Cyclic lateral response and failure mechanisms of semi-rigid pile in soft clay: centrifuge tests and numerical modelling

2017 ◽  
Vol 54 (6) ◽  
pp. 806-824 ◽  
Author(s):  
Y. Hong ◽  
B. He ◽  
L.Z. Wang ◽  
Z. Wang ◽  
C.W.W. Ng ◽  
...  
Keyword(s):  
Failure Mechanisms ◽  
Soft Clay ◽  
Bending Moment ◽  
American Petroleum Institute ◽  
Flow Mechanism ◽  
Soil Stiffness ◽  
Centrifuge Tests ◽  
Rigid Pile ◽  
Lateral Response ◽  
Soil Flow

Previous studies on laterally loaded piles in clay have mainly focused on flexible and rigid piles. Little attention has been paid to semi-rigid piles (whose pile–soil stiffness lies somewhere between those of rigid and flexible piles), which may behave as either flexible piles or rigid piles, depending on the change in soil stiffness during cycling. This study aims to understand the cyclic lateral response of a repeatedly loaded semi-rigid pile in soft clay and the failure mechanisms of the soil around the pile, through a series of centrifuge model tests and three-dimensional finite element analyses using an advanced hypoplastic clay model. Numerical parametric studies were also performed to investigate the evolution of soil flow mechanisms with increasing pile rigidity. It is revealed that the semi-rigid pile behaved as if it were a flexible pile (i.e., flexural deformation dominated) during the first few cycles, but tended to behave like a rigid pile (i.e., rotational movement prevailed) during subsequent cycles, which progressively softened the surrounding soil. As a result, the mechanisms of soil flow around the semi-rigid pile exhibited an intermediate behaviour combining the mechanisms of both flexible and rigid piles. Three distinctive mechanisms were identified: a wedge-type mechanism near the surface, a full-flow mechanism (within the transverse sections) near the middle of the pile, and a rotational soil flow mechanism (in the vertical symmetrical plane of the pile) near the lower half of the pile. By ignoring the rotational soil flow mechanism, which has a much lower resistance than the full-flow mechanism, the American Petroleum Institute code (published in 2007) underestimated the cyclic bending moment and the lateral pile displacement by 10% and 69%, respectively. Application of jet grouting around the semi-rigid pile at shallow depth significantly altered the soil flow mechanism (i.e., it was a solely wedge-type mechanism around the grouted zone).

Effect of consolidation on responses of a single pile subjected to lateral soil movement

2015 ◽  
Vol 52 (6) ◽  
pp. 769-782 ◽  
Author(s):  
L.Z. Wang ◽  
K.X. Chen ◽  
Y. Hong ◽  
C.W.W. Ng
Keyword(s):  
Soft Clay ◽  
Bending Moment ◽  
Coefficient Of Consolidation ◽  
Construction Period ◽  
Soil Movement ◽  
Centrifuge Tests ◽  
Short Period ◽  
Lateral Soil Movement ◽  
Pile Response ◽  
Pile Length

Given extensive research carried out to study pile response subjected to lateral soil movement in clay, the effect of consolidation on the pile–soil interaction is rarely considered and systematically investigated. For this reason, four centrifuge tests were conducted to simulate construction of embankment adjacent to existing single piles in soft clay, considering two typical drainage conditions (i.e., drained and undrained conditions) and two typical pile lengths (i.e., relatively long pile and short pile). The centrifuge tests were then back-analyzed by three-dimensional coupled-consolidation finite element analyses. Based on reasonable agreements between the two, numerical parametric studies were conducted to systematically investigate and quantify the influence of construction rate and pile length on pile response. It is revealed that by varying drainage conditions, the piles respond distinctively. When the embankment is completed within a relatively short period (cvt/d2 < 2, where cv, t, and d denote the coefficient of consolidation, construction period, and pile diameter, respectively), the pile located adjacent to it deforms laterally away from the embankment. Induced lateral pile deflection (δ) and bending moment reduce with construction period. On the contrary, embankment constructed within a relatively long period (cvt/d2 > 200) leads the pile to deform laterally towards the embankment, with δ and bending moment increases with construction period. By halving the length of pile embedded in the drained ground, the maximum induced bending moment (BMmax) was slightly reduced (by 23%). On the other hand, shortening the length of the pile in the undrained ground is much more effective in reducing BMmax, i.e., halving pile length resulting in 78% reduction in bending moment. A new calculation chart, which takes various drainage conditions and pile lengths into account, was developed for estimation of BMmax.

