CA2062542C - Method and apparatus for measuring three dimensional stress in rock surrounding a borehole - Google Patents
Method and apparatus for measuring three dimensional stress in rock surrounding a boreholeInfo
- Publication number
- CA2062542C CA2062542C CA 2062542 CA2062542A CA2062542C CA 2062542 C CA2062542 C CA 2062542C CA 2062542 CA2062542 CA 2062542 CA 2062542 A CA2062542 A CA 2062542A CA 2062542 C CA2062542 C CA 2062542C
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- Prior art keywords
- borehole
- slot
- cutting
- slots
- axial
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- 238000000034 method Methods 0.000 title claims abstract description 28
- 239000011435 rock Substances 0.000 title claims abstract description 24
- 238000005259 measurement Methods 0.000 claims abstract description 12
- 230000000694 effects Effects 0.000 claims abstract description 3
- 230000007246 mechanism Effects 0.000 claims description 11
- 239000000463 material Substances 0.000 claims description 4
- 229910003460 diamond Inorganic materials 0.000 description 6
- 239000010432 diamond Substances 0.000 description 6
- 238000010586 diagram Methods 0.000 description 4
- 238000011065 in-situ storage Methods 0.000 description 3
- 238000009412 basement excavation Methods 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 238000005553 drilling Methods 0.000 description 2
- NLZUEZXRPGMBCV-UHFFFAOYSA-N Butylhydroxytoluene Chemical compound CC1=CC(C(C)(C)C)=C(O)C(C(C)(C)C)=C1 NLZUEZXRPGMBCV-UHFFFAOYSA-N 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 238000013178 mathematical model Methods 0.000 description 1
- 238000005065 mining Methods 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 238000000611 regression analysis Methods 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- 238000012956 testing procedure Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
- G01L5/0004—Force transducers adapted for mounting in a bore of the force receiving structure
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B49/00—Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells
- E21B49/006—Measuring wall stresses in the borehole
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/16—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring the deformation in a solid, e.g. by resistance strain gauge
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Geology (AREA)
- Mining & Mineral Resources (AREA)
- Environmental & Geological Engineering (AREA)
- Fluid Mechanics (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Investigation Of Foundation Soil And Reinforcement Of Foundation Soil By Compacting Or Drainage (AREA)
- Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)
Abstract
A method for measuring the three dimensional stress in rock surrounding a borehole comprises the steps of cutting slots into the wall of a borehole at different angles relative to the borehole axis so as to effect stress relaxation and strain deformations which are representative of the stresses normal to the angle of the respective slots, and measuring the respective strain deformations adjacent to the slots that are being cut into the borehole wall at a sufficient number of angles to satisfy the mathematical requirement of six independent equations to solve for the three dimensional stress tensors so as to determine the three dimensional stress field surrounding the borehole from measurements in a single borehole.
Description
20625~2 METHOD AND APPARATUS FOR MBASURING THREB
DIMENSIONAL STRESS IN ROCK SURROUNDING A BOREHO~E
The invention relates to a method and an ` apparatus to measure three dimensional stress surrounding a borehole.
BACKGROUND AND PRIOR ART
The state of stress in rock plays an important role in the behaviour of the ground in response to the creation of underground openings such as found in mi ning operations or civil engineering projects. For the design of underground openings it is therefore essential that the pre-excavation in situ stress be either measured or estimated. The inability to measure or estimate satisfactorily the state of stress in many circumstances is one of the major impediments to the utility of many of the theoretical and mathematical models which have come into use for the design of underground excavations.
Stress is an intangible quantity which cannot be measured directly. It is only the manifestation of stress which is measured and used to estimate the stress. The most common methods employ stress relief or compensation techniques which result in strains which can be measured.
By knowing the mechanical properties such as the modulus of elasticity and the Poisson's ratio of the rock in which the measurements were carried out one can deduce the in situ stress.
In most mining and civil engineering applications the in situ stress is measured with overcoring methods. These methods require the installation of a strain measuring device in a borehole and the subsequent drilling of an oversized hole over the existing hole to obtain an annulus which is stress relieved. The resultant strain is measured with the device inside the annulus. The stress regime can then be calculated from the strains measured as a result of the relaxation of the rock.
