The vastness of foundation problems solvable with piling, led us to investigate new methods of execution ever more reliable, cheaper and above all with remarkable speed of execution.
That is how we are able to realize, making use of modern and powerful machines operators:
- Small diameter piles (micro piling) mm. 300;
- Medium diameter «Marflutt» piles mm. 400 – 500 – 600 – 800;
- Big diameter piles mm. 1000 – 1200 – 1500 – 2000;
- Traditional Bored piles with bentonite or polymer slurry;
- CFA (Continuous Flight Auger) piles up to mm. 1200;
- DHDS (Double Head Drive System) Secant Bulkheads;
- FDP (Full Displacement Pile) without removal of soil;
- Soil Mixing with double or triple Auger
- Spin Driven piles to prevent the connection between aquifers.
Piles without removal of soil
The technology devised by MARINI SpA, based on vibrofloatation by means of VIBROPAL© sheet pilers, allows to perform foundation piles and / or consolidation without removal of soil; the geotechnical characteristics in the neighborhood of the pile are improved significantly consequently the lateral displacement of the soil and its compaction. The work is performed under conditions of utmost cleanliness of the site with a top speed of execution to other technologies and with a layout of the site greatly simplified. A low environmental impact is achieved without additional expense and with considerable savings in the management of the site. The foundation works are carried out without the use of sludge and polymer, usually used in traditional technologies for the support of the wall of the hole: lower charges for the landfilling of excavated material and extreme cleanliness in the site and in the surrounding streets.
Foundation and Consolidation
In diameters, 300 and 400 mm and with lengths varying according to the stratigraphy are used as the foundation for footings and slabs. The execution procedure allows operating within the excavations of footings already drilled or ground level with the management of the ”empty” tract. They are reinforced with a metal cage and do not require, unlike other types of piles, the head removal: the concrete casting is controlled and interrupted at the desired altitude. The MARFLUTT pile can be quickly realized in many stratigraphic situations, cohesive soils such as clay, silt – sandy, sandy and weakly, average thickened, with Qc up to 10 MPa; the presence of water is almost irrelevant because the wall of the hole is constantly protected by the shirt driven into the ground and then by the concrete cast and heavily compacted by vibration during extraction of the shirt. The sheet piler vibropal © allows you to manage the vibration within a range of high frequencies which ensure the compatibility of working in close proximity to existing buildings or structures , it is established practice to ensure compatibility of processing through the installation of stations on these buildings. The lateral displacement of the soil and the vibration induced at the same result in an improvement of the mechanical characteristics of the soil in the neighborhood of the pile: MARFLUTT piles, cast in concrete or gravel, are often used for the consolidation of the site.
Piles with Removal of Soil
While the MARFLUTT piles without removal of soil can be performed in diameters 300 mm and 400 mm up to approx. 30 meters to make both pilings and consolidation , the MARFLUTT piles with removal of soil permit the realization of just piles with diameters 400, 500 , 600, 800 mm , reaching a depth of approx. 20 – 25m . The manner of execution of the pile with takeaway of land expect the insertion of a tube-form with vibropal without tip opening at its end, the tube-form is normally longer than the project length of the pole. The characterization of the removed material actually coincides to the realization of a survey for which are worth even more the considerations already made for the pole without removal of soil about the verification of the stratigraphy with the possibility of adjusting the lengths of the poles in the course of work . The use of the MARFLUTT pile with removal of soil allows you to run with the same technology of excavations in more complex stratigraphic contexts or with the presence of cohesive soils or inconsistent normally to heavily thickened. Sometimes MARFLUTT pile with removal of soil may be advantageous also with the pile of diameters from 1000 to 2000 mm in particular geotechnical contexts.
DHDS technology (Double Head Drive System) finds application in the realization of any type of basement and in many soldier pile walls; its use becomes almost essential if there is a precarious livelihood of the hole or complex stratigraphy. The poles are made without the use of sludge or polymers: the low environmental impact of this work with the surrounding environment makes the landfilling of the results less onerous and makes it suitable for processing in urban and polluted sites. It is a work suitable for any geotechnical context, from silt to alluvial soils; the vertical travel of the propeller respect the coating determines the exact configuration as a function of the crossed stratigraphy. During the excavation phase, the integrity of the surrounding terrain is guaranteed by the coating; during the ascent phase, the impossibility of detensioning of the ground is guaranteed from the propeller coating-group: a protection for sides and for possible siphoning of the material at the digging point, a real guarantee against injury to neighboring buildings. The realization of the DHDS pile is divide in the following steps:
- Excavation, with the rotation of the coating and counter-rotation of the continuous internal propeller; simultaneously the drill pushes the digging equipment towards the bottom of the hole while maintaining the hysteresis between the pairs of the two heads and that of the pull-down. Both the coating and the propeller are accompanied by suitable “cutters” chosen in function of the ground to cross. During the excavation, the onboard computer monitors and records the parameters related to verticality, to the depth of excavation, the speed of execution and the torque; the excavated material backs through the propeller rotation until the drum placed at the top, from which the soil is discharged to the ground.
