CN1034609C - Earth stress measuring method and apparatus with complete temp. compensation - Google Patents

Abstract

The present invention relates to an earth stress measuring method and a device with complete temperature compensation. A temperature-sensitive element is arranged at the position which is adjacent to an electric resistance strain gauge; the temperature change of the position of the strain gauge is measured in the process of strain remove; two zero-load conducting wires are led out from a measured point to form a short circuit so as to compensate the temperature strain errors caused by a lead wire of the strain gauge. The strain value of each strain gauge, which is really caused by stress relief is obtained by standardization and calculation; therefore, the purpose of the present invention is achieved. An error defect caused by environmental temperature in the existing measuring method are overcome, the effect of temperature compensation is improved, and the measuring accuracy and reliability are ensured.

Description

Earth stress measuring method and apparatus with complete temp. compensation

The present invention is a kind of rock mechanics measuring technique, the particularly measuring method of terrestrial stress and device.

The terrestrial stress data is for mining accurately, oil, water conservancy and hydropower, civil construction, railway traffic, underground structure, nuke rubbish stores and the design and the construction of other important Geotechnical Engineerings are absolutely necessary, stress relief method is a kind of earth stress measuring method that generally adopts at present, the Triaxial hole wall strainometer (OSIR Cell) of South Africa Lektratek Instrumentation (Proprietary) Ltd. development, three solid inclusion strainometers (UNSW Cell) that three shaft hollow inclusion strainometers (CSIROCell) of Australian Union's science and industrial research tissue development and University of New South Wales develop be adopt in the world at present the most extensive, the most representative three kinds of geostress survey instruments.They all adopt the principle of stress relieving, use resistance strain gage to measure strain value in the stress relieving process as sensing element, go out stress value in the rock mass by strain value according to relevant formula to calculating then.

Be based on such physical phenomenon with the strain gage testing strain, i.e. strain and resistance variations have quantitative relationship, and Here it is: $\frac{\mathrm{\ΔR}}{R}=K\·\frac{\mathrm{\ΔL}}{L}=\mathrm{K\ϵ}----\left(1\right)$

Wherein ε=△ L/L is resistance strain gage relative length changing value, i.e. strain value; R is the foil gauge initial resistivity value, and △ R is an increased resistance value; K is the foil gauge coefficient, generally equals about 2.As long as measure increased resistance value, can obtain strain value, and can being transformed into change in voltage by resistance bridge, resistance variations measures.Fig. 1 is the resistance bridge schematic diagram. $\mathrm{Vout}=\frac{R_1{R}_3-R_2{R}_4}{(R_1+R_2)(R_3+R_4)}\mathrm{Vin}----\left(2\right)$

R in the formula ₁, R ₂, R ₃, R ₄It is the resistance value of four brachium pontis; Vin and Vout are respectively electric bridge input voltage value and output voltage values.

Work as R ₁=R ₂=R ₃=R ₄The time, Vout=0, electric bridge is in equilibrium state, changes as four arm resistances, increases △ R respectively ₁, △ R ₂, △ R ₃, △ R ₄The time. $\mathrm{Vout}=\frac{\mathrm{Vin}}{4}(\frac{\mathrm{\Δ}{R}_1}{R_1}-\frac{\mathrm{\Δ}{R}_2}{R_2}+\frac{\mathrm{\Δ}{R}_3}{R_3}-\frac{\mathrm{\Δ}{R}_4}{R_4})----\left(3\right)$

In geostress survey, generally adopt 1/4th bridge circuits, it is a brachium pontis that resistance strain gage inserts in this electric bridge, for example inserts R ₁Shown in that brachium pontis, resistance value is generally 120 Ω, when foil gauge was experienced strain, resistance changed, and produced △ R ₁, other three arms R in the electric bridge ₂=R ₃=R ₄=120 Ω are measuring resistance, and theoretically, its resistance does not change, i.e. △ R ₂=△ R ₃=△ R ₄=0, so: $\mathrm{Vout}=\frac{\mathrm{Vin}}{4}\frac{\mathrm{\Δ}{R}_1}{R_1}=\frac{K}{4}\mathrm{Vin\ϵ}----\left(4\right)$

If Vin=4/K, then Vout=ε

The bridge voltage output valve of promptly measuring quantitatively just equals the strain value that resistance strain gage records.

Just strain being converted to resistance variations by formula (1), (3), (4) and resistance bridge converts change in voltage again to and measures and note.

