WO2024079506A1

WO2024079506A1 - Method for stabilizing structures

Info

Publication number: WO2024079506A1
Application number: PCT/IB2022/059764
Authority: WO
Inventors: Paolo SIANO
Original assignee: Siano Paolo
Priority date: 2022-10-12
Filing date: 2022-10-12
Publication date: 2024-04-18

Abstract

Stabilizing structures by means of geotechnical works involving treating the soil by injecting consolidating mixtures and/or installing posts to consolidate the foundations. The procedure involves performing real-time monitoring using acoustic emission (AE) technology capable of detecting the constraints induced by the above-mentioned geotechnical works on the structures.

Description

PROCESS FOR STABILIZING STRUCTURES

The present invention relates to a method aimed at stabilizing structures, in particular foundations, and which provides for monitoring carried out by means of a survey and a parametric analysis of the acoustic emissions generated in the material of the constituent elements of the structure during the construction site operations. These are consolidation interventions by injection of cement or synthetic mixtures with expansive power into the foundation soil and/or by the installation of piles in the ground up to more compact layers of soil and which are by subsequently anchored to the existing foundation structure.

As is well known in the field of soil mechanics, an elementary volume of soil can be schematized as a porous medium consisting of soil grains (solid skeleton) and voids. The latter can be not at all, partially or totally occupied by pore water: in the first case we speak of "dry soil" (degree of saturation S = 0), in the second case of "partially saturated soil" (0 < S < 1), and when all the voids are occupied by water, "saturated soil" (S = 1).

When said elementary volume is subjected to the application of an external load, depending on its intrinsic permeability, a state of tension is generated in its mass to which a state of deformation corresponds.

When these observations are transferred from the micro-scale (elementary volume) to the macro-scale (natural volume), it becomes evident how a mass of natural soil - imagined as a multitude of elementary volumes - when subjected to actions external (application of loads, variations in the degree of saturation, etc.) can deform by varying its initial volume with a corresponding variation in the vacuum index and/or the degree of saturation.

In the field of civil engineering, these geological-geotechnical aspects are of primary importance not only in the design, but also in the operational phase of the foundation structures of any artifact (building, roadway, etc.). In the process of transferring loads from the structure to the ground, it is necessary to ensure the balance of the soil-foundation node to which the stability of the superstructure is linked.

Any alteration of the foundation of an existing structure can be the potential cause of its subsidence. These subsidences can compromise the equilibrium conditions of the superstructure, leading to the appearance of deformations and cracks on structural and non-structural elements.

To restore stability conditions, it is essential to first analyze the pathology, then carry out any structural and/or geological-geotechnical diagnostics, consider the different applicable solutions among those possible, choose and design whichever is deemed most appropriate.

Among the various "traditional" solutions, as they have been used for several decades, there is undoubtedly that which consists of transferring the loads of the structure to layers of more compact soil, by means of more compact foundation piles. deep, aligned longitudinally to the existing foundation and with suitably defined spacing.

Downstream of the intervention, the compressible soil layers are bypassed and will have no load-bearing function.

To reduce the level of invasiveness of the intervention, particularly on existing structures, the installation of small diameter piles (also called micropiles) is increasingly common. The latter are generally metallic and composed of several interconnected elements which are screwed or driven into the ground to the deepest state of support. Once the desired load capacity is reached, or when the structure has been lifted using a laser level, the operations are stopped and the head of the micropile is connected to the structure, which is done in this case by means plates bolted to the foundation.

Fixation de la plaque d'acier équipée d’une bague (C) à la fondation par boulonnage (D) ;
Installation du vérin hydraulique (E) sur la plaque par le biais d’un gabarit métallique de fonçage (F) et installation du circuit hydraulique (G) relié à un groupe électrogène ;
Insertion du pieu (H) dans à travers le gabarit métallique et enfoncement du pieu par portions jusqu'à ce que la couche souhaitée (I) soit atteinte et/ou que la charge ponctuelle souhaitée (J) soit atteinte et/ou que la structure réagisse au soulèvement (K) ;
Blocage du pieu à la fondation par boulonnage (L), coupe de la portion de pieu excédante (M) et remblayage de l'excavation (N).

