CN111307355A - Soil body full-stress component sensing ball and use method thereof - Google Patents
Soil body full-stress component sensing ball and use method thereof Download PDFInfo
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- 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
- G01L5/16—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for measuring several components of force
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L1/00—Measuring force or stress, in general
- G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
- G01L1/247—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet using distributed sensing elements, e.g. microcapsules
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L11/00—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00
- G01L11/02—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00 by optical means
- G01L11/025—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00 by optical means using a pressure-sensitive optical fibre
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L19/00—Details of, or accessories for, apparatus for measuring steady or quasi-steady pressure of a fluent medium insofar as such details or accessories are not special to particular types of pressure gauges
- G01L19/04—Means for compensating for effects of changes of temperature, i.e. other than electric compensation
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L19/00—Details of, or accessories for, apparatus for measuring steady or quasi-steady pressure of a fluent medium insofar as such details or accessories are not special to particular types of pressure gauges
- G01L19/06—Means for preventing overload or deleterious influence of the measured medium on the measuring device or vice versa
- G01L19/0627—Protection against aggressive medium in general
- G01L19/0654—Protection against aggressive medium in general against moisture or humidity
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L19/00—Details of, or accessories for, apparatus for measuring steady or quasi-steady pressure of a fluent medium insofar as such details or accessories are not special to particular types of pressure gauges
- G01L19/14—Housings
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Abstract
The invention provides a soil body full stress component sensing ball and a use method thereof, wherein the soil body full stress component sensing ball comprises the following components: a regular icosahedral framework; a spherical shell; the weight adjusting mechanism is used for adjusting the overall weight of the sensing ball; one surface, far away from the conical force transmission cap, of each first steel sheet is provided with sixteen distributed optical fibers, the sixteen distributed optical fibers are used for testing the stress of the conical force transmission cap, and the two distributed optical fibers are used for carrying out temperature correction on the deformation of the distributed optical fibers. According to the soil body full-stress component sensing ball and the using method thereof, six effective stress components in the soil body are obtained through the wavelength change values of light in sixteen distributed optical fibers and through temperature correction and a conversion formula, the collected data are more, and the measurement accuracy is higher. The method does not need to determine the placement position in advance, and is also suitable for the soil body with complicated stress state change.
Description
Technical Field
The invention relates to the technical field of soil stress testing, in particular to a soil full-stress component sensing ball and a using method thereof.
Background
In the engineering activities such as house building, underground space development, geological disaster prevention and control and the like, the change process of the internal stress of the soil body is very complex, the magnitude of the main stress is continuously changed, the direction of the main stress is continuously changed, and the stress states of any two points on the space are different. In addition, rain, water pipe leakage, adjacent traffic, waves, etc. all contribute to the constant variation of stress. The stress in the soil body will develop towards the direction of destruction under unfavorable conditions, which causes immeasurable loss to engineering construction. Therefore, comprehensively mastering the current state and the change trend of the stress in the soil body is an important component part of urban and rural construction and disaster prevention and control engineering. The real-time, reliable and high-precision soil stress state test can be used for verifying the design theory, promoting design optimization, monitoring the soil and structure states and studying and judging engineering risks, thereby being the foundation of engineering activities and having irreplaceable effect on engineering construction and geotechnical engineering theoretical research.
Soil pressure cells are often adopted for measuring the internal stress of the soil body, but the soil pressure cells can only test the normal stress in a certain direction, and can not simultaneously measure all six stress components in the soil body, so that the change of the stress state in the soil can not be comprehensively reflected, and the increasingly complex engineering project construction requirements can not be met.
