If the ground does not cooperate, it can be given a helping hand. By injecting or grouting ground, the ground can be stabilized and made more or less impermeable. The freezing of the groundwater with the aid of liquid nitrogen or a saline solution produces the same effect on a temporary basis. In the past, ground improvement techniques were regularly applied as an emergency measure. Due to the better manageability of the process, however, these techniques are increasingly used as a regular method for the design of temporary or permanent structures.
Almer van der Stoel wrote his thesis on injection methods (grouting) for the improvement of pile foundations. He and other consultants from CRUX have gained unique experience with various projects in the design of ground improvement techniques. CRUX also provides the course guidance for the PAO course and lectures at the University of Twente and TU Delft in this area and has given several national and international 'state-of-the-art' lectures on this subject. CRUX has specialized computer software for ground improvement calculations.
CRUX has successfully created the design for the following ground improvement techniques in many projects.
The essence of the 'Permeation Grouting' technique rests on the fact that the pores in the ground are filled with an injection fluid, while the grain structure is left intact. If the ground has a coarse structure (gravel), this is easier to do than with fine-grained soils (fine sand).
Jet Grouting is also known in the surrounding countries as Very High-Pressure grouting (VHP) or Hohe Druck Injektion (HDI). Due to improvements, the scope has been broadened to such an extent that almost all ground types can be treated. The principle of the technique is based on jetting the ground loose under high pressure and mixing this ground with a mixture of water and cement. The ground is also partly replaced, whereby the effluent, the so-called spoil, is pushed to the ground level by the overpressure at the bottom along the injection lance, where it is pumped away.
The effect is clearly eroding, so that the grain structure, unlike with permeation grouting, does not remain intact.
Mechanical mixing of soil, commonly called Mix in Place (MIP), or Soil Mixing for short, is based on the principle of mixing the soil using a mixing tool (paddle) with lime and/or cement. The product of the technique is often referred to as a stabilized soil-column. The properties of a soil massif treated by soil mixing show great similarities with the properties of a soil massif treated by the injection methods, namely improving the permeability and strength properties.
Compaction Grouting is a term used for those injection methods where the ground is compacted by displacing the ground around the injection point with grout (water, cement and sand). The ground is thus compacted and suspended. The reasons for application may be the undoing of subsidence due to consolidation or compensating for relaxation caused by, for example, the excavation or drilling of a tunnel.
Fracturing (ground-fracturing grouting), also known as hydrofracture grouting, is a technique that aims to create a fracture surface in the ground by applying a very liquid injection fluid (usually water and cement in 1:1 ratio) under very high pressure.
The fundamental difference from permeation grouting lies in the fact that the goal is not to infiltrate the grain skeleton, but to displace (or 'jack up') the ground.
When the initial horizontal grain tensions are larger than the vertical, the injection liquid forms predominantly horizontal lenses in the ground; if the opposite is the case, the ground is fractured predominantly vertically.
This technique of 'fracturing the ground' can be usefully applied when subsidence must be compensated.
The freezing of groundwater is often used to resolve problems with regard to (ground) water during construction. Because freezing does not provide a permanent solution from a cost perspective, the technique is only used to create temporary stabilization or water inhibition.
A distinction can be made between freezing with brine (relatively cheap and slow, often for longer project duration) and freezing with nitrogen (relatively expensive and fast, often for shorter project duration).
Primarily, a distinction can be made by function for stabilizing injections (increasing strength and stability), sealing injections (reducing water permeability) and compensating injections (compacting or displacing).