Applied Mechanics and Materials Vols. 105-107

Abstract: Fracture energy, which reflects the split property of brittle materials, is a significant parameter. For present tests of measuring it, the indirect test itself has insuperable disadvantage, while the direct tension test, in spite of an ideal way, is too limited to be widely applied in ordinary labs for its over high requirement for the test machine. The paper analyzed the disadvantage of the direct tension machine and improved it: a new elastic foundation of lower clamper replaced the original rigid one. Using the improved machine, the complete stress-strain tensile curve of the brittle materials was obtained easily. Further, the fracture energy could be calculated. Basing on studies, the paper recommended it may as well to get the fracture energy by improved direct tension machine.

Abstract: To further verify the feasibility of theoretic calculation, according to similarity theory, the principles and methods of pile foundation-soil interaction in saturated soft clay are determined. It studies acceleration interaction of each test point on the soil surface under the same largest shock force with different frequency on the top of the pile. The results of experiment show that the acceleration interaction trend of each point changes with the change of shock frequency, it shapes like a down N with the shock frequency of 5Hz, like an M with the shock frequency of 10Hz, like a down V under the shock frequency of 15Hz～30Hz. With the shock frequency of 40Hz and 50Hz, it likes a plane curve (hyperbolic curve) shape.

Abstract: First describe the selecting rule of the C-M and D-P failure criterion and the rule and the relations of the D-P criterion parameter with the rock mass fracture toughness; then through overlapped stresses in the end region of crackle, the total stresses about end region of tensile and sheared crackle can be obtained. The results are introduced into D-P failure criterion and C-M failure criterion, the relation between criterion D-P failure criterion, and rock fracture toughness KⅠc,KⅡc. can be derived. Compared with the results of experiments, which proved the validity of the derivation.Through overlapped stresses in the end region of crackle, the total stresses about end region of tensile and sheared crackle can be obtained. The results are introduced into D-P failure criterion and C-M failure, the relation between criterion D-P failure criterion, and rock fracture toughness KⅠc, KⅡc. can be derived. Compared with the results of experiments, which proved the validity of the derivation.

Abstract: Permafrost is widespread in China, especially in Northeast China and the Qinghai-Tibet Plateau. Regions like Qinghai-Tibet Plateau have the most strenuous crustal movement. Therefore, earthquake-resistance of structures in permafrost region is an important issue. Furthermore, the permafrost will degenerate gradually as global warming mounts up. In some regions permafrost thickness tends to attenuate. Most bridge designs adopt pile foundation in order to reduce the effects of instable frost. The deterioration of frost leads to degradation of anti-seismic performance of bridges’ pile foundations. Pile-soil dynamic interaction numerical analysis models are established based on data of indoor low-temperature dynamic triaxial tests. Studies are performed on the dynamic stiffness and damping characters and the influencing factors of pile foundation under vertical harmonic load in frozen and thawing soil. The result shows that the dynamic response of the pile decreases along the depth, and the frictional resistance around the pile mainly distributes along the upper half of the pile, and the dynamic stiffness and damping of the pile are affected by temperature. Dynamic stiffness increases as temperature goes down, whereas the decrease of the temperature of frozen soil can notably lower the dynamic damping of the head of the pile. As the frequency of the dynamic load augments, the dynamic stiffness of the head increases marginally, whereas frequency has little influence on damping. The relative thickness of the frozen and thawing soil layer has considerable influence on dynamic stiffness, but negligible on damping.

Abstract: Based on the recursion method of shearing ragidity of soil layer, dynamic torsional impedance of the radial inhomogeneous viscoelastic soil is studied.Under the certain fundamental assumption,combined with displacement basic solution of the plane axial symmetry strain question,the displacement the continuous and boundary of the soil layers, the formula of dynamic torsional impedance of the pile-soil contact surface is deduced.Degenerated into homogeneous viscoelastic model,the model is further confirmed accurate.Finally, the conclusion is obtained:(1) The bigger is G2/G1,the larger the soil body actual stiffness is. The dynamic damping presents the trend of increase;(2)In the area of the radial disturbance soil,as ‘d’increases, the soil body actual stiffness is increasing. When G2/G1 is smaller than 1,the dynamic damping is reducing along with increases of ‘d’,when G2/G1 is bigger than 1,the dynamic damping is increasing along with increases of ‘d’.(3)Actual stiffness and dynamic damping assumes the linear variation along with increasing of material damping.

Abstract: After the impoundment of the Three Gorges Reservoir, geomorphology of the Yangtze River tributaries changed greatly. The Xiaojiang River in Chongqing is a representative tributary because of the unique local features on geographical conditions, hydrology conditions, migration and riparian zone. It is significant to explore and analyze the geomorphology change of the Xiaojiang River after the impoundment of the Three Gorges Reservoir for studying the feature of the Xiaojiang River channels. In this paper the geomorphology change law of the Xiaojiang River was calculated and analyzed based on the 2D Hydrodynamic and sediment models, and a few suggestions for protecting, developing and managing the Xiaojiang River are made from the conclusion of the analysis.

Abstract: In the smooth blasting of the tunnel, many studies indicate that the effects of joints on blasting are over than the nature of the rock itself. By analyzing the effects of joints on the strength of blasting rock, the rock surge impedance and the stress propagation, six kinds of effects of joints on blasting rock are summarized. Through the actual blasting engineering, the phenomenon of over-under break which is produced by joints is discussed. Meanwhile, the blasting effectiveness is analyzed.

Abstract: This study developed a numerical method to establish a comprehensive load-settlement curve for a driven pile. Analysis results shown that the residual forces caused by the driving of the pile can be simulated using the numerical method that proposed herein. The load was applied to the tested piles, while the incremental displacement was subjected to numerical piles. Although these two processes are distinctive, the load-settlement behaviors of various piles calculated numerically are consistent with those measured from field tests. Moreover, the proposed numerical method highlighted the post-peak behavior of a pile. Accordingly, the numerical method was very suitable to analyze the behavior of driven piles.

Abstract: In this paper, three-dimensional(3-D) finite element(FE) method is used to analyze the stresses of face slab of the 300m high concrete face rockfill dam(CFRD) before and after earthquake. Meanwhile, the effect of valley shape on the stress of face slab is considered. The results show that the maximum deflection and axial stress are located near the bottom of face slab in the central valley area before earthquake. And there are compressive stresses in mostly area of face slab. After earthquake, the positions of maximum deflection and axial stress of face slab were changed to the crest of the central valley area. As the valley aspect ratio increases, compressive stress of face slab decreases. For the 300m ultra-high CFRD, the maximum axial stresses exceed the concrete compressive strength before and after earthquake. Therefore, the compression damage of face slab should be considered during the design.

Abstract: Two of the most important parameters in dynamic analysis involving soils are the dynamic shear modulus and the damping ratio. In this study, a series of tests were performed on gravels. For comparison, some other tests carried out by other researchers were also collected. The test results show that normalized shear modulus and damping ratio vary with the shear strain amplitude, (1) normalized shear modulus decreases with the increase of dynamic shear strain amplitude, and as the confining pressure increases, the test data points move from the low end toward the high end; (2) damping ratio increases with the increase of shear strain amplitude, damping ratio is dependent on confining pressure where an increase in confining pressure decreased damping ratio. According to the test results, a reference formula is proposed to evaluate the maximum dynamic shear modulus, the best-fit curve and standard deviation bounds for the range of data points are also proposed.