Compaction grouting consists of consecutive processes:
- Displacement rod penetration – the tip of the rod imbeds in the ground to the planned depth causing sideways expansion;
- Iniection – performed in two phases: iniection into the hole under high pressure (1 – 7 Mpa) which changes into soil compaction grouting, compressing the soil and creating a column of different volume. Additionally, the injection results in the compaction of surrounding grounds through the process of grouting. The process is conducted until desired pressure is reached in a certain amount of time;
- Pulling up the rod – during the gradual pulling up the injection rod, it is made a number of individual, adjacent masses, which eventually make an injection pile;
- Piling system – soil improvement using ISR method must be performed in sequence which guarantees ground compaction as efectively as possible, i.e. as the diagram successively presents A,C,D,B.
The ISR method uses injection pumps and especially prepared plastic grout. Use a pilot test area is recommended at the beginning of each compaction grouting project to determine the following parameters: optimal grout mix composition, maximum grout injection pressure, injection time and grid of columns. The volume of grout injected into the soil during works is monitored on the ongoing basis. Drill data recording as well as injection parameters is generally an effective ISR quality control system.
This technology can be used where there are medium and favourable ground parameters on a terrain surface, with non-bearing soils below. This method is used to compact non-cohesive, loose soil (sand, gravel), but it also worksin cohesive, organic and anthropogenic soils, creating structural elements with a high load bearing capacity and stiffness. These columns can be made in water-saturated soils. The ISR compaction grout columns can be constructed under foundation of existing buildings where enhanced bearing capacity or settlement reduction is required, under foundation of special buildings in places where the risk of soil liquefaction may occur or as stiff elements filling voids and caverns. Due to a very low level of vibration during the works, ISR technology can be used in close vicinity of existing buildings.
When it is not necessary to apply compact grouting throughout the length of the column, it can be limited to areas of low-bearing soils. The column diameters are usually not constant in length and depend on the parameters of the improved soil layer, grouting pressure and a rod/drill we use. These columns are applied to the depth of even 22.0 m are usually arranged on a square grid with span range 1.50-3.50 m.
- Comprehensive soil improvement – using compaction grouting leads to significantly enhance parameters of the entire mass of improved soil;
- Good cooperation – because of the low ratio of stiffness to the cross section, after a routine cleaning and levelling ISR columns, base plates and column footings can be set up;
- Functionality – this kind of improvement can be used both under foundations of newly designed and existing buildings;
- Environmentally friendly – this technology is characterized by a very low level of vibration and noise so it can be used in close vicinity of existing building structures and engineering facilities;
- Lack of excavated spoil – during column formation process there is no excavation of the material onto the surface.