Jet-grouting Technology
14 likes3,862 views
Jet grouting is a soil improvement technique that mixes stabilizer like cement into soil in situ using high pressure injection to increase soil strength and reduce permeability. It can treat a variety of soil types to form continuous structural elements. The "multi-axis" technique allows creating multiple jet-grouted columns simultaneously to improve efficiency. MiniJet uses hollow threaded rebar as sacrificial rods for high pressure grout injection, allowing larger diameter columns to be formed faster than traditional jet grouting. Underwater anchoring uses miniJet to install horizontal anchors below sea level from above the water to reinforce seawalls during harbor deepening projects.
Jet-grouting Technology
- 2. Introduction When civil engineering works require soil improvement to build new structures or to restore the existing ones, jet- grouting is applied. Soil improvement consists in modifying and increasing the mechanical characteristic, the compressive strength and the modulus of elasticity and in the meanwhile decrease the permeability of the natural soil. Jet-Grouting is a modern, fast and effective method applied in soils and in weak rocks for the creation of deep foundation elements. Jet-Grouting is one of the most successful systems today in achieving these results. With this method soil is mixed in situ directly with the stabilizer (usually a water/cement admixture) which is injected at a very high pressure (300 bar at least); this means to obtain a grout speed of 200÷250 m/sec. The jet stream, coming out from the nozzles located on a specific “monitor”, destroys the natural soil structure and creates a mixing effect between ground and stabilizer. The result is an homogeneous and continuous structural element with pre-defined features. With Jet-Grouting it is possible to treat a broad range of grounds, consisting of different types of gravel or clay and to overcome the drawbacks of the other injection systems (permeation, compaction grouting, etc.). It is a valid alternative to these or other consolidation systems such as freezing, dewatering or micropiles, etc. The definition of J-G is not complete, if the most important difference, compared to the traditional injection, is not mentioned: with J-G the necessary quantity of the stabilizer can be established before job-site starting, so the final result as for strength and permeability and therefore costs can be defined and estimated a priori.
- 3. Description of the “Jet-Grouting” method OPERATIVE PHASES A. DRILLING Drilling is carried out with traditional methods following the local soil conditions. Commonly rotary or roto-percussion drilling methods are used. Drilling is generally carried out by using tricones or three-blade tools in loose ground, sand and cohesive soils. During drilling the fluids considered each time more suitable, water, air, bentonite slurries or cement admixture are used. The roto-percussion method consists mostly in using external hammers (Top Hammers); recently have been used even Down The Hole Hammers (DTH) systems with satisfactory results in drilling and injection phase. Since for a long time the same drill string has been used to carry out the injection at high pressure, drill strings particularly resistant to the internal pressure have been realized. B. INJECTION Once reached the designed depth, the main drilling fluid passage through the drill bit is closed by a sphere or an automatic valve; in this way the grout admixture is forced to go out from the nozzles, which are positioned laterally on a specific “monitor”. The produced high kinetic energy breaks up the adjoining ground, which mixes with the grout and forms a column of consolidated soil. The original mechanical properties of the natural soil are in this way improved. Different structures of consolidated soil can be obtained by changing speed, angle of rotation and lifting time of the rods. Pseudo-cylindrical elements (columns) are realized with the continuous 360° rotation of the drill string contemporaneously with its retrieving.
- 4. SPECIAL APPLICATIONS OF JET-GROUTING I. “MEGA-JET” Method The new MEGA-JET technology – developed to overcome the objective limits of traditional jet grouting when dealing with large diameters – introduces new operational procedures relying on the use of specific equipment and allows, depending on the conditions of the soil to be treated, to obtain larger columnar diameters (2,0÷4,0 m). Method Description The MEGA-JET system finds application on soils having the required features and leads to the formation of a significant portion of the columnar mass during the drilling (descent) phase, using a 2-fluid Water-Jet (WJ) type of procedure (with air and water); grouting of the column, as well as the final enhancement of the columnar diameter, is obtained by pumping during ascent through the same rods, at equivalent or higher delivery rates (nozzles with bigger diameter or provided in greater quantity) than those applied for the WJ phase. Cement grout and air are used as fracturing fluid throughout the operational phase named 2-fluid Grout-Jet (GJ). The possibility of achieving different delivery rates over the two phases is ensured by the use of a special monitor with differentiated pressure control, enabling the activation/deactivation of two distinct systems of nozzles, according to the different pressures of the injected fluid (WJ and GJ).