There are several different overcoring procedures and devices all of which have in common that they require the presence of a diamond drill throughout the testing procedure and, with the exception of the USBM
gauge, the measuring devices cannot be recovered. As a consequence, these determinations are very costly and time consuming and can rarely be carried out on a routine basis.
Against this background a novel instrument was recently developed at James Cook University, Australia, which does not rely on overcoring methods and is fully recoverable. A full description of the method and associated apparatus is given by H. Bock et al in the
DIMENSIONAL STRESS IN ROCK SURROUNDING A BOREHO~E
The invention relates to a method and an ` apparatus to measure three dimensional stress surrounding a borehole.
BACKGROUND AND PRIOR ART
The state of stress in rock plays an important role in the behaviour of the ground in response to the creation of underground openings such as found in mi ning operations or civil engineering projects. For the design of underground openings it is therefore essential that the pre-excavation in situ stress be either measured or estimated. The inability to measure or estimate satisfactorily the state of stress in many circumstances is one of the major impediments to the utility of many of the theoretical and mathematical models which have come into use for the design of underground excavations.
Stress is an intangible quantity which cannot be measured directly. It is only the manifestation of stress which is measured and used to estimate the stress. The most common methods employ stress relief or compensation techniques which result in strains which can be measured.
By knowing the mechanical properties such as the modulus of elasticity and the Poisson's ratio of the rock in which the measurements were carried out one can deduce the in situ stress.
In most mining and civil engineering applications the in situ stress is measured with overcoring methods. These methods require the installation of a strain measuring device in a borehole and the subsequent drilling of an oversized hole over the existing hole to obtain an annulus which is stress relieved. The resultant strain is measured with the device inside the annulus. The stress regime can then be calculated from the strains measured as a result of the relaxation of the rock.
There are several different overcoring procedures and devices all of which have in common that they require the presence of a diamond drill throughout the testing procedure and, with the exception of the USBM
gauge, the measuring devices cannot be recovered. As a consequence, these determinations are very costly and time consuming and can rarely be carried out on a routine basis.
Against this background a novel instrument was recently developed at James Cook University, Australia, which does not rely on overcoring methods and is fully recoverable. A full description of the method and associated apparatus is given by H. Bock et al in the
2 0 6 2 5 4 2 -Proceedings of the 4th Australian & New Zealand Conference on Geomechanics in Perth, Australia, 1984. The novel device is now manufactured and marketed by Interfels, Germany as the James Cook/Interfels Type 096 Borehole Slotter (hereinafter referred to as the Slotter). This is the instrument upon which the above invention is based and it is therefore described in more detail.
The Slotter works on the (St. Venant) principle that, when a crack or slot is created in the wall of a stressed borehole, virtually total stress relief will occur immediately adjacent and normal to the crack or slot. This results in a deformation of the rock which is controlled by the state of stress the rock was prior to the creation of the crack or slot as well as the mechanical properties of the rock material.
The Slotter is designed to cut, by means of a diamond saw blade, an axial slot into the sidewall of a borehole and to measure the tangential deformation of the rock caused by the resultant relaxation. The strain measurement is done with an integrated, specifically designed recoverable strain sensor. Repeated slots are cut around the circumference of the borehole wall and the deformation results are combined. To arrive at the two ~;~ensional stress field normal to the axis of the borehole, the measured deformations, expressed in microstrains, which are a function of the stress acting ~, perpendicular to the respective slots, and the physical properties such as the modulus of elasticity and the Poisson's Ratio of the rock mass, are used for a close form mathematical solution. To determine the three ~;mensional stress field in the rock mass, similar measurements are carried out in two additional, non-coplanar, non-coangular boreholes, and the results of three boreholes are combined by regression analysis.
Although the slotter is in many respects more efficient and cost effective than the overcoring methods, it has the disadvantage of needing three separate boreholes to determine the three dimensional state of stress in a rock mass. In view of the cost of drilling the required "H~' size (96-106mm) diamond drill holes, which can be as high as $5,000 per hole, considerable savings could be realized if the number of boreholes required could be reduced. In addition, the time needed to carry out measurements could also be reduced substantially if the procedures would not have to be repeated in three different boreholes. Lastly, it is difficult to combine the results of three independent, diverging boreholes into a single three dimensional stress tensor, especially when the rock is anisotropic and structured, which may cause significant differences in local stress orientations and magnitudes.
