JPH0721198B2 - A peripheral friction meter for measuring the frictional force between the peripheral surface of a structure and the ground surface during the submersible method. - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, in the field of civil engineering and construction work, is for measuring the frictional force between the peripheral surface of a structure and the ground surface when the structure is built in the ground by the submersible method. Concerning surface friction meter.

[0002]

2. Description of the Related Art The amount of structure subsided from the ground (or water) to the ground by the submarine method usually reaches several tens of meters. Therefore, the horizontal earth pressure applied to the wall surface of the structure must be 100 ton / m ² as the maximum design value.

On the other hand, the frictional force in the vertical direction on the circumferential surface of the structure during subsidence is 5 tons / m ² according to various measurement results.
Is considered a degree. Therefore, the minimum required reading (resolution) for a full scale 5 ton / m ² of the surface friction meter
Is usually 50 kg / m ² (1/100 of full scale).

A conventional peripheral friction meter is shown in FIGS. 5 and 6. FIG. 5 is a front sectional view of the peripheral friction meter, and FIG. 6 is a line VI in FIG.
FIG. 6 is a cross-sectional view taken along line VI.

This peripheral friction meter has a box-shaped outer frame 1 embedded in the concrete of a window of a structure, and in this outer frame 1, a box-shaped outer frame 1 in which concrete is placed. Inner frame 2
Are arranged with an outer frame 1 and a gap 3 therebetween, and in this gap 3,
Caulking agent is embedded to prevent the intrusion of earth and sand and pebbles from the outside. The concrete surface 4 cast into the inner frame 2 serves as a sensitive surface that comes into contact with the surrounding ground, but practically has an area of about 0.1 m ² . In order to receive the horizontal earth pressure applied to the sensitive surface 4 and to prevent the vertical movement of the sensitive surface 4 from being restricted by the horizontal earth pressure,
A steel bar guide bar 5 extends through the inner frame 2 and is supported by the outer frame 1 by slide ball bearings 6. A load cell 7 is attached to the inner frame 2 as an instrument for detecting a frictional force generated by the vertical movement of the sensitive surface 4, and the tip of a screw 8 fixed to the outer frame 1 is brought into contact with the load cell 7. Touching.

As shown in FIG. 6, this peripheral friction meter is embedded in the concrete of the window of the structure so that the peripheral surface 9 of the structure and the sensitive surface 4 of the peripheral friction meter are in the same plane. And submerge the structure in the excavated hole. The peripheral surface 9 of the structure
And the sensitive surface 4 of the circumferential friction meter are assumed to have the same friction coefficient. In measuring the vertical frictional force received by the sensing surface 4, the inner frame 2 tries to move with respect to the outer frame 1, so that the force is detected by the load cell 7 and is detected by the wire strain gauge (resistance strain gauge). It is performed by converting it into an electric signal and transmitting it to the outside through a cable.

In this peripheral friction meter, the sensing surface 4 (about 0.1
The strong horizontal earth pressure (maximum maximum of about 10 tons) received by m ² ) is transmitted to the two guide bars 5, and the force transmitted to the two guide bars 5 is two upper and lower slide ball bearings. It is supported by the outer frame 1, and thus the structure body, via 6 and the bearing receiver 6 '. In this case, the force transmission by the ball bearing 6 is performed via the tip of the steel ball, the guide bar 5 and the bearing receiver 6 ', and the respective contact points at that time are point contacts of the tip of the ball. When a force is applied to the point contact portion, a depression is always generated no matter how hard the steel material is, and rolling friction resistance in the bearing increases by an order of magnitude. Therefore, when the sensing surface 4 is subjected to horizontal earth pressure, the circumferential frictional force in the vertical direction is greatly attenuated by the rolling ball bearing 6 and is greatly attenuated, and is not properly transmitted to the load cell 7. As a result, the output signal of the surface friction meter is greatly reduced. For the rate at which this peripheral friction meter causes output reduction due to horizontal earth pressure, please refer to "Technical Report N" of Toyoko Hermes Co., Ltd.
It is reported in "O.2, Surface friction meter" that the horizontal earth pressure acting on the surface friction meter decreases to 88% at 9 tons / m ² and to 72% at 14 tons / m ² . If we estimate that the horizontal soil pressure increases at this rate, the output will be zero and disappear at 35 tons / m ² . The depth equivalent to 35 tons / m ² in horizontal earth pressure is approximately 30 (taking water pressure and effective earth pressure of soil into consideration).
Considered a little less than m depth. However, the depth of the current submarine construction method ranges from 60 m to 70 m. For this reason, this conventional circumferential friction meter completely loses its meaning to the current construction method.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a peripheral friction meter capable of accurately measuring the peripheral frictional force between the peripheral surface of a structure and the peripheral ground by removing the influence of horizontal earth pressure. Is to provide.