- 5. Water/Cement flow Air flow Low pressure 200/250 bar - Shaft upward sliding - Upper nozzle, closed - Lower nozzles opened, with water and air injection High pressure up 450 bar - Sphere launched in the internal passage to stop the shaft sliding - Shaft downward sliding - Upper nozzles opened, with cement and air injection. - Lower nozzles closed “MEGA-JET” Special Monitor
- 6. II. “SUPERJET” The optimization of the working times in relation with the technical purposes of the job-sites has point out the need to create jet-grouting columns of greater diameter. This is particularly valid for the creation of bottom plugs in granular soils with the presence of water. Thanks to the improvement of the technology with the manufacturing of bigger and more powerful high pressure pumps the above mentioned needs can be easily satisfied. In parallel to the machines Tecniwell has been developed special drill string and high efficiency tools to obtain the requested results. “Superjet” columns (2,0 m Diameter) Performed in gravely soils by using n. 01 nozzle 6,0 mm; Injection pressure: 420 bar 3,0 m double fluid (JET2) “superjet” column performed in silty-sandy soil
- 7. Introduction Is well known that Jet-grouting is a soil consolidating technique applied in several deep foundations job-sites. Nowadays in order to increase the daily production and competing in the same time with similar consolidating techniques such as deep soil-mixing (DSM) and cutter soil mixing (CSM), Tecniwell has developed special equipment to allow the contemporaneous creation of multiple jet-grouting columns (from 2 up to 4 columns for each drill rig positioning). Generally multi-axis technology are most suitable for large volume treatments (bottom plugs) or cutoff walls. In function of the local soil conditions (soft or dense soils), Tecniwell has defined two possible job-site setup organized as follows: II. “MULTI-AXIS JET GROUTING TECHNOLOGY” Triple rotary head Single rotary head Triple clamp set Single clamp set
- 8. Dense-soil “Multi-Axis” Jet Grouting Job-site setup Max Hourly production 50 m3 Tank capacity 10.000 lt TWM50 Mixing Unit Diesel Engine 700 HP Plunger ø 4” 4 ½” 5” Max. Pressure BAR 550 450 400 lt/min 560 710 875 Grout flow distribution manifold 2 Axes Jet Grouting Drill Rig TWA10 Holding Tank TW700 High Pressure Pump
- 9. Max Hourly production 50 m3 Tank capacity 20.000 lt TWM50 Mixing Unit Grout flow distribution manifold 4 Axes Jet Grouting Drill Rig TWA20 Holding Tank TW800 High Pressure Pump Diesel Engine 800 HP Plunger ø 5” 5 ½” Max. Pressure BAR 350 290 lt/min 950 1.100 Soft-soil “Multi-Axis” Jet Grouting Job-site setup
- 10. Special application of “Multi-axes” technology The “Jet Mixing” technology has been developed to combine the main advantages of the Jet-Grouting and Soil Mixing. The technique can be performed by mean of dedicated tools such as special auger monitors (Fig. 1 and 2) for drilling and high pressure injection and Auger blades (Fig. 3) for soil mixing. In particular with Jet Mixing is possible to obtain: - Optimal homogeneity of treated soil, typical of the Jet Grouting technology, with high pressure grout injection (al least 400 bar) to achieve an high level of mixing between grout and natural soil. - Thanks to the “Auger blades”, as in the Soil mixing technique, is guaranteed the standardization in the final geometry of the columns; this allows, when three drill strings are contemporaneously employed (Figg. 3 - 4 - 5), the production of homogeneous panels for the creation of continuous wall. This new technique is particularly effective, showing an high daily production, when as a.m. mentioned it is applied using a special Triple rotary head, in this way are obtained a substantial reduction of working times and optimal technical results. Double fluid monitor; 4 or 6 nozzles endowed of nozzle holder and spiral. Single fluid monitor; 4 or 6 nozzles endowed of nozzle holder and spiral. Fig. 2 Fig. 1
- 11. Triple Auger bladesFig. 3 Fig. 4 Fig. 5