There (sectional view of a generic foundation system during operational phases) diagrams a typical micropile installation intervention. After carrying out an excavation (A) which exposes the existing foundation (B), the process provides for the sequence of the following phases:

Fixing the steel plate equipped with a ring (C) to the foundation by bolting (D);
Installation of the hydraulic cylinder (E) on the plate using a metal sinking template (F) and installation of the hydraulic circuit (G) connected to a generator;
Insertion of the pile (H) into through the metal template and driving the pile in portions until the desired layer (I) is reached and/or the desired point load (J) is reached and/or the structure reacts to the uprising (K);
Blocking the pile to the foundation by bolting (L), cutting the excess pile portion (M) and backfilling the excavation (N).

These traditional repair solutions are characterized by a medium to long duration, as well as a high level of invasiveness.

Indeed, their execution requires medium to large diameter drilling operations, point or linear excavations which are often difficult to apply in contexts with reduced accessibility.

Faced with these limits, processes aimed at improving the quality of the supporting soil through cement injections ("jet grouting") or synthetic products (polyurethane resin) have been increasingly used in recent decades.

There illustrates the typical expansion diagram of a two-component polyurethane resin. Looking at the diagram it is possible to observe that once the mixing is completed (t=t0), the mixture obtained is injected into the ground through small diameter pipes, previously installed by means of a perforation made at the using a hand drill. The mixture, still liquid, exits the pipe at the desired depth and begins to impregnate the surrounding soil (impregnation phase, t0<t<t1). After a certain time, which varies depending on its composition, the mixture increases in volume (expansion phase - t1≤t<t2) until the energy generated by the chemical reaction is exhausted (t=t2) and the product polymerizes, becoming stable and inert (polymerization phase, t2≤t≤t3).

The strong expansion power is capable of generating mechanical action on the soil (consolidation) due to the increase in grain density, filling/crushing of voids and displacement of pore water.

These mechanical effects produce an increase in the bearing capacity of the volumes of soil affected by the treatment, as well as a reduction in the overall permeability of the environment with a consequent improvement in the behavior of water.

La réalisation de perforations à faible diamètre à travers la fondation ( - A), généralement positionnés à une distance en plan variant entre 0,50 m et 1,50 m (valeur qui correspond généralement au rayon d'action de la formulation dans un contexte cohésif et granulaire) ;
Continuation des mêmes perforations dans les couches de sol à traiter jusqu'à la profondeur souhaitée ( - B) ;
Installation d'une série de tuyaux à faible diamètre ( - C) implantés dans le sol à différentes profondeurs de manière à disposer de plusieurs points d'injection sur une même verticale ;
Le traitement ponctuel par des injections cycliques de ciment ou de mélanges synthétiques tout en réalisant des pauses appropriées à l'aide d'un terminal d'injection relié à une station d'injection convenablement équipée ( - D).

As illustrated by (sectional views of a generic foundation system during operational phases), for a standard intervention, all procedures involve the following phases:

Making small diameter perforations through the foundation ( - A), generally positioned at a distance in plan varying between 0.50 m and 1.50 m (value which generally corresponds to the radius of action of the formulation in a cohesive and granular context);
Continuation of the same perforations in the layers of soil to be treated until the desired depth ( - B);
Installation of a series of small diameter pipes ( - C) installed in the ground at different depths so as to have several injection points on the same vertical;
Spot treatment with cyclical injections of cement or synthetic mixtures while taking appropriate breaks using an injection terminal connected to a suitably equipped injection station ( -D).

During the implementation of micropiles, but especially during the execution of consolidation injections, one of the technical and operational problems encountered in the state of the art concerns the monitoring and management of uplifts of the superstructure. .

If the state of tension and deformation induced by the uplift is not compatible with the superstructure (that is to say, in case of exceeding the threshold tensional state of resistance), it is very probable that the The intervention could damage the structure or aggravate the pathologies already present.

Very often, these pathologies develop within the material that makes up the structure without manifesting themselves in an obvious and/or appreciable way to the naked eye. In addition to the problem of controlling variations in the "state of tension-deformation" of the structure, there is also the problem linked to the difficulty of locating any structural damage after intervention which is not visible to the eye. naked eye.

