Jet Grouting Basics
Soil improvement modifies and increases the mechanical characteristics of the treated soil, most notably its compressive strength and modulus of elasticity, while simultaneously decreasing its permeability. The jet grouting method is one of the most successful systems to achieve these results.
Jet grouting is an in-situ mixing of soils with a stabilizer (usually neat cement grout). The stabilizer is injected at very high pressures (between 300 bar and 600 bar) through a nozzle of small diameter. The grout is injected at high velocity, which enables the jet grouting process to destroy the natural matrix of the soil and creates a mixing of the stabilizer with the in-situ soils. The result is a homogeneous and continuous structural element with predetermined characteristics. Jet grouting can be applied to a wide range of soils from non-cohesive, poorly graded granular soils to cohesive plastic clays.
Key applications of the jet grouting process include soil stabilization, excavation support systems, structural underpinning, seepage barrier/cutoff walls and environmental remediation. Chief among the advantages that jet grouting offers is the comfort of knowing what you've got:
- predetermined quantity of the stabilizer to be injected per unit volume of in-situ soil
- final strength of the stabilized soil can be predetermined
- permeability of the stabilized soil can be predetermined
- estimated as a lump sum vs. unit price and contingency for other grouting methods
Jet Grouting SystemsSingle Fluid - This system is the most simple, as well as the method of choice of most qualified specialty contractors. The system has been tested and developed in Italy since the mid 1970s to its present state-of-the-art. The single fluid referred to in this method is neat cement grout. The neat cement grout is injected through a small nozzle at high pressure and mixes with the in-situ soil. This method produces the most homogeneous soil-cement element with the highest strength and the least amount of grout spoil return.
Double Fluid - The two fluids referred to in this method are neat cement grout and air. The neat cement grout is injected at a lower pressure and is aided by a cone of compressed air, which shrouds the grout injection. The air reduces friction loss, allowing the cement grout to travel farther from the injection point, thereby producing greater column diameters. However, the presence of the air reduces the strength of the column as compared to the single-fluid method and produces more spoil return.
Triple Fluid - The three fluids referred to in this method are neat cement grout, air and water. Unlike single- and double-fluid systems, water is injected at high pressure and is aided by a cone of compressed air, which shrouds the water injection. This process produces an air-lifting effect, which evacuates the soil within the intended column diameter. The grout is injected through a separate nozzle below the water and air nozzles to fill the void created by the air-lifting process. The triple-fluid system is a soil replacement method, not an in-situ mixing method.
Drilling is performed using rotary drilling techniques and an external water flush with special drill rods and bits. Upon the completion of the advancement of the drill rods to the design depth, the jet grouting process commences. The grout is forced out of the lateral nozzle at high pressure and velocity, thus destroying the soil matrix and forming consolidated elements. Many structures and geometries can be achieved by altering the parameters of the jetting procedure. The illustrated procedure details the creation of a jet grout column by continuous controlled rotation of the drill string at pre-set lifting increments.