- 12. IV. MINJET and U.W.A. - “Under Water Anchoring” ® technology (Patented) Foreword The worldwide increases in utilization of large ships for transportation has created an urgent need of deepening the seabed within port areas and consequently the rehabilitation of its wharfs. To date, traditional techniques to excavate near and reinforce seawalls have resulted in numerous and, at times, unsolved problems. SAPIR Engineering S.R.L. of Ravenna has been appointed by the local Port Authority for the drawn up of the project for the harbor seabed deepening identifying the structural reinforcement of the existing wharves by means of deep underwater tie rods as analternative solution to the traditional installation of new sheet piles (Project published in: PIANC E-Magazine n° 143, July/juillet 2011). The “U.W.A.” Under Water Anchoring System has been created to solve some of the above mentioned problems. The “simple” part was to come out with the idea of installing sub-horizontal anchors below sea level with the utilization of the miniJET® technique. Sub-horizontal anchor installation is the most efficient technical solution to support wall loads and miniJET® is the fastest and simplest way to install anchors in difficult working conditions. The “complicated” part was to design and produce a drill rig capable of installing the anchors from the top of the wharf.
- 13. Introduction to miniJET® technique The typical construction procedure for installing jet-grouted columns involves the following main operations: - Drilling a 75/100mm hole with jetting drill string to the designed depth; - Injection of a water/cement mixture at high pressure (400/500 Bars) through nozzles located on a “monitor” directly above the drill bit; - Timed incremental lifting and simultaneous rotation of the drill string during pressure injection to the designed level. Where the jet-grouted column requires steel reinforcing, the common process is to re-drill in of the centre of the column, insert the reinforce and grout. All of these operations are time consuming, significantly reduce production, and don’t guarantee the centralization of the reinforcing and the integrity of the soilcrete column. The miniJET® technique overcomes all these problems and substantially increases production. High strength hollow threaded rebar, bit/monitor and couplers with specialized internal seals designed for high pressure injection (Up to 400 Bar) are used as sacrificial drilling/injecting rods and left in place after the jetting operations. With this technique it’s possible the realization of soilcrete columns with diameters between 300 mm and 900 mm in function of the design needs and following the geological/geotechnical context where they are executed. minijET ® Drill string (Scheme)
- 14. Typical “UWA” work application
- 15. “UNDER WATER ANCHOR” REMOTE CONTROLLED DRILLING UNIT Hydraulic Crawler Steel Frame Mast Drilling Unit As shown above, the “U.W.A.” drilling system consists of three main parts: 1) Hydraulic Crawler 2) Steel Frame Mast 3) Drilling Unit
- 16. 60 Ton Hydraulic Crawler Excavator Excavator supports the mast/drilling unit and moves the drill rig along the wharf and provides hydraulic power to all drilling operations. The U.W.A. system has a total of n. 2 control cabins: A) from the left side cabin, the operator moves and sets up the hydraulic crawler over the drilling point. B) from the right side cabin, the operator manages (Fig. 1) the final positioning and the drilling operations. Fig. 1 - U.W.A. Control Room and 15” touch screen monitor
- 17. Thanks to a dedicated software the main computer of the U.W.A. is pre-set to record all the main parameters related to anchor installation and obtain a specific report for each anchor executed (Fig. 2). FIG. 2 Anchor report
- 18. Vertical movement of the internal “Mast” and of the attached “Drilling Unit” is actually accomplished with two specific winches (Fig. 3). Within the “Steel Frame Mast”, 8 (eight) angular blocks are installed which function to stiff the entire structure and to enable locking of the internal “Mast”/”Drilling Unit” at the pre-set depth. Fig. 3 – Vertical movement winch Left Winch On the hydraulic crawler main arm is mounted the “ Mast Steel Frame“, which can advance the internal movable “Mast” and the Drilling Unit to the required depth. At the lower end of the internal “Mast” is mounted a two axis sliding system (Fig. 4), for the final positioning of the Drilling Unit onto the chosen drilling point. Fig. 4 – Positioning System of the Drilling Unit
