​When Should You Choose a High Pressure Rotary Jet Rig Over Other Methods?

When Should You Choose a High Pressure Rotary Jet Rig Over Other Methods?

Ground improvement and foundation work present a variety of technical challenges, and selecting the correct methodology is crucial for project success. The high pressure rotary jet drilling rig, specializing in jet grouting, is a powerful tool, but it is not always the default choice. Its application is justified by specific soil conditions, project requirements, and site constraints that may make other methods like soil mixing, deep soil mixing, or traditional piling less effective or more costly. Understanding the unique advantages of jet grouting allows engineers to make an informed decision on when to deploy this technology.

One of the primary scenarios for choosing a high pressure rotary jet drilling rig is when dealing with complex or variable subsurface profiles. Jet grouting is remarkably effective in soils containing obstructions such as boulders, timber, or old foundation remnants. The high-energy jet can often erode and incorporate these obstructions into the soil-cement matrix, whereas a displacement pile or a continuous flight auger might be stopped entirely. Similarly, in sites with interlayered sands, silts, and clays, jet grouting can create a uniform treated mass, whereas other methods might struggle to achieve consistent results across different soil types. Its ability to create a wide range of geometries—columns, panels, and curved walls—also provides design flexibility that is difficult to match with more rigid systems.

Projects requiring the formation of structural elements in confined spaces or with limited headroom are strong candidates for a high pressure rotary jet drilling rig. Because the rig primarily uses a relatively small-diameter drill string to reach the treatment depth and then expands the column through jet action, it does not require the large excavation or heavy vibration associated with sheet piling or secant pile walls. This makes it ideal for urban environments, for work inside existing basements, or for creating underpinning elements beneath existing foundations without causing significant disturbance. The minimal vibration of the process is another critical factor when working near sensitive structures or infrastructure.

The functional objectives of the ground improvement often dictate the method selection. The high pressure rotary jet drilling rig is uniquely capable of creating very low-permeability barriers. For constructing hydraulic cut-off walls to control groundwater flow around excavations or to contain contaminated plumes, jet grouting can create a continuous, impermeable screen to significant depths. While soil-bentonite walls are an alternative, jet grouting can be performed in tighter spaces and can more easily key into an underlying impermeable layer. Furthermore, for soil stabilization to mitigate liquefaction risk, the injection and mixing process can both densify granular soils and bind them together, significantly increasing their resistance to seismic shaking.

The decision ultimately comes down to a technical and economic evaluation against alternatives like Deep Soil Mixing (DSM) or traditional piling. Deep Soil Mixing is a mechanically-based mixing process that is very efficient and cost-effective for large-volume treatment of soft soils, but it may not be suitable for soils with obstructions or for creating the same complex geometries. Traditional piling methods are excellent for transferring loads to deep strata but are less effective for creating in-situ barriers or for treating soil masses laterally. Therefore, a high pressure rotary jet drilling rig should be chosen when the project demands a combination of deep access, the ability to handle complex ground conditions, the creation of custom shapes, and the need for both strength and impermeability in the improved ground.