Permeation grouting is feasible for a wide variety of mixtures, which can be classified into two categories: suspensions, and chemical grouts. The ingredients for the preparation of grouting suspensions are Cement, Clay, sand, additives for stability, and water. The most widely used chemical grouts are aqueous solutions, which can be divided into several chemical families include: sodium silicate formulations, acrylamides, lignosufites, phenoplasts, and aminoplasts.
2.3.2.1.1 Materials for Suspensions
The main ingredient for the preparation of grout suspensions is Portland cement, generally available on the market in various types. The chemical composition must comply with a standardized range of contents of , MgO, 3 , of added inters, fly ash and pozzolanic material. The most important property for the selection of cement for grouting is its fineness, which should be as high as possible when granular soil with narrow fissures is to be grouted. Clay is added as a fine grain filler to reduce the cement consumption, and it also improves the stability and the viscosity of the suspension. Mainly used clays for grouting include kaolinite and montmorillonite clays.
Sand is added to stable grout suspensions when a system of large fissures has to be injected. The grain size distribution and the maximum grain size should match the fissure size and suit the available grouting pumps. Additives are added to maintain a stable suspension.
SO3 CaOA2O3
2.3.2.1.2 Chemical Grouting and Chemical Grouts
Chemical grouting is the process of injecting a chemically reactive fluid grout that reacts after a predetermined time to form a fluid, semisolid, or gel. Chemical grouting requires specially designed grouting equipment. Chemical grouts were developed in response to a need to develop strength and control water flow in geologic unit where the pore sizes in the soil or rock were too small to allow the introduction of conventional Portland-cement suspensions. The first description of a method for injecting soils with sodium silicate was gives as long ago as 1887 and involved a two-shot process. One-shot process was developed thereafter. At first, the two-shot approach was used for consolidation and the one-shot approach for waterproofing and excavation stabilization, while nowadays the latter may also be applied to consolidation. The technology has expanded with the addition of organic polymer solutions and additives that can control the strength and setting time of the grouts.
Sodium silicate is still the most popularly used grout material today. Other chemical grouts include acrylate, lignin, urethane, and resign grouts are also available. In recent years, colloidal silica was also used in grouting in some situations. In the selection of a grout for a particular application, certain chemical and mechanical properties should be evaluated. These include viscosity, setting time, toxicity, durability, and strength.
Viscosity: Viscosity is the property of a fluid to resist flow or resist internal forces. A common unit of measure of viscosity is the centi-poise (1 centi-poise is equal to
Pascal⋅Second). Viscosity determines the ability of grouts to penetrate the pore space of soils. Penetrability is also affected by soil hydraulic conductivity or 10−3
permeability. A conservative criterion (Karol 1982) is that grouts with viscosities less than 2 cp can usually be pumped without trouble into soils with permeability as low as
cm/s. At 5 cp, grouts may be limited to soils with permeability higher than cm/s. At 10 cp, grouts may not penetrate soils below cm/s. All grouts may have trouble penetrating soils containing 20% or more silt.
10−4 10−3
10−2
Setting time: Setting time is the interval between initial mixing of the grout components and formation of gel. The control of setting time can be an important factor in the successful completion of field projects. If all other factors are held constant, setting time is a function of the concentration of activator, inhibitor, and catalyst in the formulation. Viscosity may be constant through the entire setting time for some grouts, and it may change during this period for others. For the latter, the increased viscosity may cause trouble to the pumping. After gelation, a chemical grouts continues to gain strength. The time interval until the desired properties are attained is called the cure time.
Toxicity: Most of the toxic grouts ever used have been banned by federal agencies both in the U.S. and abroad. However, all chemical grouts should be handled with care. Manufacturer’s instructions in handling and disposing of the materials should always be followed. When large quantities of chemical grouts are to be injected, it is prudent to consulate the appropriate environmental regulatory agencies during planning.
Durability: durability is the ability of the grout to withstand exposure to hostile conditions after injection. Mechanical deterioration may occur if grouts are subjected to
alternate freeze-thaw or wet-dry cycles. Chemical deterioration can occur if the grout reacts with the soil or ground water to form soluble reaction products, or if the grout itself is inherently unstable in field. Generally, materials with those unfavorable characteristics should not be used as grouts.
Strength: Among other applications, chemical grouting is often done to add strength to formations. Thus, the strength of soil formation stabilized with chemical grouting is of very practical interest. The unconfined compression test on grout-treated samples is a useful index of the strength of the material and may serve as a screening test for the effectiveness of the grout. In many applications, the grout may be placed and remain under the water table. Drying of the grouted soil will never occur. In this situations, the most significant strength factor is the “wet” strength: the strength of the stabilized soil formed and remaining immersed in a saturated formation (Karol 1982), which may be lower than that of a dry specimen.