- 19. DRILLING UNIT MAIN MOVEMENTS “Drilling Unit” rotation on the horizontal plane (perpendicular to the main “Mast”): 95 ° + 10 ° “Drilling Unit” translation along the (x) axis (perpendicular to the drilling mast): 500 mm “Drilling Unit” translation along the (y) axis (parallel to the drilling mast): 1.000 mm Pitch movement of the Drilling Unit on the (x) axis: +5 ° / -5 ° The internal sliding “Mast” system allows set-up of the “Drilling Unit” at various levels below working level. At the maximum drilling depth can vary up to 13,10 m (Fig. 5). Fig. 5 – Actual maximum drilling depth (13,10 m)
- 20. 12 3 4 5 6 8 9 7 Fig. 6 – Drilling Unit Details DRILLING UNIT 1. Drilling mast 6. miniJET® rebar loading system 2. Rotary head 7. Video cameras and lighting system 3. Carousel for miniJET® rebars 8. Box housing hydraulic valves and logic 4. Centering device-clamps-breaker 9. Hydraulic hoses holder 5. DTH/Core-barrel loading system
- 21. “Under Water Anchor” case history DATE: March 2011- November 2013 CONTRACTOR: P.A.C. S.p.a. JOB-SITE LOCATION: Ravenna (Italy) TYPE OF WORK: Under water anchors TECHNICAL REPORT For the work of deepening of the Ravenna harbour the Port Autority in preference to reconstruction of the wharves with longer and heavier sheet piling or other equal system, they identified the structural reinforcement of the existing wharves by means of deep underwater horizontal anchors as a new technical solution with important economical savings. The whole project of anchoring has been divided in two lots of about 16.000 m/each; the first lot has been completed at the end of 2011 and the second one on November 2013. Each designed anchor has a length of 18,0 m and is installed at a depth of 8,0 m from the medium sea level. The underground soils are mainly constituted of marine sand with silty/clayely layers. The news of the job-site is represented by the fact that to realize the above mentioned anchors has been employed an innovative drilling system named “U.W.A.” (Under Water Anchors) for the automatic installation of horizontal anchors following the miniJET® technique. The miniJET ® anchor consist of a miniJET ® column, with nominal diameter of about 400 mm, endowed of a steel reinforcement consisting of: galvanized self-drilling hollow bar type R51, galvanized high pressure couplers and sacrificial drill bit with nozzle for the high pressure injection. They were subjected to various tests to ascertain the real interaction between the steel reinforcement and the miniJET ® soilcrete and also between the miniJET ® soilcrete and the surrounding natural soil; all of this to ensure compatibility of the adopted technique with future working loads applied on the anchors in question.
- 22. After the Under Water Anchors installation, the design foresees to complete the anchors with n. 1 steel plate for a better distribution of the applied loads, n. 1 nut and a plastic protection cap. The mentioned horizontal anchors have been all pre-tensioned at a load of 100 kN. Schematic representation of the anchor tensioning device miniJET ® underwater anchors installed N. About 1.800 Average miniJET® anchor unit length 18,00 m Type of soil treated with the miniJET® technique Marine sands with silty/clayly layers Water level Sea lavel miniJET ® column minimum diameter 400 mm miniJET® injection pressure 400 Bars Material used on the miniJET® job-site Self-drilling rods type R51 (Ultimate load: 800 kN; yeld load: 630 kN; max.); Pre-tensioning load applied on each miniJET® anchor 100 kN
- 23. Experienced. Equipped. Committed. Tecniwell srl Via I° Maggio, 61 – 29027 - Podenzano (PC) – ITALY Tel +39 0523 524086 – Fax +39 0523 524088 www.tecniwell.com twcomm@tecniwell.com Total Foundation Solutions FZCO Tecniwell’s representative Company for GCC Countries THANK YOU