Deep-water Foundation Research Articles

Wave current force test of deep water foundation of bridge in marine environment

As a key parameter in the design and construction of the Sea Crossing Bridge, the wave and current load on the pile foundation has been the subject of extensive research. The magnitude and distribution of wave and current loads on pile foundations are crucial for the safety of the foundation. Based on Male Airport Island Bridge Project in the Maldives, the wave current force of platform pile and steel casing in different construction stages is investigated, and the horizontal force and bending moment of the foundation under various wave and current parameters are tested using an indoor model. The results are as follows: 1) With the same effective wave height and wave period, the maximum horizontal force and bending moment on the pile exhibit a linear relationship to the wave velocity. Under the same water depth, the combined wave current force is greater than the sum of wave force and simple current force, with a maximum difference of 70%; 2) Under 2-year return period wave and current conditions, the horizontal stress on a single platform pile and steel casing increases linearly with the increase in height, and there will be nonlinear relationship with 10-year return period wave and current conditions; 3) With more platform piles and steel casing, the front row piles have obvious protective effect on the rear row piles, and the horizontal force and bending moment of the overall structure increase nonlinearly.

A probabilistic strategy to evaluate scour around bridge deepwater foundations considering a reliability assessment

Currently, an increasing number of deepwater foundations have been built in marine regions, and most of them have to deal with scour problems. Recent design codes of superstructures usually adopt the probability-based method, in which loads are treated as probabilistic parameters. However, for the design of substructures, the impact of scour is generally regarded as a deterministic value represented by the estimated scour depth. This inconsistency in the design strategies brings difficulties in considering the uncertainties associated with scour effects. Fundamentally, this is due to the challenges in the scour estimation using a probabilistic method. Based on an augmented scour database analyzed using the artificial neural-network (ANN), this study quantifies the uncertainties of four types of scour predictive methods. Based on this, it proposes a probabilistic approach for scour estimation according to different cases. Six typical conditions and two practical cases were analyzed using the probabilistic approach. The overall reliability index showed that all these existing scour estimation methods have certain limitations, including inconsistent reliability and unreliable scour depth predictions. To prevent these problems, a concept based on the probability of nonexceedance of a given scour depth has been proposed, which was determined by different target reliability requirements.

Investigating the effect of grain composition on the erosion around deepwater foundations with a new simplified scour resistance test

Bridges are critical nodes in the transportation system, especially those crossing wide rivers and seas. Once in service, bridge foundations and the surrounding soils will act as a system together and are subjected to erosion caused by the flows. For more than one century, researchers and engineers have made significant efforts to understand the scour process and its mechanisms to protect bridge foundations from failures. Past studies on bridge scour mainly started from treating scour a hydraulic problem and focused on the flow field due to the interactions between flow and structure. Actually, for a given flow condition, the erodibility of bed materials plays an important role for scour initiation and propagation. For this reason, this study developed a new laboratory apparatus, Simplified Scour Resistance Test (SSRT), that can quickly evaluate the erodibility properties of soil samples and assist in identifying the critical conditions for scour initiation and development. It was firstly validated by Toyoura sand samples with a median particle size of 0.17 mm. Additional tests were then conducted on samples sieved to be populated by single-size particles (d = 0.075 mm, 0.25 mm, 0.5 mm, and 2.0 mm, respectively) and four different soil mixtures under different flow conditions. Results indicate that the grain composition has a significant influence on the scour resistance, while the compaction or density has less influence than the grain size. Granular materials with the same median particle size showed very different scour resistance, i.e., well-graded samples have much higher scour resistance than poorly graded ones. Scour characteristics of the mixed soils can be related to the particle size distribution curve. With this new testing apparatus and the results obtained, a correction factor ks is proposed to improve the traditional predictive methods considering soil composition, which overcomes the limitation of traditional scour prediction methods that often only considered the median particle size, D50.

Study on the Dynamic Responses of a Large Caisson during Wet-Towing Transportation

Large caissons are extensively applied as deep-water foundations in marine engineering. In fact, caissons are generally prefabricated and transported to project site by wet towing. Motion responses of large caissons and those occurring during the towing process were investigated, and CO2 emissions under various conditions were calculated. These are all considered to ensure towing safety and environmental protection. The caisson resistance coefficient was simulated via Ansys Fluent software. The effects of towrope length, towing speed, and drift depth on the motion responses of caissons under the combined action of wind and wave were evaluated via Ansys AQWA software. Maximum heave value was dominantly affected by rope length and draft depth, and its fluctuation was highly influenced by towing speed and draft depth. However, all of the above mentioned factors had insignificant influences on pitch response. When towing existed, rope tension was rapidly increased from zero to a constant value that depended on towing speed and drift depth. However, the speed of achieving this stable phase depended on the length of the towrope.

