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The penetration of spudcans have adverse effects on pre-existing bucket foundations during the blade lifting process of offshore wind power systems, which brings uncertainties for the design and construction of bucket foundations. This study employs the Euler-Lagrange method to explore the influence of spudcan penetration on the adjacent caissons in homogeneous clay within a large deformation finite element (LDFE) model. The LDFE model is validated against centrifuge tests data, with good agreement obtained. Parametric study is then conducted to explore, (i) the influence of the angle between vessel and caissons on the movements of the caisson, and (ii) potential influence factors on the movements of the caisson with an optimal angle between the vessel and caissons, including soil properties, dimensions of caisson and spudcan, and the distance between spudcan and caissons. The results show that 60° is the optimal angle between the vessel and caissons that results in the smallest movement of the caisson, and the caisson foundation inclination angle ranges between 0° and 0.025°, when the pile shoe penetration progress ranges between 0.1 and 1.0. An empirical formula is proposed to predict the rotational angle of caisson with the optimal angle. The study establishes a quantitative approach to assess the influence of the spudcan penetration on existing three-caisson jacket foundations, which provides guidance for the design and construction of offshore wind turbine bucket foundations. [ABSTRACT FROM AUTHOR]

• This study addresses the impact that the size and shape of the local scour hole have on both the monotonic bearing capacities and failure envelopes of suction caisson embedded in sandy soil. • Scour depth has a stronger influence on the ultimate bearing capacity than the influences of scour width and angle. • Both the horizontal bearing capacity and the moment bearing capacity reach a plateau and a steady state manifest itself when the relative scour depth exceeds a threshold value of 0.9. • An empirical formulation to characterize the failure envelope within the horizontal force-moment (H-M) plane considering the effect of scour depth is proposed. Local scouring significantly undermines the load-bearing capacity of suction caisson foundations and poses a daunting challenge to the integrity of offshore structures. This study numerically addresses the impact that the size and shape of the local scour hole have on both the monotonic bearing capacities and failure envelopes of suction caisson embedded in sandy soil. Different loading conditions - individually and combined - by integrating local scour parameters such as scour depth (S d), scour width (S w) and scour angle (φ) while maintaining realistic scour proportions are carefully evaluated. The obtained results show that (1) scour depth has a stronger influence on the ultimate bearing capacity than the influences of scour width and angle; (2) the horizontal bearing capacity shows increased sensitivity to variations in scour depth; and (3) both the horizontal bearing capacity and the moment bearing capacity reach a plateau and a steady state manifest itself when the relative scour depth exceeds a threshold value of 0.9. An empirical formulation to characterize the failure envelope within the horizontal force-moment (H - M) plane is finally proposed, which properly considers the effect of scour depth. These findings provide a valuable reference for ensuring structural resilience to local scour phenomena. [ABSTRACT FROM AUTHOR]

The finite element analysis is conducted to study the causes of the failure of the caisson quay wall at Malaga Port Container Terminal in Spain. It was found that the marine clay lenses were the main reason for the accident because their low strength reduced the overall stability of the structure. The thickness of the marine clay lens increasing from 0 to 2.5 m decreases the factor of safety (FoS) from 1.288 to less than 1.0. The finite element analyses are also conducted to investigate the effects of dredging the marine clay lenses underneath the rubble mound and installing the vertical pipe piles on the stabilities of the caisson quay wall. The FoS increases nonlinearly with the increase of excavation depth of the marine clay lens underneath the rubble mound and the maximum magnitude is 1.267 when the excavation depth reaches ±29 m from the sea surface. Two lines of pipe pile installed in a square pattern with a spacing of 1.2 m and length of 23 m have an optimum distance to the caisson wall of 6 m to improve the FoS of the caisson quay wall with its maximum magnitude of 1.222. • The numerical analysis is conducted to study the caisson quay wall at Malaga Port Container Terminal. • Parametric studies are conducted to study the effect of the thickness and position of the marine clay lenses on the stability of the caisson quay wall. • Effects of dredging the marine clay lenses and installing the vertical pipe piles on the stabilities of the caisson quay wall are investigated. [ABSTRACT FROM AUTHOR]

