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
• 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


Jet grouting columns with diameter of 70 cm in Bandar Abbas shore, Iran (Omran Ista)


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As soon as the design depth has been reached, the rods and drill bit are slowly withdrawn from the soil.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.
All 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

  
Joint sealing - Keller                                   Groundwater exits - Keller

Jet grouting systems
There are three main jet grouting systems. Choice of the most suitable system depends on the soil to be treated, and the application and jet grouted column properties required for the application. Any system can however be used for almost all applications if the design and implementation are consistent with the system chosen.

1- Single fluid
The cement grout is pumped by the rods, emerging at high speed (approx. 200m/sec) from the horizontal monitor nozzle.
 


Single fluid process

2- Double fluid
Two-phase internal rodding is used to separate the water supply and cement grout into two vertically displaced nozzles.
 


Double fluid process

3- Triple fluid
Grout, air and water are pumped along different lines to the monitor. Air at high speed, and water, form the erosive medium.
 


Triple fluid process

Jet grouting properties
Jet grouting acts in the ground according to the specification either as a stabilization or as a sealing structure. A combination of both properties is increasingly required.

Construction forms of jet grouting
The basic geometrical form of jet grouted elements is created through movements of the drill rods:
• Pulling of the drill rods without rotation resulting in panels – if several jet nozzles are used multiple panels may be produced.
• Pulling and swiveling create segments.
• Pulling and rotating create complete columns.

 
Construction forms of jet grouting                              


Construction forms in different applications

Jet grouting equipments
Jet grouting site installations consist of storage containers, silos and a compact mixing and pumping unit. Several high pressure hose connections and control cable lines connect the pumping unit with the jet grouting drilling rig at the installation point. The mast length of the rig varies from 2.0 m in cellars or shaft sand up to 35.0 m in open areas. The bore points are normally located in small trenches equipped with sludge pumps. From there the excess material, water-cement-soil mixture is pumped to setting ponds or tanks.

 

 


Jet grouting equipments - Keller


Jet grouting equipments