scholarly journals Recent centrifuge modelling of offshore geotechnical problems at IWHR

2019 ◽  
Vol 92 ◽  
pp. 17001
Author(s):  
Jianhui Liang ◽  
Xianhui Song
Keyword(s):  
Hydraulic System ◽  
Soft Clay ◽  
Laser Scanner ◽  
Vertical Movement ◽  
Test Results ◽  
Centrifuge Modelling ◽  
Soil Stiffness ◽  
Centrifuge Tests ◽  
Load Cells ◽  
Geotechnical Problems

Centrifuge modelling has been proven to be an efficient and reliable approach for examining offshore geotechnical problems. This study reports the two series of centrifuge tests to understand the behaviour of spudcan penetration in a “soft-stiff-soft clay” stratigraphy and the behaviour of gravity anchor subjected to a lateral loading. A hydraulic system has been adopted to apply the large compressive and tensional load on the spudcan and gravity anchor, respectively. Load cells were installed on the base of the spudcan to directly measure the stress acting on the spudcan base. A 2D laser scanner was adopted to monitor the horizontal, vertical movement and tilting of the gravity anchor. The influence of the relative soil stiffness on the spudcan pentration behaviour and the soil deformation and interaction with the gravity anchor are discussed based on the centrifuge test results.

Validation of Soil Models for Wellhead Fatigue Analysis

2017 ◽  
Author(s):  
Kathrine Gregersen ◽  
Guttorm Grytøyr ◽  
Jerome De Sordi ◽  
Kristoffer H. Aronsen
Keyword(s):  
Global Analysis ◽  
Limit State ◽  
Soft Clay ◽  
Bending Moment ◽  
Full Scale ◽  
Data Uncertainty ◽  
Ultimate Limit State ◽  
Initial Stiffness ◽  
Soil Stiffness ◽  
Drilling Rigs

The focus on wellhead fatigue has increased over the last decade, both in terms of consequences of failure and methods for prediction. Wellhead Fatigue is a well integrity concern when drilling subsea wells, especially with exposure to harsh environments and extreme environmental loads. The concern increases with the use of deep water drilling rigs in shallow water. As a result, full-scale measurement has been employed in several projects to document the actual load levels experienced by the subsea wellheads during drilling. Input data uncertainty has always been a challenge when using global analysis to estimate wellhead fatigue. Instrumentation opens new possibilities to validate the global analysis results. In several measurement campaigns, it is observed that the response below the lower flex joint of the drilling riser is overestimated in global analyses. It has been suggested by some that this is an indication that global riser analyses are highly conservative. However, as suggested in previous papers (i.e. Russo et.al, ref.[11]), this discrepancy could also be explained by non-appropriate modelling of the conductor lateral soil resistance for small displacements, leading to underestimation of the soil stiffness. The soil spring model also called p-y curves are usually built following the API recommended methods that are established for foundation piles. Piles are designed for ultimate limit state focusing on displacement conditions that are not optimal for fatigue analyses, as a large part of the total fatigue damage actually occurs for small displacements. A literature review is conducted, to review the basis for the API springs, and alternative p-y-curves with increased initial stiffness have been suggested. Based on the available information four alternative soil models have been proposed. The work performed by BP on p-y curves modelling for laterally loaded conductors (ref. [2]) has been an important input for this paper. In order to illustrate the effect of initial soil stiffness in the global analysis, the present study focuses on conductors installed in homogenous and normally consolidated to slightly overconsolidated clays. This limits somewhat the number of available sites with relevant conditions for full-scale measurements, at least on the Norwegian Continental Shelf, where it is common to find layers of sand interspersed between the clay layers. However, Statoil have conducted one campaign with full-scale measurements at a location with corresponding clay conditions. In this paper, the API formula for “soft clay” and four alternative soil models, have been used as input to a global riser analysis, and the results are validated against measurements. It is the response of the lower stack, in terms of rotations and displacements of BOP, LMRP and LRS, that has been investigated. In addition, the load, in terms of wellhead bending moment has been compared. Results shows that for this given case, the Matlock-API formulation overestimates the lower stack response, compared with full-scale measurements. Comparing the proposed soil models shows that the global response is affected by selection of soil model. The soil formulations outlined by Jeanjean (2009) and Zakeri et.al (2015) give the best match with full-scale measurements for this case.

