Rigid Caisson Research Articles

Theoretical interaction diagrams of a laterally loaded rigid caisson considering base shear and moment resistances

In this study, we propose theoretical solutions and interaction diagrams of the lateral responses of a rigid caisson in three types of elastoplastic soil considering the influences of base shear and moment resistances. The interaction diagrams for the three soil types are distinct, and each diagram bounded by a failure envelope is zoned for different states of soil yielding. The effects of base moment and shear resistances are considered by modifying the loads at the caisson head in the basic solutions, which do not account for the base effects. The base effects distinctly influence the shape and size of the failure envelope: the base shear resistance increases both the moment and horizontal capacities, whereas the base moment resistance increases only the moment capacity. Based on the original interaction diagram without the base effects accounted for, the caisson displacement response considering the base effects and the associated soil states can be determined using the modified loading path. The base shear and moment resistances have different influences on the modified loading path. Examples are provided to demonstrate the validity and applications of the proposed model in centrifuge tests and field tests in cohesionless soils.

Greece's new high‐speed railway line: Detailed design and construction engineering of bridge SG26

AbstractThe paper presents the several aspects of the detailed design and the construction engineering procedure of the most important Railway Bridge of the New Double High‐Speed Railway Line connecting Athens and Thessaloniki, the two biggest cities in Greece. The total length of the bridge is 404.8m consisting of three simply supported tied arches with a width of 18.03m. The two piers, 45.5m height each, are supported on rigid caisson foundations. The bridge has been constructed using the incremental launching method due to the deep valley below. The special characteristic of the bridge is that it crosses an active fault zone, associated with large seismic events (e.g. 1954 magnitude 6.8). Seismic devices (Friction Pendulum System and Fluid Viscous Damper) are installed between the deck and the substructure in order to absorb the anticipated seismic energy and consequently reduce deck displacement and force transmission to the structural elements. I. MAVRAKIS & PARTNERS S.A. carried out the detailed design and construction engineering, including the design of the temporary steel piers, the incremental launching procedure, the precamber design of the arches, the prestressing sequence of the hangers, the seismic isolation design and the shop drawings of the whole structure.

Vertical Stiffness Functions of Rigid Skirted Caissons Supporting Offshore Wind Turbines

Suction Bucket Jackets (SBJs) need to be fundamentally designed to avoid rocking modes of vibration about the principal axes of the set of foundations and engineered towards sway-bending modes of tower vibration. Whether or not such type of jackets exhibit rocking modes depends on the vertical stiffness of the caissons supporting them. This paper therefore derives closed form solutions for vertical stiffness in three types of ground profiles: linear, homogenous, and parabolic. The expressions are applicable to suction caissons having an aspect ratio (depth: diameter) between 0.2 and 2 (i.e., 0.2 < L/D < 2). The work is based on finite element analysis followed by non-linear regression. The derived expressions are then validated and verified using studies available in literature. Finally, an example problem is taken to demonstrate the application of the methodology whereby fundamental natural frequency of SBJ can be obtained. These formulae can be used for preliminary design and can also be used to verify rigorous finite element analysis during detailed design.

Surface gravity wave scattering by multiple slatted screens placed near a caisson porous breakwater in the presence of seabed undulations

In the present study, the effectiveness of using multiple slatted screens placed in front of a caisson porous breakwater to dissipate the incident wave energy is analyzed. To model the water flow through the slatted screens, a quadratic (nonlinear) pressure drop condition which involves both the inertial and drag effects is considered. Further, for thick porous structure, the well known Sollitt and Cross (1972) model is used. To handle the nonlinear boundary conditions, an iterative multi-domain boundary element method (BEM) is used. The numerical convergence of the multi-domain BEM based solutions is presented. Energy identities for flow past a single slatted screen, multiple slatted screens and for the present problem are derived. The study shows that the minimum reflection coefficient (<1%) and maximum wave energy dissipation (>98%) can be obtained by using four slatted screens. Further, for moderate values of perforation-effect Keulegan-Carpenter number (KC), the reflection coefficient attains maximum for b1λ≈n2,n=1,2,3,⋯ (b1 is the distance between the rigid caisson and the front slatted screen, λ is the incident wavelength) irrespective of the variations in the number of slatted screens. Further, the transmission coefficient, horizontal and vertical wave forces acting on the rigid caisson attain maximum for b1/λ≈0.55n, and minimum occurs for 2n+14<b1λ<3n+26,n=0,1,2,3,⋯. The Bragg resonance in the reflection coefficient occurs at Bragg value ≈1.6 irrespective of the variations of KC number. Moreover, the reflection coefficient increases around the Bragg value for higher values of KC number without altering the peak value in the reflection coefficient.

