| Gravity dam is an important dam type,and its height is becoming higher and higher.Up to now the world has 10 gravity dams higher than 200 m.However,cracks are common on concrete gravity dams,especially for the RCC gravity dam,t he RCC la yer it se lf resu lt s in a weak int er face.Although the safety of the gravity dam which less than 200 m is well,it is an important problem whether the crack will be fractured by the hydraulic pressure when the dam's height is higher than 200 m.That has not been considered in the design specifications of gravity dams at home and abroad.Therefore,studying the hydraulic fracturing mechanism and design specification of high concrete gravity dam is of great theoretical significance and engineering application value for dam safety.In this paper,a new hydraulic fracturing test of gravity dam was proposed,and hydraulic fracturing models for gravity dam were established.The design specifications of gravity dams in different countries were compared considering hydraulic fracturing.The main work is as follows:1.A new hydraulic fracturing testing method for concrete single crack was designed.The specimen can be made by embedding a coin type crack in the 150 mm cube specimen or the 450 mm cylinder specimen.The uniaxial tension or compression force can be applied on the specimen,and high-pressure water can be injected into the embedded crack.The experiment was designed based on the stress condition of the upstream surface of the gravity dam,so that it was suitable to simulate the hydraulic fracturing of the gravity dam.A series of hydraulic fracturing tests were carried out on the horizontal and vertical cracks of the dam upstream surface,which revealed the hydraulic fracturing rule of the gravity dam.In the experiment,the author found that the water in the fracture process area enhanced the cohesion of the micro-cracks due to the presence of surface tension of water.This is discovered by comparative tests of hydraulic fracturing and nitrogen fracturing.The author established a hydraulic fracturing model that took into account the surface tension of water,which explained the discovery well.2.Based on the theory of two-dimensional cantilever beam of gravity dam and the theory of nonlinear fracture mechanics of concrete,a model of hydraulic fracturing was established for the horizontal crack at upstream surface of gravity dam.The model was a full-scale equation,and I-II complex fracture,thus it was easy to use for engineers.The influences of dam's cross section,uplift pressure and concrete strength on the hydraulic fracturing of gravity dam heel were studied by this model.3.A hydraulic fracturing model for vertical cracks was established based on the fracture criterion of crack tip opening displacement(CTOD).The vertical stress of the dam body,?,didn't lead to stress singularity at the crack tip,therefore,it was assumed that the tensile strength and the ultimate tensile strain of the concrete could be influenced by ?.And then the relationship of ? and hydraulic fracturing of vertical crack was established.Using this model,the hydraulic fracturing rule of vertical crack of gravity dam heel was studied4.Six gravity dams higher than 200 m at home and abroad were redesigned according to eight different design codes.The hydraulic fracturing model was used to analyze the anti-hydraulic fracturing ability of these dams.The results shown that,sometimes the super high gravity dams designed by current codes were not safe with hydraulic fracturing.It was suggested that the uplift pressure should be considered in the design of high gravity dam and the stress on the dam upstream face should be compressive.5.The author participated in research programs of National Basic Research Program of China(973 Program)and 12th Five-Year Plan:Study on Key Technology of Construction of High Roller Compacted Concrete Dam.Part of the results were used in the design of Huang Deng RCC gravity dam which were still under construction. |
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