The patent of publication No. CN106442109A discloses a soil three-dimensional effective stress testing device and a testing method thereof, wherein the device comprises six soil pressure cells, a pore water pressure cell, a base, a data wire, waterproof sealant and a pressure cell groove cover. Meanwhile, a testing method of the soil body three-dimensional effective stress testing device is provided. The invention has the advantages of improving the defect of indirectly acquiring the effective stress of the soil body according to the triaxial apparatus and filling the blank that the three-dimensional effective stress of the soil body can not be directly tested. Provides possibility for determining the three-dimensional effective stress of the soil body in the projects of sea reclamation, land reclamation in the surrounding lakes and the like. If the precision of the single soil pressure cell and the precision of the single pore water pressure cell are delta, the maximum positive stress precision is 2.67, and the maximum shear stress precision is 2.08. The improvement of the precision can not only solve the actual problem of the three-dimensional effective stress state of the soil body, but also provide guarantee for the research on the strength and the deformation of the soil body.
The patent of publication number CN104075944A discloses a three-dimensional soil pressure testing device based on a common soil pressure cell and a rhombic dodecahedron and an assembly calculation method, wherein six common soil pressure cells are fixed on six faces of the rhombic dodecahedron, of which normal vectors are irrelevant, to form the three-dimensional soil pressure testing device; the six faces of the rhombic dodecahedron, which are irrelevant to the normal vector, are provided with grooves for placing the soil pressure cell, the center of each groove is provided with a wire guide hole leading to the centroid of the rhombic dodecahedron, the center of any face of the rhombic dodecahedron, except the groove, is provided with a wire collecting hole leading to the centroid, and the formed six wire guide holes and the collecting hole are intersected at the centroid. Meanwhile, an assembling and calculating method of the three-dimensional soil pressure testing device is provided. The three-dimensional soil pressure testing device has the advantages that the three main stress testing accuracies of the soil pressure in the main direction obtained by the three-dimensional soil pressure testing device are 1.22 rho, the three shear stress testing accuracies are 0.71 rho, and the average testing accuracy is 0.965 rho, so that the safety reserve of engineering construction is improved, and the three-dimensional soil pressure testing device can be used for effectively evaluating the later health condition of engineering.
Above two patents all reach the multi-direction stress state of testing soil body inside based on the ordinary soil pressure cell group that the polyhedron was arranged, but because the soil pressure cell figure of arranging is less, the data of gathering is limited, and the polyhedron form of arranging is big to soil body normal position stress disturbance, leads to the error of test great. Moreover, the soil pressure box group arranged in a polyhedron can accurately reflect the soil stress by determining the installation direction in advance, and is difficult to be applied when the stress state changes in a complex way (particularly the ubiquitous situation of rotation in the stress main direction).
Therefore, a convenient, practical and accurate device for testing the internal full stress state of the soil body is urgently needed, and the device has important practical significance for solving the problem of real-time control of the internal stress state of the soil body in engineering activities.
Disclosure of Invention
In order to solve the problems, the invention provides a soil body total stress component sensing ball and a using method thereof.
In order to achieve the above purpose, the invention adopts a technical scheme that:
a soil mass full stress component sensing sphere, comprising: the regular icosahedron framework is made of metal materials, and is provided with eighteen first faces and two second faces which are arranged oppositely; a conical force transmission cap is arranged on the outer side of one first surface through a first steel sheet, a conical hole pressure sensor is arranged on the outer side of the second surface through a second steel sheet, and the conical hole pressure sensor is electrically connected with a data acquisition instrument; the spherical shell is made of hard plastic materials, the regular icosahedron framework is embedded in the spherical shell, and the spherical shell is provided with eighteen first through holes and two second through holes; the cap end of each conical force transmission cap abuts against the edge of the first through hole, and the cap end of each conical hole pressure sensor abuts against the edge of the second through hole; the outer surface of the spherical shell, the cap end of the conical force transmission cap and the cap end of the conical hole pressure sensor form a complete spherical surface; the weight adjusting mechanism is used for adjusting the whole weight of the sensing ball and is positioned in the body center of the regular icosahedron; the weight adjusting and connecting mechanism is connected with any vertex of the regular icosahedron through a metal rod; one surface, far away from the conical force transmission cap, of each first steel sheet is provided with a distributed optical fiber, the distributed optical fibers are connected with a fiber bragg grating demodulator, sixteen distributed optical fibers are used for testing stress of the conical force transmission cap, and two distributed optical fibers are used for correcting temperature of deformation of the distributed optical fibers.
