In the mechanical mixing method, deep mixing is manufactured by mixing the chemical agents, which is either in a form of slurry or powder of cement or lime, with in situ soft soil by rotating mixing blades (Fig. 2.11a,b). Prior to mixing the admixture. the mixing blade is forwarded at a specified speed into the ground to remold the soil until it reaches the specified depth of installation. It is then withdrawn at a higher speed with subsequent feeding of admixtures. The common forward rate ranges from 1.0 to 1.5 m/min, while the withdrawal rate ranges from 2.0 to 3.0 m/min. The chemical agents are injected through a nozzle located near the mixing blades. Moreover, the machinery for DM is shown in Fig. 2.13 and the typical sequence of constructing DM column in the ground is shown in Fig. 2.14.
2.5.2.2 Pressurized mixing (or jet mixing) method
In the pressurized mixing method, or sometimes called jet grouting; the admixture, water and air are supplied under high pressure into the soil to fabricate DJM piles (Fig. 2.12a,b,c). Normally, the admixture is injected in slurry form (grout). The installation procedure is similar that of mechanical mixing method, i.e., forwarding the jet rod down with the associated jet of water to remold the soil until the desired depth, and withdrawing the same with the subsequent injection of pressurized grout of stabilizing agent (Fig. 2.13). However, while the diameter of the DM column manufactured by mechanical mixing method is predefined and is dictated by the diameter of the rotating mixing blade, the diameter of the column made by pressurized mixing method is not obviously define but dependent on the applied pressure of the jetted slurry/grout (Fig. 2.12a,b,c) and on the relative density of the soil.