Quality of grouted construction joints at the Krasnoyarsk dam

Abstract

At the Krasnoyarsk hydroelectric plant, during construction of the concrete dam, double grouting of several test-construction outlines of contrac~on-shrinkage joints was carried out [i]. To evaluate the quality of the groutLug, controlholes were drilled* (Fig. 1), cores were removed from the zone of intersection with the joints, and hydraulic tests were performed. A total of 212 m of holes was drilled. During the drilling process it was found that the actual number of intersections with joints (44) amounts to 6890 of the design number (6190 in the construction outlines). This was due to the presence, in certain zones, of heavily shattered cores which made it difficult to establish the point of intersection of the hole with the joint, or to locate the toothing on the opposite side of the joint (with respect to the design).The nature of the core rupture depends on the relation between the strengths of the cement stone filling the joint and of the adjoining concrete, and the bond along the contact surfaces of these materials. In the test outlines, 12 cores were monolithic, 26 failed along the joint, and the remaining cores were shattered. As a rule, all three types of core are ex~acted from any given outline, since the conditions governing the formation and hardening of cement stone over the area of even a single outline are dissimilar.From the results of the core inspections, three characteristic types of concrete surfaces in the joints may be established (Table 1).

Studies on joint grouting stands

“…The degree to which the joints were filled was virtually the same in all stands. A similar pattern (incomplete filling of the joints with the formation of individual channels and streamlets) was also observed in experiments performed by other investigators [3,4], as well as in the surface of cores removed from the joint after its grouting~- [5]. With repeated grouting of a horizontal joint, a dense laminated mortar is formed in it; in this case, its density is virtually independent of the consistency of the injected grout.…”

Basic methods of monitoring and principles of quality assessment for the monolithizing of concrete dams

“…Diamond bits, which ensure better core integrity, are used in the zone where the joint is intersected (0.5 m on both sides of the joint) [3]. No inspection holes are drilled in the vicinity of the thrust face of the dam to avoid damaging the permanent seals of the intersectional joints situated in this zone.…”

“…During monolithizing of the Andizhan dam (Uzbekistan), the transit velocity of ultrasound was increased by an average of 65% after grouting, and a speed of 3.6 km/sec was considered a criterion of quality grouting [9]. In monolithizing the Krasnoyarsk dam, the speed of ultrasound, which had ranged from 2.4 to 3.2 km/sec prior to joint grouting, was increased to 3.6 -4.4 km/sec, and the amplitude by 1.5 -2 times (from 2 -23 to 5 -40 mm) after grouting [3]. Where ultrasonic defectoscopy was not conducted prior to grouting, comparison of the transit speed of ultrasound across a grouted joint with its transit speed through the monolithic concrete in the zone of the grouted joint may serve as an auxiliary criterion for evaluating the quality of grouting.…”