E X P E R I E N C E IN T H E O P E R A T I O N O F H Y D R A U L I C AND EQUIPMENT OF HYDROELECTRIC STATIONS

STRUCTURES

LONG-TERM SERVICE CHECKING OF THE CONCRETE OF THE CHIRKEY DAM Z. L. Zelenevskii, V. V. Draginich, and G. O. Draginich

UDC 627.825..004.1

The Chirkey concrete duouble-curvature arch dam with a height of 232.5 m (Fig. i) is equipped with a considerable numSer of embedded monitoring and measuring instruments having various purposes. The installed instruments made it possible during construction to rather effectively check the technological process of hardening of the concrete and to provide its high quality in the structure, as well as to objectively judge the stresses in the concrete in the zone of contact with the rock and to check the quality and completeness of consolidation grouting of the banks [i]. The conditions of safe operation of the dam before long required more extensive and more reliable information about the state of the concrete, since the available information did not meet the requirements imposed [2, 3]. First, its reliability was low owing to the fact that one cycle of measurements continued for about 2 weeks, and during this time the effect of external factors on the stress state of the concrete changes considerably (the level of the reservoir, wind, temperture, solar radiation, etc., change). Second, some of the instruments embedded in the concrete failed (natural aging), which made the network of stress-measurement points more sparse and led to a distortion of the picture of the stress state of individual concrete blocks. Traditional methods - drilling of cores with their subsequent testing under laboratory conditions -- could have been used for filling in the picture. However this method of checking is quite labor-intensive and, moreover, does not permit revealing changes in the properties of the concrete in each individually taken block, which is necessary for a more informative and objective analysis of the overall state of concrete in each structural element of the structure. Only nondestructive could become the most acceptable method of inspection, which permits rpeated observations at the same points according to a strictly established scheme and periodicity of the measurements. Objective information'is thereby collected on a change in the physical and mechanical characteristics of concrete with time with considerably smaller labor expenditures compared with the traditional methods. The series-produced ultrasonic apparatus is intended only for through coaxial inspection on bases (distances) between the radiator and receiver up to 3 m, which does not permit using the advantages of nondestructive methods in checking the quality of massive hydrotechnical concrete. Therefore, testing of a method of surface ultrasonic inspection as well as an acoustic method of surface and through coaxial inspection was carried out on the concrete arch dam of the Chirkey hydroelectric station, starting in 1982. Surface ultrasonic inspection was carried out by the series-produced UKB-IM instrument and piezoelectric tansducers with a natural frequency of 60 kHz. As an additional means of inspection to the UKB-IM instrument, an ultrasonic surface detector was specially developed and manufactured. The scheme of the detector is such: to the holder on a strictly fixed base (150 mm) are fastened piezoelectric transducers with a frequency of 60 kHz equipped with removable nozzles (waveguides) of two types -- cylindrical for primarily detection of longitudinal waves and inversely exponential for detecting transverse waves. Dry point contact with the investigated surface is accomplished by means of the nozzles, which in turn increases the productivity of ultrasonic inspection compared with the traditional application on the concrete surface. Since the maximum size of the concrete aggregate of the dam is 80-100 mm, it was decided to conduct surface ultrasonic inspection on a base of 300 mm. To increase the resolution and technological possibilities of nondestructive inspection, Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 3, pp. 39-41, March, 1987.

164

0018-8220/87/2103-0164512.50

O 1987 Plenum Publishing Corporation

TABLE i

Year

mf 1".~'m/ SeC Isec

1982 1983 1984 1984

]4230 14260 [ 4290

1982 1983 1984

4240 4270

Sectmon .Af9l 2610 I 0,241 3,941 2610 I 0,24l 3,951 2650 I 0,24 [ 3,961

,

.L i h

t

1 100,9

Section 2%9 3 2610 [ 0,22[ 2630 ] 0,221

4,25 1,6Ol 43,0 4,26 1,611 43,3 4,27 1,62 ! 43,5 100,5 101,2 t101,1 i

l

"I -~ "I/ ~J=#'gL2"/sec'I/ li~='5'O'/'ec 20

20

l~

fO JO00 ~000 30{20~,m/sec

t e d c

1,59 43,8 1,61 [ 44,0 1,63 ] 44,2

I ,o,. ,o,.1,oo I 100,5 l 102,5

lol,6 ,oi.511oo k_

=.

~d

I~,

$8 48

2000 2390 3&Z~ ~mlsec a.

