Caisson Foundations Research Articles

Seismic Resistant Design Method for Open-Type Wharf with Pneumatic Caisson Foundation

Seismic Resistant Design Method for Open-Type Wharf with Pneumatic Caisson Foundation

Bearing capacity of a side-rounded suction caisson foundation under general loading in clay

Abstract A novel side-rounded suction caisson foundation is proposed in this study. Compared to a conventional circular shape in plan, it has a rectangular middle section inserted in between the two circular halves for increased moment capacity. This paper presents an investigation into the bearing performance of this novel foundation in clay under uniaxial and combined loading by means of an extensive finite element parametric analysis. It is found that by adopting a dimensionless equivalent embedment ratio and a dimensionless equivalent strength heterogeneity ratio, which account for the side-rounded shape of the proposed foundation, its design approach can be unified with an existing framework established for conventional skirted circular footings. The advantage of the proposed foundation and the application of the proposed design method is demonstrated through an example application.

A LSTM surrogate modelling approach for caisson foundations

This study proposes a hybrid surrogate modelling approach with the integration of deep learning algorithm long short-term memory (LSTM) to identify the mechanical responses of caisson foundations in marine soils. The LSTM based surrogate model is first trained based on limited results generated from the SPH-SIMSAND based numerical simulations with a strong validation, thereafter it is applied to predict the mechanical responses of soil-structure interaction and the failure envelope of unknown caisson foundations with various specifications as testing. The results indicate that the LSTM based model is more flexible than macro-element method, because it can directly learn the failure mechanism of caisson foundation from the raw data, meanwhile guarantees a high computational efficiency and accuracy in comparison with physical and numerical modelling. LSTM based surrogated model shows a great potential of application in engineering practice.

Characteristic Test Study on Bearing Capacity of Suction Caisson Foundation Under Vertical Load

Suction caisson foundations are often subjected to vertical uplift loads, but there are still no wide and spread engineering specifications on design and calculation method for uplift bearing capacity of suction caisson foundation. So it is important to establish an uplift failure criterion. In order to study the uplift bearing mechanism and failure mode of suction caisson foundation, a series of model tests were carried out considering the effects of aspect ratio, soil permeability and loading mode. Test results indicate that the residual negative pressure at the top of caisson is beneficial to enhance uplift bearing capacity. The smaller the permeability coefficient is, the higher the residual negative pressure will be. And the residual negative pressure is approximately equal to the water head that causes seepage in the caisson. When the load reaches the ultimate bearing capacity, both the top and bottom negative pressures are smaller than Su and both the top and bottom reverse bearing capacity factors are smaller than 1.0 in soft clay. Combined the uplift bearing characteristics of caisson in sandy soil and soft clay, the bearing capacity composition and the calculation method are proposed. It can provide a reference for the engineering design of suction caisson foundation under vertical load.

Micro-mechanical analysis of caisson foundation in sand using DEM

Caisson foundation has been widely used for offshore structures. The micro-mechanical analysis of the behaviors of a caisson foundation during its installation, operation and failure is important but not currently available. The goal of this study is to improve the understanding of the micro-mechanisms in the installation, operation and progressive failure processes of caisson foundation and provide guidance on the design. For this, the discrete element method (DEM) is adopted to investigate the interaction of caisson foundation and sand. The DEM model is first validated by comparing the results of DEM simulations and experiments, in which similar trends are found in various load-displacement curves. With the validated model, the micro-mechanical response of soils induced by the installation process is studied firstly. Then the behavior of soils during the failure of the caisson foundation, including particle displacement, rotation, and stress distribution, are investigated for cases of different loading combinations. In addition, the fabric, including contact orientation, normal contact force, and shear contact force, and its evolution are studied by dividing the soils into four different zones based on their positions and failure mechanisms. At last, the effect of dimensionally homogenous moment to horizontal load ratio (M/(DH)) is discussed.

