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.

Deep Penetration of Spudcan Foundation Into NC Clay

2004 ◽  
Author(s):  
M. S. Hossain ◽  
Z. Myhreyar ◽  
Y. Hu ◽  
M. F. Randolph
Keyword(s):  
Bearing Capacity ◽  
Ground Surface ◽  
Deep Penetration ◽  
Test Results ◽  
Vertical Loading ◽  
Soil Failure ◽  
Penetration Ratio ◽  
Initial Penetration ◽  
Bearing Capacity Factor ◽  
Penetration Depths

The excessive penetration of spudcan foundation in jackup rigs can be costly in offshore operation. Thus, the accurate prediction of load-penetration response becomes increasingly important in offshore design. The performance of spudcan foundation during installation, subjected to vertical loading on normally consolidated (NC) clay, is investigated physically and numerically. Experiments are carried out on kaolin clay in a drum centrifuge and FE analyses are performed using AFENA. During initial penetration, soil flows towards the ground surface and therefore heave occurs close to the spudcan edges. It flows back on top of the spudcan right after the heave passes the spudcan shoulder and shortly a substantial back flow causes the spudcan to be fully embedded. When penetration ratio (d/D) reaches 0.75, a deep failure mechanism achieves. Soil failure mechanisms play a key role for evaluating bearing response at various penetration depths. By comparing FE results with centrifuge test results, an identical bearing capacity factor of Nc = 10.5 is obtained for deeply embedded spudcan. The roughness of the soil-spudcan interface has shown 10% difference in bearing capacity when d/D is larger than 1.5.

Effect of a Strong Middle Layer on Spudcan Penetration

2014 ◽  
Author(s):  
Wen Gao ◽  
Tom Harrup ◽  
Yuxia Hu ◽  
David White
Keyword(s):  
Bearing Capacity ◽  
Layer Thickness ◽  
Soft Clay ◽  
Soil Layer ◽  
Strength Ratio ◽  
Top Soil ◽  
Flow Mechanisms ◽  
Soil Flow ◽  
Jack Up ◽  
Peak Resistance

The rapid penetration of one or more of the foundations of a mobile jack-up rig into the seabed is an ongoing major problem in the offshore industry, with the potential to cause major damage to the structure and endangering any personnel on board. A recent example is the jack-up drilling rig Perro Negro 6 incident happened near the mouth of the Congo river in July 2013 with one of the rig’s crew of 103 reported missing and six others injured. This uncontrollable displacement is due to a form of failure known as punch through failure and commonly occurs on stratified seabed profiles. It has been reported that unexpected punch-through accidents have resulted in both rig damage and lost drilling time at a rate of 1 incident per annum with consequential costs estimated at between US$1 and US$10 million [1]. This paper presents the bearing capacity profiles and associated soil flow mechanisms of a common spudcan foundation penetrating into a three layer soft-stiff-soft clay soil through the use of large deformation finite element (LDFE) analysis. The Remeshing and Interpolation with Small Strain (RITSS) [2, 3] technique was implemented in the software package AFENA [4] to conduct the LDFE analysis. Both soil layer thickness and soil layer strength ratios were varied to study their effect on the spudcan penetration responses. The LDFE results of spudcan penetration into the soft-stiff-soft clay soils were calibrated by existing centrifuge test data. A parametric study was then conducted to study the bearing capacity responses and soil flow mechanisms during spudcan large penetrations by varying the soil layer strength ratio and relative layer thickness to the diameter of spudcan. It was found that there were three types of bearing responses during continuous penetration of spudcan: (a) when the top soft layer is relatively thin, the spudcan bearing response was similar to that of two layer soils with stiff over soft clays; (b) when the top soil layer thickness is medium, a peak resistance is observed when spudcan penetrates into the middle stiff layer followed by reduction; (c) when the soil layer is thick, the peak resistance occurs when spudcan gets into the bottom soft soil layer. The critical thickness of top soil layer is a function of soil strength ratio and middle stiff soil layer thickness. The bearing response types were also corresponding to the soil cavity formations during spudcan initial penetration.

