Grouting technique for soil consolidation

The need to consolidate the natural soils and rocks that will be involved in civil engineering projects, has for long time given rise to a large series of consolidation techniques including those of cement and / or chemical injections which, under controlled pressure and / or flow-rate, allow to improve the geomechanical characteristics of soils and rocks, as well as existing structures.

In general, the fluid admixtures used for injections consist of cement-based materials mixed with water. The injection technique can be used for many applications, including the filling of fractures; injections can be performed for permeation and to stop the development of settlements in the ground and to stabilize / improve the underground natural structure of the soil for subsequent construction.

The introduction of the consolidating fluid into the ground / rock takes place, in most cases, through the continuous monitoring of the injection parameters (pressure, volume and instantaneous flow-rate) which are continuously checked in order to comply with the injection specifications which will be defined during the designing phase according to the nature of the terrain and the final result required.

Some types of injections can also be used to fill artificial structures such as underground pipes, tunnels and / or mine shafts.

The carrying out of consolidation injections in natural soils and artificial fillings and / or rocks, involves the following operational phases:

1. GROUTING - DRILLING

In relation to the project treatment depth, which will be reached through the use of suitably set up common drill rigs and specific drill strings consisting of rods + casing, a hole is created up to the project depth.

The drilling fluid, generally consists of water but, in some cases, depending on the purpose of the consolidation project or the characteristics of the natural soil, fluids consisting of water plus additives such as, for example, bentonite and / or biodegradable polymers can be used.

2. GROUTING - HOLE PREPARATION

The two most widely employed injection techniques are:

Pipes with valves (T.A.M .: Tube A Manchette)
Packers located on the top of the hole

For both, however, once the drilling has been completed, the drill string must be removed, leaving in place only the casing.

The use of pipes with valves requires the following preliminary operations:

Laying the "T.A.M. Pipe" inside the casing still present into the hole
Extraction of the casing pipe
Carrying out a first injection, aimed at integrating the valved pipe with the surrounding soil or rock by injecting, from the bottom of the "valved tube", a plastic admixture named sleeve grout

The use of packer requires the following preliminary operations:

Extraction of the casing pipe
Positioning of the packer at the top of the hole
Injection of the consolidating admixture

3. GROUTING - INJECTION

As already mentioned, injections can mainly be executed through:

Valves
The valves are rubber sleeves positioned along the support piping. These injections are carried out valve by valve, through the use of special packers that are gradually positioned, inside the T.A.M. pipe in correspondence of each valve.
The execution of this type of injection involves the continuous monitoring of the injection parameters which, generally, are defined in the design phase. Normally they are recorded and plotted in order to be able to view the injection trend and identify any anomaly.
Packers
The packers are placed at the mouth of the hole, or even at pre-established quotes inside the hole itself where permeation injections are usually carried out in fractured rock masses. Also, in this case, the injection parameters are carefully monitored and recorded.

The low pressure grouting injections (Max. Press → abt. 100 bar) are applied in the following fields:

Consolidation injections of loose and / or inconsistent soils
involved in the execution of Civil Engineering works:
- Permeation Grouting Massive permeation injections of the soil mostly aimed at modifying the geotechnical conditions and permeability of the same
- Compaction Grouting Compaction injections of the foundation soil aimed at its geotechnical improvement
- Compensation Grouting Injections to compensate for any settlement of the foundation soils of existing structures when affected by underground works
Injections of consolidation, performed in more or less fractured rock masses.
These injections have the purpose of making the portion of treated rock more homogeneous, reducing the degree of cracking and its permeability. This type of injection is mostly used in the preparation of the areas on which will be built hydraulic dams or in the functional refurbishment of the same.
Construction of impermeable barriers
for the confinement of areas with particularly polluted soils and / or of impermeable volumes of soil on which an artificial reservoir will subsequently be created.
- Injections of the excavation fronts of tunnels, also under the natural water table
- Slope consolidation injections performed through the complementary “nailing” technique

The low pressure injections are carried out with a very wide range of equipment that are identified according to maximum pressure and Flow rate required in the designing phase, to geomechanical characteristics of the soils or rocks involved and to their total volumes affected by the consolidation works.

METAX, Geotechnical Division of CIMA S.p.A. designs and produces grouting equipment for soil consolidation.

MIXING & INJECTION PLANTS
MIP3-GP or MIP5-GP

Support
base | skid
Mixing Plant
Manual | Automatic
Injection Pump
Vertical | Horizontal
Installed Power
between 5,5 and 22 kW

MIXING & INJECTION PLANTS
MIP10-4V|H

Containerized
Mixing Plant
Automatic
Injection Pump
Vertical | Horizontal
Installed power
between 5,5 and 45 kW

MIXING PLANTS

MIXP8
on skid + automatic mixing system
MIXP10
containerized
MIXP24
containerized

Mixing Plants are made in order to support, with the production of an adequate quantity of consolidating mixture, two or more injection pumps (vertical | horizontal) configured according to the specific needs of each site.
The injection pumps are frequently managed by electronic instrumentation capable of:

recording the injection parameters
managing the injection itself according to the maximum preset limits of: pressure, volume and instantaneous flow-rate.