Such apparatuses are known to find application in stability diagnosis, for instance on natural and artificial slopes and excavations, in dam and tunnel monitoring, in the civil engineering works foundation soil investigation, as well as in other fields. These apparatuses are typically introduced in the soil to be monitored, i. e. in specially drilled geognostic boreholes, and secured to the soil, rock or structure to be monitored by grouting or the like. This locking method has the drawback of often providing a poor adhesion of the apparatus to the borehole walls, an imperfect water tightness in groundwater separation, particularly for deep installations, and finally rather long execution times.

A further shortcoming of prior art apparatuses is that they are constructed in such a manner as to include a single sensor for a single parameter, whereby all-parameter monitoring may be only achieved by using several single parameter dedicated apparatuses. Thus, a set of signals from different sensors are obtained, which are not strictly related to each other, and whose signal format structure may cause compatibility problems for transmission by common transmission means. Therefore, dedicated

interfaces must be provided between individual apparatuses and transmission units and between individual apparatuses and processor units.

Thus, the object of this invention is to overcome the above drawbacks and provide, by simple and inexpensive means, an apparatus as described hereinbefore, which affords a considerable functional improvement as compared with prior art apparatuses, allows easier and accurate monitoring of the relevant soil or structure, while allowing to collect a plurality of different data by using a single apparatus and by drilling a single borehole, unlike prior art. A further object is to provide an apparatus that is easily adaptable to different monitoring situations, particularly to landslide soil displacements, while providing a more accurate data detection and collection. It is further desirable to allow the apparatus to be perfectly integrated with the geognostic borehole wall in a simple, fast and possibly reversible manner, to allow an easy removal of the probe, and repositioning and/or reuse thereof in another borehole.

The invention fulfils the above objects by providing an apparatus as described hereinbefore, which comprises at least two, preferably a plurality of rigid enclosures, each for housing at least one type of sensor, which rigid enclosures are connected by non-rigid connections, allowing them to have at least one degree of freedom of motion relative to each other.

The enclosures may be arranged in succession one after the other along a predetermined line or a predetermined axis, at least one non-rigid connection

member being interposed between two immediately adjacent enclosures. Thanks to this arrangement, the apparatus may be even adapted to a borehole having an imperfect straightness, caused by landslide displacements occurring when the borehole has been already drilled and the apparatus has been introduced therein.

The enclosures and/or the non-rigid connecting members may be of the closed type, and be impervious at least to external liquids, to keep any infiltration from damaging the equipment contained in each enclosure and/or the connection members.

The enclosures may be arranged alternate with the connection members.

Advantageously, the connection members between the enclosures may be elastic, to restore the initial mutual enclosure positioning condition, with reference to the at least one degree of freedom of motion or to all the degrees of freedom of motion of the enclosures relative to each other.

The connection members may allow a relative axial displacement of two adjacent enclosures toward and/or away from each other.

Alternatively thereto or in combination thereof, these connection members may allow a relative angular displacement between two adjacent enclosures.

The non-rigid connection members may include elastic means for restoring the initial idle or unstressed condition of the apparatus.

According to a preferred embodiment of the invention, the enclosures may have a tubular, preferably cylindrical shape and particularly have

equal diameters, and equal or different axial extensions.

The connection members may also have a substantially tubular shape, and be made, for instance, of steel braided rubber, or extend along tubular, preferably cylindrical surfaces, and particularly have substantially the same diameter as the tubular enclosures.

The connection members may be stabilized in the pre-holes or in monitoring pipes by annular centralizers secured between the flexible connecting joints and the enclosures, whose outside diameter is equal to the diameter of the pre-hole or to the inside diameter of the monitoring pipe.

The connection members may be helical springs, preferably made of steel, whose elastic properties are adapted to the characteristics of the whole apparatus, which are arranged coaxially to the tubular enclosures.

Each helical spring may be fastened at its two opposite ends to the corresponding ends of two adjacent enclosures.

Each helical spring may be outwardly hermetically covered by at least one flexible sleeve or cuff, particularly bellows-shaped, preferably made of plastics, rubber or the like and having an appropriate thickness, possibly reinforced with a steel braid, to prevent infiltrations, e. g. of mud or moisture, in the connection member.

At least two adjacent enclosures may be connected by a tie having such a length as to maintain the helical spring in an intermediate pressure loading condition. This arrangement prevents

any excessive extension of the spring, which might involve the risk of distortion thereof, and possibly provides an automatic elastic adaptation, within certain limits, of the apparatus'length to any increased length of the borehole, caused by soil or structure displacements.

At least one of the ends of the tie may be dynamically connected to a sensor which detects the relative position of the two enclosures, and is accommodated in one of the two enclosures. The opposite end is fixedly anchored to the adjacent enclosure.

This sensor may be a permanent magnet which is capable of sliding in both directions toward the tie, which magnet cooperates with an induction sensor for determining magnet displacement by magnetic induction. The sensor may be equipped with elastic means for pulling the magnet toward compression of the immediately adjacent connecting spring.

