAXIS 8.2. The model was subsequently verified by the result of field observance. Consequently, the parameters of 17 types of soils from different regions in China with organic contents varying from 1.1-74.9% were assigned to the numerical model to study the settlement characteristics. The calculated results showed that the duration of primary consolidation and proportion of primary settlement in the total settlement decreased with increasing organic content. Two empirical equations, for total consolidation settlement and secondary settlement, were proposed using multiple linear regression based on the calculated results from the numerical models. The analysis results of the significances of certain soil parameters demonstrated that the natural compression index, secondary compression index, cohesion and friction angle have significant linear relevance with both the total settlement and secondary settlement, while the initial coefficient of permeability exerts significant influence on the secondary settlement only.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.03a
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• pp.373-380
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• 1999

Consolidation settlements of soft clay are often large and potentially damaging to the structures. Currently, large-scale construction projects for airport and harbor etc. are in progress in Korea and many of these structures will be constructed on thick and soft clay layers. For this kind of ground condition, evaluation of consolidation settlement is required at every design and construction stages, and the magnitude of secondary compression appears to be larger than expected. Generally, the magnitude of secondary compression is evaluated by laboratory and in-situ consolidation tests or by empirical $C_{a/}$ $C_{c}$, relationship. The use of empirical value $C_{a/}$ $C_{c}$ may be economical, fast and powerful tool in estimating secondary consolidation settlement. However, the databases of the $C_{a/}$ $C_{c}$, for typical soft clays in Korea are insufficient. The purpose of this study is to investigate the relationship of $C_{a/}$ $C_{c}$ on marine clay near the southern sea in Korea. A series of incremental loading consolidation tests with measurement of pore water pressure were performed. It was found that the $C_{a/}$ $C_{c}$ of undisturbed marine clay is 0.0397. This value is similar to that proposed by Mesri and Castro(1987) on inorganic clay and silt. and silt. and silt.