METHOD FOR EARLY DETECTION OF THE RISKS OF FAILURE OF A NATURAL OR MAN-MADE STRUCTURE

Abstract

A building rests on the soil. Vertical elongation detectors are placed at the base of pillars above bearing points of the building on the soil, in particular at the corners of the building. Variations in the measurements of vertical elongation of the pillars indicate a variation in the ability of the soil to support the building. In particular, the partial or total unloading of a pillar gives rise to suspicion of a compaction of the soil under the pillar.

The present method is usable for very early detection of risk situations that might eventually compromise the safety of a structure.

Claims

1. A method for the early detection of the risks of failure of a natural or man-made structure, in particular as a result of the geological conditions prevailing beneath the structure, comprising: placing an elongation detector on the structure directly above each of several bearing points of the structure; and a change in the soil underlying the structure is diagnosed, at least in certain cases where the elongations detected indicate a change in the distribution of the vertical loads between said several bearing points.

2. The method according to claim 1, characterized in that the detectors are vertical elongation detectors.

3. The method according to claim 2, characterized in that when the structure is a building or similar, the vertical elongation detectors are placed at the base of load-bearing pillars, in particular corner pillars of the structure.

4. The method according to claim 2, characterized in that a tendency to compaction is diagnosed below a support where the measured elongation has increased.

5. The method according to claim 2, characterized in that a tendency to swelling is diagnosed below a support where the measured elongation has decreased.

6. The method according to claim 1, characterized in that in the case of a structure comprising a raft foundation, the detectors are horizontal elongation detectors that are placed on the raft foundation.

7. The method according to claim 1, characterized in that each elongation detector comprises an optical fibre and means sensitive to the weakening of a light intensity received at one end of the optical fibre with respect to the strength of a light source supplying the other end of the optical fibre.

8. The method according to claim 1, characterized in that the optical fibre is pre-tensioned so that said weakening is also modified in the case of shortening of the optical fibre.

9. The method according to claim 1, characterized in that the measurements and their date are recorded in order to obtain dated elongation measurements and a timing chart of the elongation measurements.

10. The method according to claim 1, characterized in that the dated elongation measurements are cross-checked with information on dated known events that have modified the loading of the structure above the supports equipped with elongation detectors.

11. The method according to claim 1, characterized in that the dated elongation measurements are cross-checked with dated vertical elongation measurements obtained on another structure, above supports of the latter.

12. The method according to claim 1, characterized in that the dated elongation measurements are cross-checked with dated meteorological data.

13. The method according to claim 1, characterized in that the dated elongation measurements are cross-checked with dated seismic data.

14. The method according to claim 1, characterized in that rebalancing and/or reinforcement of the substrate and/or of the soil underlying the structure is carried out when a change in the underlying soil is diagnosed.

15. The method according to claim 14, characterized in that the rebalancing or reinforcement operations are controlled towards restoring elongations to the values prior to the deterioration.

16. The method according to claim 1, characterized in that in the case of a seismic phenomenon, the elongation values before and after the phenomenon are compared in order to determine whether the structure and/or the underlying soil have been permanently affected by the seismic phenomenon.

17. The method according to claim 1, characterized in that at least one neighbouring structure is inspected when a change is detected in the soil underlying the structure equipped with the elongation detectors.

Description

[0026] Other features and advantages of the invention will become apparent from the description below, relative to examples which are in no way limitative.

[0027] In the attached figures:

[0028] FIG. 1 is a diagrammatic perspective view of a building equipped with elongation detectors according to the invention, for implementing the method according to the invention;

[0029] FIG. 2 is a timing chart of the elongation data obtained with the four detectors of the building in FIG. 1, in the cases of two events having affected the resting conditions of the building on the underlying soil;

[0030] FIG. 3 is a diagrammatic perspective view of a cylindrical tank equipped with elongation detectors according to the invention, for implementing the method according to the invention; and

[0031] FIG. 4 is a perspective view of a structure comprising a raft foundation equipped with elongation detectors according to the invention, for implementing the method according to the invention.

[0032] As these embodiments are in no way limitative, variants of the invention can in particular be considered comprising only a selection of the characteristics described hereinafter, in isolation from the other characteristics described (even if this selection is isolated within a phrase containing these other characteristics), if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention with respect to the state of the prior art. This selection comprises at least one, preferably functional, characteristic without structural details, and/or with only a part of the structural details if this part alone is sufficient to confer a technical advantage or to distinguish the invention over the state of the prior art.

[0033] In the example shown in FIG. 1, the structure is a rectangular building 1 that is located in a known manner in an underlying soil 3.

[0034] In this example, the building is a block of flats that is parallelepiped in shape with a rectangular base, the length of which is for example 20 m. In a manner that is in itself conventional, the building is structured around vertical reinforcementsor pillars4A, 4B, 4C, 4D at its corners. These pillars are quite particularly intended to transmit to the soil at least a portion of the load constituted by the weight of the building. In this conventional example, the four pillars of the building thus form, at their base, supports on the soil 3. In practice, the corner pillars 4A, 4B, 4C, 4D can be found slightly recessed inside the building and not directly visible from the outside, FIG. 1 being simplified in this respect for greater clarity.

