Le Chi Hung - Academia.edu (original) (raw)
Papers by Le Chi Hung
Http Dx Doi Org 10 1080 1064119x 2012 735346, Oct 28, 2013
A series of three-dimensional finite element analyses was conducted to investigate the effects of... more A series of three-dimensional finite element analyses was conducted to investigate the effects of the embedment depth, the non-homogeneity of clay, and combined loads on the undrained bearing capacities of bucket foundations. The undrained shear strength and Young's modulus of clay were assumed to vary linearly with depth. Meanwhile, the stress-strain response of clay was simulated using the Tresca criterion. The numerical modeling adopted in this study was verified by comparing the calculated capacities with those from previous studies. Based on the results of the finite element analyses over 1400 cases, new equations were proposed to calculate the vertical, horizontal, and moment bearing capacities as well as to define the capacity envelopes under general combined loads. Comparisons with the capacity envelopes of previous studies showed that the proposed equations properly predicted the bearing capacities of the bucket foundation by considering the effects of the non-homogeneity of clay and embedment depth.
Ocean Engineering, 2015
Offshore wind turbine towers experience large base moments because of wind and wave loading. The ... more Offshore wind turbine towers experience large base moments because of wind and wave loading. The flexibility of the foundation should be considered when analyzing the structural response of towers. Previous studies showed that conventional p-y curves are not suitable in designing the foundation. More advanced methods, such as the finite element method, are necessary to model the offshore wind turbine foundation. In addition, these studies focused on the analysis of the foundation itself, so the effect on the structural response of the tower merits further research. The present study aimed to compare different foundation modeling approaches, focusing on their effects on the structural response of the wind turbine tower. We integrated wind turbine aerodynamic simulation with different models of the foundation. We confirmed that ignoring the flexibility of the foundation caused significant error in wind turbine tower behavior. Between the p-y curve-based model and finite element-based model, the change in maximum moment was insignificant, but the maximum tilt angle increased over 14% in the finite element model. Therefore, the finite element approach is recommended to obtain a conservative design when large tilt angles may cause serviceability issues.
As CPT penetration tends to show a similar behavior to that of pile driving, a number of methods ... more As CPT penetration tends to show a similar behavior to that of pile driving, a number of methods for estimating the toe bearing capacity of piles based on CPT data have been proposed. To evaluate the applicability of the methods in this country, a total of 172 dynamic load tests data on PHC piles and 82 CPT data at a site in the Nakdong River estuary were collected. A specific four-step procedure was adopted for the selection of the reliable data, and statistical techniques were then applied to the analysis of the applicability. The results indicated that among a total of 10 CPT-based methods applied, the best one is the Aoki method (1975), followed by the LCPC (1982), ICP (2005) methods and others.
Suction buckets have been widely used for offshore structures such as anchors for floating facili... more Suction buckets have been widely used for offshore structures such as anchors for floating facilities, and the foundations of offshore wind energy turbines. However, the design guidelines for suction buckets have not been clearly suggested. Therefore, this study performed the numerical analysis by using ABAQUS (2010) to evaluate bearing capacities and load-movement behaviors of the suction bucket in NC clay. For the numerical analysis, the depth ratio L/D (L=embedded length of skirt; D=diameter of a bucket) was varied from 0.25 to 1.0. The analysis results showed that the L/D ratio has a significant effect on the bearing capacity, and the vertical and horizontal capacities respectively increased by about 40% and 90%, when L/D ratio increased from 0.25 to 1.0. At the vertical loading, the bucket showed the similar failure mode with a deep foundation, so the shaft and toe resistances can be separately evaluated. At the horizontal loading, the bucket with L/D=O.25 showed the sliding fa...
Recently, the research on renewable energy against depletion of fossil fuel have been actively ca... more Recently, the research on renewable energy against depletion of fossil fuel have been actively carried out in the world. Especially, offshore wind turbines are very economical and innovative technology. However, offshore wind turbines experience large base moments due to the wind and wave loading, so the monopile with large diameter needs to be applied. For the economical design of the large diameter pile, it is important to consider the flexibility of the foundation to estimate the maximum moment accurately, based on studies conducted so far. In this paper, the foundation was modeled using the finite element method in order to better describe the large diameter effect of a monopile and the results were compared with those of p-y method. For the examples studied in this paper, the change in maximum moment was insignificant, but the maximum tilt angle from the finite element method was over 14% larger than that of p-y method. Therefore, the finite element approach is recommended to m...