Because resistance strain gage is very responsive to temperature variation, when environment temperature changes, resistance also changes, thereby cause additional temperature strain error, and and then cause the error of results of stress, in order to eliminate the influence of this part temperature strain error, the influence of compensates in other words, existing strainometer all adopts traditional ancillary relief sheet method, promptly in adjacent brachium pontis with foil gauge, i.e. and R among Fig. 1 ₂Shown in that arm, insert one with working strain gauge (R ₁) identical foil gauge, so that during temperature variation, they can produce identical resistance variations, according to formula (3), R ₁, R ₂Same resistance change and will cancel out each other, can not produce additional temperature strain error.The precondition that have to be noted that this compensating action is: when temperature changes, and working strain gauge (R ₁) and dummy gauge (R ₂) strain value or the resistance variations that produce must equate, when yet strainometer is in running order, they all are pasted together with hole wall, so all working foil gauge all directly or indirectly sticks on the rock, foil gauge will be out of shape together with rock mass, and in CSIR Triaxial hole wall strainometer, be as public compensating plate by a unnecessary foil gauge that sticks on the strainometer end.Because compensating plate discord rock is pasted together, so even it is under the identical temperature variation with working strain gauge, deformation values that they produced or increased resistance value also are same anything but, so can not cancel out each other, also just can not play effective compensating action.The solid inclusion strainometer of CSIRO hollow inclusion strainometer and UNSW then adopts resistance strain gage in the electric wire strain gauge or conventional, electric-resistance to make the usefulness of compensation.Because electric wire strain gauge is away from measuring point (working strain gauge position), compensating plate wherein not only can not be pasted together with rock, nor can experience identical temperature variation with working strain gauge; Its compensation effect is very poor.In addition, existing strainometer generally has 9～12 foil gauges, and they are positioned at the different parts and the direction of strainometer.After they sticked on the rock, because inhomogeneity, uncontinuity and the anisotropy of rock, the additional strain value that each foil gauge produces under identical temperature variation also was different.As adopt compensating plate method, each foil gauge that own compensating plate own all should be arranged, and promptly 12 work foil gauges must have 12 dummy gauges, and it also is not all right adopting a public compensating plate.In order to reach effective compensating action, every compensating plate all must be in identical position and direction with working strain gauge, and also is pasted together with rock.And just must experience because the strain that causes of stress relieving once being pasted together with rock, this is unallowed, so in principle, the compensating plate method is the usefulness that is not suitable for the temperature compensation of stress relieving in measuring.Laboratory examination shows, although existing each strainometer has all adopted compensating plate, when temperature variation, still has that additional strain value is measured to come out, simultaneously, because R ₂, R ₃, R ₄Be the foil gauge or the resistance of ordinary temp coefficient, thereby cause measuring error.Caused strain measurement error value when table 1 is 1 ℃ of the temperature variation that draws of laboratory examination.In many cases, the temperature variation in the stress relieving process can reach 3 ℃～5 ℃, because the error that causes of temperature variation can make the geostress survey result cause 50 percent even the above error of several times.

In the table 1, ε ax is axial strain, and ε circ is a circumferential strain, and inc becomes with axix of strain gauge ± strain of 45 ° of directions.(table 1 is seen the literary composition back)

In temperature compensation, also has a problem that caused never that people noted, promptly because the caused additional temp strain of resistance strain gage lead.Calculating shows, 10 meters long leader cables can in every foil gauge, cause about 10 μ ε/℃ temperature strain, in measuring at the scene, cable can be grown about 100 meters sometimes, so since the caused additional temp strain of lead can reach 100 μ/℃.In many cases, the overall strain value that some foil gauge records is hundreds of μ ε only, thereby big like this additional temp strain can not be ignored.

The objective of the invention is to, measure terrestrial stress, overcome the error that environment temperature causes in the existing measuring method, improve the effect of temperature compensation, to guarantee measuring accuracy and reliability with a kind of new complete temperature compensation and the isolated plant of this method.

The present invention measures according to the resistance bridge principle, the objective of the invention is to realize by following method and apparatus.

A kind of earth stress measuring method of complete temperature compensation, it may further comprise the steps:

The 1 strainometer gluing that will be made of several resistance strain gages is at the boring middle part, the resistance strain gage that each measurement strain is used inserts in the resistance bridge, arm as electric bridge, as the R1 brachium pontis among Fig. 1, three brachium pontis of in the electric bridge other all adopt the resistance of ultralow temperature coefficient, its temperature coefficient is 0.5～1ppm/ ℃, to eliminate the additional temp strain that each resistance causes with variation of ambient temperature.

2. with the temperature variation of measuring foil gauge position in the stress relieving process near the temperature-sensing element (device) at resistance strain gage position.

3. draw two unloaded lead short circuits from measuring point, these two leads and foil gauge lead-in wire specification are identical, and draw the temperature strain error that dummy gauge causes by same cable.