Solutions for Foundation Systems Subjected to Earthquake Conditions

Soil–structure interaction plays an important role in dynamic behaviour of a foundation under combined static and seismic loadings. This paper describes a few case histories with field studies of deeply embedded bridge foundations to showcase the earthquake induced lateral effects using finite element framework. Rigorous dynamic approach with detailed numerical analysis for large diameter pile foundation and pseudo-static approach for rigid caisson foundation presented in this study demonstrated the functionality of foundation systems in seismic conditions. Efficacy of barrettes over piles as a cost-effective foundation solution in high-rise buildings has also been discussed by obtaining higher resistance under static condition. Finally, an analytical methodology considering three-dimensional passive wedge developed in front of the rigid caissons is presented for estimating the ultimate soil resistance under seismic condition. Closed-form expressions to determine seismic passive earth pressure coefficient and its distribution along caisson length for different embedment ratio have been explained here that can be adopted in practice to analyse foundation systems subjected to earthquake condition.

Analytical solutions for seismic responses of shaft-tunnel junction under longitudinal excitations

Analytical solutions are deduced for seismic responses of shaft-tunnel junction under longitudinal excitations. The influence of the tunnel is incorporated by introducing terms of shaft-tunnel and soil-tunnel interactions into equations originally developed for rigid caissons. The shaft is simplified into a rigid body. The tunnel is represented by a continuous beam perpendicularly fixed onto the shaft. Firstly, solutions for displacements of the shaft are given. Then, solutions for the three major internal forces of the tunnel are proposed. Validity of the proposed solutions is examined by finite element method in respect of the shaft and the tunnel separately. The comparisons confirm that the proposed solutions could successfully predict the displacements of the shaft and the three major internal forces of the tunnel at the vicinity of the shaft-tunnel junction. However, they become less accurate with increasing distance to the shaft. Interactions among the shaft, the tunnel, and the soil are discussed based on the proposed solutions. A special emphasis is placed on the mutual influences between the shaft and the tunnel. Displacements of the shaft, especially the rotational displacements, are likely to decrease under longitudinal excitations when connected to tunnels. Shaft-soil relative displacement and soil-tunnel relative stiffness are the two key factors affecting the seismic responses of the tunnel. The former determines the amplitudes of the internal forces, while the latter governs how the internal forces distribute along the tunnel axis. A conceptual aseismic measure is studied by setting a pin joint at the shaft-tunnel junction. Theoretically, it could eliminate the influence imposed on the tunnel by the rotational displacement of the shaft.

Analytical solution for dynamic responses of the vertical shaft in a shaft-tunnel junction under transverse loads

This paper proposes an analytical solution for dynamic responses of the vertical shaft in a shaft-tunnel junction under transverse loads. The assumption is that the shaft could be regarded as a rigid body under certain circumstances. Based on that premise, equations originally developed for rigid caissons are incorporated with terms of shaft-tunnel and soil-tunnel interactions. Two specific dynamic scenarios are considered. The first one is when the shaft is subject to transverse dynamic loads above the ground surface. The second one is when the shaft-tunnel junction is under transverse seismic excitations. Validity of the proposed solution is examined in both scenarios by finite element method. Then, the proposed solution is used to evaluate influence of the tunnel. In the first scenario, the tunnel has a major influence on dynamic responses of the shaft. Displacements of the shaft are likely to be reduced because the tunnel adds to the stiffness matrix. Yet, in the second scenario, influence of the tunnel is minor enough to be neglected. Seismic responses of the shaft are approximately the same with or without the tunnel.