Foundations of Yangtze River mainstream bridges in China

Until 20 December 2019, more than 160 bridges have been built or are under construction on the Yangtze River in China, among which 132 bridges span the Yangtze River mainstream. This paper statistically summarises the 132 bridges in detail from the aspects of bridge type, span and foundation type. In addition, classic cases are picked out and introduced for each foundation type, and the future development of Yangtze River bridges is proposed. The results show that the cable-stayed bridge is the most widely adopted bridge type; the span of Yangtze River mainstream bridges is mostly concentrated between 400 and 600 m, and obeys a normal distribution; the pier foundation of Yangtze River bridges currently has the following six types: pile foundation, caisson foundation, colonnade foundation, caisson–colonnade composite foundation, caisson–pile composite foundation and spread foundation, among which the pile foundation is the most widely used foundation; there are three types of anchorage foundations for suspension bridges: tunnel anchorage foundation, gravity excavation anchorage foundation and gravity caisson anchorage foundation; and the gravity excavation anchorage foundation is the most popular type because of the ease of construction.

An investigation of seismic liquefaction damage and an anti-liquefaction technique for a gravity caisson wharf

Gravity caissons are widely used in the construction of coastal ports owing to their simplicity, high capacity, and easy construction. The verification of resistance to seismic liquefaction and earthquakes is necessary and important in the design and construction of coastal ports. In this study, a numerical program was developed based on elasto-plastic theory and a coupled finite element–finite difference method. The seismic resistance of a caisson wharf was assessed using the proposed program. Furthermore, gravel piles were designed to resist liquefaction-induced disaster. It was found that the lateral spreading of liquefied soil would cause large sliding and rotational deformation in the gravity caisson. Adding gravel piles, it can decrease the deformation of the caisson foundation, and improve the stability of the caisson wharf.

Assessment of numerical procedures for determining shallow foundation failure envelopes

The failure envelope approach is commonly used to assess the capacity of shallow foundations under combined loading, but there is limited published work that compares the performance of various numerical procedures for determining failure envelopes. This paper addresses this issue by carrying out a detailed numerical study to evaluate the accuracy, computational efficiency and resolution of these numerical procedures. The procedures evaluated are the displacement probe test, the load probe test, the swipe test (referred to in this paper as the single swipe test) and a less widely used procedure called the sequential swipe test. Each procedure is used to determine failure envelopes for a circular surface foundation and a circular suction caisson foundation under planar vertical, horizontal and moment (VHM) loading for a linear elastic, perfectly plastic von Mises soil. The calculations use conventional, incremental-iterative finite-element analysis (FEA) except for the load probe tests, which are performed using finite-element limit analysis (FELA). The results demonstrate that the procedures are similarly accurate, except for the single swipe test, which gives a load path that under-predicts the failure envelope in many of the examples considered. For determining a complete VHM failure envelope, the FEA-based sequential swipe test is shown to be more efficient and to provide better resolution than the displacement probe test, while the FELA-based load probe test is found to offer a good balance of efficiency and accuracy.

Undrained horizontal-moment bearing capacity of caisson foundations in over-consolidated clay considering effects of gap

When a caisson foundation moves laterally, a gap between the rear side of caisson and the soil is more easily formed in over-consolidated clay. The undrained horizontal-moment bearing capacity of a caisson foundation in over-consolidated clay was investigated through 3 D finite element analyses. To investigate the effects of aspect ratio, caisson size, surface soil strength, and soil strength distribution on gap formation, a parametric study was conducted for L/D ratios varying from 0.5 to 3, diameters varying from 4 m to 12 m, lengths varying from 6 m to 24 m,sum varying from 2 kPa to 20 kPa and k varying from 0 to 1.5 kPa/m. The results show that the failure mode of caisson foundation under lateral load and moment in over-consolidated clay changes due to the formation of a gap. The gap has a significant impact on the undrained bearing capacity of caisson foundations, and with the decrease of caisson size or the increase of surface soil strength, the gap has a greater impact on the bearing capacity. Based on the research, a gap-influence coefficient and horizontal-moment composite bearing capacity has been summarized to provide reference for the design of caisson foundation in over-consolidated clay.

