In 1976-1977 the Moscow Land Recl-m~tion Institute carried out model investigations of the seismic stability of a dam having a lightweight profile (Fig. i) developed with respect to the conditions at the Kurpsa hydrostatlon [1]. The height of the dam is 126 m and the ratio of base width to height is 0.514. The design of the dam allows tensile stresses inward from the upstream face and opening of horizontal construction joints even under the design static loads. In this case it is assumed that the bearing capacity of the dam is determined by the strength of the concrete in the compressed zone and loss of bearing capacity occurs as a result of shear along one horizontal section (probably in the plane of the construction joint), which is accompanied by failure of the compressed zone of the downstream face of the dam.The investigations consisted in determining the maximum seismic load leading to loss of bearing capacity of the dam and the form of its failure. It was assumed that the presens wldely used linear elastic setup of model investigations with reproduction of only the elastic characteristics of the concrete in conformity with the Cauchy criterion is insufficient. It was necessary to maintain slmilarlty of both the elastic and inertial seismic forces and of the stress state in the dam under the effect of the main static loads --the dam's own weight and the hydrostatic pressure. The problem was complicated further by the fact that in the experiments the model had to be brought to failure, i.e., it was necessary to reproduce similarity of the strength characteristics of concrete and the model material and the shear characteristics of the construction joints in the dam.This problem can be solved with the use of known brittle materials with sufficiently high moduli of elasticity and a relationship of the compressive and tensile strengths close to that for concrete [2] in a fleld of centrifugal forces (on a centrifuge) or in the natural gravitational field. In the latter case the problem of modeling seismic effects and recording the parameters of the model during experiments is greatly simplified, but it is necessary to develop special materials with very low strength characteristics.Taking into account the virtues of the latter method, we decided to investigate the seismic stability of the Kurpsa dam in a natural gravitational field. The experiments were conducted on a model made of special material [3] at a scale of 1:200 with reproduction of seven horlzontal constructlon joints and the Joint along the concrete--rock contact, and also on four monolithic models.The physical and mechanical characteristics of the model material are presented in Table i. The material was made from a plaster binder (P) with fillers in the form of limestone powder (L) and rubber crumbs (R). Lead powder (Pb) was used as the weighting substance. Mineral oil AK-10 (M) was used for neutralizing the binding properties of the lead powder [&] for the purpose of reducing the modulus of elasticity and tensile strength of the model material. Th...
No abstract
Roundhead buttress dams, being one of the economic types of lightweight concrete dams, are often constructed in regions with high seismic activity. Despite the fact that many studies in the USSR and abroad (for example. [1][2][3][4][5][6]) are devoted to an investigation of the seismic stability of these structures, the elaboration of such problems as the effect of the three-dimensional behavior of the dam, yielding of the foundation, character of the seismic load, and. finally, the construction characteristics of a particular type of dam in relation to its seismic stability is far from complete.It is necessary to note that the existing methods of investigation [2,3,4,7] do not permit a complete consideration of the entire set of factors affecting the behavior of dams under dynamic loads. We used an experimental method of investigation on physical models which permits taking into consideration the characteristics of the work of the complex structure of high concrete dams.The experiments were of a dam with a height of 100 m and section width of 25.6 m ( Fig. 1) made on models to a scale of 1 : 200 under conditions of an empty reservoir. The seismic load was simulated as the magnitudes of reduced seismic accelerations WI = ktg and reproduced in two forms: seismic shock of forward direction(type I load) y=A for t<0,reproduced by means of a seismic platform equipped with an instantaneous-action hydraulic disrupter, and a seismic load of the traveling-wave type (type!I load) propagating in the mass of the model foundation with the shock assigned on its free surface. The accelerogram of this load, recorded at a point near the base of the model buttress, and its spectrum are given in Fig. 2a.
The K/rovsk dam, about 80 m high, was constructed in the Kirgiz SSR, on the Talas River [i]. The construction site is characterized by seismlcity of magnitude 8 (Ks= 0.05). The dam (massive-buttress, 253 m in crest length) consists of i0 sections, 22 m wide each with a buttress wall thickness of 12 m, and of two bank gravity abutments. The dam foundation consists of interbedded packs of stratified sandstones, massive sandstones, and shales with a dip of 85 ~ toward the downstream side. The modulus of deformability in the direction of action of the resultants of all forces is 2.10 s kg/cm= (20 GPa) for the stratified sandstones, and i'I0 s kg/cm= (i0 GPa) for the other rocks.The investigation of the stress--straln state of the dam under seismic action and of the constructional measures for ensuring its earthquake resistance was carried out on models made to scale 1:150, which reproduced three and six dam sections and a piece of the stratified foundation. The direction of the seismic action was assumed to occur along the dam axis as well as along the flow. A schematic of one of the models is shown in Fig. 1.The seismic load was simulated according to the values of the equivalent seismic accelerations, with the aid of a seismic platform operating in the stralght-direction seismic shock
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