A SELF-CALIBRATING ELECTRONIC PRESSURE TRANSDUCER FOR LINED TUNNELS

Abstract: A transducer is foreseen comprising a rod (1) having at one end a bearing head (1a) on the rock, while the other end (3) acts on a charging cell (20). The transducer is provided in addition with an expander (2) integral with the charging cell on which the end (3) of the rod acts, the said expander (2) being realized in such a way as to fix the charging cell with respect to the civil engineering works (13). Preferably the charging cell (20) comprises a demultiplier (6) downstream of which a piezoelectrical bridge detector (8) is provided.

Description: "A SELF-CALIBRATING ELECTRONIC PRESSURE TRANSDUCER FOR LINED TUNNELS" The present invention relates to an electronic pressure transducer of the type used for example in tunnels to signal possible pressure variations of the ground on the civil engineering works. The measurement of the stress acting on the tunnel linings is 5. usually assigned to Gloetzl type hydraulic cells installed before the building work is carried out. Installation when the tunnel is operational involves economic and technological burdens, which cause inconvenience for the user and do not guarantee the real measurement of the pressures on the 10. structure, since reconstruction of the housing nog does net ensure homogeneity between this and the original building works; in addition, such cells are of necessity expendable since they are enclosed in the curtain wall concrete, so that the measuring point becomes unusuable in the case of deterioration of the facing. 15. The object of the present invention therefore is to create a pressure transducer which will transmit in a perfect way the value of the actual stress due to the ground, which will be easily inserted into and moved away from the workpiece, and which will also be such as not to require any work on the ground which might cause 20. even locally the stress produced by the latter. The aforesaid object has been attained by foreseeing a transducer ' comprising a rod whose ends rest one against the ground and the other against a charging cell, and which is further provided with an expander which makes the concrete civil engineering works integral with the charging cell. Preferably the charging cell comprises a demultiplier. Downstream of this a piezoelectric resistive bridge detector can be provided. 5. A preferred solution foresees in addition that the electronic circuit is fixed and integral with the said charging cell. From what has been said above it will be evident how the proposed device allows measurement of the radial stress at the axis of the tunnel. The device is quick to install and does not require 10. rebuilding work, since it only involves the making of a hole with a small diameter which goes through the lining and finishes inside the body of rock, for housing the transducer rod; in addition, it allows easy retrieval and possible substitution of the measuring equipment, which s outside the facing. 15. In order to position the transducer upstream of a civil engineering work, so that t can measure the pressure exerted by the ground, t is sufficient to make a hole with a diameter substantially equal to that of the rod, thus to insert the latter therein and press it to the bottom of the hole with adjustable preloading value, by bringing 20. near and moving away the charging cell, supported by the unit made integral to the concrete works. Since the rock is a rigid body which stresses the lining with πiicro-shifts, the transducer puts into relation two fixed points of the respective masses quantifying the forces acting along the 25. connecting axis represented by the rod which, resting on the sensitive surface of the charging cell, transforms such forces into a pressure which opposes the activated stress with equal value; this pressure is transmitted to the piezoelectrical detector which actuates the conversion of the reaction into an electronic quantity 5. processable by the computerized instrumentation. The invention will now be explained with reference to an exemplary embodiment which is illustrated in the enclosed drawings, in which: figure 1 is a diagrammatic view of a section of a tunnel in which three transducers according to the present invention have 10. been mounted,- figure 2 is a section of the transducer. As can be seen in the figures, the proposed transducer consists of a telescopic rod 1 which has for example a body 1 c, with a diameter of 35 mm with a bearmghead 1a in the rock, the body lc being connected 15. by being screwed to a portion J_b of gauged stainless steel with, for example, a diameter of 16 mm. This portion has a free hemisferical end 3 suitable for pressing on Belleville washers 14, which act on a movable plate 4 forming the input area for a charging cell 20. The distance existing between the head 1a and the end 3 can be regulated 20. at assembly by screwing down or unscrewing the portion 1b with respect to the body _1_c bearing the head la. ' The cell 20 consists of a body 21 which, when assembly is completed, will be locked in an adjustable way to the concrete works 13, as will be described later. 