METHOD FOR IMPROVING THE MECHANICAL AND HYDRAULIC CHARACTERISTICS OF FOUNDATION GROUNDS OF EXISTING BUILT STRUCTURES

Abstract

A method for improving the mechanical and hydraulic characteristics of foundation grounds of existing built structures, includes the following steps: a first step of two-dimensional or three-dimensional sensing of at least one portion of the built structure; a step of identifying at least one region of intervention in the foundation ground beneath the at least one portion sensed in the first sensing step; and a step of injecting, through holes provided at least at a part of the intervention region, a cement or synthetic mix. The method further includes second steps of two-dimensional or three-dimensional sensing, mutually spaced in time, of the at least one portion during the injection step; and a step of interrupting the injection step on the basis of the information gathered during second steps of two-dimensional or three-dimensional sensing of the at least one portion.

Claims

1-12. (canceled)

13. A method for improving the mechanical and hydraulic characteristics of foundation grounds of existing built structures, the method including the following steps: a first step of two-dimensional or three-dimensional sensing of at least one portion of the built structure; a step of identifying at least one region of intervention in the foundation ground beneath said at least one portion sensed in said first sensing step; a step of injecting, through a plurality of holes provided at least at a part of said intervention region, a cement or synthetic mix; second steps of two-dimensional or three-dimensional sensing, mutually spaced in time, of said at least one portion during said injection step; and a step of interrupting said injection step on the basis of the information gathered during second steps of two-dimensional or three-dimensional sensing of said at least one portion.

14. The method according to claim 13, wherein said step of interrupting said injection step is performed if the two-dimensional or three-dimensional sensing of said at least one portion sensed in said second sensing steps reveals, between two successive sensings, as a function of the intervention type: a. an overall displacement of at least one part of said at least one portion that lies above said intervention region; or b. a differential displacement of parts of the at least one portion that substantially corresponds to the allowable deformation limit of the at least one portion; or c. the reaching, on the part of the portion that lies above the intervention region, of a position that was predefined during design.

15. The method according to claim 13, wherein said at least one portion comprises at least one part of a floor structure.

16. The method according to claim 13, wherein that said at least one portion comprises at least one part of a vertical wall.

17. The method according to claim 13, wherein said at least one portion comprises at least one part of a building.

18. The method according to claim 13, wherein said first sensing step or said second sensing steps are performed by at least one optical acquisition device.

19. The method according to claim 18, wherein said optical acquisition device comprises a laser scanning device.

20. The method according to claim 13, wherein said first sensing step or said second sensing steps are performed by a radar device.

21. The method according to claim 20, wherein said radar device is of the interferometry type.

22. The method according to claim 13, wherein said first sensing step and/or said second sensing steps are performed by a device that emits/receives electromagnetic and/or acoustic waves.

23. The method according to claim 13, wherein said first sensing step and/or said second sensing steps are adapted to sense a portion from the outside or from the inside of said building.

24. The method according to claim 13, wherein said injection step is not limited to permeation only.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Further characteristics and advantages of the present disclosure will become better apparent from the description of some preferred but not exclusive embodiments of the method according to the disclosure, illustrated only by way of nonlimiting example in the accompanying drawings, wherein:

[0051] FIG. 1 is a schematic view of a built structure on which work is necessary;

[0052] FIG. 2 is a schematic view of the first sensing step;

[0053] FIG. 3 is a schematic view of the injection step and of the second sensing steps; and

[0054] FIG. 4 is a chart related to the injectability of the grounds as a function of the properties of the mix and of the ground.

DETAILED DESCRIPTION OF THE DRAWINGS

[0055] With reference to FIGS. 1-4, the present disclosure relates to a method for improving the mechanical and hydraulic characteristics of foundation grounds of existing built structures.

