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Concrete Technology
Published in P.K. Jayasree, K Balan, V Rani, Practical Civil Engineering, 2021
P.K. Jayasree, K Balan, V Rani
The most common method of handling concrete under water is by tremie. A tremie consists essentially of a vertical steel pipeline which is topped by a hopper. It is so long as to reach from a working platform above water to the lowest point of the underwater formwork.
Offshore Drilling and Production Platforms/Units
Published in Sukumar Laik, Offshore Petroleum Drilling and Production, 2018
The construction of the caisson starts from the dry dock and then it is floated to the sheltered deepwater construction site. For the proper placement of concrete, the ‘tremie method’ is adopted. A tremie is nothing but a downpipe or vertical tube about 1 ft (0.3 m) or more in diameter through which concrete enters the form. The lower end of the tremie, which is slightly flared, is always kept immersed in the concrete just deposited. As the level of concrete rises, this tremie is also raised.
Construction and testing of deep foundations
Published in An-Bin Huang, Hai-Sui Yu, Foundation Engineering Analysis and Design, 2017
Depending on the nature of the caving soil, the slurry can be as simple as the mixture of water and soil resulting from drilling of the borehole (drilling fluid), or the slurry can be made of a mixture of Bentonite (i.e., Montmorillonite) and water (Bentonite slurry). Bentonite consists of very small, plate-like clay particles capable of absorbing the large amounts of water molecules on their surface. When mixed properly, the Bentonite slurry has a unit weight slightly heavier than water, and a viscosity favorable for maintaining the stability of the borehole but not so excessive as to adversely affect the concrete placement. As shown in Figure 8.21a and b, drilling and placement of a reinforcement cage proceeds in a slurry-filled borehole. The concrete is placed in the slurry using a tremie pipe, as shown in Figure 8.21c. A tremie pipe is a funnel with a long neck that allows the concrete to be placed from the base of the slurry-filled borehole. The tremie pipe is extended to the bottom of the borehole initially. The tremie pipe is lifted by keeping the bottom of the pipe submerged at a certain distance below the rising surface of the freshly placed concrete so that the concrete that comes out of the tremie pipe does not mix with slurry.
A three-dimensional mechanism for global stability of slurry trench in frictional soils
Published in European Journal of Environmental and Civil Engineering, 2022
Wei Liu, Peixin Shi, Guoqing Cai, Penglu Gan
Concrete diaphragm wall (CDW) is widely used as support of deep excavation in soft ground in urban areas due to its excellent water tightness and high bending stiffness. The CDW is installed panel-by-panel by excavating a trench filled with bentonite slurry, placing a steel reinforcement cage inside the trench, and tremie concreting the trench. Due to the magnitude of the slurry pressure is typically smaller than that of the original at-rest lateral earth pressure on the trench walls, the trench excavation involves in stress release and consequently generates ground movement. The ground movement was documented by many field measurements, such as by Clough and O’ Rourke (1990), Ng et al. (1998), Poh and Wong (1998), Poh, Goh, and Wong (2001), Thorley and Forth (2002), Tsai, Jou, and Hsieh (2000), L’Amante, Flora, and Russo (2012), Mohammed (2017), Liu, Shi, Li, and Wang (2018) and Hsiung (2019). The field measurements show that generally the ground movement reaches maximum close to the ground surface and decays along depth due to the increase of soil stiffness along depth. The large ground movement close to ground surface may cause trench collapse which originates from a shallow depth, propagates upwards and reaches ground surface. This type of collapse is called as global failure distinguished with local failure which occurs within relatively weak soils sandwiched between strong stratums below the ground surface. The occurrence of the global instability was verified by laboratory tests, e.g. by Powrie and Kantartzi (1996) and Tsai et al. (2000).
Drilled shaft foundation construction problems
Published in International Journal of Geotechnical Engineering, 2018
On 23 September 2014, the drilling for the North 1.2 m DSF (Table 1) was begun through a 5.5 m long temporary casing with an outer diameter of 1.27 m. On 24 September 2014, (1) the excavation was completed from a depth of 9.1 m to a depth of 27.9 m below the ground surface and (2) the rebar cage was instrumented with strain gages and a BLC. Upon reaching a depth of 27.9 m there was a lack of polymer slurry due to the combination of (1) high permeability cohesionless soils below a depth of 22.9 m and (2) a limited amount of available water to add the polymer to make the polymer slurry (available water consisted of a half full, 75,708 L water tank). Although more water was delivered to the site by the afternoon of the next day, the excavation remained open for an additional day (to a depth of 21.9 m because the portion of the excavation from 21.9 to 27.9 m was backfilled in an attempt to reduce the amount of outflow of the slurry). The backfill material was removed during the morning of 25 September 2014 and a Sonicaliper® was utilised to determine the profile of the excavated diameter prior to placement of the concrete into the excavation (Fig. 2). The concrete was pumped to the bottom of the excavation through a 20.3 cm inside diameter tremie. The average slump of the concrete was 20 cm and the air content was consistently below 1.2%. The measured strength profile for the concrete, at the time of the BLC test, is presented in Fig. 3 (unconfined compressive strength values near the required strength were measured for the concrete with slump values of 24.8 cm).
Recommendation for concrete mix design to prevent bleed channels on diaphragm walls
Published in European Journal of Environmental and Civil Engineering, 2022
Chafika Djelal, Yannick Vanhove, Amin Azzi, Olivier Madec
The execution of diaphragm walls into the ground implies proceeding by concreting the tremie pipe under the bentonite slurry, which engenders a number of constraints. Even if all these conditions are being met, contractors still currently encounter a wide range of problems, tied in large part to bleeding (Kog, 2009; Larisch, 2016). As a case in point, the observations recorded subsequent to earthworks and planning of walls has revealed that concrete outside the reinforcement cage is of poorer quality than that found inside the cage.