scholarly journals Simplified analysis of chord and brace effects on jack-up leg penetration for preloading in soft clay

2018 ◽  
Vol 55 (12) ◽  
pp. 1900-1907 ◽  
Author(s):  
R. Aagesen ◽  
E.T.R. Dean ◽  
F.H. Lee ◽  
Y.P. Li
Keyword(s):  
Soft Clay ◽  
Centrifuge Model ◽  
Beneficial Effects ◽  
Codes Of Practice ◽  
Disturbed Soil ◽  
Form Part ◽  
Simplified Analysis ◽  
Jack Up ◽  
Special Case ◽  
Centrifuge Model Tests

The main codes of practice governing jack-up preloading presently do not consider the possibility of beneficial effects of soil resistance generated by leg chord and leg brace members as they move downwards through disturbed soil that has been squeezed past the spudcan to form part of the backfill. This paper argues that these effects can be significant for the special case of deep penetrations in soft clay. An approximate method of estimating the effects is proposed and discussed. Results are found to be broadly consistent with recent centrifuge model tests and numerical analyses. Further work is recommended to explore these potentially important and certainly complex effects.

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.

Numerical Simulations of Dynamic Embedment During Pipe Laying on Soft Clay

2009 ◽  
Author(s):  
D. Wang ◽  
D. J. White ◽  
M. F. Randolph
Keyword(s):  
Soft Clay ◽  
Simple Approach ◽  
Published Data ◽  
Vertical Load ◽  
Centrifuge Model ◽  
Upper Limit ◽  
Different Types ◽  
Element Approach ◽  
Pipeline Design ◽  
Centrifuge Model Tests

Prediction of the as-laid embedment of a pipeline, which affects many aspects of pipeline design, is complicated by the dynamic motions that occur during the lay process. These motions cause pipelines to embed deeper than predicted based on static penetration models, as the seabed soils are both softened and physically displaced by the pipeline motion. This paper describes the results of 2D numerical analyses using a large displacement finite element approach aimed at quantifying pipeline embedment due to cyclic lateral motion at various fixed vertical load levels. The validity of the numerical results is first assessed by comparison with published data from centrifuge model tests in two different types of clay. A parametric study varying the normalized vertical load is then presented, which suggests a simple approach for estimating an upper limit to the dynamic embedment.

Time-dependent behavior of pile groups by staged construction of an adjacent embankment on soft clay

2004 ◽  
Vol 41 (4) ◽  
pp. 644-656 ◽  
Author(s):  
Sangseom Jeong ◽  
Donghee Seo ◽  
Jinhyung Lee ◽  
Joogbai Park
Keyword(s):  
Soft Clay ◽  
Time Dependent ◽  
Bending Moments ◽  
Pile Groups ◽  
Centrifuge Model ◽  
Surcharge Loading ◽  
Short And Long Term ◽  
Centrifuge Model Tests ◽  
Soil Movements

A series of centrifuge model tests were performed to investigate the behavior of pile groups subjected to lateral soil movements by surcharge loading from approach embankments. The emphasis was on quantifying the time-dependent response in terms of deflections, bending moments, and earth pressures acting on pile groups during embankment construction and over short- and long-term periods after embankment construction. A variety of instruments were used to examine the soil–pile interaction for pile groups adjacent to surcharge loads. Through these studies, it is found that pile cap deflections and bending moments developed to their maximum values under the short-term surcharge loading and decreased gradually to minimum values under the long-term loading. The ground settlement reached its maximum value under long-term loading, however, due to the consolidation of soft clay. It is also found that the lateral mean pressure acting on the pile is about 0.75 and 0.35 times the surcharge load q (= γH, where γ is the unit weight of the soil and H is the height of the embankment) under short- and long-term loading, respectively.Key words: time-dependent response, lateral soil movements, pile groups, centrifuge model tests, surcharge loads, soft clay.

scholarly journals Centrifuge Model Tests on Double Propped Wall Excavation in Soft Clay

1999 ◽  
Vol 39 (3) ◽  
pp. 75-87 ◽  
Author(s):  
Jiro Takemura ◽  
Midori Kondoh ◽  
Taichi Esaki ◽  
Masayuki Kouda ◽  
Osamu Kusakabe
Keyword(s):  
Soft Clay ◽  
Model Tests ◽  
Centrifuge Model ◽  
Centrifuge Model Tests

Centrifuge Model Study on the Effect of Lattice Leg and Sleeve on the Postconsolidation Bearing Capacity of Spudcan Foundation

