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This invention falls within the field of Civil Engineering, class Foundation Engineering and group barriers and partitions, piles and other civil/structural systems that are especially accommodated for foundation works, thus being able to get the designation E 02 D 5/00. Likewise, the invention refers to the group encompassing methods and procedures that is to say devices for setting up retaining stone masonry, piling, tubular and other formworks classified as 7/00, as well as construction and placement of caissons, being encompassed by the group 23/00.
Since the invention includes ground i.e. soil improvement, it could also be classified into the group for soil improvement, more specifically the improvement and protection of the soil by its displacement and so it could be marked with designation E 02 D 3/02. Therefore, the invention can be classified into the following categories: E 02 D 5/00, E 02 D 7/00, E 02 D 23/00 and E 02 D 3/02.
The invention resolves the problem of load-bearing capacity of piles/caissons in soft to stiff soils through improvement of the soil around the borehole and construction of concrete piles and caissons by the use of rubber or neoprene hose of controlled stiffness, under high pressure of air or water. The essence of the invention is in the use of rubber or neoprene hoses for changing the system of soil carrying capacity so that the hoses with their elastic characteristics enable creation of forms of soil deformations which improve the main properties of the same, leading to increase in the load-bearing capacity of the pile/caisson.
There exist different types of piles within the field of bored i.e. augered piles by means of which one can solve the problem of founding in soft to stiff soils. Worth mentioning are only those in whose execution procedure it has been included treatment of the borehole and ground improvement.
Only in the cases of APGD and FUNDEX piling systems, by means of soil displacement in the borehole, it has been anticipated strengthening of the borehole sides, while in all other cases, they perform penetration of cement grout into borehole sides and with little lateral displacement of the soil due to vertical vibrations and impact.
A significant problem into the practice is the occurrence of strata of organic materials of very low load-bearing capacity and high settlement, which has to be solved separately.
And since the methods for calculation contain a number of assumptions, we apply rather high factors of safety and confirmation is practiced regarding load-bearing capacity of the piles and caissons by means of test loading.
The use of increasing the soil density by means of rubber or neoprene hose under high pressure with air or water, until now as a method has not been used. There are several instruments by the authors L. Menard and Baguelin F. Jezguel for measuring the soils compressibility for scientific purposes where inflating a rubber cushion is used.
The solution which is proposed with the invention, that is to say the method for construction of concrete piles/caissons into the augered borehole with a change of soil properties, by means of a rubber/neoprene hose inflated with air or water under high pressure and forming different shapes for increasing the load-bearing capacity of the piles/caissons—has not been performed by now, or at least it is not known to the author.
The presented invention comes out from the dependence that by deformation and improvement of soil's structure in which piles and caissons are executed, there is an increase in their load-bearing capacity, and in accordance with it reduction of their dimensions for the same loading.
The method for construction of piles/caissons consists of three working operations: drilling i.e. augering the borehole, inflating the hoses or head units and concreting.
For augering the boreholes we can employ the same types of standard drill rigs that have the capability for augering the boreholes by means of appropriate sizes and lengths in which we can put in the rubber/neoprene hoses or adequate tools, accessories and parts that are used in the course of execution of the piles/caissons. At sites which do not allow access of large drilling rigs, used are small drill rigs, and in doing so drilling is quiet, without vibration and noise, and by occupying little space and height. On the basis of previous geotechnical data for strata and densities, after drilling and by using compressometer, we measure the compressibility of soil's typical strata. This measurement determines the elastic and plastic moduli of compressibility of the soil, on the basis of which we create a representative compressibility model of the soil at that location. On the basis of the representative compressibility model, we select a proper hose that can be used, and in accordance with the obtained compressibility model, the hose is so configurated-strengthened with a gland element, as to be able to attain the required designed form.
Inflating the rubber neoprene hoses under high pressure is carried out after they are inserted into the borehole closed at one end, and then they are pulled on over a plastic or metal pipe, through which we perform inflation of air or pumping-in water under pressure is carried out. Under the effect of pressure, the hoses are getting deformed, thus displacing the soil around hose's soil, achieving the designed shapes, performing modifications of soil's characteristics. Expansion can be carried out all of a sudden and throughout the entire length, or else, in certain parts of the borehole—by means of displacement. At that, the direction of displacement goes from the borehole's bottom toward the surface.
