Sensing cable with parallel spiral transmission line structure for distributed sensing and measuring of rock-soil mass deformation

Abstract

This present disclosure provides a sensing cable of parallel spiral transmission line structure for distributed sensing and measuring of rock-soil mass deformation. A circular cross-section of a silicone strip is tightly wounded by two mutually-insulated wires. The two mutually-insulated wires form the spiral cable. The two mutually-insulated wires are wrapped around and covered by a silicone shroud. They constitute a sensing cable. A termination matching impedance is connected to one end of each of the two mutually-insulated wires. A time domain reflectometry measurement instrument is connected to the other end of the two mutually-insulated wires. The present disclosure implements a distributed positioning and measurement of rock-soil mass deformation.

Claims

1. A sensing cable of a parallel spiral transmission line structure for distributed sensing and measuring of rock-soil mass deformation, comprising: a strip comprising a first elastic material; a spiral structure wrapping around the strip, the spiral structure comprising a single layer of two mutually-insulated wires running in parallel; and a shroud comprising a second elastic material, the shroud wrapping and covering the spiral structure, wherein the two mutually-insulated wires comprise a first wire and a second wire disposed side-by-side and next to one another, the first and second wires held together by an electrically insulating scarfskin such that a distance between the first and second wires remains substantially unchanged, wherein a matched impedance is connected between a first end of the first wire of the two mutually-insulated wires and a first end of the second wire of the two mutually-insulated wires, wherein a time domain reflection measurement instrument is connected between a second end of the first wire of the two mutually-insulated wires and a second end of the second wire of the two mutually-insulated wires, and wherein a helix pitch of the spiral structure is configured to change in response to the rock-soil deformation.

2. The sensing cable of claim 1, wherein each of the first wire and the second wire of the two mutually-insulated wires comprises a single-strand copper wire, a multi-strand copper wire, or a single-strand aluminum wire.

3. The sensing cable of claim 1, wherein the first elastic material comprises silicone.

4. The sensing cable of claim 1, wherein the second elastic material comprises silicone.

5. The sensing cable of claim 1, wherein the strip has a circular cross section.

6. The sensing cable of claim 1, wherein the change of the helix pitch of the spiral structure is configured to cause a corresponding change in a characteristic impedance of the spiral structure.

7. A sensing cable of a parallel spiral transmission line structure for distributed sensing and measuring of rock-soil mass deformation, comprising: a strip comprising a first elastic material; a spiral structure wrapping around the strip, the spiral structure comprising two mutually-insulated wires running in parallel; and a shroud comprising a second elastic material, the shroud wrapping and covering the spiral structure, wherein the two mutually-insulated wires comprise a first wire having a first thickness and a second wire having a second thickness, each of the first and second wires contacting a same surface of the strip, wherein the spiral structure has a helix pitch substantially equal to a sum of the first and second thicknesses, wherein a matched impedance is connected between a first end of the first wire of the two mutually-insulated wires and a first end of the second wire of the two mutually-insulated wires, wherein a time domain reflection measurement instrument is connected between a second end of the first wire of the two mutually-insulated wires and a second end of the second wire of the two mutually-insulated wires, and wherein the helix pitch of the spiral structure is configured to change in response to the rock-soil deformation.

8. The sensing cable of claim 7, wherein each of the first wire and the second wire of the two mutually-insulated wires comprises a single-strand copper wire, a multi-strand copper wire, or a single-strand aluminum wire.

9. The sensing cable of claim 7, wherein the first elastic material comprises silicone.

10. The sensing cable of claim 7, wherein the second elastic material comprises silicone.

11. The sensing cable of claim 7, wherein the strip has a circular cross section.

12. The sensing cable of claim 7, wherein the change of the helix pitch of the spiral structure is configured to cause a corresponding change in a characteristic impedance of the spiral structure.

13. The sensing cable of claim 7, wherein each of the first wire and the second wire comprises a single-strand copper wire, a multi-strand copper wire, or a single-strand aluminum wire.

14. The sensing cable of claim 7, wherein the first elastic material comprises silicone.

15. The sensing cable of claim 7, wherein the second elastic material comprises silicone.

16. The sensing cable of claim 7, wherein the change of the helix pitch of the spiral structure is configured to cause a corresponding change in a characteristic impedance of the spiral structure.