Further, a silica gel layer wraps the spherical shell.
Further, the conical force transmission cap is arranged at the center of gravity of the first surface, and the conical hole pressure sensor is arranged at the center of gravity of the second surface; one end of the first steel sheet is connected with the top point of the first surface through a screw, and the other end of the first steel sheet is connected with the side of the first surface opposite to the top point through a screw; one end of the second steel sheet is connected with the top point of the second surface through a screw, and the other end of the second steel sheet is connected with the side of the second surface opposite to the top point through a screw.
Further, the distributed optical fiber comprises sixteen force measuring optical fibers and two temperature correcting optical fibers; each force measuring optical fiber is adhered to the inside of each first steel sheet along the length of the first steel sheet through a waterproof adhesive layer, and each temperature correcting optical fiber is only adhered to two ends of the inside of each first steel sheet through a waterproof adhesive layer; the inner surface of the first steel sheet is a surface of the first steel sheet close to the body center of the regular icosahedron; the force measuring optical fiber is used for testing the stress of the conical force transmission cap, and the temperature correction optical fiber is used for carrying out temperature correction on the deformation of the force measuring optical fiber; the force measuring optical fiber and the temperature correcting optical fiber are distributed optical fibers connected in series.
Further, the weight adjusting mechanism is a weight ball.
The invention also provides a use method of the soil body full stress component sensing ball based on any claim, which comprises the following steps: s10 calibration, namely immersing the sensing ball in water, measuring water pressure through a data acquisition instrument and a conical hole pressure sensor, measuring an average value of wavelength variation of light in sixteen distributed optical fibers through a fiber grating demodulator, correcting the temperature, and obtaining a proportionality coefficient of the sensing ball through a calibration formula; s20, testing the pore pressure of the soil body, embedding the sensing ball into the soil body, and testing the pore pressure in the soil body through the data acquisition instrument and the conical pore pressure sensor; s30, calculating according to the wavelength change value of the light in the distributed optical fiber to obtain the total stress component of a certain point in the soil body, measuring the wavelength change value of the light in sixteen distributed optical fibers through the fiber grating demodulator, correcting the temperature, and obtaining six effective stress components in the soil body through a conversion formula, thereby obtaining the total stress component of the certain point in the soil body.
Further, the calibration formula is
Wherein σisoThe water pressure value is used as the water pressure value,
is an average value of wavelength variations of the lights in sixteen of the distributed optical fibers,
and L is a proportional coefficient of the sensing ball as a temperature correction value.
Further, the conversion formula is σ ═ maf, where,
six effective stress components σ ═ σxx，σxy，σxz，σyy，σyz，σzz}T，
Compared with the prior art, the technical scheme of the invention has the following advantages:
(1) according to the soil body full-stress component sensing ball and the using method thereof, the stress measurement redundancy is high, namely six effective stress components (the redundancy is 10) in the soil body are obtained through the conversion formula through the wavelength change values of the light in sixteen distributed optical fibers and temperature correction, and the measurement precision and the measurement reliability are obviously improved. The method does not need to determine the placement position in advance, and is also suitable for the soil body with complicated stress state change.
(2) According to the soil body full-stress component sensing ball and the use method thereof, the sensing ball is spherical as a whole, and the weight of the sensing ball can be adjusted to the weight of a soil body with the same volume through the weight adjusting mechanism, so that the disturbance of the original taste stress of the soil body is greatly reduced. The error caused by the disturbance of the soil body internal full-stress component testing device is avoided.
(3) According to the soil body total stress component sensing ball and the using method thereof, the silica gel layer is wrapped outside the ball shell of the sensing ball, so that the influence of moisture in soil body on the sensing ball can be prevented.