It is therefore obvious that in this type of work, in addition to having appropriate instrumentation to control the geotechnical operations, it is equally important to monitor the possible effects induced by the backlashes linked to the driving of the piles (in the case of micropiles) and by the thrust of the expansion of the injection mixture (in the case of mechanical improvement treatment) on the overlying structure. This is to guarantee structural safety.

The proposed monitoring makes it possible to

- detect the warning signs of a crack (preventive monitoring);

- define the origin and propagation of crack precursor signals (mapping).

History of consolidation intervention by injection

In the known state of the art, the execution of soil consolidation work by injection involves lifting the aerial structures resting on the ground to be treated by means of "continuous control by laser level or other system" .

With such instrumentation, when the equipment signals the beginning of lifting of the construction or the ground surface (order of magnitude linked to the degree of precision of the instrumentation used - generally 1/ ^10th of a millimeter), the processing of the current injection point is considered completed. This uplift is associated with very strong soil compaction around the injection point, the values of which are generally higher than the minimum required values.

With such an approach, it is obvious that we are seeking to obtain uplift in order to validate each injection point as well as a reduction in the opening of cracks (permanent or temporary) if they already exist.

However, even if site operators would stop the injection cycle as soon as the instrumentation detects movement of the structure, this would not stop the expansion of the quantity already injected. Such an event would induce an increase in the stress-strain state, with the potential appearance of new cracks or the worsening of existing ones. The time at which this event occurs as well as the quantity of resin injected remain entirely random and linked to specific site conditions.

Thus, there are frequent situations in which site operators, although quickly stopping the treatment of an injection point at the moment when an uplift is detected, can only note its occurrence and wait for its end.

Patents EP1914350 and EP2543769 provide for geophysical monitoring of the treated soil during injection through the acquisition and development of 3D electrical resistivity tomographies. The assessment of mechanical improvement is carried out using penetrometric tests.

Document EP1914350 provides that the treatment of the ground is carried out until "the electrical resistivity values of the subsidence zone are reduced to those not subsidence taken as a benchmark".

The same applicant, with the introduction of patent EP2543769, found that "it is not always possible to practically provide a volume of adjacent soil that is not sagging and which, due to the chemical-physical and structural characteristics, can be taken as a benchmark in the process of stabilization and homogenization of the volume of subsided soil". The document EP2543769 indicates that the "effects induced by sequential and targeted injections of expansive mixtures in subsided soil volumes are recognized through measurements of variation of electrical resistivity Δρ expressed as a percentage (%)" (with ρ = electrical resistivity ).

Without prejudice to the usefulness and reliability of the information provided by electrical resistivity tomographies, the geophysical instrumentation used in the two patented procedures (EP1914350 and EP2543769) does not make it possible to verify the effectiveness of the intervention at each point. injection, nor to follow the uplifts induced on the structure.

Between one operation of acquisition, inversion and processing of an electrical resistivity tomography and the next, there is a certain period of time (time-lapse monitoring), during which the site operators do not have any instrumentation to carry out the correct dosage of formulation quantities and to verify in real time their effect on above-ground structures. This fact increases the risk of undesirable and unmanageable effects occurring when the resin has already been injected and is in the expansion phase.

The applicant, with patent application 102019000019789, has already proposed a process for consolidating the soil by injecting expansive resins by carrying out acoustic monitoring with very sensitive geophones.

This process provides information on the action of the resin injected into the soil in real time and allows site operators to manage the different injection cycles, confirm saturation of the volume of interest and act in a timely manner. if abnormal and out of range noises are detected.

Indeed, once a generic injection cycle has been carried out, the resin in the expansion phase generates noises induced by friction with the ground as well as by the effects of friction and compaction of the grains, the filling of the voids and the movement of pore water (if present). These noises are audible on the surface via high-sensitivity geophones located on the injection verticals close to the volume of soil impacted by the treatment and the injection point. Thanks to a control unit connected to the geophones, a series of acoustic parameters can be associated with the noise generated by the consolidation action, such as extension, smart indicator, frequency spectra.

This process therefore makes it possible to localize the expansion action in the environment of the measurement vertical and, in addition, to control the injection cycles with the execution of pauses between successive cycles relating to the same injection point in which the following cycle is resumed when said acoustic detection means no longer detect noise (the end of the expansion of the formulation will correspond to that of the noise detection).