The tie may be of such a length as to keep the magnet of the associated enclosure axial position sensor in an intermediate signaling position when the apparatus is in an idle or unstressed position, so as to be able to measure any relative movement of the two enclosures, toward and away from each other.

The tie may be a wire or a rod, particularly sheathed, and extend substantially along the central axis of the apparatus.

Eventually, the enclosures, the connection members and the connecting ties between the enclosures may form an assembly of members to transfer soil displacement stresses to position, pressure, inclination and acceleration sensors or

transducers or on further sensors for monitoring other particular parameters.

The enclosures may have closing members at their ends, which may be inserted therein and secured thereto. These members act as terminals allowing attachment and/or passage of connecting springs, sealing sleeves, ties and one or more position sensors.

Alternatively, at each opposite end of each enclosure, a substantially tubular rigid terminal may be provided for coupling each end of the enclosure to the corresponding ends of the two immediately adjacent springs. The interposition of this rigid terminal provides advantages as detailed below.

In accordance with an advantageous improvement, at least some of the connection members may have axial extension limiting means, for preventing the spring extension range from being exceeded, and the spring from being consequently permanently deformed or broken. As mentioned above, this function is at least partly accomplished by the above tie, but this invention has the object of providing means to withstand even considerable axial stresses caused by particularly wide landslide displacements.

These extension stop means may be one or more inextensible elongate members, each extending inside r, or outside each spring, parallel to the axis thereof.

One of the opposite ends of an inextensible member may have a widened shape and be slideably accommodated in a chamber which has two opposite extension and compression stop abutments. This chamber may be provided within the closing member at the end of an adjacent enclosure or within the

associated substantially tubular rigid coupling terminal, whereas the opposite end of the inextensible member may be secured at the closing member or at the rigid member for coupling the spring to the other enclosure.

Nevertheless, according to a preferred embodiment of the invention, to be further detailed in the description of the drawings, each of the opposite ends of each inextensible member may have a widened shape and be slideably accommodated inside a respective chamber having two opposite extension and compression stop abutments, each of said chambers being provided within each opposite closing member at each end of each enclosure or within the substantially tubular rigid coupling terminals.

Thanks to this arrangement, both ends of each inextensible member may slide within their respective chambers, thereby distributing the retaining action to both ends of the spring and preventing an excessive displacement of said ends. Moreover, thanks to the above arrangements, each inextensible member may also possibly accomplish the function of an axial compression stop means for the spring. In fact, as soon as an excessive compression of the spring is attempted, the widened end of the inextensible member may abut to stop the compression motion and keep the spring from being actually excessively compressed and the whole apparatus from being damaged. In this case, the inextensible members may be advantageously flexible but relatively rigid, and be thus prevented from sensibly bowing outwardly and/or inwardly.

Typically, each of these inextensible stop members may be a wire or a rod, preferably made of

harmonic steel. The inextensible members may be arranged along the outer circumference of the spring.

When the apparatus is in the idle or unstressed condition, the widened ends of each inextensible member may be in a spring compression stop abutment position, so that a longer stroke is available for spring extension.

Thanks to the provision of the inextensible members, the apparatus may be kept from being broken, e. g. due to landslide displacements. It should be noted that, when the apparatus is broken, the portion thereof that remains in the borehole would be hardly recoverable, and this would have a considerable impact on costs, due to the high cost of the sensors contained in the enclosures.

According to a further important improvement, means may be provided for removably securing at least a portion of the apparatus to the soil, rock or structure to be monitored, whereby grouting may be avoided, as well as the consequent drawbacks described above.

These securing means may be one or more anchor sections, which are arranged in a predetermined order relative to the enclosures and to the connecting springs.

Advantageously, these anchor sections may be of the closed type and be impervious to at least external liquids.

The locking action may be obtained by radial expansion of the anchor sections within the hole in which the apparatus is housed.

In accordance with a preferred embodiment, to be further detailed in the description of the

drawings, one locking section may be provided respectively immediately upstream and downstream from each enclosure. Therefore, each of these sections is interposed between an end of the enclosure and the substantially tubular rigid terminal for connection to the immediately adjacent spring.

Each locking section may have a substantially tubular cylindrical shape, with substantially the same outside diameter as the enclosures, and be formed by an inner cylindrical wall and an outer cylindrical wall which are arranged coaxially and define a space therebetween. At least one of the two walls, preferably the outer wall, may be made of an extensible or expansible material, such as rubber or the like.

The locking action may be achieved by an outward radial expansion of the outer wall of each anchor section, which is obtained by introducing a pressurized fluid, particularly air, water or oil, in the empty space between the two walls of the section.

At least one conduit, particularly a single continuous conduit may be provided for feeding pressurized fluid to the anchor sections, which is connected at its outside end to a pressurized fluid source, and extends within each anchor section, parallel to the axis thereof. This conduit may have one or more radial apertures, which communicate with the empty space between the two walls.