- Casting, at the end of the rotation the excavation system is gradually extracted and the concrete is pumped within the propeller until its end. The casting is then carried from the bottom of the pole up to its top with controlled speed in function of the saturation volume of the hole; during this session, the computer monitors and records the basic parameters of the activity.
- Adding reinforcement, in the casting of fresh concrete, with suitable additives, by free-fall.
It’s the kind of piles cast in situ most common and dated. With the advent of new substitute technologies and problems related to the management of this process bentonite slurry this work is placed in a niche, though significant, is characterized by large diameter, 1200 mm and beyond, from extremely complex stratigraphy (rock included) or from considerable depths. The execution sequence is extremely simple, the excavation is carried out by removal of soil with half clamshell buckets or other dedicated tool, the metallic armor is inserted first, and then a jet pipe up to the bottom of the trench and through the hopper at the top the jet pipe fits the concrete gradually pulling the jet pipe. Depending on geotechnical context and the presence or absence of ground water, we can have three main configurations:
- Self-bearing hole that expects dry excavation (not very common and not always accepted);
- The presence of water which forces the use of a metal coating, usually vibro-driven, at least for a portion of the length of the hole;
- Bore imposing the lining of the hole or the management of bentonite slurry or polymers.
In the event of interception of a rock layer, or another consolidated layer, or for clamping of the pile itself, special tools that work like a rock chisel are mounted. It is common practice to protect the upper part of the hole with a metal sheet to prevent erosion of the walls of the hole caused by the repeated passage of excavation tools. Variant of bored pile is the cored pile characterized by the use of a core barrel as digging tool.
CFA pile or continuous flight auger is a bored pile dry, without the burden of managing the bentonite mud for the sustenance of the walls of the hole. The technology is based on the continues rotation of a propeller with a digging tool placed at the bottom and configured according to the soil to be excavated. The propeller, welded on a hollow tube inside which passes the concrete into the casting stage, is coupled to a mast that in addition to fulfilling a mechanical functions and assuring the vertical translation of the head, allows to check the verticality of the hole. The enforcement procedure is very simple as well as the configuration of the equipment on site : The Drill-rig provides the excavation combining the torque of the propeller with the pull -down; reached the bottom of the excavation portion of the concrete is cast usually pumped by a pump crawler that receives the grout from a truck . The lift is controlled by the operator who uses the on-board instrumentation that in addition to allow monitoring, records data relevant to a possible release of the report. An excavator gives service to moving and processing accompanying the jet pipe and removing the results from hole. At completed jet, the armor is lowered in the fresh concrete to fall to its own weight. The diameters manageable from 400 to 1200 mm. (the smaller the diameter the greater the deviation of the trajectory of the propeller being excavated) and the depths are related to the stratigraphy of the site, the average length of the pole can be operated up to twenty meters. More lengths can be realized with the aid of an extension at the head of the propeller that works by passing through a spindle: this expedient is not always accepted as the first meters of excavation, remain uncovered, there is no lateral protection of the hole with danger not only of yielding of the walls, but also contamination of the concrete during casting. They are frequently used for their cost-effectiveness, the organizational simplicity, the speed of execution, but unfortunately does not provide any assurance as to the verticality / linearity of the trajectory of excavation and may be subjected to shear in the presence of water.
Lateral movement FDP
Full Displacement Pile or lateral movement pile, is the technology to perform concrete piles, possibly reinforced with metal cage, made by insertion into the ground, by rotation and thrust, of a spinner attached to a pile, the inclusion of the system in the ground is made possible thanks to high-performance equipment such as torque, thrust force and extraction of rod – wishbone system. The nose cone during penetration pierces the ground with its first stage, then compacted subsequently with the displacement body and then stabilizes it. In the ascent phase, the process is analogous less the drilling: the displacement body, smaller than the lower one, compacts the soil, which is then re-, stabilized by the central stage of the ogive. After the input of the ogive to the tip of the pile, two separate procedures can be implemented, the traditional technique or the lost bits, that differ in their use of the different tools and the different steps of concreting and installation of armor. FDP Pilings are particularly performing in silt-sand soils slightly too normally thickened, to be used where a normal bored pile should be allocated diameters and lengths well over. Piles diameter from 360 to 710 mm and lengths that under certain conditions can reach 60 meters. The excavated material being compressed laterally on the walls of the hole significantly increases the voltage of the ground that, results in an increase of the coefficient of thrust resulting in increased lateral resistance. The impetus given to the equipment excavation results in a compression on the tip of the pole by improving the soil characteristics on the basis of resistance allowing you to design with higher peak loads . The FDP is made with two distinct techniques whose peculiarities are highlighted in the context of comparison.
More powerful technique in critical soil conditions; allows a high production demand. Requires more care in choosing the concrete mix design and can present same problems as CFA in the early stages of casting and reinforcing of deep piles.
Lost Bit Technique
Technique suitable for the execution of deep piles, reinforced also partially, and with armor that is more complex. Concrete does not require any special characteristics of consistency and workability, thus compensating for the higher cost of the tips to lose.
