Application of numerical simulation for the analysis and interpretation of pile-anchor system failure

Saleem, Masood Techno-Press 2015 Geomechanics & engineering Vol.9 No.6

Progressive increase in population causing land scarcity, which is forcing construction industry to build multistory buildings having underground basements. Normally, basements are constructed for parking facility. This research work evaluates important factors which have caused the collapse of pile-anchor system at under construction five star hotel. 21 m deep excavation is carried out, to have five basements, after installation of 600 mm diameter cast in-situ contiguous concrete piles at plot periphery. To retain piles and backfill, soil anchors are installed as pit excavation is proceeded. Before collapse, anchors are designed by federal highway administration procedure and four anchor rows are installed with three strands per anchor in first row and four in remaining. However, after collapse, system is modeled and analyzed in plaxis using mohr-coulomb method. It is investigated that in-appropriate evaluation of soil properties, additional surcharge loads, lesser number of strands per anchor, shorter grouted body length and shorter pile embedment depth caused large deformations to occur which governed the collapse of east side pile wall. To resume work, old anchors are assumed to be standing at one factor of safety and then system is analyzed using finite element approach. Finally, it is concluded to use four strands per anchor in first new row and five strands in remaining three with increase in grouted and un-grouted body lengths.

Soil Arch Evolution Characteristics and Parametric Analysis of Slope Anchored Anti-slide Pile

Sifeng Zhang,Chao Li,Hui Qi,Xingji Chen,Shuaishuai Ma 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.11

The soil arching effect can significantly impact the bearing characteristics of the slope anchored anti-slide pile. Therefore, it is very important to investigate the internal force characteristics of the soil arch and the mechanism of pile-soil interaction. In this paper, the evolution mechanism and influencing parameters of the soil arching effect of anchored anti-slide pile are analyzed, from a qualitative and quantitative perspective through model tests and numerical simulation methods. Findings are summarized as follows: 1) the formation and evolution of the soil arches can be roughly divided into three stages: the initial stage, the development and formation of soil arches, and the failure and re-formation of soil arches. The stable arch feet are firstly formed, and a complete arch is generated. Then the landslide thrust is transmitted to form a stable anti-slide pile structure, so the anchored anti-slide pile can play a role in slope anti-slide. 2) During the formation and evolution of the soil arches, the soil particles between the piles transfer the landslide thrust to the anti-slide pile through the soil arches. 3) The bearing capacity of the soil arches decreases with the increase of the pile spacing. And the increase of the soil compaction can efficiently increase the bearing capacity of the soil arches and give full play to the role of slope anti-slide. 4) The growing of soil particle size, the enhancement of soil particle friction coefficient, and the decreasing of corresponding soil void ratio are all conducive to the formation of the soil arches. These can benefit the anti-sliding effect of the anchored anti-slide piles in engineering application.

현장인발시험을 통한 Screw Abchor Pile의 인발저항특성

유충식(Yoo, Chung-Sik),김대현(Kim, Dae-Hyun) 한국지반공학회 2014 한국지반공학회논문집 Vol.30 No.1

This paper presents the results of an investigation into the pullout characteristics of screw anchor pile using field pullout tests. A series of field pullout tests were performed on screw anchor piles with different geometric characteristics such as shaft and screw diameters. The results indicated that screw anchor piles exhibited significantly higher pullout capacities compared with the same diameter piles without screw. Also observed is that the set-up effect and the grouting significantly increase pullout capacities, although the magnitude of the increase depends on the ground condition. In addition the applicability of prediction methods for helical pile pullout capacity to screw anchor piles was also examined. The results are presented in such a way that the pullout characteristics of screw anchor piles with different installation conditions can be identified. Practical implications of the findings are discussed.

