Conventional and centrifuge model studies of the moment carrying capacity of short pier foundations in clay

1995 ◽  
Vol 32 (6) ◽  
pp. 976-988 ◽  
Author(s):  
G.J.W. King ◽  
M. Laman
Keyword(s):  
Carrying Capacity ◽  
Three Dimensional ◽  
Model Tests ◽  
Rotational Stability ◽  
Moment Capacity ◽  
Centrifuge Model ◽  
Model Studies ◽  
Saturated Clay ◽  
The Moment ◽  
Centrifuge Model Tests

An experimental investigation into the moment carrying capacity of short rigid pier foundations in saturated clay is described. Scale models of square piers with different breadths and depths were used in both conventional and centrifugal studies. The results show that the relationships between moment and rotation are nonlinear but do not exhibit any peak values, and that moment limits, defined by limiting angular rotations, increase with increases in pier depth and breadth. Empirical equations are derived between moment carrying capacity and pier geometry, for a range of limiting rotations, and a very close fit is demonstrated between the moment–rotation relationships obtained using these equations and the actual data obtained from the model tests. It is shown that, at the same pier rotations, the moment carrying capacities observed in the centrifugal model tests are significantly larger than those in the conventional model tests. Numerical analyses of the prototype geometries were also carried out using a three-dimensional nonlinear finite-element computer program. The results are shown to provide satisfactory agreement with the moment–rotation behaviour and working limits observed in the centrifuge model tests. Thus, even though conventional modelling is usually legitimate for determining the immediate bearing capacity of rigid foundations in saturated clay, their rotational stability is shown to be significantly affected by self-weight stresses. Some of the existing methods for designing short piers subjected to moments are examined and compared with the results from the centrifuge model tests. Key words : pier foundation, clay, moment capacity.

Centrifuge and numerical modeling of axial load effects on piles in consolidating ground

2009 ◽  
Vol 46 (1) ◽  
pp. 10-24 ◽  
Author(s):  
S. Y. Lam ◽  
Charles W.W. Ng ◽  
C. F. Leung ◽  
S. H. Chan
Keyword(s):  
Axial Load ◽  
Load Transfer ◽  
Three Dimensional ◽  
Model Tests ◽  
Neutral Plane ◽  
Depth Level ◽  
Negative Skin Friction ◽  
Centrifuge Model ◽  
Soil Settlement ◽  
Centrifuge Model Tests

This paper reports the results of four centrifuge model tests that were undertaken to investigate behavior of floating piles subjected to negative skin friction (NSF) and to study effects of axial load on the load-transfer mechanism along single floating piles and shielded center piles inside a group of sacrificing piles. In addition, three-dimensional numerical analyses of the centrifuge model tests were carried out with elasto-plastic slip considered at the pile–soil interface. Prior to applying load, the measured neutral plane position of the single floating piles was located at approximately the three-quarter depth level of the embedded pile length. The neutral plane elevation shifts lower down the pile shaft as the distance of pile tip above the bearing stratum decreases. Under the application of axial load, the dragload generated by excessive soil settlement decreases and is eventually eliminated. The amount of axial load for complete NSF elimination does not seem to be significantly affected by the presence of sacrificing piles, but it does increase with end-bearing stiffness of the pile. Numerical simulation revealed that the hang-up effect is not altered by the application of axial load.

Evaluation of the seismic response of stone pagodas using centrifuge model tests

2014 ◽  
Vol 12 (6) ◽  
pp. 2583-2606 ◽  
Author(s):  
Heon-Joon Park ◽  
Dong-Soo Kim ◽  
Yun Wook Choo
Keyword(s):  
Seismic Response ◽  
Model Tests ◽  
Centrifuge Model ◽  
Centrifuge Model Tests

scholarly journals Evaluation of seismic behavior of box culvert buried in the ground through centrifuge model tests and numerical analysis

2019 ◽  
Vol 4 (2) ◽  
pp. 147-167 ◽  
Author(s):  
Hitoshi Yatsumoto ◽  
Yasuo Mitsuyoshi ◽  
Yasuo Sawamura ◽  
Makoto Kimura
Keyword(s):  
Numerical Analysis ◽  
Seismic Behavior ◽  
Model Tests ◽  
Centrifuge Model ◽  
Box Culvert ◽  
Centrifuge Model Tests

scholarly journals Modelling the embedment process during offshore pipe-laying on fine-grained soils

