Techn i ca I Field

The present invention refers to a method for obtaining a micropi le to be used in the methodologies concerning foundations at high depth, i .e. non superficial , and in particular it refers to a micropi le for foundations of bui ldings in soi ls with poor mechanical properties.

Background Art

Three different types of methodologies exist, which are concerned with high-depth foundations of bui ldings, and they make use respectively of pi les cast in situ, driven caissons, and micropi les.

Concerning the real ization of pi les cast in situ, they are formed or assembled in the bui lding yard; after the dri l l ing of the ground, obtaining a bore of different diameters and depths, an iron reinforcement is introduced into the bore, and thereafter concrete is cast into the latter. The bore may be "free" or provided with a l ining, i .e. the wal ls of the bore may be stabi l ized by introducing permanently into the ground a sheet metal , or by temporary introducing a tubular casing which wi l l be recovered after casting of the concrete. If the "free" bore had to be stabi l ized, bentonite slurries could be used, in order to plug up an aquifer for instance, preventing the sl iding down of the

bore wal ls. Otherwise, in order to overcome the problem of stabi l ization of the bore wal ls, a dri l l ing may be performed by means of a continuos screw with a hol low shaft (auger), and casting the concrete through the shaft of the auger.

The advantages of this system are that the concrete is compressed by means of a pump and the pressure is constantly checked by a manometer in order to prevent breakage of the wal ls of the bore. This method provides a large resistance to loads of the so formed bearing pi le. However, in this case there wi l l result an extraction, even if moderate, of soi l material (less than the volume of the auger), and this soi l material must be removed, increasing transport costs. The disadvantages of the methodology which uses a l ining means permanently introduced into the ground in order to real ize bearing pi les cast in situ, are due to the descrease of lateral friction, on the one hand, and on the other hand, to high costs. The use of bentonite slurries for plugging up the aquifer or groundwater, for preventing the sl iding down of the bore wal ls, has the disadvantage that it is impossible to uti l ize again the soi l material resulting from the digging operation, since it is impregnated with bentonite and must therefore be transported to a bargage dump, therefore increasing the transport costs. Another methodology in the field of high-depth foundations is that making use of driven caissons. In

this case the tamping of pre-fabr i cated pi les is performed, wich have a longitudinal and transversal spiral shaped reinforcement, and are made of concrete by the method of centr i fugat i on , this type of pi les being provided with a metal l ic point adequate for penetrating into the ground. Another type of driven caissons is that made of ducti le cast iron T.R.M. (Tirder Roehren und Metal Iwerker A.G. , Hal l I . Tirol ). Such bearing pi les are pre-fabr i cated pi les by the method of centr ifugat i on , with a unique form and length, or pi les consisting of a corrugated sheet metal closed at the tip into wich concrete is cast.

The driven caissons have two important disadvantages. On the one side, since they are pre-fabr i cated , they must be trasported to the bui lding yard. Furthermore, their tamping l imits their appl ications in places where vibrations may cause damages.

A last type of bearing pi les for high-depth foundations, are the micropi les. The micropi les ( ital ian patent n. 497736 issued on the 3rd of november 1952) are real ized by letting penetrate into the soi l a tubular casing wich carries at the tip a perforation crown, the perforation being obtained by special rotation equipments. After the perforation, the metal l ic reinforcement is introduced into the tubular casing, for instance a steel rod, or a cage, or a steel tube with a diameter adequate to the the cross sectional area of the tube. Afterwards, the casting of mortar of

cement is performed.

Once the casting has been completed, the tubular casing is gradual ly extracted by compressing the casting material . In a further appl ication of micropi les, a bore is obtained by dri l l ing, and then a tubular steel casing provided with injection valves is inserted. The casting is performed in two steps. During the first step, l iquid mortar is poured into the air space formed by the bore wal ls and the casing. Then the cement mixture is introduced under pressure inside the tubular casing, causing the breakage of the valves and the compaction of the soi l surrounding the tubular casing.

Disclosure of Invention The present invention is concerned with the real ization of a method for obtaining a micropi le for foundations of bui ldings on soi ls having poor mechanical qual ities, which al lows to overcome the drawbacks of the prior art, prev i ous I y c i ted . This object is attained according to the conditions and principles defined in the fol lowing description and c I a i ms .

Brief Description of Drawings The invention wi l l be described with reference to the annexed drawings, in which:

Fig. 1 shows the tubular casing, a half of it having been already introduced into the soi l;

Fig. 2 shows the tubular casing completely fixed into the soi l , when the reinforcement is introduced;

Fig. 3 i l lustrates the injection step of the concrete inside the tubular casing;

Fig. 4 shows the step of extraction of the tubular cas i ng ;

Fig. 5 shows the finished micropi le.