I /

! =25/0.m/sec =2540m~sec

I#o,=~260m/sec JO / ~'':~"=4270/m/sec

I, a

2000 2 ~

d~O V't,mlsec. b

Fig. 1

Fig. 2

Fig. I. Cross section of the channel section of the Chirkey arch dam: a-k) levels of inspection platforms and service galleries. Fig. 2. Curves of the distribution of the measured values of v o and Vs: M 0) modal values; N) total number of measurements; n) number of~measure ments in a given interval of values; a) section i; b) section 2; 1) 1982; 2) 1983; 3) 1984. simultaneously with the ultrasonic method a new acoustic method of inspection was tested, in particular, with the use of an experimental model of the UK-30MI acoustic measuring complex (instrument). The UK-30MI instrument, realizing the shock wave method, made it possible to conduct surface inspection on bases from 1 to 4 mm and through inspection on bases from 2.25 to 19.3 m (inside the service galleries and between walls of the service galleries and inspection platforms). A comparative analysis of the ultrasonic and acoustic measurements with surface inspection showed their high convergence -- 98.9%. Ultrasonic and acoustic tests were conducted on the walls of the service galleries and inspection platforms of sections Nos. 1 and 3 on a i x 0.5-m grid strictly at the same points and at the same time of the year during 1982-1984, which, in turn, predetermined the equivalent effect of temperature and humidity on the measurement results. Under on-site

165

9 c qm, SPa

./Id i

1

Ed, SPa I

Gd, SPa

!

jt I ! I ,!

X

.I

>

d C

I/ i'

b

~ a

----- Sectionl . . . . Section $ Fig. 3. Distribution of the values of Rcom, M d, Ed, G d over the height of the dam (1984): a-j) levels of measurement points (see Fig. i). conditions the instruments recorded the time of transmission of the longitudinal tp and transverse t s waves. Office processing of the results of the on-site investigations amounted to calculation of the values of the velocities of the longitudinal Vp and transverse v s waves and from them a calculation by the known formulas of the values of the dynamic elast• characteristics: moduli of elasticity E d and shear G d with consideration of the average volume mass of the concrete (according to the data of the construction laboratory of the Chirkey Hydroelectric Station Construction Administration), equal to 2.46 g/cm 3, and Poisson's ratio ~d" Combined ultrasonic and mechanical tests of the concrete were carried out to obtain correlative data for establishing the "velocity--strength" calibration curves. The actual compressive strength of the concrete Rcom was determined at places of ultrasonic surface inspection. Mechanical tests of the concrete were carried out by means of the GPNV-5 instrument and anchor 11-48 by the method of pulling with shearing. From the results of the ultrasonic and mechanical tests the "longitudinal wave velocity--compressive strength of concrete" calibration relation was established, the value of the relative standard deviation of which was 10.6% and the coefficient of effectiveness 6.2. The average values of the strength and dynamic elastic characteristics (Table i) during two years did not have substantial changes, which confirmed the assumptions. The insignificant changes that nevertheless did occur can be referred either to the error of the method or to the insignificant change in the strength and elastic parameters during long service. The relatively short period of observations did not make it possible to reveal the entire picture of changes of the inspected parameters with time. In the future ~it is expedient to conduct such on-site investigations with a periodicity of three years for all sections of the arch dam. A comparison of the inspected parameters obtained in adjacent sections Nos. 1 and 3 indicates some difference in the condition of the concrete of these sections, although the number of physical inspection points for each of the sections is rather large, 1200. The calculated modal values indicate that with the course of time an increase of the values of the propagation velocities of longitudinal and transverse waves and the number of the most frequent values in a percentage ratio to the total number of cases increased (Fig. 2).

166

The character of the change in the average values of the inspected parameters over the height of the dam (Fig. 3) from the crest to the base in sections No. I and 3 makes it possible, starting from an elevation of 220 m, to distinctly trace the increase of all inspected parameters toward the base of the structure, which is related to the technology of its construction (quality and age of the concrete). It was found additionally during the on-site investigations that the propagation of visible cracks in the solid concrete and section joints can be checked more effectively to a considerable depth than by traditional methods, including water-filled cracks on the walls of the service and inspection galleries, as well as the thickness of the destructive layer of concrete in the zone of the variable water level on the upstream side by the known methods [4, 5]. The depth of certain cracks in the slid concrete was up to 40 cm and in the section joints up to 75 cm. The thickness of the destructive layer of concrete was checked at three levels on the upstream side as the reservoir was drawn down and in 1982 was 4 cm with an annual increase of 1 cm. CONCLUSIONS i. The new instruments introduced on the concrete arch dam of the Chirkey hydrostation can be recommended for wide use innondestructive methods of service checking of the state of the concrete ofhydraulic structures when evaluating their reliability and safety. 2. The adopted method of nondestructive testing of the physical and mechanical characteristics of concrete with time objectively reveals their change; it is recommended for on-site investigations of the condition of concrete of all sections of the Chirkey dam.

LITERATURE CITED I. 2. 3. 4. 5.

Z . L . Zelenevskii and N. I. Chalyi, "First results of operation of the Chirkey arch dam," Gidrotekh. Stooit., No. 12, 5-10 (1981). A . N . Marchuk, Static Work of Concrete Dams [in Russian], ~nergoatomizdat, Moscow (1983), p. 208. V. S% Serkov, "Increasing the effectiveness of monitoring hydraulic structures of electric power stations," Gidrotekh. Stoit., No. 7, 8-11 (1980). G. Ya. Pochtovik, V. G. Lipnik, and A. M. Filonidov, Ultrasonic Flaw Detection in Power Construction [in Russian], ~nergiya, Moscow (1977). V . S . Yamshchikov and M. L. Nisnevich, Quality Control at Nonmetallic Construction Materials Enterprises [in Russian], Stroiizdat, Leningrad (1981).

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