Method for optimizing processes for increasing the load-bearing capacity of foundation grounds

Abstract

A method for optimizing processes for increasing the load-bearing capacity of foundation grounds includes the following steps: detecting at least one part of a built structure and/or of ground; identifying at least one region to be treated of the foundation ground; and injecting, at least one injection point located substantially within the at least one region to be treated, a cement and/or synthetic mixture. The method further includes at least one second step of detecting at least one part of the built structure and/or of the ground that lies above the injected foundation ground. The method further includes a step of interrupting the injection step, and measuring at least one physical parameter that is susceptible of varying as a consequence of the injection step.

Claims

1. A method for optimizing processes for increasing the load-bearing capacity of foundation grounds, the method including the following steps: a first step of detecting at least one part of a built structure and/or of ground; identifying at least one region to be treated of the foundation ground that lies below at least one portion of said at least one part of the built structure and/or of ground; injecting, at at least one injection point located substantially within said at least one region to be treated, a cement and/or synthetic mixture; at least one second step of detecting at least one part of the built structure and/or of the ground that lies above the injected foundation ground; interrupting said injection step upon the detection of an upheaval movement of at least one portion of the built structure and/or of the ground that lies above said foundation ground; measuring at least one physical parameter that is susceptible of varying as a consequence of said injection step substantially at the volume of ground affected by said injection step; and identifying an optimum spatial distribution of the successive injection points as a function of the values and of the spatial distribution of said at least one physical parameter measured in said measurement step; said at least one physical parameter being chosen from the group consisting of: electrical resistivity; seismic wave propagation speed; and gravitational acceleration, wherein the optimum spatial distribution of the injections corresponds to a two-dimensional or three-dimensional grid that has a distance between the injection points that is equal to or smaller than twice the minimum distance between the injection point and the external surface of the volume of ground that is improved.

2. The method according to claim 1, wherein said step of identifying the optimum spatial distribution of the injection points is determined by considering that the volume of ground improved with the injection corresponds to the volume of ground in which values of electrical resistivity at least 5% higher than those measured in the vicinity of that same volume of ground are observed.

3. The method according to claim 1, wherein the variation of said physical parameter is measured before and after said injection step and wherein said step of identifying the optimum spatial distribution of the injection points is determined by considering that the volume of ground that is improved with said injection step corresponds to the volume of ground in which values of electrical resistivity at least 5% higher than those present in that same volume of ground before said injection step are observed.

4. The method according to claim 1, wherein said step of identifying the optimum spatial distribution of the injection points is determined by considering that the volume of ground improved with the injection corresponds to the volume of ground in which values of electrical resistivity that are higher than a predefined value are observed.

5. The method according to claim 1, further comprising a step of storing the amount of cement and/or synthetic mixture that is injected in said first step of injection, said amount of injected mixture corresponding to the amount of cement and/or synthetic mixture that is necessary in order to produce, in said injection step, a displacement of said built structure and/or overlying ground that is at least equal to 0.1 mm.

6. The method according to claim 5, wherein the amount of cement and/or synthetic mixture to be injected in the injection points identified in said identification step corresponds substantially to the amount injected in said injection step before said step of interrupting the injection.

7. The method according to claim 1, wherein said first step of detecting is carried out with one-dimensional laser systems, two-dimensional laser systems, or three-dimensional laser systems.

8. The method according to claim 1, wherein said first step of detecting is carried out with radar systems.

9. The method according to claim 1, wherein the injection step corresponds to an injection in a single injection point of cement and/or synthetic mixtures.

10. The method according to claim 1, wherein the injection step corresponds to multiple injections, which may or may not be simultaneous, of cement and/or synthetic mixtures distributed in a volume of ground.

11. The method according to claim 1, wherein said step of measuring the electrical resistivity of the ground after said injection step is carried out in a spherical neighborhood of the injection point with a radius of more than one meter.

12. The method according to claim 1, wherein the spatial distribution of the injection points is preset in the design phase, said step of identification of the optimum spatial distribution being suitable to determine the amount of cement and/or synthetic mixture to be injected in each point and/or to increase or decrease the injection points, creating ones or leaving some unused.

Description

DETAILED DESCRIPTION OF THE DISCLOSURE

(1) 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.

