Effects of embedding depth and load eccentricity on lateral response of offshore monopiles in dense sand: A centrifuge study

Géotechnique ◽  
2021 ◽  
pp. 1-34
Author(s):  
Zhong-Sen Li ◽  
Matthieu Blanc ◽  
Luc Thorel
Keyword(s):  
Ground Level ◽  
Outer Diameter ◽  
Pivot Point ◽  
Dense Sand ◽  
Geotechnical Centrifuge ◽  
Incremental Method ◽  
Lateral Response ◽  
Fibre Bragg Gratings ◽  
Tension Compression Asymmetry ◽  
Analytical Program

Two model piles with outer diameter D = 50 mm are loaded laterally at 100×g in a large-beam geotechnical centrifuge. The normal strains on both the tensile and compressive sides are measured using fibre Bragg gratings. An incremental method is introduced to define the pivot point. The testing and analytical program enables the effect of the embedding depth and load eccentricity to be quantified. The key findings are as follows. 1) The piles generate asymmetric tensile and compressive strains during bending, and the tension-compression asymmetry becomes more pronounced at the pile toe and for shorter piles. 2) The piles transition from flexure to rotation as the embedding depth is decreased from 9D to 3D, where the uniqueness of the ground-level rotation and deflection (θg–yg) relationship disappears. 3) The reaction and deflection (P–y) relationship flattens with increasing embedding depth but seems independent of the load eccentricity.

scholarly journals Lateral Response of a Single Pile under Combined Axial and Lateral Cyclic Loading in Sandy Soil

2018 ◽  
Vol 4 (9) ◽  
pp. 1996 ◽  
Author(s):  
Muqdad Abdallah Kahribt ◽  
Jasim M. Abbas
Keyword(s):  
Lateral Displacement ◽  
Slenderness Ratio ◽  
Offshore Structures ◽  
Lateral Loading ◽  
Loading Conditions ◽  
Lateral Loads ◽  
Dense Sand ◽  
Lateral Response ◽  
Loading System ◽  
Vertical Displacements

According to practical situation, there have been limited investigations on the response of piles subjected to combined loadings especially when subjected to cyclic lateral loads. Those few studies led to contradictory results with regard to the effects of vertical loads on the lateral response of piles. Therefore, a series of experimental investigation into piles in dense sand subjected to combination of static vertical and cyclic lateral loading were conducted with instrumented model piles. The effect of the slenderness ratio (L/D) was also considered in this study (i.e. L/D= 25 and 40). In addition, a variety of two-way cyclic lateral loading conditions were applied to model piles using a mechanical loading system. One hundred cycles were used in each test to represent environmental loading such as offshore structures. It was found that under combined vertical and cyclic lateral loads the lateral displacement of piles decreased with an increase in vertical load whereas it causes large vertical displacements at all slenderness ratios. In addition, for all loading conditions the lateral, vertical (settlement and upward) displacements and bending moments increased as either the magnitude of cyclic load or the number of cycles increases. 

scholarly journals Using the Generalized Inverted Pendulum to Generate Less Energy-Consuming Trajectories for Humanoid Walking

2016 ◽  
Vol 63 (2) ◽  
pp. 245-262 ◽  
Author(s):  
Sahab Omran ◽  
Sophie Sakka ◽  
Yannick Aoustin
Keyword(s):  
Energy Consumption ◽  
Inverted Pendulum ◽  
Center Of Pressure ◽  
Ground Level ◽  
Vertical Position ◽  
Pivot Point ◽  
Joint Torques ◽  
Walking Gait ◽  
Consequent Reduction ◽  
New Feature

AbstractThis paper proposes an analysis of the effect of vertical position of the pivot point of the inverted pendulum during humanoid walking. We introduce a new feature of the inverted pendulum by taking a pivot point under the ground level allowing a natural trajectory for the center of pressure (CoP), like in human walking. The influence of the vertical position of the pivot point on energy consumption is analyzed here. The evaluation of a 3D Walking gait is based on the energy consumption. A sthenic criterion is used to depict this evaluation. A consequent reduction of joint torques is shown with a pivot point under the ground.

scholarly journals Interrogation of fibre Bragg gratings through a fibre optic rotary joint on a geotechnical centrifuge

