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Extended finite element method (XFEM) is based on the idea of unit decomposition. The jump function that can reflect the discontinuity of the crack surface and the progressive displacement field function of the crack tip is added to the conventional finite element displacement mode, which avoids the inconvenience of remeshing the crack tip and the heavy calculation. Then the conventional finite element method calculates the fracture problem, and the crack propagation is independent of the mesh. When the standard finite element deals with time integration, the degree of freedom of the overall stiffness matrix will continue to increase in the process of crack propagation, which makes iterative calculation impossible. This paper proposes a novel Newmark implicit time integration scheme based on the XFEM to simulate dynamic crack growth. This method enriches all the nodes with the Heaviside function and the asymptotic displacement field function at the crack tip, that is, each node has 12 degrees of freedom, so that the overall stiffness matrix is consistent without making iterative calculation impossible. At the same time, a sparse matrix technology is proposed to solve the problems of large memory and long calculation time occupied by the matrix.

To reduce the water pressure acting on the lining of the Shantou Bay cross-harbour tunnel and determine a reasonable design scheme for the controlled drainage of water inflow of the underwater tunnel under high-water pressure, ABAQUS software is used to numerically simulate the water inflow and water pressure acting on the lining of the tunnel with different relief values of three schemes for controlled drainage. Theses three schemes of controlled drainage are the "longitudinal blind tube only", "longitudinal blind tube+circular blind tube with an interval of 12 m", and "longitudinal blind tube+circular blind tube with an interval of 6 m". The comparison analysis shows that the water inflow of tunnel decreases linearly with the increase of valve pressure, and the water pressure of monitoring points acting on the tunnel cross-sectional lining increases linearly as the valve pressure increases. The denser the distribution of circular blind tubes, the more sensitive the water inflow of the tunnel to the change of the valve pressure, and the higher the degree of influence on the water pressure of monitoring points acting on the tunnel cross-sectional lining due to the change of the valve pressure. Besides, the farther the monitoring point in the tunnel cross-section from the longitudinal blind tube, the lower the degree of influence on the water pressure of the monitoring point acting on the tunnel cross-sectional lining due to the change of the valve pressure. When the "longitudinal blind tube+circular blind tube with an interval of 12 m" with the pressure relief value of 600 kPa is used for the controlled drainage, the water pressure acting on the lining at the arch foot of the most unfavorable tunnel cross-section can be minimized. The reasonable design scheme of the controlled drainage of water inflow for the Shantou Bay cross-harbour tunnel can be determined objectively. [ABSTRACT FROM AUTHOR]

Rice allelopathy is implemented through its release of allelochemicals to environment. Many researchers considered that rice allelochemicals were phenolics. The action mechanisms of rice against weeds allelochemicals included the inhibition of seed germination and emergence, the effect on the balance of hormones, the damage on the integrity of cell membrane systems, the effect on photosynthesis and respiration, the disturbance of nutrient and water uptake and the effect on the protein synthesis and gene expression. Rice allelopathy is controlled by polygenes, and inherited quantitatively. Several QTLs were identified by the methods of molecular biological techniques and allelopathic bioassay. It might be the important research work to locate the QTLs accurately and to clone the allelopathic genes with the method of marker-assisted selection and the near isogenic lines.