It is therefore the object of the present 2062S~2 invention to provide a method and an apparatus, based on the slotting principle, which would allow the determination of the three ~;m~nsional stress regime in rock i) in a single borehole, ii) without the requirement of an on-site diamond drill and iii) with a device that can be recovered and reused.
SU~ARY OF THE INVENTION
The method in accordance with the present invention for measuring three ~;m~n~ional stress in rock surrounding a borehole comprises cutting slots into the wall of a borehole at different angles relative to the borehole axis so as to effect stress relaxation and strain deformations which are representative of the stresses normal to the angle of the respective slots and measuring the respective deformations adjacent to the slots that are being cut into the borehole wall at a sufficient number of angles to satisfy the mathematical requirement of six independent equations to solve for the three ~;men,sional stress tensors so as to determine the three ~imensional stress field surrounding the borehole from measurements in a single borehole.
Cutting of the slot is done by inserting into the borehole an instrument having a first device for cutting an axial slot in the wall of the borehole and a second device for cutting a second slot at an angle of about 45 to the axis of the borehole. Then after axial rotation of the instrument another slot is cut at about 325 relative to the axial slot and perpendicular to the former angular slot, thus creating a series of three slots of independent angles. In order to arrive at the m;n;mlim required number of angles, the three-angle cutting procedure is repeated at different axial borehole rotations, preferably but not exclusively, at the two rotational angles of 60 i 10 and 120 i 10 from the rotational angle of the first slot series.
The apparatus for carrying out the above method comprises a tubular main housing adapted to be inserted and maintained in position in a borehole during measurement, and two stress relief mechanisms mounted coaxially within the housing. The first one comprises a slot cutting device for cutting an axial slot into the borehole wall parallel to the borehole axis, a strain sensor assembly adapted to be located adjacent to the centre of the slot to measure the deformation of the rock normal to the slot while the slot cutting is taking place, and means for moving the slot cutting device against the borehole wall. The second one comprises a slot cutting device for cutting a slot into the borehole wall at an angle of about 45 to the borehole axis, a strain sensor assembly adapted to be located adjacent to the centre of the 45 slot to measure the deformation of the rock material normal to the 45 slot while the slot cutting is taking place, and means for moving the slot cutting device against the borehole wall.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be disclosed, by way of example, with reference to a preferred embodiment illustrated in the accompanying drawings in which:
Figure 1 is graphic representation of the stress relief orientations when slots are cut at different angles into the sidewall of a borehole;
Figure 2 illustrates a preferred sequence of slot cutting; and Figures 3a and 3b are schematic diagrams illustrating top and side views, respectively, of an embodiment of an apparatus for measuring three ~;m~nsiona stress in rock surrounding a borehole.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring to Figure 1, diagram (a) illustrates the orientation A of stress relief when a single slot 10 is cut axially into the wall of a borehole 12. The corresponding strain deformation may be measured by placing a suitable strain sensor 14 adjacent the center of slot 10. Diagram (b) illustrates the orientations A and B of stress relief when an additional slot 16 is cut at an angle of 45 to the axis of the borehole. The corresponding strain deformation may be similarly measured by placing a strain sensor 18 adjacent the centre of the ~_ 2062542 slot 16. Diagram (c) illustrates the orientations A, B
and C of stress relief when an additional 45 slot 20 is cut after rotation of the instrument by 180 from the first two slots. In order to arrive at the m; n;mllm required number of angles, the three-angle cutting procedure is repeated at different axial borehole rotations, preferably but not exclusively, at the three rotational angles of 60 i 10 and 120 + 10 from the rotational angles of first slot series. A graphic representation is given in Figure 2. Sequence a illustrates the axial slots at the top and the bottom of the borehole after cutting the first series of axial and 45 slots. Sequence b illustrates axial slots at 60 and 240 from the top of the borehole after cutting the second series of axial and 45 slots. Sequence c illustrates the axial slots at 120 and 300 from the top of the borehole after cutting the third series of axial and 45 slots.
