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Research on Deformation Characteristics of New Type of Cofferdams Structure
Liu, Aimin (Tian Jin Port Engineering Institute Ltd. of CCCC, CCCC First Harbor Engineering Company Ltd., Key Laboratory of port geotechnical engineering, ministry of communications, PRC, Key Laboratory of port geotechnical engineering of Tianjin) | Li, Bin (Tian Jin Port Engineering Institute Ltd. of CCCC, CCCC First Harbor Engineering Company Ltd., Key Laboratory of port geotechnical engineering, ministry of communications, PRC, Key Laboratory of port geotechnical engineering of Tianjin) | Tong, Xinyao (College of Civil Engineering, Tianjin University)
ABSTRACT With the increasingly stringent environmental protection requirements in China, the research on dredged soil treatment technology has become important. A new type of cofferdam with a mud-sand interbedded structure is described in this paper, including construction equipment, construction technology and design methods. The dredged soil is filled with a membrane bag and interbedded with a sandy membrane bag, which gradually forms a stable new cofferdam core structure. Through the finite element simulation results, it is known that after 55d of consolidation, the maximum displacement of mud-sand interbedded structure is 2.73 m, the top surface of the mudsand interbedded structure is 1.9 m from the back surface. The compression of the mud-sand bed structure occurs in the middle of the body, the bottom and top are less compressed. The design and construction of the cofferdam meets engineering requirements, and is a feasible, fast method to build a soft soil foundation for cofferdam's. INTRODUCTION Offshore cofferdams are barriers against wind and wave erosion in coastal areas. In the past few decades, the types of cofferdam have emerged in an endless stream (Wang, C, 2008; Wang, H, 2014). However, most of them are made of rock, sand or a membrane bag soil. With the shortage of sand and rock and the continuous increase of costs, the construction cost of cofferdams increases greatly (Wei, 2017; Yang, 2009). On the other hand, dredged soil disposal, which is produced by dredging of waterway every year, brings great pressure to related enterprises. How to utilize resources without affecting the environment is the bottleneck of dredged soil management. So far, in addition to the traditional sloped cofferdam type, new types of cofferdam structures such as a large-diameter vertical cylinder cofferdam, vertical caisson structure and semicircle cofferdam have appeared which are more suitable for deep water areas (Zhang, 2016). The sand cofferdam with a bag has been widely used in water conservancy projects. After entering the 21st century, the cofferdam with a mold bag with solidified soil core materials has appeared.
- Construction & Engineering (1.00)
- Energy > Oil & Gas > Upstream (0.71)
ABSTRACT A case history of constructing offshore breakwater on soft clay is presented. The breakwater were constructed near the Shanghai Port, China, for deepening of navigation channel along the Yangtze Estuary. The breakwater were designed as gravity retaining structures using prefabricated, semi-circular shaped concrete caissons. Some sections of the breakwater were installed on a thick layer of soft soils. During the construction, the caissons in one section failed under a heavy storm. The causes of failure were investigated by running dynamic triaxial tests on undisturbed soil samples taken from the construction site. It was found that the dike failure was induced by the strength weakening of the soft soil layer below the foundation. The design of the guide dike and the soil improvement works are described in this paper. Surcharge preloading and prefabricated vertical drains was adopted to improve the soft soils below the caissons. The soil improvement measure was proven to be effective in maintaining the stability of the breakwater against subsequent heavy storms. GENERAL INTRODUCTION As part of the Yangtze Estuary Development Project, breakwater were constructed 40 km away from a busy port in Shanghai, China. These breakwater were used to facilitate the deepening of navigation channels and prevent future sedimentation within the channels. The water depth ranged from 7.0 to 8.5 m. The design wave height was 3.32 to 5.90 m with a return period of 25 years. The breakwater were designed as gravity retaining structures using prefabricated, semi-circular shaped concrete caissons to resist the rough waves (FAN, et al., 2005). The prefabricated, semi-circular shaped concrete caissons for guide dike construction were used in the Channel Deepening Project for the Yangtze Estuary, which has the following advantages:All the wave and water pressures acting on the semi-circular shaped surface pass through the centre of the circle.
_ A new design of geotextile sandbag embankment, named non-uniform geotextiles reinforcement, is proposed in this study. This proposed design optimizes the arrangement of geotextiles in the traditional design to increase the strength of the embankment base to improve its stability. The behaviour of the reinforced embankments is investigated using finite-element modelling. The advantages of this new design are elaborated via comparison with the traditional design. A design framework of the construction of the embankments is established based on a parametric study. Introduction Geotextile sandbag embankments have been widely used in coastal and offshore engineering in recent years because of their fast construction, high stability, good drainage, environmental and economic advantages, and easy decommission compared with the traditional methods of constructing shoreline structures using earth, rock, or precast concrete units (Gao, 2010; Yan and Chu, 2010; Wei et al., 2013; Yan et al., 2016). Similar to geotextile tubes (or containers), which have been used widely in the world (Leshchinsky et al., 1996; Shin and Oh, 2004; Saathoff et al., 2007; Lawson, 2008; Gao, 2010; Chu et al., 2011; Shin et al., 2016; Yan et al., 2016), geotextile sandbags have been employed to be filled with sandy soil by pumping in slurry, as shown in Fig. 1, panels a and b. However, the geometry of the cross section of the geotextile sandbags is flat, which is different from the circle of the geotextile tubes (Yan and Chu, 2010; Chu et al., 2011), and the horizontal dimensions of the geotextile sandbags (which range from almost tens to hundreds of meters) are much larger than that of the geotextile tubes (which are less than 10 m).