Recently, as large structures, which should support large design loads have been constructed, the... more Recently, as large structures, which should support large design loads have been constructed, the study on the large diameter composite pile becomes necessary. The large diameter composite pile has the diameter over 700mm and consists of two parts of the upper steel pipe pile and the lower PHC pile by a mechanical joint. In this research, to analyze the bearing capacity and the material strength of the composite pile, three dimensional numerical analyses were performed. First, the numerical modeling method was verified by comparing the calculated load-movement curves of the pile with those of the field pile load tests. Then, a total of twelve analyses were performed by varying pile diameter and loading direction for three pile types of PHC, steel pipe and composite piles. The results showed that the vertical and the horizontal load-movement curves of the composite pile were identical with those of the steel pipe pile and the horizontal material strength of the composite pile was 60-...
Asian And Pacific Coasts 2011, 2011
Three-dimensional finite element analyses were performed to evaluate the undrained bearing capaci... more Three-dimensional finite element analyses were performed to evaluate the undrained bearing capacities of suction bucket foundations in homogenous clay. The loading conditions were vertical (V), horizontal (H), and combined (V-H). The effect of the aspect ratios (skirt length to diameter ratios, L/D) of a suction bucket on the bearing capacities was investigated. Dimensionless and normalized failure envelopes in a V-H load space were developed. The sizes and shapes of failure envelopes, as well as the failure mechanism, were clearly shown to be dependent on the aspect ratios of the foundations.
Ocean Engineering, 2014
Tripod bucket foundations are being used as alternative foundations to resist large horizontal an... more Tripod bucket foundations are being used as alternative foundations to resist large horizontal and moment loadings from offshore wind turbines. The bearing capacity of the tripod bucket foundation differs particularly from that of the single bucket foundation due to the interaction among individual buckets of the tripod. This paper investigated the group effect of tripod bucket foundations in clay by three-dimensional finite element analysis. Parametric studies were performed varying the spacing between each bucket foundation, embedded depth of the bucket foundation, and loading directions. Normally consolidated clay under an undrained condition was modeled using a linear elastic-perfectly plastic model obeying the Tresca failure criterion. The undrained shear strength and Young 0 s modulus of clay were assumed to linearly increase with depth. The group efficiency factor, which is the ratio of the bearing capacity of the tripod bucket foundation to that of the single bucket foundation, was evaluated based on finite element analysis for vertical, horizontal and moment loadings. Results showed that the efficiency factors were functions of the bucket spacing and embedment depth of the foundations.
Ocean Engineering, 2014
A series of three-dimensional finite element analyses was conducted to evaluate the combined hori... more A series of three-dimensional finite element analyses was conducted to evaluate the combined horizontal-moment bearing capacities of tripod bucket foundations for offshore wind turbines in undrained clay. The tripod bucket foundation consists of three single bucket foundations, which enhance the bearing capacities because of the effect of the interaction among individual buckets. A linear-elastic perfectly plastic model, which obeys the Tresca failure criterion, was used to simulate the stress-strain response of clay, in which Young's modulus and undrained shear strength were assumed to increase linearly with depth. The effects of bucket spacing, embedment depth, vertical load, and nonhomogeneity of clay on the combined horizontal-moment capacities were analyzed. Finally, the design equation of the combined horizontal-moment capacities was developed as a function of the aspect ratios (skirt length/diameter) of the foundations.
Ocean Engineering, 2012
The present paper presents the results of three-dimensional finite element analyses of bucket fou... more The present paper presents the results of three-dimensional finite element analyses of bucket foundations in normally consolidated uniform clay under undrained conditions. The stress-strain response of clay was simulated using the Tresca criterion. The bearing capacities were calculated and found to be largely dependent on the aspect ratio of the bucket foundation. Based on the results of the analyses, new equations were proposed for calculating vertical and horizontal bearing capacities. In the proposed equations, the vertical capacity consisted of an end-bearing resistance and a skin friction resistance, whereas the horizontal capacity consisted of a normal resistance, a radial shear resistance, and a base shear resistance. Comparison of the numerical results showed that the proposed equations properly predicted the capacities of the bucket foundations in uniform or non-uniform clays.