Ultimate bearing capacity of foundations on layered soils under inclined load

1978 ◽  
Vol 15 (4) ◽  
pp. 565-572 ◽  
Author(s):  
G. G. Meyerhof ◽  
A. M. Hanna
Keyword(s):  
Bearing Capacity ◽  
Ultimate Bearing Capacity ◽  
Model Tests ◽  
Clay Soils ◽  
Layered Soils ◽  
Inclined Load ◽  
Soft Layer ◽  
Soil Failure ◽  
Strip Footings

The ultimate bearing capacity of footings resting on subsoils consisting of two layers has been investigated for the cases of a dense or stiff layer overlying a weak deposit, and a loose or soft layer overlying a firm deposit. The analyses of different modes of soil failure are compared with the results of model tests on circular and strip footings on layered sand and clay soils.

Large-deformation finite element analysis of pipe penetration and large-amplitude lateral displacement

2010 ◽  
Vol 47 (8) ◽  
pp. 842-856 ◽  
Author(s):  
Dong Wang ◽  
David J. White ◽  
Mark F. Randolph
Keyword(s):  
Finite Element ◽  
Large Deformation ◽  
Lateral Displacement ◽  
Soil Surface ◽  
Element Analysis ◽  
Rate Dependent ◽  
Soil Failure ◽  
Lateral Resistance ◽  
Flow Mechanisms ◽  
Soil Flow

Seabed pipelines must be designed to accommodate thermal expansion — which is commonly achieved through controlled lateral buckling — and to resist damage from submarine slides. In both cases, the pipe moves laterally by a significant distance and the overall pipeline response is strongly influenced by the lateral pipe–soil resistance. Here, the process of pipe penetration and lateral displacement is investigated using a large-deformation finite element method, with a softening rate–dependent soil model being incorporated. The calculated soil flow mechanisms, pipe resistances, and trajectories agree well with plasticity solutions and centrifuge test data. It was found that the lateral resistance is strongly influenced by soil heave during penetration and the berm formed ahead of the pipe during lateral displacement. For “light” pipes, the pipe rises to the soil surface and the soil failure mechanism involves sliding at the base of the berm. In contrast, “heavy” pipes dive downwards and a deep shearing zone is mobilized, expanding with continuing lateral movement. The different responses are reconciled by defining an “effective embedment” that includes the effect of the soil berm or wall ahead of the pipe. The relationship between normalized lateral resistance and effective embedment is well fitted using a power law.

Spudcan Penetration in Loose Sand Over Uniform Clay

2009 ◽  
Author(s):  
Long Yu ◽  
Yuxia Hu ◽  
Jun Liu
Keyword(s):  
Finite Element ◽  
Clay Soil ◽  
Clay Soils ◽  
Loose Sand ◽  
Finite Element Analyses ◽  
Flow Mechanisms ◽  
Soil Flow ◽  
Jack Up ◽  
Penetration Depths ◽  
Sand Plug

Punch through failures of spudcan foundations of mobile jack-up rigs have been reported every year. The potential of punch through failure of spudcan foundations on loose sand over uniform clay soils was studied numerically in the present paper. Large deformation finite element analyses were carried out to simulate the load-penetration responses of a 14m diameter spudcan during continuous penetration into this sand over clay soil. The numerical results were compared with existing centrifuge data. The critical penetration depths were derived from the load-penetration responses. The soil flow mechanisms, the shape of sand plug and the distribution of plastic points were also reported.

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).

Large Deformation FE Analyses of Cone Penetration in Single Layer Non-Homogeneous and Three-Layer Soft-Stiff-Soft Clays

2014 ◽  
Author(s):  
Hongliang Ma ◽  
Mi Zhou ◽  
Yuxia Hu ◽  
Muhammad Shazzad Hossain
Keyword(s):  
Bearing Capacity ◽  
Large Deformation ◽  
Single Layer ◽  
Offshore Structures ◽  
Capacity Factor ◽  
Cone Penetration ◽  
Soft Clays ◽  
Flow Mechanisms ◽  
Soil Flow ◽  
Bearing Capacity Factor

