CN101736728A - Elastic beam type side wall frictional resistance dynamometer - Google Patents

Abstract

The invention relates to a spring beam type side wall friction resistance meter, which belongs to the technical field of measuring equipment. The elastic beam type side wall friction resistance meter provided by the invention solves the problems in the prior art, such as low precision and resolution of friction resistance testing, interference by earth pressure, and indeterminability of the friction resistance direction. The elastic beam type side wall friction resistance meter includes an embedded plate, a panel, an elastic beam, a strain gauge and a protective box; the embedded plate and the panel are arranged parallel to each other, and the embedded plate is fixedly connected to one end of the protective box; the panel is connected to the The other end of the protection box, and the panel can be shifted in translation relative to the embedded plate; the elastic beam and the strain gauge are arranged in the protective box, and the two ends of the elastic beam are respectively fixedly connected with the panel and the embedded plate; the two ends of the strain gauge They are respectively fixedly connected with the panel and the embedded plate. The elastic beam type side wall friction resistance meter of the present invention can be used to measure the friction resistance between the side walls of rigid structures such as caissons and driven piles and the surrounding soil, and can also be used in special occasions such as indoor geotechnical model tests.

Description

Spring Beam Side Wall Friction Meter

technical field

The invention relates to a measuring device, in particular to a spring-beam type side wall friction resistance meter, which can be used to measure the friction resistance of the side wall and the surrounding soil of rigid structures such as caissons and driven piles, and can also be used for geotechnical models The friction force test between the soil mass and the side wall of the structure in the test.

Background technique

Rigid structure and soil side wall friction problems are often involved in large underground engineering, such as pile side friction resistance, side wall and soil body friction resistance during caisson construction, etc. Knowing the true distribution of frictional resistance is of great significance for structural design, mechanical model research (such as the contact mechanics relationship between pile foundation and pile surrounding soil) and guiding engineering construction. However, since side wall friction belongs to shear stress, it is difficult to monitor directly, and there is a lack of effective monitoring instruments at present. Therefore, indirect monitoring methods are usually used to obtain friction in actual engineering, such as using concrete strain gauges or steel bar gauges to monitor piles. The axial force or the vertical stress of the caisson structure is used to indirectly calculate the side friction. The disadvantage of this method is that it can only obtain the average frictional resistance between two calculated sections, but not the sidewall frictional resistance of the point to be investigated; at the same time, because the measured strain or stress is very small, sometimes it is in the same order of magnitude as the observation error, Therefore, the accuracy of this method is very low.

For the frictional resistance in the caisson construction stage, sometimes the method of burying pressure cells on the side is used, and the frictional resistance is converted by measuring the normal stress and multiplying it by the friction coefficient. However, this method also has obvious defects: firstly, it is difficult to accurately measure the friction coefficient; secondly, even if the accurate friction coefficient is obtained, if it is not in the critical sliding friction state, the frictional resistance is not equal to the product of the normal stress and the friction coefficient; in addition, in some cases The direction of the lower friction force cannot be determined. If the foundation of the anchorage caisson deflects after bearing the tension of the large cable, the direction of the friction force may be reversed at this time. These are problems that cannot be solved by the method of embedding pressure cells on the side.

In the geotechnical model test, it is often necessary to simulate and measure the friction between the soil and the side wall of the model structure. The objects faced are similar to the actual ones, but smaller in size. That is to say, because the model test is generally a scale model, the load and its response are very small, so the measuring instrument is required to have a high resolution, which is also a difficulty at present.

Contents of the invention

The elastic beam type side wall friction resistance meter provided by the present invention solves the problems in the above-mentioned prior art, such as low precision and resolution of friction resistance testing, interference by earth pressure, and indeterminability of the friction resistance direction.

The present invention includes an embedded plate, a panel, an elastic beam, a strain gauge and a protective box; the embedded plate and the panel are arranged parallel to each other, and the embedded plate is fixedly connected to one end of the protective box; the panel connected to the other end of the protective box, and the panel can be shifted in translation relative to the embedded plate; the elastic beam and the strain gauge are arranged in the protective box, and the two elastic beams The two ends of the strain gauge are respectively fixedly connected with the panel and the embedded plate; the two ends of the strain gauge are respectively fixedly connected with the panel and the embedded plate.