Due to the vulnerability of wharves against accidental attacks, the reinforced concrete (RC) caisson quay wall, as a widely adopted wharf form, is faced with the potential threat of underwater explosions. The present work aims to study the dynamic responses and damage modes of caisson against underwater explosions through the underwater explosion test and numerical simulations. Firstly, four shots of underwater explosion test were conducted, including two cases for different focuses, i.e., two shots of the free field underwater explosion with a charge weight of 0.2 and 1 kg respectively, and another two shots of a 1/5 reduced scale caisson specimen subjected to the underwater explosion with a charge weight of 0.2 and 1 kg successively. The underwater explosion overpressure-time histories and periods of bubble pulsation, as well as the deflection-time histories and damage modes of caisson specimen were experimentally obtained. Then, the refined finite element (FE) models were established, including the 1D model for explosion loading and the 3D model for predicting the dynamic behaviors of caisson with adopting the Coupled-Eulerian-Lagrangian algorithms and remapping technology, which were validated by comparing with the test data. Finally, the influences of explosion conditions, such as explosion standoff, depth of burst, and charge weight on the dynamic behaviors of caisson specimens were numerically discussed. It derives that, the existing calculation formulas of overpressure and period of bubble obtained from the spherical charge are also applicable to the group charge; the reflection coefficient of hydraulic RC structure is around 1.7; the bubble pulsation induced by the underwater explosion could further deteriorate the damage level of RC caisson when the blast wave has already led to an inelastic structural response. The present work could provide beneficial references for the blast-resistance evaluation and design of hydraulic RC structures against underwater explosions. • Underwater explosion test in free field and on RC caisson specimen was conducted. • Overpressure-time histories including blast wave and bubble pulsation were recorded. • Reflection coefficient of underwater blast wave on structure is determined around 1.7 • FE approach to predict overpressures and structural dynamic behaviors was validated. [ABSTRACT FROM AUTHOR]

Abstract Floating structures are often secured in position with a taut mooring system and suction caissons. Large seabed trenches have been observed adjacent to some suction caisson anchors with taut-line mooring systems. The trenches may jeopardise the geotechnical capacity of the caissons and in turn the stationkeeping of the floating structures. Finite-element method is employed to examine the geotechnical capacity of suction caissons in a trenching seabed. The results show that the reduction in the geotechnical capacity becomes more significant with increasing trench width due to the loss of soil support and a change in failure mechanism as the caisson rotates into the trench. For a given trench width, the reduction in capacity becomes more significant as the load inclination angle to the horizontal decreases. However, the shape of the normalised failure envelopes for combined vertical and horizontal load is insensitive to trench width. A strategy to design for inevitable trenching by moving the padeye shallower to reduce the depth of trench formation is not straightforward. The gain from a shallower trench may often be outweighed by the reduction in capacity from rotation of the caisson at failure for loading angles typical of taut moorings. Highlights • Geotechnical capacity of the suction caisson anchors exposed to large seabed trenches. • Governing soil flow failure mechanisms around suction caisson anchors in trenching seabed. • The effects of trench configurations, caisson-soil interface conditions and loading paths are examined. • Design for inevitable trenching by moving the padeye to a shallower depth is not straightforward. • A strategy to overcome the challenge of seabed trenching is presented based on a case study. [ABSTRACT FROM AUTHOR]

Passive resistance offered by soil to any embedded structure has been of significant interest to researchers since the inception of the concept. The present study deals with the estimation of passive earth pressure coefficients in seismic conditions that will control the passive resistance offered to a caisson embedded in c (cohesion) – φ (friction) soil in presence of surcharge loading. The three-dimensional (3D) geometry of failure wedge (log-spiral in vertical plane and oval in horizontal plane) has been obtained from the results of numerical analysis and past experimental studies. The critical failure surface has been obtained in the presence of all resisting components [unit weight (γ), cohesion (c) and surcharge (q)] by minimizing the passive resistance. Thereafter, seismic passive earth pressure coefficients for cohesion component (K spc), surcharge component (K spq) and unit weight component (K spγ) have been obtained separately corresponding to the critical failure wedge obtained in the previous analysis. Limit equilibrium method of analysis in conjunction with pseudo-static approach has been used to perform the analyses. Charts for a variety of caisson geometry, soil and site condition and seismic condition have been prepared to facilitate prediction of passive resistance in a more economical and reliable manner since unique failure wedge has been considered for all the components instead of separate failure wedge which would be impractical. • A single failure wedge due to mobilization of all the resisting components has been considered. • Realistic 3D failure wedge was idealized based on numerical analysis and past experimental studies. • Variation of width of caisson has been studied for wide range of geotechnical structures. • Extensive design charts have been prepared. [ABSTRACT FROM AUTHOR]