In certain cases, the lessons described by 102019000019789 can reduce the risk of the occurrence of untimely uplifts of above-ground structures (of the artifact itself or its ancillary elements) even before they occur, thanks to the possibility of stopping the treatment when the characteristic acoustic parameters show volume saturation around the generic injection point.

However, it is not always possible to avoid undesirable effects on the structure by "auscultating" the soil, especially when the geological-geotechnical and structural conditions are unfavorable (saturated soils or overconsolidated stratigraphic alternations, fragile structures already damaged by previous pathologies).

In general, it must be assumed that, in the case of the application of expansive polyurethane resin in the ground, its expansion path remains very random and is strictly influenced by the site-specific confinement conditions (content in water, vacuum index, level of heterogeneity) as well as by the consolidation effect of previous injection cycles.

The resin, at each injection cycle, will therefore diffuse following the simplest path, that is to say the least confined, until complete saturation of the treated soil. From this point on, there is a sharp increase in the risk of uplift of structures above ground, which justifies the use of structural monitoring instruments in addition to ground monitoring instruments.

Presentation of the invention

The aim of the present invention is to propose an alternative monitoring method at the laser level when carrying out injections of cement or synthetic mixture, as well as during the installation of piles. This is to guarantee the level of security that these operations require.

The aim of the present invention is to overcome the disadvantages highlighted above by providing a process for stabilizing structures and consolidating soils which drastically reduces the risk of structural damage which can potentially occur during injections (uplifts, cracking, etc.). .).

A particular objective is to provide a procedure which, through continuous monitoring, makes it possible to

- increase the level of sensitivity of monitoring the tension-deformation state of the structure resting on the treated soil;

- locate and map any structural cracks not visible to the naked eye.

These objectives, as well as others which will be specified later, are achieved by means of a method according to claim 1 and to which reference is made for greater conciseness of the presentation.

Advantageous embodiments of the invention are obtained in accordance with the dependent claims.

Detailed description of the preferred embodiments

Some preferred embodiments of the process, illustrative but not exclusive of the invention, will be better understood on reading the description which follows with reference to the appended figures. These achievements are generally applied to existing structures showing signs of instability, such as cracks or deformations of structural and non-structural elements (curative interventions after disaster).

The method can also be implemented when volumes of foundation soil must be treated with a view to increasing permanent or accidental loads on the overlying structure, such as the elevation and/or installation of heavy machinery ( preventive interventions).

These are essentially cement mixtures or synthetic mixtures with monitoring of the overlying structure using acoustic emission (AE) technology.

This is a non-destructive monitoring method already known for testing structures and/or for checking/diagnosing phenomena such as damage, microcracks, degradation, corrosion, etc. It is based on the detection of ultrasonic pulses emitted by the precursor signals of a fracture which are generated and propagate in the material from the first moments when they begin to occur (for example due to the subsidence of the foundation soil ).

Acoustic emissions technology bases its principles on the detection and conversion of acoustic emissions into voltage signals through transducers installed on the structure to be monitored. These transducers, thanks to special crystals, are capable of generating electrical signals at the slightest stress detected. Suffice it to say that modern transducers are capable of capturing a mechanical stress of the order of 10 ^-9 mm and transforming it into an electrical pulse of 10 ^-6 volts.

There (axonometric view of a corner of a damaged building) shows a generic application of AE to monitor corner cracking (A) due to foundation subsidence (B). The instrumentation consists of a series of transducers (C) installed on the structure to be monitored and connected by cables (D) to a reading unit (E) which collects the readings. Software installed on a personal computer (F) processes and stores acoustic emission signals propagating in the structure. Readings can also be viewed remotely in real time.

The EA technology is carried out with central units capable of filtering the signals acquired by the transducers after having defined an appropriate threshold value. The definition of the latter makes it possible to exclude the background "noise" linked to the environmental context in which we operate and to only consider the AE signals which exceed the pre-established threshold value. Setting a threshold value also determines the degree of sensitivity and precision to be adjusted.

The basic acoustic parameters that characterize an AE pulse are amplitude and frequency, as well as the number of events produced.