2018 ◽  
Vol 140 (4) ◽  
Author(s):  
Yu Ping Li ◽  
Jiang Tao Yi ◽  
Fook Hou Lee
Keyword(s):  
Bearing Capacity ◽  
Model Tests ◽  
Capacity Enhancement ◽  
Centrifuge Model ◽  
Model Study ◽  
Operation Period ◽  
Capacity Improvement ◽  
Jack Up ◽  
Two Sides ◽  
Centrifuge Model Tests

Up to now, the postconsolidation bearing capacity enhancement of jack-up spudcan foundation has been explored using centrifuge model tests and numerical analyses, which however ignored the realistic jack-up lattice leg. This paper investigates both typical lattice leg and sleeve effects on the postconsolidation spudcan bearing capacity using centrifuge model tests, by replicating the entire process of spudcan in normally consolidated clay: “penetration–unloading–consolidation–repenetration.” The experimental results show that the lattice leg and sleeve affect the spudcan bearing capacity in two sides compared with spudcan without leg. First, it increases the transient bearing capacity during initial spudcan penetration; second, less postconsolidation bearing capacity improvement is yielded by the presence of the leg. The former effect is of importance on the prediction of jack-up leg penetration, and the latter effect would suggest a lower risk of spudcan punch-through for realistic offshore jack-up rig during preloading and operation period.

scholarly journals Centrifuge Model Tests on Soft Clay Improved by Fabri-Packed Sand Drain.

1993 ◽  
pp. 107-115
Author(s):  
Tadashi KATAYAMA ◽  
Sosuke HITACHI ◽  
Masaki KITAZUME ◽  
Naohiro AIHARA
Keyword(s):  
Soft Clay ◽  
Model Tests ◽  
Centrifuge Model ◽  
Centrifuge Model Tests

Study of Soil Responses Adjacent to Jack-Up Spudcan Foundation

2010 ◽  
Author(s):  
Yi Xie ◽  
C. F. Leung ◽  
Y. K. Chow
Keyword(s):  
Soft Clay ◽  
Digital Camera ◽  
Extraction Process ◽  
Processing Technique ◽  
Image Processing Technique ◽  
Image Velocimetry ◽  
Adjacent Field ◽  
Jack Up ◽  
Soil Responses ◽  
Centrifuge Model Tests

Centrifuge model tests have been conducted to investigate the soil responses during penetration, jack-up rig operation and extraction of a jack-up spudcan foundation in soft clay. The penetration and extraction process of a half-cut spudcan were captured by a digital camera at 100g. Image processing technique involving Particle Image Velocimetry was then applied to evaluate the induced soil movements in the adjacent field of the moving spudcan. The development of pore pressures adjacent to the spudcan was also monitored.

Using a thin sand layer to ease spudcan extraction in clay

2015 ◽  
Vol 52 (8) ◽  
pp. 1023-1034 ◽  
Author(s):  
Muhammad Shazzad Hossain ◽  
Stefanus Safinus ◽  
Mark J. Cassidy
Keyword(s):  
Penetration Depth ◽  
Soft Clay ◽  
Extraction Process ◽  
Sand Layer ◽  
Pipe System ◽  
Bottom Face ◽  
Jack Up ◽  
Underlying Soil ◽  
Insight Into ◽  
Centrifuge Model Tests

Difficulties are encountered, in soft clay and silt sediments, during extraction of the spudcan foundations of “mobile” jack-up rigs. This paper reports results from centrifuge model tests undertaken to provide a simple, effective, and practical means for easing spudcan extraction in soft normally consolidated and lightly overconsolidated clay. The tests were carried out on model spudcans of two different geometries typically used in the field. The spudcans were extracted from penetrations of 2∼3 diameters and after an operation period of ∼19 months. The measured pore pressure at the bottom face of the spudcan during extraction process provided insight into the development of suction at the interface between the spudcan base and the underlying soil. The tests were carried out with and without a sand layer placed locally in between the spudcan and the mudline at the onset of penetration. In the field, a gravel layer can be placed by means of a flexible fall pipe system. The presence of a sand layer (with a thickness less than the spudcan tip length) beneath the penetrated spudcan assisted in easing leg extraction difficulties allowing the base suction to be reduced by 73%∼83% and hence the breakout force by 31%∼32%. For a given penetration depth, the installation resistance was also increased by 24%∼26%. This yielded a 15%∼17% reduction of spudcan penetration depth under a given preload and hence the breakout force as much as 50%. Guidelines and cautions for using the proposed measure are provided. Additional advantages of the new recommended method in enhancing the efficiency of the conventional measures of lessening spudcan extraction difficulties are discussed.

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