EP1956147B1

EP1956147B1 - Local seismic protection method for existing and/or possible construction sites destined for the foundation areas and those surrounding the building construction

Info

Publication number: EP1956147B1
Application number: EP08001690A
Authority: EP
Inventors: Marco Occhi; Andrea Occhi; Daniele Gualerzi
Original assignee: GEOSEC Srl
Current assignee: GEOSEC Srl
Priority date: 2007-02-09
Filing date: 2008-01-30
Publication date: 2012-04-18
Anticipated expiration: 2028-01-30
Also published as: ES2388154T3; ATE554235T1; EP1956147A1; ITRE20070014A1

Abstract

A method for local seismic protection of building and/or built areas and/or of foundations and building adjacent zones, consists of interventions for injecting into the ground products, also expanding ones, effective even in the presence of water and/or humidity, and directed through special injection pipes (8) to act on the portions of ground (9) that require a reduction in the potential seismic effect towards overlying structures. Such portions of ground are localized and monitored with predetermined frequency and geometries before, during and after said injection interventions through a series of seismic sources (6) (energizers) and series of receivers (4) (transducers) for geophysical instrumental measurement connected to multi-channel acquisition systems (5) (seismograph/accelerometer). The attenuation of seismic effects is controlled by an increase in the mechanical features (elastic moduli) of the treated ground, in turn influenced by the progress of the surface Vs wave speed in the ground, essential parameter for the evaluation of the potential local seismic attenuation or amplification phenomenon.