(2) The present disclosure relates to a method for optimizing processes for increasing the load-bearing capacity of foundation grounds, which comprises: a first step of detecting at least one part of a built structure and/or of ground; a step of identifying at least one region to be treated of the foundation ground that lies below at least one portion of the at least one part of the built structure and/or of ground; a step of injecting, at at least one injection point located substantially within the at least one region to be treated, a cement and/or synthetic mixture; at least one second step of detecting at least one part of the built structure and/or of the ground that lies above the injected foundation ground; a step of interrupting the injection step upon the detection of an upheaval movement of at least one portion of the built structure and/or of the ground that lies above the foundation ground; a step of measuring at least one physical parameter that is susceptible of varying as a consequence of the injection step substantially at the volume of ground affected by the injection step; a step of identifying the optimum spatial distribution of the successive injection points as a function of the values and of the spatial distribution of the at least one physical parameter measured in the measurement step.

(3) In particular, such method is adapted to identify the best possible position of the injection points and to define the optimal amount of cement and/or synthetic mixtures to be injected at such points in the injection operations aimed at improving the hydraulic or mechanical characteristics of grounds.

(4) Conveniently, the physical parameter is selected from the group comprising: electrical resistivity; seismic wave propagation speed; gravitational acceleration.

(5) Conveniently, the step of identifying the optimum spatial distribution of the injection points is determined by considering that the volume of ground improved with the injection corresponds to the volume of ground in which values of electrical resistivity at least 5% higher than those measured in the vicinity of that same volume of ground are observed.

(6) Preferably, the variation of the above mentioned physical parameter is measured before and after the injection step.

(7) The step of identifying the optimum spatial distribution of the injection points is determined by considering that the volume of ground improved with the injection step corresponds to the volume of ground in which values of electrical resistivity are observed at least 5% higher than those present in the same volume of ground before the injection step.

(8) It is possible that the step of identifying the optimum spatial distribution of the injection points is determined by considering that the volume of ground improved with the injection corresponds to the volume of ground in which values of electrical resistivity that are higher than a predefined value are observed.

(9) The method comprises a step of storing the amount of cement and/or synthetic mixture that is injected in the first step of injection: in particular, the amount of injected mixture corresponds to the amount of cement and/or synthetic mixture that is necessary in order to produce, in the injection step, a displacement of the built structure and/or overlying ground of at least 0.1 mm.

(10) In this regard, the amount of cement and/or synthetic mixture to be injected into the injection points identified in the identification step corresponds substantially to the amount injected in the injection step before the step of stopping the injection.

(11) Preferably, the scanning of the built structure is carried out by way of using at least one one-, two- or three-dimensional laser scanning device, or with radar systems.

(12) Advantageously, the reconstructions performed by way of laser scanning devices or by way of radar systems are digital.

(13) Such scanning device can comprise a 3D laser scanner detector or a radar system such as ARAMIS (Advanced Radar for Microwave Interferometric Surveys) to be positioned in proximity to the built structure, at a point that allows the scanning of the entire facade or of a part thereof (or of a portion of floor) below which the injection of the ground will be carried out, with mixtures under pressure or expanding resins.

(14) Once the 3D laser scanner system or ARAMIS is positioned, one or more scans of the facade (or of the floor) are carried out in order to record the state of consistency of the built structure before the injections are begun. There is no reason why the first scanning step and/or the second scanning steps cannot be carried out by other types of scanning devices such as for example a laser level.

(15) It is likewise possible for the first and/or the second scanning step to be carried out by an emitter/receiver device of electromagnetic waves and/or of sound waves or by similar devices.

(16) The method proceeds with executing a hole or a plurality of holes, vertical or inclined with respect to the vertical, in the ground or even through the foundation of the built structure, of diameter that can vary from 6 mm to 200 mm. The initial geometry with which the hole or the holes are distributed below the built structure is determined by a computer model or in simpler cases by experience. Usually the depth of these holes is a function of the characteristics of the foundation ground and is usually comprised between the depth corresponding to the intrados of the foundation and 15-20 meters from that intrados and their center distance is usually comprised between 0.50 and 3.0 m.

(17) Subsequently, pipes are accommodated in the hole or holes and the mixtures and/or the synthetic resins are injected into the ground through these pipes.

