• Geotechnical Engineering
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• v.5 no.4
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• pp.47-60
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• 1989

Soft offshore sediments quite frequently contain undissolved gas, probably methane pro- duced biogenically. The presence of gas bubbles can have a significant effect on the engineering behaviours of the seabed. One of the main difference between saturated and gassy soils is that the undrained response is not incompressible, and without volume change, may be assumed for a fully saturated soil. This paper describes the basic experimental work to further understanding of a gassy soil. The test has been performed for a gassy soil under undrained and drained conditions. It was confirmed that the gas inclusions deformed due to changes in the total stress on the sample and also the pore gas pressure response to change in total stress. but not directly to those in pore water pressure. And the test which applied the repeated load under undrained state also showed the similar behaviour as the simple load.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.06a
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• pp.251-256
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• 2007

The aim of this paper is development of resistivity seismic dilatometer (RSDMT) system. The resistivity module for obtaining apparent resistivity depth plot and seismic module for obtaining shear wave velocity (Vs) depth plot are attached to the conventional flat dilatometer testing equipment. From shear wave velocity profile, the stiffness at low strains of a site can be evaluated in undisturbed condition. And the resistivity value contains some information about water content and mineral characteristics of clayey soil. Specially manufactured resistivity and seismic modules were connected between commercialized DMT blade and drilling rod. To enhance reliability and repeatability of RSDMT test, automatic testing system including notebook based data acquisition system and automatic surface source system were developed. RSDMT system can be performed rapidly and can obtaine more reliable data at the same point compared with the separated testing system. The verification studies for the developed RSDMT system are going to be performed. From these studies, the effectiveness of integrated hybrid testing system will be checked in light of proper evaluation of geotechnical design parameters of clayey soils.

• Journal of the Korean Geosynthetics Society
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• v.1 no.1
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• pp.23-29
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• 2002

Since 1980's in U.S.A and Japan, the studies on increasing the bearing capacity of railway roadbed using geocell system have been conducted for repair and reinforcement of railways constructed on soft soils. In this study, the railway roadbed reinforced with geocell system, used for repair and reinforcement of existing railways in Korea, has been analyzed and investigated the results of the previous studies conducted in Korea and other nations. And the method for estimating the railway roadbed thickness was developed based on the equivalent method using the multi-layer theory and the deformation modulus Ev.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1090-1097
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• 2008

This study conducted the decision method of lateral flow in abutment structures founded on the soft soils and the reliability analysis on the foundation pile for abutment. On the basis of the results, this study proposed the reliability design model. Reliability analysis was conducted by applying second moment method, point estimation method, and expected total cost minimization to lateral movement index, lateral movement decision index, modified lateral movement decision index, and circular failure safety factor for the decision criteria of lateral flow. The reliability index by analysis method had a similar tendency each other. Point estimation method was found as a practical method in the aspect of convenience because it could conduct the analysis only by mean and standard deviation as well as the partial derivative on random variables was not necessary. Optimum reliability index and optimum safety according to increasing in failure factors and load ratio were analyzed and loads and resistance factors of the design criteria of optimum reliability were estimated. It presented rational design model which can consider construction level and stability and economical efficiency overall.

• Computers and Concrete
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• v.15 no.1
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• pp.37-54
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• 2015

In general, cracks significantly deteriorate the in-situ performance of concrete members and structures, especially in urban metro tunnels that have been embedded in saturated soft soils. The microcapsule self-healing method is a newly developed healing method for repairing cracked concrete. To investigate the optimal microcapsule parameters that will have the best healing effect in concrete, a 3D analytical probability healing model is proposed; it is based on the microcapsule self-healing method's healing mechanism, and its purpose is to predict the healing efficiency and healing probability of given cracks. The proposed model comprehensively considers the radius and the volume fraction of microcapsules, the expected healing efficiency, the parameters of cracks, the broken ratio and the healing probability. Furthermore, a simplified probability healing model is proposed to facilitate the calculation. Then, a Monte Carlo test is conducted to verify the proposed 3D analytical probability healing model. Finally, the influences of microcapsules' parameters on the healing efficiency and the healing probability of the microcapsule self-healing method are examined in light of the proposed probability model.

• Geomechanics and Engineering
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• v.17 no.5
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• pp.439-444
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• 2019

It is generally known that high strength soil is indicative of well-graded particle size distribution. However, there are some special cases of firm ground despite poor grade distribution, especially a specific gap-graded soil. Based on these discoveries, this study investigated the development of an additive of gap-graded soils designed to increase soil strength. This theoretical concept was used to calculate the mixed ratio required for optimal soil strength of the ground sample. The gap-graded aggregate was added according to Plato's polyhedral theory and subsequently calculated ratio and soil strength characteristics were then compared to characteristics of the original soil sample through various test results. In addition, the underground stress transfer rate was measured according to the test conditions. The test results showed that the ground settlement and stress limit thickness were reduced with the incorporation of gap-graded soil. Further field tests would confirm the reproducibility and reliability of the technology by using gap-graded soil to reinforce soft ground of a new construction site. Gap-graded soil has the potential to reduce the construction cost and time of construction compared to other reinforcing methods.