Description

This invention relates to a method for local seismic protection intended for opposing potential damages resulting from energized mechanical actions of seismic events on building and/or built areas in general, in particular, on foundations and on the zones surrounding the buildings.
German patent application n. DE 4304816 discloses a displacement tip designed as a tapered slide at the end of a pipe driven into the ground. When the pipe is withdrawn, an annular gap opens up through which a granular paste or a dry powder penetrates into the cavity produced by the withdrawal. When the pipe is advanced again, the granulate is displaced and compacted together with the surrounding subsoil; axial and torsional vibrations assist this action without disturbing the sensitive environment. The implement is pressed in by a protective and guide pipe and is repeatedly withdrawn and advanced for injecting and compacting the granulate in various working positions. The implement is set up as a pump with drive and control members. The same implement also serves as a probe so that the type and quantity of the granulate can be adapted. A group of injection rods of this type can be fed in such a way that economically optimum, reliable and careful stabilising occurs. Rods or pipes for further improvement, reinforcement or test monitoring can subsequently be inserted into the column-shaped improved areas.
This document describes an equipment to measure vibrations in static conditions.
International patent application n. WO 2004044335 describes a method in which holes (1) are drilled into the ground for the injection of highly expansive grouts (5), so that the subsoil is void filled and compacted and thus the liquefaction potential under earthquake and vibration forces are reduced.
In this patent application, a control based on distance which is performed during injection is described.
It is known that when an earthquake occurs, the accumulated elastic energy releases into the ground, partly in the form of elastic seismic waves that propagate with variable speed according to the medium they cross. In particular, during a seismic event the waves that propagate on the surface "S" are responsible for the most serious damages to buildings in general, and are those that must be taken into major consideration for local seismic problems. These effects on sites are particularly important in the vertical section of the ground (for example, within the first 30 meters from the surface level) and especially in urban areas where, during earthquakes, most damages often tend to concentrate in zones where, for example, strong structural and underground heterogeneity favour complex seismic wave interference phenomena that can locally produce considerable amplifications of the ground motion.
Considering that seismic danger is defined as the probable level of ground shaking associated with the occurrence of an earthquake, in order to meet current regulations each territory has been divided into dangerousness categories according to a procedure called Seismic macrozonation; however, we know that such division does not take into account the possible effects of amplification due to the passage of the seismic motion through the sedimentary layers closer to the surface, and therefore it may be inadequate in representing local situations that, because of particular features thereof, can show very different seismic dangerousness levels. This is the reason why it is essential to refer to the seismic microzonation of the territory wherein the dangerousness values more strictly reflect local conditions. In this case, the Local Seismic Response analysis constitutes the fundamental part of Microzonation activities: it requires a multidisciplinary approach that integrates contributions provided by seismology, geophysics, geotechnics and structural engineering.
The object of this invention is based on these assumptions.
It is known that various defence/control techniques are currently adopted in order to protect buildings in general from the seismic action, mainly applied to building structures. These interventions are planned passively taking "the ground context" at seismic dangerousness level and mainly concentrating the attention on the structure of the buildings.
Therefore, several different types of intervention on supported structures exist. The active types (more complex and expensive) exert dynamic counter force against the seismic action during the event occurrence, whereas passive control types (more recent) in some cases pursue isolation effects that envisage the interposition of disconnecting elements with strong (horizontal) deformability and strong axial (vertical) rigidity between foundations and superstructures, in an attempt to disassociate the ground motion from that of the structures above the earth, as an alternative to dissipation effects which envisage the insertion of dissipating wind braces into the building structures suitable for absorbing the seismic energy themselves.
It is also known that it is possible to oppose seismic effects also through hybrid controls, that is, combinations of active and passive control techniques; as a consequence, therefore, in certain cases it is very complex and expensive to plan and carry seismic adaptation works on existing buildings.
The method for seismic protection according to this invention aims at focussing mainly on the ground under and around the buildings, with the aim of attaining a higher level of local seismic response in that ground, by suitably modifying the chemical and physical features thereof.
Only at a later stage, after having attained a better local seismic response, it will be possible to provide the structure designers with the basic geotechnical and seismic project parameters for a suitable and more accurate intervention on the buildings, to great advantage of the safety and costs of the works.
For this purpose, we know that the propagation of surface seismic waves in the ground occurs in a heterogeneous medium according to dispersive modes, and also taking into consideration that different frequencies correspond to different phase speed; in particular, geometric dispersion, as opposed to the intrinsic dispersion of materials, depends on the geometries (thickness) of the layers crossed. In fact, in non-homogeneous or stratified ground having variable mechanical properties, heterogeneity is also reflected on the propagation of surface waves.
Different wavelengths, relating to different depths, affect materials with unequal mechanical properties and propagate according to phase speed depending on mechanical properties (elastic moduli). As a result, surface waves are those which are most reliable in providing accurate information on the mechanical features of the crossed ground because, as mentioned above, they do not propagate in fluids but only in the solid framework. For this reason, besides introducing new calculation methods, recent technical standards for seismic-proof project design in adaptation to European and world standards, have also introduced a new ground classification to define the project seismic action based on the Vs₃₀ parameter. The latter represents the average propagation speed of waves "S" within the first 30 meters of depth (under the building foundation levels) and depends on the thickness in meters and on the speed of the shear waves through the layer, nth by a total of N layers into which such depth is divided.
