Application of Ultrasonic Technology in Highway Tunnel Inspection
Abstract This paper studies the problem that the traditional method is not easy to detect the lining concrete of highway tunnels. According to the correlation between the ultrasonic longitudinal wave wave velocity in cement concrete and concrete strength, the strength measurement is discussed. In the end, the method of non-destructive testing was mainly used, and the method of secondary testing was used to carry out actual inspections of highway tunnels and achieved the expected results. It provides a reference for the detection of highway tunnels and related structures.
With the use of the country's western development strategy, highways as an important infrastructure have become increasingly important to ensure their smooth progress. The main framework for highway traffic construction in the west is the construction of highway tunnels. Compared with railway tunnels, highway tunnels require more and more specific requirements. With the construction and opening of a large number of highway tunnels, can traditional inspection methods be carried out? Tunnel structure inspection has become a new topic. For example, when the strength test of the lining concrete in the tunnel is performed according to the traditional damage detection method, it will cause irreparable damage to the tunnel structure; at the same time, it cannot guarantee the minimum number of samples required for evaluation, indicating that the traditional damage detection method It can no longer be used to detect the strength of the tunnel lining. Therefore, this paper researches on the strength testing of tunnel lining concrete.
1. Brief introduction of sound wave detection principle:
As we all know, the mechanical properties of concrete are closely related to the propagation law of sound waves, which is the physical prerequisite for the measurement of sound wave detection mechanical parameters. Acoustic wave testing is one of the elastic wave testing methods, and its theoretical basis is based on the theory of elastic wave propagation in solid media. This method is to emit sound waves to the medium (concrete structure) by artificial excitation, accept sound waves modulated by the physical properties of the medium at a certain spatial distance, and observe and analyze the acoustic wave propagation speed, amplitude, frequency, etc. Parameters to solve related problems in the project. The biggest advantage of this method is that it is simple, fast, economical, and easy to repeat the test, and it has no damage to the test object.
For cement concrete, its mechanical properties are also closely related to wave speed. Generally speaking, the higher the strength of concrete, the higher the corresponding wave speed. Since the second lining concrete in the tunnel to be tested has basically the same strength grade (mostly C20 strength grade concrete) and the density value is relatively close, it can be considered that there is a proportional relationship between strength and wave velocity. However, there are also certain problems in measuring the strength of concrete by wave speed alone. Because no damage detection is based on the correlation between the two, during the specific test process, the test results are also affected by the following factors:
Lateral size effect (requires longitudinal wave velocity to be measured in an infinite medium.); Temperature and humidity (when the ambient temperature is between 5 and 30 ° C, the velocity decreases due to temperature increase. When the ambient temperature is at 40 When the temperature is between ～ 60 ℃, the speed is reduced by 5%. When the temperature is below 0 ℃, the free water of the concrete freezes, which increases the pulse speed. 1.9 times); the effect of aggregate type, particle size, and content (the propagation speed of ultrasonic waves in aggregate is higher than the speed in concrete. Therefore, there are more coarse aggregates on the soundtrack road, and the speed of sound is higher, and vice versa); As the water-cement ratio and the amount of cement are reduced, as the water-cement ratio decreases, the strength, compactness, and elastic properties of the concrete increase accordingly, and vice versa.
Second, the treatment method It can be seen from the above that the test results are affected by many factors, so how to eliminate these effects is very important for the use of this method for related detection. At present, at home and abroad, a number of concrete specimens with the same technical conditions must be used for calibration experiments in the procedures, methods, and recommendations of ultrasonic testing of concrete strength, that is, to establish a strength calibration curve in advance, and then use the speed of sound to estimate the strength of the concrete. In order to achieve a more satisfactory accuracy. The method is suitable for detecting the strength of concrete products under the same technical conditions as the test piece, and the test accuracy is high. And because the test pieces made of the same material are used, there are no influencing factors when estimating the concrete strength, so there is no need to modify the test results. (1)
The process of analyzing and processing the sound speed test data in the indoor test is as follows;
First determine the speed of sound and calculate it using Equation 1:
v = l ÷ t × 10 (km / h) (Formula 1)
Among them: v—wave speed of ultrasonic wave in concrete medium (km / h)
l—The test distance of the receiving and sending transducer, the width of the test piece (cm) during indoor testing
t—the average sound time value of the measuring area (test piece) (unit: μs)
When the acoustic time deviation from the individual points in the test exceeds 5%, the test piece is invalid.
