CN85100680A - The electric measuring method of Non-Destructive Testing coagulate layer thickness - Google Patents

Abstract

" electric measuring method of Non-Destructive Testing coagulate layer thickness " is to be used for detecting concrete layer, even the thickness of the such thin-lift concrete of shotcrete layer (band reinforcing bar or not with reinforcing bar).It is characterized in that measuring the apparent resistivity ρ s of different depth to the size of the pole span (AO) of its transmitting electrode, determine the thickness of concrete layer by ρ s-AO curve break by changing at concrete surface.For accurately recording ρ s-Ao curve, adopt the fixing electrode system on the top of the shelf of retractable electrode, fixing with the bracket leg top, multi-group electrode is once installed finish and can be with rough, become various angles, crooked concrete surface contact with surface level.

Description

The electric measuring method of Non-Destructive Testing coagulate layer thickness

The present invention is a kind of method that detects thickness, it can not destroy concrete and detect the thickness of concrete or reinforced concrete floor on its surface, be fit to measure the thick concrete layer of 2～150cm, be particularly suitable for the Non-Destructive Testing concrete surface uneven or for curved surface or concrete by the thickness of shotcrete layer in the underground chamber of multiple dielectric surface injustice.

For by multiple concrete layer on scar, soil layer, its thickness of Non-Destructive Testing be a difficult problem for this reason, detect its thickness normally with the way of holing and measuring.For sprayed concrete, also can be before spraying the standard of control jet thickness when fixedly survey pin or other flag things are as construction on scar.At home with the regulation of external relevant design and construction in, all stipulated in concrete brill inspection hole or the method and the quantity of burying survey pin.For example " anchor shoring shotcrete design and construction regulation ", the State Planning Commission of State Infrastructure Commission's promulgation in 1979 were about to " State Standard of the People's Republic of China-anchor shoring shotcrete design and construction and the acceptance specification " of promulgation in 1985, " New Austrian Tunneling Method construction guide " (drafts) that units such as Japan state-owned railway construction office carried out March nineteen eighty-three etc. all are to stipulate like this.According to railway tunnel spray anchor technology rule request, 1 kilometer single-track tunnel shotcrete bolt lining need detect 450 points at least, and double track tunnel then will detect 1300 points

The method that adopts boring directly to measure has been destroyed xoncrete structure itself, and is time-consuming, and in engineering intact man-hour, acceptance feels more that then no matter inconvenience especially when by again or lining cutting when thing such as splash guard is arranged, holes or plug in pricker, does not allow use behind.

So measure its difficulty of concrete thickness with physical method, also because concrete itself is aggregate and the fixed potpourri that forms of hydrated cementitious that is not waited by particle size, reinforcing bar is also often arranged in the xoncrete structure, physical property is extremely inhomogeneous, when bed thickness was thin, this unevenness was more obvious.In addition, basal plane that it is topped and sprayed concrete surface, also often rough and uneven in surface or be curved surface, this brings many difficulties to thickness measuring.So for thin or rough, or contain the concrete layer of reinforcing bar, also do not meet the method for the nondestructive measurement thickness of construction requirement at present.

Task of the present invention is the method that a kind of harmless measurement coagulate layer thickness will be provided, and no matter this concrete is that newly lay or of the remote past, and the still non-reinforced of reinforcing bar arranged, the still thick-layer of thin layer, the surface is smooth or uneven.

Task of the present invention realizes as follows, its principle of first accompanying drawings:

Fig. 1-measurement apparent resistivity method synoptic diagram

The section survey apparent resistivity synoptic diagram of Fig. 2-two-layer dielectric is formed

Fig. 3-electrode synoptic diagram

1-insulator cap 2-contact tube wherein

3-conducting rod 4-conductive rubber cap

The 5-spring

Fig. 4-three-pole device electrode system synoptic diagram

1-insulation fixed mount wherein

2-spring retractable electrode

3-bull socket, each contact conductor all causes socket

Fig. 5-four utmost point device electrode is a synoptic diagram

1-insulation fixed mount wherein

2-spring retractable electrode

3-bull socket, each contact conductor all causes socket

Fig. 6-support and be synoptic diagram with bracket leg top fixed electorde

1-electrode system wherein

2-bull plug

The 3-polycore cable

4～6 supports

The rack leg of the extending shortening of 4-

The Zhi Dingtou of 5-support

6-can make bracket head change the hinge joint joint of a drift angle degree

The ρ that Fig. 7-south mountain tunnel measuring point 5 records _S-AO curve is the plain concrete layer, and electrical measurement thickness 10Cm chisels and measures thickness 9～9.5Cm