4. carry out stress relieving, the strain value that now measures is measured by strain-resistance-voltage conversion device, the measuring point temperature change value is measured by temperature-sensing element (device), and is got off by the data acquisition unit automatically and continuously recording.

5. after stress relieving was measured, the trepanning core was placed in the constant temperature oven of an adjustable temperature together with interior sticking strainometer, carries out temperature-strain rating test.

6. according to the temperature change value in the stress relieving process of the temperature strain rate of each foil gauge of demarcating and record, calculate each foil gauge in the stress relieving process because the caused additional temp strain value of variation of ambient temperature, remove away in the strain value that this additional strain value is recorded from the stress relieving process, it is real because the strain value that stress relieving causes to obtain each foil gauge.

The measurement mechanism of realization said method is made up of strainometer, conversion equipment, data acquisition unit three parts.

Fig. 2 is the measurement mechanism wiring diagram.

Several resistance strain gage R11～1n in the strainometer 2 and n+2 ultralow temperature coefficient low-resistance R41～4n, R2, R3 forms n electric bridge, the right half-bridge R2 of electric bridge, R3 is that each bridge is shared, R11～1n, a R4～left side, 4n place half-bridge is that each bridge is independent, R11～1n is a n foil gauge in the strainometer, each foil gauge one end is a bridging line, the other end is drawn n root line and is connected conversion equipment reception socket 5, the pot 7 that n+2 ultralow temperature coefficient resistance and n 1～2K zeroing usefulness is arranged in the conversion equipment, each potentiometric termination electric bridge, the other end is n and measures the passage positive output end that output voltage signal connects the reception socket 4 of data acquisition unit 3.1 is bridge power supply, and 6 is concentric line, and wherein n equals to constitute the resistance strain gage number of strainometer.

Fig. 3 is the strain gauge structure synoptic diagram.

Several foil gauges are divided into the n/4 group and paste into the strain rosette 2 that each foil gauge intersects, near arbitrary foil gauge position one temperature-sensing element (device) 8 is being installed, draw two unloaded leads 9 from measuring point, in adjacent that brachium pontis with working strain gauge, 10 is cable among the figure in the access electric bridge.

Embodiment:

14 120 Ω low-temperature coefficient resistance have been carried out the temperature calibration test, and test drawing the increased resistance value of 14 resistance when temperature variation, the increased resistance value (seeing Table 2) when wherein △ R is 1 ℃ of a temperature variation

Table 2 120 Ω low-temperature coefficient resistance temperature-resistance change rates

The resistance numbering	??1	??2	??3	??4	??5	??6	??7
								??△R(1×10 -6Ω)	??78	??52	??97	??86	??74	??49	??83
The resistance numbering	??8	??9	??10	??11	??12	??13	??14
								??△R(1×10 -6Ω)	??94	??76	??70	??89	??102	??65	??82

This shows in each electric bridge, R ₂, R ₃, R ₄Its resistance change rate △ R/R (R=120 Ω) is not more than 1 * 10 when temperature variation ^-6/ ℃, thereby each resistance additional temp strain error rate that may cause be not more than 0.5 μ ε/℃, this is negligible.

Be that example is illustrated now with the test in the marble test block.The marble test block is of a size of 300 * 300 * 300mm (see figure 4), and two-way uniform pressure σ X °, σ Y ° is applied by two groups of hydraulic jacks.

Using up the total temperature compensation technique, to carry out the step of stress measurement as follows:

Fig. 4 is a test block stress relieving synoptic diagram.

(1) the two-way homogeneous state of stress is applied in the test block;

(2) beat the aperture that diameter is 38mm at the test block center;

(3) with the strainometer gluing at boring middle part, thereby the three groups of strain rosettes (twelve earthly branches foil gauge) on the strainometer all stick on the hole wall rock thermistor and unloaded compensating wire that this strain is used in respect of the thermometric degree.

(4) with in strainometer lead (comprising two unloaded leads) access strain-resistance-voltage conversion device as shown in Figure 2, the 12 channel voltage output lines of drawing from this device insert the automatic data acquisition device, and the lead of thermistor is also inserted data acquisition unit;

(5) be that the thin drilling bit of 150mm bores concentric macropore with diameter, make aperture around rock break away from sillar, thereby realization stress relieving.Because stress relieving causes boring distortion, each foil gauge promptly observes such distortion, and the strain value that will observe separately by strain-resistance-voltage conversion device by data acquisition unit automatically and continuously recording get off (12 passages write down simultaneously).The measuring point temperature variation is also got off by thermosensitive resistance measurement and by the data acquisition unit continuous recording.

