Jet-Grout Technologies by Foundation Specialists, Inc.
Jet-Grout Technologies by Foundation Specialists, Inc.
Jet-Grout is a ground improvement technology which, by mixing in-situ soil with Cement Grout, strengthens the Soil’s mechanical properties, solidifies lose soil, eliminates the soil liquefaction potential and stabilizes the Ground, in a process where high speed jets of cement grout from nozzles provided on rotating drilling rods, or on rotating deep mixing tools, are impregnating the soil within a certain pre-determined radius, forming a shaft of Soil-Cement material of predetermined strength, shape and cross sectional area. A figure is here provided to visualize the process.
YEAR 1983 - THE BEGINNING OF FS JET-GROUT TECHNOLOGIES' DEVELOPMENT
Foundation Specialists Inc. [FS] had developed in 1983, in the Philippines, its own methods and tools for the execution of Jet-Grouting adapted to the prevailing local soil conditions, i.e. high water table, soil formations prone to liquefaction during seismic events, and a relatively high seismicity.
Before Proposing the use of the FS Jet Grout Technologies to Clients, FS had conducted extensive trials during the whole year 1983, in testing fields chosen for the very poor soil conditions, (a) within the Reclamation Area at that time created by the Construction & Development Corporation of the Philippines (CDCP), (b) along the reclaimed portions of CDCP- FS R-10 Road Project in Manila & Navotas, (c) in the (at that time) swamps of Dagat Dagatan in Navotas MM, d) in the area of National Steel Corporation Plant along the shores of Iligan Bay. After 1 week curing period, the Jet-Grout Columns and Soil-Cement Piles were cored and the cores tested in Laboratory for compressive strength, shear strength and cement content . Third Party Consulting Engineers were invited and witnessed the trials
The results of tests conduced on the treated soil were then compared with the results of field and Lab Tests Conducted on the original untreated soil, to evaluate the degree of improvement produced by Jet-Grouting.
Initially, in 1983, FS had developed three Jet-Grout technologies and related tools, 1) Mechanical Deep Mixing “”FS SOIL-CEMENT COLUMNS”” with one fluid component , i.e Cement Grout to be jetted from within the mixing tool ; 2) Two Components FS Jet-Grout to be directly Jetted by the “Monitor” into the surrounding soil, Water jetted at very high speed , and Cement Grout likewise jetted at high speed from two distinct nozzles of the Monitor; 3) Three Components FS Jet-Grout also to be directly jetted from 3 distinct nozzles of the Monitor, Water, followed by Cement Grout and by compressed air, where the compressed air has the function of extending the reach of the cement grout into the surrounding ground fractured by the water jetting. The Procedures developed by FS found immediate applications in various industrial projects, in bridge foundations retrofitting, to control local scouring around bridge foundations, in buildings foundations on liquefiable soils. The FS Mechanical Deep Mexing Method (FS Soil Cement Columns) was found to produce exceptionally good results not only in sandy and silty formations, but also for water saturated clay, which produced a steady request of the treatment.
After a good number of successful applications, the three FS developed Jet-Grout Technologies were described by a “paper” of Dr. Armando Cazzola, published by the Philippine Institute of Civil Engineers (PICE) Journal in 1985.
Both Jet Grout Methods, 2 and 3 are most indicated for “Alluvium” formations. i.e. formations composed of fines and gravel, pebbles and boulders, where the fines are floated and removed upwards and above ground by the high speed water jets, and replaced by cement grout to eventually form a sort of cyclopean concrete. Jet Grout Method 1 is instead most indicated for clay, silt, sand formations , which are mechanically mixed, combined with cement grout .
Methods 2 & 3 float and remove as liquid mud most or all of the fines, and replace it with cement grout, while Method 1 mixes the in situ soil with Cement Grout. In silt and clay the quantity of soil to be removed to disposal is mostly equal to the volume of grout injected, while in sandy soil formations with high percentage of voids the soil to be disposed is near zero in volume, since the cement grout displaces interstitial water and fills the voids so produced.
For FS Soil- Cement Columns the most common diameter is 800MM, but the Method can be very efficiently executed also with smaller and larger diameters. The diameter of the mixing tool used for the FS Soil Cement Columns is exactly the same as the diameter of the columns specified by the designe. The strength of the improved soil is verified by coring the columns and testing the cores in Lab by Unconfined Compression Test.
Proper design pattern of jet grout eliminates the potential for liquefaction of the areas treated, so the FS Soil Cement Columns is the designers’ favorite system for Tanks Foundations in Tank Farms , Warehouses, Bridge Approaches, Slope Protection, Excavation Support, Buildings’ Foundations, Underpinning of Structure, Cofferdams, Pre-consolidation in preparation for Large Diameter Piles or DW in unstable soil formations; Bottom Plugs to seal bottom of pits, and as FS Composite Soil-Cement Columns (with “I”-beams embedded in it), used as Diaphragm Walls, Fs has successfully completed already hundreds of jet grout projects, in various Countries, with FS Soil Cement Columns having the Lion’s share of it.