The ρ that Fig. 8-Wu Zhuan tunnel measuring point 8 records _S-AO curve, for containing the sprayed concrete of bar-mat reinforcement, electrical measurement thickness 20Cm chisels and measures thickness 19～19.5Cm

At least lay two pairs of electrodes on the surface of intending the survey coagulate layer thickness, a pair of is A, B, uses for passing into electric current; Another is used for measuring the potential difference Δ V between MN to being M, N_MN(see figure 1), after the energising, recording current strength is I, then the apparent resistivity ρ of medium_SFor

ρ _S＝K (△V _{M N})/(I) ……（1）

Wherein

$K\frac{\pi }{(\frac{1}{\mathrm{A\; M}}-\frac{1}{\mathrm{A\; N}}\mathrm{)\; -\; (}\frac{1}{\mathrm{B\; M}}-\frac{1}{\mathrm{B\; N}})}$

If A, B, M, N are point-blank, and are symmetrical in MN mid point O, and AB＞＞MN, then be called four utmost point devices, at this moment

K＝π (AM·AN)/(MN)

This device uses when concrete layer is thin, and measuring accuracy is higher.

If wherein the B point places (BO＞10MN), then be called three-pole device, at this moment at a distance

K＝2π· (AM·AN)/(MN)

Three-pole device is used for concrete layer when thicker, and its measuring accuracy is lower than with four utmost point device persons.

When medium was switched on, the distance of the distance of transmitting electrode or transmitting electrode and MN was big more at dielectric surface, and the degree of depth of then measured apparent resistivity reflection is big more.Change polar distance of supplying power ascendingly and record corresponding apparent resistivity, just can reflect the electric conductivity of different depth in the medium from shallow to deep.

Because concrete resistivity and its resistivity by multiple rock or soil have tangible difference, so its separatrix can be at " ρ _S-AO " reflect on the curve.

In fact, can change the AO size at the scene one by one, record corresponding Δ V _MNAnd electric current I, try to achieve corresponding ρ with formula (1) calculating _S, and draw " ρ _S-AO " curve, curve draws concrete thickness h thus.

For avoiding continuous mobile A, the B electrode, accelerate measuring speed, guarantee accuracy of observation, electrode used therein of the present invention (Fig. 3), be that an end of garden shape conducting rod (3) is put into the contact tube (2) that inside keeps spring (5) and connects power supply, this contact tube (2) internal diameter is greater than conducting rod external diameter 0.1～0.2mm and be fixed on the insulator cap (1), the other end that conducting rod (3) contacts with concrete is installed conductive rubber cap (4), one end of spring (5) and insulator cap (1) offset, its other end then joins with an end of conducting rod (3), so conducting rod (3) can freely stretch in contact tube (2), become retractable electrode (Fig. 3), so that electrode and concrete layer are closely connected.

Fig. 4 and shown in Figure 5 be electrode system figure, they are with a plurality of retractable electrodes (2), according to the required whole spread of electrodes of testing, be fixed on the insulating frame (1) with four utmost point devices and three-pole device form, Figure 5 shows that four utmost point device electrodes system, this be in each electrode spread point-blank, corresponding a pair of A, B electrode are symmetrical in the mid point O of MN electrode; Figure 4 shows that the three-pole device electrode system, each A electrode and M, N electrode spread are point-blank in this electrode system, do not establish the B electrode on the insulating frame, and when measuring a shared B electrode, this electrode places near the measuring point, make BO greater than 10 times AO maximal value, and with conducting medium that the testing concrete layer links to each other in.Each electrode is drawn with polycore cable by bull socket (3), by switch, needs and can connect respectively according to test.(Fig. 6) is by a length-adjustable rack leg (4), by changing the hinge joint joint (6) of direction, connects a support that the Zhi Dingtou (5) of top electrode system (1) is constituted, and electrode system (1) is fixed on the concrete surface.Make electrode grounding resistance surpass the instrument allowed band as if the concrete surface too dry, can spray water in concrete surface.

For avoiding the transmitting electrode polarization, between AB, adopt low frequency ac.