Drawings
The technical solution and the advantages of the present invention will be apparent from the following detailed description of the embodiments of the present invention with reference to the accompanying drawings.
Fig. 1 is an overall effect diagram of a soil body full-stress component sensing sphere according to an embodiment of the present invention (a silica gel layer is only shown in half);
fig. 2 is a structural view of a spherical shell of a soil mass total stress component sensing sphere according to an embodiment of the invention;
FIG. 3 is a schematic diagram of a regular icosahedron and weight adjustment mechanism of a soil mass total stress component sensing sphere according to an embodiment of the present invention;
fig. 4 is a view showing an internal structure of a spherical shell of a soil mass total stress component sensing sphere according to an embodiment of the present invention;
FIG. 5 is a view showing a structure of fixing force-measuring optical fibers of a soil mass total stress component sensing sphere according to an embodiment of the present invention;
fig. 6 is a view showing a temperature correction optical fiber fixing structure of a soil mass full-stress component sensing sphere according to an embodiment of the present invention;
FIG. 7 is a flow chart of a method for using a soil mass full-stress component sensing sphere according to an embodiment of the present invention
FIG. 8 is a connection diagram of a soil mass full stress component sensing sphere according to an embodiment of the present invention;
FIG. 9 is a global coordinate system established according to an embodiment of the present invention;
FIG. 10 illustrates a local coordinate system established according to an embodiment of the present invention.
Reference numerals
The device comprises a regular icosahedron framework, a first surface 11, a second surface 12, a first steel sheet 13, an inner surface 131, a second steel sheet 14, a conical force transmission cap 15, a conical hole pressure sensor 16, a distributed optical fiber 17, a force measuring optical fiber 171, a temperature correcting optical fiber 172, screws 18, a waterproof glue layer 19, a spherical shell 2, a first through hole 21, a second through hole 22, a silica gel layer 3, a weight adjusting mechanism 4, a metal rod 41, a data acquisition instrument 5, a fiber bragg grating demodulator 6 and a hole pressure sensor 7.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1 to 7, the embodiment of the invention discloses a soil body total stress component sensing ball, which comprises a regular icosahedron framework 1, a ball shell 2, a silica gel layer 3 and a weight adjusting mechanism 4.
The regular icosahedron skeleton 1 is made of a metal material, and the regular icosahedron has eighteen first faces 11 and two second faces 12. The two second faces 12 are oppositely disposed. A conical force-transmitting cap 15 is arranged outside one of said first faces 11 via a first steel sheet 13. A conical hole pressure sensor 16 is arranged on the outer side of the second surface 12 through a second steel sheet 14, and the conical hole pressure sensor 16 is electrically connected with the data acquisition instrument 5.
The conical force-transmitting cap 15 is arranged at the center of gravity of the first face 11, and the conical hole pressure sensor 16 is arranged at the center of gravity of the second face 12. One end of the first steel sheet 13 is connected with the vertex of the first surface 11 through a screw 18, and the other end of the first steel sheet 13 is connected with the side of the first surface 11 opposite to the vertex through a screw 18. One end of the second steel sheet 14 is connected to the vertex of the second face 12 by a screw 18, and the other end is connected to the side of the second face 12 opposite to the vertex by a screw 18.