Vibration‐Based Damage Assessment in Gravity‐Based Wind Turbine Tower under Various Waves

In this study, the feasibility of vibration‐based damage assessment in a wind turbine tower (WTT) with gravity‐based foundation (GBF) under various waves is numerically investigated. Firstly, a finite element model is constructed for the GBF WTT which consists of a tower, caisson, and foundation bed. Eigenvalue analysis is performed to identify a few vibration modes of interest, which represent complex behaviors of a flexible tower, rigid caisson, and deformable foundation. Secondly, wave‐induced dynamic pressures are analyzed for a few selected wave conditions and damage scenarios are also designed to simulate the main components of the target GBF WTT. Thirdly, forced vibration responses of the GBF WTT are analyzed for the wave‐induced excitation. Then modal parameters (i.e., natural frequencies and mode shapes) are extracted by using a combined use of time‐domain and frequency‐domain modal identification methods. Finally, the variation of modal parameters is estimated by measuring relative changes in natural frequencies and mode shapes in order to quantify the damage‐induced effects. Also, the wave‐induced variation of modal parameters is estimated to relatively assess the effect of various wave actions on the damage‐induced variation of modal parameters.

Modelling of soil-structure-interaction for flexible caissons for offshore wind turbines

Published foundation models and procedures for calculation of caisson foundation response typically assume a rigid caisson in deformable soil. However, recent published measurement data from a prototype suction bucket jacket has revealed that the lid flexibility of the caisson foundations significantly influences the dynamic foundation stiffness felt by the jacket legs. This paper investigate this soil-structure-interaction problem and presents a modelling approach for including the effect of caisson flexibility in a macro-element. The macro-element, originally developed by assuming a rigid foundation, was modified by included a stiffness correction and a procedure to account for changes in the elastic coupling between horizontal load and moment due to the caisson flexibility. The modified macro-element successfully re-produced the response to general load paths computed by geotechnical finite element analyses, where the foundation was modelled in detail with structural elements and the surrounding soil was represented by continuum elements. The general principles behind the modification is generic in the sense that it can be implemented in other foundation models.

Using the Elastic Vertical Vibration of a Rigid Caisson at Low Frequencies to Stabilize the Foundation of Coastal Engineering Structures

ABSTRACT He, R.; Zhang, J., and Chen, W., 2017. Using the elastic vertical vibration of a rigid caisson at low frequencies to stabilize the foundation of coastal engineering structures. A suction caisson or a bucket foundation offers a suitable and economic foundation type for many coastal structures (such as breakwaters and wind turbines). Because of the relative stiffness of a caisson foundation compared with the surrounding soil is high, the caisson is treated as a rigid cylindrical shell in this article. Seawater and seabed are treated as a coupled seawater–seabed half-space. In that way, the elastic, vertical vibration of a caisson can be modeled as the vertical vibration of a rigid shell embedded in a fully saturated, porous seabed. The solution to the problem is obtained with the ring-load Green's function and proper boundary conditions at the caisson–soil interface. With integral equations, the governing equations are transformed to Fredholm equations and are solved numerically. Numerical results ...

Kinematic Response of Bridge Piers

This paper deals with the soil-structure interaction that occurs in deep foundations of bridge piers in seismic areas. In particular, the kinematic response of rigid caisson foundations under the passage of obliquely incident polarized shear waves is highlighted and discussed. A Winkler model with translational and rotational impedances is used to analyze the dynamic behavior of both the foundation and the superstructure. Analyses are carried out in the hypothesis of linear elastic soil.

Assessing Unit Skin Friction of Pneumatic Caissons

A study was carried out to establish an empirical method to estimate unit skin friction of rigid large-size pneumatic caissons. Field instrumentation during construction and installation of the rigid pneumatic caissons was in place, where the water load, air pressure, and reaction force (contact pressure) were measured accordingly. Using these data and the weight of caisson, the unit skin friction was estimated. The unit skin friction distribution with depth decreased in a parabolic shape. The unit skin frictions predicted by the K n and λ methods used for deep foundations were compared with the measured data. The comparison showed that the K n method is more suitable for estimating the skin friction of the large-size rigid pneumatic caisson than the λ method in this particular construction project.