Calculate ρ for asking _S, available various types of transistorized millivoltmeters are measured the potential difference (PD) Δ V between supply current intensity and MN _MNSupporting with the present invention, manufactured and designed direct-reading ρ _SLittle sounder, can shorten Measuring Time.If instrument is equipped with microprocessor, directly print ρ _S-AO curve will make measurement greatly convenient.

Measure the ρ of different transmitting electrode distances _SAfter, with ρ _SWith AO be coordinate, draw ρ _S-AO curve is the decidable coagulate layer thickness then.According to known concrete resistivity and its by complex-rock or soil-resistivity, can find the concrete leading portion curve of reflection easily, its ρ _SApproximate concrete resistivity, and reflect by concrete by the back segment curve of rock cover body, its ρ _SApproximate the resistivity of rock mass.With the curve leading portion to the corresponding AO numerical value of back segment turning point, promptly equal the thickness of concrete layer.If contain bar-mat reinforcement in the concrete, then must make ρ _SThe stage casing ρ of-AO curve _SValue reduces, at this moment by the curve stage casing to the pairing AO numerical value of the turning point of back segment, be the thickness that contains the bar-mat reinforcement concrete layer.

Through consulting foreign data, the Jap.P. spy opens clear 51-39157 " conductive layer thickness determination method " though be that electrode is placed on the method that detects skin depth on the surface of measured object, but measure the method for conductive layer as thin as a wafer, regulation is wanted the etched portions conductive layer, observe electric current then and change required time, or utilize the convex-concave meter, survey conductive layer thickness, so be to belong to destroy to detect, can not be used to measure concrete thickness fully.

Utilize sound wave or ultrasonic reflections to measure the method for concrete thickness, though also belong to Non-Destructive Testing, but it is smooth that it is only applicable to surface measurements at present, it is by the thick concrete layer more than the 30Cm of multiple basic unit-rock or soil layer-also more smooth, for thin layer, shotcrete layer particularly then can not satisfy the needs of engineering.(seeing that it is " the non-damaged research report that detects of Geng Cun Tunnel Engineering concrete quality " of writing that ore deposit, Jiaozhuo institute mines).

In addition, also the someone attempts to measure with the difference of concrete layer and underlying bed resistivity the thickness of highway pavement and bridge deck concrete layer.They have directly quoted the mathematical model that the infinity plane bottom is arranged under even, isotropy conductive layer, the formula that utilizes this mathematical model to derive is measured the thickness of superstratum, and the condition of measurement is bigger highway pavement and the bridge floor of the also more smooth thickness of surfacing, substrate.

For example, deliver in U.S. PB in 1972 report (PB-210245) by Russell, in the test report " Nondestructive Determination of Pavement Thickness using Electrical Resistivity Techniques " (" coming non-destructive determination highway pavement thickness ") of propositions such as James E., introduced relevant test method with resistivity technique.It is to utilize the wire electrode (12 " and 24 " are long) that is provided with in a big wooden frame (60 " * 25 9/16 ") to be placed on the concrete surface of firm pouring, electrode is all contacted with the road surface, traveling electrode position one by one in wooden frame, after measuring the resistivity that the electrode of several different distance obtains, with the electricalresistivity of it and concrete layer ₁, concrete by the electricalresistivity of multiple medium ₂The input robot calculator utilizes in electrically even, isotropy, infinity, is calculated concrete thickness by the formula that mathematical model derived of another different layer of multiple infinitely great planar interface, resistivity under the conducting medium of uniform thickness.The test of quoting in the report is thick 8 " the road surface on carry out.Report is pointed out, their test method is applicable to that substrate can regard infinity plane as, overcoat be electrically evenly, the situation of isotropy, absolute conductive layer, so just can measure accurate result, and be not suitable for the concrete road surface of having solidified to the road surface of firm pouring.For guaranteeing that near last cap rock be the testing precondition of electrical homogeneous isotropism, so adopt wire electrode.But the kind electrode heaviness, requiring has 1～2 foot contacting with the survey concrete surface, so only be applicable on the flat road surface of surfacing.Will constantly change the position of electrode in wooden frame during measurement, use calculation by computer then, this method wastes time and energy, and institute's Thickness Measurement by Microwave can not be thinner than 5Cm.After 1973, do not see the report that further research and use are arranged.Relevant measurement concrete component, lining cutting, also excluded this method in multiple handbook, the standard.