(6) the trepanning core (the still glued 38mm small bore middle part within it of foil gauge) of 145mm diameter is put into the controllable constant-temperature constant humidity cabinet and carry out the temperature calibration test, test findings equally through the intermediate conversion device by the data acquisition unit record, in the hope of each foil gauge because the additional temp rate of strain that causes of temperature variation, according to the temperature change value in calibration result and the stress relieving process that records, can obtain the additional temp strain value that each foil gauge causes owing to temperature variation in the stress relieving process, this part strain value is removed away from the final strain value that records the stress relieving process separately, promptly obtained because the pure strain value that stress relieving causes.

(7) can obtain stress value in the rock mass according to 12 pure strain values calculating.

The stress value that records is compared with the actual stress value that applies, can be judged the accuracy of measurement result, the existing stress result that records is shown in table 3.

Table 3

Temperature compensation	The surveying instrument modified	Measure stress		Stress application
						??σx (MPa)	??σy (MPa)	σx° (MPa)	σy° (MPa)
		Complete technique for temperature compensation	CSIR?Cell	2.59	3.48					2.79	3.29
CSIRO?Cell	3.75					2.81	3.83	2.64
			INSW?cell	3.70	2.74				3.52	2.80

The stress result value of measuring is compared and can be found with the stress application value, use complete technique for temperature compensation of the present invention to survey the stress error all in 10%, such measuring accuracy is complete acceptable, and three kinds of surveying instruments have all been done necessary repacking or improvement according to complete technique for temperature compensation in the table 3.

The earth stress measuring method that uses the total temperature compensation can make measuring accuracy be greatly improved, this is to improving the scientific level of Geotechnical Engineering design and construction, reduce construction investment, increase project benefit, guarantee that engineering safety has extremely important meaning, for a large-scale mine, carry out appropriate design and construction according to terrestrial stress data accurately, the year economic benefit of its increase can reach more than ten million yuan.

The strain measurement error value that table 1 variations in temperature causes

The test block material	Strain measurement error (μ/℃)
										CSIR  Cell			CSIRO  Cell			UNSW  Cell
	ax	inc	circ	ax	inc	circ	ax	inc	circ
										Coal	-15.52	-22.27	-12.65	24.78	28.37	25.45	49.82	44.39	39.58
Sandstone	-11.74	-16.56	-15.38	20.62	21.57	26.18	52.18	50.64	46.06
										Griotte	-14.67	-19.12	-25.93	9.73	19.26	38.48	67.23	54.56	27.67
Concrete 1#	-8.41	-18.84	-22.39	40.21	32.62	25.37	61.94	44.20	31.72
										Concrete 2#	-13.76	-23.40	-16.22	28.66	21. 87	15.32	57.36	47.25	30.07
Cement	-17.86	-14.29	-12.68	34.17	26.53	21.90	54.18	39.32	29.83

Claims (2)

1. the earth stress measuring method of a complete temperature compensation, its steps in sequence is:

A. the strainometer gluing that will be made of several resistance strain gages is at the boring middle part, the resistance strain gage that each measurement strain is used inserts in the resistance bridge, arm as electric bridge, three brachium pontis of in the electric bridge other all adopt the resistance of ultralow temperature coefficient, its temperature coefficient is 0.5～1ppm/ ℃, to eliminate the additional temp strain that each resistance causes with variation of ambient temperature;

B. with the temperature variation of measuring foil gauge position in the stress relieving process near the temperature-sensing element (device) at resistance strain gage position;

C. draw two unloaded lead short circuits from measuring point, these two leads and foil gauge lead-in wire specification are identical, and draw the temperature strain error that dummy gauge causes by same cable;

D. carry out stress relieving, the strain value that now measures is measured by strain-resistance-voltage conversion device, the measuring point temperature change value is measured by temperature-sensing element (device), and is got off by the data acquisition unit automatically and continuously recording;

E. according to the temperature change value in the stress relieving process of the temperature strain rate of each foil gauge of demarcating and record, calculate in the stress relieving process each foil gauge because the caused additional temp strain value of variation of ambient temperature, remove away in the strain value that this additional strain value is recorded from the stress relieving process.

2. the device of the complete temperature compensation earth stress measuring method of employing as claimed in claim 1, comprise strainometer, conversion equipment, data acquisition unit, it is characterized in that: form by several resistance strain gages in the strainometer, near arbitrary foil gauge position being installed by one temperature-sensing element (device), drawing two unloaded leads from measuring point inserts the electric bridges in adjacent that brachium pontis with working strain gauge, each foil gauge one end is a bridging line, the other end is drawn several threads and is connected conversion equipment reception socket, n+2 ultralow temperature coefficient of resistance and n zeroing pot are arranged in the conversion equipment, each pot one termination electric bridge, the other end is n and measures the passage positive output end, connect the reception socket of data acquisition unit, wherein n equals to constitute the resistance strain gage number of strainometer.

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