Bearing Behaviour of Spudcan Foundation on Uniform Clay During Deep Penetration

2004 ◽  
Author(s):  
M. S. Hossain ◽  
Y. Hu ◽  
M. F. Randolph
Keyword(s):  
Bearing Capacity ◽  
Failure Mechanisms ◽  
Model Tests ◽  
Deep Penetration ◽  
Centrifuge Tests ◽  
Soil Failure ◽  
Flow Mechanisms ◽  
Soil Flow ◽  
Piv Analysis ◽  
Penetration Depths

In order to design a safe spudcan foundation, it is important to predict its bearing behaviour accurately based on the corresponding soil failure mechanisms. Thus, the performance of spudcan foundation, during deep penetration into uniform soil, is investigated physically and numerically. In physical testing, a series of centrifuge tests are carried out in a drum centrifuge. The half-spudcan model tests with subsequent Particle Image Velocimetry (PIV) analysis are conducted to reveal soil failure mechanisms during spudcan penetration. And the full spudcan model tests are conducted to investigate the bearing capacity of spudcan. In numerical simulation, FE analyses are performed considering smooth and rough soilspudcan interface. From the physical tests and numerical analyses, it is observed that the cavity is formed above the spudcan as it is penetrating into uniform clay. At certain penetration depths, the soil underneath the spudcan starts to flow back on top of the spudcan, which leads the spudcan to be embedded with further penetration. Soil flow mechanisms, at various penetration depths, play a key role in footing bearing response. And the ultimate undrained bearing capacity factor of Nc = 10.5 (smooth) and 12 (rough) are obtained at deep penetration.

Development of Experimental P-Y Curves from Centrifuge Tests for Piles Subjected to Static Loading and Liquefaction-Induced Lateral Spreading

2020 ◽  
Vol 14 (1) ◽  
Author(s):  
Milad Souri
Keyword(s):  
Static Loading ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Pressure Ratio ◽  
Lateral Spreading ◽  
American Petroleum Institute ◽  
Unique Contribution ◽  
Pile Groups ◽  
Centrifuge Tests ◽  
Centrifuge Models

The results of five centrifuge models were used to evaluate the response of pile-supported wharves subjected to inertial and liquefaction-induced lateral spreading loads. The centrifuge models contained pile groups that were embedded in rockfill dikes over layers of loose to dense sand and were shaken by a series of ground motions. The p-y curves were back-calculated for both dynamic and static loading from centrifuge data and were compared against commonly used American Petroleum Institute p-y relationships. It was found that liquefaction in loose sand resulted in a significant reduction in ultimate soil resistance. It was also found that incorporating p-multipliers that are proportional to the pore water pressure ratio in granular materials is adequate for estimating pile demands in pseudo-static analysis. The unique contribution of this study is that the piles in these tests were subjected to combined effects of inertial loads from the superstructure and kinematic loads from liquefaction-induced lateral spreading.

Character Analysis of Balance and Imbalance of Varying Rigidity of Rigid Pile Composite Foundation under Seismic Load

2014 ◽  
Vol 1065-1069 ◽  
pp. 19-22
Author(s):  
Zhen Feng Wang ◽  
Ke Sheng Ma
Keyword(s):  
Finite Element ◽  
Bending Moment ◽  
Horizontal Displacement ◽  
Element Model ◽  
Composite Foundation ◽  
Seismic Load ◽  
Seismic Loads ◽  
Element Analysis ◽  
Rigid Pile ◽  
Rigid Pile Composite Foundation

Based on ABAQUS finite element analysis software simulation, the finite element model for dynamic analysis of rigid pile composite foundation and superstructure interaction system is established, which selects the two kinds of models, by simulating the soil dynamic constitutive model, selecting appropriate artificial boundary.The influence of rigid pile composite foundation on balance and imbalance of varying rigidity is analyzed under seismic loads. The result shows that the maximum bending moment and the horizontal displacement of the long pile is much greater than that of the short pile under seismic loads, the long pile of bending moment is larger in the position of stiffness change. By constrast, under the same economic condition, the aseismic performance of of rigid pile composite foundation on balance of varying rigidity is better than that of rigid pile composite foundation on imbalance of varying rigidity.