Having previously placed appropriate reinforcement, concreting can be carried out in an open borehole, through a plastic pipe which would follow the filling up of the borehole with concrete, in order to prevent cave-in of the borehole, or else by means of gradual concreting through appropriately worked out head, which simultaneously performs both expanding and filling in with concrete. The third possible way refers to concreting in swampy and very soft soils, in which case we use synthetic grids and fabrics, and in doing so concrete is pumped under pressure after expanding the hose, or direct without hose.
Explanation of the method, alternatives of application and shapes achieved, are presented in continuation of the description of figures, in which denoted are stages and procedures as well as employed members and apparatus.
FIG. 1 is a review of elevation of uninflated neoprene/rubber hose along with all appurtenant members ready for use.
FIG. 2 is a presentation of the method for construction of piles with denoted stages and parts being implied.
2a) drilling;
2b) insertion of prepared hose and connection to pressure generator set;
2c) inflation of the hose and deforming the borehole;
2d) elevation of a treated borehole;
2e) placement of the reinforcement cage;
2f) filling with concrete.
FIG. 3 is a presentation of a caisson execution, carried out of previously prepared concrete members, along with designated stages of construction and members being used.
3a) elevation of a prepared unopened pile;
3b) drilling the borehole;
3c) inflating the previously prepared pile hose inserted into the borehole;
3d) placement of a reinforcement cage;
3e) filling with concrete.
FIG. 4 is a frontal view presentation of a detail of prepared concrete members in relation to the construction as presented in FIG. 3 in a closed position (4a)(4c) and in an inflated position, FIGS. (4b) and (4d).
FIG. 5 is a presentation of construction and elevation of a pile/caisson in very soft soils along with denoted stages and parts being used in construction;
5a) elevation of a prepared hose and mesh fabric prior to lowering into the borehole;
5b elevation of expanded hose and mesh fabric;
5c) drilling and insertion of the prepared hose and mesh fabric into the borehole
5d) partial withdrawal of the casing pipe and commencement of inflating the hose or fabric;
5e) termination of inflation in one stage;
5f) and 5g) withdrawal of the pipe and inflation of the second and third stage;
5h) placement of reinforcement
FIG. 6 is a presentation of a single (a) and double (b) inflation head upon which denoted are the specific parts and the form they could achieve.
FIG. 7 is a presentation of a single inflation head with an integrated concreting pipe which serves for simultaneous inflation and deformation of the borehole.
FIG. 8 is a presentation of the method of execution of a pile/caisson with a simultaneous filling the deformed parts of the channel with concrete.
8a) Elevation of the lowered inflation head down to the bottom of the borehole;
8b) Deforming the borehole's bottom with a head unit for inflation;
8c) Deflating of the head unit, and concreting of the treated part;
8d) Deforming of the second part of the borehole, along with a head unit for inflation;
8e) Deflating of the head unit and concreting of the second deformed part of the borehole;
8f) Deforming the last part of the borehole.
FIG. 9 is a presentation of construction of a large pile/caisson by using a number of inlet ports for inflating the air.
9a) elevation of a prepared hose for lowering into the borehole and with denoted characteristic parts;
9b) elevation of the borehole prior to lowering the hose;
9c) deforming the borehole with the hose;
9d) placement of the reinforcement cage and concreting pipe;
9e) elevation of a constructed pile/caisson.
FIG. 10 is a presentation of the load-bearing distribution model for the piles/caissons carried out with the application of the method as described with the presented invention.
10a) elevation of a standard pile;
10b) elevation of a pile/caisson with a denoted zone of change of soil's structure;
10c) elevation of a pile/caisson constructed by the method presented in FIG. 8;
10d) elevation of a pile/caisson constructed by the method presented in FIG. 9;
10e) &10f) elevation of a pile/caisson carried out by means of previously prepared concrete members which have been expanded in the form of a bell, FIGS. 4b and 4d.
Owing to the different characteristics of the soils for which are intended to be used, the piles/caissons presented in this invention and also depending on their function and size, there exist a number of ways for their execution and elevation which are generally divided into two groups:
1) Methods of construction of piles/caissons in which the hose extends along the entire length of the borehole;
2) Methods for construction of piles/caissons in which improvement is carried out by means of head units with one or two waves of inflation.
