Low pressure grouting with cementitious or chemical binder

---

Description

Grouting consistis of the injection of pumpable material into soil or rock under pressure through vertical or inclined boreholes, typically to a maximum depth of 50 m. Depending on the method of injection, grouting can be classified as slurry (intrusion) and permeation (penetration) grouting, where disturbance to the original soil structure is minimized (Figure 1), and displacement (compaction) grouting; jet grouting and fracture grouting, which deliberately disturb the original soil structure (Townsend and Anderson, 2004; Warner, 2004).

Slurry grouting (injection of flowable suspensions of cement/clay grouts into open cracks, fissures and voids) and permeation grouting (filling pore spaces in soil and joints in rock) are described here generally as “grouting”. Jet grouting is described in fact sheet 5.7, while displacement and fracture grouting are not generally applicable to slope stabilization.

The most common grout materials are cement, microfine cement, lime, gypsum, sodium silicate chemicals and polymers (Warner, 2004; Mc Carthy, 2007). Different grout materials have different viscosity; the more viscous materials, such as cement grouts, are used for coarse grained soil and rock masses with open fractures; the less viscous materials, such as the chemical grouts, are used for fine grained materials (Figure 2). Indicatively, Ordinary Portland cement may be used in soils with D10 > 0.6 to 1.0 mm, while microfine cements may be used in soils with D10 > 0.08 to 0.1 mm. (Mitchell, 1981; Townsend and Anderson, 2004). Chemical grouts may be used in even finer soils. The most common chemical grout used for structural applications is sodium silicate. Other chemical grouts are acrylates and polyurethanes. In 1997 a release of acrylamide into the groundwater caused serious environmental problems in the area of the Hallandas Tunnel, near Baastad in Sweden (Lofstedt, 1999; Littlejhon, 2003), leading to the withdrawal of this chemical from the market. Since then the materials used in chemical grouts come under very close scrutiny for their potential environmental effects.

The process of injection is usually done by a movable injection rig according to the following steps and the same procedures apply for all methods of grouting and injection material:

1. An injection pipe is inserted into the ground to the required depth, either by static pressure (in loose soils) or more commonly by lowering it into a predrilled hole. Drilling is normally carried out by rotary/percussive or more commonly by  percussive methods. Careful consideration is required in the selection of the appropriate flushing medium.

2. Typically the grout is injected from the end of the injection pipe while the pipe is withdrawn, either continuously or in predetermined discrete intervals for the full thickness of interest, resulting in vertical or inclined continuous columns of soil with improved characteristics, e.g. increased stiffness and strength and reduced permeability.

3. The procedure is carried out in several holes, usually in a close grid pattern. If the injection grid is made with small spacing the ground treatment may becomes “continuous” also in the horizontal direction.

Alternative procedures include injection through a pipe in an open hole sealed at the surface or through a grout pipe left in place as “tube a’ manchette”, although the latter is seldom used for low pressure grouting in stabilization projects, where the geometry of the grouted mass is not critical.

To ensure that the injections do not disturb the in-situ structure of the soil, special care is required in adjusting injection rates and pressures, as too high rates and pressures may displace grains or even worse result in hydraulic fracturing.

To confirm the geometry and effectiveness of treatment, injections rates, pressures and volumes must be accurately monitored and recorded, in association with corings for inspection and testing of the treated soil.

Grouting can be used to stabilize rock masses (Figure 3), for selective treatment of weak soil layers at depth or for stabilizing coarse grained soils susceptible to liquefaction related phenomena When grouting is carried out in slopes, drainage must be provided to avoid build up of pore water pressures behind the treated area.

 

---

Design methods

The true cohesion given by the treatment must be sufficiently high to resist the static and seismic loads without damage; in this case excess pore pressures may be considered negligible. In static conditions, the analyses may be carried out using limit equilibrium or FEM methods. In seismic conditions they may be carried out by limit equilibrium methods, modelling the seismic actions pseudo-statically, or by dynamic FEM methods in the time domain. The mechanical properties of the treated soil may be estimated initially from laboratory tests on samples compacted to the in situ density and permeated with the selected binder in the laboratory. These initial estimates will then need to be validated by laboratory tests on undisturbed samples of treated soil. The tests should be carried out at different confining pressures to determine the strength envelope in terms of effective stress. For preliminary estimates, unconfined compressive strengths of cement grouted soil typically range between 0.35 and 0.7 MPa, occasionally up to 2.0 MPa

---

Functional suitability criteria

---

Reliability and feasibility criteria

---

Urgency and consequence suitability

References

• Andrus R.D., Chung R.M. (1995). “Ground improvement techniques for lquefaction remediation near existing lifelines”. Report No. NISTIR 5714, Building and Fire Research laboratory,  National Institute of Standards and Technology, Gaithersburg, MD, USA.

• Littlejohn S. (2003). “The development of practice in permeation and compensation grouting.: a historical review (1802-2002). Part 1: permeation grouting”. Proceeding of 3rd International Conference on Grouting and Ground Treatment, 10-12 February 2003, New Orleans, Louisiana, L.F. Johnsen, D.A. Bruce, M.J. Byle eds., ASCE, Reston, Virginia, 50-99.

• Lofstedt R. (1999). “Off track in Sweden (Scanlink environmental disaster”. Environment, may issue, Heldref Publications.

• Mc Carthy D.F. (2007) ”Essentials of soil mechanics and foundations: basic geotechnics” Upper Saddle River, N.J., Pearson Prentice Hall.

• Mitchell J.K (1981). “Soil improvement: state-of-the-art”. State of the art report, Session 12, Proceedings of 10th International Conference on Soil Mechnaics and Foundation Engineering, Stockholm, Sweden.

• Townsend F.C:, Anderson J.B. (2004). “A compendium of ground modification techniques”. Florida Department of Transportation.

• Warner J. (2004) ”Practical handbook of grouting: soil, rock and structures” Hoboken, New Jersey, John Wiley and Sons

back to top

Print