WO2005098165A1

WO2005098165A1 - Instrumented bars and system

Info

Publication number: WO2005098165A1
Application number: PCT/CN2005/000456
Authority: WO
Inventors: Noriman Sai Chi Mak; Lai Kwong Yeung
Original assignee: Hong Kong Fiberglass Technology Limited
Priority date: 2004-04-08
Filing date: 2005-04-07
Publication date: 2005-10-20

Abstract

An instrumented bar or soil nail (10) for use in reinforcing a slope comprises a first externally threaded tubular member (16), a second externally threaded tubular member (18), and an internally threaded coupler (20). One end of the coupler is threadably engaged with the first tubular member and the other end of the coupler is threadably engaged with the second tubular member. The first and second tubular members are arranged in colinear alignment to form a longitudinally extending conduit (34) therein. The external threads of each tubular member extend along the entire length thereof. A head plate (40) is provided at one end of the soil nail by means of threaded nut (50, 52). A cap (60, 62) is used to cover each tubular end of the soil nail. The soil nail is made of fiberglass. Measuring instruments are adapted to be inserted into the conduit of the soil nail.

Description

INSTRUMENTED BARS AND SYSTEM

FIELD OF THE INVENTION

The present invention relates to instrumented bars and system and, in particular, to instrumented soil nails and system.

BACKGROUND OF THE INVENTION

Soil nails are basically structural bars installed from the ground surface of a slope, through the depth of an analyzed potential unstable ground body mass, and anchored into the underlying stable earth zone beneath the potential unstable body mass. Conventional soil nails are made from steel bars. Firstly, a hole of sufficient length and dimension is drilled to provide a nominal cover for a soil nail to be inserted. The soil nail is then inserted into the hole. Grout is then injected into the hole from a bottom up manner using tremie pipes. The installed soil nail will have an exposed headpiece comprises a head plate and fastening means for securing the bars in the ground.

Soil nails are passive structural elements in that force will only be exerted onto the installed bars when movement of the potential unstable body mass occurred. The movement of the mobilized body mass causes a structural bar to extend from one end as the other end of the bar is firmly secured in the stable earth mass beyond the mobilized body. Stress will be distributed onto the bars and the composite action of the soil and bar will take action to restrain further movement.

The structure bars are normally steel bars that are installed in drilled holes and grouted to have minimal cover for protecting the steel material from corrosion and to enable gradual load transfer of the steel bars to the ambient soil surroundings.

Steel bars of specific lengths are normally prefabricated off site. A hot-dip galvanized process, protecting the steel material from corrosion, is applied to the steel bars before they are transported to the site for installation. In this conventional practice, the user orders a set of steel bars of a particular length, and then the soil nail manufacturer would cut the bars to the required length accordingly, carve the appropriate thread on one end of the bar, and then subject the precut bars to the galvanization process to provide protection from oxidation in the ground. This prevents corrosion and ensures long-term functionality of the steel material.

Once the steel bars are properly galvanized, however, they cannot be cut again to avoid exposure of un-galvanized parts. The lengths of the soil nails, however, are only estimations at best, as the lengths of the soil nails depend on the subsoil condition such as depth to rock head. If the lengths are unnecessarily long, the steel bars would need to be cut to fit on site. This on-site cut-to-fit practice will damage the pre-treated galvanization protection by exposing cut faces and threaded zones of the steel bars to corrosion. Therefore, this on-site cut-to-fit practice is not desirable, but is often necessary for practical reasons. Even if the bars are not cut after galvanization, the insertion process may scrape the protective coating somewhere along the length of the bar, causing damage to the galvanized surface, leading the corrosion therealong.

Recently, the issue on the corrosion problem of the steel soil nail bars is so serious that methods of checking the integrity of the steel soil nail bars utilizing instruments for detection are becoming a necessity. In one method, wires are attached to the steel bars externally during installation and in particular during grouting of the holes, and need to be protected and firmly secured at desired positions to properly detect the condition of the steel bars. Different electronic instruments that check, for example, the conductivity or resonance frequency of the wire or the bar, are used to check the integrity of the steel bars installed. A sheared bar should give a different signal as compared to an intact bar. However, interference and misplacement often occur, often rendering the measurements hard to interpret and unreliable.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved reinforcing bar and soil nail system.