[0056] The method comprises: [0057] a first step of two-dimensional or three-dimensional sensing of at least one portion 2 of the built structure 1; [0058] a step of identifying at least one region of intervention 3 in the foundation ground beneath the at least one portion 2 sensed in the first sensing step; [0059] a step of injecting, through a plurality of holes 4 provided at least at a part of the intervention region 3, a cement or synthetic mix; [0060] second steps of two-dimensional or three-dimensional sensing, mutually spaced in time, of the at least one portion 2 during the injection step.

[0061] In particular, there is a step of interrupting the injection step on the basis of the information gathered during the second steps of two-dimensional or three-dimensional sensing of the at least one portion 2.

[0062] In greater detail, the step of interrupting the injection step is performed if the two-dimensional or three-dimensional sensing of the at least one portion 2 sensed in the second sensing steps finds, between two successive sensings, as a function of the intervention type:

[0063] a. an overall displacement of at least one part of the at least one portion 2 that lies above the intervention region 3; or

[0064] b. a differential movement of parts of the at least one portion 2 that substantially corresponds to the limit of allowable deformation of the at least one portion 2; or

[0065] c. the reaching, on the part of the portion that lies above the intervention region 3 of the built structure 1, of a position that was predefined during design.

[0066] Conveniently, the portion 2 comprises at least one part of a building or of a built structure, such as for example a vertical wall, a face or a floor.

[0067] Preferably, the first sensing step and/or the second sensing steps are performed by using at least one device for the optical acquisition of the two-dimensional or three-dimensional portion.

[0068] Advantageously, the acquired images are of the digital type.

[0069] Preferably, the optical acquisition device 20 comprises a 3D laser scanning device, which, placed at a suitable distance from the built structure, is capable of emitting laser beams along all directions and of obtaining the exact position of a cloud of points that lie on the built structure being considered.

[0070] The data thus acquired can be displayed in real time on the device proper or also on a computer, so that they can be examined more easily.

[0071] The first sensing step is adapted to sense two-dimensionally or three-dimensionally a portion from the outside or from the inside of the building.

[0072] The second sensing steps are adapted to detect two-dimensionally or three-dimensionally a portion from the outside or from the inside of the building.

[0073] Conveniently, the first sensing step and/or the second sensing step substantially relate to placing the optical acquisition device 20, which comprises for example a laser scanning device such as a 3D scanner laser detector, in the vicinity of the building, in a point that allows to sense the entire face or a part thereof (or part of the floor) below which the steps of injection in the ground of cement or synthetic mixes will be performed.

[0074] Nothing prevents the first sensing step and/or the second sensing steps from being performed by other types of sensing devices.

[0075] By way of example, it has been found that it is particularly effective to perform the first sensing step and/or the second sensing steps by means of a radar device.

[0076] Conveniently, the radar device is of the interferometer type.

[0077] It is further possible to provide for the first sensing step and/or the second sensing steps to be performed by a device for emitting/receiving electromagnetic waves and/or acoustic waves or by similar devices.

[0078] The first sensing step can provide for one or more scans of the built structure to determine the exact position, and specifically of the intervention region 3, prior to the beginning of the injection step.

[0079] The method continues with the provision of a plurality of holes in the ground beneath the intervention region 3, even through the foundation of the built structure.

[0080] Typically, the diameter of the holes varies between 6 mm and 200 mm.

[0081] The depth of the holes is a function of the dimensions of the foundation ground and their center distance is usually comprised between 0.50 m and 3.0 m.

[0082] Pipes are then accommodated in the holes and the cement or synthetic mixes are injected into the ground through such pipes.

[0083] The non-expanding mixes or synthetic resins are injected into the ground by means of pressure pumping systems, which force the entry of the mixes or synthetic resins in the intergranular voids or, in the presence of grounds having a finer texture, produce hydro-fracturing, i.e., local breakup of the ground and the forming of lattices of mix which, once set, improve the mechanical characteristics of the mass. The pumping systems for the non-expanding mixes or synthetic resins deliver flow-rates on the order of 5-30 liters per minute and usually generate pressures comprised between 10 and 30 bars.