2013 ◽  
Vol 50 (1) ◽  
pp. 15-27 ◽  
Author(s):  
Z.J. Westgate ◽  
D.J. White ◽  
M.F. Randolph
Keyword(s):  
Deep Water ◽  
Small Amplitude ◽  
Model Tests ◽  
Soil Parameters ◽  
Sea State ◽  
Field Surveys ◽  
Centrifuge Model ◽  
Fine Grained ◽  
Displacement Patterns ◽  
Centrifuge Model Tests

Subsea pipelines are becoming an increasingly significant element of offshore hydrocarbon developments as exploration moves into deep-water environments further from shore. During the lay process, pipelines are subject to small amplitude vertical and horizontal oscillations, driven by the sea state and lay vessel motions. Centrifuge model tests have been used to simulate these small-amplitude lay effects, with varying degrees of idealization relative to the real lay process. In the soft soils found in deep water, pipe embedment can exceed a diameter or more, thus significantly affecting the lateral pipe–soil interaction, axial resistance, and thermal insulation. In this paper, results from centrifuge model tests are used to calibrate a model for calculating the dynamic embedment of a subsea pipeline. The model uses elements of plasticity theory to capture the effects of combined vertical and horizontal loading, and incorporates the softening of the surrounding soil as it is remoulded due to the pipeline motions. Influences from the lay rate, lay geometry, and sea state are included in the calculation process. The model is compared with observed as-laid pipeline embedment data from field surveys at three different offshore sites. Using site-specific soil parameters obtained from in situ testing and idealized pipe loads and motions to represent the load and displacement patterns during offshore pipe-laying, respectively, the model is shown to capture well the final as-laid embedment measured in the field surveys.

RESPONSE OF SOFT CLAY STRATA AND CLAY-PILE-RAFT SYSTEMS TO SEISMIC SHAKING

2007 ◽  
Vol 01 (03) ◽  
pp. 233-255 ◽  
Author(s):  
SUBHADEEP BANERJEE ◽  
SIANG HUAT GOH ◽  
FOOK HOU LEE
Keyword(s):  
Soft Clay ◽  
Ground Surface ◽  
Model Tests ◽  
Pile Foundations ◽  
Kaolin Clay ◽  
Natural Period ◽  
Soil System ◽  
Centrifuge Model ◽  
Inertial Loading ◽  
Centrifuge Model Tests

The behavior of pile foundations under earthquake loading is an important factor affecting the performance of structures. Observations from past earthquakes have shown that piles in firm soils generally perform well, while the performance of piles in soft or liquefied ground can raise some questions. Centrifuge model tests were carried out at the National University of Singapore to investigate the response of pile-soil system under three different earthquake excitations. Some initial tests were done on kaolin clay beds to understand the pure clay behavior under repetitive earthquake shaking. Pile foundations comprising of solid steel, hollow steel and hollow steel pile filled with cement in-fill were then embedded in the kaolin clay beds to study the response of clay-pile system. Superstructural inertial loading on the foundation was modeled by fastening steel weight on top of the model raft. The model test results show that strain softening and stiffness degradation feature strongly in the behaviour of the clay. In uniform clay beds without piles, this is manifested as an increase in resonance periods of the surface response with level of shaking and with successive earthquakes. For the pile systems tested, the effect of the surrounding soft clay was primarily to impose an inertial loading onto the piles, thereby increasing the natural period of the piles over and above that of the pile foundation alone. There is also some evidence that the relative motion between piles and soil leads to aggravated softening of the soil around the pile, thereby lengthening its resonance period of the soil further. The centrifuge model tests were back-analyzed using the finite element code ABAQUS. The analysis shows that the simple non-linear hypoelastic soil model gave reasonably good agreement with the experimental observations. The engineering implication arising from this study so far is that, for the case of relatively short piles in soft clays, the ground surface motions may not be representative of the raft motion. Other than the very small earthquakes, the raft motion has a shorter resonance period than the surrounding soil.

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