Referring to Figures 3a and 3b, the apparatus is contained in a tubular main housing 30, which is adapted to be inserted, and to be maintained in position by means of hydraulic jacks 32, in a, preferably but not exclusively, "H" diamond drill borehole (not shown) at a depth of up to 25 metres.
The stress relief mechanisms within the apparatus are divided into two sections, one to create and measure the strain perpendicular to an axial slot, ~A
.
referred to as the axial mechanism 34, and one to create and measure the strain perpendicular to a slot angled at 45 to the borehole axis, referred to as the angular mechanism 36.
The axial mechanism 34 is comprised of a tangential strain sensor assembly 38, similar but not exclusively identical, to the strain sensor of the Slotter, which is pressed by means of a hydraulic jack 40 or other device against the wall of the borehole in such a way that it is located within approximately 3 mm from, in the centre of, and perpendicular to the slot to be cut.
The axial mechanism is further comprised of a slot cutting device which consists of a 75 to 80 mm diameter, 0.8 to 1.0 mm thick diamond impregnated cutting wheel 42 attached to a motor 44 in such a way that it allows the cutting of a radial slot approximately 25 mm deep and up to 75 mm in length into the borehole wall parallel to the borehole axis. The motor is mounted on a wedge assembly 46 or other device which is operated by a hydraulic or electric motor 48 to move the cutting wheel against the borehole wall. The deformation of the rock material adjacent and normal to the slot is measured with the strain sensor while the slot cutting is taking place. The procedure is deemed terminated when there is no longer any deformation registered while the slot is being cut. The deformation is measured directly in micro strains.
~ 2062542 The angular mechanism 36 is similar to the axial mechanism, however with the difference that it comprises a tangential strain sensor assembly 50 which is mounted in such a way that it allows the measurement of the deformation of the rock in the centre of, and perpendicular to a radial slot to be cut at an angle of 45 to the borehole axis. The slot cutting device is similar to the axial mechanism with the difference that it comprises a cutting wheel 52 which is attached to the motor in such a way that it allows the cutting of a radial slot approximately 25 mm deep and up to 75 mm in length into the borehole wall at an angle of about 45 to the borehole axis. The cutting and measurement procedure is similar to that of the axial.
To obtain the minimum number of deformation measurements at independent angles - with sufficient redundancy - to solve for the three stress tensors, ~1, ~2 and ~3 the preferred overall test procedure is the following:
- The apparatus is inserted into the horizontal or sub horizontal "H" size borehole to the appropriate depth.
- The first axial and angular slots are cut at the top of the borehole.
- The apparatus is then rotated in the borehole by 180 and another axial ,_ 2062542 and angular slot is cut at the bottom of the borehole.
- The apparatus is advanced 10 cm deeper into the borehole and the above procedures are repeated at 60 and 240 respectively from the top of the borehole (sequence 2, Fig. 2).
- The apparatus is advanced 10 cm deeper into the borehole and the above procedures are repeated at 120 and 300 respectively from the top of the borehole (sequence 3, Fig. 2).
Although the invention has been disclosed with reference to a preferred embodiment, it is to be understood that it is not limited to such embodiment and that other alternatives, within the scope of the following claims, are also envisaged.
The Slotter works on the (St. Venant) principle that, when a crack or slot is created in the wall of a stressed borehole, virtually total stress relief will occur immediately adjacent and normal to the crack or slot. This results in a deformation of the rock which is controlled by the state of stress the rock was prior to the creation of the crack or slot as well as the mechanical properties of the rock material.
The Slotter is designed to cut, by means of a diamond saw blade, an axial slot into the sidewall of a borehole and to measure the tangential deformation of the rock caused by the resultant relaxation. The strain measurement is done with an integrated, specifically designed recoverable strain sensor. Repeated slots are cut around the circumference of the borehole wall and the deformation results are combined. To arrive at the two ~;~ensional stress field normal to the axis of the borehole, the measured deformations, expressed in microstrains, which are a function of the stress acting ~, perpendicular to the respective slots, and the physical properties such as the modulus of elasticity and the Poisson's Ratio of the rock mass, are used for a close form mathematical solution. To determine the three ~;mensional stress field in the rock mass, similar measurements are carried out in two additional, non-coplanar, non-coangular boreholes, and the results of three boreholes are combined by regression analysis.