The present invention then is inhomogeneous at thin layer, electric conductivity, and concrete surface is uneven, is curved surface sometimes, its designed by the unequal situation of multiple substrate, its advantage is:

1, directly by the ρ that surveys _S-AO curve break interpretation coagulate layer thickness, and need not utilize the concrete layer electricalresistivity ₁With it by multiple resistivity of media ρ ₂Exact value calculate its thickness, thereby even the electric conductivity of concrete layer is inhomogeneous, anisotropy, concrete resistivity along degree of depth gradual change or concrete resistivity do not detect situations such as accurate numerical value and concrete by multiple dielectric surface injustice, can not influence the employing of this method.

Even variation has taken place in the resistivity of 2 same measuring point concrete layers, so that the ρ of two different times gained _S-AO curve is all or part of not to be overlapped, sentence read result that can influence curve yet.

3, the retractable electrode that has spring that the present invention is designed, make this method not be only applicable to the smooth concrete of test surfaces, and under the situation of or surface curvature rough and uneven in surface at concrete surface, can be closely connected with it because of electrode, still can measure correct relevant data.

4, the electrode system of the present invention's use, comprising the electrode of the required whole spread of electrodes of testing, select the electrode of required usefulness by switch, so once installing, electrode system finishes, can record a series of data rapidly, avoid in rotating detection process traveling electrode repeatedly, thereby accelerate measuring speed, reduce the error of arranging electrode.Simultaneously, allow the testing instrument not near testing point, even put not intervisibility or the also normally testing of conversation difficulty with testing.

5, electrode system used herein is comparatively light, and cooperation can be regulated the support of a length and a conversion drift angle degree, all can install horizontal by the place of various angles at concrete surface, is particularly useful for testing each different parts in the underground chamber.

6, the present invention both can measure the coagulate layer thickness of new perfusion, also can measure the thickness of fixed concrete layer, both can be used for plain concrete, also can be used for reinforced concrete, big can the arriving more than the 1m of test thickness, little can be thinned to 2Cm, and especially measuring thin-lift concrete is its speciality.

Therefore, the present invention is at present unique for practical Non-Destructive Testing thin-lift concrete, the particularly method of sprayed concrete layer thickness, simultaneously, also can measure the thickness than the concrete layer of thick-layer that might measure with sound wave and ultrasonic reflection method.

Illustrate below in conjunction with accompanying drawing:

＜example 1〉south mountain tunnel inducer employing concrete spraying support, detected some places jetting thickness in this Duan Zhongyong the present invention.Wherein, recognize that according to this section geologic map geology belongs to carbonaceous limestone and limestone, on exposed scar, measure its resistivity and be higher than 100 Ω m that the resistivity of spray-up then is lower than 80 Ω m as NO 5 measuring points.

NO 5 measuring points are at the tunnel side wall place, estimate that jetting thickness in 20Cm, adopts four utmost point devices, and adopting four pole spans is MN=1Cm, and AO is respectively 1.5,3.5,4.5 6,8,12,14,20Cm.According to the spray-up surface undulation, with the electrode system horizontal positioned, and make all electrodes all can be closely connected with the spray-up surface, fixing with the bracket leg top.Power to spray-up by A, B with 50 all industrial-frequency alternating currents, measure Δ V with the DA-16 transistorized millivoltmeter _MNAnd I, calculate ρ then _SMeasure the ρ of different AO _SAfter, draw ρ _S-AO curve (Fig. 6).From the curve as can be seen, curve leading portion resistivity is that a section of 30～40 Ω m has reflected spray-up resistivity, one section resistivity that reflects rock of curve back segment 120 Ω m, with the corresponding AO numerical value of turning point that changes to back segment by the curve leading portion be 10Cm, determine that thus jetting thickness is 10Cm.

Chisel the spray-up check subsequently, can be observed its back rock is the carbonaceous limestone, measures the thick 9～9.5Cm of being of spray-up with steel ruler, very close with the electrical measurement result.