해저케이블 매설 안전성 확보를 위한 토질에 따른 앵커 파일의 관입 특성 평가

김정훈(Jeong-Hun Kim),송창용(Chang Yong Song) 대한기계학회 2020 大韓機械學會論文集A Vol.44 No.5

해저케이블 매설 해역에서 앵커 파일의 낙하로 인한 해저케이블 파손 사고가 자주 보고되어 오고 있다. 앵커 파일의 낙하로부터 해저면에 매설되어 있는 해저케이블의 안전성을 확보할 수 있는 매설 심도를 결정하기 위해 앵커 파일의 지반 관입 특성이 합리적으로 산정되어야 한다. 본 연구에서는 수치시뮬레이션과 실증 시험을 통해 해저케이블이 매설되는 토질에 대한 앵커 파일의 관입 특성을 평가하였다. 앵커 파일의 토양 관입 현상에 대한 수치 시뮬레이션은 외연 시간 적분법 기반의 범용 비선형 유한요소 해석 코드를 이용하여 유체-구조 연성 해석 방법을 적용하였다. 앵커 파일이 관입되는 토질은 실제 해저케이블 매설 시공이 많이 이루어져 있는 국내 서남 해역의 대표 토질인 모래층과 점토층의 두가지 형태를 고려하였다. 수치 해석 결과, 점토 지반에서의 최대 관입량이 모래 지반보다 86% 이상 높게 나타났다. 실증 시험과 수치 해석의 오차율은 모래 지반과 점토 지반에서 각각 10.1%와 2.5%로 나타났고, 앵커 파일의 낙하 충격으로 인한 지반 관입에 대한 수치 해석임을 고려할 때 오차율은 합리적인 수준으로 판단되었다. Subsea cable damages caused by anchor pile dropping in the seabed have been reported frequently. The soil penetration characteristics of the anchor pile should be reasonably estimated to determine the burial depth capable for ensuring the safety of the subsea cable from anchor pile dropping. In this study, the penetration characteristics of the anchor pile for the soil in which the subsea cables are buried were evaluated through numerical simulations and verification tests. The numerical simulations of the soil penetration phenomena due to the anchor pile were conducted through the fluid–structure interaction analysis method using a general-purpose nonlinear finite element analysis code based on an explicit time integration method. The soils considered in this study were two types of sand and clay layers, which are representative soils for the southwestern seabed of Korea, where many subsea cables have been buried. Numerical analysis results showed that the maximum penetration in the clay layer was 86% higher than that in the sand layer. The error rates of the field test and numerical analysis were 10.1% and 2.5% in the sand and clay layers, respectively. The error rates were reasonable considering the numerical analysis results of the soil penetration due to the drop impact of the anchor pile.

축소모형실험을 이용한 사질토 지반에 근입된 Screw Anchor Pile의 인발저항특성

김대현,유충식 한국지반공학회 2013 한국지반공학회논문집 Vol.29 No.1

This paper presents the results of an investigation into the pull-out capacity characteristics of screw anchor piles. Theoretical background of screw anchor pile (SAP) was first discussed. A series of reduced-scale model tests were performed on a number of cases with different SAP geometries such as pitch and diameter of screw as well as relative density of the model ground. The applicability of the pull-out capacity prediction equations were also examined based on the test results. It was shown that the pitch of screw has negligible effect on the pull-out capacity, while the diameter of screw has relatively large effect on pull-out capacity under a given condition. Practical implications of the findings from this study are discussed in great detail.

콘크리트 파일앵커의 설치 매니퓨레이터의 개발을 위한 모형실험에 관한 연구

윤길수(GIL-SU YOON),김호상(HO-SANG KIM) 한국해양공학회 2004 韓國海洋工學會誌 Vol.18 No.1

Greater holding force of an anchor is required for maintaining the position of a larger floating structure. According to the series of model tests of pile anchors with movable fluke, the square type pile anchor, with fluke, showed more than 6 times of the uplift pulling force, compared to the same type pile anchor, without fluke. This uplift force is 100 times its weight. When the water depth is more than 40 m, it is difficult to install the pile anchor. For a convenient installation method, a type of manipulator is proposed for the separation of a weight and buoyancy controller, using TRIZ.