Continuous profiles from in-situ penetrometer tests are now identified as essential for site specific soil investigation as part of designing offshore structures in deep and ultradeep waters and in highly layered seabed conditions. This paper describes the results from large deformation FE (LDFE) analysis undertaken to provide insight into the behavior of cone penetrometer penetrating through single layer non-homogeneous clays and three-layer uniform soft-stiff-soft clays. For the smooth cone penetration in non-homogeneous clays, the soil strength non-homogeneity factor was shown to have insignificant effect on the cone bearing capacity factor. However, for the rough cone, the bearing capacity factor in non-homogeneous clay was about 10∼12% lower than that in uniform clay. Bearing capacity factors for smooth and rough cones were also similar for non-homogeneous clay. For cone penetration in stratified soft-stiff-soft clays, a minimum layer thickness of 20 diameters was required to mobilise the full resistance of the stiff layer. The corresponding soil flow mechanisms are also discussed linking directly to the profile of penetration resistance.

Lateral Boundary Effect in Centrifuge Tests for Spudcan Penetration in Uniform Clay

2014 ◽  
Vol 553 ◽  
pp. 458-463 ◽  
Author(s):  
Shah Neyamat Ullah ◽  
Yu Xia Hu ◽  
David White ◽  
Samuel Stanier
Keyword(s):  
Smooth Boundary ◽  
Boundary Effect ◽  
Penetration Resistance ◽  
Fe Analysis ◽  
Cavity Wall ◽  
Rough Boundary ◽  
Lateral Boundary ◽  
Centrifuge Tests ◽  
Flow Mechanisms ◽  
Soil Flow

The effect of the centrifuge strongbox boundary on the penetration resistance of a spudcan foundation in uniform clay has been studied using Large Deformation FE analysis. Both smooth and rough strongbox boundaries were considered with various strongbox sizes. The spudcan penetration resistance and soil flow mechanisms were analysed. It was observed that, when the strongbox size was reduced, the spudcan penetration resistance was decreased for a smooth boundary and increased for a rough boundary. The depth of cavity formed above the spudcan during its penetration, in most cases, was determined by the soil flow around mechanism without cavity wall failure. However, cavity wall failure could be initiated when a smooth strongbox boundary was very close to the spudcan. The strongbox boundary effect on the spudcan penetration resistance can be avoided when the distance of the strongbox boundary to the spudcan centre is larger than 1.5 times of spudcan diameter for a rough boundary; or 2 times of spudcan diameter for a smooth boundary.

Effect of Pile and Load Inclination on the Pile Resistance In both Compression and Tension

2014 ◽  
Vol 2 (1) ◽  
pp. 11-29
Author(s):  
Ahmad Jabber Hussain ◽  
Alaa Dawood Salman ◽  
. Nazar Hassan Mohammad
Keyword(s):  
Bearing Capacity ◽  
Inclination Angle ◽  
Theoretical Study ◽  
Pile Installation ◽  
Soil Failure ◽  
Inclined Pile ◽  
Uplift Resistance ◽  
Lift Forces ◽  
Batter Piles ◽  
Pile Resistance

      According to this theoretical study which was about loading of piles under different condition of loading (compression and up-lift forces ) and for deferent pile installation (vertical and inclined pile ) by which it called (positive batter pile ) when the inclination of the load and pile is in the same direction and called (negative batter pile) when the inclination of load is opposite to the pile inclination, and from studying these cases the results of analysis can be summarize in the flowing points: 1-Variation of load inclination on piles effects on the bearing capacity and uplift resistance. It was found that bearing capacity of the piles increase with increasing of load inclination up to the inclination angle (37.5ͦ) which represents the maximum bearing capacity and then the bearing capacity decrease with increasing of load inclination. 2- Variation of batter pile affects the bearing capacity of the pile and up-lift resistance. by which equivalent angle will be used as result between the load and piles inclination and this angle will be used in calculation of piles resistance . 3- It was noticed the shape of soil failure is highly affected by the inclination of pile. The shape of failure for the soil which is in contact with pile and this include (vertical and batter piles) is highly affected by the angle of inclination.

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