＜example 2〉the Wu Zhuan tunnel outlet section, adopt sprayed concrete as preliminary bracing, detected some somes jetting thicknesses with the present invention here, as measuring point 8, learn that according to geologic information this place passes sand shale alternating layers section, contain reinforcing bar in the pneumatically placed concrete.Measure ρ by example 1 described program _SAnd draw ρ _S-AO curve (Fig. 7), because of not clear thickness, so adopt three-pole device employing MN=1Cm, AO is respectively 1.5,2.5,3.5,4.5,6,8,10,14,20,30,40Cm.As seen from the figure.Curve leading portion ρ _SBe about 30 Ω m, reflected the pneumatically placed concrete layer, from AO greater than 2.5Cm after, ρ _SUtmost point sharp fall is low, has reflected the influence of reinforcing bar, curve back segment ρ _SRise to again more than the 10 Ω m, reflected shale, the corresponding AO of turning point that changes to back segment with the curve stage casing is 20Cm, determines that thus jetting thickness is 20Cm.

Chisel the spray-up check subsequently, run into reinforcing bar at the 2.0Cm place, run into aubergine shale through measuring at 19～19.5Cm place with steel ruler, the result is consistent with electrical measurement.

With the present invention the result of 6 tunnel survey jetting thicknesses with chisel thickness that the pneumatically placed concrete layer measures subsequently to such as shown in the subordinate list.In 90 measuring points, 42 of the persons that has the bar-mat reinforcement in the concrete, 48 of no-reinforcing-bar net persons wherein have 1～2 day person in the back of injection for concrete, have after the injection still less than support the survivor in 14 days, and existing 1～2 year person in the back of injection is arranged.Its rock behind has eight kinds.Through check results, have only 2 points to declare mistake, account for 2.7% 1 actual concrete thickness of point and surpass and to require the thickness measured, all the other 87 some electrical measurement thickness h with chisel concrete and measure h ' contrast as a result, use formula

$\mathrm{\sigma \; =\; \pm }\sqrt{\frac{{\mathrm{\sum \; (\; h\; -\; h\; \prime )}}^2}{\mathrm{2\; h}}}$

Calculate meansquaredeviation, then σ=± 0.87Cm.

Claims (2)

1, a kind of electric measuring method of harmless measurement coagulate layer thickness, utilize concrete and it between multiple medium resistivity contrasts is arranged, surface at concrete layer, at least be provided with two pairs with top electrode, a pair of is A, B, is used for low frequency ac is fed concrete, and another is to being M, N, its mid point is O, is used for measuring the potential difference (PD) Δ V of concrete surface MN point-to-point transmission _MNChange the transmitting electrode distance one by one, measure Δ V correspondingly simultaneously _MNWith supply current I, utilize formula ρ s=K Δ V _MN/ I obtains the apparent resistivity ρ s of medium, in the hope of calculating the thickness of concrete layer, it is characterized in that employed electrode is to adopt point contact electrode, the ρ s of different spread of electrodes will be recorded, draw out the ρ s-AO curve of broken line shape, then according to the leading portion of the concrete resistivity of this curve reflection or the stage casing that reflection is influenced by reinforcing bar, to the reflection concrete by the pairing AO of the turning point of the back segment of multiple resistivity of media, the direct method of interpretation coagulate layer thickness.

2, a kind of electrode system of fixed combination, multi-group electrode is assembled on the insulating frame, it is characterized in that a plurality of gardens form point contact electrode, according to the required whole spread of electrodes of testing, be fixed on the insulating frame, constitute electrode system, each electrode is drawn by polycore cable, connects respectively on demand by switch; Electrode is arranged by the form of four utmost point devices or three-pole device, in four utmost point devices each electrode spread point-blank, electrode A, B are symmetrical in the mid point O of MN electrode; Each A electrode and MN electrode spread are not established the B electrode point-blank in the three-pole device on the insulating frame, and when measuring shared one place near the B electrode that links to each other with conducting medium with the testing concrete layer measuring point, and make BO greater than 10 times maximum AO value; No matter use four utmost points or three-pole device, set electrode on insulating frame, its each all is that an end of a garden shape conducting rod is put into the contact tube that inside keeps spring and connects power supply, this contact tube internal diameter is greater than conducting rod external diameter 0.1-0.2mm and be fixed on the insulator cap, the other end that conducting rod contacts with concrete is installed conductive rubber cap, one end and the insulator cap of spring offset, its other end then joins with of conducting rod, conducting rod can freely be stretched in contact tube, become retractable electrode, so that electrode and concrete layer are closely connected.

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