A novel perforated-wall caisson concept, the so-called LOW REflection Breakwater (LOWREB), based on a three-chamber perforated-wall and inner weirs, is under development in the University of Porto – Faculty of Engineering, Portugal. Physical model tests, carried out in the wave basin of the Hydraulics Laboratory of the Hydraulics, Water Resources and Environment Division, Civil Engineering Department, have been used to study the hydraulic processes related to wave reflection. The physical model was built to a Froude scale of 1:50. Test conditions covered two water levels and irregular waves at three significant wave heights (3.0, 4.0 and 5.0 m) and three peak wave periods (10, 14 and 18s). Three models of varying porosity, and vertical slots' arrangements were tested under the same hydrodynamic conditions to study how these affect the LOWREB performance, namely how these affect the wave reflection from the structure, as compared to a plain caisson tested under the same conditions. The experimental study demonstrates that the LOWREB caisson is a valid concept for marine structures, namely harbour breakwaters, because of its wave energy dissipation capacity, for which the inner weirs were found to play a major role. Results indicate that the hydraulic efficiency of the LOWREB caisson increases with wave height for the lower water level, and decreases with it for the highest. Greater efficiency with respect to wave reflection was accomplished with the highest water level. [ABSTRACT FROM AUTHOR]

• A well-defined analysis methodology for the system-level structural design verification. • It quantifies the load, deformation, cracking, and failure response both at the SLS and ULS. • It encourages better reinforcement detailing and facilitates iterative design improvements. • Valid and efficient analysis models presented are suitable for the use of engineers. • Proposed methodology is independent of the computer program used. Many existing monopole towers rely on caisson foundations to resist the effects of large overturning moments. Increased loading on these towers, coupled with material deterioration and more stringent code requirements, often results in the overloading of the existing caissons. The strengthening of these caissons for additional overturning resistance presents many challenges and typically requires the installation of new piles. A pile cap is commonly used to connect the existing caisson to the new piles. The proper design of the pile cap has a critical importance in ensuring an effective stress transfer and creating a resilient foundation system. While a number of strengthening design approaches are repeatedly used in industry, there is a dearth of guidance and proven analysis methods to verify the performance achieved with these approaches. This study proposes a well-defined analysis methodology for the system-level structural design verification of the strengthened foundation systems. The methodology provides two routes, using either the strut-and-tie or nonlinear finite element analysis methods, to quantify the load, deformation, cracking, and failure responses. The methodology helps expose and address the weak aspects of the design using an iterative design improvement process. A common strengthening design approach from industry, involving a moment-resisting caisson strengthened with four concrete piles and a pile cap, is used as a case study to demonstrate the application of the methodology. The results demonstrate that the methodology provides significant insight into the system-level behavior both at the serviceability and ultimate limit states. The analysis results are found useful in identifying the locations where modified bar detailing could significantly improve the system performance. The improved design from the methodology provided a 56 % increase in the load capacity for the case-study foundation while still using the same amounts of reinforcing steel and concrete as compared to the initial design before the application of the proposed methodology. This paper presents the studies undertaken, conclusions reached, and recommendations made for developing resilient pile cap designs for strengthening moment-resisting caisson foundations. [ABSTRACT FROM AUTHOR]

Passive resistance computation for caissons embedded in layered soil is a complicated problem. In the present study, modified pseudo-dynamic method of analysis has been used to determine both amplification of earthquake waves through the soil strata and the resulting passive earth pressure on the embedded structure. The failure wedge has been idealized based on the results of experimental and numerical studies by previous researchers as log-spiral in vertical plane and oval in the horizontal plane. Earthquake waves are assumed to propagate harmonically in vertically upward direction through layered strata considering modified pseudo-dynamic approach with the entire failure wedge assumed to be lying in a single soil layer. Both, dry and submerged soil conditions, have been considered in the present study. The effect of increase in volume of failure wedge compared to corresponding plane strain condition on earth pressure coefficient has also been discussed in the current study. The earth pressure coefficient due to unit weight component has been reported. The earth pressure coefficient obtained from the current study for structures of different widths are found to be smaller in magnitude than corresponding pseudo-static analysis results. [ABSTRACT FROM AUTHOR]

Finite element limit analysis with axisymmetric condition is employed to determine plasticity solutions of undrained pullout capacity of cylindrical suction caissons in clay with linear increase of strength with depth and zero strength at the seabed. A closed-form approximation of numerical solutions of a suction caisson is proposed from nonlinear regression analysis. The proposed equation is used to check the accuracy and validity of the total pullout force and reverse end bearing force by conventional methods. The three-dimensional effect of suction caissons between axisymmetric and plane strain conditions is also deduced to evaluate the validity of conventionally assumed shape factor. [ABSTRACT FROM AUTHOR]