In accordance with a preferred embodiment, the feeding conduit may be formed by perforating the thickness of the inner non expandable tubular wall of each anchor section.

Level with each enclosure, this feeding conduit may extend therein, parallel to the axis thereof, or be obtained by perforation of the thickness of the enclosure wall.

Level with the helical connecting springs, the conduit may be formed by a portion of flexible tube, particularly spiraled with a smaller radius than the springs themselves, to be able to accommodate spring deformations with no possible interference therewith.

Therefore, the anchor members are connected in series by a single feeding conduit.

One or more enclosures may contain, particularly in an intermediate position of their axial extension, at least one member for carrying the monitoring sensor unit, which is composed of one or more sensors.

In at least some of the enclosures, inclination sensors may be provided for inclinometric measurements and/or displacement transducers and/or seismic sensors and/or temperature sensors, and/or pressure or piezometric level sensors, and/or electric potential meters and/or any other sensor required for monitoring particular parameters, for instance soil radioactivity.

An electronic card may be provided in at least one enclosure, for collecting and/or locally processing the data provided by the sensors of the corresponding enclosure.

A multicore cable may be further provided for transmitting the data collected by sensors, which extends from the last enclosure to the first enclosure of the succession of enclosures, and is

successively led outside through a liquid-tight passage.

Advantageously, level with the helical connecting springs this multicore transmission cable may be spiraled with a smaller radius than the springs, to ensure a perfect fit thereof with no risk of pinching.

According to an improvement, the spring winding may contain at least one element which extends axially from one end to the other of the spring, which element is made of an elastically deformable material, to be axially compressible/extensible and deformable. At least one helical groove may be provided on the outer surface of this element, for accommodating the pressurized fluid feeding conduit and/or the multicore transmission cable. This advantageously allows an orderly arrangement of the multicore cable and the feeding conduit level with the springs, thereby avoiding any interference therebetween and/or between spring turns.

The multicore transmission cable may be discontinuous and connect the cards for collecting the data provided by the sensors associated to the enclosures. To this end, these data collection cards may have inputs and outputs for the transmission line, and a receive and transmit section based on multichannel or multitasking protocols or transmission buses. All these arrangements advantageously allow the system to provide a high electronic modularity, thanks to the fact that a variable number of cards may be provided and connected"in series", as a function of the number of enclosures of the system.

The temperature sensor and/or the pressure sensor may communicate with the outside of their respective enclosures. To this end, the sensitive portion of these sensors may be housed or communicate with an outer side recess or undercut of the enclosure, while being hermetically isolated from the inside of the enclosure.

The peripheral wall of the enclosure may have an outer wall with microslots at the recess for communication between the sensors and the outside.

Particularly, the recess used by temperature and/or pressure sensors to communicate with the outside may be filled with a porous material.

A local data collection control unit may be advantageously provided, which is connected to the transmission cable and transmit controls to the data collection cards and/or the sensors, e. g. to reset a sensor, or to toggle a sensor on and off whenever data is to be detected at given time intervals.

The unit, which may be separate or integrated in a first enclosure, may further have means for radio transmission/reception of controls and data to/from a central supervision location.

Finally, the local unit may be programmable relative to the functions to be accomplished, such as sensor actuating and/or reading times, alarm thresholds or the like.

The advantages of this invention are self- evident from the above description and consist in that it allows simultaneous multiparameter monitoring, by using a single apparatus in a single borehole. The particular modular design of the apparatus allows to perform differential detections

of the main physical and mechanical parameters of the soil and structures in three dimensions (angular deviation on the azimuthal plane and extension or compression on the zenithal plane), of inclination (inclinometric parameters), and extension (extensometric parameters), piezometric, acceleration (accelerometric parameters), seismic, temperature and spontaneous potential detections, all at the same time and in a single borehole, obviously as a function of the equipment contained in the apparatus.

Prior art monitoring apparatus do not allow to perform simultaneous inclinometric, extensometric, piezometric detections (in the same borehole).

Simultaneous and concurrent detection of these parameters is particularly convenient in stability diagnosis on natural and artificial slopes and excavations, in dam and tunnel monitoring, in the analysis of civil engineering works foundation soils.

The special flexible and extensible/compressible spring-like joint allows the enclosures to fit the features of the hole, while maintaining the azimuthal directionality with respect to a preset external reference system. The apparatus further allows automatic and continuous remote detection of all the above parameters by using a single control unit. The local detection unit allows continuous detection of all parameters with a single control unit, which is preferably installed at the top of the borehole. This allows to set alarm thresholds, transmit information in real time to control locations and request civil protection interventions. The monitoring chain formed by the succession of enclosures and elastic joints is highly adaptable to the deformations caused by soil

or structure displacements. The particular design of the enclosure and elastic joint assembly also provides a high adaptability to any subsoil deformation (landslide displacements), as well as a high protection of the sensors and electronic components installed therein, while ensuring an optimized soil-sensor coupling and a long life (for instance as compared with prior art inclinometer tubes). Another considerable advantage is the possibility to restore and use highly deviated boreholes, which are no longer suitable for measurements by prior art equipment. The maintenance of the so-called azimuthal direction and the high flexibility provided by the particular joint that connects sensor enclosures allow the apparatus to be free from prior art mechanical references (guides and inclinometer tubes). This allows to restore and measure damaged conventional inclinometer tubes which cannot be read by prior art inclinometer apparatuses.

