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.

Time-Dependent Changes in Excitability After One-Trial Conditioning of Hermissenda

1997 ◽  
Vol 78 (6) ◽  
pp. 3460-3464 ◽  
Author(s):  
Terry Crow ◽  
Vilma Siddiqi
Keyword(s):  
Time Dependent ◽  
Control Group ◽  
Type B ◽  
Control Groups ◽  
Phototactic Behavior ◽  
Parallel Processes ◽  
Short And Long Term ◽  
A Site ◽  
Different Levels

Crow, Terry and Vilma Siddiqi. Time-dependent changes in excitability after one-trial conditioning of Hermissenda. J. Neurophysiol. 78: 3460–3464, 1997. The visual system of Hermissenda has been studied extensively as a site of cellular plasticity produced by classical conditioning. A one-trial conditioning procedure consisting of light paired with the application of serotonin (5-HT) to the exposed, but otherwise intact, nervous system produces suppression of phototactic behavior tested 24 h after conditioning. Short- and long-term enhancement (STE and LTE) of excitability in identified type B photoreceptors is a cellular correlate of one-trial conditioning. LTE can be expressed in the absence of STE suggesting that STE and LTE may be parallel processes. To examine the development of enhancement, we studied its time-dependent alterations after one-trial conditioning. Intracellular recordings from identified type B photoreceptors of independent groups collected at different times after conditioning revealed that enhanced excitability follows a biphasic pattern in its development. The analysis of spikes elicited by 2 and 30 s extrinsic current pulses at different levels of depolarization showed that enhancement reached a peak 3 h after conditioning. From its peak, excitability decreased toward baseline control levels 5–6 h after conditioning followed by an increase to a stable plateau at 16 to 24 h postconditioning. Excitability changes measured in cells from unpaired control groups showed maximal changes 1 h posttreatment that rapidly decremented within 2 h. The conditioned stimulus (CS) elicited significantly more spikes 24 h postconditioning for the conditioned group as compared with the unpaired control group. The analysis of the time-dependent development of enhancement may reveal the processes underlying different stages of memory for this associative experience.

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.

Behaviour of friction piles in soft sensitive clays

1980 ◽  
Vol 17 (2) ◽  
pp. 203-224 ◽  
Author(s):  
R. Blanchet ◽  
F. Tavenas ◽  
R. Garneau
Keyword(s):  
Precast Concrete ◽  
Soft Clay ◽  
Load Test ◽  
Pile Groups ◽  
Test Program ◽  
Shear Creep ◽  
Soft Clays ◽  
The North ◽  
Effective Stress Analysis

During the construction of heavy structures, such as bridges and overpasses, on soft clays on the north shore of the St. Lawrence Valley, a detailed load test program on friction piles was performed to establish the characteristics of the most suitable type of pile and to study its long-term behaviour. Three types of piles, timber, steel pipe with closed end, and precast concrete Herkules H-420 piles, were tested. Four timber piles driven in a group and submitted to a 712 kN load served to study the long-term settlement of a small group of piles. Three deep settlement gauges were installed in the centre of this group for measuring settlements in clay at various depths.This test program was completed by the instrumentation of two bridge piers in order to verify the behaviour of larger groups of piles.The paper presents the results of the test piles, the long-term behaviour (4 years) of the bridge pier foundations resting on friction piles in soft clay, and the interpretation of the results.This study shows that the pore pressures induced by pile driving are related to the pre-consolidation of the clay and that they are much larger for tapered piles. It is demonstrated that the effective stress analysis method proposed in 1976 by Meyerhof determines adequately the ultimate pile bearing capacity, but that the effect of the timber pile taper doubles the skin friction.The settlement analysis of pile groups shows that settlements are due to the reconsolidation of the clay and shear creep deformations in the clay close to the pile wall.

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.

Delayed arteriolar relaxation after prolonged agonist exposure: functional remodeling involving tyrosine phosphorylation

2003 ◽  
Vol 285 (2) ◽  
pp. H849-H856 ◽  
Author(s):  
Michael A. Hill ◽  
Simon J. Potocnik ◽  
Luis A. Martinez-Lemus ◽  
Gerald A. Meininger
Keyword(s):  
Tyrosine Phosphorylation ◽  
Prolonged Exposure ◽  
Time Dependent ◽  
Physiological Salt Solution ◽  
Microtubule Network ◽  
Biochemical Alterations ◽  
Dependent Behavior ◽  
Functional Remodeling ◽  
Short And Long Term