In this paper, results of a three-dimensional finite element study addressing the effect of embedment ratio (L/D) of caisson foundations on the undrained bearing capacity under uniaxial and combined loadings are discussed. The undrained response of caisson foundations under uniaxial vertical ( V ), horizontal ( H ) and moment ( M ) loading are investigated. A series of equations are proposed to predict the ultimate vertical, moment and maximum horizontal bearing capacity factors. The undrained response of caisson foundations under combined V-H and V-M load space is studied and presented using failure envelopes generated with side-swipe method. The kinematic mechanism accompanying failure under uniaxial loading is addressed and presented for different embedment ratios. Predictions of the uniaxial bearing capacities are compared with other models and it is confirmed that the proposed equations appropriately describe the capacity of caisson foundations under uniaxial vertical, horizontal and moment loading in homogenous undrained soils. The results of this paper can be used as a basis for standard design codes of off-shore skirted shallow foundations which will be the first of its kind. [ABSTRACT FROM AUTHOR]

Rigorous upper and lower bound solutions of pullout capacity for planar caissons in clay are solved by two dimensional plane strain finite element limit analysis. The planar caisson is embedded in a deep clay layer with an undrained shear strength of zero at the mudline that increases linearly with depth. To perform finite element limit analysis, clay is modeled as the triangular element with the rigid-plastic Tresca material in an undrained condition. The planar caisson is modeled as the rigid plate element. Soil-structure interfaces with full tension are used around the contacted length between caisson and clay. Mesh adaptivity is employed to obtain very tight upper and lower bounds on the true pullout load. Parametric studies are carried out for the complete range of input dimensionless variables including adhesion factor and embedment ratio. The results of analyses are summarized in the form of the dimensionless pullout factor which is a function of the dimensionless variables. Empirical closed-form expressions for the dimensionless pullout factor and reverse end bearing factor of a planar caisson are proposed. [ABSTRACT FROM AUTHOR]

Finite element analyses of suction caissons are performed under seepage flow in elastic soil. Poroelastic water elements are used underneath the caisson lid allowing for modelling of suction and inducing seepage flow into the caisson compartment. A detailed parametric study is undertaken exploring the effects of caisson aspect ratio, soil-caisson interface roughness, caisson inner ring stiffeners, and potential gap formation between caisson outer wall and soil, and soil permeability on caisson upward displacement. The results indicate that caisson roughness and stiffeners affect caisson displacement behaviour. A rough caisson causes earlier dissipation of suction hence caisson upward displacements are minimal for a rough caisson compared to a smooth caisson. A steady state seepage condition is only achieved for a smooth caisson with no stiffeners. Presence of stiffeners and surface roughness leads to a halt in caisson upward displacement. Any potential gap along the outer skirt interface enhances the upward displacement for a smooth non-stiffened caisson, but not for a caisson with stiffeners or a rough caisson. For the smooth non-stiffened caissons, unified equations are proposed to estimate seepage length and caisson displacement for soils with different permeabilities. [ABSTRACT FROM AUTHOR]

GFRP caisson technology was developed for construction of two mooring dolphins in Puerto del Rosario (Fuerteventura, Spain) in a more environmentally friendly way than traditional solutions. The construction technique marks a milestone in civil engineering because of its highly innovative nature that will significantly reduce time and complexity of construction operations. Glass fiber and gel-coated UV-protected epoxy resins were used to build a cylindrical structure of 12 m diameter and 13.3 m height, filled with granular aggregates and topped with a 2 m concrete slab, where mooring bollards were fixed. GFRP caissons were manufactured in a factory in Jerez (Spain), transported by ship to the Canary Islands, assembled on site and launched into the sea with a light crane. The construction and environmental advantages include: savings of 75% in CO 2 emissions and 90% reduction in the need for construction surfaces. Economically, the GFRP caisson solution was competitive compared to the original project solution. [ABSTRACT FROM AUTHOR]

The dual boundary element method (DBEM) is applied to investigate the wave scattering and wave loads on a vertical wall with a horizontal plate, over wide ranges of relative widths, porosities, relative depths of submergence, inclinations, and relative depths of vertical barrier. The structure rests on a submerged porous breakwater. It is observed that a smaller relative width of the plate is more effective for reducing the vertical load. Furthermore, varying the relative width from 0.2 to 1.0 does not alter the wave transmission noticeably. It is observed that increasing the porosity of the horizontal plate helps to reduce the vertical wave force, but increases the horizontal wave force and wave-induced moment. Moreover, a variation in the relative depth of submergence of horizontal plate from 0.05 to 0.4 has an insignificant effect on wave transmission. However, it helps reduce the vertical load and increases horizontal wave force and moment. It is observed that an anticlockwise rotation of the horizontal plate by 5° reduced the vertical load and moments by 10%–20%. These results would be effective for the optimal design of similar wave barriers. • Dual boundary element method to solve wave interaction on vertical wall with horizontal plate. • A smaller plate-width helps reduce the vertical wave force. • Increasing the porosity of plate reduces the vertical wave force, but increases the horizontal force and moment. • Anticlockwise rotation of horizontal plate by 5° reduces vertical wave force and moment by 10%–20%. [ABSTRACT FROM AUTHOR]