FIG. 1 presents the elevation of the neoprene/rubber hose (10) placed, set up, on a stiff metal or plastic pipe (12), which is closed by means of a vulcanized stop (13) strengthened with appropriate bandages i.e. rings (11) selected of preferred gland materials and set up on suitable spots, so that during the expansion of the hose under the effect of high pressure, they facilitate appropriate deformations. The arrangement of bandages (11) for strengthening depends on the representative model of cormpressibility of the borehole in which the hose is inserted, while their form and the way of realization is not limited and is presented in the figure only for illustration.
FIG. 2 presents the method of execution of a pile by means of insertion of a hose along the entire length of the borehole (21). After the drilling (FIG. 2a) with an appropriate drill rig (23), in the borehole with a compressometer we measure and make a representative compressibility model, according to which the hose is configurated (10). The new forms are accomplished by means of putting on bandages (11) i.e. rings cut out from the original hose and put on over it, thus obtaining stiffnesses appropriate to the measured representative model. The hose (10) which is placed over the plastic or steel pipe (12) is fastened in the upper part at a certain safe distance, prevented is bursting out of the soil under pressure when it is in the borehole, while at the lower part with a vulcanized cover (13). If the pipe (12) does not extend along the entire length, the upper part of the pipe is connected with the lower cover (13) by means of polyester strips, steel strips or angle bars which are not illustrated in the figure. The steel or polyester pipe (12) could be used for filling the concrete (25). The hose that has been prepared in this manner, is lowered into the borehole. What follows is opening of the valve (26) and delivering pressure from the apparatus for pressure generation (27); then it follows deforming the walls of the borehole under the effect of pressure (FIG. 2c). Following the completion of the deformation, the pressure is decreased, hose is deflated and pulled out, while the borehole gets an elevation as presented in FIG. 2d in which we insert the reinforcement cage (28) (FIG. 2e); what follows is concreting with a pipe that has been lowered through the reinforcement cage (28) down to the bottom, by means of which the borehole is gradually filled, from the bottom upward.
In the group of piles/caissons that are constructed by means of a hose, which is brought in along the entire length of the borehole, also falls the execution whose method is presented in FIG. 3. Prefabricated concrete members (31, 32) are connected with a synthetic grid (33) and are used for piles/caissons of large scales. The hose (10), which is of neoprene and protected against damaging, is inserted inside and serves for inflation and displacing of the concrete members (31) aside, while in the lower part it serves for formation of a peculiar bell made up of concrete members (32) of the pile/caisson and so increases the load-bearing base of the pile/caisson.
In the realization of this type of piles/caissons, a rubber/neoprene hose (10) has been used for large diameters, and in doing so the inflation can be performed between the hose (10) and the pipe (12), while concreting is carried out through the pipe (12) or through a pipe in the reinforcement cage (28).
Elevation detail of the previously prepared concrete members is shown in FIG. 4, in a closed position as presented in FIGS. 4a) and 4c) and in an open inflated position, FIGS. 4b) and 4d). While being lowered into the borehole, the members are closed, while under the effect of expansion of the hose they open and form deformation of the borehole.
FIG. 5 presents construction of a pile or a caisson, at which the hose has been placed along the entire length of the borehole, and is intended for applications during foundation in very loose soils as well as for bridging organic peat or muck interbeds i.e. intercalations where the hose (10) is placed into a grid (51) of synthetic material or fabric, while the hose serves for inflation aiming at shaping the prepared cage of synthetic grids or fabric. In certain cases expansion is achieved by means of filling in concrete into the grid (51). The device for generation of pressure (27) from figure can be such a device that distributes fluids under pressure (water or air), and in the event of a specific execution at which expansion is carried out by filling with concrete, the device (27) could also be a special configuration of a concrete pump (29).
The second group of methods and procedures for the construction of concrete piles encompasses the use of special head units as shown in FIGS. 6 and 7. By means of these heads, inflation is carried out gradually. They also can be divided into several constructions, depending on the shapes they could form and the way of filling with concrete.
FIG. 6a) presents elevation of an inserted head unit in which (through the supply hose (61) we bring in air/water under pressure by means of which the elastic gland element (62) is being inflated, and which is secured by means of suitable bandages i.e. stiffening rings (65), and thus, it increases its diameter and creates deformations on the walls of the borehole (64). Following the deformation of one part, the cushion is deflated, while the head unit is being raised upward gradually up to the surface. Variation in the execution of the head unit for inflation is shown in FIG. 6b), at which with one positioning and inflating we can form deformations comprising two waves i.e. stages. Construction is similar, as the one causing deformations with one wave i.e. stage, the only difference being that the unit is of bigger size, while in the middle there are bandages (rings) (65) by means of which we can define the form.
