Centrifuge modelling of uplift response of suction caisson groups in soft clay

2020 ◽  
Vol 57 (9) ◽  
pp. 1294-1303 ◽  
Author(s):  
Bin Zhu ◽  
Jia-lin Dai ◽  
De-qiong Kong ◽  
Ling-yun Feng ◽  
Yun-min Chen
Keyword(s):  
Soft Clay ◽  
Soil Surface ◽  
Displacement Curve ◽  
Soil Plug ◽  
Suction Caisson ◽  
Vertical Displacements ◽  
Caisson Foundations ◽  
Shadowing Effect ◽  
Uplift Resistance ◽  
Centrifuge Model Tests

This paper describes a program of centrifuge model tests on the uplift behaviour of suction caisson foundations. The parameters considered were the loading rate, caisson diameter (D), soil strength profile, and type of footing (i.e., mono-caisson and tetra-caissons group). The loading responses were examined in terms of total uplift resistance, suction beneath the caisson lid, and the vertical displacements of the caisson and at the soil surface. There exists a critical uplift displacement, approximately 0.02D and 0.01D for the mono-caisson and the tetra-caissons groups, respectively, at which a turning point can be identified in the load–displacement curve. This was found to be attributed to the adhesion on the caisson–soil interface reaching a peak response and then dropping. Of interest is that the tetra-caissons group exhibits much greater normalized uplift resistance than the mono-caisson group before reaching an uplift displacement of about 0.02D, suggesting superiority of the former in term of serviceability. However, a reversed trend was observed at greater displacement, and accordingly an empirical model was derived to quantify the shadowing effect of caisson groups. Regarding the cyclic response, several cycles of large-amplitude loading are sufficient to reduce the ultimate bearing capacity of caisson(s) to below the self-weight of the inner soil plug(s), indicating a transition of failure mechanism.

Numerical Simulation of Cone Penetration Tests Inside Suction Caisson Foundations in Sand

2020 ◽  
Author(s):  
Marc Stapelfeldt ◽  
Diaa Alkateeb ◽  
Jürgen Grabe ◽  
Britta Bienen
Keyword(s):  
Cone Penetration Test ◽  
Service Performance ◽  
Small Scale ◽  
Penetration Test ◽  
Cone Penetration ◽  
Soil Plug ◽  
Suction Caisson ◽  
Cone Penetration Tests ◽  
Caisson Foundations ◽  
Penetration Tests

Abstract Offshore wind is increasingly utilised as a renewable energy source. A growing number of bottom fixed wind turbines installed offshore are supported by suction caisson foundations. The suction-assisted installation remains a source of uncertainty towards the in-service performance due to the unknown post-installation soil plug state. Cone penetration tests within the suction caisson can help to improve the reliability. Therefore, cone penetration tests were employed in centrifuge tests to investigate the plug state in a previously installed suction caisson. However, the performance of a cone penetration test in a small-scale experiment is connected to uncertainties: A relatively large diameter device is required to conduct the cone penetration test — especially in a centrifuge test. Different finite element models are developed in order to visualise and investigate a cone penetration test inside a suction caisson. The numerical analysis results are validated through the back-calculation of centrifuge cone penetration tests. The results of the simulated cone penetration tests inside a suction caisson are evaluated and compared to the centrifuge experiments. This investigation reinforces the scope of the centrifuge experiments and emphasises a considerable effect of the pressure transferral through the caisson lid in the soil plug state. Hence, the results of this study reduce existing uncertainties regarding possible suction installation effects on the in-service performance of caisson foundations.

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.

Seismically-induced displacements of a suction caisson in soft clay

2010 ◽  
pp. 711-716 ◽  
Author(s):  
A Brennan ◽  
S Madabhushi ◽  
P Cooper
Keyword(s):  
Soft Clay ◽  
Suction Caisson

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.

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.

