Experimental and numerical analysis on thermal performance of large-diameter cast-in-place energy pile constructed in soft ground

Park, Sangwoo,Lee, Dongseop,Lee, Seokjae,Chauchois, Alexis,Choi, Hangseok Elsevier 2017 ENERGY Vol.118 No.-

<P><B>Abstract</B></P> <P>An energy pile equipped with a W-type heat exchange pipe was constructed in reclaimed soft ground, which is fabricated in a large-diameter cast-in-place pile. The diameter of the energy pile is 1.5 m and the drilled depth reaches to a 60 m whilst the heat exchange pipe is inserted to 30 m depth from the ground surface. To evaluate thermal performance of the constructed energy pile, a series of in-situ thermal performance tests was carried out by controlling intermittent cooling and heating loads, in which the inlet and outlet fluid temperatures, flow rate, and temperatures inside the energy pile were recorded. The test results show that a large-diameter cast-in-place energy pile can provide sufficient heat exchange compared with other types of ground heat exchangers. A series of CFD analyses was performed to simulate the thermal performance tests and provide the designer with preliminary estimation of thermal performance of energy piles. The numerical model was verified by comparing with the field measurements. Using the developed numerical model, the thermal behavior of the energy piles was evaluated with various parameters, and effects of the thermal interference and the temperature difference between the fluid and ground formation on the thermal performance were discussed.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A large-diameter cast-in-place energy pile was constructed in reclaimed soft ground. </LI> <LI> Thermal performance tests were performed to estimate thermal performance of the energy pile. </LI> <LI> The heat exchange in cooling operation was about two times as large as that in heating operation. </LI> <LI> A parametric study was conducted to estimate the effect of temperature difference between fluid and ground formation. </LI> <LI> Tighter pipe layout causes thermal interference that reduces thermal performance of energy piles. </LI> </UL> </P>

Relative constructability and thermal performance of cast-in-place concrete energy pile: Coil-type GHEX (ground heat exchanger)

Park, Sangwoo,Lee, Dongseop,Choi, Hyun-Jun,Jung, Kyoungsik,Choi, Hangseok Elsevier 2015 ENERGY Vol.81 No.-

<P><B>Abstract</B></P> <P>Energy piles encase heat exchange pipes in a pile foundation to use geothermal energy. This paper evaluates the constructability and thermal performance of energy piles equipped in a large-diameter drilled shaft. Two energy piles were constructed by fabricating coil-type heat exchange pipes in cast-in-place concrete piles. The coil pitch was designed to be 200 mm and 500 mm, respectively. The constructability of each energy pile was evaluated in terms of time and ease for installing. In-situ TRTs were performed to compare the thermal performance of energy piles. The relative heat exchange efficiency for the coil pitch 200 mm is only 1.2 times greater than that of the coil pitch 500 mm energy pile, even though the coil pitch 200 mm energy pile encases the heat exchange pipe 2.4 times as longer as the coil pitch 500 mm. In addition, the result of TRTs was compared with two well-known analytical to estimate thermal properties of ground formation. A thermal performance test was carried out by applying artificial cooling operation to the energy piles, and indicates the heat exchange rate is not directly proportional to the pipe length because the tighter coil pitch configuration may cause thermal interference between the coil loops.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Two large-diameter cast-in-place energy piles set with coil-type heat exchange pipes. </LI> <LI> TRTs and thermal performance tests to study effect of coil pitch configuration. </LI> <LI> The longer heat exchange pipe, the more heat exchange rate. </LI> <LI> Heat exchange rate is not directly proportional to encased pipe length. </LI> <LI> Tighter coil pitch configuration causes thermal interference between coil loops. </LI> </UL> </P>

현장타설 콘크리트 말뚝의 두부 품질관리 개선

오주한(Ju-Han Oh),김영하(Young-Ha Kim),이민수(Min-Soo Lee) 한국철도학회 2017 한국철도학회 학술발표대회논문집 Vol.2017 No.05

현장타설 콘크리트 말뚝의 두부부분은 일반적으로 콘크리트 타설 도중 안정액 및 진흙의 혼입, 블리딩에 의한 레이턴스 등으로 품질이 저하됨에 따라 여유 있게 타설하고, 굳은 후에 설계높이까지 깨내고 있다. 그러나 이러한 여분 콘크리트 제거만으로 말뚝 상부의 목표품질을 만족하였는지에 대한 확인기준이 없어, 실제 일부 시공 현장에서는 품질미달인 말뚝이 그대로 시공되는 등 제대로 된 품질관리가 이루어 지지 않고 있는 실정이다. 따라서 본 연구는 현장타설 콘크리트 말뚝의 두부에 대한 품질관리방안을 수립하기 위하여, 현장타설 콘크리트 말뚝의 상부 높이별 비파괴시험 및 파괴시험을 통해 비교분석을 시시하였다. 이를 통해 구조물 손상과 원지반의 교란을 최소화하는 범위에서 말뚝두부의 품질을 확인하는 시험절차를 제시하였으며, 관련 시방서 개정을 통해 현장타설 콘크리트 말뚝의 품질 신뢰도 향상에 기여할 것으로 판단된다. Cast-in-place concrete pile heads are currently being installed with a margin. This is to compensate for a reduction in quality of the pile as a result of stabilizer liquid, mixing mud and laitance after consolidation to the height of design. Currently, no standard exists to confirm if the upper section of the pile is of satisfactory quality through the removal of the pile head. This is leading to the likelihood that low quality piles are being constructed in the field. In this study, in order to manage quality, cast-in-place concrete piles are compared through both non-destructive and destructive tests to the height of each head. This paper is a proposal of test procedures to confirm the quality of pile heads that are within the appropriate range, while minimizing extensive breaking to the pile or ground disturbances. These procedures will thereby improve the reliability and quality of case-in-place concrete piles through revised specification.