천해역 점성토 지반에 적합한 오탁방지막 기초 앵커

권기철(GI-CHUL KWEON),홍남식(NAM-SEEG HONG),송무효(MU-HYO SONG),최창규(CHANG-GYU CHOI) 한국해양공학회 2003 韓國海洋工學會誌 Vol.17 No.3

The Navy has tested the holding capacity of many kinds of anchors in order to propose the design chart for the holding capacity of drag-embedment anchors. The design chart is only applicable up to the cable bottom angle 6° when load is raised to the ultimate weight. However, the anchor experiences a significant uplift force when the angle is above 6° in shallow seas. In this paper, the procedure for the estimation of the holding capacity of anchors in mud is proposed. Drag-embedment anchors do not function well when there is a significant uplift component of load in soft seafloor materials, such as mud. Under these loading and seafloor conditions, gravity anchors seems to be more efficient. However, they are too heavy for their holding capacity. Therefore, suction pile (hollow concrete block) is more beneficial to the foundation of silt protector in shallow sea with mud seafloor materials.

현장인발시험 결과 분석을 통한 Screw Anchor Pile의 인발저항특성

유충식,김대현 한국지반공학회 2014 한국지반공학회논문집 Vol.30 No.1

본 논문에서는 현장인발재하시험을 통한 스크류 앵커 파일의 인발 저항 특성에 관한 연구내용을 제시하였다. 현장시험에서는 동일한 피치를 가지나 샤프트나 스크류 직경이 다른 스크류 앵커 파일에 대해 다양한 시공조건을 도출하고 이에 대한 시험을 수행하였다. 실험결과 스크류 앵커 파일은 스크류가 없는 파일에 비해 현저히 큰 인발저항력을발휘하는 것으로 검토되었으며 시간경과 효과와 그라우팅 여부에 따른 검토 결과 일반 파일과 유사하게 시간경과에따라 인발저항력이 증가하는 셋업효과와 그라우팅시 인발저항력 상승효과를 기대할 수 있는 것으로 분석되었다. 이와아울러 기존의 헬리컬 파일의 인발저항력 산정식을 스크류 앵커 파일의 인발저항력 평가에 있어서의 적용성을 검토하였으며 현장인발재하 시험결과를 다양한 측면에서의 상관관계를 파악할 수 있도록 제시하고 연구결과의 실무적 관점에서의 검토 내용을 기술하였다.

Analytical Parametric Study on Pullout Capacity of Embedded Suction Anchors

Sorrawas Boonyong,박기철,김인철 한국해안,해양공학회 2015 한국해안해양공학회 논문집 Vol.27 No.3

The Embedded Suction Anchor (ESA) is a type of permanent offshore foundation that is installed by a suction pile. To increase the loading capacity against pullout, three wings (vertical flanges) are attached along the circumference at 120 degrees apart. Analytical parametric study using the proposed analytical solution method has been conducted to identify the effects of several parameters that are thought to influence the behavior of ESAs. The analysis results show that the pullout capacity increases as the anchor depth and the soil strength increase, and decreases as the load inclination angle increases. The anchor having square projectional area and being pulled horizontally at the middle of its length provides the highest pullout capacity.

Numerical analysis of sheet pile wall structure considering soil-structure interaction

Jiang, Shouyan,Du, Chengbin,Sun, Liguo Techno-Press 2018 Geomechanics & engineering Vol.16 No.3

In this paper, a numerical study using finite element method with considering soil-structure interaction was conducted to investigate the stress and deformation behavior of a sheet pile wall structure. In numerical model, one of the nonlinear elastic material constitutive models, Duncan-Chang E-v model, is used for describing soil behavior. The hard contact constitutive model is used for simulating the behavior of interface between the sheet pile wall and soil. The construction process of excavation and backfill is simulated by the way of step loading. We also compare the present numerical method with the in-situ test results for verifying the numerical methods. The numerical analysis showed that the soil excavation in the lock chamber has a huge effect on the wall deflection and stress, pile deflection, and anchor force. With the increase of distance between anchored bars, the maximum wall deflection and anchor force increase, while the maximum wall stress decreases. At a low elevation of anchored bar, the maximum wall bending moment decreases, but the maximum wall deflection, pile deflection, and anchor force both increase. The construction procedure with first excavation and then backfill is quite favorable for decreasing pile deflection, wall deflection and stress, and anchor forces.