One surface, far away from the conical force transmission cap 15, of each first steel sheet 13 is provided with a distributed optical fiber 17, the distributed optical fibers 17 are connected with a fiber grating demodulator 6, sixteen distributed optical fibers are used for testing stress of the conical force transmission cap 15, and two distributed optical fibers are used for correcting temperature of deformation of the distributed optical fibers. The distributed optical fiber includes sixteen force measuring fibers 171 and two temperature correcting fibers 172. Each force measuring optical fiber 171 is adhered to the inner surface 131 of one first steel sheet 13, and each force measuring optical fiber 171 is adhered to the inner surface 131 of each first steel sheet 13 along the length of the first steel sheet 13 through a waterproof adhesive layer 19. Each temperature correction optical fiber 172 is adhered to the inner surface 131 of one first steel sheet 13, and each temperature correction optical fiber 172 is only adhered to two ends of each inner surface 131 through a waterproof adhesive layer 19. The middle of the inner face 131 is not connected to the temperature correction fiber 172. The inner surface 131 is a surface of the first steel sheet 13 close to the center of the regular icosahedron body. The force measuring optical fiber 171 is used for testing the stress of the conical force transmission cap 15, and the temperature correction optical fiber 172 is used for performing temperature correction on the deformation of the distributed optical fiber. The force measuring fiber 171 and the temperature correcting fiber 172 are distributed fibers connected in series.
The spherical shell 2 is made of hard plastic materials, and the regular icosahedron framework 1 is embedded in the spherical shell 2. Eighteen first through holes 21 and two second through holes 22 are formed in the spherical shell 2, the first through holes 21 and the second through holes 22 may be in any shape such as a circle, a square, a triangle, and the like, and the circular shape is preferred in the embodiment. The cap end of each conical force-transmitting cap 15 abuts against the edge of the first through-hole 21, and the cap end of each conical hole pressure sensor 16 abuts against the edge of the second through-hole 22. The outer surface of the spherical shell 2, the cap end of the conical force transmission cap 15 and the cap end of the conical hole pressure sensor 16 form a complete spherical surface.
The silica gel layer 3 wraps the outer surface of the spherical shell 2.
The weight adjusting mechanism 4 is used for adjusting the overall weight of the sensing ball, and the weight adjusting mechanism 4 is positioned in the body center of the regular icosahedron. The weight adjusting and connecting mechanism is connected with any vertex of the regular icosahedron through a metal rod 41. The weight adjusting mechanism 4 is a weight ball.
As shown in fig. 8, an embodiment of the present invention further provides a method for using a soil full-stress component sensing sphere, including the following steps: s10 calibration, namely immersing the sensing ball in water, measuring the water pressure through the data acquisition instrument 5 and the conical hole pressure sensor 16, measuring the average value of the wavelength change of the light in sixteen distributed optical fibers 17 through the fiber grating demodulator 6, correcting the temperature, and obtaining the proportionality coefficient of the sensing ball through a calibration formula. S20, testing the pore pressure of the soil body, burying the sensing ball in the soil body, and testing the pore pressure in the soil body through the data acquisition instrument 5 and the conical pore pressure sensor 16. S30, calculating according to the wavelength variation value of the light in the distributed optical fiber 17 to obtain the total stress component of a certain point in the soil body, measuring the wavelength variation value of the light in sixteen distributed optical fibers through the fiber grating demodulator 6, correcting the temperature, and obtaining six effective stress components in the soil body through a conversion formula, thereby obtaining the total stress component of the certain point in the soil body.
For the test of undisturbed soil field needing no disturbance, a drilling method is adopted to embed the sensing ball. Firstly, drilling to the depth to be tested by adopting a traditional mud wall protection drilling method, and sinking the sensing ball to the bottom of the hole. And slowly backfilling soil materials which are the same as the surrounding soil bodies in the drilled hole, and ensuring the backfilling to be compact. And arranging the sensing ball lead 7 and the distributed optical fiber 17 along the hole wall in the backfilling process, and measuring and reading in real time to ensure that the sensing ball, the sensing ball lead 7 and the distributed optical fiber 17 are not damaged in the burying process, otherwise, the points are preferably selected again for arrangement.
For the test of the backfill field, in the process of filling from bottom to top, when the testing depth is reached, the sensing ball is buried and the periphery of the sensing ball is ensured to be densely filled, and then the filling is continued. The sensing ball wire 7 and the distributed optical fiber 17 are naturally arranged loosely in the backfilling process and pay attention to protection. And the reading is measured regularly in the filling process, so that the sensing balls, the sensing ball lead 7 and the distributed optical fiber 17 are not damaged in the embedding process, and otherwise, the point selection and arrangement are preferably carried out again.