The device of the invention provides a very high space resolution of measurements. In fact, enclosures may have a very small axial size, particularly 20 centimeters, and allow a considerable spatial resolution improvement for the analysis of localized discontinuities, as compared with prior art stationary inclinometer apparatuses (In-place Inclinometers). The modular design of enclosures and connecting joints, the capability of monitoring within a single borehole and of continuing detections even when the monitoring chain is highly deformed allow to considerably reduce construction, installation and monitoring costs. The particular radial expansion system for securing the apparatus to

its geognostic borehole adds effectiveness to the anchorage and to groundwater level separation (in case of geologically existing groundwaters) with lower execution times. The anchor sections provide a perfect attachment of the apparatus to the soil, rocks or structure to be monitored, even when groundwater is present, and prevent it from sliding and/or moving relative to the soil. Moreover, when needed, fluid may be removed from anchor sections for probe recovery and/or repositioning. Finally, the inextensible members provide a high tensile strength of the spring connecting member, and keep it from being permanently deformed and/or broken.

Further characteristics and improvements will form the subject of the dependent claims.

The characteristics of the invention and the advantages derived therefrom will be more apparent from the following detailed description of the annexed drawings, in which: - Fig. 1 is a schematic sectional view of a first embodiment of the inventive apparatus, when installed in the soil.

Fig. 2 shows the behavior of the apparatus of Fig. 1 after a landslide displacement.

- Figs. 3A and 3B are sectional views of a first preferred embodiment of a sensor enclosure and a connection member.

Fig. 4 is a sectional view as taken across line A-A'of fig. 3.

Fig. 5 is a partly exposed perspective view of a portion of a second embodiment of the apparatus according to the invention.

FIG. 6A is a side view of the portion of the apparatus of FIG. 5.

Fig. 6B is an enlarged view of the inclinometer/extensometer joint of Fig. 6A.

Fig. 6C is a view of Figure 6A with the apparatus introduced in a hole drilled in the soil and with hydraulic packers dilated for securing the apparatus in said hole.

Fig. 7 is a sectional view as taken across line B-B'of fig. 6.

- Figs. 8A to 8E are longitudinal axial sectional views of a portion of the apparatus of Fig.

5, with the locking sections in an unexpanded condition.

Fig. 9 is a sectional view, as taken across a diametrical plane, of a third embodiment of an enclosure element of the inventive apparatus.

- Fig. 10 is a sectional view, as taken across a diametrical plane, of a third embodiment of a joint according to the invention, whose ends are fastened to the ends of successive enclosures.

- Figs. 11 to 13 show in greater detail the embodiment of the previous Figures 9 and 10.

Referring to Fig. 1, the apparatus of the invention, regardless of the embodiments being used, is introduced in a borehole 1 which extends through the thickness of the soil 3 to be monitored until it reaches a stable substrate 4, and somewhat deeper therein. Landslide displacements are known to be typically caused by the sliding motion of a mass 3 over a stable substrate 4. In certain particular instances, the apparatus may have a smaller axial extension and not reach a stable substrate 4, e. g.

when a surface layer of soil 3 is only to be monitored. In the particular case of the embodiment that is shown in Fig. 1, the apparatus is secured to the soil by appropriate grout and/or resin injections 2, to perfectly accommodate any displacement.

Nevertheless, as previously mentioned and better explained hereafter, this invention proposes a second embodiment of the apparatus, having locking means alternative to grouting, which obviate the drawbacks associated to the latter. At its outside end, the apparatus is secured to the surface of the soil 3 by an anchor plate 5.

The apparatus is composed of a succession of tubular enclosures 6 or container modules, alternated with connection joints, formed by springs 7. Hence, these joints are flexible, extensible and compressible and allow the individual enclosures 6 to perform relative motions, and particularly allow them to move away and toward each other and to angularly offset or displace one enclosure 6 relative to another, to fit any change of the borehole 1 caused to translational soil displacements, as shown by the arrows of Fig. 2. The amount of displacement of soil 3 may vary from one layer to the other, and the apparatus can be axially"deformed"in different manners, depending on such amounts. As is better explained hereafter, the connection between enclosures 6 provides a modular system, whose length may be adapted to different needs, by simply assembling an appropriate number of enclosures 6 and springs 7.