Best Mode for carrying out the Invention Referring to Fig. 1 , a hol low tube 1 of variable diameter (between 150 mm and 300 mm) is introduced into the soi l 2, the latter being loose or composed by a material of fine particle size or having poor mechanical qual ities, also in presence of an aquifer or a confined aquifer. This operation is carried out by making the tube to vibrate and fixing it to the ground at the same ti e. The vibrations cause a compaction of the soi l by compression, increasing its density. The hol low tube 1 carries at its lower end a hinge-tip 3. When the hol low tube 1 has reached its final position shown in Fig. 2, according to predetermined refusal values, a reinforcement 6 is introduced (fig. 2) .

Then, a special seal ing head 4 is appl ied to the tubular casing, which by means of sleeves is connected to a pump 5 for concrete (Fig. 3) .

During casting of the concrete 7, the tubular casing is extracted, making it vibrate at the same ime, and transmitting the vibrations to the concrete 7. During this operation, the lower end of the tubular casing where the hinge-tip is located is submitted to the weight of the overlying column of concrete, the hinge opening itself because of the lack of a reaction force from the underlying soi l . Alternati ely, in a variant of the embodiment of the invention, it is proposed to apply an advancement tip into the soi l to the tubular casing, said tip being appl ied in a removable way to the tubular casing, and being formed by a conical element permanently introduced into the ground, remaining "anchored" to it by gravity, due to the weight of the tubular casing and of the overlying column of concrete. The tubular casing 1 is extracted with variable velocity, according to the l ithotypes being crossed (Fig. 4). The vibrations transmitted to the concrete by the tubular casing, together with the pressure exerted by the pump 5 on the concrete 7, wi l l plug up a possible groundwater, and at the same ti e they wi l l prevent expansion of the concrete assuring its continuity. Before extracting completely the tubular casing from the soi l , the hinge-tip wi l l be closed, in order to avoid a leakage of the remaining concrete, or, alternati ely, the rema i n i g concrete wi l l be pushed out completely from the tubular casing by means of compressed air feeded into said tubular casing just a few meters before the

complete extraction of the latter.

The so formed micropi le wi l l have a diameter with a width wich varies considerably, according to the sol idity of the l ithotypes adjacent to the surface 5 portion of the stem, and the micropi le wi l l also have a particularly rough surface, advantageously increasing the lateral friction of the micropi le, which for example in the case of the bearing pi les with a casing permanently introduced into the ground, was particularly

10 low.

Contrary to what happens for other types of micropi les, the vibration of the tubular casing wi l l assure, as has already been said, an excel lent compaction of the ground and of the concrete.

15 Concrete is used instead of a mixture sand - cement, the latter being uti l ized for micropi les of the type RADICE or TUBFIX.

The advantages of the above described method with respect to the prior art are that the breaking load is

20 high (unti l 100 tons for a micropi le with a diameter of 16.00 ml ) and that the micropi le is cast by avoiding contact with water also in presence of groundwater (aquifer) , and the groundwater is plugged up by the very pressure of the concrete, only the outermost part of the

25 stem contacting the groundwater. Furthermore, there wi l l exist the possibi l ity of checking and control l ing the absorption of concrete by the soi l at every instant of time and at every depth during the process. At last, and

this is a fundamental feature of the invention, the reinforcement (which is conventional is introduced before casting, and contrary to what happens for other types of expanded- bu I b bearing pi les, the compaction of the concrete is not real ized by means of a "crushing" element, i .e. mechanical ly, but through injection under pressure employing a pump, as already described in detai l . Therefore, no such difficulties arise wich are due to the introduction of the reinforcement after cast i ng .

It has been proved that the vibrations of the concrete produced by the vibrations of the tubular casing, are perfect, and that the vibrations in the soi l are dampened within a few meters, without causing trouble to the surrounding bui ldings.

Industrial Appl icabi l ity

The method according to the present invention is appl icable to a type of soi l with poor mechanical qual ities, for example: peats, si lts, low density sands, but also for clays, sands and loose gravel , and in the presence of a confined aquifer.

Therefore the method may be appl ied to the real ization of foundations in al luvial deposits and for off-shore platforms.

The low costs of the method of the invention also al lows to substitute the use of a traditional pi le by more than one micropi le, by maintaining an advantageous load/cost

ratio, by el iminating the cost l imit set by the use of traditional micropi les in the field of foundations of bu i I d i ngs .