(18) The cement and/or synthetic mixtures are injected into the ground through pressure pumping systems, which force the entry of the mixtures into the intergranular spaces or, in grounds with finer texture, produce hydraulic fracturing, i.e. the local breakage of the ground and the formation of grids of mixture that, once hardened, improve the mechanical characteristics of the mass. The pumping systems for the cement and/or synthetic mixtures dispense flow rates of the order of 5-30 liters per minute and usually develop pressures comprised between 10 and 30 bar. These pressures are capable of forcing the entry of the cement and/or synthetic mixture into the intergranular spaces of sandy and gravelly grounds and of enabling the cement and/or synthetic mixture to access silty or clayey grounds through local breaks called hydraulic fractures.

(19) The cement and/or synthetic mixtures, further, can be injected into the ground through high or very high pressure pumping systems (from 200 to 400 bar), which break up the existing ground and enable the remixing of the matrix with the mixture. This latter system is called jet grouting.

(20) The expanding cement and/or synthetic mixtures are injected into the ground through low-pressure pumping systems. The entry of the expanding cement and/or synthetic mixtures into the intergranular spaces of coarser grounds or the hydraulic fracturing of finer-textured grounds occurs by virtue of the pressure that develops during the step of expansion which, usually, occurs by chemical reaction, reaching values comprised between 0.5 bar and 150 bar. In finer-textured grounds, the process of hydraulic fracturing is produced by the same pressure of expansion of the cement and/or synthetic mixture. The subsequent hardening of the mixture spread through the ground produces the improvement of the geotechnical characteristics.

(21) The diffusion of the cement and/or synthetic mixtures in the grounds, be they expanding or non-expanding, produces the compaction of the ground surrounding the injection points with consequent displacement of the matrix, reduction of intergranular spaces, and expulsion of water. The dimension of the portion of ground affected by the compaction depends mainly on the amount of cement and/or synthetic mixture dispensed as well as on the characteristics of the ground. During the injection process, as the dispensing proceeds of the cement and/or synthetic mixture into a point in the ground, the surrounding volume affected by the compaction gradually increases radially starting from the injection point until vertical displacements are generated of the surface of the ground and of any built structure overlying it, which can be detected with the monitoring system. The vertical movement of the built structure or of the surface of the ground following the injection indicates that the amount of cement and/or synthetic mixture dispensed up to that moment is sufficient to produce an adequate consolidation of the ground for the loads in play.

(22) However, within the possible modes of diffusion of the cement and/or synthetic mixtures, be they linked to the pressure of a pumping system or to expansion by chemical reaction, it is known that the path and the location follow criteria that at the moment cannot be determined. It can happen therefore that the cement and/or synthetic mixtures injected, although producing a rise of the built structure or of the overlying ground, do not occupy the intended design volumes, but migrate to areas where their action may not be needed or even where their presence could aggravate the situation or cause unwanted effects.

(23) It can also happen that the rigidity of the built structures built on the surface produces vertical displacements of portions overlying volumes of ground that are not adequately compacted. To monitor the effectiveness of the method of consolidating the ground by way of injection of cement and/or synthetic mixtures, the building monitoring system is therefore necessarily integrated with the 2D or 3D electrical tomography, which returns almost in real time the path of the cement and/or synthetic mixtures in the ground by detecting the variation of electrical resistivity.

(24) The aim of a geoelectrical survey is to indirectly reconstruct the electrical properties of a given medium and, in particular, of the electrical resistivity, the converse of electrical conductivity. Electrical resistivity is an intrinsic characteristic of a material that directly influences the flow of current, which flows with greater ease in regions of the material that are characterized by low resistivity, and vice versa.

(25) A material characterized by high resistivity values (low conductivity) is said to be resistive, and, as a consequence, a material with low resistivity (high conductivity), is said to be conductive.

(26) The geoelectrical method is by nature indirect and involves, in general, generating an electrical potential field created by the injection of current through two metal electrodes driven into the material to be investigated. These two electrodes are called current dipoles.

(27) By measuring the electrical potential difference (voltage) through a pair of electrodes (referred to as a potential dipole), it is possible to relate the measured voltage to the current introduced. Such ratio is referred to as resistance, which is converted to apparent resistivity by way of a geometric factor that takes account of the reciprocal arrangement of the electrodes.

(28) The distance between the electrodes and the configuration used influence the depth and the spatial resolution of investigation.

(29) The apparent resistivity is an average value of the volume of ground affected by the measurement, and therefore it can deviate from the real value if heterogeneities are present.

(30) To overcome this problem, an operation called electrical tomography is carried out, which involves the acquisition of a dataset of apparent resistivity covering the affected region in a spatially uniform manner.