Referring now to Fig. 3, tubular enclosures 6 may have varying diameters and lengths, depending on

the sensor/s to be housed therein, on the diameter and depth of the hole 1 and on the purposes of the geognostic survey. These enclosures may be made either of metal (such as stainless steel, aluminum, light metals) or plastic and synthetic materials (PVC, nylon, ABS, reinforced plastics, polycarbonates, or the like). Each enclosure 6 has at both ends a member 8, 8'for sealably closing the enclosure 6 and connecting it to the spring 7. The members 8, 8'are introduced in the enclosure from opposite ends, by forming a male/female coupling, and are fastened by peripheral locking screws 9. A rubber O-ring may be further provided. Each closing member 8, 8'has an annular groove 10, having a given axial extension, for accommodating one end of the spring 7, which extends from a member 8 to a member 8' immediately adjacent thereto and forms the connection between two adjacent enclosures 6. The helical springs 7 are preferably made of steel, and their elastic properties are suitable to the characteristics of each enclosure 6 and of the whole modular monitoring apparatus. Each spring is externally protected by a bellows 11, preferably made of rubber, whose opposite ends lie over the outer surface of the member 8, 8'on a peripheral flaring portion 30. This ensures the outward tightness, particularly liquid-tightness, of the whole apparatus, which is hermetically sealed all along its extension, except one or more very small portions, as described in greater detail below.

Each tubular enclosure 6 contains a position transducer 12, which may be kept in its axially central position on the closing member 8, by gluing

or the like. This transducer 12 may be, for example, a permanent magnet which is capable of sliding in both directions, and which cooperates with an induction sensor for determining magnet displacement by magnetic induction. The magnet is subjected to the action of an elastic means which stably keeps it in the starting end-of-stroke position and restores such position upon return or cessation of the displacement stress. By way of example, the miniature LVDT straight position transducer, sold by RS, may be used. The purpose of this transducer 12 is to measure the amount of displacement of two adjacent enclosures 6 toward/away from each other. The mechanical connection for carrying the sensor of the position transducer 12 is obtained by a flexible wire 13, which may be made, for instance, of Invar or Kevlar, and is contained in an elastic sheath made of silicone, rubber or the like. The sheath further ensures the tightness of the system even when the bellows 11 is torn. The wire 13 is connected between the fork 112 of the transducer 12 and the axially central portion of the immediately adjacent closing member 8', by a coupling block 108', which is fastened in an axially central hole 15 of said member 8'and is held in position by inner radial projections 218, like the transducer 12. The closing member 8 also has a central axial hole 15 for the passage of the wire 13, which wire extends axially inside the helical spring 7. By gluing the transducer 12, tightness is ensured at the hole 15.

A holder 16 is provided in an intermediate portion of the enclosure 6, for supporting additional sensors 17,18 and an electronic control card 19. The

holder 16 has a circular section, whose diameter substantially corresponds to the inside diameter of the tubular enclosure 6, may be introduced in the enclosure 6 from the end that carries the member 8', to abut against an annular projection 20 provided on the inner surface of the enclosure 6. The holder 16 may be also fastened by using glue. It has a seat for fastening a tilt (inclinometer) sensor 17 and a hole 23 for the passage of a multicore cable 22, to be described in greater detail below. Regarding the tilt sensor 17, the biaxial electrolytic tilt sensor Spectron SP. An acceleration (accelerometer) sensor 18 is further fastened on the holder 16, to measure accelerometric variations induced by displacements, which sensor may be, for instance, the ADXL sensor sold by Analog Devices.

As mentioned above, the holder 16 further carries an electronic card 19, which is connected to all the sensors 12,17, 18,21 and has the function to collect and possibly locally process the data provided by the sensors 12,17, 18,21 in the enclosure 6. Each electronic card 19 further collects data from the electronic cards 19 in the previous tubular enclosures 6, down toward the substrate 4, and to transmit such data to the card 19 in immediately adjacent enclosures 6, to allow all detections to reach a local control unit 25 shared by the whole apparatus. Each electronic card 19 is also capable of receiving control and/or monitoring signals from the local unit 25 regarding one or more sensors 12,17, 18,21. Information is transferred among the various electronic cards 19 by a special multicore cable 22, which connects all the cards 19

in series, thereby forming a direct communication line. This cable 22 projects out of the two opposite ends of the enclosure 6 through two holes 31, 31' that are formed in each of the two end members 8, 8' respectively. At the inner end of each of the two holes 31, 31', a cable fastener 24, 24'is provided to ensure tightness even in case of accidental break of the protective bellows 11. At the connection between two adjacent enclosures 6, i. e. at the springs 7, the cable 22 is spiraled with a smaller radius than the springs, to accommodate the mutual displacements of the two enclosures 6, and to fit the motion of springs 7, with no risk of pinching.

Therefore, the information from all electronic cards 19 reaches the control unit 25 or local unit, which may be housed in the first enclosure 6, i. e. the one in the proximity of the surface of the soil 3, or in a separate position, outside the borehole 1. Local electronic cards 19 have both functions of monitoring the sensors 12,17, 18,21 of each enclosure 6 and of acting as a connecting unit for the data and/or control transmission line which extends all along the apparatus, and passes through all the units formed by the enclosures 6. This feature, when combined with the construction features of the enclosures and the joints provides high modularity to the apparatus. In fact, the addition or removal of a unit-formed by an enclosure with the associated sensors and the electronic data transmission and control card-from an apparatus that contains a given number of these units is very simple, both mechanically and as regards the extension of the data transmit/receive line all along the apparatus, i. e. the electronic

control and communication card of the new unit simply needs to be connected with the one of the terminal unit of the apparatus. The card may simply form the physical housing for a connector designed for extension of the data transmission line without having, as mentioned above, a section for communication control and management. This essentially depends on the selection of a transmission protocol from the group of currently available protocols.