[0035] According to the invention, a respective elongation detector 6A, 6B, 6C, 6D has been placed directly above each of these supports, along the pillars. By directly above is meant at a vertical distance from the actual support, short enough for the detector to be directly influenced by the entire load transmitted to the soil by this support. The detectors have been diagrammatically shown on the outer face of the building but mounting on an inside or side face of the pillars is also possible.

[0036] In the example shown, each detector is a vertical elongation detector.

[0037] Preferably, each detector comprises an optical fibre 8 which extends in the detection direction, here the vertical direction. The fibre is fastened to the structure (to the pillar) so as to extend and shorten in the same manner as the zone of the pillar where it is fastened. The elongation detector also comprises a light source (not shown) that injects light at one end of the optical fibre, and a light sensor (not shown) sensitive to the transmitted light, i.e. the light arriving at the other end of the optical fibre having passed through the entire length of the optical fibre. In a known manner, by comparison with a reference state of the optical fibre, corresponding for example to its state at the time of its installation, when the optical fibre undergoes stretching with respect to its reference state, the sensor detects increased weakening of the transmitted light intensity with respect to the light intensity of the source. Conversely, when the optical fibre is compressed longitudinally or is entirely or partially relaxed from its reference stretch, the sensor detects less weakening of the light intensity transmitted with respect to the light intensity of the source. Thus, the light sensor provides a measurement signal indicating the length and variations in length of the support of the optical fibre, here the vertical length of a lower zone of the pillar where the optical fibre is fastened. In order for the fibre to be reliably shortened if the support, here the pillar, is compacted, it is known to pre-tension the fibre during its fastening to the support such that in the event of compaction of the support, the fibre reacts by means of an elastic relaxation reducing its pre-tensioned state.

[0038] Each optical fibre 8 is connected to a box 7 in which is typically found both the light source and the light sensor. In this case, the fibre is folded in the middle such that the two ends thereof are adjacent, the folded middle of the fibre being found at the end of the device opposite the box. The box 7 contains a transmitter that transmits the results of the detection to a computer 11 making it possible to visualize and record the results. The mode of transmission between the boxes 7 and the computer 11 can take several forms, for example wireless transmission to a central box 12 installed in the building 1 or close by, and capable of communicating via the Internet and/or by GPRS and/or other means with the computer 11.

[0039] FIG. 2 shows an example of results obtained such that they can for example be visualized by means of the computer 11 in FIG. 1. Four timing charts can be seen, namely those of the elongations EA, EB, EC, ED read by the detectors 6A, 6B, 6C, 6D respectively, as a function of the time t.

[0040] Between the time points t1 and t2, an event takes place that greatly increases the elongation EA, more weakly decreases the elongations EB and ED, while the elongation EC is hardly affected. This means that the pillar 4A has been significantly unloaded, the pillars 4B and 4D have been further loaded and the pillar 4C has a load that is substantially unchanged. After the time point t2, the elongation states EA, EB, EC, ED remain stable at the new values.

[0041] In the absence of modifications taking place to the block of flats itself between the time points t1 and t2, it can be concluded that the soil 3 has been compressed under the pillar 4A which thus becomes unable to transmit the weight of the building to the soil as efficiently as before, and the weight of the building is partially transferred to the adjacent pillars 4B and 4D, which are thus further compressed.

[0042] According to the invention, first it is checked if these variations of the distribution of the load have damaged the building. If necessary, the building is made safe by means of temporary reinforcements, and/or the building is evacuated. Then, if the building can be repaired, or if it is not damaged, the soil 3 under the building is reinforced, for example by injecting the appropriate materials therein, in particular under the pillar 4A. Preferably, at the same time as the injection is carried out, the change of the elongations 4A, 4B, 4C and 4D is monitored with the aim of restoring the values prior to the time point t1. When this is reached, the injection is stopped. Other corrective measurements can constitute placing new piles under the building, in particular in the zone of the pillar 4A. The definitive repair of the building can then take place, for example repair of fissures, installation of definitive reinforcements etc.

[0043] In the right portion of FIG. 2 is shown an example of observations that can be made in the case of an earthquake taking place between the time points t3 and t4. The detectors preferably used according to the invention, operating by measuring the weakening of the light transmitted by an optical fibre, take account of both the vibration phenomena of the earthquake in real time and the consequences of the earthquake in the form of the elongations EA and ED which stabilize at values that are different from those before the earthquake. The process of inspection and repair of the building is then substantially the same as in the previous example.

[0044] In the example shown in FIG. 3, the structure is a tank 11 of large dimensions having a vertical axis, of the type used in oil installations. There are no structural elements where the load is concentrated. The vertical elongation detectors 16 are distributed at various points, here four points, distributed over the perimeter of the base of the side wall of the tank.

[0045] In the example shown in FIG. 4, the structure 21, shown in the diagrammatic shape of a parallelepiped like structure 1 in FIG. 1, this time comprises a raft foundation 22 forming a support base on the soil 3. In this case, horizontal elongation detectors 26 have been placed at points distributed over the perimeter of the raft foundation 22. In the example shown the detectors 26 are placed on the side surfaces of the raft foundation but installation on the upper face thereof, in particular all around the structure 21 itself, can also be envisaged.

[0046] Of course, the invention is not limited to the examples described and shown.