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Advanced Engineering Science

Gongcheng Kexue Yu Jishu/Advanced Engineering Science
Journal ID : AES-16-10-2021-29
Total View : 1

Abstract :

In mountain rivers with coarse sediments, the ratio of water depth to sediment diameter (h/d) is relatively small especially under the condition of shallow water depth. Therefore, the vertical velocity distribution along the river cannot be described accurately with traditional logarithmic or logarithmic-wake law. In this paper, flume experiments were carried out with two kinds of sediments (glass beads d=1.4 cm and pinpong d=4 cm) to test the influence of coarse sediment on vertical velocity distribution under different h/d. In the presence of coarse sediment bed, one of the problems encountered is how to determine the reference level y0. For practical purpose, the present study assumes that y0 does not varies with h/d, namely, y0=0.2d. The measured data were first converted to dimensionless and then compared to theoretical results calculated by logarithmic-wake law. In addition, the coefficient B and another wake coefficient Π in in logarithmic compensation formula were calibrated to fit for the measured data. The results indicate that when the value of h/d is small, the coefficient B decreases with the increase of h/d while the wake coefficient Π presents an opposite trend, when the value of h/d becomes larger, both B and Π tend to a constant. Finally, a modified logarithmic-wake law is derived to describe the velocity distribution in mountain river flows with small h/d. The modified model agrees well with the experimental data conducted in the present laboratory flume. Furthermore, it also has a good adaptability to riverbed with coarse sediments.

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Gongcheng Kexue Yu Jishu/Advanced Engineering Science
Journal ID : AES-16-10-2021-28
Total View : 1

Abstract :

In order to perfect the salt expansion theory of coarse-grained saline soil and explore the influencing factors and mechanism of the salt−frost heaving force, 96 groups of coarse-grained sulphate saline soil samples are prepared artificially then indoor model tests have been carried out by self-designed test device. Test results showed that the sensitive range of temperature on the salt−frost heaving force is −0.2℃~−1.0℃. The salt content had no influence on the rules that the salt−frost heaving force increasing with temperature and determines the maximum salt−frost heaving force together with water content. For samples with same void ratio, the increasing water content led to an increased amount of the salinity which resulted in the maximum salt−frost heaving force. When the salt content kept constant, however,the increase of water content caused the decrease of maximum salt−frost heaving force. The maximum salt−frost heaving force achieved the maximum and minimum values ​​when the void ratio was 0.58 and 0.55, respectively, which was related to the crystallization position of salt in the soil frame. Furthermore, based on the test results, a mathematical expression of frost heaving limit depth of coarse-grained sulphate saline soil is given by the hierarchical synthesis method, which is expected to provide guidance for the quantitative evaluation and design of salt− frost heaving deformation of coarse-grained sulphate saline soil.which was related to the crystallization position of salt in the soil frame. Furthermore, based on the test results, a mathematical expression of frost heaving limit depth of coarse-grained sulphate saline soil is given by the hierarchical synthesis method, which is expected to provide guidance for the quantitative evaluation and design of salt−frost heaving deformation of coarse-grained sulphate saline soil.which was related to the crystallization position of salt in the soil frame. Furthermore, based on the test results, a mathematical expression of frost heaving limit depth of coarse-grained sulphate saline soil is given by the hierarchical synthesis method, which is expected to provide guidance for the quantitative evaluation and design of salt−frost heaving deformation of coarse-grained sulphate saline soil.

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