Jet Grouting

Jet grouting is a ground modification system used to create in situ, cemented formations of soil. Jet grouting is a technique characterized by the use of a pressurized fluid jet to hydraulically erode soil either before or concurrent with the addition of grout materials. Jet grouting is an alternative to traditional grouting systems, deep slurry trenching, proprietary underpinning systems, micropiling, or the use of compressed air or freezing in tunneling. Applications of the jet grouting system fall into three broad categories:

  • Underpinning and/or excavation support
  • Temporary or permanent stabilization of soft and/or liquefiable soils
  • Jet grouting columns with diameter of 70 cm in Bandar Abbas shore, Iran (Omran Ista)
  • Groundwater or pollution control

The ability to construct jet grouting column in confined spaces and around subsurface obstructions such as utilities, provides a unique degree of design flexibility. Indeed, in any situation requiring control of groundwater or excavation of unstable soil (water-bearing or otherwise) jet grouting should be considered. Usually, jet grouting can be accomplished without disrupting normal facility operations. Jet grouting is not only one of the safest methods of construction available but in many cases the process is so fast that construction schedule savings are realized. The recent development of small containerized, highly mobile support equipment has enabled starting work on the first day of setup, greatly reducing mobilization and demobilization costs. This ability will enable many projects previously considered too small to absorb these costs to become usable.

Jet grouting columns after construction

Jet grouting columns after construction

Jet grouting column with diameter of 1.4 m

Construction sequence
To construct a jet grouted column, a small diameter bore is drilled with the jet rods and drill bit down to the design depth. Drilling gear and drill fluid are chosen to be appropriate for the soil type. To increase the diameter of the jet grouted column and to optimize usage of cement and efficiency in dense, cohesive or very compact soils, pre-cutting with high pressure water may be employed during the initial drilling.
As soon as the design depth has been reached, the rods and drill bit are slowly withdrawn from the soil. During the withdrawal, grout is injected at high pressure (up 700 bar) into the soil from jet nozzles which are situated horizontally just above the bottom of the drill bit. The speed of particles in the jet is approx. 200m/s. Because the drill rods and drill bit are kept rotating during withdrawal and jetting, a homogenous cylindrical body is produced consisting of a mix of injected grout and displaced soil.
Form and size of the jet grout body can be influenced by varying jet pressure, withdrawal rate and rotation of the jetting gear.
Some of the soil-grout mixture overflows through the drill hole onto the ground surface. This spoil is collected and removed.
materials used in the jet grouting process (water, cement, occasionally bentonite and the soil) are natural inert materials which have no negative impact on groundwater and environment. Jet grouted columns can be executed as vertical columns or in any inclination.

Construction sequence of jet grouting

Applications of jet grouting

  • Underpinning of existing structures
  • Downward extension of foundations in the case of settlements or increased load
  • Soil improvement, even underneath existing structures
  • Vertical impervious barriers
  • Impermeable base for excavations
  • Bracing and stiffening of excavations underneath their base
  • Connection of sealing walls to existing structures and/or services and utilities
  • Walls for cylindrical or polygonal excavations
  • Horizontal screens and canopies for tunneling
  • Soil stabilization between neighboring excavations or foundation works
  • Impervious connection of individual piles in pile walls

Jet grouting for shaft support

Jet grouting for wall stabilization

Jet grouting for underpinning of existing structures

Underpinning - Keller              /        Foundation restoration - Keller

Foundation modification - Keller      /  Deep foundation - Keller

Tunnel protection - Keller        /         Horizontal jet grouting for tunnel stabilization - Keller

Shaft support  - Keller   /        Earth pressure relief - Keller

Panel walls  - Keller    /            Column walls - Keller

Dam sealing - Keller        /             Sealing slabs - Keller

Vault slabs - Keller     /           Sealing cover - Keller