The calibration formula is
Wherein σisoThe water pressure value is used as the water pressure value,
is an average value of wavelength variations of the lights in sixteen of the distributed optical fibers,
and L is a proportional coefficient of the sensing ball as a temperature correction value.
The conversion formula is sigma-maf, wherein,
six effective stress components σ ═ σxx，σxy，σxz，σyy，σyz，σzz}T，
The test principle and the key calculation process of the sensing ball are as follows:
three rectangular reference surfaces are made in a regular icosahedron inside the sensing sphere, and an OXYZ global coordinate system is established as shown in FIG. 9. The 12 vertices of a regular icosahedron are numbered "1" to "12", and each face of the regular icosahedron may be defined by three vertices, as shown in table 1; the unit normal vectors (nx, ny, nz) for each face are shown in table 2.
TABLE 1 Twenty-positive face body number and vertex number correspondence
TABLE 2 Unit Normal vectors of each of the twenty regular surfaces
| Noodle numbering | nx | ny | nz | Noodle numbering | nx | ny | nz |
| 1 | 0.5774 | -0.5774 | 0.5774 | 11 | -0.9342 | -0.3568 | 0 |
| 2 | 0.3568 | 0 | 0.9342 | 12 | -0.9342 | 0.3568 | 0 |
| 3 | -0.3568 | 0 | 0.9342 | 13 | 0.3568 | 0 | -0.9342 |
| 4 | -0.5774 | -0.5774 | 0.5774 | 14 | 0.5774 | 0.5774 | -0.5774 |
| 5 | 0.5774 | -0.5774 | -0.5774 | 15 | -0.5774 | 0.5774 | -0.5774 |
| 6 | 0.9342 | -0.3568 | 0 | 16 | -0.3568 | 0 | -0.9342 |
| 7 | 0.9342 | 0.3568 | 0 | 17 | 0 | -0.9342 | 0.3568 |
| 8 | 0.5774 | 0.5774 | 0.5774 | 18 | 0 | 0.9342 | 0.3568 |
| 9 | -0.5774 | 0.5774 | 0.5774 | 19 | 0 | -0.9342 | -0.3568 |
| 10 | -0.5774 | -0.5774 | -0.5774 | 20 | 0 | 0.9342 | -0.3568 |
The relationship between the force measured on the conical force-transmitting cap 15 and the soil stress to be measured will be described by taking the "plane 2" formed by the vertexes 2, 3 and 6 in fig. 9 as an example. First, a coordinate system transformation as shown in FIG. 9 is performed, in the global OXYZ system, the Z 'axis in the local coordinate system OX' Y 'Z' of "face 2" corresponds to the normal of the regular icosahedron "face 2" along the axis of the conical force-transfer cap 15 under analysis (given by Table 2). The conversion relation of the stress to be solved in the global-local coordinate system is
σi′j′＝ai′kaj′lσkl(1)
In the formula (1), the reaction mixture is,
the matrix components are transformed for the stress tensor coordinates,
is the basis vector of the local coordinate system OX ' Y ' Z ' in the global coordinate system,
is the basis vector of the global coordinate system OXYZ.
In the local coordinate system OX ' Y ' Z ' shown in FIG. 10, the shaded area is the top spherical crown surface of the conical force-transmitting cap 5, where R is the radius of the sensing sphere and θ is the radius of the sensing sphere0Is the spherical crown opening angle of the conical force transmission cap 5. The resultant force of the soil body can be obtained by integrating the force applied to the spherical crown surface. The integral derivation process is as follows: for a certain orientation
A surface of micro-elements subjected to a force of
dFi′＝σi′dS (2)
Wherein σi′＝σi′j′nj′，
Infinitesimal area of
The pair of spherical cap portions dF is shaded in FIG. 9i′Is integrated to obtain
Taking i ═ 3' to obtain
This F3′Namely the stress value directly measured by the conical force-transferring cap 5. Let pi R in formula (5)2(1-cos2θ0) If/2 is K, then equation (5) is modified to
F3′＝Kσ3′3′(6)
Note that R represents the radius of the measuring sphere, θ0Representing the spherical cap opening angle, it can be seen that K is a constant related to the internal geometry of the sensing sphere, which is the same for each conical force-transmitting cap 5.