[0009]

In order to achieve the above object, in the circumferential friction meter according to the present invention, the horizontal earth pressure applied to the concrete sensitive surface of the inner frame is supported by the outer frame and the inner frame is removed from the outer frame. A support mechanism for supporting the frame so as to be displaceable in the vertical direction, at least two rings coupled via an intermediate connecting member, so that the central axes of these rings intersect the sensing surface at a right angle, The intermediate connecting member is fixed to the surface of the inner frame opposite to the sensing surface, and the opposite side of the ring to the intermediate connecting member is fixed to the outer frame via the outer frame connecting member, respectively. To do.

The following arrangement is conceivable as one arrangement mode of the support mechanism and the instrument. That is, the inner frame is formed in a rectangular box shape, and the outer frame is formed so as to have a corresponding square inner contour with a gap in the outer contour of the inner frame. A pair of support mechanisms consisting of at least two rings coupled together are provided at positions symmetrical to the vertical center axis of the circumferential friction meter, and the center axis between these two sets of support mechanisms is provided. Instruments can be placed on the line.

Further, as another aspect of the arrangement of the support mechanism and the measuring instrument, the inner frame is formed in a box shape having a round contour, and the outer frame is provided with a gap on the outer contour of the inner frame so as to correspond to the round inner side. A set of support mechanisms formed of at least two rings that are formed to have a contour and that are connected to each other through an intermediate connecting member is provided on the central axis of the instrument in the vertical direction. It can also be arranged. Such an arrangement reduces the overall size of the circumferential friction meter as compared to the above arrangement.

In the above arrangement of the supporting mechanism and the measuring instrument, if the O-ring is arranged in the annular gap formed between the outer frame having the circular inner contour and the inner frame having the circular outer contour, the water stop can be achieved. Is advantageous for.

Further, a protective case is fixed to the surface of the outer frame on the side opposite to the concrete-sensitive surface of the inner frame so as to surround the support mechanism, and water is stored in the space formed by the outer frame, the inner frame and the protective case. If it is filled with water, not only the support mechanism but also the water itself can receive the horizontal earth pressure of the peripheral ground of the structure.

Further, it is advantageous that the instrument for measuring the frictional force on the peripheral surface is a differential transformer type strain gauge for the reason described later.

[0015]

The present invention will be described in detail below with reference to the embodiments shown in the drawings.

1 and 2 are a plan view and a vertical sectional view of a first embodiment of a circumferential surface friction meter of the present invention.

The outer frame 12 joined to the window of the structure 11 by concrete has a flat flange portion 13 and a square tubular portion 14 in the center. The inner frame 16 arranged in the outer frame 12 with a square gap 15 is composed of a flat plate portion 17 and a square tubular portion 18, and is formed by the flat plate portion 17 and the tubular portion 18. Concrete is placed in the space of the inner frame, and the concrete surface 20 serves as the sensing surface of the peripheral friction meter as described later.

In the gap 15 between the inner frame 16 and the outer frame 12,
Caulking agent is filled to prevent intrusion of sediments and pebbles in the surrounding ground. This caulking agent has a sensitive surface 20
The vertical movement of is not restricted within the range of measurement (within 0.15 mm).

