• 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.

• The Journal of Engineering Geology
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• v.23 no.3
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• pp.247-256
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• 2013

The carbonate sands of the Sabkha layer in the Middle East have very low shear strength. Therefore, instant settlement and time-dependent secondary settlement occur when inner voids are exposed, as in the case of particle crushing. We analyzed settlement of the Sabkha layer under a large-scale foundation by hydrotesting, and compared the field test results with the results of laboratory tests. With ongoing particle crushing, we observed the following stress-strain behaviors: strain-hardening (Sabkha GL-1.5 m), strain-perfect (Sabkha GL-7.0 m), and strain-softening (Sabkha GL-7.5 m). General shear failure occurred most frequently in dense sand and firm ground. Although the stress-strain behavior of Sabkha layer carbonate sand that of strain-softening, the particle crushing strength was low compared with the strain-hardening and strain-perfect behaviors. The stress-strain behaviors differ between carbonate sand and quartz sand. If the relative density of quartz sand is increased, the shear strength is also increased. Continuous secondary compression settlement occurred during the hydrotests, after the dissipation of porewater pressure. Particle crushing strength is relatively low in the Sabkha layer and its stress-strain behavior is strain-softening or strain-perfect. The particle crushing effect is dominant factor affecting foundation settlement in the Sabkha layer.

• Journal of the Korean Geotechnical Society
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• v.28 no.6
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• pp.31-38
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• 2012

In this present study, the long-term consolidation tests were performed using the remolded Kwang-Yang port clayey soil to clarify the effect of stress history and over-consolidation ratio (OCR) on the long-term consolidation characteristics of the soft clayey soil. For the over-consolidated state clayey soils, in case OCR exceeds 1.5, there are no great differences of secondary consolidation settlement and final settlement even if OCR increases from 2.0 to 3.0. Therefore, it has been understood that the value of OCR applied on the field site to reduce the secondary consolidation settlement and the final settlement is about 1.5. In addition, in order to investigate the relationship between the pre-loading period and the characteristics of long-term consolidation behavior obtained from the test results using the remolded Kwang-Yang port clayey soils, the influence on long-term consolidation behavior was not large though the pre-load was unloaded with the consolidation degree 70~80% exceeded.

• Journal of the Korean Geotechnical Society
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• v.36 no.5
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• pp.17-24
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• 2020

In order to analyze the effect of applying the bioreactor landfills on the waste landfill for acceleration of waste biocompression, a settlement experiment was performed. The secondary compression indices (C_α) were analyzed, and compared with the results of experimental studies conducted in other countries. Analyses of C_α from the experiment showed that the recirculation method of mixing leachate and FWL could accelerate the waste settlement as much as 2.9 times and 2 times more than the leachate recirculation and the sanitary landfills due to additional biocompression generated by the organic matter in FWL. The C_α in this study was smaller than the C_α of the other studies due to the low organic content of the waste in accordance with domestic waste policies to reduce food waste. The relation between biodegradable waste content and C_α was analyzed. The C_α of the waste was shown to be sensitive to biodegradable waste content, and become higher as the content of the biodegradable waste increases.

• Journal of the Korean Geotechnical Society
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• v.20 no.8
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• pp.113-121
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• 2004

The present study is suggested to estimate the degree of secondary consolidation caused by various changes of stress such as loading, unloading and reloading in improving poor subsoil through pre-compression loading construction method and, for this purpose, examined the characteristics of the consolidation of Kunsan clay through incremental loading test (IL) using standard consolidation tester and constant loading rate test (CLR), which were adapted from the constant rate of strain test (CRS). In addition, after CRS test, this study determined the characteristics of secondary consolidation and relationships among void ratio, effective stress and time according to the ratio of effective over-consolidation on reloading at the point of time of random expansion. Kunsan clay had larger expansion and smaller secondary consolidation settlement when the ratio of effective over-consolidation was high. In addition, when loading was applied after the load was removed at once, the secondary consolidation coefficient $C'_{\alpha}$ was smaller than that when the load was removed gradually, and when the ratio of effective over-consolidation was over 1.4 a similar value was produced. Based on the entire settlement resulting from reloading, the secondary consolidation coefficient $C"_{\alpha}$ increased non-linearly with the lapse of time but the final value was similar to that in the case of rapid removal. The strain velocity of void ratio was in a regular linear relationship with the increase of loading time regardless of the ratio of effective over-consolidation in both tests and it grew smaller with the increase of the ratio of effective over-consolidation.tion.

