9.3.1 Chemical grouting method
The chemical grouting method is to inject the grouting material into soil strata through existing pores and voids by low pressure.With the condensation of the grouting material，the soils will be strengthened and the permeability and settlement be decreased.The grouting pressure for the chemical grouting method is usually lower than 20 kg／cm2 and the method is，therefore，also called the low pressure grouting method.Figure 9.1 diagrams the implementation of the chemical grouting method（the single packer method in the example）.
Figure 9.1 Schematic diagram of chemical grouting
Various materials are used for grouting，depending on the purpose of grouting and the properties of rock and soil.Grouting materials are usually categorized into four major types on the basis of the flowing properties and major contents of the materials：
①Suspension type：including cement，clay（or bentonite），or clay（or bentonite）mixed with cement.
②Waterglass solution type：waterglass is a solution of sodium silicate.Adding some chemicals in waterglass brings about different grouting effects.Table 9.1 lists the general categories of the grouting materials for waterglass solution.
③Suspension and waterglass solution type：mixtures of waterglass solution and other suspension materials，such as waterglass mixed with cement or waterglass mixed with fly ash and cement.The characteristics are a blend of the suspension type and the solution type.
④Polymer solution type：polymer materials include the urea type，the acrylic type，the urethane type，and the lignin type.Generally，polymer materials have good effects.Nevertheless，most of them are highly poisonous and are forbidden for use.
Table 9.1 Classification of waterglass solutions as grouting materials
If chemical grouting is used in pure sandy soils with a pressure lower than 10 kg／cm2，the grout will permeate into the voids of the sand and achieve a good effect of soil improvement without destroying the soil structure.The method is then sometimes called permeation grouting.The solution type of grouting material is often adopted for this method.
For clayey soils，the permeation method is not applicable.A higher pressure（about 20 kg／cm2）is usually needed to inject the grout into soils，which will produce many cracks.The phenomenon is called hydraulic fracturing.The grouting⁃induced hydraulic fracturing will form an arborescent structure，which acts like reinforced soil and is certainly useful to improve the strength of soils.The method，sometimes also called fracturing grouting，usually adopts the suspension type of grouting materials.
Table 9.2 lists the grouting materials for various soils，and serves as a reference for a preliminary plan of chemical grouting.
Table 9.2 Grouting materials for different soils
