References
Tenay Viaduct - Argis-Tenay diversion
FRANCE, 1994
Building round protective excavation structures in order to protect a viaduct pile bedplate-micropile link.
Between Ambérieu-en-Bugey and Belley, national road 504 crosses the South of the Ain department, via "Cluse des Hôpitaux", a narrow valley cut by the River Albarine, in the limestone massif of the Jura. This route, also used by a railway line, is located on a main transalpine link with busy heavy goods vehicle traffic. At right angles from the little town of Tenay, the valley is particularly deep and installing a diversion requires building a viaduct with piles sunk into fallen rocks at the foot of limestone cliffs, to a depth below the river level.
In order to perform excavation for these foundations out of the water, a round protective cover using 80-cm diameter, double jet, overlapping columns, spaced out every 60 cm with a minimum of 20 bars resistance to ordinary compression was built from a riverside works platform.
In order to work out the parameters of the process to be used in the fallen rocks or alluvium with on-site blocks, 4 test columns, including 2 standing alone and 2 with a centre-to centre distance between them of 60 cm, were produced and unearthed at the start of the works.
Two types of ground were found:
- raw fallen rocks,
- fallen rocks set in a clayey mould.
In both cases, the required diameter and resistance were easily found, and we could check that blocks present didn't have any major masking effect with columns spaced out every 60 cm, as long as, and taking into account the sometimes clayey nature of the mould, overlapping columns were produced in a "fresh-in-fresh" sequence, if possible.
On this building site, Bachy also produced viaduct pile bedplate foundation micropiles, whose size was checked by a haulage test on a test micropile.
Techniques
Jet grouting is a construction process that uses a high-pressure jet of fluid (generally 20 – 40 MPa) to break up and loosen the soil at depth in a borehole and to mix it with a self-hardening grout to form columns, panels and other structures in the ground. The parameters for the jet-grouting process and the desired final strength of the treated soil depend on a number of characteristics, such as the soil type, the technique used and the objective to be reached. In granular soils, the high-pressure jet breaks up the grains through erosion, while in a cohesive soil, such as clay, the jet breaks the mass up into small particles. High pressure is needed to produce the kinetic energy required for the jet through a small-diameter nozzle. Waste material from the process (a mix of soil, water and binder) is recovered at the surface before being taken away for disposal.
A pile is a structural element driven into the soil for transferring loads and prevent deformation. Its slenderness ratio is not limited.
Pile shafts can be uniform and rectilinear, telescopic and belled out.
Piles can be installed either separately or in groups. They can also form a retaining wall, a mixed curtain wall, contiguous piles, secant piles and composite curtain walls, such as Berlin walls and similar. Piles are also used as precast beams to be placed in the structure of the building they support.
Ouvrages
Soletanche Bachy has developed a number of techniques for use in road structures; cut and cover tunnels, viaduct etc.
Voyage au coeur de l'ingénierie de pointe
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