Caisson Foundations Research Articles

Incremental dynamic analysis of caisson–pier interaction

This paper presents a 3D finite element Incremental Dynamic Analysis (IDA) study of caisson foundations carrying single-degree-of-freedom (SDOF) structures on clayey soil. The emphasis is given to the interplay between the nonlinearities developed above (superstructure) and, mainly, below ground surface, either of material (soil plasticity) or of geometric (caisson–soil interface gapping and slippage) origin. The study is performed with respect to the static (FS) and the seismic (FE) safety factor of the foundation and involves SDOF oscillators of varying mass (to account for vertical loading, FS) and height (relating to moment loading, FE) founded on similar rigid cubic caissons. Structural nonlinearity is considered through a simplified moment-curvature law and the yield strength is deliberately chosen so that the following three configurations are obtained: (a) a lightly loaded (FS=5) seismically under-designed (as compared to the superstructure) caisson, (b) a lightly loaded seismically over-designed caisson, and (c) a heavily loaded (FS=2.5) seismically under-designed caisson. The analysis is performed with several earthquake records, each scaled to multiple levels of intensity. IDA curves are produced for a single intensity measure, (peak ground acceleration, PGA), and appropriate engineering demand parameters (EDP) describing both the maximum and the residual response of the system. The results emphasize a potentially beneficial role of foundation nonlinearities in reducing the seismic demands on the superstructure, but at the cost of residual foundation settlements and rotations.

Foundation impedance and tower transfer functions for offshore wind turbines

This article investigates the dynamic interaction between a horizontal-axis wind turbine, modelled as a discrete Euler–Lagrangian system, and the soil–foundation system, modelled in a finite element framework. The model comprises a rotor blade system, a nacelle and a flexible tower connected to the soil–foundation system using a substructuring approach. The aerodynamic loading on the rotor blades is modelled using blade element momentum theory. The offshore wind turbine is founded on a monopod suction caisson foundation. The soil–foundation system is modelled using a finite element method (Plaxis 3D dynamics) and a 1D strength of materials based on wave propagation approach (cone method) for comparison. A dynamic-stiffness matrix and a static stiffness matrix formulation are used to represent the soil–foundation behaviour at the mudline. Tower displacement response transfer functions are generated using each soil–foundation model at various soil stiffness. The effects of the soil stiffness on the displacement transfer functions and the wind turbine dynamics are discussed. Results from a static stiffness formulation (with coupling) are seen to match those given by frequency-dependent models, indicating that such simplified models maybe used for analysis under certain conditions.

Challenges in Bridging Indian Rivers

The Indian subcontinent has been gifted with several major rivers, most of them meeting either the Arabian Sea or the Bay of Bengal. Constructing bridges across major rivers and creeks has been a challenge in view of the large flood plains, deep scour of river beds, bank erosion, etc.Long-span bridges with caisson foundations have been the preferred choice for major river/creek bridges in view of the high cost of the foundations. The foundations of these bridges are usually very deep and the construction proceeds at a relatively slow pace, with an element of uncertainty in the time required for completion. With better equipment and corresponding quality control, construction of large-diameter pile foundations has emerged as a faster and reliable option. Developments in pre-cast segmental construction have also contributed to a gradual shift in the preferred span and foundation type to ensure much shorter construction periods.This paper presents a brief history of the landmark bridges constructed across the major rivers in India and also discusses the present scenario and engineering challenges in bridging Indian rivers, including a case study.

Application of bi-directional static loading test to deep foundations

Bi-directional static loading test adopting load cells is widely used around the world at present, with increase in diameter and length of deep foundations. In this paper, a new simple conversion method to predict the equivalent pile head load-settlement curve considering elastic shortening of deep foundation was put forward according to the load transfer mechanism. The proposed conversion method was applied to root caisson foundation in a bridge and to large diameter pipe piles in a sea wind power plant. Some new load cells, test procedure, and construction technology were adopted based on the applications to different deep foundations, which could enlarge the application scopes of bi-directional loading test. A new type of bi-directional loading test for pipe pile was conducted, in which the load cell was installed and loaded after the pipe pile with special connector has been set up. Unlike the conventional bi-directional loading test, the load cell can be reused and shows an evident economic benefit.

