| The security and durability is particularly important for high arch dam, because of its great height and large storage capacity, it has significant economic and social benefits. The operation monitoring data, computational analysis and model tests of many high arch dams at home and abroad showed that, the concrete in high arch dam heel part are very prone to cracking during the construction period and operation period, high-pressure reservoir water will enter into the cracks and lead to hydraulic fracturing and a variety of secondary disasters, then endangering dam’s safety. To avoid the occurrence of such a situation, it is extremely necessary to strengthen the protection of anti-seepage treatment in the heel area of high arch dams. As a new protection technology, there are many advantages for spray polyurea elastomer technology, such as green protection, good protection properties and advanced construction technology and so on, so be widely used in the civil engineering structures. In Water Resources and Hydropower Engineerings, spray polyurea elastomer have been mainly used in anti-abrasion protection of the concrete surface in the sluice, spillway and other parts, however, its application in anti-seepage treatment of high arch dam heel is still in infancy, both of key properties and construction methods of laying are lack of reliable theoretical supporting. To better understand the properties of spray polyurea elastomer applied to the anti-seepage treatment in high arch dam heel, in this paper, some key properties of it were tested, and to determinate its resistance to water pressure breakdown property, some simulation tests were carried out on a coating resistant to water pressure test device which is self-designed and produced. Using finite element calculation to numerically simulate the simulation tests, then the resistance to water pressure breakdown property was proved from the union of tests and numerical calculation data. Finally, combined with project examples, construction methods of laying were analyzed.(1) The tensile properties of polyurea elastomer material was tested, stress-strain curve, the tensile strength, breaking elongation, thickness-elongation relationship are measured. In the case of uniaxial stretching, the elastic stage of polyurea is between0to0.1, corresponding to an elastic modulus of about50MPa, after the elastic stage, the tensile behavior shows nonlinear deformation. The polyurea tensile strength greater than22MPa, the elongation at break greater than450%. Polyurea thickness increases with the elongation decreases, the rate of decrease slow down after first speed, the polyurea specimen thickness is about0.6times the initial thickness when the elongation of100%, about0.5times when the elongation of300%.(2) In order to obtain the tensile failure morphological characteristics of polyurea elastomer material, the whole coating tensile failure test and scanning electron microscopy (SEM) for fracture were carried out, then combined with the uniaxial tensile test results, the descriptions of the macro and microscopic failure characteristics when uniaxial tension, the failure characteristics when the overall coating tensile were made. The tests results showed that polyurea elastomer material in uniaxial tension shows a typical super-elastic material toughness failure characteristics, there is some rebound after fracture and the permanent deformation is less than0.4. In the microscopic state, the natural polyurea surface structure shows dense defect, and the fracture characteristics of tensile failure shows typical ductile fracture and permanent deformation in a small scale, it’s consistent with the macro-fracture. The emergence of needle shape hole marked the tensile failure of overall polyurea coating, then holes expand and connect and eventually cause the coating to tear failure, tensile strain is between500～600%when emergence of needle shape hole on polyurea surface, it’s also consistent with the results of quasi-static tensile test, so the emergence of a needle hole as the symbol of polyurea anti-seepage coating is appropriate.(3) A coating resistant to water pressure test device was self-designed and produced. The device has high flexibility, on it simulation of different degrees cracking can be achieved by fast replacement of specimens, and the time of a single test program is greatly shorten by independent specimen and volume spraying. In the device, A organic glass windows was designed to ensure reliable observability and security, and before each experiment, post a water-soluble fluorescent paper and install a camera video at the bottom of device. Accurately load can be achieved with hydraulic servo system of high precision triaxial apparatus, and the load of each level is precisely adjustable. A encapsulation test was carried out before the test, and results showed that the overall encapsulation of the device meet the test requirements, on this basis, a back-pressure curve was plotted to ensure accurately load and stable water pressure. The entire test device with good versatility suitable for all kinds of coating material breakdown test of resistance to water pressure. By the device, the breakdown resistance tests in case of different thickness polyurea coatings with different cracking on the back were carried out, and the tests results showed that the breakdown resistance to water pressure property of polyurea coating is related to the coating thickness and the crack width on the back. Under300m head of water, polyurea coating that thickness is2mm and4mm can meet the concrete’s anti-seepage requirements with its cracks that width is2mm and5mm. (4) The Ogden constitutive equation is adopted to fitting the stress-strain curves of tests, on this basis, by using Ogden constitutive model and4node bilinear plane strain quadrilateral element CPE4RH, the numerical simulations to the test of polyurea coating resistant to water pressure were carried out with ABAQUS finite element software. The results shows that, in the condition of the same thinkness h and under3MPa water pressure, the certical displacement Umax in midpoint is proportional to the crack wodth, and when the free section with the same width, Umax increase with the decrcase of h, if they are assumed a linear relationship, the descending slope K increase with the increase of the width d. It’s undesirable for directly using h/d thick-width ratio as the control amount of polyurea coating thickness, however, the trend between Umax and h/d in two conditions that h=2mm and h=4mm seems similar. Distributions of the strain and the stress components under3MPa water pressure is obtained, the results shows thar the local stress in the outer area of deformation is up to11MPa and it’s easily damaged.(5) Based on existing equipment and engineering experience, construction methods of laying applied to spray polyurea elastomer anti-seepage coating in heel area of high arch dam were analyzed from view of the construction equipment, raw material control, construction technology, construction safety protection, prone to quality problems and their reasons and so on. The results showed that, the existing equipment and raw materials of spray polyurea technology used in high arch dam heel anti-seepage treatment are mature and feasible, but the key to successful application lies in the construction technology of spraying polyurea, and to the construction technology, well deal with concrete substrate processing and quality control of spraying polyurea is particularly important according to the specific construction conditions. |
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