An increase in the Vs₃₀ measurement leads to an increase in the mechanical properties of the medium crossed with consequent increase in the rigidity thereof. Similarly, a reduction in the Vs₃₀ value would correspond to less rigidity of the medium itself.
It is also known that, in particular conditions of mechanical stress from the exterior, the more a medium is mechanically rigid, the stronger its resistance to seismic action, as far as its final rupture point, where inevitably it collapses.
Therefore, in the hypothesis of any anthropic action on the ground that will favour an increase in the "S" wave speed, called Vs, this would result in an increase in the rigidity of the medium crossed, with consequent improvement of the mechanical features of the volume of the ground concerned.
Therefore, in some cases where it may be necessary, an increase in the rigidity of the medium could result in a reduction in the potentially dangerous seismic effects on buildings.
Therefore, the object of this invention is to propose a non-invasive and effective anthropic intervention method, capable of acting directly not on the structures but on the foundation grounds of existing buildings, in building areas in general and in surrounding grounds, by injecting products, also expanding ones, such as to modify the chemical and physical features, and consequently, the mechanical properties of grounds themselves, favouring the attenuation of any seismic effects directed to the buildings in ways that are different and customised according to their context.
The problem is solved by a method according to claim 1.
The invention solves the problem by a method that varies the physical and chemical features and consequently, the mechanical features of the foundation grounds in general, which consists of targeted injections of products, also expanding ones, into the ground, effective even in the presence of water and/or humidity, performed through special injection pipes and directed to act on the portions of ground that require a reduction in the potential seismic effect towards the overlying structures, with improvement of the local seismic response.
Such portions of ground are localised and monitored with predetermined frequency and geometries before, during, and after said targeted injection interventions, through a series of seismic sources (energizers) and series of receivers (transducers) for geophysical instrumental measurement connected to multi-channel acquisition (seismographs/accelerometers) and computer electronic processing systems capable of analysing and verifying the features of the grounds themselves and of establishing the extent of the injection interventions to be performed to oppose the effects generated by potential seismic phenomena at a local level. This is in order to create uniform conditions in the same portions of ground corresponding to those present in the zones wherein local seismic phenomena are naturally attenuating in a satisfactory manner.
A primary object of the invention is to obtain attenuation of the potentially dangerous seismic effects on building grounds and on existing buildings and surrounding zones by acting directly on the ground, modifying with targeted injection of products, also expanding ones, effective even in the presence of water and/or humidity, the weight/volume correlations of the various phases: solid, liquid and gaseous, considering that these correlations may be variable and different according to the components constituting the grounds concerned, such as: peat, clay, silt, sand, gravel, rock, mixed fractions of the same or as classified by recent standards.
Another object of this method, aimed at ensuring both a satisfactory attenuation of seismic effects and effective stability over time of the interventions carried out, is to perform monitoring that also takes into account the correct distribution of the products injected, and above all, the effects they have in the ground, in order to select the same according to the most suitable features thereof, such as: density, dimensional stability level over time, iteration with humidity or water over time, shear resistance, elastic modulus, and so on, according to the specific applications that appear to be necessary in each intervention point.
For further research, it may be useful to integrate the step of injection into the ground with an electric surface or depth tomography or with punctual quantitative tests (CPT) and core sampling.
Furthermore, thanks to monitoring also during operation, it is possible to suitably modify both the injection system parameters on site, such as product temperature and correct mixing of the formulas used, and the chemical, physical and mechanical features during ground mutation.
In achieving the reduction/attenuation of the potential seismic effects in the ground and improve the local seismic response, it is advantageously and cost-effectively possible to intervene using an integrated action system, with targeted injections, and a direct control during operation, with geophysical readings, and perform the suitable changes to the initial project on the basis of data constantly measured in the total monitoring, completing and/or correcting any deficiencies in the primitive elements available.
A further object consists in the fact of using a method for measuring and controlling the injection system in the ground, not simply punctual, but based on the overall analysis and on the cross-referenced comparison of the main parameters of the ground during mutation; this is obtained with an integrated system of injection and monitoring allows managing the different intervention steps: planning, execution and final validation, by determining the distribution of precise geotechnical parameters underground and the variation thereof over time; the geophysical monitoring adopted can attain different levels of graphical/interpretive restitution even at a three dimensional (3D) level and allows measuring the conditions of the ground in question, the effects induced by the injections on the same and the consequent attenuation of seismic waves, even under the imprint of the buildings, without having to perform excavation or demolition works for traditional inspection and diagnostic purposes.
In the substance, in attenuating local seismic effects in the vicinity of buildings, by intervening directly on the ground by the method of this invention, it is possible to obtain also a considerable optimisation of costs and final benefits, advantageously defining an accurate seismic microzonation of that treated ground, modifying suitably and as needed the relative local seismic response with the achievement of the following main advantages:

reduction of any structural adaptation and improvement of buildings;
actual increase of seismic safety according to the relative local seismic response and consequent limitation of damages provided by potential earthquakes to the structures;
targeted and localised definition of ground volumes whereon it is necessary to intervene.

Furthermore, monitoring of the effects encountered on ground volume during operation also provides the following further advantages:

targeted definition of the required quantities and features of the products, also expanding ones, to be injected;
optimisation of intervention times.

The invention is described in detail according to a non-limiting embodiment with reference to the annexed drawing, wherein:

the figure shows the injection-monitoring system according to the invention, applied on a typical ground in the vicinity of a building.

With reference to the figure and to the exemplifying embodiment of the invention to a building F with foundations (3), set on a ground, which over a compact substratum (1), has ground features (2) (layer 1, layer 2) favourable for amplification of the potential seismic phenomena effects towards the same building unlike the deeper layers, the object is to monitor the behaviour of the ground in question before, during and after the injection interventions, and it is achieved by arranging into the same ground, on the surface with seismic arrays or in depth through vertical probing holes (not shown), at least one series of source transmitter elements (6) (energizers) of simulated elastic waves, and at least one aligned series of receivers (4) (transducers) which, after the controlled generation of simulated seismic waves in a predetermined ground point, by means of explosive charges, seismic cannons, pounding hammer or the like, receive the arrival thereof in other predetermined geometric points.
Energizers and transducers are connected to at least one multi-channel data acquisition system (5) (seismograph/accelerometer) that detects the data measured so as to allow at least one electronic processor (PC, 7) to trace ground models characterised by a different propagation/acceleration speed of the elastic waves, to determine the geometries and the spatial distribution thereof, to accurately obtain all the important mechanical parameters that characterise the medium crossed. The number of measurements of the transmitter and receiver elements (4) is increasingly higher according to the necessary level of precision to be achieved. The various combinations of measurements performed, as well as the geometrical arrangement of the monitoring elements are then selected so as to ensure specific coverage of the ground volume in question and of the resting structure. The operating measurement techniques can be different according to the level of precision required; in fact, it is possible to operate both at natural ground level, by arranging receivers and transmitters on predetermined lines and distances, and by using one or more drilled holes wherein both receivers and transmitters are inserted.
By processing the data acquired by PC and dedicated software, and a graphical reconstruction is executed that allows performing controlled and targeted injections of the required products, in the specifically determined proportions and combinations. The electronic PC calculator(s) can, without distinction, be set up directly on site or in separate locations and connected over a network, for example via the Internet.
The injection systems (11) and the data acquisition and processing units can be positioned on the ground or on self-moving means. Numeral (8) indicates examples of targeted positioning of injection pipes for the products, also expanding ones, to be injected, numeral (9) the zone being reclaimed, numeral (10) an injection terminal connected to a mobile injection unit, not illustrated.
The operating procedure of this method is substantially articulated in the following main operating steps:

a) Arrangement of at least one series of receivers (4) anchored to the virgin ground and/or to the structure to be examined and connected to at least one multi-channel data acquisition unit (5) (seismograph/accelerometer) and at least one electronic processor (PC 7), located on site or in a separate location, with connection over a network.
b) Arrangement of one or more energizing sources (6) of elastic waves in the ground.
c) Energizing of the ground by means of explosive charges or pounding hammers or equivalent and preliminary measurement of the simulated seismic wave propagation speed values in the medium crossed.
d) Computer processing with dedicated software of the measured data and consequent graphic representation (mapping) even in multiple dimensions of the features found in the surveyed ground (Pre-intervention Local Seismic Response) that allows setting the first level of targeted injection project; more specifically: possible geometry of the injection interventions, number and horizontal and vertical levels of the injection points, type and features of the product or products to be injected.
e) Drilling of holes in the ground, intended to attain the lithological volumes that require an improvement of the local seismic response also according to the required level of attenuation of the mechanical effects of seism on the building.
f) Insertion of injection pipes (8) into the above holes, preferably but not limitedly provided with static mixers, and execution of the targeted injection into the ground according to sequences established on the basis of the data monitored and processed by electronic calculator (PC, 7); the injection products, also expanding ones, by way of a non-exhaustive example being bi-component polyurethane foams consisting of dedicated chemical formulas or others, either with open cells or closed cells for the prevalently mechanical actions, and preferably natural or synthetic zeolites, molecular sieves or alternatively, silica gel and the like, for "paralysing" actions of the volume of ground treated, in order to reduce the effects of swelling and sagging of the treated lithology, and to ensure an increase in the duration of the mechanical compacting benefits over time, thanks to the hydrophobic action of capture of interstitial water molecules that may be present in the ground, or alternatively, to crystallize the bonds thereof with the ground itself.
Said "paralysing" chemical mixtures can be introduced even on multiple injection levels, in holes drilled in the ground both vertically and inclined, and at any distance between two adjacent ones, in a single solution or separately for each component thereof, either with compressed air or in liquid form by slow or pressurised permeation, using injection systems provided or not provided with terminal nozzles to control the flow direction.
g) In the case of medium-high water saturation in the underground being treated, where deemed necessary, it is possible to activate also an effective draining effect to favour at least a partial expulsion thereof, thus preventing it from being accidentally confined or concentrated subsequent to the injections in other portions of surrounding ground. Such actions can be developed optionally using special pipes inserted into injection channels not yet used and suitably positioned according to the images obtained from the ground readings.
h) During the following targeted injections of products also expanding ones, effective even in the presence of water and/or humidity, and directed at acting on the identified portions of ground (2) that require a reduction of the potential seismic effect towards the overlying structures, the monitoring system continues to measure, according to timed frequency and even on possible different installation geometries, the variations of the geophysical parameters on the ground portion concerned, allowing continuous and direct comparison on site with the previous measurements acquired.
i) The acquired data are then inverted/modelled/processed by the electronic PC which, by means of dedicated software comprising simulator algorithms of the variable speed and/or acceleration features for mathematical system analysis, determines and directly on site arranges graphical interpretive restitutions also on multiple dimensions up to 3D level, of the ground volumes being treated, according to the geophysical features thereof at that moment.
l) Based on the comparisons between the measurements carried out at different and sequential times, it is possible to correct and/or modify the project injection parameters during operation, comparing the latest acquired data and intervening with additional and more accurately targeted injections, acting on the physical mechanical parameters of the injection systems, such as: injection levels, temperatures, pressures, amounts of products injected, types of injection products, degree of any mixing, density and so on, until the required local seismic response level is achieved.

The injection/monitoring system according to the invention can optionally be integrated, besides as already mentioned above with electric tomography quality surveys, also with traditional punctual quantitative tests without departing from the scope and object thereof.
In the injection steps specifically regarding the interface: foundation ground, and volumes underneath the foundation structure and the perimeter thereof, it is necessary to integrate above ground monitoring, preferably with one or more precision motion sensors suitably fixed to both the ground and the building structure (vertical and horizontal) also in order to anticipate and consequently avoid possible damages to the structures during the injections of expanding resins. In the substance, in order to work close to buildings, the method is carried out safely by previously positioning a series of further motion sensors x, y, z on the ground and on the structure concerned. Said motion sensors, different from the previous ones for ground monitoring, are arranged in relation to each other to form a suitable geometrical grid mesh and connected via cable or wireless with PC processors that process the acquired data in real time and return movement, rotation and inclination values consequent to the anthropic actions on the ground to the display and as a whole.
While this invention has been described and illustrated according to embodiments thereof, provided by way of a non-limiting example only, it will be evident to those skilled in the art that it is possible to make changes to the operating steps, measurements, data acquisition and processing and targeted injection interventions in order to modify the physical and chemical features of the grounds in order to attenuate the potentially dangerous seismic effects, without departing from the scope and object of the appended claims.

Claims

A method for local seismic protection of building and/or built areas directed at foundation grounds and/or surrounding ground of said buildings and/or built areas consisting of integrated and/or simultaneous injections of chemical products, also expanding ones, into the ground, characterised in comprising the following steps:
i. arranging a plurality of receivers (4) on said foundation grounds and/or surrounding ground or on the structure to be examined, said receivers being connected to an electronic processor (PC 7);

ii. arranging one or more seismic sources (6) on the ground;

iii. performing a controlled generation of seismic waves by means of said seismic sources (6);