Numerical and experimental study on evaluating the depth of caisson foundation with Sonic Echo method

Using nondestructive testing techniques to evaluate the length or depth of an existing foundation is an important issue with potential high application values. One of these is to evaluate whether the foundation is broken after severe earthquakes. In this aspect, academic research related to nondestructive evaluation for caisson foundations is rarely reported. The objective of this paper is to study the feasibility of using Sonic Echo method to evaluate the depth of caisson foundations. Two types of caissons, simple cylindrical caisson and compound caisson with chambers, were studied for their responses to the Sonic Echo tests. The study was carried out in numerical simulation with finite element method and experimental way with in-situ tests. A bridge system which spans over Sofong Brook in Taiwan was selected for the tests in situ. The bridge system is still under construction and therefore the effect of different construction stages on the testing results may be studied. In this paper, the parameters to be varied for the studies include the testing locations and the existence of chamber plates, the bottom plate and the top plate. Finally some preliminary conclusions can be reached for a successful test.

Testing and analysis of a laterally loaded bridge caisson foundation in gravel

This paper presents the results of an in situ lateral load test on a caisson-type foundation of the old Niu-Dou Bridge in Ilan County, Taiwan. The caisson was 12m long and had circular cross-sections whose diameters were 5m in the upper portion and 4m in the lower portion. The test site was located on soil with a high gravel content. A site investigation, including laboratory and field tests, was carried out. A six-component Winkler-beam model was applied to simulate the caisson response in the lateral load test. To determine the nonlinear properties of the Winkler springs, a method based on large-scale geotechnical field testing was proposed. With this method, the soil springs could be properly set and the Winkler-beam model could reasonably capture the lateral behavior of the caisson foundation.

Numerical Simulation of Ultimate Capacity of Suction Caisson Foundations by FEM

As a newly developed type of foundation for deep water offshore and marine engineering, the suction caisson is usually subjected to combined loading of vertically uplift load, horizontal load and moment. Performance evaluation and design theory for such a new type of foundation can not meet the basic requirements of engineering practice sufficiently at present. In this paper, the general-purpose finite element analysis package ABAQUS is employed to conduct three-dimensional numerical analyses on load-carrying features of suction caisson foundation. Then the ultimate bearing capacity of suction caisson foundation under monotonic load for two drainage conditions of the soil is evaluated by displacing-controlling procedure.

Long-Term Lateral Cyclic Response of Suction Caisson Foundations in Sand

AbstractSkirted gravity base foundations and suction caisson foundations are considered as viable alternatives to monopile foundations for offshore wind turbines. While recent work has focused on the monotonic moment-rotation response for shallow foundations, the cyclic response and the accumulation of rotation over the life of the turbine must also be addressed. This paper presents cyclic loading tests where approximately 10,000 cycles, with different loading characteristics, were applied to a model shallow foundation (a caisson) in loose sand. On the basis of these tests, a framework for assessing the accumulated angular rotation because of cycling was developed. The settlement and cyclic stiffness response of the caisson were also assessed. It was found, not unexpectedly, that the accumulated settlement of the caisson increased with the number of cycles and cyclic amplitude. It was also found that a cyclic loading regime intermediate between one-way and full two-way cycling produced the largest rotatio...

Interaction of caisson foundations with a seismically rupturing normal fault: centrifuge testing versus numerical simulation

Dramatic failures have occurred in recent earthquakes as a result of the interplay of surface structures with outcropping fault ruptures, highlighting the need to account for fault-induced loading in seismic design. Current research into the mechanisms of fault rupture–foundation–structure interaction has revealed a potentially favourable role of caissons in comparison with other foundation types. This paper explores the mechanisms of normal fault rupture interaction with rigid caisson foundations, with an integrated approach using both experiments and analysis. A series of centrifuge model tests were first conducted to study the response of a square (in plan) caisson foundation of dimensions 5 m × 5 m × 10 m, founded on a 15 m thick layer of dry dense sand. A non-linear three-dimensional numerical simulation of the problem was then developed, and adequately validated against centrifuge test results. Depending on its position relative to the fault, the caisson interacts with the fault rupture, sometimes modifying spectacularly the free field rupture path. Acting as a kinematic constraint, the caisson ‘forces' the rupture to divert on either one, or both, of its sides. The numerical study was subsequently extended to gain further insight into the effect of the exact position of the caisson relative to the fault outcrop. Different mechanisms taking place for different caisson positions are identified, and their effect on the response of the system is discussed.