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

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.

Upper Bound Solutions for Uplift Ultimate Bearing Capacity of Suction Caisson Foundation

Suction caisson foundation derives most of their uplift resistance from passive suction developed during the pullout movement. It was observed that the passive suction generated in soil at the bottom of the caisson and the failure mode of suction caisson foundation subjecting pullout loading behaves as a reverse compression failure mechanism. The upper bound theorems have been proved to be a powerful method to find the critical failure mechanism and critical load associated with foundations, buried caissons and other geotechnical structures. However, limited attempts have been reported to estimate the uplift bearing capacity of the suction caisson foundation using the upper bound solution. In this paper, both reverse failure mechanisms from Prandtl and Hill were adopted as the failure mechanisms for the computation of the uplift bearing capacity of the suction caisson. New equations were proposed based on both failure mechanisms to estimate the pullout capacity of the suction caisson. The proposed equations were verified by the test results and experimental data from published literature. And the two solutions agree reasonably well with the other test results. It can be proved that both failure mechanisms are reasonably and more consistent with the actual force condition.

Equivalent seismic coefficients for caisson foundations supporting bridge piers

Safety of a foundation under seismic loading is strongly dependent on the inertial forces transmitted by the superstructure, exchanged with the surrounding soil and acting into the foundation itself. The latter contribution, typically neglected for shallow and pile foundations, should be considered for caisson foundations, much more massive and rigid than the foundation soil. In this paper, the inertial forces acting in caisson foundations during seismic shaking are extracted from the results of a parametric study where different caissons supporting bridge piers are subjected to severe ground motions. The parametric study was carried out in the time domain via 3D Finite Element (FE) dynamic analyses performed in terms of effective stresses but assuming an undrained response of the foundation soil. Non-linear and inelastic soil behaviour was described in the analyses by an elastic-plastic constitutive model with isotropic hardening.In the framework of a pseudo-static approach, the caisson inertia is represented by equivalent horizontal and rotational seismic coefficients, kh eq and krot eq, relating the generalised inertial forces to the caisson weight. The coefficient kh eq turns out to be always remarkably smaller than the maximum value computed at ground surface in free-field conditions, kh max(g.s.). The equivalent seismic coefficients kh eq and krot eq are expressed via empirical relationships as a function of the dynamic properties of the whole system and the seismic input, through dimensionless parameters. Calculation examples are finally given, where safety assessment of bearing capacity is made for different systems using the pseudo-static approach, showing that use of the seismic coefficients computed by the proposed relationships yields results consistent with the ones obtained from the dynamic analyses.

Suction caisson foundations for offshore wind energy: cyclic response in sand and sand over clay

This technical note considers experimental data on the long-term response of a suction caisson in sand and sand over clay to lateral cyclic loading. Installation of the caisson under suction in a geotechnical centrifuge provides insight into the contribution of this installation process, as well as the effects that soil drainage and consolidation in the clay layer have on the accumulated caisson rotation and change in stiffness. The tests focused on sand over clay, and considered variations in the cyclic load magnitude and symmetry. One-way cyclic loading in sand over clay is seen to result in higher rotation than two-way loading, which contrasts with findings from previous studies in sand. Excess pore pressure dissipation in the clay layer leads to strength increases that stabilise caisson rotation and increase stiffness. The rate of accumulation in caisson rotation is observed to be the same from centrifuge and single gravity tests, while the initial rotation differs with stress level, drainage regime, loading magnitude, soil profile and installation method. The centrifuge tests are considered collectively with equivalent single gravity tests to form a basis for predicting the long-term response of a monopod suction caisson.