Marine Georesources & Geotechnology, 2014
A series of three-dimensional finite element analyses was conducted to investigate the effects of... more A series of three-dimensional finite element analyses was conducted to investigate the effects of the embedment depth, the non-homogeneity of clay, and combined loads on the undrained bearing capacities of bucket foundations. The undrained shear strength and Young's modulus of clay were assumed to vary linearly with depth. Meanwhile, the stress-strain response of clay was simulated using the Tresca criterion. The numerical modeling adopted in this study was verified by comparing the calculated capacities with those from previous studies. Based on the results of the finite element analyses over 1400 cases, new equations were proposed to calculate the vertical, horizontal, and moment bearing capacities as well as to define the capacity envelopes under general combined loads. Comparisons with the capacity envelopes of previous studies showed that the proposed equations properly predicted the bearing capacities of the bucket foundation by considering the effects of the non-homogeneity of clay and embedment depth.
This paper presents a study on applicability of predicting toe bearing capacities from cone penet... more This paper presents a study on applicability of predicting toe bearing capacities from cone penetration test (CPT) for PHC (pretensioned spun high-strength concrete) driven piles into deep sandy deposits in the Nakdong River deltaic area west of Busan City in South Korea. Using toe bearing capacities obtained from pile driving analyzer (PDA) tests as reference values, which were reliably calibrated by on-site O-cell tests, the applicability of the CPT-based methods was evaluated using a statistical rank index (RI). A total of 82 piezocone penetration test soundings and 190 PDA test piles were used for reliability analysis in this study. Three correction steps were applied to obtain reliable PDA and CPT data sets before ranking is carried out. The RI index is combined from four criteria: (1) the best-fit line, (2) the arithmetic mean and standard deviation, (3) the cumulative probabilities, and (4) the log-normal and his-togram distributions. Based on these criteria the performance of some SPT-based methods in the literature is evaluated.
Http Dx Doi Org 10 1080 1064119x 2012 735346, Oct 28, 2013
A series of three-dimensional finite element analyses was conducted to investigate the effects of... more A series of three-dimensional finite element analyses was conducted to investigate the effects of the embedment depth, the non-homogeneity of clay, and combined loads on the undrained bearing capacities of bucket foundations. The undrained shear strength and Young's modulus of clay were assumed to vary linearly with depth. Meanwhile, the stress-strain response of clay was simulated using the Tresca criterion. The numerical modeling adopted in this study was verified by comparing the calculated capacities with those from previous studies. Based on the results of the finite element analyses over 1400 cases, new equations were proposed to calculate the vertical, horizontal, and moment bearing capacities as well as to define the capacity envelopes under general combined loads. Comparisons with the capacity envelopes of previous studies showed that the proposed equations properly predicted the bearing capacities of the bucket foundation by considering the effects of the non-homogeneity of clay and embedment depth.
Ocean Engineering, 2015
Offshore wind turbine towers experience large base moments because of wind and wave loading. The ... more Offshore wind turbine towers experience large base moments because of wind and wave loading. The flexibility of the foundation should be considered when analyzing the structural response of towers. Previous studies showed that conventional p-y curves are not suitable in designing the foundation. More advanced methods, such as the finite element method, are necessary to model the offshore wind turbine foundation. In addition, these studies focused on the analysis of the foundation itself, so the effect on the structural response of the tower merits further research. The present study aimed to compare different foundation modeling approaches, focusing on their effects on the structural response of the wind turbine tower. We integrated wind turbine aerodynamic simulation with different models of the foundation. We confirmed that ignoring the flexibility of the foundation caused significant error in wind turbine tower behavior. Between the p-y curve-based model and finite element-based model, the change in maximum moment was insignificant, but the maximum tilt angle increased over 14% in the finite element model. Therefore, the finite element approach is recommended to obtain a conservative design when large tilt angles may cause serviceability issues.