In this paper, the occurrence rate of caisson sliding of a vertical breakwater during a storm and the probabilistic distribution of the individual sliding distances are derived as functions of such important design variables as water depth, significant wave height, and caisson width. The expressions for various representative sliding distances such as the significant sliding distance are also derived. The derived statistical characteristics of individual sliding distances are then used for calculating the first passage probability of an allowable individual sliding distance during a storm. A method is also proposed to calculate the time-dependent first passage probability for the case where wave climate and mean water depth change with time. Finally, tentative design criteria for the allowable individual sliding distance are proposed. The proposed method is applied to fictitious breakwaters in different water depths near the Port of Hitachinaka in Japan. The time-dependent first passage probability is calculated for the next 50 years in which the wave height may increase due to climate change. The first passage probability increases as time elapses, as the water depth increases, and as the allowable individual sliding distance decreases. Comparison with a previous study that uses a performance-based design method shows that the allowable first passage probability should be in the range between 0.05 and 0.09. For the proposed method to be used in a practical design, however, more detailed study should be made to determine the allowable values of individual sliding distance, first passage probability, and representative sliding distance, by comparing with current design methods. [ABSTRACT FROM AUTHOR]

Abstract: Suction buckets can be used instead of driven piles for the support of jacket or tripod foundations for offshore wind energy converters (OWECs). However, due to the relatively small self weight of offshore wind structures, considerable tensile loads can occur for instance during storms; these loads usually govern the dimensioning of the buckets. Under rapid tensile loading, suction pressures are induced inside the bucket, which can considerably increase the tensile capacity. This paper presents results of numerical simulations based on a coupled pore fluid diffusion and stress analysis which allow for the description of the partly drained load-bearing behavior as well as the quantification of the tensile resistance. It is shown that a high pull-out rate leads to a large increase of the tensile capacity. The maximum capacity is reached when the soil behaves fully undrained or when cavitation of the pore water occurs. In this regard, the main influence parameters are the bucket geometry, the soil permeability, the pull-out rate (loading rate) and, regarding cavitation, also the water depth. It is shown that the mobilization of suction pressures requires a large heave of the bucket, which might be inadmissible with respect to serviceability requirements. Simulations in which variable tension loads are applied with a specific loading rate and then kept constant are also presented. It is found that an accumulation of heave over time occurs when the load exceeds the drained capacity of a bucket. This indicates that cyclic loading of buckets with tensile loads often exceeding the drained capacity might lead to excessive heave. [Copyright &y& Elsevier]

Abstract: This paper proposes a steel pipe sheet pile (SPSP) reinforcement method for existing caisson foundations in water. The technique involves driving SPSPs around the caisson foundation and connecting them to it with reinforcing footing. To support the rational design of reinforcements using this method, the following factors influencing the technique׳s effectiveness and related mechanical behavior should be considered: (1) the conditions of the caisson/SPSP reinforcement footing connection; (2) the caisson/SPSP flexural rigidity ratio; (3) the distance between the caisson and the SPSP wall; and (4) the pile length. However, as the influence of these factors on the reinforcement effect and mechanical behavior has not yet been clarified, the current method has no standardization for the concept of the load transfer mechanism in reinforced foundation systems, and the ultimate lateral bearing capacity of existing caissons has been largely ignored in previous construction. This paper describes centrifuge model tests and three-dimensional elasto-plastic finite element total stress analysis conducted in relation to real cases in order to identify a more effective and rational reinforcement structure. The static lateral bearing capacity and seismic performance of reinforced foundations were investigated, and the following factors were considered: (1) the conditions of the caisson/SPSP reinforcement footing connection; (2) the caisson/SPSP flexural rigidity ratio; and (3) the pile length. Finally, a structural design flow is proposed based on the experimental and numerical simulation results. A chart to facilitate determination of appropriate reinforcement structures is also presented. [Copyright &y& Elsevier]

Abstract: The observational method was introduced into geotechnical engineering to improve both theories and construction techniques. This method was developed to avoid highly conservative assumptions about soil properties in geotechnical design when faced with unavoidable uncertainties of natural ground conditions. The assumptions involved in soil mechanics theories usually differ to a certain extent from reality. These assumptions can be improved by employing an observational database. Thus, theories of geotechnical engineering can be developed by observations during the construction stage. Moreover, precise management of construction work by close observations is essential to avoid risk and to alter the design if needed to match the real conditions. This paper sheds some light on the importance of the observational concept in deep foundations through three case studies. The first one demonstrates the effect of working hypotheses on design outputs of an open caisson of 22m internal diameter. The other two case studies present the difference between theory and reality during construction stage of auger cast-in-place piles (ACIP) in difficult subsoil conditions. Importance of merging the documented theories with the available observations is discussed. The study shows that working hypotheses and engineering models affect the cost and the time required for construction of deep foundations. Field observations are essential during installation of ACIP at a site. Some precautions should be considered when drilling ACIP through sandstone of inclined top surface. These precautions are mainly dependent upon field observations during construction. ACIP can be used effectively in soil formations that have galleries and caves using a cement–bentonite mixture to fill the holes of the unsuccessful piles. Finally, the paper shares a series of practical guidelines with engineering community all over the world that may assist in design and construction of deep foundations. [Copyright &y& Elsevier]