Although the slotter is in many respects more efficient and cost effective than the overcoring methods, it has the disadvantage of needing three separate boreholes to determine the three dimensional state of stress in a rock mass. In view of the cost of drilling the required "H~' size (96-106mm) diamond drill holes, which can be as high as $5,000 per hole, considerable savings could be realized if the number of boreholes required could be reduced. In addition, the time needed to carry out measurements could also be reduced substantially if the procedures would not have to be repeated in three different boreholes. Lastly, it is difficult to combine the results of three independent, diverging boreholes into a single three dimensional stress tensor, especially when the rock is anisotropic and structured, which may cause significant differences in local stress orientations and magnitudes.
It is therefore the object of the present 2062S~2 invention to provide a method and an apparatus, based on the slotting principle, which would allow the determination of the three ~;m~nsional stress regime in rock i) in a single borehole, ii) without the requirement of an on-site diamond drill and iii) with a device that can be recovered and reused.
SU~ARY OF THE INVENTION
The method in accordance with the present invention for measuring three ~;m~n~ional stress in rock surrounding a borehole comprises cutting slots into the wall of a borehole at different angles relative to the borehole axis so as to effect stress relaxation and strain deformations which are representative of the stresses normal to the angle of the respective slots and measuring the respective deformations adjacent to the slots that are being cut into the borehole wall at a sufficient number of angles to satisfy the mathematical requirement of six independent equations to solve for the three ~;men,sional stress tensors so as to determine the three ~imensional stress field surrounding the borehole from measurements in a single borehole.
Cutting of the slot is done by inserting into the borehole an instrument having a first device for cutting an axial slot in the wall of the borehole and a second device for cutting a second slot at an angle of about 45 to the axis of the borehole. Then after axial rotation of the instrument another slot is cut at about 325 relative to the axial slot and perpendicular to the former angular slot, thus creating a series of three slots of independent angles. In order to arrive at the m;n;mlim required number of angles, the three-angle cutting procedure is repeated at different axial borehole rotations, preferably but not exclusively, at the two rotational angles of 60 i 10 and 120 i 10 from the rotational angle of the first slot series.
The apparatus for carrying out the above method comprises a tubular main housing adapted to be inserted and maintained in position in a borehole during measurement, and two stress relief mechanisms mounted coaxially within the housing. The first one comprises a slot cutting device for cutting an axial slot into the borehole wall parallel to the borehole axis, a strain sensor assembly adapted to be located adjacent to the centre of the slot to measure the deformation of the rock normal to the slot while the slot cutting is taking place, and means for moving the slot cutting device against the borehole wall. The second one comprises a slot cutting device for cutting a slot into the borehole wall at an angle of about 45 to the borehole axis, a strain sensor assembly adapted to be located adjacent to the centre of the 45 slot to measure the deformation of the rock material normal to the 45 slot while the slot cutting is taking place, and means for moving the slot cutting device against the borehole wall.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be disclosed, by way of example, with reference to a preferred embodiment illustrated in the accompanying drawings in which:
Figure 1 is graphic representation of the stress relief orientations when slots are cut at different angles into the sidewall of a borehole;
Figure 2 illustrates a preferred sequence of slot cutting; and Figures 3a and 3b are schematic diagrams illustrating top and side views, respectively, of an embodiment of an apparatus for measuring three ~;m~nsiona stress in rock surrounding a borehole.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring to Figure 1, diagram (a) illustrates the orientation A of stress relief when a single slot 10 is cut axially into the wall of a borehole 12. The corresponding strain deformation may be measured by placing a suitable strain sensor 14 adjacent the center of slot 10. Diagram (b) illustrates the orientations A and B of stress relief when an additional slot 16 is cut at an angle of 45 to the axis of the borehole. The corresponding strain deformation may be similarly measured by placing a strain sensor 18 adjacent the centre of the ~_ 2062542 slot 16. Diagram (c) illustrates the orientations A, B
and C of stress relief when an additional 45 slot 20 is cut after rotation of the instrument by 180 from the first two slots. In order to arrive at the m; n;mllm required number of angles, the three-angle cutting procedure is repeated at different axial borehole rotations, preferably but not exclusively, at the three rotational angles of 60 i 10 and 120 + 10 from the rotational angles of first slot series. A graphic representation is given in Figure 2. Sequence a illustrates the axial slots at the top and the bottom of the borehole after cutting the first series of axial and 45 slots. Sequence b illustrates axial slots at 60 and 240 from the top of the borehole after cutting the second series of axial and 45 slots. Sequence c illustrates the axial slots at 120 and 300 from the top of the borehole after cutting the third series of axial and 45 slots.