The enclosure 6 further contains one or more pressure and/or temperature and/or moisture and/or piezometric level sensors. Suitable temperature sensors may be, for instance, those from the LM series by National Semiconductor, or from the TMP series by Analog Devices, whereas suitable piezo- resistive pressure sensors may be for instance those sold by RS. The sensors for measuring this kind of parameters need to communicate directly with the outside. To this end, the sensitive portion of these one or more sensors 21 communicates with an external side recess of the enclosure 6, while being tightly isolated from the inside of the enclosure 6. The recess 26 contains a porous material, such as monogranular sand, and has a microslotted aperture 126 for communication with the outside.

The enclosure 6 may further contain other types of sensors, for detecting additional parameters. For example, a spontaneous potential detector may be provided, which may be a voltmeter, or the like, and/or a seismic detector.

The assembly of all the above elements forms the apparatus of the invention, which allows

differential detection of the main physical and mechanical parameters of the relevant soil or structures.

The tubular enclosure 6'at the internal end of the apparatus, i. e. level with the stable substrate 4, may have an end closing member 8', acting as a sealing plug.

Referring now to Figs. 5 to 9, a second embodiment of the inventive apparatus is shown which, while providing essentially the same general functions as the first embodiment, further suggests some embodiments aimed at improving the behavior of the apparatus in certain situations. This embodiment also provides a succession of enclosures 6 and helical springs 7, whose respective construction features are essentially as described above regarding the first embodiment except that an anchor section is interposed between each opposite end of each enclosure 6 and the end of the immediately adjacent spring 7, for removably securing the device to the soil, rock or structure to be monitored. Therefore, an anchor section 32 is respectively provided immediately upstream and immediately downstream from each enclosure 6, which sections keep the enclosure 6 securely anchored to their respective portion of wall of the hole 1, whereas the portions of the apparatus which are level with the springs 7 are totally free to deform to accommodate any displacements of the soil 3. Nevertheless, while the design in the figures represents a preferred arrangement, described herein by way of example, a different arrangement and/or number of anchor sections 32 may be provided in each apparatus. Each section 32 has a substantially

cylindrical shape, having essentially the same outside diameter and axial extension as the enclosures 6. However, sections 6 with different axial extensions or differentiated axial extensions within the same apparatus, may be provided, to adapt the behavior of the latter to the special stratigraphic composition of the soil. At one end, the section 32 is directly fastened to an end of the immediately adjacent enclosure 6 whereas a rigid terminal 33 for connection to the spring 7 is interposed between the opposite end and the spring 7, to accomplish another important function to be described in detail below. The anchor section 32 provides outward hermetic tightness, at least to liquids, and the connections with the enclosures 6 and the springs 7 are themselves designed in such a manner as to ensure an overall infiltration-tightness of the apparatus. Each anchor section 32 has an inner cylindrical wall 132 made of a rigid material, and an outer cylindrical wall 232 made of an extensible and expansible material, such as rubber or the like. The two walls 132,232 are arranged coaxially and define a space therebetween wherein a pressurized fluid is fed, to cause outward radial expansion of the outer wall 232, as shown in Fig. 6C, which adheres against the inner surface of the hole 1, thereby locking the apparatus in position. One conduit 34 is provided for feeding pressurized fluid to the anchor sections 32, which conduit continuously extends within the apparatus and is connected at its outside end to a pressurized liquid source (not shown). In each anchor section 32, this conduit 34 is formed by perforating the thickness of the inner tubular inexpansible wall

232 parallel to the axis of the section 32, and has a few apertures 134 in communication with the space between the two walls 132,232 for feeding fluid therein. The tubular shape of the anchor section 32 advantageously allows the axial passage of the wire or rod 13 for actuating the position transducer 12.

A further important characteristic of this second embodiment consists in that means for stopping the axial extension/compression stroke of the springs 7 are provided, which are a plurality of inextensible wires 35, particularly made of harmonic steel, which extend outside each spring protecting bellows 11, parallel thereto. Each of the opposite ends of each wire 35 has a widened head 135, which is slidably housed in a chamber formed in the rigid terminal 33 for connection of the spring 7 to the anchor member 32. The area of the expandable packer is formed by a chamber defined by an inner tubular wall 132 and an outer tubular wall 232. This chamber is provided in the form of a sleeve, and in the exploded view of Fig. 5 it is shown beside the wall 132, while the latter is fitted on the apparatus. The two tubular walls have end threads or corrugations which form tight joints for mutual clamping by using terminal ring nuts 332, which may be tightened or press-fitted on the tubular extensible wall 232, at these threaded or corrugated ends, that are complementary to each other. Other packer constructions may be obviously provided.