From these values, also thanks to statistical analysis analysis methods of interpretation (Beta_t fractal interpretation, b-value, b-collapse), it is possible to predict at an early stage whether there is an evolution of the pathology. Indeed, it is known that the evolution of structural cracks is associated with

- an increase in the number of acoustic events occurring in the unit of time;

- an increase in the amplitude of the event;

- a reduction in frequencies.

From the above, referring again to the , only high frequency signals (50 kHz - 1 MHz) are associated with the initiation of cracking (corresponding to the moment when cracks in a small part of the structure, called "damage zone" start to evolve, G) .

The same pathology will develop if there is an increase in the number of EA signals in the same area, accompanied by a gradual decrease in frequency (1 - 10 kHz).

When there is a sudden increase in the number of low frequency AE signals and a reduction in the number of high frequency signals, it means that the damage is progressing and there is potential structural failure.

To measure the intensity of an event we will refer to the number of oscillations, a parameter which is directly proportional to the amplitude. An event will be more intense as the number of oscillations is high.

There are two approaches to counting acoustic emissions: "ring counting" and "event counting":

- “Ring-Down Counting” consists of counting how many times the signal exceeds the threshold value;

- “Event counting”, for its part, analyzes a single event by taking into account all the oscillations caused by a given microcrack.

Regardless of the type of approach, the first crossing that exceeds the threshold value is the one that advances the count.

As an example, the summarizes a measurement campaign lasting 30 days characterized by 148 AE events having exceeded a given threshold value (A). The increasing trend in the cumulative number of EA events (B) is symptomatic of an ongoing irreversible cracking phenomenon. In addition to the increasing number of events, the reduction in frequencies (C) and the increase in amplitudes (D) also confirm the progressive nature of the pathology.

The present invention provides monitoring, by means of acoustic emission technology, of structures covering ground subject to consolidation with injections of cement or synthetic mixtures, including expansive resins, and/or with the installation of deep stakes.

There shows an axonometric view of a corner of a damaged generic building with grouting work in progress. This angle is the same as that of the but with the additional treatment of an injection point (H) through cyclical injection of expansive resin.

As indicated previously, during injection, once the expansion of the mixture has exhausted its soil consolidation actions (filling of voids, movement of pore water, thickening of grains, etc.), the conditions of increased confinement around the injection point are likely to exert a thrust (I) which could induce an uplift of the ground and/or the overlying structure, with a modification of the stress-strain state.

Before undergoing an uplift itself and detectable by a conventional laser or a radar instrument (i.e. greater than 1/10 mm), the structure goes through a phase where it begins to be stressed with microscopic movements, so small that they cannot be detected by a conventional laser or radar instrument (less than 1/10 mm).

During this phase, the "stress" induced on the structure by the expansion of the resin in the ground generates acoustic emissions which propagate in the material of the structure itself. Although it is a different physical quantity than uplift (EA detects ultrasonic pulses, laser or radar a length), knowing that sound pulses propagate through the structure is like saying that the The current injection cycle is about to exhaust the ground consolidation actions and is beginning to produce the first thrust effects on the overlying structure.

This information allows site operators to interrupt the current injection cycle for a given injection point, permanently or temporarily.

Indeed, when an increase in the number of acoustic events, an increase in amplitude and a corresponding reduction in frequencies occurs, the processing of the current injection point would be definitively interrupted (permanent interruption), because it is of a condition predictive of the evolution of damage.

On the other hand, if the acoustic parameters do not undergo changes predictive of an evolution of the damage, and in any case only when significant sound emissions are no longer recorded, the treatment can be resumed by more carefully measuring the quantities of the cycles of injections (temporary interruption).

The invention in question also proposes to use the same monitoring approach with the EA for the execution of consolidation interventions using piles.

There (axonometric view of a corner of a damaged generic building with pile installation work in progress) shows the same subsided angle as on the where two dark micropiles are being installed on two verticals.

Once the excavation (H) has been carried out and the current part of the foundation exposed, steel plates with slip ring (I) are bolted to the foundation. Hydraulic cylinders (J), powered by an electrical unit (K), provide the thrust energy necessary to drive the piles.

The piles are driven in portions until the desired layer is reached and/or the desired point load (L) is reached. If the structure allows it, a controlled lifting of the structure (M) can be carried out.

