Building ground improvement in the full displacement process
The Geopier Impact® system is a gravel stuffing column that is inserted into the ground via a patented displacement mandrel. For this purpose, the thorn is retracted into the ground in the full displacement process. After reaching the final depth (depending on the soils up to more than 12 m possible), the drill spreader is filled with gravel and compacted from bottom to top when pulling the thorn. The process is suitable to improve low-load soils such as loosely stored sands, soft slurs and clays, mixed-grained soils, inhomogeneous fillings and soils below the groundwater level. The use of a patented displacement mandrel does not cause soil excavation, so that the system is also suitable for contaminated soils.
- Very fast production.
- Can be built immediately, as no setting time is required.
- High depths achievable.
- No increased risk of liquefaction in thixotropic soils as with the use of oscile deep vibrators (RSV – vibrating pot compaction).
- Cost-saving floating start-ups are possible. Due to the high tension with the surrounding soil and the improvement of the load-bearing effect of the surrounding soil by increasing the stresses, the columns do not necessarily have to be placed on a load-bearing floor. An improved sustainable soil package is produced without having to completely replace the soil.
- There is no drilling material.
- Due to the system-related always existing piping can be carried out even in non-stable floors.
- Drainage effect of the columns ensures an accelerated consolidation of enlargesoils.
- Can be produced as pure drainage columns.
Due to the lateral displacement of the existing soil when the drilling pipe (filler pipe) is re-entered, the soil is (pre)compressed during the borehole. The subsequent layer-wise vertical compaction of the introduced gravel or split with the special compaction head pushes the material additionally into the surrounding soil, whereby a tension with the soil structure and thus a very high sheath friction is caused. The subsequent load application leads to an expansion of the column, whereby resistance/voltage is built up in the surrounding soil. With the insertion of settlings at the top of the terrain, the vertical stresses in the ground increase, which also leads to an increase in the horizontal stresses and thus to the lateral support of the column. The interaction between the column, the floor and the load application justifies the overall load behaviour of the building site improvement.
The built-in material has a higher shear strength than the surrounding floor. This improves the subsurface in terms of its load capacity or limit load capacity. This improves the stability of the foundation. The column and the reinforced soil structure enable an effective reduction and homogenization of settlings and support of highly loaded foundations and floor slabs.
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Column production GEOPIER Impact
The gravel stuffing columns according to the impact® process are produced by first pressing a sleeve tube with a special compaction head (approx. 35 cm) into the substrate up to the scheduled lowering depth (mäklergeführt) (Fig. 1a). The pipe is protected against the penetration of soil material on its compaction head. If the penetration resistance is too high, the insertion is supported by vibration.
In the second step, the envelope tube is filled with gravel or grit (preferable grain approx. 8/32 mm) via the mixing container mounted at the top of the hem tube as well as the mixed material container itself (preferably grain approx. 8/32 mm) (Fig. 1b). The envelope tube is then pulled by a certain amount, while at the same time the cavity below fills with gravel from the envelope tube (Fig. 1c). The gravel is compacted by vertical ramming with the specially formed compaction head, whereby the gravel penetrates into the surrounding ground (fig. 1d) and the adjacent ground is displaced sideways. The surrounding soil matrix is thereby compacted. The column diameter is therefore also determined by the stiffness of the upcoming soils. In horizons of lower stiffness, larger column diameters occur, conversely, smaller diameters are to be expected for stiffer soils. The layer-wise compaction and manufacturing process is repeated up to the final height of the column (Fig. 1e). Inhomogeneities in the building ground are compensated in this way.