As shown in Figs. 8A to 8E, the terminal 33 progressively tapers toward the spring 7 whereto it is fastened, and the diameter difference between the terminal and the inspection hole 1 forms the chamber

wherein the widened heads 135 slide. This chamber has two opposite flanges 133,233, which form two opposite end-of-stroke abutments, for the extension and the compression of the spring 7 respectively. The use of steel wires 35 is particularly advantageous due to the inextensibility of this material, which maintains a sufficient flexibility to accommodate any side deformation of the spring 7. If the spring extends abnormally, the widened heads 135 of the wires 35 abut against the wall 133 and prevent any further extension of the spring, which might cause the permanent deformation or rupture thereof.

Like in the first embodiment, a continuous multicore cable 22 is provided for series connection of the various electronic cards 19 in the enclosures 6 that contain the sensors 12,17, 18, 21. An element 36 is provided at the springs 7, to prevent any interference between the cable 22 and the feeding conduit 34 and between the latter and the spring 7, which element 36 extends axially from one end to the other of the spring 7, and is made of an elastically deformable material, to be axially compressible/extensible and deformable. This element 36 has a helical groove 135 on its outer surface for housing the feeding conduit 34 and the multicore transmission cable 22, to form a spiral winding core for both. Obviously, two separate spiraled grooves may be provided, for separately housing the conduit 34 and the cable 22.

Figs. 9 and 10 show a third variant embodiment, which simplifies the above construction, by avoiding the presence of separate anchor sections 32 and a different type of deformable elastic joint. In this

third embodiment, each enclosure 6 is formed by a tubular metal element, in the form of a sleeve or the like, which is externally fitted with anchor means 32, i. e. a tubular chamber surrounding the tubular metal element of the enclosure 6 and extending along a certain extension thereof. The anchor element 32 is made of an extensible material and the chamber thereof communicates with a conduit for feeding an expanding fluid, like water or air, which is pressure-fed through this conduit. Another rigid coaxial sleeve 106 is provided in the rigid tubular element 6, which sleeve forms at its ends an abutment step for two end closing members 206,306, each being sealably coupled with the inner surface of the tubular element of the enclosure by means of an O- ring. The end closing members 206,306 have at least one T-shaped conduit, with a radial stem opening on the peripheral outer surface of each closing member, preferably in a chamber that is formed by a groove or a peripheral recess, and with an axial stem opening on both ends of the closing member. The T-shaped conduit 406 is formed in the thickness of the closing members. In one case, and particularly for the closing member 306, the T-shaped conduit puts the expansion chamber of the anchor element 32 in communication with a tube for feeding an expansion fluid, such as pressurized water or air, which tube extends all along the enclosure until it reaches the opposite closing member 206, which has a through hole for the tube. Similarly, the two closing members 206, 306 have a through hole for the cables 22 connecting the various electronic measuring units in the enclosure 6 and possibly for the extensometer sensor

pulling wire 13. The opposite closing member 206 has a T-shaped conduit that is closed on one of the two end sides and puts the environment outside the enclosure 6 in communication with a sealed space, which is either formed as a part of the chamber defined by the enclosure 6 or in the thickness of said closing member 206, and which houses a piezometric sensor for detection of water in the soil. In this case, the opening of the axial stem of the T-shaped conduit, on one side of the closing member 206 is sealed by a plug 75, whereas the opening turned toward the inside of the enclosure 6 is sealed by the piezometric element 76, which is connected to the electronic units in the enclosure 6 by suitable cables. This operating condition of the two closing members 206,306 is achieved by providing that the closing member 206 has such a position, relative to the axial extension of the external enclosure 6 and anchor element 32 that said closing member 206 is in a portion of the enclosure 6 which is not covered by the anchor element 32.

Advantageously, the closing members 206,306 are provided in the form of pistons, with o-ring seals being provided between their outer peripheral surface and the inner surface of the enclosure 6 and/or of the tubular element 106 inside the enclosure 6, which forms the axial abutment steps for these two closing members 206,306. As shown in the previous description, the closing members 206 and 306 are formed from a single construction part, which is mounted in the proper axial position for its function and is connected to the expansion fluid feeding tubes 34 for the anchor elements 32 and to the piezometric

sensor respectively. obviously, the two closing members 206,306 are locked in an axial abutment position against their respective end step, which is formed by the sleeve 106 in the tubular enclosure 6, by fastener means, which one or more radial screws or in any other manner.

The two closing members 206,306 further have a through hole for an extensometer sensor control wire.

In this case, the wire is fastened to the closing member 206 or 306 of the enclosure 6 of an adjacent rigid module of the apparatus, extends through the elastic joint for connecting the latter to the previous rigid module, and passes into the enclosure 6 of this previous rigid module through the corresponding closing member 206 or 306 at the end of the enclosure 6 of this module, which faces toward the joint 1, in which enclosure the extensometer unit controlling cable is connected to the sensors of the extensometer unit.