Once the desired layer has been reached and/or the target load value has been reached (in accordance with current technical standards), the pile is bolted to the foundation, the excess part of the pile is cut off and the excavation is backfilled.

Even in this case, already during the driving of the pile, but above all and once more resistant deep layers capable of counteracting the driving force are reached, acoustic emissions linked to the "mechanical stress" transmitted by the advancement of the pile will begin to be generated in the material of the structure above ground.

Although the thrust induced by the pile on the structure is more easily manageable than the thrust induced by the expansion of the injection mixture - since the cessation of the advancement of the hydraulic cylinder will correspond to the instantaneous cessation of the uplift effects - having warning signs of potential damage makes it possible to optimize operations on the site, reduce the risk of possible damage and increase the level of control of an uplift of the structure, if it were to be research.

Under these conditions, site operators can record precursor signals of the crossing of an overconsolidated layer, the interception of a rock or the approach of the compact layer, even before a real uplift detectable by a laser level does not occur.

Monitoring the parameters recorded by the transducers will make it possible to guide site operations, which may be temporarily interrupted at the moment when the driving of the pile corresponds to an increase in the number of acoustic emissions associated with stability or a reduction in the number of acoustic events in the unit of time, as well as stability of the amplitudes and frequencies of the event.

When such an eventuality occurs prematurely, i.e. when it is still far from the compacted layer at known depths and/or the design peak load, pile driving operations can be resumed. with increased caution and with appropriate measures to facilitate driving: use the reduced and strictly necessary value of thrust and forward speed, drive two or more piles placed in the immediate vicinity. The sinking operations only continue if the noise emissions are not significant.

On the other hand, the driving of the pile will be stopped definitively if, at the time of resumption of driving and despite the measures taken, there are indications of potential damage in progress, that is to say when there is a increase in the number of acoustic events in the unit of time, an increase in the amplitude of the event and a decrease in frequencies.

As mentioned previously, EA is implemented with CPUs capable of filtering the signals acquired by the transducers after setting an appropriate threshold value. This setting makes it possible to exclude the background "noise" linked to the environmental context in which we operate and to consider as significant for monitoring only those AE signals which exceed the pre-established threshold value.

In the case of applying EA, the initial threshold value is also set depending on the type of structure and the desired degree of monitoring sensitivity. Its value can then be calibrated during construction based on the response of the structure itself to injections. In this way, by proceeding by construction site areas homogeneous in structural and geological-geotechnical terms, site operators will be able to calibrate on an observational basis the minimum quantities capable of starting to transfer the "mechanical stress" from the ground to the structure in the case injections, as well as critical depths and limit thrusts in the case of piles.

A sufficient number of transducers suitably installed and georeferenced with respect to a local reference system, through appropriate modeling, also makes it possible to locate and map the source points and distribution of all acoustic emissions induced by the critical injections which may have cause damage (micro- or macro-fractures not perceptible to the naked eye).

At the end of the consolidation or stabilization intervention of the structure or foundations, it will therefore be possible to define in a precise and targeted manner the damaged areas which could require repair work.

The way in which a structure is damaged, and therefore how sound emissions propagate, is closely linked to its fragility (or ductility) in relation to certain constraints (compression, traction, torsion, etc.) as well as to its geometric characteristics ( shape, size, complexity), its complexity and the connections existing between the elements that compose it. Therefore, the number and positioning of transducers to be installed to carry out the control with the EA - in addition to taking into account the pathology that affects the structure - must also and above all consider the type of structure and its geometry.

In structures characterized by low rigidity (this is the case for masonry structures), any damage induced by uplift will mainly be found near the intervention zone on the ground. In contrast, in structures with greater rigidity (e.g. frame structures with reinforced concrete beams and pillars), damage will not necessarily occur close to the treated areas. This is due to the fact that elements with greater rigidity (beams, pillars, joists, etc.) can transfer the state of tension and deformation to portions of the structure further away from the intervention zone, rigidly and without being damaged.

In masonry structures, we can therefore limit ourselves to placing the transducers near the soil treatment areas, while in the case of frame structures it is good to also cover the more distant areas, but structurally connected to the intervention zone. This is in order to detect and locate possible microcracking phenomena induced by the transfer of the tension state by more rigid elements such as reinforced concrete beams and pillars.