(31) The data acquired are processed by virtue of specific inversion software, which makes it possible to find the distribution of resistivity, which best approximates the experimental data in a finite element model below the measurement electrodes. The estimate is made by way of an iterative process of minimization (least squares or least absolute values).

(32) The tomography investigation is conducted by positioning in the ground, proximate to the volume to be investigated, starting from the surface, a number of electrodes comprised between 8 and 72 according to regular spreads with a center distance comprised between 0.3 m and 1.5 m.

(33) The dataset is usually acquired at the end of the injection operations. The apparent/inverted resistivity differences between the treated volume of ground and the surrounding ground untreated by injections represent the volume of ground within which the cement and/or synthetic mixture has diffused over the course of the preceding injection step.

(34) It can sometimes be necessary to acquire datasets on two steps, which relate to the starting condition (step 0) in the pre-injection situation and, upon conclusion of the work site activity, the post-injection condition (step 1).

(35) In this case the background acquisition (step 0) relates to the pre-injection step, and best represents the geoelectrical characteristics of the site, while step 1 describes the final status of the operation, after completion of the injections under the affected foundations.

(36) In this case the volume of ground within which the mixture has diffused over the course of the injection process can be identified by analyzing the differences in apparent/inverted resistivity between the configurations of step 1 with respect to step 0.

(37) Among the instruments used for acquisition are the P.A.S.I. Polares frequency modulable alternating current georesistivity meter, and the Electra frequency modulable direct current georesistivity meter produced by Micromed.

(38) The data acquired are then processed according to a procedure that entails the 2D or 3D inversion of the dataset relating to each step analyzed by way of dedicated software and calculation of the differences from the conditions present outside the treated volume or in step 0.

(39) From 2D or 3D reconstructions of the resistivity volume underlying the built structure or the ground surface, it is possible to identify the zones influenced by the injection.

(40) After the injection of the cement and/or synthetic mixtures into the ground and after the consequent detection of the displacement of the built structure or of the surface of the ground overlying the treated volume and at the end of the electrical tomography readings of the improved ground, comes the step of reexamination of the process.

(41) The reexamination step entails the analysis of the amount of cement and/or synthetic resin mixture dispensed in the individual injection points in order to obtain the vertical displacement of the built structure or of the surface of the ground overlying the injection and the evaluation of the volumes of diffusion of the cement and/or synthetic resin mixture in the various injected points.

(42) If the reexamination step confirms that consolidation has been achieved for all the points of the volume underlying the portion of built structure or of ground surface to be treated, then the design technician assesses, based on the readings obtained, the advisability of increasing the distance between the injection points while keeping the amount of cement and/or synthetic resin mixture per single injection unaltered. Differently, the technician analyzes the possibility of increasing the number of injections, globally or locally, and/or of increasing the amount of cement and/or synthetic resin mixture per single point.

(43) The injection step corresponds to an injection in a single injection point of cement and/or synthetic mixtures.

(44) In any case it is possible that the injection step corresponds to multiple injections, which may or may not be simultaneous, of cement and/or synthetic mixtures distributed in a volume of ground.

(45) The step of measuring the electrical resistivity of the ground after the injection step is carried out in a spherical neighborhood of the injection point with a radius of more than one meter.

(46) The optimum spatial distribution of the injections corresponds to a two-dimensional or three-dimensional grid that has a distance between the injection points that is equal to or smaller than twice the minimum distance between the injection point and the external surface of the volume of ground that is improved.

(47) The spatial distribution of the injection points is preset in the design phase: the step of identification of the optimum spatial distribution is suitable to determine the amount of cement and/or synthetic mixture to be injected in each point and/or to increase or decrease the injection points, creating new ones or leaving some unused.

(48) In practice it has been found that the method according to the disclosure fully achieves the aim of identifying the best possible position of the injection points and defining the optimal amount of cement and/or synthetic mixtures in the injection operations aimed at improving the hydraulic or mechanical characteristics of the grounds at low cost, simply, rapidly, effectively and definitively, by integrating the systems for monitoring the built structure with systems for monitoring the electrical resistivity of the ground.

(49) The integration between the system for monitoring the built structure, which constitutes a necessary criterion for the effectiveness of the operation, and control by way of 2D or 3D electrical tomography makes it possible to obtain the assurance of complete and homogeneous treatment of the volume of ground underlying the built structure.

(50) The disclosures in Italian Patent Application No. 102016000066045 (UA2016A004665) from which this application claims priority are incorporated herein by reference.