In order to support the horizontal earth pressure applied to the sensing surface 20 of the inner frame 16 to the outer frame 12 and the inner frame 16 so as to be displaceable in the vertical direction with respect to the outer frame 12, according to the present invention, the proving is performed. The steel rings 21 and 21 'as rings are connected via an intermediate connecting member 22, and the rings 21 and 2'
A set of supporting mechanisms is constructed by connecting T-shaped outer frame connecting members 23 and 23 'to the side opposite to the intermediate connecting member 22 of 1'. As shown in FIG. Are arranged one by one at positions symmetrical with respect to the vertical center axis line Y-Y, and the respective intermediate connecting members 22 are fixed to the flat plate portion 17 of the inner frame 16 by welding, and the outer frame connecting members 23, 23 are also provided. ′ Are fixed to the flange portion 13 of the outer frame 12 by welding. In order to detect a slight displacement of the inner frame 16 with respect to the outer frame 12, a differential transformer type strain gauge (FIG. 1) 25 is mounted on the central axis Y-Y of the circumferential surface friction meter at the upper and lower ends of the inner frame 16 and the outer frame. Each is fixed to the frame 12. Since this differential transformer type strain gauge is located on the central axis, it is possible to maintain the function of always capturing the average value of the left and right sides with respect to the left and right imbalance (eccentricity) received by the sensing surface 20.

Further, in order to separate the peripheral friction meter from the concrete of the structure, the flange portion 13 of the outer frame 12 is provided with
Box-shaped protective case 24 surrounding the two sets of support mechanisms
Is attached, and the protective case 24, the outer frame 12, and the inner frame 16 are attached.
The space surrounded by is filled with water.

The circumferential friction meter constructed in this way is shown in FIG.
As described above, concrete is poured and buried in the window of the structure 11, but the sensing surface 20 is on the same plane as the concrete peripheral surface 11 'and has the same friction coefficient. When the structure 11 is submerged in a hole excavated in the ground by the submersible method, the sensitive surface 20 acts as a part of the peripheral surface of the structure, and receives the vertical peripheral frictional force in proportion to the area thereof. This frictional force causes the inner frame 16 to be displaced with respect to the outer frame 12, so that the rings 21 and 21 'are slightly displaced in the vertical direction by the spring action with respect to the outer frame 12 via the intermediate connecting member 22. This small vertical displacement is measured by a differential transformer strain gauge 25.
To detect.

As is well known, the differential transformer measures the induced electromotive force generated in the secondary coil due to the displacement of its iron core. As described above, the circumferential surface friction meter receives a vertical circumferential surface frictional force, and at the same time, receives a strong horizontal earth pressure as a noise source from the horizontal direction (the direction perpendicular to the sensing surface 20). However, in the present invention, the support mechanism including the intermediate connecting member 22, the rings 21, 21 ', and the outer frame connecting members 23, 23' balances the circumferential frictional force in the vertical direction by the elasticity of the ring, and Due to the very high lateral rigidity of the ring, it can also support strong horizontal earth pressure. Therefore, this support mechanism plays the role of one bird and two birds with one stone. The influence of horizontal earth pressure as a noise source, which is about 2000 times larger than the minimum read signal, on the signal is firstly removed by the lateral rigidity of this support mechanism, and secondly in the protective case 24. The volume of hermetically filled water is completely removed by supporting horizontal earth pressure,
As a result, the output signal of the meter can be detected accurately and precisely.
This is also confirmed by the result of the experiment. In addition, according to a trial calculation from the Science Chronology 1991 edition [Compressibility of liquid 25 (445) liquid], the receding displacement of the sensing surface 20 when the water pressure is 100 m deep is about 11 microns. Is calculated as
Since this amount is extremely small, it hardly affects the output of the strain gauge 25. The water in the protective case 24 also functions to support the caulking agent from the inside and completely prevent the earth and sand and pebbles of the peripheral ground from entering the gap 15 between the inner frame 16 and the outer frame 12. .

Further, in the circumferential surface friction meter of the present invention, as a measuring instrument for detecting the vertical displacement of the sensitive surface 20, a differential gauge is used instead of the wire strain gauge type used in the conventional circumferential surface friction meter. The transformer strain gauge was used, and the reason for this will be described below.

