Consolidation and Waterproofing Grouting
Deep soil stabilization technique by injecting high-pressure Jet Grouting, done by mono/bi or tri-fluid technique even at considerable depths, with cement or chemical injections for consolidation or waterproofing:
- For foundations of buildings;
- Bridge piers;
- For the excavation of cortical tunnels;
- Slope landslides stabilization;
- Active and Passive anchor tie rods;
- Waterproofing diaphragms;
- Consolidation of road embankments.
Allows to realize columns and bulkheads through the treatment of the soil on site; it’s done with high pressure injection of a stabilizing mixture, usually based on cement, through nozzles placed at the end of a rotating rod which is progressively extracted. Jet Grouting is a process extremely flexible, yet some types of soil make this technological choice ineffective or uneconomic: in principle, the limits are represented by the consolidated clays and coarse gravels (pebbles) with significant sizes, as pebbles and boulders limit the effectiveness of this technology, in certain projects jet grouting is also chosen in this conditions, and boulders are clamped by the injection. The size of the columns, from 60 cm to over 400 cm in diameter, albeit conditioned by the type of soil, is a function of the jetting technique used:
The cement mixture is pumped at a pressure up to 600 bar, through the hollow rods, up to one or more nozzles placed at the end of the same;
The rod used has a double cavity, one for the mixture under pressure and one for compressed air, which promotes the cutting of the soil by implementing the projection of the mixture;
Similarly, as well as the compressed air a jet of water under pressure is added for the same purposes.
Currently with the Jet Grouting technology, we realize:
- Circular columns isolated from vertical to sub-horizontal for soil consolidation;
- Circular columns reinforced with armor-beam or tubular steel, for the formation of bulkheads;
- Linked circular columns for the formation of end caps;
- Circular or secant elliptical columns for the formation of bulkheads or baffles;
- Thin diaphragms with mono-directional jetting.
MARINI Ermenegildo spa has considerable experience acquired over the decades and has a wide range of modern equipment.
Jet grouting – Elliptical and FAN columns
While in circular columns the rotation of the rods is at a constant speed, for the elliptical and FAN columns rotation speed is variable (V + and V-) and associated to S + and S- sectors, the other basic parameters of jetting remain constant regardless of the sector.
Are those columns in which there is only one sector S +, and thus a single sector S-; the diameter of the column is in function of the basic parameters and the speed of S-; the amplitude of the S-field determines the geometry of the column and identifies the portion in which the column has theoretical constant diameter. From the Amplitude of the sector comes the nomenclature of the column (180 ° Fan, Fan 240 ° etc.)… The speed V + is the maximum manageable because the column does not require a minimum or specific diameter in its S + portion.
Are those columns in which there are two sector S + of equal amplitude, diametrically opposite, and thus two sectors S-; there is no longer a diameter in the generated column, but a longitudinal length and a minimum thickness of the column Smin. The amplitude of the sector S- determines the maximum thickness of the column Smax and has influence on the whole geometry of the column and its minimum thickness Smin. By varying the parameters S +, S-, V +, V-, you get different columns aimed at their practical use:
- Elliptic pseudo-laminated columns.
- Non standard Elliptical Columns
Are those columns, that for the management of multiple sectors at different speeds, fall into the category of the elliptical columns; they are characterized by sectors of a varying number, of different amplitude, not necessarily opposed, in which the speed of rotation are extremely variable. The multiplicity of geometric figures that can be generated by combining sectors and speed makes them suitable a precise study to individual project assumptions, to which the discussion herein would be at the same time limited and extremely challenging. The realization of the column takes place in a similar manner to that envisaged for the circular columns since the rotation of the rod, albeit at a variable rotation speed, and its ascent in steps, allows the nozzles to inject, and then treat, the whole volume of the column.
Elliptical Jet grouting – Bulkheads
They are elliptical columns placed at a distance less than the longitudinal length; they are made in sequence or in alternating sequence (primary / secondary). The techniques used for the construction of a Jet Grouting bulkhead take up the schemes used in micro perforation, joining the established practice to the possibility of waterproofing the excavation front to implement higher standards of safety during excavation to avoid the treatment of the fronts with spritz concrete. Their execution is faster, with fewer joints, with less bleeding and without waste of mixture Stabilizer, necessary to ensure the thickness of the bulkhead in the case of use of circular columns; their longitudinal length, in function of the treated soils, is equal to the diameter obtainable in a circular column over 450 cm, with the advantage that the thickness, regardless of the length of the ”panel” may be contained in the order of 40-60-80-100 cm. In function of their overall structure, bulkheads are classified into:
- Simple Bulkhead made with elliptical columns usually of considerable thickness to counteract the thrust on the back of the bulkhead; is suitable for small depth excavations.
- Reinforced Bulkhead, like the previous one, but using lower thicknesses, with the inclusion of beams or tubular steel to provide greater inertia to the bulkhead. The use of elliptical columns allows the use of ”off-axis” reinforcements thus increasing the inertia of the bulkhead.
- Complex Bulkhead, is a set of bored piles (primary piles) and elliptical columns, reinforced or not (secondary piles), this ensures the bulkhead hydraulic retention, while providing a high degree of inertia given by the structure of the piles. Sensitive are the benefits in terms of execution time as in the implementation of the secondary piles it’s not necessary to provide the reduction of the intersections of the primary piles.
- Tie-bared Bulkhead; allows to reach considerable digging depth in function of the order number rods adopted; in order to reduce the costs and time of creation, the contrast to the push from the back can be increased with an order of tie rods in the head (on the capping beam), or with the use of metal contrasts seated on the capping beam in the vicinity of the edges or between parallel sides of modest length.
Repeated selective injections IRS
Processing of small diameter making repeated injections selective, (IRS) is aimed at the consolidation of the surrounding soil or the sealing of joints, bulkheads or piles. The processing consists in the realization of a vertical or sub-vertical hole with the techniques of the small diameter even if the diameter is usually considerably lower; in it is inserted a valved rod better known as cane manchettes on whose walls are inserted restraint valves that allow the injection of the mixture under pressure; a sealing injection is carried out with plastic mixture. It serves for fastening the tube to the hole and to prevent the reflux the next injection into the external circulation. The valves are placed at predetermined distance (from 25 cm to approx. 100 cm) on the length of the tube equal to the portion of the soil to be consolidated or sealed , while the complementary part of the tube only serves as a fitting. Inside the tube is slid a packer, rigid or spring-loaded, mechanical or hydraulic, within which is channeled the injecting mixture pressurized by an injector; less than use of evolved injection systems from the witch console can be monitor and record the amounts and pressures, the operator relays on the readings of the pressure gauge on a tripod before the packer to interpret the saturation of the surroundings of each valve. At the end of the first phase, he shall wash the barrel to allow the repetition of the same phase, in a selective manner, until the achievement of the goals or design specifications. The type of mixture is usually cement and the recipe is the result of the evaluation of the ground according to the purpose; special mixtures silicate based or polyurethane additives are used for the sealing of portions of land especially where it is necessary to proof the soil behind bulkhead if it is in the presence of groundwater dynamics. The IRS are sometimes also used in the construction of micro piles and tie rods that take the name of ”valved” . In these cases, the purposes are different from the permeation and concern the principle of hydro-fluctuation and resulting pressure-filtration, whose effect procured by dense cake mixture in the neighborhood of the bulb increases the side friction.