Changing Soil Responses During Episodic Cyclic Loading in DSS Tests
Laham, Noor (University of Southampton) | Kwa, Katherine (University of Southampton) | Deeks, Andrew (Norwegian Geotechnical Institute) | Suzuki, Yusuke (Norwegian Geotechnical Institute) | White, David (University of Southampton) | Gourvenec, Susan (University of Southampton)
ABSTRACT Whole life geotechnical design is an emerging philosophy in offshore geotechnical engineering to improve design outcomes by considering the whole life of imposed actions coupled with geotechnical properties that evolve with each action. Softening of normally consolidated clays from undrained cyclic loading intervened with consolidation has been shown to lead to hardening, manifested by evolving strength, stiffness, and coefficient of consolidation. This paper presents results from a set of stress-controlled direct simple shear (DSS) tests. The tests follow pre-failure episodic cyclic loading stress paths where each episode comprises a packet of undrained cycles of loads followed by full consolidation. The soil response under different numbers of cycles per loading packet and number of loading packets with intervening consolidation is investigated. The results from this study quantify the effect of the undrained cyclic loading history, for the same final number of cycles, on the evolution of the soil properties, to support the application of whole life geotechnical design in practice. Outcomes allow calibration of design curves that are traditionally used to capture softening, by introducing consolidation effects. This enables capturing the whole life softening and hardening processes, by extending the traditional contour diagram representation for undrained cyclic loading without consolidation to allow for consolidation periods. INTRODUCTION Renewable Energy Future The global offshore energy industry is going through a significant period of transition aiming to net zero greenhouse gas emissions in the coming few decades, where renewable energy is expected to be one of the fastest-growing energy sources globally in this domain (IEA, 2021). In line with the Paris agreement for climate neutral energy or energy with no greenhouse gas emissions in the coming 30 years, investments and technologies are needed to decarbonize the energy system. East Asia is responsible for 34% of the global energy-related emissions, where 53% reduction in carbon emissions is planned by 2050 through the transition towards renewable energies (IRENA, 2019). Asia's share of the global offshore market is expected to grow from 24 % in 2019 to 42% in 2025 (Reglobal, 2020). In addition, Europe is aiming to increase its offshore capacity from wind and other ocean energy (e.g., wave and tidal) to at least 340 GW by 2050, i.e., multiplying the capacity for offshore renewable energy by nearly 30 times (EC, 2020). In parallel, the UK is aiming to quadruple the amount of offshore wind generated to 40 GW by 2030 and to 100 GW or more by 2050 (CCC, 2020). Fig. 1 presents the global growth of the offshore wind market over the next decade where Asia is expected to double its share by 2030 although Europe is still expected to remain as the largest regional offshore wind market. The transition towards a clean decarbonized energy future is underway. To cope with the rapid development the world is witnessing, offshore industries are aiming for advancement of efficient offshore renewable energy structures through increasing the capacity and efficiency of designs.
- Europe (1.00)
- Asia (0.89)
- North America > United States > California (0.28)
Nonlinear Numerical Study On Performance of Cofferdam With Double-walled Steel Sheet Piles
Cui, Chun-yi (Institute of Road and Bridge Engineering, Dalian Maritime University, State key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology) | Huang, Jian (State key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology) | luan, Mao-tian (State key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology) | Li, Mu-guo (State key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology)
ABSTRACT At present, there are many international engineering practices of double-walled cofferdam with steel sheet piles. Double-walled cofferdam with steel sheet piles is widely employed in port engineering due to its good integrity, construction convenience and multifold testing measures. For computational convenience, conventional methods are mainly based on earth-pressure theory. In the present work, nonlinear numerical computation is conducted by developing elasto-plastic FE model in plane strain state, employing Mohr-Coulomb yield criterion to describe the elaso-plasticity of subsoil and Coulomb contact pair theory with penalty algorithm to simulate the discontinuous contact behavior between foundation and soil, as well as using infinite element in model boundary to avoid static boundary effects. The features of internal forces and deformation of double-walled cofferdam with steel sheet piles at varied water heights are analyzed through comparative computations. Based on computational results and theoretical analyses, several conclusion remarks are drawn to provide valuable references for engineering practice and design. INTRODUCTION Due to its good integrity, construction convenience and multifold testing measures, double-walled cofferdam with steel sheet piles is widely employed in worldwide engineering practices. So far, many studies have been conducted for cofferdams with double-walled steel sheet piles and fruitful achievements have been obtained. In conventional methods, both inner and outer steel sheets are often simplified by cantilever beam theory. An example illustrating how these design charts can be used to facilitate computation of the required quantities including seepage rates factors of safety against basal heave, and piping have been included (Sunirmal, 1993). The influence of the shell relative thickness applied to the design of a single cellular cofferdam whose stability under gravity forces was examined, with the strength of the granular backfill material being described by a Mohr- Coulomb criterion (Buhan and Corfdir, 1994).