The reason for instability in a rock mass with a weak interlayer is not only the sliding failure of the rock interlayer structural plane but also the tip crack propagation caused by the stress concentration at the tip of the interlayer. In this study, a uniaxial compression test of an anchored rock mass with a weak interlayer was carried out to determine the influence of the anchorage on the failure pattern and the strength of samples with different interlayer dip angles. In addition, the coupled DEM–FEM numerical simulation method was used to study the internal stress evolution of the sample and the stress distribution of the anchor under the anchorage effect. The results showed that the anchorage effect on reinforcement and strength enhancement was greatest for the sample with an interlayer dip angle of 30°. Under the anchorage effect, crack initiation was limited and there was more shear failure in the samples. The reinforcement range of the anchorage effect for anchors with restrained ends was larger than for anchors with free ends. When the rock–anchor interface was unbonded, the effect of the free-ends anchor reflected the residual friction, but the restrained-ends anchor still worked by limiting the lateral expansion of the rocks. The stress values and deformation of the anchors decreased gradually with an increase in dip angle.
The interval section of the Liuyang River flood control levee project of the Changsha Metro Line 6 is used as the engineering background of this study. A three-dimensional finite element numerical model of a tunnel shield containing complex interfaces is established by using the multifield coupling software COMSOL. The paper studied the deformation of flood control levees under shield tunnel excavation working conditions. The results show that when the left line shield machine is excavated below the Liuyang River flood control levee, the deformation of the flood control levee and the surrounding rock of the tunnel is biased towards the built right line tunnel. And it has an impact on the bridge pile near the tunnel. When the shield of the left line crosses the flood control levee, it can easily cause a large deformation and displacement of the levee above the area between the two shields. To ensure the controlled deformation of the levee, the construction should ensure the spacing between the two tunnel palm faces as far as possible and should be far away from other structures on the levee. When the shield crosses the levee, the deformation that occurs at the base of the levee is significantly higher than the deformations that occur at other locations of the levee. Displacement monitoring and secondary reinforcement at the base of the flood control levee appear to be necessary. The numerical simulation results validate the feasibility of using the multifield coupling software COMSOL to study the construction modeling of shield tunnels through rivers and its advantages. This method provides a practical framework for similar tunnel performance engineering or displacement monitoring in future projects.
:A series of experiments were conducted to study the damage response of
rock-like specimens on the water content and the unloading rate of the
incremental amplitude cyclic loading experiments. Under the conditions
of five unloading rates and three water contents, the influence of the
incremental amplitude cyclic loading on the rock-like specimens was
analyzed. The damage characteristics of the rock-like specimens were
discussed, and a damage model was proposed. The test results indicate
that the rock-like specimens are sensitive to the water content and the
unloading rate of the incremental amplitude cyclic loading. Compared to
the monotonic uniaxial compression tests, the rock-like specimens’
elastic modulus and failure stress subjected to incremental amplitude
cyclic loading are generally lower. As the unloading rate increases, the
failure stress generally decreases, while the elastic modulus first
decreases and then increases. Moreover, water can amplify the effect of
the unloading rate on failure stress, elastic modulus, and damage
variable of rock-like specimens. The influence of the unloading rate on
the damage variable has a critical value. A lower unloading rate below
the critical value has little effect on the damage variable. In
contrast, an enormous unloading rate that exceeds the critical value
will enhance the damage variable. The established damage model is
suitable for describing and assessing the plastic strain damage variable
and the energy damage variable of rocks with different water contents
subjected to an incremental amplitude cyclic loading with different
unloading rates.
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