The construction of the head unit for inflation is presented in FIG. 7, in, which case concreting can be executed after each expansion through the pipe, for which we need a modified construction of the head unit, as shown in FIG. 6a. This construction possesses a pipe (66) over the entire length of the head unit as well as a pipe for supply of concrete (63) through which we can perform filling with concrete of already deformed parts of the borehole.
FIG. 8 presents a procedure for execution of the pile/caisson with only one wave i.e. stage and continuous concreting, utilizing the water pressure and concrete. Since there is a permanent support, this unit is being used in cases where there exists danger for cave-in of the borehole. The special head, shown in FIG. 7 on which connected are a concreting pipe (63) and inflating pipe (61), is being lowered at the bottom of the borehole (21) FIG. 8a) and by means of apparatus for generation of pressure (81) the gland head (62) is being inflated, FIG. 8b. Once the desired form has been achieved, the cushion (62) is being deflated, while through the concreting pipe (63) and the pipe/chute (66) passing through the middle of the head—we perform filling, with concrete under pressure of the already expanded part, using concrete pump (29), FIG. 8c, under the effect of which the head lifts upward, up to the next designed stage, FIG. 8d). The same procedure is repeated up to the last stage, FIG. 8e) and FIG. 8f).
FIG. 9 presents a summary review of the procedure for the construction of caissons/piles by using a number of inlet ports (16) for inflating air. In a plastic or metal pipe (12), upon which a neoprene hose is fitted, there are appropriate inlet ports (16) connected with a system of valves and supply ports (15) adapted for performing distribution of a suitable medium under pressure up to a certain part of the hose. The prepared whole rubber/neoprene hoses are lowered into the borehole, the system of pipes (15) is connected to the unit for pressure generation (27) and by opening the valve (26), the pressure is raised up to a value that is greater than the elastic modulus of compressibility of the soil in the part of the borehole where deformation is being performed. The assigned pressure causes plastic deformations and forms shapes of lasting deformations. Pressure is applied between pipe and hose. If there occur clays with pored water, the pressure is maintained until pore pressures withdraw.
After the shaping of the borehole into forms that had been designed, the hose deflates and is carefully pulled, out of the borehole. If need should arise, the borehole can be scanned by means of a depth inspection camera, and if there is caved-in material it is being cleaned out. This procedure is applied especially with large caissons.
In such a formed and cleaned out borehole, the reinforcement cage (28) is being lowered, in the middle of the reinforcement cage we place a plastic or metal pipe (91) for concrete filling (25). While pouring the concrete the plastic or metal pipe (91) should be immersed into concrete, that is to say, it must not be allowed falling of concrete from such a height as to cause a cave-in of soil from the walls of the pile/caisson.
Should there occur strata and interbeds i.e. intercalations of organic peat or muck and other kinds of weak soils, bridging is performed by means of special expansions for that zone. Synthetic grids and fabrics are used in loose soils or else in boreholes in which water causes problems. The grid, or the fabric, is pulled on over the hose and is filled with concrete under pressure. In a number of cases, the grid or the fabric, serves as a bearing reinforcement.
The mechanism of load-bearing for so executed piles/caissons for different types of construction is presented in FIG. 10. It makes use of the advantages of enlarging the diameter (d) of borehole up to (Dp) and also enlarging of densification zone (D) of the soil, which results in an increase of density, angle of internal friction, friction stresses, cohesion and adhesion. Diameters (Dp) and (D) for various soils of different moduli of compression are different.
With the increase of these parameters we increase the load-bearing capacity of the soil i.e. the piles/caissons, and so two bearing models are being formed:
The first model of bearing capacity covers:
1. Loadbearing by friction around the pile/caisson (skin friction) of the soil with increased density, as a result of deformation.
2. Base loadbearing of parts which occur owing to the specific forms of deformation—use like many bases.
3. Loadbearing of the base of each of the piles as a cylinder or a bell, FIG. 10
The second model of bearing capacity is through the formed virtual bearing cylinder of diameter D.
1. With original friction around the vizualized cylinder of diameter D (skin friction).
2. With base loadbearing of the base of the virtual cylinder of diameter D.
The smaller of these two models yields the loadbearing capacity of the pile/caisson. By increasing the density around the pile/caisson, we also increase the load-bearing capacity. And with increased load-bearing capacity, the pile/caisson can be shorter, while the piles could be positioned at larger distances.