In addition, the ultimate compressive strength of the test piece is calculated according to formula 2:
Fmax = F / A * k (Formula 2)
In the formula: Fmax-ultimate load (Kn)
A—Pressure area of ​​test piece (cm2)
k—coefficient of sample size conversion (standard part is 15 × 15cm)
In the test, three test pieces are used as a group. The data processing principle is the same as the concrete strength test processing principle. The maximum or minimum value is compared with the intermediate value to see if the deviation exceeds 15%. (2)
Therefore, in the actual inspection, the same material and mix ratio should be used to prepare the concrete of the same strength grade for the tunnel to be inspected. On this basis, the wave velocity value of the second liner concrete was actually measured. Draw the wave speed curve of each tunnel, and find out the wave speed and mileage of unfavorable road sections. Evaluate its strength. For some necessary retest points, re-test or actually take cores on site to measure the strength.
3. Examples:
A highway tunnel, with a total length of 1.060 kilometers, was completed in 2000. The design strength grade of the lining concrete is C20 concrete. Before the actual test, the cement concrete specimen (15 × 15cm cube specimen) was formed with the same material as the tunnel construction. The standard curing time was 28 days. The strength and corresponding wave velocity were measured indoors The relationship curve between intensity and wave speed is shown in Table 1.
Table 1 Summary table of the relationship between concrete strength and wave velocity
1 15 * 15 3 5.7 3448.0 39.5
2 15 * 15 3 4.5 3333.0 38.6
3 15 * 15 3 5.8 3333.0 39.3
4 15 * 15 3 4.6 3000.0 35.9
5 15 * 15 3 5.8 3846.0 43.9
6 15 * 15 3 4.7 3846.0 44.8
7 15 * 15 3 6.1 3571.0 40.7
8 15 * 15 3 4.5 3333.0 45.9
9 15 * 15 3 3.9 3448.0 41.2
10 15 * 15 3 6.0 3571.0 39.5
11 15 * 15 3 5.5 2857.0 30.2
12 15 * 15 3 4.9 3333.0 40.8
On the basis of establishing the relationship curve, the actual testing of related projects was carried out in the same year. The actual measured data of a tunnel is shown in Table 2.
Table 2 Summary table of ultrasonic inspection results of a tunnel
Left vault Right side Left vault Right 1 k183 + 949 20 61.0 59.0 62.0 3278.7 3389.8 3225.8
2 990 20 62.0 62.0 56.0 3225.8 3225.8 3571.4
3 k184 + 030 20 59.0 56.0 55.0 3389.8 3571.4 3636.4
4 70 20 55.0 60.0 58.0 3636.4 3333.3 3448.3
5 110 20 54.0 59.0 58.0 3703.7 3389.8 3448.3
6 150 20 53.0 55.0 56.0 3773.6 3636.4 3571.4
7 190 20 54.0 56.0 58.0 3703.7 3571.4 3448.3
8 230 20 54.0 55.0 61.0 3703.7 3636.4 3278.7
9 270 20 54.0 56.0 55.0 3703.7 3571.4 3636.4
10 310 20 55.0 55.0 53.0 3636.4 3636.4 3773.6
11 350 20 53.0 54.0 58.0 3773.6 3703.7 3448.3
12 390 20 54.0 55.0 55.0 3703.7 3636.4 3636.4
13 430 20 56.0 56.0 53.0 3571.4 3571.4 3773.6
14 470 20 53.0 53.0 52.0 3773.6 3773.6 3846.2
15 510 20 57.0 55.0 56.0 3508.8 3636.4 3571.4
16 550 20 60.0 57.0 54.0 3333.3 3508.8 3703.7
17 590 20 54.0 54.0 60.0 3703.7 3703.7 3333.3
18 630 20 58.0 54.0 61.0 3448.3 3703.7 3278.7
19 670 20 55.0 55.0 59.0 3636.4 3636.4 3389.8
20 690 20 54.0 59.0 55.0 3703.7 3389.8 3636.4
21 730 20 59.0 59.0 58.0 3389.8 3389.8 3448.3
22 770 20 57.0 60.0 58.0 3508.8 3333.3 3448.3
23 810 20 50.0 55.0 52.0 4000.0 3636.4 3846.2
24 850 20 56.0 54.0 53.0 3571.4 3703.7 3773.6
25 890 20 52.0 55.0 53.0 3846.2 3636.4 3773.6
26 930 20 61.0 54.0 60.0 3278.7 3703.7 3333.3
27 970 20 63.0 55.0 59.0 3174.6 3636.4 3389.8
28 k185 + 010 20 62.0 66.0 58.0 3225.8 3030.3 3448.3
The regression curve determined indoors and the wave velocity value measured outdoors determine the corresponding value between the measured wave velocity and intensity, as shown in Table 3 for details.