Visualizing Failure Surfaces in Soft Clay Due to Suction Caisson Loading

IFCEE 2018 ◽  
2018 ◽  
Author(s):  
Jeff F. Wallace ◽  
Cassandra J. Rutherford ◽  
Junxing Zheng
Keyword(s):  
Soft Clay ◽  
Suction Caisson

Feasibility Study of Lateral Buckling Using Residual Curvature Method for Deep Water Pipelines

2020 ◽  
Author(s):  
Qiang Bai ◽  
Fengbin Xu ◽  
Mark Brunner
Keyword(s):  
Deep Water ◽  
Twist Angle ◽  
Soft Clay ◽  
Soil Surface ◽  
Lateral Buckling ◽  
Finite Element Software ◽  
User Subroutine ◽  
Maximum Value ◽  
Water Pipelines ◽  
Residual Curvature

Abstract In recent years the residual curvature (RC) method has been used to provide buckle initiators to control and mitigate the lateral buckling of pipelines for some shallow water projects. With the appropriate planning of the controlled buckles using RC sections, an acceptable design of the pipeline in-place behavior is achieved. However, the RC method has not yet been applied to deep-water pipelines. The twist of RC sections in the sagbend during installation has been observed, and the orientation of as-laid RC section on the seabed is difficult to control in deep-water pipelines. The effects of as-laid RC-section orientation on in-place lateral buckling in deep water are unknown. The FRIC user subroutine in the Abaqus finite-element software suite has been developed for modelling pipe-soil interactions based on uncoupled axial and lateral soil resistances that are assumed to be independent of vertical pipe penetration after initial embedment into the soil surface. However, the penetration of a twisted RC section can vary dramatically from a normal pipeline on the seabed. The UINTER user subroutine in Abaqus was selected for presenting 3D pipe-soil interactions that incorporate the variations of independent axial and lateral soil resistances as a function of pipe penetration more accurately. UINTER is used in the present study to account for the effects of soil penetration on the lateral buckling performance of a pipeline with RC sections in soft clay. The analysis results show that the RC section twists in the sagbend area during installation, and the twist angle reaches its maximum value just prior to the RC section touching the seabed. The in-place lateral buckling analysis is carried out after the installation analysis is finished. The analysis results demonstrate the feasibility of applying the RC method as the primary buckle triggering mechanism for deep water pipelines, and it shows how the RC orientation affects the pipeline in-place performance in terms of strength and fatigue damage (only the stress ranges for use in fatigue calculations are shown in the paper).

Numerical Investigation of Vertical Penetration of Steel Catenary Riser Near the Touch Down Zone

2016 ◽  
Author(s):  
Sujan Dutta ◽  
Bipul Hawlader ◽  
Ryan Phillips ◽  
Mike Paulin
Keyword(s):  
Soft Clay ◽  
Sea Waves ◽  
Factors Affecting ◽  
Steel Catenary Riser ◽  
Rate Dependent ◽  
Physical Experiments ◽  
Ansys Cfx ◽  
Waves And Currents ◽  
Steel Catenary Risers ◽  
Uplift Resistance

Steel catenary risers (SCR) are widely used in offshore to transport hydrocarbon from the seabed to floating or fixed platforms. The fatigue life of SCR near the touchdown zone (TDZ) is one of the main design concerns because the risers are often subjected to cyclic loading (vertical penetration/uplift, lateral and axial displacements) from various sources of environmental loadings, such as sea waves and currents. Numerical modeling of the penetration and uplift behaviour of an SCR is a challenging task. Most of the models available in the literature for uplift resistance are empirical, which have been developed mainly from the results of physical experiments. In this study, numerical simulation of vertical resistance is presented. Analysis is performed using ANSYS CFX software. Strain-softening and strain-rate dependent undrained shear strength behavior of soft clay sediment has been reported by many researchers. Unfortunately, these models were not available in CFX. Numerical simulations presented in this paper are performed implementing this behavior in CFX. Numerical results are compared with available empirical models. The present CFX modeling explains some mechanisms involved in trench formation and suction development during uplift. Factors affecting uplift resistance such as the size and shape of the trench are also discussed from a parametric study.

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