Jet grouting is a grouting technique that creates soilcrete (grouted soil) by using a grouting monitor attached to the end of a drill stem which mixes the grout with in situ soil. Nozzle diameter, pressure, torque and withdraw speed as well as the soil type and characteristics are important parameters for building a proper jet grout column with desired dimensions.
Jet grouting application starts with a small diameter (40-90mm) hole drilled in to the required depth.
Then, drill string is slowly withdrawn and rotated. High pressure (300-700 Bar) grout is pumped through the drill string to crush the soil and mix with the pumped cement to form a column. The grout is pumped by one or more nozzles at the foot of the drill head. The nozzle sizes vary from 1.5 to 4 mm in diameter according to the flow rate of the grout.
The high pressure cement-water mixture (1:1 ratio) pumped through the nozzles at the foot of the auger behaves as a solid which crushes and mixes with the soil to create a simple concrete column in the soil. Excess material of soil cement mix during jetting should rise and flow out from the auger hole collar to avoid unwanted disturbance and fractures of the surrounding ground. This excess material is removed from the site as it emerges to avoid blockage of the flow.
The distance between nozzles is 2.5cm on a multiple nozzle drill string. The rotation of the drill string at 10 revolutions per 4cm crushes the section of the soil to create a soilcrete (grouted soil) while automatically withdrawn every 4 cm.
When column diameter increases, the operation becomes more efficient if the drill revolution and withdrawal speed and nozzle pressure is adjusted according to the soil type. Thus jet grout column diameters of 40-80 cm on cohesive soils and 50-120 cm on cohesionless soils can be constructed.
JET GROUT APPLICATIONS
- Foundation reinforcement
- Soil improvement
- Excavation support
- Scour protection
- Underpinning
- Bottom sealing
- Tunneling stabilization
- Access shaft building
- Cut off wall building
Testing columns should be constructed for determining pressure, revolution speed, cement-water ratio, withdraw speed, and jet configuration parameters. The test column is then removed by digging out to inspect for soil-cement mixture shear strength and soil interaction of the mixture. The construction parameters defined by the tests then applied for construction.
Load tests are also required for jet grout columns constructed as load bearing structural elements. The load tests are made until the break load or maximum settlement is reached. The test loads must be at least 1.5 times greater than the required load.
Settlement load can be evaluated as the constant load which causes the settlement. The load which causes total settlement by 10% of the column diameter, and final settlement curve value for 0.25mm settlement per 1 metric ton of test load.
OUR FOUNDATION REINFORCEMENT APPLICATIONS BY JET GROUTING
New development zones are permitted for construction with the rapid grow of the Antalya city. Various geotechnical problems were raised by insufficient soil report knowledge and experience combined with urban sprawl. Our company has been reinforcing problematic foundations and super structures with various techniques.
A compact machinery small enough to operate within buildings was demanded for reinforcing operations. The electric power was preferred to avoid poisonous exhaust gases, noise and vibrations since operations were done in basements and low ventilated areas. Deep Soil Mixing Method was also applied with improved attachments.
Jet grouting was preferred since the application is possible on almost all soil types. 300-500 bar and 60lt/min capacity was reached with 381BHP diesel power source on application.
Ease of working conditions were provided by the high pressure hose reaching into the building and the smaller machinery designed to work in basements quietly.
Reinforced concrete foundation was only drilled 60mm in diameter with 42mm rod bit for application. Therefore, the intrusion and damage to the existing structure.
Small machinery can be operated as close as 30cm for jet grouting to the reinforced concrete column. Additional socketing is not required since newly made jet grout columns create additional moments to the foundation system.
Jet grout columns can be constructed at required lengths and to required depths. There are no additional foundation connection or socketing required since application is made from an intrusion of 42mm diameter hole to create a larger column diameter (60-100cm) beneath the foundation.
Jet grout columns compact the soil. With the fringe lengths up to 3 meters provides additional strength to load bearing capacity of the existing foundation.
Before The jet grout application, various testing and monitoring equipment’s are placed on the building to constantly monitor the structural system during the application.