17. A sensing cable of a parallel spiral transmission line structure for distributed sensing and measuring of rock-soil mass deformation, comprising: a strip comprising a first elastic material and having a circular cross section; a spiral structure wrapping around the strip, the spiral structure comprising two wires running in parallel, the two wires held together by an electrically insulating scarfskin such that the two wires are mutually insulated from one another and that a distance between the two wires remains substantially unchanged; and a shroud comprising a second elastic material, the shroud wrapping and covering the spiral structure, wherein the two wires comprise a first wire and a second wire each wrapping around the strip with a same radius, wherein a matched impedance is connected between a first end of the first wire of and a first end of the second wire, wherein a time domain reflection measurement instrument is connected between a second end of the first wire and a second end of the second wire, and wherein a helix pitch of the spiral structure is configured to change in response to the rock-soil deformation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of the structure of the present disclosure.

(2) FIG. 2 is an example structure of two parallel straight wires.

(3) FIG. 3 is a structural change in distributed deformation measurements before and after the local cable tension.

(4) FIG. 4 is an example sensing method of the present disclosure.

(5) FIG. 5 is an example TDR waveform.

(6) In the Figures: 1) silicone strip; 2) mutually-insulated wires; 3) silicone shroud; 4) TDR measurement instrument; 5) incident signal; 6) reflected signal; 7) sensing cable.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(7) The present disclosure will be further described with accompanying drawings and instances.

(8) As shown in FIG. 1, FIG. 2, FIG. 3 and FIG. 4, the present disclosure provides a circular cross-section silicone strip 1 that is tightly wounded by a single layer of two mutually-insulated wires 2. The two mutually-insulated wires 2 are spirally-wound wires. A silicone shroud wraps and covers the spiral wires to form a sensing cable 7. A matched impedance Z.sub.L is connected to one end of each of the two mutually-insulated wires. A TDR measurement instrument 4 is connected to the other end of each of the two mutually-insulated wires.

(9) An electrically-insulated scarfskin of the straight parallel wires is connected together so that the distance between the wires remains unchanged. Initially the wires tightly wind around the surface of the circular cross-section of the silicone strip. Such structural characteristic allows the sensing cable to have a relatively large elongation under stretch. The change of the helix pitch of the spirally-wound wires causes impedance changes when the sensing cable is stretched.

(10) Principle of the Sensing Cable

(11) FIG. 3 shows the structure changes of sensing cable before and after stretch. FIG. 3(a) is the sensing cable before stretch. FIG. 3(b) is the sensing cable with local elongation under stretch. As can be seen in FIG. 3, when the sensing cable is locally stretched, the number of windings by the wires is fixed and the length of the sensing cable is increased. Thus, the thread pitch of stretched part of the sensing cable and the local characteristic impedance are increased.

(12) FIG. 4 depicts a measuring method is showed in FIG. 4. Numeral reference 5 indicates an incident signal and numeral reference 6 indicates a reflected signal. One end of the sensing cable is connected to TDR measurement instrument 4. According to the principle of the transmission line, when TDR instrument sends a step signal or a pulse signal from the end of the cable, the reflected voltage U.sub.t and the input voltage U.sub.r have the following relationship

(13) $U_r=\frac{Z_d-Z_c}{Z_d+Z_c}*U_t$
where Z.sub.c is the initial characteristic impedance of the cable, Z.sub.d is the characteristic impedance of the stretch section. Initially Z.sub.c=Z.sub.d and reflected voltage U.sub.r=0. When the cable is locally stretched, Z.sub.d increases and TDR waveform produces a reflected voltage U.sub.r greater than zero. The TDR measurement instrument records the reflected voltage waveform as shown in FIG. 5.

(14) According to time difference T between the reflected voltage U.sub.t and the incident voltage U.sub.r and spread speed v, the distance S between the cable terminal and stretch point can be calculated as shown below.

(15) $S=\frac{1}{2}*T*v$

(16) If the cable is buried in rock or soil, the deformation of rock or soil will cause local stretch in the sensing cable. According to the time T and the reflected voltage U.sub.r, deformation L and deformation position S can be measured.