Abstract: To utilize cast-in-place self-consolidating concrete (SCC) for caissons on a rural bridge replacement, specifications were first written as guidelines. A mix design was developed and tested in a reusable trial caisson that would simulate field casting conditions. A fresh sampling technique was devised to investigate the distribution of SCC within the trial caisson. Petrographic analysis of hardened samples was done to quantify the amounts of aggregates present at twenty different locations within the trial caisson. The SCC mix design was then successfully used to cast caissons of one of the two bridge abutments, with no major defects detected by cross-hole sonic logging (CSL). Hardened property tests revealed SCC compressive strengths and modulus of elasticity values that were similar to a traditional caisson concrete used on the project, while the total measured shrinkage and the splitting tensile strengths of the field SCC were seen to be lower than those of the traditional caisson concrete. [Copyright &y& Elsevier]

Abstract: This paper presents two methods that evaluate the target reliability of caisson sliding of a vertical breakwater. First, the statistical characteristics and probability density function are obtained for the safety factors of the breakwaters designed by deterministic methods in the past. The first method calculates the probability density of reliability index by applying the Monte Carlo simulation to the safety factor for various combinations of uncertainties of load and resistance. The significant target reliability index is then calculated by averaging the highest one third of the reliability index. The second method uses the Chebyshev inequality which describes the lower limit of reliability index. Again the Monte Carlo simulation is used to calculate the probability density of the lower limit of reliability index. The maximum of the possible lower limits is then taken as the target reliability index. The application of the methods has given the target reliability indices close to one another and also close to the value used in a recently published design standard. [Copyright &y& Elsevier]

Abstract: Local scour of sediments around subsea caisson structures was investigated experimentally by carrying out flume tests. The horizontal shape of the caissons is rectangular and the incident directions of the flow were 0°, 45° and 90°, with 0° representing flow parallel to the long boundary of the caisson and 90° representing flow parallel to the short boundary of the caisson. The study was focused on the low caissons whose vertical dimensions were equal to or less than their horizontal dimensions. It was found from the test results that the horseshoe vortex played a less important role compared with the velocity amplification at the sharp corners of the caisson if its height is smaller than its horizontal dimension. As the incident angle of flow is either 0° or 90°, scour started at the two upstream corners of the caisson, while scour at the centre of the upstream boundary did not start until the scour pits at the side corners extended there. This was also true for the case with 45° incident angle of the flow. The development of the scour depth was fitted according the exponential function and the hyperbolic function. It was found that the hyperbolic function fits the experimental data better than the exponential function because its correlation factor is larger. [Copyright &y& Elsevier]

Abstract: This study adopts Multivariate Adaptive Regression Spline (MARS) model for determination of uplift capacity (Q) of suction caisson in clay. MARS is a non-parametric adaptive regression procedure. The model inputs included the L/d (L is the embedded length of the caisson and d is the diameter of caisson), undrained shear strength of soil at the depth of the caisson tip (s u), D/L (D is the depth of the load application point from the soil surface), inclined angle (θ) and load rate parameter (T k). The output of MARS is Q. The results of MARS are compared with Artificial Neural Network (ANN) and Finite Element Method (FEM). An equation has been presented from the developed MARS. The results show the strong potential of MARS to be applied to uplift capacity of suction caisson in clay. [Copyright &y& Elsevier]

Abstract: In D-T fusion power plants, large amounts of tritium would be handled. Tritium is the radioisotope of protium, and is easily taken into the human body, and thus the behavior of tritium accidentally released in fusion power plants should be studied for the safety design and radioprotection of workers. Therefore, it is necessary to investigate the behavior of tritium released into large rooms with objectives, since complex flow fields should exist in such rooms and they could influence the ventilation of the air containing released tritium. Thus, tritium release experiments were conducted using Caisson Assembly for Tritium Safety Study (CATS) in TPL/JAEA. Some data were taken for tritium behavior in the ventilated area and response of tritium monitors. In the experiments, approximately 17GBq of tritium was released into Caisson with the total volume of 12m3, and the room was ventilated at the rate of 12m3/h after release of tritium. It was found that placement of an objective in the vessel substantially affects decontamination efficiency. With regard to an experimental result, numerical calculation was performed and the experimental result and the result of numerical calculation were compared, which indicates that experimental results are qualitatively reproduced by numerical calculation. However, further R&D needs to be carried out for quantitative reproduction of the experimental results. [ABSTRACT FROM AUTHOR]