Design and Construction of Double-wall Steel Cofferdam in Deep Water Foundations

Deep water foundation is constructed by cofferdam in bridge engineering. Safety, quality, cost, and duration of bridge construction depend on the reasonable and feasible deep water cap cofferdam design and construction scheme. “Pile first, cofferdam back” construction program of double-wall steel cofferdam for deep water cap is applied in second SongHua river bridge. The results show that structural stiffness of steel cofferdam, strength of each component both meet work requirements under the most unfavorable conditions in the life-span of the construction process. This scheme effectively solves the technical difficulties in cofferdam construction and improve the working environment of installation and subsidence process. The project is going on well and the duration of construction time is reduced. This technique serve as a helpful reference to similar engineering.

Analysis of Lateral Dynamic Response of Caisson Foundation in Layered Clayey Soils considering Scour-Hole Dimensions

As a cross-sea or river deep-water foundation, it is clear that the caisson foundation will be subjected to significant lateral dynamic loads due to winds or waves and suffer from scouring under its long-term effect. In order to obtain the scour effect on the dynamic response of the foundation, an analytical model describing the scour-hole effect in terms of scour depth, scour width, and slope angle was constructed. Combined with the nonlinear Winkler theory, a method for the dynamic response of the caisson foundation considering the scour-hole dimensions was proposed. Comparisons against the results from the dynamic FEM demonstrate the reliability of this method. The effects of the scour width, slope angle, and scour depth on the dynamic response of the caisson were discussed. The results show that the scour depth affects the dynamic displacement and resonant frequency of the foundation most, whereas the scour width does less and the slope angle does the least; the dynamic response of caisson can be approximated as the case of the slope angle 5° and the scour width 5B when the slope angle is less than 5° and the scour width is greater than 5B, respectively; the effects of scour width and slope angle on the dynamic response of caisson have the similar change pattern in the displacement and resonant frequency when the scour depth is different. However, the effect of amplitude on dynamic response shows a nonlinear increase trend when the scour depth is relatively large.

Dynamic behavior of laterally loaded caisson foundations based on different cushion types: an experimental and theoretical study

Bridge foundations located in deep water are usually subjected to horizontal dynamic loads and moments which may be caused by the wind, waves, earthquake, and the possibility of boat crashing or vehicle braking. Caisson foundations based on gravel or sand cushions are a new type of deep-water foundation for bridges, suitable for meizoseismal areas. In this paper, harmonic horizontal excitation tests for the study of the lateral dynamic response of caisson foundations based on cushion layers are described. Different lateral loads and two different cushion types are considered. The results show that the lateral dynamic responses of caisson foundations based on sand and gravel cushions both show strong nonlinear characteristics, and the resonant frequency of the foundation decreases with the increase of the excitation force. The dynamic displacement of a foundation based on a sand cushion is far less than that based on a gravel cushion, and the rate of decrease of the resonant frequency of a foundation based on a gravel cushion is faster than that of a foundation based on a sand cushion under the same conditions. Under dynamic loading the gravel cushion can more effectively dissipate vibration energy and isolate the vibration, than the sand cushion can. A simplified nonlinear analysis method is proposed to simulate the lateral dynamic response of caisson foundations, and the predicted response shows a reasonable match with the results observed in laboratory tests. Scaling laws have also been applied in this small-scale vibration model test to predict the dynamic behavior of the prototype foundation.

Experimental and analytical investigations on nonlinear dynamic response of caisson-pile foundations under horizontal excitation

As a deep-water foundation, composite caisson-pile foundation (CCPF) is usually subjected to horizontal dynamic loads and moments due to the complicated marine environment. In this study, model tests were performed on three different types of deep-water foundation, including caisson, caisson with four piles and eight piles to investigate their lateral nonlinear dynamic characteristics under various excitation forces. Meanwhile, the effect of scour depth on the dynamic response of the foundations were also studies. The test results indicate that the excitation force and scour depth significantly affect the vibration amplitude and resonant frequency of the foundations with an obvious nonlinear behavior. Compared with the caisson, adding piles beneath the caisson results in a decrease of the vibration amplitude and an increase of resonant frequency, and the configuration of the pile also has an influence. The experimental results are compared with the results obtained by a simplified dynamic Winkler analysis model proposed here. Despite its simplicity, a reasonable agreement between the experimental and the calculated responses was observed. Moreover, scaling laws have been applied in the CCPF model to discuss the dynamic behavior of the prototype foundation.

Finite Element Analysis of Double-Walled Steel Box Cofferdam

Steel cofferdam has an abroad application in high pile cap construction in deep water foundations. Because of the obvious three-dimensional effect and its complex stress and strain, the traditional simplified calculating method couldn’t reach the requirements of practical engineering. The general purpose finite element software Ansys was used to analyze the stress and strain of steel cofferdam and sealing concrete, and achieved a good effect to ensure the engineering safety.