Referring to Figures 3a and 3b, the apparatus is contained in a tubular main housing 30, which is adapted to be inserted, and to be maintained in position by means of hydraulic jacks 32, in a, preferably but not exclusively, "H" diamond drill borehole (not shown) at a depth of up to 25 metres.
The stress relief mechanisms within the apparatus are divided into two sections, one to create and measure the strain perpendicular to an axial slot, ~A
.
referred to as the axial mechanism 34, and one to create and measure the strain perpendicular to a slot angled at 45 to the borehole axis, referred to as the angular mechanism 36.
The axial mechanism 34 is comprised of a tangential strain sensor assembly 38, similar but not exclusively identical, to the strain sensor of the Slotter, which is pressed by means of a hydraulic jack 40 or other device against the wall of the borehole in such a way that it is located within approximately 3 mm from, in the centre of, and perpendicular to the slot to be cut.
The axial mechanism is further comprised of a slot cutting device which consists of a 75 to 80 mm diameter, 0.8 to 1.0 mm thick diamond impregnated cutting wheel 42 attached to a motor 44 in such a way that it allows the cutting of a radial slot approximately 25 mm deep and up to 75 mm in length into the borehole wall parallel to the borehole axis. The motor is mounted on a wedge assembly 46 or other device which is operated by a hydraulic or electric motor 48 to move the cutting wheel against the borehole wall. The deformation of the rock material adjacent and normal to the slot is measured with the strain sensor while the slot cutting is taking place. The procedure is deemed terminated when there is no longer any deformation registered while the slot is being cut. The deformation is measured directly in micro strains.
~ 2062542 The angular mechanism 36 is similar to the axial mechanism, however with the difference that it comprises a tangential strain sensor assembly 50 which is mounted in such a way that it allows the measurement of the deformation of the rock in the centre of, and perpendicular to a radial slot to be cut at an angle of 45 to the borehole axis. The slot cutting device is similar to the axial mechanism with the difference that it comprises a cutting wheel 52 which is attached to the motor in such a way that it allows the cutting of a radial slot approximately 25 mm deep and up to 75 mm in length into the borehole wall at an angle of about 45 to the borehole axis. The cutting and measurement procedure is similar to that of the axial.
To obtain the minimum number of deformation measurements at independent angles - with sufficient redundancy - to solve for the three stress tensors, ~1, ~2 and ~3 the preferred overall test procedure is the following:
- The apparatus is inserted into the horizontal or sub horizontal "H" size borehole to the appropriate depth.
- The first axial and angular slots are cut at the top of the borehole.
- The apparatus is then rotated in the borehole by 180 and another axial ,_ 2062542 and angular slot is cut at the bottom of the borehole.
- The apparatus is advanced 10 cm deeper into the borehole and the above procedures are repeated at 60 and 240 respectively from the top of the borehole (sequence 2, Fig. 2).
- The apparatus is advanced 10 cm deeper into the borehole and the above procedures are repeated at 120 and 300 respectively from the top of the borehole (sequence 3, Fig. 2).
Although the invention has been disclosed with reference to a preferred embodiment, it is to be understood that it is not limited to such embodiment and that other alternatives, within the scope of the following claims, are also envisaged.
