Seismic stability of the Toktogul dam

Abstract

The Toktogul hydrodevelopment is being constructed in a zone of high seismic activity, in designing the dam an earthquake with an intensity of 9 with verification for i0 was adopted as the design seismic load [i, 2].In consideration of the extremely high intensity of the seismic load, the uniqueness of the structure, and the increased requirements imposed on the reliability of the hydrodevelopment, a cycle of experimental and theoretical investigations for substantiation of the seismic stability of the dam was carried out in the research department of the All-Union Planning, Surveying, and Scientific-Research Institute (Gidroproekt).* Numerical investigations of the stresses and strains in the dam were conducted on orders of the research department of Gidroproekt at the Institute of Hydromechanics, Academy of Sciences of the Ukrainian SSR, under the supervision of Doctor of Technical Sciences L. I. Dyatlovitskii; model investigations of the stress state of a dam sectioned by contraction joints were carried out on orders of the research department of Gidroproekt at the department of hydraulic structures of the Moscow Institute of Engineering Reclamation under the supervision of Doctor of Technical Sciences N. P. Rozanov. EVALUATION OF SEISMIC LOADSComputations of the seismic loads for large hydraulic structures are based on the selection or construction of a representative seismogram characterizing the displacement or other kinematic characteristic (velocity, acceleration) of the motion of an arbitrary horizontal surface of the earth at the structure site.The analog accelerogram a(t) of the Yurek earthquake (Fig. i), selected and transformed on the basis of seismogeological and geophysical characteristics in conformity with the method developed at Gidroproekt, was used as the initial seismologic information in investigations to evaluate the seismic stability of specific design variants of the Toktogul dam. This seismogram is referred to an arbitrary horizontal surface.The effect of the relief and presence of the hydrodevelopment structure and reservoir was studied on a three-dimensional elastic model with a linear scale of 1:4000, which reproduced the main geophysical characteristics of the region, encompassing a zone with an area 6 x 6 km to a depth of 4 km from the surface.The method of such investigations is known [3,4], but practical testing of a three-dimensional model of such scale was apparently performed here for the first time.The investigations were carried out for the following states of the canyon: without the dam, with the dam, and with water in the reservoir.Three-component piezoelectric receivers measuring 3 x 2 x 3 mm recorded the vibrations of the model at a height to 2H (H is the height of the dam) from the bottom of the river.The seismic load was assigned successively in the following directions:vertically from below under the dam; horizontally from the right flank; at an angle of 45 ~ to the horizontal from the reservoir.The following premises were used on converting the accelerograms from mode...

Investigation of the seismic stability of a lightweight concrete gravity dam

“…4. The overturning resistance of dam rocks served by horizontal cracks is not determining in evaluating the seismic stability of the structure when it is represented in the form of a system of rigid!blocks.…”

“…The results obtained, the character of damage to the Koyna dam and the results of investigating the seismic stability of the Kolkewadi gravity dam in India [8] and Toktogul dam [4] carried out on strength models show that the seismic stability of a concrete gravity dam is determined by the strength of its upper part and strength of the foundation.…”

“…The condition of such approximate similarity is a small change in the quantity D = /I'~ + k~ in the investigated regions of the dam M==Mb (4) Since Eqs. (3) or (4) should be fulfilled at all times, the static and dynamic stresses should, strictly speaking, be reproduced to the same scale.…”

“…The scale of accelerations was determined on the basis of the condition of similarity of the forces of inertia and weight, which are most essential in this problem, and the time scale on the basis of an examination of the movement of perfectly rigid bodies [4]. The relative vertical and horizontal movements of the dam blocks and accelerations of the dam foundation and crest were recorded on the model.…”

“…The time scale, which when modeling elastic vibrations can be selected comparatively freely (just from the condition of preserving in the prototype and model the relationship between the characteristic natural frequency of the structure and frequency of the action [4]), is selected with great limitations when modeling failure processes. (3) or (4) pertain only to the dynamic components, the static components being disregarded.…”