[0084] These pressures are capable of forcing the penetration of the cement or synthetic mixes in the intergranular voids of sandy and gravelly grounds and to allow access of the cement or synthetic mix in silty or clayey grounds by means of local ruptures known as hydro-fractures.

[0085] The non-expanding mixes or synthetic resins, moreover, can be injected into the ground by means of high- or very high-pressure pumping systems (200 bar to 400 bar), which break up the ground in place and allow the stirring of the matrix with the mix. This last system is known as jet grouting.

[0086] The expanding synthetic or cement mixes are injected into the ground through low-pressure pumping systems.

[0087] The penetration of the cement or synthetic mixes in the intergranular voids of coarse grounds or the hydro-fracturing of grounds having a finer texture occurs by means of the pressure that is generated during the expansion step, which usually occurs by chemical reaction, reaching values comprised between 0.5 bar and 150 bar.

[0088] In the presence of grounds having a finer texture, the hydro-fracturing process is produced not only by the injection pressure but also by the expansion pressure of the cement or synthetic mix. Subsequent hardening of the mix diffused in the ground produces the improvement of the geotechnical characteristics.

[0089] In all of the cases cited above, both by pumping into the ground under pressure non-expanding synthetic or cement mixes and by pumping into the ground at low pressure expanding synthetic or cement mixes, inevitably the injection treatment produces a significant volume variation of the ground.

[0090] This significant volume variation of the ground produces a displacement of the adjacent and overlying volumes of ground that have not been injected, which, as the injection proceeds, necessarily entail evident displacements of the overlying built structure and therefore of the intervention region 3. The pressure generated in the ground by the injection process, be it performed by means of non-expanding synthetic or cement mixes or by means of expanding synthetic or cement mixes, exceeds the pressures transmitted to the ground by the built structure.

[0091] For this reason, during the entire injection step one proceeds with the second sensing steps (two-dimensional or three-dimensional scanning) of the entire built structure or a portion thereof.

[0092] The second sensing steps repeated during the injection step provide operators with a complete picture of the built structure and indicate in real time any critical regions that might generate angular distortions that are not allowable for the structure.

[0093] This monitoring system, in addition to providing information regarding safety against displacements of the structure during the injection step, is used to return indications as to the overall response of the built structure and therefore the effectiveness of the step of injection into the ground.

[0094] With the introduction of the first sensing step and of the second sensing steps by means of the device 20 for two-dimensional or three-dimensional optical acquisition of the portion (for example by means of a 3D scanner laser monitoring device, or by means of a radar device or the like), the function of controlling the effectiveness of the injection, typically performed by traditional laser monitoring topographic systems, as disclosed extensively in EP 0851064, improves significantly, since it does not merely monitor some points of the structure but it extends the observation to a two-dimensional or three-dimensional portion of the built structure.

[0095] The injection step proceeds until the device 20 for optical acquisition (by radar or by means of similar devices) provides indications of a global displacement of the portion 2 of built structure that lies above the intervention region 3 that is detectable but as small as desired (a displacement on the order of magnitude of the tolerance of the instrument used). In this manner one of the best-known criteria for verifying the effectiveness of an intervention for injection into the ground is upheld.

[0096] For example, the displacement is global when it affects a certain number of points (from a few tens to several thousand) that are distributed preferably evenly on the portion of built structure that is the subject of the intervention.

[0097] If necessary, as an alternative, the injection step can proceed beyond the minimal global displacement and can produce the lifting or in general the displacement of the built structure.

[0098] There is a second category of interventions for which injection proceeds until the optical acquisition device 20 detects on any portion of the built structure the forming of angular distortions that are proximate to the allowable tolerances for the structure.