In the conventional circumferential friction meter shown in FIGS. 5 and 6, the load cell conversion type is a wire strain gauge type, and this type converts a minute displacement into a change in electric resistance, and a weak electric resistance is converted. The change is detected and the load is calculated. In order to reliably detect weak changes in electrical resistance,
It is necessary to keep the insulation state of the electric system in an extremely good state, but it is not possible to keep the wire strain gauge in that state for a long time at the construction site of the sea or river where the submarine method is often adopted. As you can see from the following comparison, it is extremely difficult in reality.

The differential transformer strain gauge measures the induced electromotive force generated in the secondary coil due to the displacement of the iron core. Since the signal is converted into the induced electromotive force in this way, by properly selecting the electric circuit and its constant, it is possible to reduce the influence of changes in the electric resistance, including insulation deterioration, on the signal amount infinitely. . Practically, the insulation degradation of 60kΩ is 1
It is improved to the extent that it corresponds to the error signal of μ (micro).

On the other hand, since the wire strain gauge converts a signal into an electric resistance as described above, when a change in the electric resistance including the insulation resistance occurs somewhere in the electric resistance, this change and the signal It is impossible to discriminate it from the change in the electric resistance of, and it appears as a large error signal. Taking the reduction of insulation resistance for a normal practical device as an example,
A decrease in insulation resistance of 2 MΩ appears as an error signal of 1 μ. Comparing this with the case of a differential transformer type strain gauge, it becomes 60 kΩ: 12 MΩ = 1: 200. That is, comparing only insulation resistance,
Differential transformer is 20 compared to wire strain gauge
0 times better.

Next, a second embodiment of the surface friction meter of the present invention will be described with reference to FIGS. Parts similar to those of FIGS. 1 and 2 have similar reference numerals plus 100.

The second embodiment differs from the first embodiment in that, firstly, the outer contour of the tubular portion 118 of the inner frame 116 is not a square tube but a cylinder and the tube of the outer frame 112. The ridges 114 are correspondingly cylindrical, so that the annular spacing 115 formed between them has an O-ring 126, especially for the purpose of stopping water.
And secondly, the intermediate connecting member 122 and the ring.
Only one set of support mechanism consisting of 121, 121 'and outer frame connecting members 123, 123' has a vertical central axis YY of the peripheral friction meter.
And the two differential transformer type strain gauges 125 are arranged on both sides of the central axis YY in parallel with the above.

In the second embodiment, from the shape of the structure,
This is used when it is difficult to install two sets of support mechanisms, each of which includes an intermediate connecting member, a ring, and an outer frame connecting member, on the left and right sides of the central axis YY as shown in FIG. That is, in this embodiment, since the space between the outer frame and the inner frame is circular and only one set of support mechanisms are used, the overall size of the peripheral friction meter is reduced, and the reinforcing ribs of the iron plate of the structure, etc. It is advantageous when is an obstacle. In this case, the circumferential frictional force in the vertical direction can be obtained from the average value of the measured values of the differential transformer strain gauge. In addition, this second embodiment uses an inner frame 116 and an outer frame 112.
Since the O-ring 126 can be used in the gap 115 between them, the sealing effect can be further improved.

[0030]

According to the present invention, there is provided a support mechanism configured as described in claim 1, and the large lateral rigidity of this support mechanism enables a strong horizontal earth pressure as a noise source from the peripheral ground to be generated. Since it supports, the influence of horizontal earth pressure on the signal can be almost eliminated.

According to a third aspect of the present invention, there is provided a surface friction meter having an annular gap and having a pair of central support mechanisms and two instruments on both sides thereof, which is a square tribometer of the second aspect. The peripheral friction of the structure according to claim 2 having a reinforcing rib or the like of the structure because the size thereof is smaller than that of an arrangement having a large gap and having one central instrument and two sets of support mechanisms on both sides thereof. This is advantageous when it is difficult to arrange the meter.

As described in claim 4, by disposing the O-ring in the annular gap formed between the outer frame having the circular inner contour and the inner frame having the circular outer contour, the stop is provided. The water effect can be further enhanced.