According to one aspect of the present invention, there is provided a system for reinforcement utilizing instrumented bars or soil nails. The system comprises a first hollow bar having a first end and a second end. The first hollow bar has a first bore therein and an external threads extending along at least a section thereof. A head cap is adapted for removably covering the first end of the first hollow bar. The system further comprises an end cap for covering the second end of the first hollow bars.

In an embodiment, there is provided a system further comprising a second hollow bar and a sleeve or coupler. The second hollow bar has a first end and a second. The second hollow bar has a second bore therein and an external threads extending along at least a section thereof. The coupler is provided with internal threads. One end of the coupler is adapted for threaded engagement with the second end of the first hollow bar and the other end of the coupler is adapted for threaded engagement with one of the first and second ends of the second hollow bar. In the assembled position, the first and second hollow bars are disposed in collinear alignment and end-to-end relationship to form a longitudinally and continuously extending conduit. An end cap is adapted to cover the other one of the first and second ends of the second hollow bar.

In an embodiment, the system further comprises a head plate. The head plate has a central aperture adapted for receiving therethrough the first end of the first hollow bar; and at least one threaded nut for securing the head plate in a predetermined position at the first end of the first hollow bar.

In another embodiment, the system has a spacer coupled to each of the first and second hollow bars for centralizing the first and second hollow bars within a formation.

The instrumented bars or soil nails of the system are made of fiberglass.

The system allows a measuring instrument, such as a scale, a waveform meter, an optical fiber device, and a miniature camera to be inserted into the conduit through the first end of the first hollow bar right up to the entire length of the soil nail.

The continuous fiberglass threaded hollow bar soil nail system of the present invention provides a total solution in overcoming the shortcomings of the current steel soil nail system such as corrosion, long-term integrity, the necessity and lead time of pre- treatment of steel soil nails offsite, and the offsite estimation of length of steel bars. Fiberglass is a nonconductive material and is fairly inert. It has no corrosion problem. It has strength equivalent to or greater than those of steel. The specific gravity of fiberglass in general is of the order of one-fifth the specific gravity of steel.

The use of continuous fiberglass threaded hollow soil nail bars and attachments in enhancing soil stability greatly reduces the problem of safety during installation. The bars can be handled manually at ease on the construction site. Its non-corrosive characteristics enable longevity on a functional soil nail system once installed.

The continuous fiberglass threaded hollow bars are designed so that cutting can be made easily on site to desired lengths. The bars can be threaded and connected together by means of couplers. This allows the length of each soil nail be specifically made according to specific location and can accommodate changes easily to suit actual site conditions and measurements in a very cost effective manner.

The continuous fiberglass threaded hollow bar soil nail provides a channel or conduit that can be instrumented easily and protected during installation and grouting of the holes. It is therefore an objective to provide a fiberglass soil nail system that can be safely installed by workers on site with good durability characteristics and with access to monitor using instrumentation when required.

BRIEF DESCRIPTION OF THE DRAWINGS

Specific embodiments of the invention will now be described by way of example with reference to the accompanying drawings wherein:

FIG. 1 is an illustrative diagram of a soil nail for use in reinforcing a slope in accordance with a preferred embodiment of the present invention;

FIG. 2 is a longitudinal cross sectional view of the soil nail;

FIG. 3 is an exploded view of the soil nail;

FIG. 4 is an enlarged fragmentary view of an end of a hollow bar of the soil nail; FIG. 5 is an enlarged view of a coupler of the soil nail;

FIG. 6 is an enlarged view of an end cap of the soil nail;

FIG. 7 is an enlarged view of a nut of the soil nail;

FIG. 8 is an enlarged view of a bearing plate of the soil nail;

FIG. 9 is an exploded view of a reinforcing bar according to an embodiment of the present invention;

FIG. 10 is the reinforcing bar of FIG. 9 in an assembled condition;

FIG. 11 is an enlarged fragmentary view of an end of the reinforcing bar of FIG. 9;

FIG. 12 is an enlarged fragmentary view of an end of another embodiment of the reinforcing bar of FIG. 9;

FIG. 13 shows a foldable integrity checking instrument; and

FIG. 14 shows the foldable integrity checking instrument of FIG. 13 being inserted into the soil nail.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, in which like reference numerals represent like parts throughout the drawings, FIG. 1 is an illustrative diagram showing a soil nail generally designated by reference numeral 10. The soil nail 10 is inserted into a drilled hole 12 of a slope 14 for reinforcing and stabilizing the slope 14.