2016 ◽  
Author(s):  
Ricardo Correia ◽  
Stephen W. James ◽  
Alec Marshall ◽  
Charles Heron ◽  
Sergiy Korposh
Keyword(s):  
Bragg Gratings ◽  
Fibre Optic ◽  
Geotechnical Centrifuge ◽  
Rotary Joint ◽  
Fibre Bragg Gratings

On the potential for using bridge natural frequencies to detect scour: an experimental study

2021 ◽  
Author(s):  
Kasun Kariyawasam ◽  
Campbell Middleton ◽  
James Talbot ◽  
Paul Fidler ◽  
Stuart Haigh ◽  
...  
Keyword(s):  
Natural Frequency ◽  
Natural Frequencies ◽  
Repair Process ◽  
Small Scale ◽  
Bridge Scour ◽  
Dense Sand ◽  
Geotechnical Centrifuge ◽  
Bridge Model ◽  
Experimental Findings ◽  
Bridge Failure

<p>Monitoring bridges for precursors of failure has the potential to improve their safety and resilience. However, the most prominent cause of bridge failure, scour, is difficult to monitor as it occurs underwater. The potential to identify scour by monitoring changes in the natural frequencies of a bridge is studied experimentally in this research. A field study was carried out on a bridge with pre- existing scour confined to a section of a piled pier foundation, which was monitored throughout a repair process involving controlled backfilling of the scoured region, i.e. scour in reverse. The changes in natural frequency due to backfilling of the scour hole were unable to be captured experimentally as the estimated magnitudes (9% and 6 % for the first and second modes respectively) were of the same order as the variability of the natural frequency estimates. In order to study the relationship between natural frequency and scour in a more controlled environment, a geotechnical centrifuge experiment was conducted to simulate scour in a small-scale integral bridge model in dense sand. The model showed a significant (up to 40 %) change in natural frequency as a result of a scour depth equivalent to 30 % of the piled foundation depth. These experimental findings suggest that natural frequencies can potentially aid in detecting extensive bridge scour for piled foundations, but it may be challenging to detect localised scour limited to only a small portion of a foundation.</p>

scholarly journals Experimental and numerical investigation of the effect of vertical loading on the lateral behaviour of monopiles in sand

2021 ◽  
Author(s):  
Qiang Li ◽  
Kenneth Gavin ◽  
Amin Askarinejad ◽  
Luke J Prendergast
Keyword(s):  
Slenderness Ratio ◽  
Offshore Wind ◽  
Combined Loading ◽  
Initial Stiffness ◽  
Dense Sand ◽  
Geotechnical Centrifuge ◽  
Lateral Capacity ◽  
Vertical Loading ◽  
Load Tests ◽  
Observed Behaviour

The influence of combined loading on the response of monopiles used to support offshore wind turbines (OWTs) is investigated in this paper. In current practice, resistance of monopiles to vertical and lateral loading is considered separately. As OWT size has increased, the slenderness ratio (pile length, L, normalised by diameter, D) has decreased, and foundations are tending towards intermediate footings with geometries between those of piles and shallow foundations. Whilst load interaction effects are not significant for slender piles, they are critical for shallow footings. Previous research on pile load interaction has resulted in conflicting findings, potentially arising from variations in boundary conditions and pile slenderness. In this study, monotonic lateral load tests were conducted in a geotechnical centrifuge on vertically loaded monopiles in dense sand. Results indicate that for piles with L/D = 5, increasing vertical loading improved pile initial stiffness and lateral capacity. A similar trend was observed for piles with L/D = 3, when vertical loading was below ≈ 45% of the pile’s ultimate vertical capacity. For higher vertical loads considered, results tended towards the behaviour observed for shallow footings. Numerical analyses conducted show that changes in mean effective stress are potentially responsible for the observed behaviour.

Physical modelling of the push-over capacity of a jack-up structure on sand in a geotechnical centrifuge

2009 ◽  
Vol 46 (2) ◽  
pp. 190-207 ◽  
Author(s):  
B. Bienen ◽  
M. J. Cassidy ◽  
C. Gaudin
Keyword(s):  
Wind Waves ◽  
Physical Modelling ◽  
Three Dimensions ◽  
Combined Loading ◽  
Silica Sand ◽  
Foundation Soil ◽  
Experimental Development ◽  
Dense Sand ◽  
Geotechnical Centrifuge ◽  
Jack Up