軸対称ケーソン基礎に作用する津波波力

軸対称ケーソン基礎に作用する津波波力

Overview of geology and foundations of bridges on the East Coast of USA

The densely populated corridor along the Atlantic coast between Boston and the capital of Washington, DC is home to many important bridges in the country. The regional geology is very old, tracing the history of the earth, with bedrock formed more than a billion years ago and surface geology that is very complex and variable. A thorough understanding of the local geologic and tectonic environment is essential to bridge foundation design, which has evolved tremendously from the underwater hand excavation of the caisson foundations of the Brooklyn Bridge to the sophisticated design of the new Woodrow Wilson Bridge. The paper presents local issues of subsurface conditions, seismic hazard, foundation solutions of old and new bridges, and retrofit schemes for seismic protection of historical bridges based on experience collected over more than a century from Mueser Rutledge Consulting Engineers.

Caisson Foundation Design for Offshore Anchorage

The cross-sea suspension bridge is one of the most important development branches of long-span Bridge. The anchorage construction on the sea is a key issue of cross-sea suspension bridge. This paper introduces a new kind of caisson foundation of offshore anchorage. This new design may reduce the construction cost and speed the process of working. In this paper the structural features and the construction gist are detailed.

Key Technology of Construction for Middle Tower of Three-Tower and Two-Span Suspension Bridge

Tai-Zhou Bridge, which has a three-tower and two-span, is 1080 meters long and 2 meters wide. The middle tower is a huge caisson foundation and chevron steel tower structure. It is important to make some effective technical measures to control the processes of caisson foundation’s installation, such as floating, orientation, implantation and final sunk, especially in complex conditions. Eroding model tests for the caisson foundation’s floating phase and sunken phase play an important role in the prophase installation. Information control technology could exactly guidance the sunk of cession. Finally, the linkage control of steel tower’s manufacture and operation is necessary for the precision of installation.

Installation and lateral loading tests of suction caissons in silt

A number of potential offshore wind turbines in China will be constructed in sandy silt seabeds, and the mono-caisson foundation is an important choice for these offshore wind turbines. A program of large-scale model tests on suction installation and lateral loading of caisson foundations in saturated silt were carried out in a large soil tank at Zhejiang University. Test results of installation resistance during suction installation show that the seepage effect is limited in silt, and the suction required to penetrate the caisson can be well predicted based on the sleeve friction and cone resistance of cone penetration tests. The deformation mechanism and soil-structure interaction of a caisson subjected to lateral loads were investigated. The instantaneous rotation center of the model caisson at failure was at the depth of about four-fifths of the skirt length, almost directly below the lid center. Based on the assumption of a common position of the instantaneous rotation center and dominating resistance forces on the caisson, an analytical expression for the ultimate moment capacity was presented.

Taizhou Bridge South Anchor Caisson Construction Drainage System Optimization Model of Settlement and Deformation as Constraint Conditions

Since construction drainage will inevitably cause ground settlement, it is necessary that a system optimization model is established with source (sink) distribution and intensity being the object function, minimum requirements of settlement and deformation of surroundings caused by draining and dynamic water levels during different working procedures being constraints, and the design parameter of pumping (injection) wells being the variable. The system optimization model solved the problem of which Taizhou bridge south anchor caisson foundation construction drainage induced settlement, so as to lower the damage of surrounding buildings. So the system optimization model provides a new method for active control over settlement during draining. Such a method of drainage based on system optimization model should be of significance for similar projects involving drainage.