Comportement de pieux d'essais instrumentés sous charge horizontale

1993 ◽  
Vol 30 (1) ◽  
pp. 1-11
Author(s):  
R. Frank ◽  
H. Zervogiannis ◽  
S. Christoulas ◽  
V. Papadopoulos ◽  
N. Kalteziotis
Keyword(s):  
Pile Foundation ◽  
Bending Moment ◽  
Standard Penetration Test ◽  
American Petroleum Institute ◽  
Full Scale ◽  
Test Method ◽  
Cohesionless Soil ◽  
Penetration Test ◽  
Cohesionless Soils ◽  
Final Design

This paper describes the behaviour of two test piles (one bored and postgrouted and one simply bored, both 31.7 m long and 0.75 m in diameter) subjected to horizontal loads. These full-scale pile tests were carried out for the actual design of the pile foundation of a pier of the Evripos cable-stayed bridge. This bridge will link the Euboea Island to mainland Greece. The two piles have already been subjected to bearing capacity tests under axial loadings. The inclinometer measurements, taken during the present tests, yielded, in particular, the deformed shape of the piles as well as the bending moments. Conclusions could be drawn for the final design of the pile foundation with respect to horizontal loadings. Furthermore, various calculation methods using p–y reaction curves for cohesionless soils have been checked: the Ménard pressuremeter method, the method of the American Petroleum Institute recommendations, and the Standard penetration test method of Christoulas. These pile tests show that simple measurements, taken on construction sites, can yield interesting results on the actual behaviour of horizontally loaded piles. Key words : pile, horizontal loading, full-scale test, horizontal loads, bending moment, subgrade reaction modulus, p–y curve, cohesionless soil, Standard penetration test, pressuremeter test.

scholarly journals Experimental observation on laterally loaded pile in unsaturated silty soil

2019 ◽  
Vol 56 (11) ◽  
pp. 1545-1556 ◽  
Author(s):  
L.M. Lalicata ◽  
A. Desideri ◽  
F. Casini ◽  
L. Thorel
Keyword(s):  
Water Table ◽  
Ground Surface ◽  
Bending Moment ◽  
Data Interpretation ◽  
Partial Saturation ◽  
Laterally Loaded Piles ◽  
Silty Soil ◽  
Centrifuge Tests ◽  
Surface Data ◽  
Laterally Loaded

An experimental study was carried out to investigate the effects of soil partial saturation on the behaviour of laterally loaded piles. The proposed study was conducted by means of centrifuge tests at 100g, where a single vertical pile was subjected to a combination of static horizontal load and bending moment. The study was conducted on a silty soil characterized with laboratory testing under saturated and unsaturated conditions. During flight, two different positions of water table were explored. The influence of density was investigated by compacting the sample with two different void ratios. Finally, the effects of a variation of saturation degree on the pile response under loading were studied by raising the water table to the ground surface. Data interpretation allows drawing different considerations on the effects of partial saturation on the behaviour of laterally loaded piles. As expected, compared to saturated soils, partial saturation always leads to a stiffer and resistant response of the system. However, the depth of the maximum bending moment is related to the position of the water table and the bounding effects induced by partial saturation appear to be more important for loose soils.

Effect of Bend Angle on Gross Plastic Deformation of Pipe Bends: A Finite Element Based Study

2015 ◽  
Author(s):  
Anindya Bhattacharya ◽  
Sachin Bapat ◽  
Hardik Patel ◽  
Shailan Patel
Keyword(s):  
Plastic Deformation ◽  
Finite Element ◽  
Failure Mechanisms ◽  
Bending Moment ◽  
Bend Angle ◽  
Piping System ◽  
Plastic Collapse ◽  
Collapse Load ◽  
Pipe Bend ◽  
Bend Angles

Bends are an integral part of a piping system. Because of the ability to ovalize and warp they offer more flexibility when compared to straight pipes. Piping Code ASME B31.3 [1] provides flexibility factors and stress intensification factors for the pipe bends. Like any other piping component, one of the failure mechanisms of a pipe bend is gross plastic deformation. In this paper, plastic collapse load of pipe bends have been analyzed for various bend parameters (bend parameter = tRbrm2) under internal pressure and in-plane bending moment for various bend angles using both small and large deformation theories. FE code ABAQUS version 6.9EF-1 has been used for the analyses.

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