In this variant, the elastic joints 7 between the various enclosure sections 6 are also constructed in a different manner, as shown in Fig. 10.

Particularly, each joint comprises a flexible sleeve 70, containing a spring 7. Two terminals 71 are fastened to the two ends of the flexible joint 70 and of the spring 7 respectively. The two terminals 71 have a tubular shape and each contain an axial slider 72, which has a radially widened portion 172, movable between two opposite radial abutments 171, which particularly have an annular shape, and are the ends of the terminals 71 in this particular embodiment. These end sides have a non-round central hole, for the passage of the accordingly non-round

shaft of the slider 72, respectively housed in the terminal 71. The radially widened portion 172 of the slider allows the latter to slide axially along a stroke that essentially corresponds to the distance between the two radial abutments 171, whereas an elastic element, such as a helical spring 73, is provided between each side of the radial widened portion 172 of each slider 72 and the facing inner radial abutment 171 of the corresponding tubular terminal 71. Therefore, each slider is mounted with its radially widened portion 172 interposed between two helical springs. Outside the terminals 71, each slider 72 carries a coupling head 272, having a ring nut to be tightened to the corresponding measuring device. In order to ensure continuous electrical connection to the electronic measuring units and continuous feeding of expanding air or water to anchor elements 32, as well as the passage of the extensometer sensor control wire, connected on one side to the closing member 206, 306 of a tubular element 6 connected to an end of the joint 3, i. e. to a slider, and on the other side to the extensometer sensor in the tubular enclosure 6 of the module connected to the opposite slider 72 of the joint 3, the two sliders have an axial through hole for the passage of said wires, tubes and cables.

Particularly, the tubes and cables and the extensometer sensor control wire coaxially pass through the helical spring 7. The cables and the tubes for feeding pressurized fluid to the anchor elements 32 advantageously have a helical design in this area which allows transverse bending and possibly elongation thereof.

Then, the coupling heads 27 of the sliders 72 are fastened to the facing ends of the tubular enclosures 6 of two adjacent successive rigid modules by using ring nuts.

According to a further improvement, the elastically extensible walls, and particularly the outer walls of said locking elements which come in contact with the soil may be reinforced with a braid or a mesh, particularly a metal braid or mesh. Such braid or mesh may be laid over the anchor section 32 or integrated in the material that forms at least the outer wall, designed to expand and be compressed against the soil. This embodiment of the extensible or flexible joints 3 allows to separate radial and axial axes thereof and to provide a dampening effect when tensile forces are applied on the apparatus, e. g. when the apparatus is removed from the borehole after extensive use. Furthermore, the non-round shafts of the sliders 72 allow to apply rotary forces to the apparatus to release it from the soil when it has to be extracted from the borehole.

Fig. 11 shows the above design in greater detail. Figs. 12 and 13 show the monitoring apparatus with a measuring unit equipped with a packer, i. e. expandable anchor elements and plugs to be connected to joints with separate axes, as shown in Figure 13.

Fig. 11 shows the arrangement of cables and ties in the joint of Fig. 13.

The figures clearly show the tubular body 81 having a hexagonal shape, the stainless steel shaft 82, the perforated hexagon 83, the ring nut 84 for connection to the rigid enclosures 6, the o-ring seals 85, and the Teflon rings 86 to promote sliding.

A spacer 87 and two terminal fastening half-shells 88 are further provided. Numeral 89 designates a pressure ring for the tube and 810 designates further o-ring seals. The wire springs are designated by numeral 811 whereas 813 designates the bottom of the tubular sliding terminal which forms the end-of- stroke abutment. Numeral 812 designates the flexible tube covering the joint spring between the two terminals.

Numeral 814 designates the tube for feeding fluid to the packers and numeral 815 designates the tie associated to the extensometer sensor. Numeral 16 designates the power and signal transmission cable, whereas 817 designates the plug on the conduit for feeding expansion fluid to the packers. Numeral 181 designates the extensometer sensor. Numeral 819 designates the frame and supports for the electronic units, whereas 820 designates the electronic control units.

The piezometric and temperature sensors are designated by numeral 822, and the inclinometer sensor is designated by 823. Numeral 821 designates the straight inner tubular element of the tubular enclosure 6. Numeral 824 designates the pressure plug and 815 designates the porous filter at the opening of the tubular enclosure 6, allowing the passage of water to the piezometric sensor 822. Numeral 826 designates the wall of the packer, i. e. the expandable anchor device, in the idle condition, whereas 827 designates the wall in the expanded condition. Numeral 828 designates the power and signal cable and the tube for feeding the expansion

fluid to the packers, whereas 829 designates the extensometer sensor driving tie.

Obviously, the invention is not limited to the embodiments described and illustrated herein, but may be greatly varied, especially as regards the number and arrangement of its elements, without departure from the guiding principle disclosed above and claimed below.