The data in the present paper are the results of the initial phase of the program of integrated survey of the state and operating conditions of power conduits ferroconcrete shells at the Krasnoyarsk Hydroelectric Station (HES). The program is oriented to improving the reliability of conduit shells and extending their safe service period. The structures at the Krasnoyarsk HES have been in service for over 30 years, therefore, the problem of estimating the physicomechanical parameters of concrete used in the conduit shells is rather urgent.It has been noted in [1] that there is an extended network of cracks on the outer surface of the ferroconcrete shells of power conduits at the Krasnoyarsk HES. The hydrostation design, as well as the current regulatory documents consider the formation of cracks in ferroconcrete shells virtually inevitable and admit this phenomenon, however, the guidelines [2] limit the maximum crack opening to 0.3 mm, which is dictated by the need to prevent corrosion of ferroconcrete reinforcement. During the construction of conduits at the Krasnoyarsk HEC no attempts were made to prevent the initiation of cracks or decrease their opening by observing a certain sequence of technological operations. The temperature-shrinkage cracks originated in the conduit shells in power unit number eight (the prototype one) already during the construction; after the conduits were filled with water, tensile stresses increased the opening of existing cracks and some new ones were formed. The opening of some cracks exceeds the permissible values and reaches 0.7 -0.8 mm. Some cracks have leakage of ceramic stone leaching products. This points to the undesirable processes of chemical corrosion and removal of the binder from the facing concrete. In some cases brown-shade deposits are found, which may indicate the corrosion of the reinforcement.In summer of 2003 cores were taken from ferroconcrete shells of power conduits of hydroelectric power unit number eight. The core diameter was 94 mm, One core was drilled out from a shell site free of cracks and the other three from cracked sites. The boreholes were drilled in the direction perpendicular to the outer faces of the conduits. The length of each core is up to 143 cm, which is slightly less than the shell thickness amounting to 150 cm. Each drilled out core consists of at least four sectors of length up to 40 cm.Our research had two purposes: identifying the depth of crack propagation in the concrete shell and taking samples to determine the strength and deformation parameters of concrete. The assumption of cracks extending from the outer shell surface to the metal casing of the conduits was fully corroborated. Drilling out cores has established that the position of longitudinal cracks on conduits is determined by their reinforcement scheme. The stress concentrators in the formation of these crack are angles 75´75´7 installed along the conduits above the exterior circular reinforcement.The visual inspection of the cores indicates that concrete has a mixed compositi...
The specifications SNiP 11-54-77 and SNiP 11-56-77 when designing concrete dams recommend, along with other factors, taking into account swelling of concrete in the zone of the upstream face. However, these recommendationsare seldom used in dam designs in connection with an insufficient study of the givenproblem. Heretofore swelling of concrete was investigated only under laboratory conditions. The investigations conducted at the B. E. Vedeneev All-Union Scientlfic-Research Institute o~ Hydraulic Engineering (VNIIG) showed that additional compressive stresses reaching S ~MPa can occur from swelling of concrete of the upstream face of the dam, which can have a substantial effect on the static work of the entire structure [I], Observations of the stress--strain state of gravity dams shows that during filling of the reservoir, compressive stresses exceeding by 1.5-2 MPa the stresses calculated with consideration of the weight of the concrete, hydrostatic load, and temperature effects are noted at the upstream face [2~ In the author's opinion these additional compressive stresses in the structure occurred due to swelling of concrete. However, in connection with the fact that several factors affect the work of a dam, it has not been possible so far to isolate and estimate quantitatively molsture-lnduced stresses, which is related to the absence of data on a change in the moisture content of concrete in a structure.The Siberian Branch of VNIIG has developed apparatus for remote measurements of the moisture content of concrete in structures based on a thermophysical method. Tests of the apparatus conducted on concrete of various compositions showed that the thermophysical method can be used for determining moisture changes in concrete caused by external effects of moisture, in which case the maximum error of measurements was 0.3% [3].The apparatus based on the thermophysical method is rather simple, but, as investigations showed, the method does not permit determining changes in the moisture content of concrete during its intense structural formation. When dams are put into temporary operation at intermediate heads the concrete is often under water soon afterlts placement in the block. The use in this case of the thermophysical method becomes difficult, and therefore investigations of the relation between moisture content and the dielectric constant of concrete were conducte@ and apparatus based on the "dielcometric" method was developed. Laboratory tests showed that it is expedient to calibrate a moisture gauge on concrete of the investigated structure~ Thus, for the concrete being placed in the Sayano-Shushenskoe dam the maximum error of measuring the moisture content was 0.32% and the standard deviation was 0.04%[41.Moisture-induced stresses in a dam can be determined from the results of on-site investigations of the moisture content of concrete.For approximate calculations a concrete dam can be regarded as a free wall, one side face of which is in contact with water. In this case, at any point located at distance x ...
Results of inspections of a concrete dam are presented.The massive-buttress dam retaining the Kirovsk Reservoir on the Talas River (Kyrgyzstan) was built in 1975 in accordance with a design developed by the "Kirgizgiprovodkhoz" Institute [1]. The dam is 84 m high, and has a crest length of 260 m, concrete volume of 310,000 m 3 , and a triangular profile with the thrust and downstream faces sloped at 0.45. The lower portion of the downstream face is at a greater incline (m = 0.70). The dam is divided by expansioncontraction and settlement joints into sections 22 m wide. Each channel section consists of a massive support haunch 22 m wide and a buttress 12 m wide, and a downstream haunch with a wall thickness of 4.5 m. Closed recesses 10 m wide are formed between the buttresses. The upstream haunches from the thrust face are curvilinear in plan with a radius of 28.1 m; this eliminates bending of the haunch in the cantilevered sections. Effective discharge ports are situated at elevation 832.0 m in sections 5 and 6. At its inlet, a port has a rectangular 3 × 4-mm section, which transitions to a circular section with a diameter of 2.2 m. The flow rate of water is regulated by conical gates. A surface spillway with a threshold at elevation 881.5 m is designed to draw down excess water in section 7 during a flood (Fig. 1).Two passageways 3 m wide and 3.5 high were specified at elevation 822.0 and 845.5 m for inspection of the internal surfaces of the concrete of the thrust haunches and buttresses, and also for observations of monitoring and measuring equipment. The passageway at elevation 822.0 m permits communication between channel recesses, and maintenance of equipment. The passageway at 845.5 m runs through the buttresses, and cuts into the bank. For open communication along the passageways, metallic bridges are established in the recesses. Metallic staircases and platforms, which provide for communication between the passageways are installed at various elevations and approaches to water levels.In conformity with the design, the dam was partitioned into three concreting zones, depending on the conditions under which the concrete was to function. The sections from the rock bed to elevation 836.0 m, and also the thrust haunches over their entire height were constructed of M250, R18, V8, and Mrz200 concretes. The buttresses and downyarsk Division of the JSC "Sibirskii Énergeticheskii Nauchno-Tekhnicheskii Tsentr," Krasnoyarsk, Russia. 886.5 (Normal backwater level) 888.5 832.0 815.0 836.0 822.0 845.5 m = 0 .4 5 m = 0 .4 5 77.0 1 1 Fig. 1. Section of dam through intersectional joint.
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