As CPT penetration tends to show a similar behavior to that of pile driving, a number of methods ... more As CPT penetration tends to show a similar behavior to that of pile driving, a number of methods for estimating the toe bearing capacity of piles based on CPT data have been proposed. To evaluate the applicability of the methods in this country, a total of 172 dynamic load tests data on PHC piles and 82 CPT data at a site in the Nakdong River estuary were collected. A specific four-step procedure was adopted for the selection of the reliable data, and statistical techniques were then applied to the analysis of the applicability. The results indicated that among a total of 10 CPT-based methods applied, the best one is the Aoki method (1975), followed by the LCPC (1982), ICP (2005) methods and others.
Suction buckets have been widely used for offshore structures such as anchors for floating facili... more Suction buckets have been widely used for offshore structures such as anchors for floating facilities, and the foundations of offshore wind energy turbines. However, the design guidelines for suction buckets have not been clearly suggested. Therefore, this study performed the numerical analysis by using ABAQUS (2010) to evaluate bearing capacities and load-movement behaviors of the suction bucket in NC clay. For the numerical analysis, the depth ratio L/D (L=embedded length of skirt; D=diameter of a bucket) was varied from 0.25 to 1.0. The analysis results showed that the L/D ratio has a significant effect on the bearing capacity, and the vertical and horizontal capacities respectively increased by about 40% and 90%, when L/D ratio increased from 0.25 to 1.0. At the vertical loading, the bucket showed the similar failure mode with a deep foundation, so the shaft and toe resistances can be separately evaluated. At the horizontal loading, the bucket with L/D=O.25 showed the sliding fa...
Recently, the research on renewable energy against depletion of fossil fuel have been actively ca... more Recently, the research on renewable energy against depletion of fossil fuel have been actively carried out in the world. Especially, offshore wind turbines are very economical and innovative technology. However, offshore wind turbines experience large base moments due to the wind and wave loading, so the monopile with large diameter needs to be applied. For the economical design of the large diameter pile, it is important to consider the flexibility of the foundation to estimate the maximum moment accurately, based on studies conducted so far. In this paper, the foundation was modeled using the finite element method in order to better describe the large diameter effect of a monopile and the results were compared with those of p-y method. For the examples studied in this paper, the change in maximum moment was insignificant, but the maximum tilt angle from the finite element method was over 14% larger than that of p-y method. Therefore, the finite element approach is recommended to m...
Recently, as large structures, which should support large design loads have been constructed, the... more Recently, as large structures, which should support large design loads have been constructed, the study on the large diameter composite pile becomes necessary. The large diameter composite pile has the diameter over 700mm and consists of two parts of the upper steel pipe pile and the lower PHC pile by a mechanical joint. In this research, to analyze the bearing capacity and the material strength of the composite pile, three dimensional numerical analyses were performed. First, the numerical modeling method was verified by comparing the calculated load-movement curves of the pile with those of the field pile load tests. Then, a total of twelve analyses were performed by varying pile diameter and loading direction for three pile types of PHC, steel pipe and composite piles. The results showed that the vertical and the horizontal load-movement curves of the composite pile were identical with those of the steel pipe pile and the horizontal material strength of the composite pile was 60-...
Asian And Pacific Coasts 2011, 2011
Three-dimensional finite element analyses were performed to evaluate the undrained bearing capaci... more Three-dimensional finite element analyses were performed to evaluate the undrained bearing capacities of suction bucket foundations in homogenous clay. The loading conditions were vertical (V), horizontal (H), and combined (V-H). The effect of the aspect ratios (skirt length to diameter ratios, L/D) of a suction bucket on the bearing capacities was investigated. Dimensionless and normalized failure envelopes in a V-H load space were developed. The sizes and shapes of failure envelopes, as well as the failure mechanism, were clearly shown to be dependent on the aspect ratios of the foundations.