By filling the space formed by the outer frame, the inner frame, and the protective case with water as described in claim 5, in addition to the support mechanism according to claim 1, the peripheral surface can be adjusted by the volume of water. Since it is possible to receive the horizontal earth pressure from the ground, it is possible to more completely eliminate the influence of the horizontal earth pressure on the measured value. As a result, it has become possible to measure the frictional force at a depth of 30 m or more, which was impossible with conventional frictional meters.

Further, as described in claim 6, since the measuring instrument comprises a differential transformer type strain gauge, the influence of the insulation reduction of the electric resistance is exerted on the long-term measurement at the sea or the river as described above. Compared with the conventional wire strain gauge type, the workability is greatly improved because it is reduced.

[Brief description of drawings]

FIG. 1 is a plan view showing a first embodiment of a surface friction meter according to the present invention with a protective cover removed.

FIG. 2 is a cross-sectional view of the circumferential friction meter of FIG. 1 taken along line II-II.

FIG. 3 is a plan view showing a second embodiment of the circumferential friction meter according to the present invention with a protective cover removed.

FIG. 4 is a cross-sectional view of the peripheral friction meter taken along the central axis Y-Y of the peripheral friction meter of FIG.

5 is a cross-sectional view of the conventional circumferential friction meter taken along line VV in FIG.

6 is a cross-sectional view of the conventional surface friction meter of FIG. 5 taken along line VI-VI.

[Explanation of symbols]

 12; 112 Outer frame 15; 115 Gap 16; 116 Inner frame 21,21 '; 121,121' Ring 22; 122 Intermediate connecting member 23,23 '; 123,123' Outer frame connecting member 24; 124 Protective case 25; 125 instruments

Claims (6)

[Claims] 1. An outer frame connected to a structure, an inner frame arranged in the outer frame with a gap and in which concrete is placed therein, and a horizontal part added to a concrete sensitive surface of the inner frame. A support mechanism for supporting earth pressure on the outer frame and for supporting the inner frame so as to be displaceable in the vertical direction with respect to the outer frame, and an instrument provided for detecting the displacement between the outer frame and the inner frame. In the peripheral friction meter for measuring the frictional force between the peripheral surface of the structure and the peripheral surface of the ground when the structure is built in the ground by the submersible method, the support mechanism includes an intermediate connecting member. The at least two rings joined together by means of an intermediate connecting member on the surface of the inner frame opposite to the sensing surface so that the central axes of these rings intersect the sensing surface at a right angle. By fixing the opposite side of the connecting member to the outer frame via the outer frame connecting member, A peripheral friction meter characterized by being constructed. 2. The inner frame is formed in a rectangular box shape, and the outer frame is formed to have a corresponding inner square contour with a gap from the outer contour of the inner frame. A pair of support mechanisms consisting of at least two rings connected via members are provided at positions symmetrical with respect to the vertical central axis of the circumferential friction meter, and the center between the two support mechanisms is provided. The circumferential friction meter according to claim 1, wherein the measuring instrument is arranged on an axis. 3. The inner frame is formed in a box shape having a round contour, and the outer frame is formed so as to have a corresponding round inner contour with a gap between the outer contour of the inner frame and a vertical direction of the instrument. 2. A circumference of claim 1 characterized in that a set of a support mechanism composed of at least two rings connected via an intermediate connecting member is provided on the central axis of said, and instruments are arranged on both sides of this support mechanism. Surface friction meter. 4. A peripheral surface according to claim 3, wherein an O-ring is arranged in an annular gap formed between the outer frame having the circular inner contour and the inner frame having the circular outer contour. Tribometer. 5. A space formed by an outer frame, an inner frame and a protective case, wherein a protective case is fixed to the surface of the outer frame opposite to the sensing surface so as to surround the support mechanism according to claim 1. The circumferential friction meter according to any one of claims 1 to 3, wherein the circumferential surface friction meter is filled with water. 6. The circumferential friction meter according to claim 1, wherein the measuring instrument is a differential transformer type strain gauge.