Jet grouting is a procedure for mixing soil with injected cement grout insitu to create a cement stabilized soil. With proper quality control, the stabilized soil exhibits increased strength and decreased permeability. These modified properties allow the stabilized soil to be used as an engineered product for foundation support and groundwater control. Underpinning of existing structures and cutoff walls for excavation support are two typical applications.
The jet grout process involves the drilling or jetting of a small diameter pipe, typically around 4 inches in diameter, to the bottom of the desired treatment depth. Once that depth is reached, a neat cement grout is injected under high pressure, typically around 6,000 psi, through ports at the bottom end of the drill pipe as the pipe is rotated and withdrawn to create a circular column of treated soil. The rate of withdraw can be varied to increase or decrease the diameter of the jet grout columns. These columns are located as required for vertical support or overlapped to create a wall or barrier to the horizontal movement of weak soil and groundwater. Jet grouting is particularly effective when the subsurface to be treated contains existing utilities or other buried obstructions since the small diameter pipe can fit between them and create a larger diameter column in the soil below.