دانلود رایگان مقاله انگلیسی بررسی اتصال هسته-پلسنگ آسفالت در سد خاکی - الزویر 2017

ABSTRACT

The asphalt core itself is a no-joint water barrier in embankment dams and is connected to the concrete plinth on the bottom of the core. A reliable asphalt core-plinth connection is crucial and must remain watertight when the core deforms due to deformations in the embankment and foundation and due to reservoir water pressure. A large number of tension tests were conducted to determine the best ratios, joint thickness and suitable additives for the sandy asphalt mastic (SAM) mix used for the connection. With the ratios of bitumen to filler to sand of 20%:35%:45% and by adding 4% SBS in the bitumen, one got a very suitable composition for the asphalt coreplinth connection in tensile conditions. Model tests were conducted to study the connection behavior when subjected to large shear displacements and high water pressure. The joint model test results indicate that the plane-surface plinth, curved-surface plinth, and plinth with or without copper water-stop showed no significant difference for the connection in the joint shear behavior. However, plinth with copper water-stop is suggested to enhance its tensile and shear behavior.

8. Summary and conclusions

Asphalt core is a no-joint impervious barrier in embankment dams and has to be connected with the concrete plinth. The asphalt core-plinth connection is crucial and must remain watertight when the core and plinth undergoes deformations (displacements) during construction and operation with full reservoir pressure. For asphalt core dams located in gorges with steep abutments the asphalt core-plinth connection towards the top of the dam may be subjected to tensile strain and significant shear displacements. In practice, sandy asphalt mastic (SAM) is used between the asphalt and plinth as a connection material. A large number of tension tests were conducted to determine the best ratio, joint thickness and suitable additives for the SAM mix.

The temperature of an asphalt core is about 5 °C for embankment dams located in sub-arctic climate, and about 20 °C in sub tropical climate. The temperature of 15 °C was used in the study based on the consideration that is the approximate average temperature for asphalt cores in operation for ACEDs in China. Temperature has a significant effect on strength and stiffness (deformation modulus). Wang and Höeg [4] found the cyclic modulus to increase from 900 MPa at 20 °C to 2500 MPa at 3.5 °C in the cyclic strain range of 10−4 –10−3 . Gheibi et al. [18] carried out resonant column tests on asphalt specimens and found the dynamic shear modulus to be about 8000 MPa at 22 °C, being about 10000 MPa at 0 °C in the strain range of10−8 –10−7 . At low strain rates or creep rates the strength of asphalt is significantly affected by the magnitude of strain rate while the strain at cracking is insignificantly affected [7]. The tests reported herein were run at a strain rate of 1.0%/min to investigate the asphalt core-plinth connection behavior mainly for dam construction and normal dam operation conditions.