It is understood that an array of soil nails 10 spaced apart from one another can be utilized. The number of soil nails 10 depends on the area of the slope 14 and the length of the soil nails 10 depends on the depth of the drilled hole 12. According to an embodiment of the present invention, the soil nail 10 comprises a first hollow bar 16, a second hollow bar 18, and a coupler 20 for coupling the first hollow bar 16 to the second hollow bar 18. The first hollow bar 16, the second hollow bar 18, and the coupler 20 are preferably made of fiberglass.

Although it is shown in this embodiment that there are two hollow bars 16, 18, it is appreciated that the soil nail 10 of the present invention may have more than two hollow bars 16, 18 for deeper holes.

The first and second fiberglass hollow bars 16, 18 are made from a long and continuous fiberglass externally threaded hollow bar. The long and continuous fiberglass externally threaded hollow bar can be easily cut on site to any lengths, as desired. This allows each soil nail to be specifically made according to its location and can accommodate changes easily to suit actual site conditions and measurements in a very cost effective manner.

FIGS. 2 and 3 are longitudinal cross sectional and exploded views of the soil nail 10 respectively.

The first hollow bar 16 has a first end 16a and a second end 16b. The second hollow bar 18 has a first end 18a and a second end 18b. The hollow bars 16, 18 have respective external threads 26, 28 provided along the entire length thereof. The external threads 26, 28 may be continuous or intermittent. The coupler 20 is preferably in the form of a sleeve having a first end 20a, a second end 20b, and internal threads 32. One end 20a of the coupler 20 is threadably engaged with one end 16b of the first hollow bar 16. The other end 20b of the coupler 20 is threadably engaged with one end 18a of the second hollow bar 18.

As best illustrated in FIG. 2, the first and second hollow bars 16, 18 are arranged in collinear alignment to form a continuously and longitudinally extending bore or channel or conduit 34 therein. The first and second hollow bars 16, 18 are in an end-to-end relationship wherein the end 16b of the first hollow bar 16 abuts against the end 18a of the second hollow bar 18 generally at a middle portion of the coupler 20. The soil nail system of the present invention allows measuring instrument to be installed or inserted into the conduit 34 of the fiberglass soil nail 10 to check the integrity of the fiberglass soil nail any time subsequent to the installation. The measuring instrument adapted for depth measurement may be a scale, a waveform meter, an optical fiber, a miniature camera, or any other instruments.

According to an embodiment of the present invention, the soil nail 10 comprises a head plate 40. As depicted in FIG. 3, the head plate 40 has a central aperture 42. The central aperture 42 has a diameter which is slightly greater than the outmost diameter of the first hollow bar 16 such that the end 16a of the hollow bar 16 can be inserted through the aperture 42. The head plate 40 has a slope-facing surface 44. When the soil nail 10 is inserted into the hole 12 of the slope 14, the slope- facing surface 44 of the head plate 40 is disposed outside the hole 12.

Preferably, two threaded nuts 50, 52 are threadably engaged with the first hollow bar 16 on opposite sides of the head plate 40 respectively. The two threaded nuts 50, 52 are employed to secure the head plate 40 in a desired position adjacent the face of the slope. It is appreciated that the length of the soil nail 10 is longer than that of the hole 12 and that the dimension of the head plate 40 is greater than the diameter of the hole 12 so that the head portion of the soil nail 10 is exposed outside the hole 12 once the soil nail 10 is finally installed into the hole 12.

An internally threaded head cap or end cap 60 is adapted to threadabfy engaged with the externally threaded end 16a of the first hollow bar 16 for removably covering the exposed end of the soil nail 10. This end cap 60 allows instruments to be installed or inserted into the soil nail 10 to check the integrity of the fiberglass soil nail at any time subsequent to the installation of the soil nail 10.

In addition, another identical internally threaded end cap 62 is adapted to threadably engaged with the externally threaded end 18b of the second hollow bar 18 for removably covering the other end of the soil nail 10 at the bottom of the hole 12.

According to an embodiment of the present invention, a spacer 70 is coupled to each of the first and second hollow bars 16, 18 for centralizing the soil nail 10 when it is inserted and disposed inside the hole 12. The spacer 70 is preferably in the form of a one-piece torus-shaped plastic member. The spacer 70 has opposite openings 72 for receiving therethrough the first and second hollow bars 16, 18. Fasteners such as plastic bands or ties (not shown) can be utilized to tie the opposite ends 72 of the spacer 70 to the first and second hollow bars 16, 18.