Thermo-mechanical behavior of cast-in-place energy piles

Sung, Chihun,Park, Sangwoo,Lee, Seokjae,Oh, Kwanggeun,Choi, Hangseok Elsevier 2018 ENERGY Vol.161 No.-

<P><B>Abstract</B></P> <P>An energy pile induces heat exchange with the ground formation by circulating heat carrier fluid through a heat exchange pipe, which is encased in pile foundation. During heat exchange, temperature variation in energy pile generates thermally-induced stress due to the different thermo-mechanical behavior between the pile and surrounding ground, and the restriction of pile deformation. A series of full-scale field tests was performed to identify the thermo-mechanical behavior of a cast-in-place energy pile equipped with 5-pair-parallel U-type heat exchange pipe. During the field investigation, each cooling and heating test lasted for 30 days, including a 15-day operating period and 15-day resting period, and the thermal stress generated in the energy pile was monitored. The maximum thermal stress was evaluated to be 2.6 MPa in the cooling test, which is about 10% of the design compressive strength of concrete. In addition, a finite element (FE) numerical model was developed to simulate the thermo-mechanical behavior of the energy pile. In the numerical analysis, relevant boundary conditions and interface model were determined by comparing with the field measurement. Finally, a parametric study was performed to estimate the thermal stress and deformation of a cast-in-place energy pile for various ground conditions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A large-diameter cast-in-place concrete energy pile was constructed in a test bed. </LI> <LI> The maximum thermal stress was evaluated to be 2.6 MPa in the cooling test. </LI> <LI> This value is about 10% of the design compressive strength of concrete. </LI> <LI> A parametric study for the thermos-mechanical behavior of energy piles. </LI> </UL> </P>

현장타설콘크리트말뚝의 건전도 평가를 위한 geotomography의 적용 연구

이재경,박종남 한국지반공학회 2005 한국지반공학회논문집 Vol.21 No.4

Recently, geophysical prospecting methods have played very important roles in civil and environmental engineering problems. Technical advances in geophysical instruments and computer system made it possible to get underground images with very high resolution for purposes to resolve those problems. It was possible partly due to ever increasing demand for development of technologies needed to precisely detect polluted areas and prevent ground-related accidents. Based on the same demand, integrity tests of cast-in place piles draw more attention and development of accurate test procedures is required. Ultrasonic methods is one of most advanced non-destructive procedures. In the paper, a geotomography method is employed for the cast-in place pile integrity test using ultrasonic waves. The image of pile interior is scanned and scrutinized for better and more accurate decision in the cast-in place pile integrity. In this study, we firstly examined the accuracy for tomography program with idealized synthetic models built in water tank: their position and size were changed in the tank and each case was studied. In the next stage, real concrete pile models were fabricated and images of anomaly areas inside the pile were scanned to successfully locate those areas.

Shaft resistance of bored cast-in-place concrete piles in oil sand - Case study

Barr, L.,Wong, R.C.K. Techno-Press 2013 Geomechanics & engineering Vol.5 No.2

Pile load tests using Osterberg cells (O-cell) were conducted on cast-in-place concrete piles founded in oil sand fill and in situ oil sand at an industrial plant site in Fort McMurray, Alberta, Canada. Interpreted pile test results show that very high pile shaft resistance (with the Bjerrum-Burland or Beta coefficient of 2.5-4.5) against oil sand could be mobilized at small relative displacements of 2-3% of shaft diameter. Finite element simulations based on linear elastic and elasto-plastic models for oil sand materials were used to analyze the pile load test measurements. Two constitutive models yield comparable top-down load versus pile head displacement curves, but very different behaviour in mobilization of pile shaft and end bearing resistances. The elasto-plastic model produces more consistent matching in both pile shaft and end bearing resistances whereas the linear elastic under- and over-predicts the shaft and end bearing resistances, respectively. The mobilization of high shaft resistance in oil sand under pile load is attributed to the very dense and interlocked structure of oil sand which results in high matrix stiffness, high friction angle, and high shear dilation.

