Performance of suction caissons in sand and clay

2002 ◽  
Vol 39 (3) ◽  
pp. 576-584 ◽  
Author(s):  
Magued Iskander ◽  
Sherif El-Gharbawy ◽  
Roy Olson
Keyword(s):  
Load Capacity ◽  
Strength Properties ◽  
Drilled Shafts ◽  
Soil Conditions ◽  
Driven Piles ◽  
Suction Caisson ◽  
Axial Tensile ◽  
Axial Load Capacity ◽  
Shearing Strength ◽  
Suction Caissons

The use of suction caissons (suction piles) in marine environments has been increasing in the last decade. A suction caisson is a steel pipe with an open bottom and a closed top that is inserted into the ground by pumping water out of it. Pumping creates a differential pressure across the caisson's top that pushes it into place, thus eliminating the need for pile driving. There are a number of uncertainties in the design of suction caissons. First, the state of stress and soil conditions adjacent to a suction caisson differs from those around typical driven piles or drilled shafts. Second, the axial load capacity of suction caissons depends on the rate of loading, hydraulic conductivity, drainage length, as well as the shearing strength properties of the foundation material. Finally, during pullout, volume change characteristics of the surrounding soils may change the theoretical suction pressures. A review of the existing knowledge relating to the design and construction of suction caissons is presented in this paper along with the results of a laboratory study on model caissons in sand and clay. Test results indicate that the use of suction pressure for installation of caissons is a viable alternative to conventional methods. Suction was also shown to resist some axial tensile loads.Key words: suction, pile, bucket, foundation, anchor, capacity.

Uplift Capacity of Suction Caissons in Sand for General Conditions Of Drainage

2021 ◽  
Author(s):  
Ragini Gogoi ◽  
Charles P. Aubeny ◽  
Phillip Watson ◽  
Fraser Bransby
Keyword(s):  
Constitutive Model ◽  
Load Capacity ◽  
System Capacity ◽  
Soil Conditions ◽  
Uplift Capacity ◽  
Soil Response ◽  
Dense Sand ◽  
Centrifuge Tests ◽  
Numerical Predictions ◽  
Suction Caissons

Abstract Suction caissons have emerged as a viable solution for the foundations of offshore wind turbines, which are gaining momentum worldwide as an alternate energy source. When used in a multi-bucket jacket system, the system capacity is often governed by the uplift capacity of the windward bucket foundation. Seabed conditions at offshore windfarm sites often comprise dense sand where the soil response may be drained, partially drained or undrained depending on the loading regime, the foundation dimensions and the soil conditions. Given the large difference in uplift capacity of caissons for these different drainage conditions, predicting the behavior of a suction caisson under a range of drainage conditions becomes a paramount concern. Consequently, this paper presents the findings of a coupled finite element investigation of the monotonic uplift response of the windward caisson of a multi-bucket jacket system in a typical dense silica sand for a range of drainage conditions. The study adopts a Hypoplastic soil constitutive model capable of simulating the stress-strain-strength behavior of dense sand. This choice is justified by conducting a comparative study with other soil models — namely the Mohr Coulomb and bounding surface sand models — to determine the most efficient soil failure model to capture the complex undrained behavior of dense sand. The numerical predictions made in this study are verified by recreating the test conditions adopted in centrifuge tests previously conducted at the University of Western Australia, and demonstrating that the capacity from numerical analysis is consistent with the test results. The Hypoplastic soil constitutive model also provides an efficient method to produce accurate load capacity transition curves from an undrained to a drained soil state.

Refined Model for Inclined Load Capacity of Suction Caissons

2003 ◽  
Author(s):  
Charles P. Aubeny ◽  
Seungwoon Han ◽  
J. Don Murff
Keyword(s):  
Load Capacity ◽  
Full Range ◽  
Skin Resistance ◽  
Cohesive Soil ◽  
Offshore Structures ◽  
Resistance Coefficient ◽  
Soil Conditions ◽  
Aspect Ratios ◽  
Inclination Angles ◽  
Suction Caissons

Suction caissons used as mooring anchors for offshore structures can, depending on design concept, be subjected to pullout forces ranging from nearly vertical for tension leg platforms, to intermediate inclination angles for taut mooring systems, to nearly horizontal for catenary moored systems. Hence, the ability to understand and predict suction anchor pullout resistance for a full range of load orientations is becoming of increasing importance. A previous paper by the authors presents a plastic limit analysis for estimating the load capacity of suction anchors over a full range of load inclination ranging from horizontal to vertical. The model was capable of predicting load capacity for various load attachment (padeye) depths, caisson aspect ratios, and soil undrained strength profiles that vary linearly with depth. Loading conditions are assumed to be undrained; therefore, a purely cohesive soil is assumed. The original analysis assumed full adhesion on the boundaries of the caisson; i.e., a skin resistance coefficient α equal to unity. However, actual values of this coefficient are less than unity, with specific values varying according to soil conditions and the method of caisson installation. To overcome the limitation of the original model, this paper presents a modified formulation that allows a skin resistance less than unity. The modified formulation develops an interaction relationship between vertical and horizontal soil resistance on the sides of the caisson that is applicable for any skin resistance conditions ranging from no to full adhesion.