Bearing Capacity of Suction Caisson Foundations Using FEM Analysis

To understand features of bearing capacity of suction caisson foundation is one of the key issues in design and construction of deep-water marine structures. In this paper, the general-purpose finite element analysis package ABAQUS is employed to conduct three-dimensional numerical analyses on load-carrying features of suction caisson foundation under vertically uplift load, horizontal load and moment. Then the ultimate bearing capacity of suction caisson foundation for undrained condition of the soil is evaluated by displacing-controlling procedure. Moreover, three-dimensional failure envelope of suction caisson foundation under combine loading condition are established by the proposed numerical procedure.

Bearing Capacity of Suction Caisson for Offshore Floating Wind Turbine

Presented in this paper are the three-dimensional nonlinear finite element analyses of the failure envelopes of suction caisson under torsion, vertical and lateral pullout combined load in soft clay. The soft clay under undrained condition is simulated by perfectly elasto-plastic Tresca model. Through the numerical analyses, the failure envelopes for combined loading (V-T、H-T、V-H-T) of suction caisson is reviewed. And the mathematical expression of failure envelope is deduced. It is shown that (1) the circular plastic failure area is outward-extending. (2) The bearing capacity of suction caisson foundation in V-T、H-T load spaces is increasing with the aspect ratio L/D. (3) The equation of failure envelope can be used to evaluate the stability of suction caisson foundation for offshore floating wind turbine.

VALIDITY OF SIMPLIFIED ANALYSIS OF STABILITY OF CAISSON BREAKWATERS ON RUBBLE FOUNDATION EXPOSED TO IMPULSIVE LOADS

Wave slamming on vertical breakwaters cause a sudden, impulsive load that may cause a caisson to slide on its foundation. Alternatively, geotechnical failure may occur in the subsoil. This paper investigates whether simple analytical solutions, accounting only for the sliding along the caisson-foundation interface, can be utilized to properly determine the deformations of the breakwater. Comparisons are made with results obtained by numerical models that include the material response of the soil. Firstly, a computational model is suggested that assumes a fully drained behavior of the subsoil. Secondly, a fully coupled dynamic pore-water-flow model is introduced. The computational examples clearly demonstrate that the deformations of the soil as well as the pore pressures must be
 accounted for in order to get a reliable prediction of caisson deformations during wave impact.

Caisson Foundations Subjected to Reverse Fault Rupture: Centrifuge Testing and Numerical Analysis

Recent large-magnitude (M>7) earthquakes have caused numerous failures induced by surface faulting, demonstrating the need to account for tectonic deformation in seismic design. Thanks to their usually high rigidity, embedded (e.g., caisson) foundations may divert the fault rupture and lead to favorable performance, whereas surface or piled foundations may fail. We present a series of centrifuge model tests to investigate the response of caisson foundations embedded in a cohesionless soil stratum, the base of which is subjected to reverse faulting. We elucidate the interplay between the propagating fault rupture and the caisson, focusing on the role of the location of the outcropping rupture relative to the caisson. The rigid-body of the caisson causes diversion and/or bifurcation of the shear localization, which is forced to develop preferentially around the edges of the caisson. The observed failure pattern and the consequent caisson response depend strongly on the exact caisson position relative to the...

Model testing of suction caissons in clay subjected to vertical loading

A wide range of new offshore applications are emerging in the energy sector. The oil and gas industry is targeting minimum facility applications, whilst the renewable energy sector is developing offshore wind turbines, as well as a number of wave and tidal energy devices. The design and installation of the foundations are key considerations in the financial viability of such offshore engineering projects. Suction caisson foundations are a potential solution for these new developments, but design guidance is relatively sparse. This paper considers the vertical loading response of a caisson foundation in clay, during installation and under both monotonic and cyclic vertical loading. The main contribution is the presentation and interpretation of high quality experimental data. Vertical loading is critical for the design of a multi-footing structure of the type that might be used for large offshore wind turbines. We first consider the installation behaviour and compare data from pushed installations and a suction installation with results from a theoretical calculation. We then consider cyclic vertical loading tests, focussing on cyclic amplitudes that take the foundation into tension. Detailed displacement data and pore pressure data are presented.