The working principle of the present invention is: the frictional force of the soil on the panel causes the translational displacement between the panel and the embedded plate under the elastic constraint of the elastic beam, and the displacement causes the change of the length of the strain gauge; the strain measured by the strain gauge value to calculate the value of the translational displacement; since the translational displacement value is also equal to the deflection deformation of the elastic beam, according to the relationship between the deflection deformation of the elastic beam and the load, the panel can be further calculated The frictional resistance suffered.

When using the elastic beam type side wall friction meter proposed by the present invention to monitor the frictional resistance between the structure and the soil, it needs to be installed and buried on the outer surface of the structure to be measured. The measurement and calculation process is as follows: 1) the elastic beam type side wall The wall friction resistance meter is installed in the hole reserved on the side wall of the rigid structure, so that the outside of the panel is flush with the surface of the rigid structure, and the direction of the strain gauge is parallel to the movement direction of the caisson and other structures. When the structure moves or moves When , the friction force of the soil on the panel causes a translational displacement δ between the panel and the embedded plate. The stiffness of the beam is inversely proportional; 2) The strain ε is measured by the strain gauge, and the relative slippage between the panel and the embedded plate is obtained, that is, the deflection of the elastic beam, δ=εl, where l is the length of the strain gauge; 3) According to the mechanics of materials, it can be obtained that the tangential force on the panel is T=δ·n(12EI)/h ³ , where h is the height of the elastic beam, EI is the section stiffness, and n is the number of elastic beams; if a variable-section beam is used And considering the manufacturing error of the instrument, in actual application, the tangential force on the panel can be determined according to T=α·δ, where α is the calibration parameter; 4) Side wall frictional resistance τ=T/A, where A is the effective Area, that is, the area where the outer surface of the panel is in contact with the soil.

The elastic beam described in the present invention is a key sensing element and is the core of the present invention. Its characteristic is that the deflection deformation of the beam member is very sensitive to the force perpendicular to the beam axis and insensitive to the force parallel to the beam axis. In the actual working state of the present invention, the panel bears the earth pressure and friction resistance at the same time, and the earth pressure is usually greater than the friction resistance, but from the direction of the force, the friction resistance direction is perpendicular to the elastic beam, and the earth pressure direction is parallel to the elastic beam . Therefore, although the earth pressure suffered by the panel is greater than the frictional resistance, the present invention still guarantees that the frictional resistance that we care about is automatically screened for measurement, and ignores the influence of the earth pressure, and the anti-interference ability of the instrument is strong; secondly, due to the elastic beam The deflection deformation is very sensitive to frictional resistance and can capture small changes in frictional resistance. Therefore, the resolution of the instrument is very high, and it can be used in occasions with special requirements for resolution such as geotechnical model tests; in addition, elastic beams and panels, embedded The solid plate is integrally welded into an elastic deformation body, and there is a linear relationship between the deflection deformation of the elastic beam and the frictional resistance, so it can fully reflect the special circumstances such as the change of the frictional resistance direction, and has good stability and precision.

As an improvement of the present invention, a card slot is provided on the inner side of the protective box, and the side edge of the panel fits into the card slot.

As an improvement of the present invention, the connecting end of the elastic beam and the embedded plate is extended outward to form an anchoring end.

The above-mentioned anchoring end can make the connection between the whole instrument and the surrounding concrete more stable and reliable.

As an improvement of the present invention, the two ends of the strain gauge are respectively fixedly connected with the panel and the embedded plate by means of a rigid transmission block.

The aforementioned rigid transfer block facilitates the connection of the strain gages to the panel and the mounting plate.

As a further improvement of the present invention, the embedded panel, the panel, the protective box, the elastic beam and the rigid transmission block are all made of steel.

As an improvement of the present invention, a piercing hole is provided on the elastic beam, and the strain gauge passes through the piercing hole.

Piercing holes are provided on the elastic beams to facilitate the insertion of strain gauges, thereby making the internal structure of the instrument more reasonable.

As an improvement of the present invention, concrete is arranged on the outer side of the panel.

The concrete on the panel is of the same type as the component to be tested to ensure that the friction coefficient between the instrument and the soil is the same as the actual situation.

As a further improvement of the present invention, several grooves are opened on the outer surface of the panel, and the concrete is filled in each groove.

