• Digital Contents
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• no.5 s.144
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• pp.24-27
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• 2005

‘PC방들은 손님의 발길이 뚝 끊기 면서 폐업하는 곳이 늘어난다. 전국에 17개나 되던 사이버대학들도 내년부터는 신입생을 모집 하지 않는다고 발표하고, 언론사들은 인터넷 미디어 부서를 정리하기 시작한다. 관공서 앞에서는 공짜로 인터넷을 사용하기 위 해 줄이 늘어서 있다.’사용한 만큼 금액을 지불하는‘인터넷 종량제’가 시행된 이후의 가상 시나리오다. 최근 도마 위에 오른 종 량제에 대한 우려의 목소리가 높다. 종량제를 둘러싼 찬반논쟁을 살펴봤다.

• Journal of the Korean Geotechnical Society
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• v.17 no.1
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• pp.47-56
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• 2001

본 논문에서는 단일 및 군말뚝의 수평변위를 예측하기 위하여 신경망 학습속도의 향상과 지역 최소점 수렴을 방지하는 Readjusting 기법을 적용한 인공신경망을 도입하였다. 이 인공신경망을 M-EBPNN 이라고 한다. M-EBPNN에 의한 결과는 낙동강 모래지반에서 단일 및 군말뚝에 대하여 수행한 일련의 모형실험결과와 비교하였으며, 그리고 신경망의 학습속도와 지역 최소점의 수렴성을 평가하기 위하여 오류 역전파 신경망(EBPNN)의 결과와도 비교 분석하였다. M-EBPNN의 적용성 검증을 위하여 200개의 모형실험결과들을 이용하였으며, 신경망의 구조는 EBPNN의 구조와 동일한 한 개의 입력층과 두 개의 은닉층 그리고 한 개의 출력층으로 구성되었다. 전체 데이터의 25%, 50% 그리고 75% 결과는 각각 신경망의 학습에 이용되었으며 학습에 이용하지 않은 데이터들은 예측에 이용되었다. 그리고, 신경망의 최적학습을 위하여 적합한 은닉층의 뉴런 수와 학습률은 EBPNN에서 결정한 값들을 본 신경망에 이용하였다. 해석결과들에 의하면, 동일한 학습패턴에서의 M-EBPNN이 학습 반복횟수는 EBPNN 보다 최고 88% 감소하였으며 지역 최소점에 수렴하는 현상은 거의 나타나지 않았다. 따라서, 인공신경망 모델이 수평하중을 받는 말뚝의 수평변위 예측에 적용될 수 있는 가능성을 보여 주었다.

• Geotechnical Engineering
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• v.13 no.2
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• pp.137-154
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• 1997

Piling engineers in limit state design should consider both capacity of a pile and settlements of pile for stability of a structure. This paper analyzes the prediction of the settlements of single piles and nine-group piles installed at an overconsolidated clay site by common prediction methods and cone penetrometer test data obtained closely at pile locations. The effects of Young's modulus, which varies spatially in soil profile, on estimating the set tlements of piles have been investigated briefly. The predicted settlements for single piles and nine-pile group by using simple linear elan tic methods, Vesic's method and Poulos's method, overestimated overalls the measured valroes, and the assumption of Youngs modulus, which are to be varied linearly through the soil layers. did not significantly affect the settlement predictions.

• Journal of the Korean Geotechnical Society
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• v.32 no.12
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• pp.15-22
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• 2016

The magnitude of the lateral resistance that resists the lateral movement of the pile is controlled by the amount of the pile movement and the strength and stiffness of soil. In this paper, we proposed an equation which produces the ultimate lateral resistance of the laterally loaded single pile in sand using the strain wedge model of the soil deformation. The ultimate lateral resistance in strain wedge model is composed of earth pressure of wedge rear, the shear resistance on the side of the wedge, and the frictional resistance between pile and ground. The ultimate lateral resistance determined by the proposed equation was compared with the Ashour, F.D.M., field test in sand. As a result, the error of the proposed equation and Ashour theory, field test, F.D.M were respectively 1.03%, 0.40~3.32%, 6.02%.

• Geotechnical Engineering
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• v.14 no.5
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• pp.143-162
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• 1998

In the present study, a procedure to predict the depth from the ground surface to the center of bulging failure zone in each of the square granular group piles under a rigid mat foundation is proposed. This analytical procedure is established on the basis of the conical modeling of bulging failure shape and the replacement ratio of soft foundation soils. considering the effect of a share of procedure to estimate the ultimate cylindrical pressure in the area reinforced with granular piles and the ultimate bearing capacity of each of granular piles in group. This analytical procedure is also established on the basis of the pre-determined depth to the zone of bulging failure and an iterative solution technique. Finally the analytical procedures proposed in this study are verified by analyzing the results of 3D finite element analyses, and the predictions of ultimate bearing capacity of granular piles are compared with the results obtained from the tests, empirical equation and 3D finite element analyses.