Advanced numerical modelling of caisson foundations in sand to investigate the failure envelope in the H-M-V space

This paper focuses on the identification of the failure envelope of a caisson foundation in sand using an advanced critical state-based sand model (SIMSAND) and the Combined Lagrangian Smoothed Particle Hydrodynamics Method (CLSPH). The parameters of the SIMSAND constitutive model are first calibrated using triaxial tests on Baskarp sand. In order to validate the combined CLSPH-SIMSAND approach, a cone penetration test, model tests and a field test on a reduced scale caisson foundation are simulated. After full numerical validations with different scales from laboratory to in-situ conditions, a numerical parametrical study is then introduced considering different sand properties (density, friction angle, deformability, crushability) and caisson dimensions (soil-structure contact surface area, diameter-depth ratio) and complex combined loading paths to identify the failure envelope in the horizontal force (H), bending moment (M), vertical force (V) space. The influence of the caisson foundation contact surface area, aspect ratio and soil parameters are considered and quantified. Finally, an analytical formula is proposed for the 3D failure envelope in the H-M-V space.

BRIDGE RE-DESIGN CLASS A COMPOSITE GIRDER (GIRDER BRIDGE CASE STUDY OF COMPOSITE CLASS C+) RANTAU BAKULA BANJAR DISTRICT

In Rantau Bakula village are its main bridge girder composite construction. Due to the condition of the existing bridge is felt not designed for vehicles with a large payload then re-design bridge girder composite with spans of 25 m and 9 m wide bridge.In this planning will be carried out load analyzes include: self weight, additional dead load (weight of asphalt and rainwater), load lane "D", pedestrian live load, brake force, load the truck "T", the wind load and earthquake load. Loading method refers to the imposition Standards For RSNI Bridge T-02-2005 whereas the method of structural design of composite bridges refers RSNI T-03-2005 Steel Structural Design For Bridge and SNI 03-1729-2002 on Procedures Design Steel Structures. From the planning to the pavement reinforcement obtained using principal reinforcement D 13-150 mm with shear D 13-90 mm. The main girder profiles used WF 900 x 300 x 16 x 32 and diaphragm WF 400 x 200 x 8 x 13 shear connector used stud with a size of 12 x 190 mm. The connection between girders using screws with a diameter of 20 mm. Abutment has a height of 2.75 m and a length of 10 m. Used caisson foundation amounted to 2 pieces with a length of 2 meters and a diameter of 3.5 m. Keywords: Rantau Bakula, bridge, girders, composite abutments, caisson.

Analysis of in situ bridge columns with exposed caisson foundations in a gravel stratum under lateral loading

In this study, three in situ laterally loaded tests on bridge columns with caisson foundations in gravels were numerically explored. The three tests differed in the application position of lateral loads and the exposed length of the foundations. The analysis model used beam–column elements with distributed plastic hinges to simulate the column and a six-component Winkler beam model to simulate the foundation. The lateral stiffness of the foundation with combined moment and horizontal loading and a large exposed length was the smallest. Although the foundations were situated in a gravel stratum, the caisson with a large exposed length underwent significant foundation flexibility and nonlinearity; however, with increasing lateral loading, the influences of foundation flexibility and nonlinearity on the lateral displacement of the columns were reduced because column yielding limited the load transfer to the foundation. The horizontal soil reactions in front of the foundation and the side horizontal shear soil reactions along the caisson shaft provided major resistances to lateral loading (horizontal load and overturning moment). With increasing foundation exposure, the contribution of the base soil reactions increased, but the contribution of the side horizontal soil reactions decreased accordingly. The side vertical shear soil reactions and base normal soil reactions contributed moment resistance to reduce the foundation displacement and rotation and thus promoted the overall lateral capacity of the caisson foundations although they did not provide direct counterbalances to horizontal loads.