Claims (5)
1. A method for measuring the three dimensional stress in rock surrounding a borehole comprising the steps of:
a) cutting slots into the wall of a borehole at different angles relative to a borehole axis to effect stress relaxation and strain deformations which are representative of the stresses normal to the angle of the respective slots; and b) measuring the respective strain deformations adjacent to the slots that are being cut into the borehole wall with stress sensors to determine the three dimensional stress field surrounding the borehole from measurements in a single borehole.
a) cutting slots into the wall of a borehole at different angles relative to a borehole axis to effect stress relaxation and strain deformations which are representative of the stresses normal to the angle of the respective slots; and b) measuring the respective strain deformations adjacent to the slots that are being cut into the borehole wall with stress sensors to determine the three dimensional stress field surrounding the borehole from measurements in a single borehole.
2. A method as defined in claim 1 wherein cutting of the slots is done by inserting into the borehole an instrument having a first device for cutting a first axial slot in the wall of the borehole and a second device for cutting a second slot at an angle of about 45° to the axis of the borehole, and then after axial rotation of the instrument cutting another slot which is oriented at about 325° relative to the axial slot and perpendicular to the former angular slot, thus creating a series of three slots of independent angles, and in order to arrive at the minimum required number of angles, repeating the three-angle cutting procedure at different axial borehole rotations.
3. A method as defined in claim 2 wherein the method for measuring is repeated at the rotational angles of 60° 10° and 120° 10° with respect to the borehole axis from the first axial slot.
4. A method according to claim 1 wherein the number of slots is at least 3.
5. An apparatus for measuring the three dimensional stress in rock surrounding a borehole comprising:
a) a tubular main housing inserted and maintained in position in a borehole during measurement;
b) a first stress relief mechanism comprising a slot cutting device for cutting a first axial slot into the borehole wall parallel to a borehole axis, a first strain sensor assembly adjacent to the centre of the slot to measure deformation of the rock normal to the first axial slot while the first axial slot cutting is taking place, and means for moving the first axial slot cutting device against the borehole wall; and c) a second stress relief mechanism comprising a second slot cutting device for cutting a second slot into the borehole wall at an angle of about 45° to the borehole axis, a second strain sensor assembly adjacent to the centre of said 45° slot to measure deformation of the rock material normal to said 45° slot while the second slot cutting is taking place, and means for moving the second slot cutting device against the borehole wall.
a) a tubular main housing inserted and maintained in position in a borehole during measurement;
b) a first stress relief mechanism comprising a slot cutting device for cutting a first axial slot into the borehole wall parallel to a borehole axis, a first strain sensor assembly adjacent to the centre of the slot to measure deformation of the rock normal to the first axial slot while the first axial slot cutting is taking place, and means for moving the first axial slot cutting device against the borehole wall; and c) a second stress relief mechanism comprising a second slot cutting device for cutting a second slot into the borehole wall at an angle of about 45° to the borehole axis, a second strain sensor assembly adjacent to the centre of said 45° slot to measure deformation of the rock material normal to said 45° slot while the second slot cutting is taking place, and means for moving the second slot cutting device against the borehole wall.
Priority Applications (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2062542 CA2062542C (en) | 1992-03-09 | 1992-03-09 | Method and apparatus for measuring three dimensional stress in rock surrounding a borehole |
| AU33886/93A AU662956B2 (en) | 1992-03-09 | 1993-03-01 | Method and apparatus for measuring three dimensional stress in rock surrounding a borehole |
| DE19934307252 DE4307252A1 (en) | 1992-03-09 | 1993-03-08 | Measuring three=dimensional stress in rock surrounding borehole - measuring strain deformation adjacent to slots cut into borehole wall at different angles. |