[0099] The angular distortions are defined as the ratio between the differential vertical displacement between two points of the same built structure (differential subsidences or differential rise) and their minimum distance. The person skilled in the art is always capable of determining the allowable tolerances with the aid for example of tables that list the allowable values and the limit values for the angular distortions as a function of the type of building. By way of nonexhaustive example, the most significant are given hereafter:

TABLE-US-00001 Limiting angular distortions according to Bjerrum (1963) Category of potential damage tan Limit beyond which problems can arise in machines that are 1/750 sensitive to subsidences Danger limit for lattice structures 1/600 Safety limit for buildings in which no cracking is allowed 1/500 First cracking in panel walls and difficulty in using bridge cranes 1/300 Limit beyond which tilting of tall buildings can be visible 1/250 Considerable cracks in panel walls and load-bearing brick walls 1/150 Safety limit for load-bearing brick walls with h/L < 1/150 Limit beyond which structural damage to the buildings is to be 1/150 feared

TABLE-US-00002 Allowable angular distortions according to Sowers (1962) Type of structure tan Multistory load-bearing masonry 0.0005 0.001 Single-story load-bearing masonry 0.001 0.02 Damage to plasters 0.001 Reinforced concrete frames 0.0025 0.004 Walls of structures with reinforced 0.003 concrete frame Steel frames 0.002 Simple steel structures 0.005

[0100] The allowable values of the angular distortions for the built structure being studied are defined during design.

[0101] Finally, a third category of possible interventions which is intermediate between the two described earlier is pointed out in which injection might be interrupted when the portion of built structure that lies above the intervention region 3 reaches a position that has been predefined during design.

[0102] This is the case of lightweight built structures, such as flooring or roads, which do not offer a sufficient contrast to the injection pressure or to the expansion pressure of the cement or synthetic mixes. In most of these cases, the overall displacement of the built structure portion that lies above the intervention region may be insufficient to verify the effectiveness of the intervention and it is therefore preferable to determine during design the desired displacement as a function of the characteristics of the ground and of the built structure.

[0103] Another example of intervention that lies within this category relates to industrial or civil flooring that has significant hollows, such as to prevent its normal use. The design in this case might provide for the local lifting of the flooring to a level that is deemed sufficient to regain its planarity but in any case much higher than the tolerance of the sensing instrument used (for example on the order of centimeters), while remaining well below the limit of allowable deformation of such flooring.

[0104] Other examples of interventions that lie within this category relate to historical buildings or built structures that are close to collapse and cannot tolerate significant displacements and for which the injections are sized appropriately in terms of quantity of mix to be injected and in terms of injection pressures. Or very heavy buildings for which the sensing of an overall displacement, especially with the first injections, might require quantities of cement or synthetic mixes that exceed those strictly necessary in order to improve the mechanical and hydraulic characteristics of the ground.

[0105] In these cases, the injection step is interrupted upon reaching predefined quantities of mix during design although the above cited criterion of effectiveness has not been upheld in every injection point.

[0106] If the design requires that the built structure must not undergo significant displacements, the injections will be interrupted when the displacement sensing system detects a minimal displacement, on the order of instrument precision, even in a single point of the built structure.

[0107] The injection step can also be performed by using alternately or in succession mixes of different types.

[0108] For example, in order to reduce the costs of the intervention, there might be a first step of injection of cement mixes followed by the injection of synthetic mixes.

[0109] Otherwise, if the foundation ground has nonuniformities in the intervention region, different types of synthetic mix might be used in order to optimize consumptions and the obtained results.

[0110] The injection step can also be performed by using simultaneously a plurality of injection pumps. In this case, the injections can be performed by limiting the angular distortions that are induced on the structure, allowing the injection of more cement or synthetic mix before the limit of allowable deformation is reached, thus achieving a better result.

[0111] In practice it has been found that the method according to the disclosure achieves fully the intended aim, since it allows, in a simple, quick, effective and final manner to preserve the built structure against excessive distortions that might be produced during execution of work for improving the mechanical and hydraulic characteristics of the grounds, replacing or integrating spot monitoring systems with a system for two-dimensional or three-dimensional monitoring of portions of the building.

[0112] The disclosures in Italian Patent Applications No. 102015000035300 (UB2015A002280) and No. 102016000017692 (UB2016A000937) from which this application claims priority are incorporated herein by reference.