Offshore jack-up drilling rigs are subjected to loading from wind, waves, and current in addition to their self-weight. This applies combined loading in all six degrees-of-freedom in space on the footings. Although the foundation–soil interaction is crucial to the overall response of a jack-up structure, current state-of-the-art models to predict jack-up footing behaviour, developed using data from single footing experiments, have not been validated for such multi-footing systems under general combined loading. This paper introduces the experimental development of a three-legged model jack-up and loading apparatus designed to investigate the rig’s response — in particular the footing load paths — under combined loading in three dimensions. Push-over experiments were performed in a geotechnical beam centrifuge on silica sand. Experimental results of two tests on dense sand are discussed, highlighting differences in response and mode of failure depending on the loading direction of the jack-up. The importance of three-dimensional modelling is also stressed by experimentally demonstrating that the symmetric load case is not necessarily conservative.

scholarly journals Predicting the resistance profile of a spudcan penetrating sand overlying clay

2014 ◽  
Vol 51 (10) ◽  
pp. 1151-1164 ◽  
Author(s):  
Pan Hu ◽  
Dong Wang ◽  
Mark J. Cassidy ◽  
Sam A. Stanier
Keyword(s):  
Penetration Resistance ◽  
Clay Layer ◽  
Interface Shear ◽  
Element Analysis ◽  
Resistance Profile ◽  
Dense Sand ◽  
Geotechnical Centrifuge ◽  
Centrifuge Tests ◽  
Full Penetration ◽  
Stress Dependent

Assessment of the risk of punch-through failure of spudcan foundations on sand overlying clay requires prediction of the full penetration resistance profile, from touchdown and through punch-through to equilibrium of the vertical resistance at depth in the underlying clay layer. This study uses the Coupled Eulerian–Lagrangian approach, a large deformation finite element analysis method, to model the complete penetration resistance profile of a spudcan on sand overlying clay. The sand is modeled using the Mohr–Coulomb model, while the clay is modeled using a modified Tresca model to account for strain softening. The numerical method is then used to simulate a series of spudcan penetration tests, performed in a geotechnical centrifuge, on medium dense sand overlying clay. The punch-through behavior observed in the experiments is replicated, and the penetration resistance profiles from numerical analyses are generally a reasonable match to the experimental measurements. The influences of the sand layer height to foundation diameter ratio, sand–clay interface shear strength, and strength gradient in clay on the penetration resistance profiles are explored in a complementary parametric study. The penetration resistance in the underlying clay layer is well predicted using a simple linear expression for the bearing capacity factor for the spudcan and underlying sand plug. This expression is combined with an existing failure stress dependent model for predicting peak resistance to form a simplified method for prediction of the full penetration resistance profile. This new method provides estimates of the vertical penetration that the spudcan will run during the punch-through event. It is validated against both medium dense and dense sand centrifuge tests.

scholarly journals Influence of scour protection layers on the lateral response of monopile in dense sand

2022 ◽  
Vol 244 ◽  
pp. 110377
Author(s):  
Amin Askarinejad ◽  
Huan Wang ◽  
Giorgos Chortis ◽  
Ken Gavin
Keyword(s):  
Dense Sand ◽  
Lateral Response ◽  
Scour Protection

Effects of Vibration on the Preparation of Ultrathin Sections

1973 ◽  
Vol 31 ◽  
pp. 358-359
Author(s):  
Joseph M. Blum ◽  
Edward P. Gargiulo ◽  
J. R. Sawers
Keyword(s):  
Cutting Speed ◽  
Ground Level ◽  
Environmental Vibration ◽  
Block Face ◽  
Ultrathin Sections ◽  
Embedding Medium ◽  
Thickness Variations ◽  
Building Walls ◽  
Cutting Direction ◽  
Diamond Knife

It is now well-known that chatter (Figure 1) is caused by vibration between the microtome arm and the diamond knife. It is usually observed as a cyclical variation in “optical” density of an electron micrograph due to sample thickness variations perpendicular to the cutting direction. This vibration might be induced by using too large a block face, too large a clearance angle, excessive cutting speed, non-uniform embedding medium or microtome vibration. Another prominent cause is environmental vibration caused by inadequate building construction. Microtomes should be installed on firm, solid floors. The best floors are thick, ground-level concrete pads poured over a sand bed and isolated from the building walls. Even when these precautions are followed, we recommend an additional isolation pad placed on the top of a sturdy table.

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