Ocean Engineering, 2014
Tripod bucket foundations are being used as alternative foundations to resist large horizontal an... more Tripod bucket foundations are being used as alternative foundations to resist large horizontal and moment loadings from offshore wind turbines. The bearing capacity of the tripod bucket foundation differs particularly from that of the single bucket foundation due to the interaction among individual buckets of the tripod. This paper investigated the group effect of tripod bucket foundations in clay by three-dimensional finite element analysis. Parametric studies were performed varying the spacing between each bucket foundation, embedded depth of the bucket foundation, and loading directions. Normally consolidated clay under an undrained condition was modeled using a linear elastic-perfectly plastic model obeying the Tresca failure criterion. The undrained shear strength and Young 0 s modulus of clay were assumed to linearly increase with depth. The group efficiency factor, which is the ratio of the bearing capacity of the tripod bucket foundation to that of the single bucket foundation, was evaluated based on finite element analysis for vertical, horizontal and moment loadings. Results showed that the efficiency factors were functions of the bucket spacing and embedment depth of the foundations.
Ocean Engineering, 2014
A series of three-dimensional finite element analyses was conducted to evaluate the combined hori... more A series of three-dimensional finite element analyses was conducted to evaluate the combined horizontal-moment bearing capacities of tripod bucket foundations for offshore wind turbines in undrained clay. The tripod bucket foundation consists of three single bucket foundations, which enhance the bearing capacities because of the effect of the interaction among individual buckets. A linear-elastic perfectly plastic model, which obeys the Tresca failure criterion, was used to simulate the stress-strain response of clay, in which Young's modulus and undrained shear strength were assumed to increase linearly with depth. The effects of bucket spacing, embedment depth, vertical load, and nonhomogeneity of clay on the combined horizontal-moment capacities were analyzed. Finally, the design equation of the combined horizontal-moment capacities was developed as a function of the aspect ratios (skirt length/diameter) of the foundations.
Ocean Engineering, 2012
The present paper presents the results of three-dimensional finite element analyses of bucket fou... more The present paper presents the results of three-dimensional finite element analyses of bucket foundations in normally consolidated uniform clay under undrained conditions. The stress-strain response of clay was simulated using the Tresca criterion. The bearing capacities were calculated and found to be largely dependent on the aspect ratio of the bucket foundation. Based on the results of the analyses, new equations were proposed for calculating vertical and horizontal bearing capacities. In the proposed equations, the vertical capacity consisted of an end-bearing resistance and a skin friction resistance, whereas the horizontal capacity consisted of a normal resistance, a radial shear resistance, and a base shear resistance. Comparison of the numerical results showed that the proposed equations properly predicted the capacities of the bucket foundations in uniform or non-uniform clays.
Marine Georesources & Geotechnology, 2014
A series of three-dimensional finite element analyses was conducted to investigate the effects of... more A series of three-dimensional finite element analyses was conducted to investigate the effects of the embedment depth, the non-homogeneity of clay, and combined loads on the undrained bearing capacities of bucket foundations. The undrained shear strength and Young's modulus of clay were assumed to vary linearly with depth. Meanwhile, the stress-strain response of clay was simulated using the Tresca criterion. The numerical modeling adopted in this study was verified by comparing the calculated capacities with those from previous studies. Based on the results of the finite element analyses over 1400 cases, new equations were proposed to calculate the vertical, horizontal, and moment bearing capacities as well as to define the capacity envelopes under general combined loads. Comparisons with the capacity envelopes of previous studies showed that the proposed equations properly predicted the bearing capacities of the bucket foundation by considering the effects of the non-homogeneity of clay and embedment depth.
This paper presents a study on applicability of predicting toe bearing capacities from cone penet... more This paper presents a study on applicability of predicting toe bearing capacities from cone penetration test (CPT) for PHC (pretensioned spun high-strength concrete) driven piles into deep sandy deposits in the Nakdong River deltaic area west of Busan City in South Korea. Using toe bearing capacities obtained from pile driving analyzer (PDA) tests as reference values, which were reliably calibrated by on-site O-cell tests, the applicability of the CPT-based methods was evaluated using a statistical rank index (RI). A total of 82 piezocone penetration test soundings and 190 PDA test piles were used for reliability analysis in this study. Three correction steps were applied to obtain reliable PDA and CPT data sets before ranking is carried out. The RI index is combined from four criteria: (1) the best-fit line, (2) the arithmetic mean and standard deviation, (3) the cumulative probabilities, and (4) the log-normal and his-togram distributions. Based on these criteria the performance of some SPT-based methods in the literature is evaluated.