As shown in the formula (1), σ3′3′Is the 6 stress component sigma to be solved in the global coordinate systemxx，σxy，σxz，σyy，σyz，σzzThe function (1) is taken into the normal vector of the corresponding azimuth in Table 2 to obtain sigma3′3′And further F is obtained according to formula (6)3′. The function expression is established for twenty surfaces, and F is usedniThe force applied to each conical force-transmitting cap 5 (where the subscript i is the surface number in table 1 corresponding to the conical force-transmitting cap 5) is shown in the form of a matrix, and is arranged as follows:
note Fn17To Fn20And σxx，σxy，σxzThis is not relevant because of the global coordinates in FIG. 9Is a special result of the selection. Therefore, these four orientations of open circular holes are not used for force measurement, but are used to arrange the temperature correcting optical fiber 172 and the tapered hole pressure sensor 16.
Deletion of F from formula (7)n17To Fn20Corresponding elements, and are abbreviated as
Fn＝Tσ (8)
In the formula: fn＝{Fn1，...，Fn16}T，σ＝{σxx，σxy，σxz，σyy，σyz，σzz}T，
In the formula (8), the unknowns to be solved are 6 stress components, the equations are 16, the number of the equations is more than the number of the unknowns, the equations are incompatible equations, and the least square method is adopted to obtain the optimal solution
σ＝(TTT)-1TTFn(9)
As can be seen, the device adopts 16 'distributed optical fibers 17+ first steel sheets 13' to cooperatively test and calculate 6 stress components, the redundancy of the system is 10, and the measurement error of the system is greatly reduced.
According to the force measuring principle of each spherical cap,
wherein B is the constant of the optical fiber force measuring system, delta fiThe wavelength variation value of the light in the optical fiber is caused by the extrusion deformation and the temperature variation of the ith force-measuring steel sheet due to the conical force-transmitting cap 5,
the value of the wavelength change in the light in the fiber due to temperature change (averaged over the two temperature-corrected fibers). Bringing formula (10) into formula (9)
σ＝B(TTT)-1TTΔf (11)
In the formula (I), the compound is shown in the specification,
the wavelength variation value of the light in the optical fiber corresponding to each conical force-transmitting cap 5 after temperature correction.
Bringing the matrix T into formula (11) and letting the scaling factor L be B/K, the final result is:
σ＝MΔf (12)
in the formula (I), the compound is shown in the specification,
it can be seen that σ can be obtained by conversion as long as Δ f is measured, and the constant L in M is a proportionality coefficient that needs to be calibrated in advance, and is related to parameters such as geometric dimensions of the device.
The above description is only an exemplary embodiment of the present invention, and not intended to limit the scope of the present invention, and all equivalent structures or equivalent processes that are transformed by the content of the present specification and the attached drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.