FIG. 4 is an enlarged fragmentary view of the end 16a, 16b, 18a, 18b of the hollow bar 16, 18. The hollow bar 16, 18 defines the channel or conduit 34 of the soil nail 10. The outer diameter of the hollow bars 16, 18 is preferably 2.5cm and the inner diameter of the hollow bars 16, 18 is preferably 1.0cm.

An enlarged view of the coupler 20 of the soil nail 10 is shown in FIG. 5. It is noted that the outer surface of the coupler 20 has a hexagonal cross section. This facilitates gripping of the coupler 20 by a user when the first and second hollow bars 16, 18 are being threaded into the coupler 20. The length of the coupler 20 is preferably 24cm.

FIG. 6 is an enlarged view of the head cap or end cap 60, 62 of the soil nail 10. Each end cap 60, 62 is provided with internal threads 64. The end cap 60, 62 may have a round cross section or a hexagonal cross section. The length of the end cap 60, 62 is preferably 5.0cm.

FIG. 7 is an enlarged view of a nut 50, 52 of the soil nail 10. The nut 50, 52 is provided with internal threads 54. The length of the nut 50, 52 is preferably 3.0cm.

An enlarged view of the head plate 40 of the soil nail 10 is shown in FIG. 8. The dimension of the head plate 40 is preferably 15cm x 15cm.

FIG. 9 is an exploded view of a reinforcing bar 110 according to an embodiment of the present invention. The reinforcing bar 110 comprises a first threaded bar segment 116, a second threaded bar segment 118, and an internally threaded coupler 120. The structures of the first and second bar segments 116, 118 and the coupler 120 are similar to those of the first and second hollow bar 16, 18 and coupler 20 of the soil nail 10 previously described, except that the first and second bar segments 116, 118 are solid bar segments. The reinforcing bat- 110 is preferably made of fiberglass.

The first and second fiberglass bar segments 116, 118 are made from a long and continuous fiberglass threaded solid bar. The long and continuous fiberglass threaded solid bar can be easily cut on site to any length, as desired. This allows each reinforcing bar to be specifically made according to its location and can accommodate changes easily to suit actual site conditions and measurements in a very cost effective manner.

FIG. 10 is the reinforcing bar 110 of FIG. 9 in an assembled condition. An enlarged fragmentary view of an end of the first and second bar segments 116, 118 is shown in FIG. 11.

FIG. 12 is an enlarged fragmentary view of an end of another embodiment of the first and second bar segments 116, 118 wherein the bar segments 116, 118 are hollow defining therein a channel or conduit 134.

The instrumented bar or soil nail system of the present invention allows a measuring instrument adapted for depth measurement, such as a scale, a waveform meter, an optical fiber device, and a miniature camera to be inserted into the conduit of the bar or soil nail. FIG. 13 shows a foldable integrity checking instrument such as a scale 90 having a plurality of hinged sections 92. Each section 92 of the scale 90 preferably has a length of about lm. FIG. 14 shows the end cap 60 being removed and the scale 90 being unfolded and inserted into the conduit 34 of the soil nail 10. The foldable integrity checking instrument 90 can be utilized to check the soil nail condition and distance.

While the present invention has been shown and described with particular references to a number of preferced embodiments thereof, it should be noted that various other changes or modifications may be made without departing from the scope of the present invention. For example, the opposite ends of the soil nail may be covered by snap fitting end caps instead of internally threaded end caps. Alternatively, the opposite ends of the soil nail may be covered by plugs. With regard to the soil nail centralizing member, it may be in the form of a washer. The measuring instruments to be inserted into the bar or soil nail of the present invention may be instruments for checking the depth and integrity of the bar or soil nail. Other measuring instruments adapted to be inserted into the bar or soil nail of the present invention may include instruments for measuring water, gas, contamination, soil movement, etc. in the bar or soil nail system.

Claims

What is claimed is:

1. A system for reinforcement comprising: (a) a first hollow bar having a first end and a second end, said first hollow bar having a first bore therein and having external threads extending along at least a section thereof; and (b) a head cap adapted for removably covering said first end of said first hollow bar, wherein said first bore is adapted to receive therein a measuring instrument.