25. On the inside the cell 20 has two diaphragms M which enclose a hydraulic chamber 5. When the diaphragms M are moved a demultiplier 6 with a 1/10 ratio is actuated, which acts on a further diaphragm P with a large diameter which defines a second hydraulic chamber 7, having an outlet into which an electronic piezoelectric pressure 5. detector is inserted, indicated with reference number 8. A threaded pipe 12 integral with the block 11 which contains the Belleville washers 14, a.cting on the movable plate 4 is provided externally the portion Vh of the rod 1. The block 11 is provided with a hole 11a into which the end 3 of the rod can enter. The block 10. is fastened to the body 21 of the cell 20 by means of bolts which are net shown. Onto the externally threaded pipe 12 a conical nog 31 is screwed, which extends outwards with a hollow externally threaded pin 31a onto which a conical ring 32 slides. The said ring 32 is m contact with a washer 34, which s in contact with a nut 35 which 15. screws onto the hollow threaded pin 31a. Onto the block 31 and the ring 32, which are both conical in such a way that their respective apexes are facing, expander members 2 are located in the shape of sectors, which are formed in such a way as to lock against the civil engineering works 13 every time that the two conical surfaces of the 20. block 31 or the ring 32 respectively move towards each other. The expander members 2 are held back, when at rest, on the nog 31 and the ring 32 by the O-ring 33...Screwing down the nut 35 causes washers 34 and the conical ring 32 to move, and go towards the block, causing the expansion of the expansion organs 2, which lock 25. the cell to the concrete works 13. The externally threaded pipe 12, integral with the block 11 which is anchored to the cell 20, is screwed onto the nog 31; this allows the adjustment of the Belleville washers 14 in contact with the hemispherical end 3 of the rod, permitting preloading of the same, so as to allow the cell 20 to monitor not only phenomena of positive stress but also of ground sink on the concrete works 13. 5. The chambers 5 and 7 have stoppers 10 for filling with degassed, dehumidified oil. The proposed transducer will be mounted for example in a tunnel (figure 1) by making a 35 mm hole for a length for example of 1 m; then the first part of the hole will be widened to 50 mm for about 20 cm. The proposed device will be introduced 10. with the expander closed and the nut 35 will be acted upon to lock the expander to the works 13. The initial adjustment of the transducer is carried out as follows: By screwing down or unscrewing the body 1c of the rod with respect to the portion JJD of the same, the projection of the end 3 of the 15. rod 1 with respect to the hollow pin 31a is preset at a millimetre tolerance. The cell 20 integral with the pipe 12 is screwed nto the nog 31. This screwing down brings the end 3 of the rod 1 in contact with the 3elleville washers 14. By rotating the cell 20 clockwise or anticlockwise on its 20. longitudinal axis the washers 14 are wound more or less, and they generate pressure in the chambers 5 and 7. By measuring the pressure value in chamber 7 by means of the piezoelectric detector 8 and the electronic apparatus connected to it, the reference pressure is set in the work zone. From this moment it is possible to quantify the 25. variation of pressure on the transducer. A temperature compensated analogue-digital conversion electronic - _ - circuit 9 is foreseen integral with the cell, having a transmission buffer on a three-pole line which transmits the data to a computer. The thermal expansion of the rod is regenerated by a series of Belleville washers 14 positioned between the end 3 of the rod and 5. the movable plate 4. It is immediately compensated by the electronic circuit of the sensor and by the computerized processing of the measuring instrument which obviously comprises a thermometer. Preferably the pressure transducer is equipped with a power driver for piloting a ultipolar line for data transmission, with the 10. standard communication certificate for the CLIOS SET computer line, interfaceable with the local and remote automatic operating system.

Claims: C L A M S 1. A transducer comprising a rod (1), one (1a) of whose ends rests against the ground and the other (3) against a charging cell (20) , characterized in that it is further provided with an expander unit (31, 32, 2) which makes the concrete civil engineering works 5. (13) integral with the charging cell (20) . 2. A transducer according to claim 1, characterized in that the charging cell (20) comprises a demultiplicator (5, 7). 3. A transducer according to the claim 1 or 2 , characterized in that a bunch of Belleville washers (14) is interposed between the 10. end (3) of the rod (1) and the charging cell (20). 4. A transducer according to any one of the previous claims, characterized in that the charging cell (20) comprises a piezoelectric resistive bridge detector. 5. A transducer according to any one of the previous claims, 15. characterized in that the charging cell (20) is fastened in an adjustable way to the concrete works (13). 6. A transducer according to claim 5, characterized in that the cell (20) is provided with a pipe (12) integral with it, which is screwed to the expander unit (31, 32, 2).

Inventors: CARGNEL GIANANGELO, CARGNEL, GIANANGELO
Applicants: CARGNEL GIANANGELO, CARGNEL, GIANANGELO
Application year: 1989
Main classification: G01B5
IPC codes: E21F17, G01B5, G01L5