• Geomechanics and Engineering
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• v.16 no.6
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• pp.635-642
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• 2018

Braced excavation systems are commonly required to ensure stability in construction of basements for shopping malls, underground transportation and other habitation facilities. For excavations in deposits of soft clays or residual soils, stiff retaining wall systems such as diaphragm walls are commonly adopted to restrain the ground movements and wall deflections in order to prevent damage to surrounding buildings and utilities. The ground surface settlement behind the excavation is closely associated with the magnitude of basal heave and the wall deflections and is also greatly influenced by the possible groundwater drawdown caused by potential wall leakage, flow from beneath the wall, flow from perched water and along the wall interface or poor panel connections due to the less satisfactory quality. This paper numerically investigates the influences of excavation geometries, the system stiffness, the soil properties and the groundwater drawdown on ground surface settlement and develops a simplified maximum surface settlement Logarithm Regression model for the maximum ground surface settlement estimation. The settlements estimated by this model compare favorably with a number of published and instrumented records.

• Geomechanics and Engineering
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• v.23 no.6
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• pp.561-573
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• 2020

The creep and consolidation behaviors of clays subjected to thermal cycles are of fundamental importance in the application of energy geostructures. This study aims to numerically investigate the physical mechanisms for the temperature-triggered volume change of saturated clays. A recently developed thermodynamic framework is used to derive the thermo-mechanical constitutive model for clays. Based on the model, a fully coupled thermo-hydro-mechanical (THM) finite element (FE) code is developed. Comparison with experimental observations shows that the proposed FE code can well reproduce the irreversible thermal contraction of normally consolidated and lightly overconsolidated clays, as well as the thermal expansion of heavily overconsolidated clays under drained heating. Simulations reveal that excess pore pressure may accumulate in clay samples under triaxial drained conditions due to low permeability and high heating rate, resulting in thermally induced primary consolidation. Results show that four major mechanisms contribute to the thermal volume change of clays: (i) the principle of thermal expansion, (ii) the decrease of effective stress due to the accumulation of excess pore pressure, (iii) the thermal creep, and (iv) the thermally induced primary consolidation. The former two mechanisms mainly contribute to the thermal expansion of heavily overconsolidated clays, whereas the latter two contribute to the noticeable thermal contraction of normally consolidated and lightly overconsolidated clays. Consideration of the four physical mechanisms is important for the settlement prediction of energy geostructures, especially in soft soils.

• Proceedings of the Korean Geotechical Society Conference
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• 1991.10a
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• pp.332-347
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• 1991

Accurate prediction of future settlement is essential for the settlement control of soft soil by pre-loading method. To predict future settlement in clayey soft soils, several methods like Asaoka method, Hyperbolic Method and Hoshino method are currently being used. These methods predict the future sett1ement by mathmatical treatment of the measured settlement data on the basis of consolidtion theory and empiricism. But the correlation coefficient between the measured and the predicted settlement was relatively low (0.8~0.9). Also, the prediction of future settlemet for the design load is very difficult. In this article, the measured field settlement data was treated as the the field consolidation test. Hence, condolidation coefficient(Cv) and compression index(Cc) was evaluated from the field settlement data. Cv and Cc values from field data was used to calculate the degree of consolidation and settlement at desired time. By this method, the correlation coefficent between the measured and the predicted settlement was significantly increased(0.97~0.99). Also the settlement by the design load after the improvement of soft soil could be predicted reasonably. This method is quite rational and sound but it requires thousands of calculation steps. Today, by the aid of low priced personal computers above mentioned technique could be used much acre economically and effectively than conventional methods. This article presented the mechanisms and capacities of this method and demonstrated the enhanced correlation coefficient when applied to actual field settlement data.

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.217-225
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• 2003

An experimental study was conducted to evaluate the smeared effect due to mandrel penetration into soft ground for a vertical drain installation. Laboratory tests were performed to investigate the formation of a smear zone, the variations of strength, and the consolidation characteristics in the disturbed zone using two types(CL at Yangsan site and OH at Pohang site) of soft clayey soils. The smear zone effect was evaluated focusing on mandrel shape, mandrel size, penetration speed, and ground condition. Based on laboratory test results, the diameter of the smear zone$(d_s)$ ranged from 3.08 and 3.92 times that of mandrel$(d_m)$. It was also found that the $(d_s/d_m)$ value of the circular shape of the mandrel is smaller than those of square and rectangular shapes. The value of $(d_s/d_m)$ decreased with larger mandrel size, lower penetration speed in the CL soil, and higher penetration speed in the OH soil. However, natural water content was minimally affected by $(d_s/d_m)$. Respectively, the coefficients of horizontal consolidation$(C_{hs})$ and horizontal Permeability$(K_s)$ of smear zone ranged from 0.81 to 0.87 times, and 0.73 to 0.83 times those of the undisturbed zone. Based on this study, the values of $C_{hs}, K_s$ and unconfined compressive strength$(q_{us})$ in the smear zone were the lowest at close vicinity of the mandrel and increased linearly with distance from the mandrel. Further, the $(q_{us})$ varied from 0.5 to 0.9 times that of the undisturbed zone strength.