Strain Path Analysis of Setup Time Around Piles and Caissons

2015 ◽  
Author(s):  
Charles Aubeny ◽  
Francisco Grajales
Keyword(s):  
Path Analysis ◽  
Strain Path ◽  
Load Capacity ◽  
Setup Time ◽  
Driven Piles ◽  
Pore Pressures ◽  
Side Resistance ◽  
Excess Pore Pressures ◽  
Suction Caissons ◽  
Excess Pore

Installation of driven piles and suction caissons in clayey soils generates excess pore pressures that temporarily reduce load capacity due to side resistance. Time dependent dissipation of these excess pore pressures leads to recovery of side resistance, a process known as ‘setup’. Since many facilities cannot be put into operation until sufficient pile load capacity has been mobilized, realistic predictions of setup time can be important. This study consists on the analysis of setup time following open ended pile and caisson installation. Initial excess pore pressures due to installation disturbance are predicted based on a strain path analysis based on a ring source moving at constant velocity in an incompressible medium. It is assumed that the setup occurs primarily due to dissipation of excess pore pressures generated during the installation process; thixotropic effects are neglected. The analysis employs an elastic perfectly plastic model of soil behavior and an uncoupled analysis of consolidation to simulate conditions on the pile shaft outside of the influence of tip effects. A parametric study shows that wall thickness and soil rigidity index can exert order of magnitude differences on setup time. Strain path solutions show reasonable agreement to laboratory and field measurements of pore pressure dissipation around thin-walled piles typical of suction caissons. Strain path solutions tend to underestimate setup time for driven piles, likely due to partial plugging during pile driving.

Reliability Based Stiffness Analysis for Application During Installation of Suction Caissons

2017 ◽  
Author(s):  
Hendrik Sturm ◽  
Alireza Mirdamadi
Keyword(s):  
Wind Farm ◽  
Offshore Wind ◽  
Soil Conditions ◽  
Optimized Design ◽  
Immediate Feedback ◽  
Foundation Design ◽  
Suction Caisson ◽  
Load And Resistance Factors ◽  
Geotechnical Design ◽  
Suction Caissons

The design of suction caissons for offshore wind turbines is generally performed deterministically, using load and resistance factors taken from relevant codes and standards. This approach has been widely accepted for the geotechnical design of suction caissons in well-characterised soil conditions. However, soil layering and properties often vary considerably from location to location within an offshore wind farm. Furthermore, the installation process can also cause changes in the soil state in the vicinity of the skirts, which will affect noticeably the response of the suction caisson during operation. While this can be considered implicitly in the geotechnical design by means of assumptions, the inherent uncertainty of the soil state will impact the overall performance of the structure considerably. On the other hand, an optimized design for the system requires an accurate prediction of the foundation stiffness. The authors present a reliability-based framework for the assessment of foundation stiffness, taking into account the most important input parameters and their expected variability. The framework can be applied both in foundation design as well as during actual installation in order to provide immediate feedback to permit adjustment or mitigation before the installation is finalized. Using a reliability-based approach in design allows an assessment of the probability of reaching the limiting design criteria and to quantify the related risk. The proposed reliability-based framework can be applied to other design aspects. This is exemplified using the example of coupled foundation installation and capacity assessment. The authors further discuss how the framework can be extended to more complex design procedures.

Axial load-capacity of rectangular cement stabilized rammed earth column

2015 ◽  
Vol 99 ◽  
pp. 402-412 ◽  
Author(s):  
Deb Dulal Tripura ◽  
Konjengbam Darunkumar Singh
Keyword(s):  
Axial Load ◽  
Load Capacity ◽  
Rammed Earth ◽  
Axial Load Capacity

Axial load capacity of cylindrical shells with local geometric defects

1991 ◽  
Vol 31 (2) ◽  
pp. 104-110 ◽  
Author(s):  
S. Krishnakumar ◽  
C. G. Foster
Keyword(s):  
Axial Load ◽  
Load Capacity ◽  
Cylindrical Shells ◽  
Axial Load Capacity
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