Abstract: This research is to investigate the effects of deformable panels on reducing the seaward displacement, settlement and tilting of caisson quay walls. In this regard, a series of shaking table 1-g tests are performed for a scaled-down caisson quay wall with two different seabed interface conditions. Here, the wall is tested in two cases: with and without (no-mitigation case) applying the deformable panels. Being installed behind the walls, the panels applied in the tests have different mechanical properties. In the model test, the harmonic base motions are used with constant frequency and amplitude. In all tests, the foundation soil beneath the caisson wall is assumed as dense and non liquefiable. However, in order to reproduce a loose backfill situation in the model, the backfill soil is constructed with relative density of 25%. Furthermore, to support the experimental results, a series of finite difference effective-stress analyses are performed in the prototype scale. The mitigation results show that the deformable panels can significantly decrease the seaward movement, settlement and inclination of wall as well as the total pressure recorded behind the caisson wall. Here, these panels are called Displacement Reducer Panels (DRP) based on the obtained results. [Copyright &y& Elsevier]

This paper presents a new wave reduction method, called the Net Buffer Method, to reduce caisson joint waves for suppressing internal erosion and collapse behind seawalls and quaywalls. Caisson joints may fail or widen due to the repeated action of waves that pass though the joints. The new method, in which a net fiber material is installed within the joints, is capable of reducing such caisson joint waves by more than 80% in terms of the maximum and average wave pressures. Unlike previous countermeasures, it is applicable to joints of variable width and can autonomically adjust to changes in the configuration and surrounding environment due to continued wave impacts and other dynamic forcing such as earthquakes. Based on a three-year follow-up survey of its application, the proposed method has proven itself effective in suppressing the occurrence of re-collapse behind seawalls that repeatedly collapsed under severer wave loading. • A new method to suppress internal erosion and collapse behind seawalls and quaywalls is presented. • Consistent reduction of waves that pass through caisson joints by more than 80% under severe wave impacts. • The method is applicable to new, existing and aging caisson structures. • The validity has been confirmed at Major and Strategic International Ports in Japan. • The proposed method can contribute to a sustainable management of caisson-type seawalls and quaywalls worldwide. [ABSTRACT FROM AUTHOR]

• The effect of local scour on the ultimate bearing capacities and failure envelopes of the monopiles and caissons is investigated. • Parametric studies including scour depth, scour hole angle and soil strength heterogeneity ratio are performed. • The formulas are proposed to simulate the failure envelopes of the monopiles and caissons with scour. • A procedure of designing the monopiles and caissons to consider local scour effect is proposed. Local scour may induce bearing capacity loss of the foundation significantly by removing soil around the foundation and it has become one of the pivotal factors causing the failure of structures in offshore engineering. Therefore, it is indispensable to investigate the effect of local scour on bearing capacity behaviour of foundations. This paper focuses on the effects of dimensions of local scour hole on both ultimate bearing capacities and failure envelopes of the monopile and the caisson in undrained soil with different soil strength heterogeneity ratios using three-dimensional finite element method. The results show that the scour depth has a more significant effect on the ultimate bearing capacity than the scour hole angle. Meanwhile, the scour depth has a more significant effect on the lateral bearing capacity (i.e., horizontal bearing capacity and moment) than on the vertical bearing capacity. For given dimensions of local scour hole, the effect of local scour on the bearing capacity decreases as soil strength heterogeneity ratio increases. Moreover, local scour affects not only the size of the failure envelopes of the monopile and the caisson, but also their shape. Based on the above findings, a procedure of designing the monopile and the caisson to consider local scour effect is proposed, which could be helpful to the design of the foundations in practical engineering. [ABSTRACT FROM AUTHOR]

Abstract: This paper introduces a strain-hardening plasticity model that describes the behaviour of caisson foundations when subject to combined vertical, horizontal and moment loads in clay. Development and calibration of the model is based on centrifuge experimental results, theoretical knowledge (bearing capacity and upper bound plasticity theory) and numerical finite element studies. It is applicable to integrated wave-structure-soil analysis. This is demonstrated with example dynamic analyses of a proposed three legged jack-up in over 140 m water depth. Results presented show how the caisson model can be used to study (a) optimum caisson geometries, (b) penetration and relative movement of the foundations, including permanent deformation in extreme events, and (c) comparative behaviour between different footing types. [Copyright &y& Elsevier]

