It is a ground reinforcement technique which is applied at locations where the grounds are not suitable for construction by drilling piles into the ground utilizing the jet grouting equipment described below and creating colons with soilcrete (ground and concrete mixture).
Initially, the ground is drilled with a Ф 90 cm by the equipment with special attachments and hammers that are operated generally with the rotary technique. The liquid applied during the drilling phase is a mixture of water, air and bentonite suspansion or concrete-water mixture. In the second phase, jet injection is applied with 400 ~ 600 bar pressure through 1~4 e.a injection nozless 1.5~4.0 mm in diameter attached onto the monitor horizontally by closing the bit of the boring rod. The material which is injected through the nozzles approzimately with a velocity of 250m/s will mix the ground by tearing the ground with high load of kinetical energy. Meanwhile, jet grout colons are created with the new material consisting of materials the features of which has been changed into a mixture of ground and cement homegenously and continuesly by pulling the rotating the rod upwards. It is possible to create various types of reinforced grounds by changing the the parameters such as the injection speed, angle, the speed of traction and the quantity of the nozzles. Unlike other classical injection methods, it is necessary to know the quantity of thee required materials, the load capacity of the reinforced ground, permability of the ground and it is only possible to determine the cost depending on these factors. The grounds with cohesion such as clay and the grounds without cohesion such as sand and gravel can be rehabilitated with jet grouting technique. During the process, some grouting materials may overflow out of the pile. This is the sign that there is no pressure in the ground. As a summary it is possible to create durable colons in diameter and size as required by the scope of the work.
As a result of the strong pressures of lithostatic loads and tectonic forces, In the natural environment over very long periods of time the the cohensionless sand transforms into the sand Stone during process of diagenesis. Jet grouting technique is now available for the constructors to produce the same effect in the construction sites.
The origins of jet grout application goes back to the experience of the oil drilling company while unblocking strings of the drill rods locked at great depths. It was initially applied by Cementation Company in Pakistan 1950s and afterwards the Japanese construction industry started to use it. It is then systematically be used in various construction applications all over the world.
It has gained a great success thanks to the advancements in the pumping technologies including pumps, automatic drilling rigs and other associated equipment. It is stil a new technology which is open to the new advancements. Through out the page, we provide the following information;
- Applicability to different ground types
- Design criteria
- Control measures during the construction
- Latest technological advancements
- Jet grout applications in civil and environmental engineering
- Example works completed with jet grouting in the history
Jet Grouting Methods and Operations
In the jet grouting procedure the controlled quantities of cementitious grout is injected into the ground through a bore hole with a diameter variance between 7 to 10 cm to the ground which is to be treated.
Currently, there are three different methods used in the industry. The first two of them were developed in Italy and the third was developed in Japan;
- Monofluid system injecting grout only
- Bifluid system injecting air and grout
- Trifluid system injecting air, water and grout
In the monofluid system the ground is disrupted by the action of the cement grout which produces the cementation.
In the bifluid system entrustment of a high speed grout limiting the dispersion and increasing the penetrating power consequently, provides the distruptive action.
In the trifluid system, the jet grouting distruption is performed with an air guided jet of water with a pressure variance of 5 bar to 400 bars, breaking down and washing out the soil partially, which is subsequently replaced by grout at a pressure of 50 bars.
Operating conditions and requirements on site, in terms of available space, construction stages and most importantly the type of soil to be treated determine the choice of the most suitable jet grouting method to be utilized.
The string of the drill rods on the rig has joints that will withstand high pressure,; att the bottom end it is connected to the injection chamber and to the bit, usually a tricone. In the monofluid system, the upper rod is connected to the high pressure grout pump by a swivel-joint and a flexible pipe. The Standard rod strings are 60, 70, 90 mm in diameter. Equipment used to perform bifluid and trifluid jet grouting are provided with a swivel for separate grout/air abd grout/air/water supply, respectively, fed by appropriate pumps and compressors. The rods used for bifluid jet-grouting (76 to 90 mm) have to coaxial ducts to allow separate flow of air and grout. The trifluid system requires tripple-duct rods (76 to 96 mm) in order to allow air, water and grout to flow separately. The injection chamber is located just above the bit. Fort he monofluid system , it is a hollow steel cylinder about 40 cm long, usually of the same outer diameter as the drilling rods. The walls have one or more radial holes fitted with nozzles and there is a central neck on the inside at the bottom of the chamber, 2 cm in diameter, to allow the drilling fluid to reach the bit when drilling. The neck can be blocked by dropping a 2-5 diameter steel ball inside the rods thus forcing the grout to be injected through the side nozzles. Grout nozzles can be 1 to 4 in number with iner diameters ranging from 1-5 to 3-0 mm; they are usually staggered 1 to 2 cm, from each other. They obviously require high pressure capacity pumps.
Drilling operations are usually performed by rotation or rotary percussive action, with or without the use of drilling fluid. Rotary drilling requiring light drill rigs is preferred in medium to fine-grained soils while in chosionless coarse grained soils and when large boulders are found rotary-percussive drilling can be better in terms of performance, although heavier equipment is required. The same rig is generally used for drilling and high pressure grouting.
Once drilling has been finished and the required depth reached, the neck at the bottom of the injection chamber is blocked so that grouting can be performed. The pump starts operating at very high pressure (40-60 MPa) pushing the grout through the nozzles, radially into the ground.
The drill rod is the carefully extracted at a controlled rate and rotated to provide the correct angular velocity to produce the cylindrical columns required. The fluid can be pumped into the ground at very high energy levels; in fact the jet penetrates the ground at a high energy level of 800 km/h or more.