Claims (8)
1. A soil mass full stress component sensing sphere, comprising:
the regular icosahedron framework is made of metal materials, and is provided with eighteen first faces and two second faces which are arranged oppositely; a conical force transmission cap is arranged on the outer side of one first surface through a first steel sheet, a conical hole pressure sensor is arranged on the outer side of the second surface through a second steel sheet, and the conical hole pressure sensor is electrically connected with a data acquisition instrument;
the spherical shell is made of hard plastic materials, the regular icosahedron framework is embedded in the spherical shell, and the spherical shell is provided with eighteen first through holes and two second through holes; the cap end of each conical force transmission cap abuts against the edge of the first through hole, and the cap end of each conical hole pressure sensor abuts against the edge of the second through hole; the outer surface of the spherical shell, the cap end of the conical force transmission cap and the cap end of the conical hole pressure sensor form a complete spherical surface; and
the weight adjusting mechanism is used for adjusting the whole weight of the sensing ball and is positioned in the body center of the regular icosahedron; the weight adjusting and connecting mechanism is connected with any vertex of the regular icosahedron through a metal rod;
one surface, far away from the conical force transmission cap, of each first steel sheet is provided with a distributed optical fiber, the distributed optical fibers are connected with a fiber bragg grating demodulator, sixteen distributed optical fibers are used for testing stress of the conical force transmission cap, and two distributed optical fibers are used for correcting temperature of deformation of the distributed optical fibers.
2. The soil mass full stress component sensing sphere of claim 1, wherein the spherical shell is wrapped with a layer of silica gel.
3. The soil mass full stress component sensing sphere of claim 2, wherein said conical force-transmitting cap is disposed at the center of gravity of said first face and said conical bore pressure sensor is disposed at the center of gravity of said second face; one end of the first steel sheet is connected with the top point of the first surface through a screw, and the other end of the first steel sheet is connected with the side of the first surface opposite to the top point through a screw; one end of the second steel sheet is connected with the top point of the second surface through a screw, and the other end of the second steel sheet is connected with the side of the second surface opposite to the top point through a screw.
4. The soil mass full stress component sensing sphere of claim 3, wherein said distributed optical fibers comprise sixteen force measuring optical fibers and two temperature modifying optical fibers; each force measuring optical fiber is adhered to the inside of each first steel sheet along the length of the first steel sheet through a waterproof adhesive layer, and each temperature correcting optical fiber is only adhered to two ends of the inside of each first steel sheet through a waterproof adhesive layer; the inner surface of the first steel sheet is a surface of the first steel sheet close to the body center of the regular icosahedron; the force measuring optical fiber is used for testing the stress of the conical force transmission cap, and the temperature correction optical fiber is used for carrying out temperature correction on the deformation of the force measuring optical fiber; the force measuring optical fiber and the temperature correcting optical fiber are distributed optical fibers connected in series.
5. The soil mass full stress component sensing sphere of claim 4, wherein the weight adjustment mechanism is a weight sphere.
6. The use method of the soil mass full stress component sensing sphere according to any one of claims 1 to 5, comprising the following steps:
s10 calibration, namely immersing the sensing ball in water, measuring water pressure through a data acquisition instrument and a conical hole pressure sensor, measuring an average value of wavelength variation of light in sixteen distributed optical fibers through a fiber grating demodulator, correcting the temperature, and obtaining a proportionality coefficient of the sensing ball through a calibration formula;
s20, testing the pore pressure of the soil body, embedding the sensing ball into the soil body, and testing the pore pressure in the soil body through the data acquisition instrument and the conical pore pressure sensor;
s30, calculating according to the wavelength change value of the light in the distributed optical fiber to obtain the total stress component of a certain point in the soil body, measuring the wavelength change value of the light in sixteen distributed optical fibers through the fiber grating demodulator, correcting the temperature, and obtaining six effective stress components in the soil body through a conversion formula, thereby obtaining the total stress component of the certain point in the soil body.
7. The method of using a soil mass full stress component sensing sphere according to claim 6, wherein the calibration formula is
Wherein σisoThe water pressure value is used as the water pressure value,
is an average value of wavelength variations of the lights in sixteen of the distributed optical fibers,
and L is a proportional coefficient of the sensing ball as a temperature correction value.
8. The method of using a soil mass full stress component sensing sphere according to claim 6, wherein said conversion formula is σ ═ M Δ f, wherein,
six effective stress components σ ═ σxx,σxy,σxz,σyy,σyz,σzz}T，
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