The technology of the spin-driven pile preserves and maintains the hydrogeological situation present in the site prevents the hydraulic connection between the flaps and maintains the continuity of the upper waterproof clay layer with the lower layers. It is an in-situ pile, made by inserting up to the project depth of a tube – shape of the pile length with at the end a closed toe to lose. The ramming of the shirt (tube – shaped) occurs without removal of soil by means of a combined system of rotation and compression, called spin-drive that does not create vibration and percussion. The soil penetration of the tube – shaped without removal of material due to a compression of the clay layers with a consequent increase of the characteristics both mechanical and permeability of the soil itself that after the extraction of the shirt for effect of its own relaxation is adapted perfectly to the concrete pile, ensuring and preventing the connection between the aquifers crossed. To ensure that both the impermeability and perfect adherence of the concrete to the ground a concrete with high-class consistence like ” SCC ” ( Self Compacting Concrete ) or F6 will be used. This type of concrete in addition to being particularly suitable for the execution of foundation piles in an aggressive environment, thanks to the particular characteristics of workability ensures a perfect filling of small holes in the subsurface in addition to the complete filling of the same pile and the perfect grip with the ground. This technology is usually used in polluted sites and where there is the need not to connect the flaps.
Foundations of the “small diameter” reach a maximum diameter of 300 mm and considerable depth in relation to the terrain. The micro piles are essentially constituted by a metal reinforcement, (bars, tubular or steel joists) embedded in the sheath that can be of grout or cement mortar; in particular situations the tubular reinforcements are valved in proximity of the bulb, and there is provided, in addition that the constitution of the sheath with low pressure injection, the repeated selective injection valves (IRS) through a packer. The scope of the micro piles is extremely vast, in terms of stratigraphy and in relation to the site logistics, and this because the equipment that can be used are lightweight, easily transportable and can be configured according to the architectural constraints. The main procedures for the excavation of a micro pile and then the configurations of the equipment are:
- Rotary and percussion drilling by means of a hammer swing operated from the air of a connected compressor; the hammer is placed at the end of a series of modular rods. The compressed air contributes to the perforation and is responsible for the transport of the dirt to the surface;
- In rotation with the aid of water pressurized from an external pump, the excavation is carried out from the tips (tricone, triblade etc…) Positioned at the end of the battery of rods, the water under pressure contributes to the excavation and provides the transport of dirt to the surface.
We have internal fluid circulation when they are conveyed between the temporary lining and the battery of the rods; circulation is external when the fluid pushed through the rods or the temporary lining, ascend in contact with the walls of the hole. One of the most common variants is the drilled micro pile, achieved with the aid of modular propellers; it is used in soils where the hole is mainly dry and self-sustained.
Is a technology for consolidation of land that allows the formation of columns or partitions of size between 40 and 80 cm and depth up to 25 meters, through the mechanical mixing of the soil and the contribution of the binder. One or more parallel rods, equipped with blades or rotating elements on vertical rods, ensure during excavation the mixing of the soil; during the ascent phase dry cement is injected, assisted by a jet of compressed air, which is mixed to the soil forming a stable mixture of treated soil. Where there is reduced presence of water in the soil, to overcome the difficulties of the hydration reaction of the cement, water is injected contextually. This technology is powerful:
- For the resolution of the problems of soil liquefaction;
- Achieving underpinning;
- In the formation of columns and continuous bulkheads in “soft” soils
The bulkhead of secant piles is a series of piles carried out at a distance less than the diameter; it follows a structure where each pile has in common with its neighbor a region of intersection. The series consists of alternating primary and secondary piles, from this classification derives the execution order, the type of armor and choking in the executive phase. The quality of the work is the result of the correct application of the executive criteria fundamentals: positioning, spacing, verticality. The positioning and the wheelbase is guaranteed by the guiding curb, structured to limit the tolerance to a few millimeters for positioning and of an order of magnitude lower for the wheelbase ;to guarantee this result is the use of proprietor metal formworks for the realization of the curb guide . The verticality is controlled, during both placement and execution, directly and continuously from the DHDS Drill on board computer, that verifies and records in real time the verticality of the drilling with a biaxial tolerance of 0.3 °. The rigidity of the helix – coating group, with no intermediate connections, does not allow the slightest deviation or deflection maneuver even at greater depths.
Complex Geometry in Contact with Buildings
Reduced vibrations generated during processing and absolute protection of the surrounding terrain allow us to maximize space by placing the bulkhead almost in contact with the buildings with the adoption of any geometry, even the most complex, using DHDS piles diameter from 400 to 1000 mm.
Hydraulic Seal of DHDS Bulkhead
The secant DHDS bulkhead is a set of piles perfectly aligned and free of swelling; has a low permeation rate and the hydraulic retention is ensured without the use of additional elements such as joints, injectable or not. It is the process most suitable for underground car parks, tunnels, berliner and top-down sites, both for the accuracy of the work and for the low environmental impact in urban areas.