Claims

Process for stabilizing structures, comprising the following phases
(a) application of one or more constraints induced by geotechnical works to obtain consolidation of the foundations;
b) Structural monitoring carried out during the aforementioned application phase a) and characterized by the use of acoustic emission (EA) technology capable of detecting acoustic emissions attributable to the stresses induced by the aforementioned geotechnical works.
Method according to claim 1, in which said monitoring step b) is capable of evaluating in real time one or more characteristic parameters of said acoustic emissions associated with the frequency and/or amplitude and/or the number of acoustic emissions exceeding a predetermined threshold value.
Method according to claim 1 or 2, in which said characteristic parameters are chosen from the group comprising the number of acoustic events, the frequency, the amplitude, the temporal scaling (Beta_t), the level of damage reached ( b_ value ), the level of collapse damage (b_ rupture ) and the like.
A method according to one of the preceding claims, wherein said acoustic detection means comprises transducers or similar detection devices for converting ultrasonic pulses into electrical signals using acoustic emission technology (AET) or an equivalent system.
Method according to one of the preceding claims, in which said application step a) comprises a step of consolidating the soil by means of cyclic injections of a consolidating mixture, said control step b) being adapted to detect the number of acoustic emissions attributable to the stresses induced by the expansion of said mixture once it has exhausted the consolidation actions on the ground.
Method according to claim 5, in which said consolidating mixture is chosen from expanding polyurethane resins, expanding formulations, cement-based mixtures, synthetic mixtures.
A method according to claim 5 or 6, wherein said injection consolidation step, at a given injection point, is temporarily interrupted when the injection cycle produces an increase in the number of said associated sound emissions, for a corresponding period of time to the expansion phase of the mixture, to a stability or reduction in the number of acoustic events in the unit of time, to a stability of the amplitude of the event and to a stability of the frequencies; said injection treatment being resumed when significant acoustic emissions are no longer recorded, that is to say above a predetermined threshold value.
Method according to claim 6 or 7, wherein said injection consolidation step comprises the following steps:
- creation of small diameter perforations through the foundation;
- continuation of the same perforations in the layers of soil to be treated until the desired depth;
- installation in the perforations of one or more small diameter pipes through the layers of soil to be treated to the desired depth.
Method according to claim 8, wherein said step of monitoring the acoustic parameters is carried out during said injection consolidation phase and during the pauses between one injection cycle and the next with respect to the same injection point and wherein the definitive interruption of treatment at each of the injection points occurs once the current injection cycle, in relation to a given injection point, highlights potential damage in progress or when, with reference to a cycle acoustic emissions induced by the treatment, it is recorded in a period of time corresponding to the expansion phase of the mixture
- an increase in the number of acoustic events in the unit of time;
- an increase in the amplitude of the event;
- a reduction in frequencies.
Method according to any one of claims 5 to 9, in which said injection consolidation step can occur on one or more injection points located on the same injection vertical.
Method according to one of the preceding claims, in which said application step (a) comprises the implementation of piles in the ground by driving them into more compact layers of soil, then anchoring them to the existing foundation structure, in which the acoustic emissions are at least partially generated by the "mechanical stress" transmitted to the structure by the counterthrust exerted by the piles once they have reached deeper and more resistant layers which are capable of counteracting the force driving or screwing with a reaction at least equal and opposite to the loads transferred from the part of the structure located above, said step of controlling the acoustic parameters being carried out during the operations of implementing the piles in the ground.
Method according to claim 11, in which the operations of implementing said piles in the ground are temporarily interrupted at the moment when said operations produce an increase in the number of said acoustic emissions associated with stability or a reduction in the number of acoustic events in the unit of time, stability of the amplitude of the event and stability of frequencies.
Method according to claim 12, in which said operations of implementing said piles only resume if, during the continued advancement of said pile in depth, no significant sound emissions are recorded, that is to say say above a predetermined threshold value.
Method according to one of claims 11 to 13, in which the final interruption occurs once the resumption of pile driving operations in the ground presents potential damage in progress, that is to say when There is :
i. an increase in the number of acoustic events in the time unit;
ii. an increase in the magnitude of the event;
iii. a reduction in frequencies.