Strengthening the walls of the No. 8 lock of the Moscow Canal by prestressed anchors

Abstract

The scientific-technical conference "Provision of Safety of Hydraulic Structures of Hydroelectric Stations (SHES-94)" (Gidrotekhnicheskoe Stroitel'stvo, No. 2, 1995) focused the attention of the engineering community on problems of the increasing hazards of structures with an age of 30, 40, and more years, where aging processes have occurred and are developing. The resolutions of this conference pointed out the need "to continue developing new technologies of performing repair works with consideration of foreign experience." Of definite interest in connection with this matter is our experience in repair works on the Moscow Canal --one of the oldest hydraulic structures in Russia, the "age" of which is 60 years. Here was used, and on a large scale, a new domestic technology of prestressed anchoring, developed in 1986-1988 by the State Planning, Surveying, and Research Institute (Gidroproekt). Beginning in 1989 it was used by the specialized construction firm Geotekhnika during overhaul of the walls of the No. 8 lock carried out to order of the "Moscow Canal" state enterprise. The consequence of long aging processes of the reinforced-concrete walls of the lock chambers began to appear on this lock, as on many other locks of this canal, already after its 50-year operation (in the 1980s). These processes were expressed in developing cracking of the front and rear faces of the walls, opening of the cracks in excess of the allowable values, occurrence of through cracks (Fig. 1), overstressing of reinforcement, and its intense corrosion. These processes are described in detail for the example of other canal locks in [1, 2, 3, 4], where they occurred more intensely and their consequences occurred earlier. On the No. 8 lock these occurrences were expressed in increasing residual (inelastic) movements of the top of the walls (their tilting) toward the chamber at rates from 1 to 5 ram per year on various wall sections of both the upper and lower chambers (two-chamber lock). With each year these unfavorable occurrences encompassed an ever greater number of sections.To compensate these phenomena and increase the reliability of the walls, starting in 1983 various measures to strengthen them were examined and taken. The primary measures included works to stop the irreversible movements of the top of the walls; repair of their front faces was relegated to secondary measures. Of all possible variants of primary measures, as shown in [4], the most effective was the use of the method of prestressed anchoring of the walls. The method consists, successively, in drilling holes in the reinforced concrete with a depth of about 20 m (Fig. 1); installing in them reinforcing bundles (anchors of type APN-K-1, Fig. 2) consisting of high strength reinforcement of class K-7 assembled in a special way; fastening of the lower part of these reinforcing bundles in the lower part of the holes by injecting cement grout under pressure; tensioning of the bundles with a large force and fastening them in the remaining part of the hole in tension for th...