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The use of JET GROUTING reinforced columns is also widely employed today thanks to its suitability in a variety of soils ranging from gravel to clay, but especially in very difficult conditions, where both weak soils and thin overburden are found. In fine soils, the column has a static function, while where there is water inflow it works as a barrier against the water. The execution phases of the so called Trevi Reinforced Jet Grouting in Progress (normally T1 single fluid is suggested) can be described as follows.
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1. The treatment is performed by driving both the rod and the casing simultaneously and performing the jetting during the penetration phase. The space between the rods and the pipe allows the jetting spoil to escape. On completion of the drilling/treatment, the jetting string is extracted from the casing which remains in place, acting as reinforcement.
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| Tunnel Consolidation Method with Jet Grouting |
2. This type of consolidation obviously requires a rig fitted with double head.
3. Drilling Is carried out by using a rod string fitted with a monitor and a drilling tool, either by rotation or roto-percussion.
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| Grout Reinforcement Colums |
4. During the drilling phase, the inside fluid escapes from the tool tip, easing therefore the soil penetration and keeping the drilling tool blades clean.
5. When the drilling is over, the jet is diverted by closing the bottom valve and the grout escapes at high speed through the side nozzles, disaggregating and mixing the soil with the grout and thus creating the consolidated column. During this phase the drilling string is rotated and withdrawn at a pre-set rate.
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| Grouted steel pipe |
6. The peculiarity of this system Is that the reinforcing steel pipe is installed during the jet grouting column execution. The jetting string and the casing rotate in opposite senses.
7. The jetting rod itself, fitted with the monitor, is located Inside the string with the jet grouting monitor over-passing the reinforcement pipe mouth of 20 cm approximately.
8. The grouts used are generally binary. Cement/Water following a ratio of 0.8 to 1 and 1.3 with, in case, of use of admixtures.
9. The High Pressure Jetting is carried out by suitable High Pressure Pumps. Soilmec tunneling rigs have been specially designed and adapted to complete this type of work in the most efficient and effective way, where speed and precision are demanded. In addition, such a process allows easier and more cost effective treatment of either soft soli or fractured and soft rock. Today, Soilmec can offer a wide range of equipment capable of covering radius of consolidations from 1880 mm to 6600 mm at 0°, thus applicable both in large tunneling sections for High Speed Railways and highways projects and in those tunnels thought for the city underground system, which consists normally of small sections.
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