2. A system as claimed in claim 1 further comprising an end cap for covering said second end of said first hollow bars.

3. A system as claimed in claim 1 further comprising: (a) a second hollow bar having a first end and a second end, said second hollow bar having a second bore therein and having external threads extending along at least a section thereof; (b) an internally threaded sleeve, one end of said sleeve adapted for threaded engagement with said second end of said first hollow bar and the other end of said sleeve adapted for threaded engagement with one of said first and second ends of said second hollow bar, said first and second hollow bars in the assembled position being disposed in collinear alignment and end-to-end relationship to form a longitudinally and continuously extending conduit therein; and (c) an end cap adapted for covering the other one of said first and second ends of said second hollow bar.

4. A system as claimed in claim 2 or 3 further comprising a head plate, said head plate having a central aperture adapted for receiving therethrough said first end of said first hollow bar; and at least one tlireaded nut for securing said head plate in a predetermined position at said first end of said first hollow bar.

5. A system as claim in claim 3 further comprising a spacer coupled to at least one of said first and second hollow bars for centralizing said first and second hollow bars within a formation.

6. A system as claimed in claim 3 wherein said external threads extend along the entire length of said first and second hollow bars.

7. A system as claimed in any one of the preceding claims wherein said system is a soil nail system.

8. A system as claimed in any one of the preceding claims wherein said system is made of fiberglass.

9. A system as claimed in any one of the preceding claims further comprising a measuring instrument adapted for insertion into said system through said first end of said first hollow bar.

10. A system as claimed in claim 9 wherein said measuring instrument is adapted for depth measurement and is selected from the group consisting of scale, waveform meter, optical fiber, and miniature camera.

11. An instrumented soil nail system comprising: (a) a first hollow bar having a first end and a second end, said first hollow bar defining a first bore therein and having external threads extending along at least a section thereof; and (b) a head cap adapted for removably covering said first end of said first hollow bar, wherein said first bore is adapted to receive therein a measuring instrument.

12. A system as claimed in claim 11 further comprising an end cap for covering said second end of said first hollow bars.

13. A system as claimed in claim 11 further comprising: (a) a second hollow bar having a first end and a second, said second hollow bar defining a second bore therein and having external threads extending along at least a section thereof; said first and second bores having the same diameter; (b) an internally threaded sleeve, one end of said sleeve adapted for tlireaded engagement with said second end of said first hollow bar and the other end of said sleeve adapted for threaded engagement with one of said first and second ends of said second hollow bar, said first and second hollow bars in the assembled position being disposed in collinear alignment and end-to-end relationship to form a longitudinally and continuously extending conduit therein; and (c) an end cap adapted for covering the other one of said first and second ends of said second hollow bar.

14. A system as claimed in claim 12 or 13 further comprising a head plate, said head plate having a central aperture adapted for receiving therethrough said first end of said first hollow bar; and at least one threaded nut for securing said head plate in a predetermined position at said first end of said first hollow bar.

15. A system as claim in claim 13 further comprising a spacer coupled to at least one of said first and second hollow bars for centralizing said first and second hollow bars within a hole of a slope.

16. A system as claimed in claim 13 wherein said external threads extend along the entire length of said first and second hollow bars.

17. A system as claimed in any one of claims 11 to 16 wherein said system is made of fiberglass.

18. A system as claimed in any one of claims 11 to 17 further comprising a measuring instrument adapted for insertion into said system through said first end of said first hollow bar.

19. A system as claimed in claim 18 wherein said measuring instrument is adapted for depth measurement and is selected from the group consisting of scale, waveform meter, optical fiber, and miniature camera.

20. A soil nail for use in reinforcing a slope, said soil nail comprising: (a) a first tubular member having a first end and a second end, said first tubular member defining a first bore therein and having external threads extending along the entire length thereof; (b) a second tubular member having a first end and a second end, said second tubulai- member defining a second bore therein and having external threads extending along the entire length thereof; (c) an internally threaded coupler, one end of said coupler adapted for threaded engagement with said first tubular member and the other end of said coupler adapted for tlireaded engagement with said second tubulai- member, said first and second tubular members in the assembled position being disposed in collinear alignment and end-to-end relationship to form a longitudinally and continuously extending channel adapted for receiving therein a measuring instrument; (d) a head plate adapted to couple to one of said first and second tubular members; (e) an internally threaded cap adapted for threaded engagement with each end of said soil nail; and (f) a spacer coupled to at least one of said first and second tubulai" members for centralizing said soil nail within a hole of the slope when said soil nail is inserted into the hole.

21. A soil nail as claimed in claim 20 wherein said soil nail is made of fiberglass.