| AU30152/95A AU3015295A (en) | 1992-03-09 | 1995-08-18 | Method and apparatus for measuring three dimensional stress in rock surrounding a borehole |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2062542 CA2062542C (en) | 1992-03-09 | 1992-03-09 | Method and apparatus for measuring three dimensional stress in rock surrounding a borehole |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2062542A1 CA2062542A1 (en) | 1993-09-10 |
| CA2062542C true CA2062542C (en) | 1996-01-16 |
Family
ID=4149398
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2062542 Expired - Fee Related CA2062542C (en) | 1992-03-09 | 1992-03-09 | Method and apparatus for measuring three dimensional stress in rock surrounding a borehole |
Country Status (3)
| Country | Link |
|---|---|
| AU (2) | AU662956B2 (en) |
| CA (1) | CA2062542C (en) |
| DE (1) | DE4307252A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102628716A (en) * | 2012-04-05 | 2012-08-08 | 中国科学院武汉岩土力学研究所 | Method and device for testing geo-stress in deep soft rock based on flow stress restoration principle |
| EP4189362A4 (en) * | 2020-07-31 | 2024-09-04 | Hamed Soroush | Downhole flat-jack in-situ stress tool (dfiss) for direct in-situ stress measurement in deep wells |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102141544B (en) * | 2010-12-02 | 2013-04-10 | 中国水电顾问集团华东勘测设计研究院 | Method for testing surrounding rock relaxation depth |
| CN103076128B (en) * | 2013-01-04 | 2015-06-24 | 西南交通大学 | Tunnel three-dimensional stress field simulator |
| CN103538140B (en) * | 2013-10-21 | 2016-03-30 | 中国科学院武汉岩土力学研究所 | The preparation method of crustal stress sensing post and device |
| CN104596673A (en) * | 2013-10-31 | 2015-05-06 | 北京科技大学 | Rock three-dimensional stress monitoring system and measuring device |
| CN104453849A (en) * | 2014-10-20 | 2015-03-25 | 成都创源油气技术开发有限公司 | Shale gas reservoir three-dimensional geological stress predication evaluation method |
| CN108414129B (en) * | 2018-04-02 | 2023-07-14 | 长江水利委员会长江科学院 | Device and method for testing relief of direct patch ground stress of semi-enclosure |
| CN110470419B (en) * | 2018-05-09 | 2024-01-26 | 中国科学院地理科学与资源研究所 | Drilling omnidirectional stress measuring device and method |
| CN110375704B (en) * | 2019-07-26 | 2020-10-30 | 华中科技大学 | Prediction method for wall rock-lining stress and deformation of deep-buried round tunnel excavation |
| CN112923879B (en) * | 2021-02-04 | 2022-06-21 | 中水北方勘测设计研究有限责任公司 | Method for evaluating relaxation thickness and grade of surrounding rock of cavern by utilizing sound wave speed |
| CN113756781B (en) * | 2021-08-17 | 2023-01-24 | 西南交通大学 | Low-cost ground stress testing method |
| CN114858317B (en) * | 2022-03-27 | 2023-08-25 | 中南大学 | Method for measuring stress relaxation by using intrinsic flexible pressure sensitive device |
| CN117268617B (en) * | 2023-09-13 | 2024-05-28 | 中国科学院武汉岩土力学研究所 | Stress tensor determination method comprising three-layer medium model |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4899320A (en) * | 1985-07-05 | 1990-02-06 | Atlantic Richfield Company | Downhole tool for determining in-situ formation stress orientation |
| US4813278A (en) * | 1988-03-23 | 1989-03-21 | Director-General Of Agency Of Industrial Science And Technology | Method of determining three-dimensional tectonic stresses |
| US5113707A (en) * | 1991-05-02 | 1992-05-19 | Her Majesty The Queen In Right Of Canada | Three-dimensional strain monitor for rock boreholes |
-
1992
- 1992-03-09 CA CA 2062542 patent/CA2062542C/en not_active Expired - Fee Related
-
1993
- 1993-03-01 AU AU33886/93A patent/AU662956B2/en not_active Ceased
- 1993-03-08 DE DE19934307252 patent/DE4307252A1/en not_active Withdrawn
-
1995
- 1995-08-18 AU AU30152/95A patent/AU3015295A/en not_active Abandoned
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102628716A (en) * | 2012-04-05 | 2012-08-08 | 中国科学院武汉岩土力学研究所 | Method and device for testing geo-stress in deep soft rock based on flow stress restoration principle |
| EP4189362A4 (en) * | 2020-07-31 | 2024-09-04 | Hamed Soroush | Downhole flat-jack in-situ stress tool (dfiss) for direct in-situ stress measurement in deep wells |
Also Published As
| Publication number | Publication date |
|---|---|
| AU3388693A (en) | 1993-09-16 |
| DE4307252A1 (en) | 1993-09-16 |
| AU662956B2 (en) | 1995-09-21 |
| AU3015295A (en) | 1995-10-26 |
| CA2062542A1 (en) | 1993-09-10 |
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