• Geomechanics and Engineering
• /
• v.25 no.2
• /
• pp.143-157
• /
• 2021

Expansive soil is the most predominant geologic hazard which shows a large amount of shrinkage and swelling with changes in their moisture content. This study investigates the macro-mechanical and micro-structural behaviours of dredged natural expansive clay from coal mining treated with ordinary Portland cement or hydrated lime addition. The stabilised expansive soil aims for possible reuse as pavement materials. Mechanical testing determined geotechnical engineering properties, including free swelling potential, California bearing ratio, unconfined compressive strength, resilient modulus, and shear wave velocity. The microstructures of treated soils are observed by scanning electron microscopy, x-ray diffraction, and energy dispersive spectroscopy to understand the behaviour of the expansive clay blended with cement and lime. Test results confirmed that cement and lime are effective agents for improving the swelling behaviour and other engineering properties of natural expansive clay. In general, chemical treatments reduce the swelling and increase the strength and modulus of expansive clay, subjected to chemical content and curing time. Scanning electron microscopy analysis can observe the increase in formation of particle clusters with curing period, and x-ray diffraction patterns display hydration and pozzolanic products from chemical particles. The correlations of mechanical properties and microstructures for chemical stabilised expansive clay are recommended.

• Proceedings of the Korean Geotechical Society Conference
• /
• 1992.10a
• /
• pp.75-86
• /
• 1992

The elevation of reclamation work in the coastal area for the industrial complex is determined through the investigation and review of marine conditions, drainage plan and fill materials. The embankment to be constructed with crushed stone on the soft soil should be safe against the wave force, immediate and long term consolidation settlement, overturning and sliding due to self-weight and other forces. Because of lack of fill material from the borrow pit, the soft marine clay to be dredged shall be used as the reclamation material. And Paper Drain Board is used as the improvement method for the deep soft clay strata.

• Journal of the Korean GEO-environmental Society
• /
• v.18 no.2
• /
• pp.59-65
• /
• 2017

The costal reclamation construction is for making reclaimed land by dredging marine clay with seawater, and then bringing the dredged soil into the reclaimed land. During the process, the dredged soil in the reclaimed land undergoes the sedimentation-consolidation process. Among the processes, the consolidation is a very critical factor when planning reclaimed land because of its requiring time and settlement. In order to predict the requiring time and settlement, the Column test, which was suggested by Yano, has been usually used in the nation. However, the test method needs a very long time to identify the characteristic of sedimentation-consolidation of dredged soil. Therefore, in this study, in order to supplement the weakness of the Column test which needs such a long time, and in order to identify the characteristic of the sedimentation-consolidation for dredged soil in a short time, the Geo-centrifuge test was examined as an alternative method. The result considered that Geo-centrifuge test would be useful to identify the characteristic of sedimentation-consolidation for dredged soil efficiently.

• Journal of the Korean Geosynthetics Society
• /
• v.16 no.4
• /
• pp.93-101
• /
• 2017

In this study, a subjective weighting factors were awarded based on some indication of the difficulty of assessing the preconsolidation stress using traditional methods (Casagrande, Onitsuka et al., Silva, Becker et al., Janbu and Karlsrud methods) such as those proposed by Casagrande and Janbu using undisturbed sample obtained from Gwangyang dredged clay with high plasticity located in the southern area of Korean peninsular. These numbers only assess the relative ease of finding preconsolidation stress and say nothing regarding the accuracy of the value. The data were compared with measurements of undrained shear strength using strength incremental ratio, checking where or not the values are in the range of 0.25 to 0.35 (typical values of Korean marine clay) and analyzing standard deviation(degree of variability). The measurements of undrained shear strength were obtained from unconfined compression tests (UCT). When determining preconsolidation stress of Korean marine clay, at first, the work method proposed by Becker et al. and the bilogarithmic method proposed by Onitsuka et al. should be used. In addition, preconsolidation pressure should be estimated using the traditional Casagrande method as a basic of comparison.

• Journal of the Korean Geotechnical Society
• /
• v.24 no.8
• /
• pp.61-79
• /
• 2008

Consolidation settlements on marine dredged clays are often greatly and potentially damaging to structures. Currently, large-scale projects are in planning or progressing in Korea. These projects have been performed on thick and soft clay layers. So, the evaluation of consolidation characteristics for dredged and reclaimed ground is very important in design and construction. Therefore, in this study, a series of conventional consolidation tests were performed to investigate the consolidation characteristics of marine dredged clays near Gwang-yang Port. Preconsolidation pressures were evaluated by applying previously proposed 8 methods for the conventional tests results in order to evaluate the legitimacy of these methods. In these methods, when estimating maximum past pressures for dredged and reclaimed ground, it was proved that Becker (1987), Silva (1970), Sridharan (1991)'s methods are excellent in legitimacy.