• 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.

• Journal of the Korean Geotechnical Society
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• v.21 no.3
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• pp.133-140
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• 2005

In order to accelerate the rate of consolidation settlement and gain a required shear strength for a given soft clay deposit, vertical drain method combined with a preloading technique has been widely applied. In this paper, a theory of axisymmetric nonlinear consolidation fer drainage-installed deposit, which considers secondary compression (or creep) during primary consolidation, as well as the variations of compressibility and permeability during the consolidation process, has been developed. A computer program named AXICON based on Hypothesis B fur the analysis of axisymmetric nonlinear consolidation was developed by adopting finite difference method. The results of AS(ICON were compared with Hansbo's solution based on Hypothesis A, as well as in-situ settlements and pore pressures measured in test embankment of Ska-Edeby. The results indicated that Hypothesis A usually underestimated the in-situ settlement and Hypothesis B was considered to be logically correct. It was also shown that one may able to appropriately predict the real in-situ behaviors using the proposed program.

• Journal of the Korean Society of Safety
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• v.32 no.3
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• pp.66-73
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• 2017

This study examined the structural behavior of bracket scaffolds reflecting the influence of bracket's deflection. Even though the supporting condition of bracket scaffolds is different to that of general earth-supported scaffolds, there is no clear standards about the installation of bracket scaffolds. To compare the structural behaviors of the earth-supported scaffolds without settlements in columns and those of bracket scaffolds installed on the bracket structure, the finite element analysis was performed. The results show that the differential settlement between the scaffold columns installed on the bracket was occurred due to the deflection of the bracket. The differential settlement gave birth to remarkable secondary stress to the scaffold columns. It is resonable to locate all scaffold columns on the brackets, and if unavoidable situation is faced at a site, the horizontal members should not placed alone without columns on the brackets. Moreover, the structural analysis should be performed to ensure structural safety of bracket scaffolds before installation. In addition, the location of wall connection to the structures is recommended to the scaffolds columns installed on the brackets.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.905-917
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• 2008

Road or Railway construction over soft ground is needed to be considered on secondary consolidation which will be caused differential settlement, lack of transport serviceability, higher maintenance cost. Especially for the railway construction in the second phase of Gyung-Bu or Ho-Nam high speed railway, concrete slab track has been adapted as a safe and cost effective geotechnical solution. In this case controlling the total settlement under the tolerance is essential. And pile supported geogrid reinforced construction method is suggested as a solution for the problem of the traditional method on soft soil treatments. Pile supported geogrid reinforced construction method consists of piles that are designed to transfer the load of the embankment through the compressible soil layer to a firm foundation. The load from the embankment must be effectively transferred to the piles to prevent punching of the piles through the embankment fill creating differential settlement at the surface of the embankment. The arrangement of the piles can create soil arching to carry the load of embankment to the piles. In order to minimize the number of piles geogrid reinforced pile supported construction method is being used on a regular basis. This method consists of one or more layers of geogrid reinforcement placed between the top of the piles and the bottom of the embankment. This paper presents several methods of pile supported geogrid reinforced construction and calculation results from the several methods and comparison of them.

• Journal of The Geomorphological Association of Korea
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• v.27 no.4
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• pp.89-112
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• 2020

The purpose of this study is as follows: First, we restore the optimal topographical environment of the Bronze Age settlements in the Yongdu Stream and its surrounding area in Asan City. Second, we reveal the relative importance of the topographical factors that the Bronze Age people considered when selecting their dwelling locations. We compared and analyzed topographical factors (ridge scale, ridge direction, slope direction of the ridge, micro-landform of the ridge, position of the ridge) from the ridge's environmental perspective of 123 Bronze Age dwellings (hereinafter referred to as dwellings) found in the survey area for that purpose. The results are as follows: First, from a macro perspective, the optimal topographical environment for the location of the Bronze Age settlement is the second ridge that have the E-W direction. And from a micro perspective, it is the southeast direction slope of the Crest slope at the summit. Second, it appears that the Bronze Age people have taken important consideration in determining the location of their dwelling in the following order: ① position (eg. summit), ② micro-landform (eg. Crest slope, Upper slope), ③ slope direction (eg. southward, South, Southeast), ④ scale (eg. sub-ridge, secondary, tertiary), ⑤ direction (eg. E-W, NNE-SSE).