• Journal of the Korean Geotechnical Society
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• v.30 no.4
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• pp.93-99
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• 2014

Use of geothermal energy has been increased for its economical application and environmentally friendly utilization. Particularly, for energy piles, a spiral coil type ground heat exchanger (GHE) is more preferred than line type GHEs such as U and W shaped GHEs. A PHC energy pile with spiral coil type GHE was installed in an area of partially saturated dredged soil deposit, and a thermal response test (TRT) was conducted for 240 hours under a continuous operation condition. Besides, remolded soil samples from different layers were collected in the field, and soil specimens were reconstructed according to the field ground condition. Non-steady state probe methods were conducted in the lab, and ground thermal conductivity and thermal diffusivity were measured for the different soil layers. An equivalent ground thermal conductivity was calculated from the lab test results and it was compared with the field TRT result. The difference was less than 5%, which advocates the use of an equivalent ground thermal conductivity for the multi-layered ground. Furthermore, this paper also represents an equivalent ground thermal diffusivity evaluation method which is another very important design parameter.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.2
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• pp.58-64
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• 2012

Due to the influence of global oil prices, industrial productivity, which oil consumption is high, was significantly reduced. AC type of high-strength PHC piles is being manufactured through twice the steam curing process and this have resulted in a significant rise for product's manufacturing costs. NAC way other types of file manufacturing process has the advantage of reducing manufacturing costs by a turn of the steam curing. Nevertheless, because the initial strength be poor than that of AC method, shipment is being after the curing period of approximately three days. In addition, the growth of the product enhance with curing period can not be avoided, as a result, cost of inventory is acting as the rise. Piles by the AC method is immediately shipped after curing, damaging problems does not occur when they are introduced to the field site (for example, pile on-site). In the case of NAC, however, at least after the curing period of three days and after expressing the strength of 80 MPa or more, they are shipped on the scene. Therefore, NAC type has problems as follows: (1) increase in moderate inventory holding costs with type and (2) breakage in the field due to lack of strength. In this study, for NAC-typed PHC files, mixing characteristics research for the strength development at 1 day equivalent to AC method were conducted and strength characteristics with changes of original materials were evaluated were also identified.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.6
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• pp.687-695
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• 2020

Micropile is used to improve the stability of existing structures as well as solve various geotechnical problems, such as suppressing slope activity and shearing keys of retaining walls. The existing micropile method has a significantly less capacity to resist a horizontal force than a vertical force0355 Therefore, it is necessary to develop and study an umbrella-type micropile method with excellent seismic performance that can secure seismic performance economically while minimizing structures and ground disturbance areas in the limited space of existing structures. In this study, numerical analysis was performed on the umbrella-type micropile, in which the sloped pile and vertical pile were combined, and the horizontal behavior in soft clay ground during earthquakes was analyzed. Numerical analysis showed that umbrella-type micropile suppresses horizontal displacement in soft ground, and the effect of reducing the horizontal displacement was more pronounced when the embedded depth of the slope pile was 15 m or more. The embedded depth of the micropile and horizontal displacement suppression effect was proportional. Therefore, the umbrella-type micropile has an excellent effect of suppressing horizontal displacement during earthquakes on soft clay ground.