• Journal of the Korean Geotechnical Society
• /
• v.37 no.7
• /
• pp.13-23
• /
• 2021

If roads, bridges, buildings, etc. are built on the ground with soft clay or organic soil, there may be a lot of problems in geotechnical engineering such as settlement and stability due to the large settlement and lack of bearing capacity. In extreme cases, it may appear due to shear failure or collapse of the constructed structure, so a ground improvement method is indispensable to increase the strength of the ground and to suppress settlement. In this study, the settlement according to each groundwater level condition was analyzed using the measurement results for the groundwater level conditions, one of the important factors in predicting the settlement in dredged and reclaimed ground, and the groundwater level conditions applied to the settlement analysis were proposed by comparing it with settlement generated 5 years after construction. As a result of the analysis, it is judged that it is reasonable to apply the measured groundwater level during construction and the low water ordinary neap tide (L.W.O.N.T) during load application for the groundwater level in the settlement analysis. In addition, in the case of the dredged and reclaimed ground, it is estimated that the water pressure acting on the clay layer is nonlinear, as the result of the observations of the head of water at the observation points above and below the in-situ clay layer were different.

• Journal of the Korean Geotechnical Society
• /
• v.38 no.12
• /
• pp.67-78
• /
• 2022

In this study, the measurement results of the coastal deep soft ground buried in the upper part of the dredged clay were analyzed and compared with the current specification standards. Based on the results, a suitable proposal was suggested for the selection, installation, data arrangement, and analysis of each instrument used in the deep soft ground improvement construction. The pore water pressure meter has a range of 1.5 times or more of the expected measurement range, considering the field conditions of the soft ground. The groundwater level meter installed in the horizontal drainage layer checks the change in the groundwater level during the embanking as well as the performance of the catchment well and the horizontal drainage layer. Therefore, it is important to manage so that the groundwater level exists inside the horizontal drainage layer during embanking. It is enough to install the inclinometer in the gravel layer below the soft ground or weathered rock with an N value of 40 or more for the deep soft ground. It seems desirable to install a screw type for differential settlement meter. However, the screw type should not settle due to its own weight. Considering that it is a dredged landfill where subsidence occurs significantly, it is sufficient to manage the tolerance of leveling at about 10 mm (L is the one-way distance (km)).

• Journal of the Korean Geosynthetics Society
• /
• v.3 no.1
• /
• pp.17-25
• /
• 2004

A horizontal drain method, which applies vacuum pressure at the end of a horizontal drain for discharging pore water, is used often for improving surface reclaimed clay in the field. In this study, to examine the effectiveness of improving consolidation or shear strength depends by varying vacuum pressure, laboratory chamber horizontal drain test using vacuum pressure is performed and the results is compared with that of self-weight consolidation. The results show that water content reduces with the increase of soil depth in case of self-weight consolidation, while it reduces near the horizontal drain and increases with the increase of the distance from the horizontal drain in case of applying vacuum pressure. The shear strength of dredged soil was improved as well, when the vacuum pressure is applied. The optimized consolidation was achieved at the vacuum pressure range of 30 to 50kPa in the laboratory box test of 50cm wide, considering the range of drain interval in the field was between 0.7 and 1.2m.

• Journal of the Korean Geosynthetics Society
• /
• v.22 no.1
• /
• pp.87-96
• /
• 2023

There are a lot of difference between the surface settlement and the differential settlement measured at the Busan New Port, where the dredged and reclaimed clay layer exists and below the clay is originally thickly distributed. To find the cause and solution of this, the actual conditions of each differential settlement used for the soft ground improvement, characteristics, installation method, measurement frequency, measurement data management, and data analysis of each type were considered. In the deep soft ground improvement work where large deformation occurs, the bending deformation of the screw-type differential settlement gauge is less than that of other types of measuring instruments, so there is less risk of loss, and the reliability of data is relatively high as the instruments are installed by drilling for each stratum. Since the greater the amount of high-precision settlement measurement data, the higher the settlement analysis precision. It is necessary to manage with higher criteria than the measurement frequency suggested in the standard specification. For the data management of the differential settlement gauge, it is desirable to create graphs of the settlement and embankment height of the relevant section over time, such as surface, differential, and settlement of pore water pressure gauge for each point. In the case of multi-layered ground with different compression characteristics, it is more appropriate to perform settlement analysis by calculating the consolidation characteristics of each stratum using a differential settlement data.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2003.03a
• /
• pp.767-772
• /
• 2003

The clay which transported into a pond under the high water content condition have no effective stress which develop from the starting point of sedimentation and self-weight consolidation. Since sedimentation and self-weight consolidation dependent on self-weight of solids is made progress over a long time, to accelerating it have many advantages in the economic view In this paper, sand spreading method which is one of sedimentation and self-weight consolidation acceleration method is studied through a series of experiments considering the mixing ratio of sand and clay. The test results show that the mixing ratio of clay and sand of 1:0.2 is the biggest rate of consolidation and the pouring at the end point of sedimentation considerably effects on consolidation rate.