On fluid-filled mixture model for suction pile foundation analysis

The purpose of this study was to investigate the installation water pressure of the offshore wind turbine suction bucket caisson foundation. The fluid-filled mixture theory was used in the study and the theoretical equations are derived from the basic theory of ocean fluid dynamics and flow in porous media and they were solved by finite difference methods. Benchmark verification was performed prior to further simulation cases. Numerical examples were made based on several penetration depths and different suction pressures. Different boundary conditions were tested and the most reasonable boundary conditions were proposed. Suction induced stresses in response to various suction pressures and penetration depths were investigated. The overall lateral resistance and possible piping potential were studied. The frictional stress and bearing capacity on the outside of the caisson are greater than those on the inside. Even the critical suction pressure is given and the penetration depth increases to 2.5 m, the suction induced stress at the outer corner of the caisson tip only increases to 70% of the static effective soil stress and does not reduce the effective vertical soil stress to zero, and no piping is occurred.

Effect of foundation type and modelling on dynamic response and fatigue of offshore wind turbines

AbstractThis paper presents dynamic response and fatigue analyses of several bottom‐mounted offshore wind turbine (OWT) models, simulated in the aero‐hydro‐servo‐elastic simulation tool FAST. The distinction between the models is the foundations, which are modelled with different methods, concepts, and dimensions. The US National Renewable Energy Laboratory has developed a 5‐MW reference turbine supported on a monopile, the NREL 5MW, which was used as a reference model in this paper. The paper presents the implementation and comparison of two different foundation modeling methods, referred to as the simplified apparent fixity method and the improved apparent fixity method. Furthermore, sensitivity analyses of different monopile dimensions were performed, followed by sensitivity analyses of suction caisson foundations of different dimensions. The final part of the paper presents fatigue analyses for the foundation models considered in this study subjected to 17 load cases. Fatigue damage, fatigue life, and damage equivalent loads were calculated, as well as the relative fatigue contribution from each load case.

Model tests on performance of offshore wind turbine with suction caisson foundation in sand

The performance of steel caisson during and after installation with different penetration velocities in medium dense sand is presented. The applied jacking forces, the amount of formed soil heave and bearing capacity were measured in the model tests. The influence of penetration velocities on jacking forces, soil heave and bearing capacity were also discussed in detail. The results indicated that the jacking forces for caisson in medium dense sands were significantly affected by the penetration velocity. The larger the penetration velocity, the more soil flowed into the caisson cavity during installation. This will lead to larger inner shaft resistance and in turn more jacking forces required for the same penetration depth. The height of soil heave during installation increases with penetration velocity. The m value calculated by the ratio of the volumes of the soil heave to that of the penetrated caisson wall can be used to evaluate the soil heave. The larger the applied velocity, the larger the m value and larger bearing capacity of caisson after installation. The relationship between the m value and penetration velocity can be used to control the soil heave for a steel caisson with a wall thickness to external diameter ratio of 4.2% in medium dense sand by jacking method.

Application of the Hilbert–Huang transform to identify the dynamic characteristics of a caisson foundation during liquefaction

This paper presents the application of a Hilbert–Huang transform data processing technique in a dynamic response analysis to identify the dynamic characteristics of a caisson foundation during liquefaction. The degradation of structural modal frequencies during liquefaction under strong earthquakes directly related to a reduction in the stiffness of the soil-foundation structure due to the loss of strength, and the nonlinearity of the liquefied soil layer always occur in a short time. Thus, the short-duration variation of frequencies provided a good indicator for the occurrence of the liquefaction and geometric distortion of a soil foundation system during strong earthquakes and was a very important step in the structural health monitoring work of foundation structures. This study shows that the proposed approach was effective in identifying the instantaneous downshift of frequency of caisson foundation system during liquefaction. This study was based on the measured acceleration response data of a test foundation model from a 1-G shaking table test. Additionally, 2D numerical modeling using a total stress analysis stipulated in the highway bridge specification (JRA 2002), an equivalent linear method in the liquefaction calculation of foundation, was conducted to evaluate the consistency with vibration testing.