Although arteriolar contraction is dependent on Ca2+-induced myosin phosphorylation, other mechanisms including Ca2+ sensitization and time-dependent phenomena such as cytoskeletal and cellular reorganization may contribute to contractile events. We hypothesized that if arteriolar smooth muscle exhibits time-dependent behavior this may be manifested in differences in relaxation after short- and long-term exposure to contractile agonists. Studies were conducted in isolated arterioles pressurized to 70 mmHg. In initial experiments ( n = 10), rate of relaxation was measured after acute (5 min) or prolonged (4 h) exposure to 5 μM norepinephrine (NE). Prolonged exposure to NE resulted in significantly ( P < 0.05) increased time for relaxation in physiological salt solution. Rapid relaxation of vessels exposed to NE for 4 h was observed after superfusion with 0 mM Ca2+ buffer, indicating that the alteration in relaxation was reversible and Ca2+ dependent. A similarly impaired dilation was not observed with 4-h exposure to KCl (75 mM). To determine mechanisms contributing to the effects of prolonged NE exposure, studies were performed in the presence of the microtubule depolymerizing agent demecolcine (10 μM) or a series of tyrosine phosphorylation inhibitors. Although demecolcine caused significant vasoconstriction ( P < 0.05) and potentiated NE vasoconstriction, it did not prevent the effect of long-term NE exposure on relaxation. Genistein, although having no effect on acute NE-induced contraction, concentration-dependently inhibited prolonged NE constriction. Similarly, Src (PP1) and p42/44 MAP kinase (PD-98059) inhibitors prevented maintenance of long-term NE contraction. The data indicate that prolonged exposure to NE induces biochemical alterations that impair relaxation after removal of the agonist. The contractile effects are Ca2+ dependent and involve tyrosine phosphorylation but do not appear to involve the polymerization state of the microtubule network.

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.

Ultimate Soil Pressures for Pile Groups in Soft Clay Subjected to Lateral Soil Movements

2008 ◽  
Vol 2 (1) ◽  
pp. 42-51 ◽  
Author(s):  
L. F. Miao ◽  
A.T.C. Goh ◽  
K.S. Wong ◽  
C.I. Teh
Keyword(s):  
Soft Clay ◽  
Pile Groups ◽  
Soil Movements

Failure of a Test Embankment On a Sensitive Champlain Clay Deposit

1974 ◽  
Vol 11 (1) ◽  
pp. 142-164 ◽  
Author(s):  
P. La Rochelle ◽  
B. Trak ◽  
F. Tavenas ◽  
M. Roy
Keyword(s):  
Research Program ◽  
Factor Of Safety ◽  
Soft Clay ◽  
New Approach ◽  
Short And Long Term ◽  
Undrained Strength ◽  
The Stability ◽  
Long Term Behavior ◽  
Test Embankment

The present paper reports on the failure of a test embankment built on a soft, sensitive, and cemented clay in Saint-Alban, Quebec. The embankment was built as a first stage of a research program aimed at studying the short and long term behavior of embankments on soft clay foundations.A complete description of the embankment, of the instrumentation, and of the failure is given, followed by the analysis of the failure performed on the basis of different assumptions of fill behavior and of vane strength values mobilized in the clay crust. The analyses show that the assumptions of full mobilization of friction in the fill seems to be the most representative of the fill behavior in the present case and that a suitable factor of safety is obtained only when a reduction of vane strength is assumed to act in the crust.A new approach based on the residual undrained strength is suggested and seems to offer some potential as a valuable means of analyzing the stability of embankments on clay foundations.

Association of adrenal hormone metabolites and mortality over a 6-year follow-up in COPD patients with acute exacerbation

2018 ◽  
Vol 56 (4) ◽  
pp. 669-680 ◽  
Author(s):  
Seline Zurfluh ◽  
Manuela Nickler ◽  
Manuel Ottiger ◽  
Christian Steuer ◽  
Alexander Kutz ◽  
...  
Keyword(s):  
Cox Regression ◽  
Time Dependent ◽  
Chronic Obstructive ◽  
Short Term ◽  
Therapeutic Implications ◽  
Adrenal Hormone ◽  
Copd Patients ◽  
Short And Long Term ◽  
Long Term Mortality

Abstract Background: The release of hormones from the adrenal gland is vital in acute and chronic illnesses such as chronic obstructive pulmonary disease (COPD) involving recurrent exacerbations. Using a metabolomic approach, we aim to investigate associations of different adrenal hormone metabolites with short- and long-term mortality in COPD patients. Methods: We prospectively followed 172 COPD patients (median age 75 years, 62% male) from a previous Swiss multicenter trial. At baseline, we measured levels of a comprehensive spectrum of adrenal hormone metabolites, including glucocorticoid, mineralocorticoid and androgen hormones by liquid chromatography coupled with tandem mass spectrometry (MS). We calculated Cox regression models adjusted for gender, age, comorbidities and previous corticosteroid therapy. Results: Mortality was 6.4% after 30 days and increased to 61.6% after 6 years. Higher initial androgen hormones predicted lower long-term mortality with significant results for dehydroepiandrosterone (DHEA) [adjusted hazard ratio (HR), 0.82; 95% confidence interval (CI), 0.70–0.98; p=0.026] and dehydroepiandrosterone sulfate (DHEA-S) (adjusted HR, 0.68; 95% CI, 0.50–0.91; p=0.009). An activation of stress hormones (particularly cortisol and cortisone) showed a time-dependent effect with higher levels pointing towards higher mortality at short term, but lower mortality at long term. Activation of the mineralocorticoid axis tended to be associated with increased short-term mortality (adjusted HR of aldosterone, 2.76; 95% CI, 0.79–9.65; p=0.111). Conclusions: Independent of age, gender, corticosteroid exposure and exacerbation type, adrenal hormones are associated with mortality at short and long term in patients with COPD exacerbation with different time-dependent effects of glucocorticoids, androgens and mineralocorticoids. A better physiopathological understanding of the causality of these effects may have therapeutic implications.

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