Consolidation and dynamics of 3D unsaturated porous seabed under rigid caisson breakwater loaded by hydrostatic pressure and wave

In this study, based on the dynamic Biot’s theory “u-p” approximation, a 3D finite element method (FEM) numerical soil model is developed, in which the Generalized Newmark-method is adopted to determine the time integration. The developed 3D FEM soil model is a part of the coupled model PORO-WSSI 3D for 3D wave-seabed-marine structures interaction problem, and is validated by the analytical solution proposed by Wang (2000) for a laterally infinite seabed loaded by a uniform force. By adopting the developed 3D soil model, the consolidation of seabed under a caisson breakwater and hydrostatic pressure is investigated. The numerical results show that the caisson breakwater built on seabed has very significant effect on the stresses/displacements fields in the seabed foundation after the transient deformation and primary consolidation are completed. The parametric study indicates that the Young’s modulus E of seabed is the most important parameter to affect the settlement of breakwater, and the displacement fields in seabed foundation. Taking the consolidation status as the initial condition, the interaction between ocean wave, caisson breakwater and seabed foundation is briefly investigated. The 3D ocean wave is determined by solving the Navier-Stokes equations with finite volume method (FVM). The numerical results indicate that there is intensive interaction between ocean wave, caisson breakwater and seabed foundation; and the breakwater indeed can effectively block the wave energy propagating to the coastline.

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.

Ultimate lateral capacity of short rigid caisson in soft clay incorporating base shear

Short rigid caissons are proposed as appropriate foundation in soft ground with high water table. This paper presents a simple method for estimating the lateral load capacity of this composite foundation embedded in a clay deposit considering shear stresses mobilized at the base. The ultimate lateral soil resistance is considered to increase from two times at ground level to nine times the undrained strength at a depth three times the diameter of the caisson. Parametric studies quantify the effect of considering base shear on the ultimate lateral capacity of the short rigid caisson.

Reply to the discussion by Chugh on “Analysis of active earth pressure against rigid caissons backfilled with crushed rock and sand”Appears in Canadian Geotechnical Journal, 47(9): 1036–1043.

Reply to the discussion by Chugh on “Analysis of active earth pressure against rigid caissons backfilled with crushed rock and sand”Appears in Canadian Geotechnical Journal, <b>47</b>(9): 1036–1043.

Discussion of “Analysis of active earth pressure against rigid caissons backfilled with crushed rock and sand”Appears in Canadian Geotechnical Journal, 46(10): 1216-1228.

Discussion of “Analysis of active earth pressure against rigid caissons backfilled with crushed rock and sand”Appears in Canadian Geotechnical Journal, <b>46</b>(10): 1216-1228.

Analysis of active earth pressure against rigid caissons backfilled with crushed rock and sand

Arching effects in backfill materials generate a nonlinear active earth-pressure distribution behind a rough, rigid retaining wall. There are several analyses for estimating the nonlinear active earth pressures on a retaining wall exerted by a homogeneous backfill in the presence of arching. However, it is not possible to use these analyses for a caisson backfilled with crushed rock and sand, which is common in marine structures. In this study, a new formulation is proposed for calculating the nonlinear active earth pressure acting on a caisson backfilled with crushed rock and sand. The new formulation allows important insights, including the dependence of the slope angle of the crushed rock – sand interface that minimizes the active force and overturning moment on the caisson on the shear strengths of the crushed rock and sand and the geometry of the problem.

Analysis of Rigid Short Caisson with Granular Core Incorporating Nonlinear Interface and Base Responses

It is difficult to construct a conventional shallow foundation in alluvial lowlands because of soft soils and high ground water table. A rigid short caisson foundation with granular core is being proposed for alluvial lowlands. The proposed foundation is analyzed using non-linear hyperbolic stress–displacement responses of homogeneous alluvial deposits. Extensive parametric studies are carried out to study the effects of length ratio (L/d0), diameter ratio (d/d0) of granular core with respect to casing, relative stiffness of shaft (ατ), relative casing base stiffness (αb), and friction angle of granular material (ϕgp) on the load sharing and the settlement of the proposed foundation.

Seismic response of bridge pier on rigid caisson foundation in soil stratum

An analytical method to study the seismic response of a bridge pier supported on a rigid caisson foundation embedded in a deep soil stratum underlain by a homogeneous half space is developed. The method reproduces the kinematic and inertial responses, using translational and rotational distributed Winkler springs and dashpots to simulate the soil-caisson interaction. Closed-form solutions are given in the frequency domain for vertical harmonic S-wave excitation. Comparison with results from finite element (FE) analysis and other available solutions demonstrates the reliability of the model. Results from parametric studies are given for the kinematic and inertial responses. The modification of the fundamental period and damping ratio of the bridge due to soil-structure interaction is graphically illustrated.