현장 열성능 평가시험을 통한 강관 에너지파일의 적용성 평가

이석재,최항석 한국 지열 · 수열에너지학회 2022 한국지열에너지학회논문집 Vol.18 No.2

A novel steel-pipe energy pile is introduced, in which the deformed rebars for main reinforcing are replaced with steel pipes in a large diameter cast-in-place energy pile. Here, the steel pipes act as not only reinforcements but also heat exchangers by circulating the working fluid through the hollow hole in the steel pipes. Under this concept, the steel-pipe energy pile can serve a role of supporting main structures and exchanging heat with surrounding mediums without installing additional heat exchange pipes. In this study, the steel-pipe energy pile was constructed in a test bed considering the material properties of steel pipes and the subsoil investigation. Then, the thermal performance test (TPT) in cooling condition was conducted in the constructed energy pile to investigate thermal performance. In addition, the thermal performance of the steel-pipe energy pile was compared with that of the conventional large diameter cast-in-place energy pile to evaluate its applicability. As a result, the steel-pipe energy pile showed 11% higher thermal performance than the conventional energy pile along with much simpler construction processes.

CSL(Cross-hole Sonic Logging) 시험 자료를 이용한 현장 타설말뚝 3D 영상화 기법 연구 및 프로그램개발

이재경,박종남,박인석,한원태 東亞大學校 建設技術硏究所 2005 硏究論文集 Vol.29 No.1

The CSL(Cross-hole Sonic Logging) is a method of the integrity test of cast-in-place pile. since it was introduced to domestic applications in early 1990s, it was been widely used at construction sites. Generally, We calculate the ultrasonic velocity by measuring the emission time between Tx-Rx probes moving at the same time while keeping vertical level equal in the tubes at the cast-in-placed pile for evaluating the pile integrity. We detect position, size and existence of weak zone by comparing results which are acquired in each ray-path profile. Vertical position of defect is comparatively correct, but horizontal position and size of defect is inaccurate. We studied 3D imaging techniques for pile integrity test by applying geotomography and Kriging. In this study, we have also developed pc-based software (CSL 3D Imager) for displaying of 3D images.

Influence of coil pitch on thermal performance of coil-type cast-in-place energy piles

Park, S.,Lee, S.,Lee, D.,Lee, S.S.,Choi, H. Elsevier Sequoia S.A 2016 Energy and buildings Vol.129 No.-

Recently, the energy pile has been introduced as a viable alternative to the conventional closed-loop vertical ground heat exchanger (GHEX). The energy pile contains a heat exchange pipe inside the pile foundation and allows a circulation of working fluid through the pipe inducing heat exchange with the ground formation. In this paper, a series of thermal performance tests was conducted on two coil-type cast-in-place energy piles with different coil pitches, 200mm and 500mm, to evaluate the effect of coil pitch on the heat exchange performance of energy piles. Thermal performance tests were carried out by applying intermittent (8h operating-16h pause) artificial cooling and heating loads with the aid of a constant-temperature water bath. The experimental result indicated that the heat exchange rate per pile length was not directly proportional to the installed pipe length because the tight coil pitch caused thermal interference between each pipe loop. In addition, a parametric study was conducted by computational fluid-dynamic (CFD) simulations to assess the effect of coil pitch and thermal interference on the thermal performance. The CFD model was verified by comparing the numerical simulation results with the field test data. Finally, an optimum coil pitch in the test bed condition was proposed considering the thermal performance and the economic feasibility of coil-type cast-in-place energy piles.

A simple approach for quality evaluation of non-slender, cast-in-place piles

Ray Ruichong Zhang 국제구조공학회 2008 Smart Structures and Systems, An International Jou Vol.4 No.1

This study proposes a conceptual framework of in-situ vibration tests and analyses for quality appraisal of non-slender, cast-in-place piles with irregular cross-section configuration. It evaluates a frequency index from vibration recordings to a series of impulse loadings that is related to total soil-resistance forces around a pile, so as to assess if the pile achieves the design requirement in terms of bearing capacity. In particular, in-situ pile-vibration tests in sequential are carried out, in which dropping a weight from different heights generates series impulse loadings with low-to-high amplitudes. The high-amplitude impulse is designed in way that the load will generate equivalent static load that is equal to or larger than the designed bearing capacity of the pile. This study then uses empirical mode decomposition and Hilbert spectral analysis for processing the nonstationary, short-period recordings, so as to single out with accuracy the frequency index. Comparison of the frequency indices identified from the recordings to the series loadings with the design-based one would tell if the total soil resistance force remains linear or nonlinear and subsequently for the quality appraisal of the pile. As an example, this study investigates six data sets collected from the in-situ tests of two piles in Taipu water pump project, Jiangshu Province of China. It concludes that the two piles have the actual axial load capacity higher than the designed bearing capacity. The true bearing capacity of the piles under investigation can be estimated with accuracy if the amplitude of impact loadings is further increased and the analyses are calibrated with the static testing results.