Instructions attached

Fig. 1 is the structural representation of the elastic beam type side wall friction resistance instrument;

Fig. 2 is a sectional view along line A-A in Fig. 1 .

Detailed ways

As shown in FIG. 1 and FIG. 2 , the elastic beam type side wall friction meter in this embodiment includes an embedded plate 1 , a panel 2 and a protective box 3 . The embedded plate 1 and the panel 2 are arranged parallel to each other, the embedded plate 1 is fixedly connected to one end of the protective box 3; the panel 2 is connected to the other end of the protective box 3, and the panel 2 can be connected to the embedded plate 1 translational misalignment. Preferably, a card slot 3-1 is provided on the inner side of the protective box 3, and the sides of the panel 2 are fitted into the card slot 3-1.

A first elastic beam 4 and a second elastic beam 5 are arranged in the protective box 3, the two elastic beams 4 and 5 are arranged parallel to each other, and the two ends of each elastic beam are respectively embedded with the panel 2 and the Board 1 is fixedly connected. The connecting end of the above-mentioned first elastic beam 4 and the embedded plate 1 is extended outward to form a first anchoring end 4-1; similarly, the connecting end of the above-mentioned second elastic beam 5 and the embedded plate 1 is extended outward to form a second anchor end 5-1. Both the first anchoring end 4 - 1 and the second anchoring end 4 - 2 are outside the protective box 3 .

A strain gauge 6 is also arranged in the protective box 3, the strain gauge 6 is parallel to the panel 2 and the embedded panel 1, and the two ends of the strain gauge 6 are connected to the panel 2 and the embedded panel 1 respectively. The fixed plate 1 is fixedly connected. Preferably, one end of the strain gauge 6 is fixedly connected to the panel 2 by means of a first rigid transmission block 7 , and the other end is fixedly connected to the embedded plate 1 by means of a second rigid transmission block 8 . Preferably, a piercing hole 9 is provided on each elastic beam, and the strain gauge 6 passes through the piercing hole 9 .

In addition, concrete 10 is arranged on the outer side of said panel 2 . Preferably, several grooves 1-1 are opened on the outer surface of the panel 2, and concrete 10 is filled in each groove 1-1.

The embedded panel 1, the panel 2, the protective box 3, the first elastic beam 4, the second elastic beam 5, the first rigid transmission block 7 and the second rigid transmission block 8 are all made of steel material.

Claims (8)

1. elastic beam type side wall frictional resistance dynamometer is characterized in that: comprise build-in plate, panel, spring beam, strain meter and protection box; The layout that is parallel to each other between described build-in plate and the described panel, described build-in plate is fixedly connected on an end of described protection box; Described panel is connected the other end of described protection box, and described panel can be with respect to the described build-in plate translation changing of the relative positions; Described spring beam and described strain meter are arranged in the described protection box, fixedly connected with described build-in plate with described panel respectively in the two ends of described spring beam; Fixedly connected with described build-in plate with described panel respectively in the two ends of described strain meter.

2. elastic beam type side wall frictional resistance dynamometer according to claim 1 is characterized in that: on the medial surface of described protection box draw-in groove is set, the side cooperation of described panel places described draw-in groove.

3. elastic beam type side wall frictional resistance dynamometer according to claim 1 is characterized in that: the link of described spring beam and described build-in plate prolongs laterally and forms an anchored end.

4. elastic beam type side wall frictional resistance dynamometer according to claim 1 is characterized in that: the two ends of described strain meter are mutually permanently connected by means of a rigid of transmission piece and described panel and described build-in plate respectively.

5. elastic beam type side wall frictional resistance dynamometer according to claim 4 is characterized in that: described build-in plate, described panel, described spring beam, described protection box and described rigid of transmission piece are made by steel.

6. elastic beam type side wall frictional resistance dynamometer according to claim 1 is characterized in that: be provided with one and place the hole on described spring beam, described strain meter passes the described hole that places.

7. elastic beam type side wall frictional resistance dynamometer according to claim 1 is characterized in that: arrange concrete on the lateral surface of described panel.

8. elastic beam type side wall frictional resistance dynamometer according to claim 7 is characterized in that: offer several trough on the lateral surface of above-mentioned panel, described concrete filling is in each groove.

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