Over the years, the drilling rigs featuring increased power have been developed and the flexibility and reliability is higher with the aim of obtaining more versatile equipment reducing the operating times and improving the size, shape and final properties of the treated ground.
Rotary and rotary-percussive drilling rigs have been developed to work in restricted spaces and also to perfomr horizontal jet-grouting , required for many ground improvement operations especially in underground constructions.
The figure below shows one of the first rigs manufactured in Italy, specifically designed for near horizontal rotary-percussive drilling and jet grouting . Hydraulic Jacs allow the mast to rotate 180 degrees with adjustable inclination up to 14 degrees with respect to horizontal. The first horizontal Jet grouting was perfomed in the Campiolo Tunnel on the Udine-Tarvisio railway line of the Italian State Railways, using a rig of this type.
OPERATION PRINCIPLES
The operations to be performed ofr monofluid and bifluid jet grouting are the most often used systems
First stage, insertion of the drill-rods equipped with the nozzle bearing chamber , down to the design treatment depth by drilling. To achieve good results this stage requires skill as the treatment could be compromised by unwanted rod deviations. At this point, Temeltek’s operators and technicians are highly experienced and skill in this sort of operations that we only employ certified operators.
Second Stage, return and extraction stage. The drill-rod is extracted with rate of ascent and angular velocity carefully controlled while injecting grout through the nozzless; as mentioned above, with a bifluid system the grout jet is air guided to gain more penetrating power.
The following parameters are controlled to obtain volumes of improved soil of the desired shape and size; grout pressure, rate of ascent, angular velocity, numbers of nozzles. The treatment improves the mechanical properties of the soils to the point where permeability and strength is comparable to that of a concrete.
Operating Parameters
The main operating parameters are (1) injection pressure, (2) number and diameter of nozzles, (3) water/cement ratio of the grout, (4) injection time. Presure gauges controls the injection pressure , so the presure determines the jet energy and eventually the radius of trhe action. The capacity of the pumps used necessarily determines the upper limit of the pressure. The parameters fort he operational pressures will be 40 to 60 MPa.
The injection capacity, volume of the grout to be injected into the ground per unit of the time and finally the treatment rate will be determined by the number and the diameter of the nozzles. High power pumps are required to achieve the high pressure rates in order to maintain high pressure. Larger nozzle diameters will be more efficient in the utilization of the power while while the larger number of nozzles by holding the total delivery rate constant decreases the performance because of the greater loss of head. On the conditions where the high-power pumps are not available, limiting the number of the nozzles will provide effective pressure rate.
The most important parameter with regard to the mechanical properties of the treated soil and the primary behaviour of the soil-great mixture is trhe water/cement ratio of the grout. On the condition that the ground water flow is existent, the low water/cement ratio is highly significant and the injected grout could be washed away by the flowing ground water.
Şekil: Yatay jet grout süreci
Ascent rate and the angular velocity of the drilling rod will determine the injection time. A timer placed on the drill rig controls the ascent rate of the drilling rod. The raising action is performed usually in 4cm steps, so it will allow the jet act of the surrounding ground for the time intervals to be set on the timer. Ascent rate will affect the mechanical properties of the ground in addition to the required time for the operation. There is a minimum ascent rate below which the operations will not be feasible for any specific soil type, delivery rate and pressure rate. It has been seen that if the extraction speed is too slow , the jet will start the flow along the outer surface of the drill rod as it will not have the sufficient energy.
The ascent rate determines the angular velocity of the rods and two of these elements should organized to work simultaneously in order to optimize the distrupting action of the jet. There is a lower limit for angular velocity below which the jet reflection occurs. If the special precautions are not taken, this will reduce the efficiency of the operation. The table below provides the typical values for the basic operating parameters of the jet grouting.
Şekil: Jet Grout Operasyonu ile oluşturulmuş jet grout kolonları
The properties of the Columns In Accordance With The Method Used
Columns of various diameters ranging from 0-40 to 1-40 can be produced by utilizing the monofluid system depending on the factors associated with the mechanical properties of the treated ground and with the operating parameters used.
Jet power can be increased by using the bifluid system and eventually its percussive capacity. The diameters of the columns which are obtained by using a bifluid system is 30-70% greater than that of obtained by using a monofluid system. On the other hand The effect of the air entertained within the treated ground may decrease the mechnical strength.
The trifluid system cannot be used for the horizontal operations but it produces columns with diameters larger than 2 meters. However, the cost will be higher with less operating flexibility. The most important of all the surrounding ground can be lost while the soil is disprupted and washed out. This is a limit to the use of this method.
“Two stage” system provides the ability to produce columns in larger diameters. Preceding the grout injection, very high pressure of water is injected into the grout to achieve a preliminar breakdown in the treated ground. Water and the washed-out finer soil particules are replaced subsequently by the injection of the grout. As it encounters less resistance from the already remoulded ground, the grout penetrates deeper. Morever, Better mechanical properties are given to the treated earth materials by the removal of the finest fractions.
| System | Fluid | Bar | Nozzle (mm) | Ascent Rate (cm/min) | Angular Velocity
r.p.m |
Water/Cement Ratio | Discharge
(l/min) |
| Monofluid | Grout | 400-500 | 1-2×2-5 | 15-100 | 5-15 | 1.0-1.5 | 70-600 |
| Bifluid | Grout+air | 400-550
10-12 |
1-2×2-5
– |
10-30
10-30 |
4-8 | 1.0-1.5 | 70-600
4000-10000 |
| Trifluid | Grout+Air+Water | 50-100
10-12 400-500 |
1-2×4-5
1-2×2-3 |
6-15
6-15 6-15 |
4-8
– – |
1.2-1.5
– – |
80-200
4000-10000 40-100 |