Table 3 List of wave speed-strength test results No. Pile No. Wave speed (m / s) Strength (MPa)
Left vault Right side Left vault Right 1 k183 + 949 3278.7 3389.8 3225.8 37.5 38.9 36.9
2 +990 3225.8 3225.8 3571.4 36.9 36.9 41.1
3 k184 + 030 3389.8 3571.4 3636.4 38.9 41.1 41.9
4 +70 3636.4 3333.3 3448.3 41.9 38.2 39.6
5 +110 3703.7 3389.8 3448.3 42.7 38.9 39.6
6 +150 3773.6 3636.4 3571.4 43.6 41.9 41.1
7 +190 3703.7 3571.4 3448.3 42.7 41.1 39.6
8 +230 3703.7 3636.4 3278.7 42.7 41.9 37.5
9 +270 3703.7 3571.4 3636.4 42.7 41.1 41.9
10 +310 3636.4 3636.4 3773.6 41.9 41.9 43.6
11 +350 3773.6 3703.7 3448.3 43.6 42.7 39.6
12 +390 3703.7 3636.4 3636.4 42.7 41.9 41.9
13 +430 3571.4 3571.4 3773.6 41.1 41.1 43.6
14 +470 3773.6 3773.6 3846.2 43.6 43.6 44.5
15 +510 3508.8 3636.4 3571.4 40.3 41.9 41.1
16 +550 3333.3 3508.8 3703.7 38.2 40.3 42.7
17 +590 3703.7 3703.7 3333.3 42.7 42.7 38.2
18 +630 3448.3 3703.7 3278.7 39.6 42.7 37.5
19 +670 3636.4 3636.4 3389.8 41.9 41.9 38.9
20 +690 3703.7 3389.8 3636.4 42.7 38.9 41.9
21 +730 3389.8 3389.8 3448.3 38.9 38.9 39.6
22 +770 3508.8 3333.3 3448.3 40.3 38.2 39.6
23 +810 4000 3636.4 3846.2 46.3 41.9 44.5
24 +850 3571.4 3703.7 3773.6 41.1 42.7 43.6
25 +890 3846.2 3636.4 3773.6 44.5 41.9 43.6
26 +930 3278.7 3703.7 3333.3 37.5 42.7 38.2
27 +970 3174.6 3636.4 3389.8 36.3 41.9 38.9
28 k185 + 010 3225.8 3030.3 3448.3 36.9 34.5 39.6
Table 4 Test results of lining concrete strength
Average value of strength (MPa) Standard deviation (MPa) Coefficient of variation (%) Minimum value of tunnel strength Maximum value of tunnel strength (MPa) Pile strength at measuring point (MPa) Pile number at measuring point 40.9 2.72 6.65 34.5 28 k185 + 010 46.3 23 k184 + 810
The conclusion of the test data is shown in Table 4. The results show that the strength of the tunnel lining concrete has reached the design C20 strength level.
The strength of concrete structures in tunnels can be accurately determined by the combination of non-destructive detection and damage detection technology. This method has the advantages that traditional testing methods cannot compare with, so it is worthy of popularization and application in highway inspections .
References 1. Non-destructive testing technology for concrete National Construction Engineering Quality Supervision and Inspection Center China Building Materials Press 1996
2. Highway engineering cement concrete test specification (JTJ053-94)
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