1991 - TWO ADDITIONAL FS JET_GROUT METHODS WERE ADDED :
In 1991, while FS was the General Contractor constructing the 4th ADB “Dapitan Manucan Road Project and the Polo Bridge in Zamboanga Del Norte, part of the work was to stop the sinking and rehabilitate several Box Culverts which were under-scoured by heavy floods. To restore proper ground support to the under-scoured Box Culverts, FS proposed to use Jet Grouting. Soil Cement Jet Grout required the opening of too many large holes on the top and bottom slabs of Box Culvert, to allow the passage of the mixing tool, and we decided to consolidate the soil under the Box Culverts with a “modified” FS Types 2 and 3 Jet Grout. The “modified Method consisted of the original method minus the high speed water jetting. The scoured sandy soil underneath the Culverts was then subjected to a high speed Jet Grouting of Cement Grout . The speed of the Grout Jets was increased by employing a pump which produced high speed and large volume of grout suitable to perform at once the fine fragmentation of the soil and the impregnation of the”fragmented” soil by Cement Grout The results were found to be excellent and FS proceeded to consolidate the ground underneath the Box Culvert with that method which was dictated by local conditions . It was thus that the Methods 4 and 5 were created and immediately applied, with success.
Method 4) , Jetting at very high speed One Fluid to break and impregnate the soil formation i.e. jetting at high speed Cement Grout only, to breaks and impregnate the soil.
Method 5), of Jet-Grouting is a variant of the Fourth Method, with the addition of the introduction of Compressed Air, which sharply increases the reach of the Cement Grout and thus creates Jet- Grout Piles of considerably larger diameter than those created by Method No.4
HORIZONTAL JET-GROUT APPLICATIONS
A misconception about Jet-Grout is that the Technology is only applicable for vertical soil treatment, with downward orientation. Howeever the methods 4 & 5 described in this site are successfully used also for horizontal soil treatment: e.g. impermeabilization and consolidation of unstable soil masses, prior to excavating tunnels in such formations. On the other hand, methods 2 & 3 are ideally suited to the consolidation and impermeabilization of alluvium formations, prior to excavating tunnels in it.
FS-Soil-Cement Columns / Mechanical Deep Mixing /Jet-Grout . Partial view of FS Projects
Foundation Specialists, Inc. has developed and perfected over the last forty years a Soil-Cement Consolidation Ssystem initially called and patented with the name “CSS” (or “Chemical Soil Strengthening” system) and lately improved and likewise patented with the name “FS Soil-Cement Columns”. The “FS Soil-cement Column” system is particularly suited for the very poor mechanical properties and , high liquefaction potential, for water saturated soil formations found in the coastal areas of the Philippines, where the soil in general is characterized by very low bearing capacity and low shear values. FS has developed the technology, the tools, and the in-situ mixing procedures, which have permitted to establish the method’s complete reliability. The “FS Soil-Cement Column” method produces high shear and compressive strength for the soil treated, maintaining the costs affordable and competitive. FS uses different tools and procedures for different soil types in order to achieve maximum soil strength. The method applies well for clay, silt, sand, peat, gravel, organic material and all combinations of the above. Unlike other soil improvement systems, “FS Soil-cement Column” system works equally well with high or low water table, various granulometries of the soil to be treated, in presence of organic material, and with soil having high liquefaction potential. One application of "FS Soil Cement Column" is Slope Control, increasing the soil shear strength to form stable slopes, forming retaining walls with contiguous Soil-Cement Columns to protect excavation in areas where the high water table and the unstable soils do not permit unprotected excavation, and where the presence of existing structures does not permit driving sheet piles, in which case Composite Soil-Cement Columns with H beams inserted are the perfect solution. Note: Soil-Cement Columns for about one hour after completion allow the insertion of H-Beams for their entire length, the results can be observed in the attached picture. The relatively low cost and the versatility of this technology as compared to steel or concrete sheet piling walls or diaphragm walls are very strong reasons for this method's increasing favor amongst structural engineers. The photos show among other the 550mm. diameter FS Soil-Cement Composite Columns with embedded H-beams as reinforcement executed by FS as foundations sub-contractor of TAISEI for the new Bulletin Building in Intramuros, Manila. The size of the column (550 mm) is smaller than the standard one of 800 mm because space between the old building’s footings and the new building’s foundations to be excavated and installed could only accommodate 550 mm diameter columns. Purpose of the reinforced FS Soil-Cement Column as in the figure, was to form a secant-column retaining wall to protect the very old adjacent building from the effects of the pit excavation for the new building’s foundation. In the National Museum (formerly Finance Building in Rizal Park, Manila), retaining wall for 4m. and 5m. deep excavation in very soft soil (SPT count = 2) was executed by use of “FS Soil Cement Column” 800 mm diameter on two parallel lines. The FS Soil Cement Columns are widely installed as foundations for Tanks in oil firms’ Tank Farms, in coastal areas, in liquefiable soil, because the treatment with FS Soil Cement Colums System in addition to providing increased soil bearing capacity and shear strength, eliminates the Potential for Liquefaction during earthquakes.