Abstract: As an extension of the elastic multi-spring model developed by the authors in a companion paper [Gerolymos N, Gazetas G. Winkler model for lateral response of rigid caisson foundations in linear soil. Soil Dyn Earthq Eng; 2005 (submitted companion paper).], this paper develops a nonlinear Winkler-spring method for the static, cyclic, and dynamic response of caisson foundations. The nonlinear soil reactions along the circumference and on the base of the caisson are modeled realistically by using suitable couple translational and rotational nonlinear interaction springs and dashpots, which can realistically (even if approximately) model such effects as separation and slippage at the caisson–soil interface, uplift of the caisson base, radiation damping, stiffness and strength degradation with large number of cycles. The method is implemented in a new finite difference time-domain code, NL-CAISSON. An efficient numerical methodology is also developed for calibrating the model parameters using a variety of experimental and analytical data. The necessity for the proposed model arises from the difficulty to predict the large-amplitude dynamic response of caissons up to failure, statically or dynamically. In a subsequent companion paper [Gerolymos N, Gazetas G. Static and dynamic response of massive caisson foundations with soil and interface nonlinearities—validation and results. Soil Dyn Earthq Eng; 2005 (submitted companion paper).], the model is validated against in situ medium-scale static load tests and results of 3D finite element analysis. It is then used to analyse the dynamic response of a laterally loaded caisson considering soil and interface nonlinearities. [Copyright &y& Elsevier]

Abstract: A generalized spring multi-Winkler model is developed for the static and dynamic response of rigid caisson foundations of circular, square, or rectangular plan, embedded in a homogeneous elastic. The model, referred to as a four-spring Winkler model, uses four types of springs to model the interaction between soil and caisson: lateral translational springs distributed along the length of the caisson relating horizontal displacement at a particular depth to lateral soil resistance (resultant of normal and shear tractions on the caisson periphery); similarly distributed rotational springs relating rotation of the caisson to the moment increment developed by the vertical shear tractions on the caisson periphery; and concentrated translational and rotational springs relating, respectively, resultant horizontal shear force with displacement, and overturning moment with rotation, at the base of the caisson. For the dynamic problem each spring is accompanied by an associated dashpot in parallel. Utilising elastodynamic theoretical available in the literature results for rigid embedded foundations, closed-form expressions are derived for the various springs and dashpots of caissons with rectangular and circular plan shape. The response of a caisson to lateral static and dynamic loading at its top, and to kinematically-induced loading arising from vertical seismic shear wave propagation, is then studied parametrically. Comparisons with results from 3D finite element analysis and other available theoretical methods demonstrate the reliability of the model, the need for which arises from its easy extension to multi-layered and nonlinear inelastic soil. Such an extension is presented in the companion papers by the authors [Gerolymos N, Gazetas G. Development of Winkler model for lateral static and dynamic response of caisson foundations with soil and interface nonlinearities. Soil Dyn Earthq Eng. Submitted companion paper; Gerolymos N, Gazetas G. Static and dynamic response of massive caisson foundations with soil and interface nonlinearities—validation and results. Soil Dyn Earthq Eng. Submitted companion paper.]. [Copyright &y& Elsevier]

This paper presents a numerical study to investigate the seismic behavior of mudmat and caisson foundations supporting subsea structures, such as manifolds, in liquefiable sand. In seismic areas, substantial earthquake loads can be imparted to subsea structures during ground shaking, threatening their stability. In particular, soil liquefaction in sandy soil arising from strong ground motions could significantly influence the performance of subsea structures founded on liquefiable sand. The results of this study can provide a better understanding of the response of subsea manifolds in liquefiable soil during and after the earthquake. Three-dimensional, non-linear, dynamic analyses are performed using a finite difference scheme, and the ability of the model to reproduce the site response of a saturated sand deposit is assessed using the results of available centrifuge data. This study includes six computational models representing manifolds with different sizes and weights supported by caissons and mudmats in shallow and deep liquefiable sand subjected to moderate and strong earthquake shakings. The response is evaluated in terms of excess pore water pressure generated in the soil medium and displacements of the subsea foundation during and after the shaking. The results show that manifolds may experience considerable movement during liquefaction and post-liquefaction settlements. In addition, depending on the characteristics of the seismic motion and structural system, the manifold could also experience large tilting. • Use of advanced constitutive model for simulation of the dynamic response of liquefiable soil. • Modelling response of subsea structures on typical foundations during liquefaction. • Modelling of co-seismic and post-seismic response of these structures. • Highlighting general features of the above complicated response for the first time. • Highlighting the key parameters governing the response. [ABSTRACT FROM AUTHOR]