• Journal of the Korean Geotechnical Society
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• v.25 no.7
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• pp.23-33
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• 2009

In this study the characteristics of piled raft was investigated by using both centrifuge and numerical modeling. The ultimate bearing capacities of single pile, unpiled raft, freestanding pile group and piled raft were compared in order to investigate load sharing of each element : pile and raft. The comparison determined parameters to simply evaluate the ultimate bearing capacity of piled raft. Centrifuge test results were simulated by numerical simulation to verify the parameters.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.6
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• pp.637-652
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• 2015

In the present work, a number of three-dimensional (3D) parametric numerical analyses have been carried out to study the influence of tunnelling on the behaviour of adjacent piles considering the transverse distance of the pile tip from the tunnel. Single piles and $5{\times}5$ piles inside a group with a spacing of 2.5d were considered, where d is the pile diameter. In the numerical modelling, several key issues, such as the tunnelling-induced pile settlements, the interface shear stresses, the relative shear displacements, the axial pile forces, the apparent factors of safety and zone of influence have been rigorously analysed. It has been found that when the piles are inside the influence zone, the pile head settlements are increased up to about 111% compared to those computed from the Greenfield condition. Larger pile settlements and smaller axial pile forces are induced on the piles inside the pile groups than those computed from the single piles since the piles responded as a block with the surrounding ground. Also tensile pile forces are induced associated with the upward resisting skin friction at the upper part of pile and the downward acting skin friction at the lower part of pile. On the contrary, when the piles were outside the influence zone, tunnelling-induced compressive pile forces developed. Based on computed load and displacement relation of the pile, the apparent factor of safety of the piles was reduced up to about 45%. Therefore the serviceability of the piles may be substantially reduced. The pile behaviour, when considering the single piles and the pile groups with regards to the influence zone, has been analysed by considering the key features in great details.

• Journal of the Korean Geotechnical Society
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• v.15 no.6
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• pp.239-249
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• 1999

In this study, experimental work has been carried out to investigate the effect of lateral soil movement on passive piles. This paper consists mainly of two parts: the first, performance of a series of laboratory experiments on a single pile and one-row pile groups, and the second, comparison between the measured and the predicted results. In the laboratory experiments, a quadrilateral soil movement profile was imposed on model piles embedded in both sandy soils and weathered soils. The maximum bending moment and pile deflection induced in passive piles were found to be highly dependent on pile stiffness, pile spacing, relative densities and pile head fixity condition. It was shown that the group effect might either increase or decrease the maximum bending moment and pile deflection, depending on the aforementioned influence factors. Based on the results obtained, a spacing-to-diameter ratio of 7.0 seems to be large enough to eliminate the group effect, and a pile in such a case behaves essentially the same as a single pile.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.2
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• pp.485-495
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• 2017

A development of underground space is very useful solution to slove problem occurred from ground surface enlargement in urban areas due to the growth of population, tunnelling is the most popular way and widely used. Researches regarding tunneling-induced pile-soil interactive behaviour have been conducted by many researchers. A study on pile axial force distribution due to tunnelling through laboratory model test, however, is being rarely carried out. In this study, therefore, authors investigate ground behaviour due to tunnelling below grouped pile subjected vertical load as well as pile axial force distribution. A concept of volume loss is used to express tunnel excavation, which is normally applied to 1~2% for tunnelling in soft ground. In this study, however, 10% of that applied to investigate failure mechanism. As a result of laboratory model test, a decrease of pile axial force occurs at 1.5% of volume loss, settlement of grouped pile is 1.2~4.7 times greater than the adjacent ground surface one. Ground deformations at 1.5% of volume loss are measured using Close Range Photogrammetry and compared with results from numerical analysis.

• Journal of Korean Tunnelling and Underground Space Association
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• v.14 no.4
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• pp.337-356
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• 2012

Three-dimensional (3D) numerical analyses have been performed to study the behaviour of single piles and grouped piles to adjacent tunnelling in the lateral direction of the pile. In the numerical analyses, the interaction between the tunnel, the pile and the soil next to the piles and shear transfer mechanism have been analysed allowing soil slip at the pile-soil interface by using interface elements. The study includes the shear stresses at the soil next to the pile, the axial force distributions on the pile and the pile settlement. It has been found that existing elastic solutions may not accurately estimate the pile behaviour since several key issues are excluded. Due to changes in the shear transfer between the pile and the soil next to the pile with tunnel advancement, the shear stresses and axial force distributions along the pile change drastically. Downward shear stress develops above the tunnel springline while upward shear stress is mobilised below the tunnel springline, resulting in a compressive force on the pile. In addition, mobilisation of shear strength at the pile-soil interface was found to be a key factor governing pile-soil-tunnelling interaction. It has been found that grouped piles are less influenced by the tunnelling than the single pile in terms of the axial pile forces. The reduction of apparent allowable pile capacity due to pile settlement resulted from the tunnelling seemed to be insignificant.