Finite Element Analysis and Simplified Model of Searing Bottom Concrete for Steel Cofferdam

Steel cofferdam is an advanced technology for high pile cap construction in deepwater foundation. Using Xiangjiang river bridge of Changsha-Xiangtan expressway as engineering background, we use software ANSYS to analyze the stress states of sealing bottom concrete layer of steel cofferdam of this bridge, and obtain some results of deformation, direct stress, principal stress, shear stress and equivalent stress. At the same time, a fixed-ends beam under uniform pressure is used to simplify the analytical model, and results show that this model can give relatively correct stress state with proper precision, but give poor deformation state. As for the design of steel cofferdam, engineers are mainly interested in the stress results. So the simplified model can be used in the design and analysis procedure.

Computation of Dynamic Characteristics of Deepwater Group Pile Foundation for Bridges

In the design of deepwater foundation for bridges, the interaction between water and the structure especially under earthquake motions should be addressed. This paper presents a practical simplified method to analyze deepwater pile group foundation to determine its dynamic characteristics by combining approximate analytical solutions with the finite element method. The applicability of this proposed method is shown in a case study of a nine-pile foundation. Compared with those from complete numerical method, the analysis results from this simplified method are in agreement when the pile cap is not submerged in water. Furthermore when ignoring the vertical hydrodynamic added mass of the pile cap, the vertical vibration mode results are greatly affected, but not for other non-vertical vibration modes. This simplified method is also used in the study of the influence of water on the dynamic characteristics. The deeper the water is, the more obvious the impact of water is, particularly for the pile cap lateral bending modes, and there appears no evident difference for the pile lateral bending modes, on which water effect is stronger than that on pile cap lateral bending mode.

Zhoushan Xihoumen Bridge with the World Record Span Length of Steel Box Girder, China

Connecting the two islands Jintang and Cezi in the Zhoushan Archipelago in the East China Sea, the Zhoushan Xihoumen Bridge was constructed as a two-span, continuous steel-box girder suspension bridge with a main span of 1650 m because deep-water foundation could be avoided. Since the bridge site is located in a typhoon-prone area with very high wind speed, the stiffening girder of the bridge was designed as a twin-box steel girder, innovatively adapted for the purpose of wind-resistant design. The design criteria, construction conditions and structural design of the bridge are systematically introduced in this paper.

Aerodynamic challenges in span length of suspension bridges

The potential requirement of extreme bridge spans is firstly discussed according to horizontal clearances for navigation and economical construction of deep-water foundation. To ensure the technological feasibility of suspension bridges with longer spans, the static estimation of feasible span length is then made based on current material strength and weight of cables and deck. After the performances of the countermeasures for raising the aerodynamic stability are reviewed, a trial design of a 5 000 m suspension bridge, which is estimated as a reasonable limitation of span length, is finally conducted to respond to the tomorrow’s challenge in span length of suspension bridges with the particular aspects, including dynamic stiffness, aerodynamic flutter and aerostatic stability.

THE EFFECT OF SUCTION ON THE FOUNDATIONS OF SUPER LONG SPAN BRIDGES DURING AN EARTHQUAKE

A rational method for the design of deep-water foundations of super long span bridges is desired. Attention is paid to the suction acting on the foundation bottom, which resist the rise of an under-water foundation during an earthquake. The results of a laboratory model experiment conducted in order to grasp the characteristics of suction are presented, and a rational seismic design method considering the efiect of suction is proposed.

Second Nanjing Cable-Stayed Bridge

The Second Nanjing cable-stayed bridge over the Yangtze river, China is 11 km downstream from the first Nanjing bridge and passes through Baguazhou, the third largest island in the Yangtze river. The main bridge in the southern section is a cable-stayed bridge with five continuous spans of steel box girder with an orthotropic deck and an epoxy asphalt concrete pavement. The main span is 628 m long. The technical specifications are listed: deck width, design speed, design load, design wind speed, ship collision force, navigational clearance, design flood frequency, deck slope and seismic scale. The design and construction of the deep water foundation of the tower, the reinforced concrete cable tower and main girder are described. The zinc-plated steel cables and their installation are described.

Probabilistic stability analysis for deep-water foundations : Ronol, K O; Bysveen, S J Geotech Engng Div ASCEV118, N3, March 1992, P394–405

Probabilistic stability analysis for deep-water foundations : Ronol, K O; Bysveen, S J Geotech Engng Div ASCEV118, N3, March 1992, P394–405

Selection of the most effective designs and methods of construction of deepwater pile foundations for hydraulic structures in mud soils

1. The use of large batter screw piles with considerable bearing capacity in easily penetrated mud bottons with interlayers of dense clay increases the level of standardization of the construction of deepwater foundations for hydraulic structures and leads to a rational design having better technical and economic indices even in comparison with vertical thick-walled rubular piles (labor costs, consumption of materials, and construction machines—their cost, and operating time). 2. The slightly greater specific consumption of steel, in this case can be reduced by using cylindrical reinforced-concrete centrifuged thick-walled shells in place of steel shafts for the screw piles. 3. The specific expenditures for maintenance and operation of the construction equipment can be reduced additionally by manufacturing a powerful electric transportable capstan (MZS). .