iv. measuring the speed values of the simulated seismic waves and other geophysical parameters indicative of the seismic response of the foundation ground and/or of the surrounding ground to said seismic waves generation;

v. computer processing said measured geophysical parameters setting a first injection project;

vi. injecting into the ground said chemical expanding products, which are polyurethane resins, according to said first injection project;

vii. continuously measuring said geophysical parameters during said injection of said expanding chemical products;
processing and comparing said measured geophysical parameters at different and sequential times to correct and/or modify said first injection project during injection to obtain an acceptable local seismic response.
Method according to claim 1, characterised in that said first step of injections acts to reduce the plastic tendency of the treated lithology towards swelling and sagging effects, according to the hydrophobic action of capture of interstitial water molecules in contact, according to the generation of new and stronger bonds aimed at increasing the mechanical benefits of compacting and rigidity over time resulting from subsequent injections of expanding chemical mixtures.
Method according to claims 1 to 2, characterised in that the definition of the position of injection points, the amount of chemical mixtures or products, and the reaction features of such products, are determined and modified on the basis of the effects identified during operation in the ground volumes before and during the targeted injections, and in that the conditions of the treated volumes are sequentially compared with the conditions prior to the latest injection performed, until a safer local seismic response level is achieved, also obtained through comparison with surrounding ground volumes having suitable seismic parameters.
Method according to claims 1 to 3, characterised in that it uses measurements and controls of the targeted injections in the ground based on the overall analysis and on the comparison of the main ground parameters during the dynamic phase of re-equilibration by an integrated system of geophysical monitoring and injection that manages the various intervention steps
Method according to claims 1 to 4, characterised in that it comprises a monitoring step to control the effects obtained during "above ground" to "underground" operations in the ground volumes treated with injections of chemical mixtures by means of tomographic geophysical scans up to the 3D level.
Method according to claims 1 to 5, characterised in that said chemical expanding products are introduced into the ground either with compressed air or in liquid form for slow or pressurized permeation using injection systems.
Method according to claims 1 to 6, characterised in that said chemical expanding products are introduced into the ground in a single solution or separately for each component thereof.
Method according to claims 1 to 7, characterised in that said chemical expanding products for the preliminary stage are composed according to the lithological context of synthetic and/or natural zeolites, molecular sieves in general, or alternatively silica gel.
Method according to claims 1 to 8, characterised in that said chemical expanding products are introduced into the ground also at multiple injection levels.
Method for local seismic protection of building and/or built areas directed at foundation grounds and/or at those surrounding the buildings according to claims 1 to 9, characterised in that said chemical expanding products_are injected simultaneously through holes drilled in the ground which can be both vertical or inclined and at any distance between two adjacent ones.
Method according to the previous claims, characterised in that said targeted injection interventions are based on corrections and/or modifications of the first project injection parameters during operation and are obtained and performed on the basis of the comparisons between the measurements carried out at different and sequential times, based on the evaluations of the latest measurements and based on interventions performed on the physical mechanical parameters of the injection systems, such as: injection levels, temperatures, pressures, times, amounts of injected products, types of injection products, degree of any mixing, density, viscosity.
Method according to the previous claims, characterised in that the monitoring, carried out with predetermined frequencies and geometries before, during and after said targeted injection interventions comprises energizers (6) simulators of seismic waves, and at least one series of geophysical instrument measurement receivers (4), positioned on the ground or inserted in probing holes and/or fixed to the structure to be protected and connected to at least one multi-channel component (5) for acquiring series of measurements; said multi-channel unit (accelerometer/seismograph) being connected to at least one electronic processor (PC-7), provided with dedicated software comprising algorithms simulators of the seismic features of the grounds being treated, directly necessary for determining the multidimensional graphical configurations thereof.
Method according to the previous claims, characterised in that for interventions to be carried out in the vicinity of buildings, the method is safely carried out by previously positioning a series of further motion sensors x, y, z on the ground and on the concerned structure; said sensors, different from the previous ones for ground monitoring, are connected to each other to form a suitable geometrical grid mesh and connected over a network via cable or wireless to PC processors capable of returning the set of measured data in real time.