Failure mechanical behaviors and prevention methods of shaft lining in China

Loess is a common soil layer of geological movement. It has macropores, vertical joints, and tubular pores and also low strength and strong water sensitivity. When building a tunnel in a weak loess stratum (Q3 loess or Q4 loess), the poor geological characteristics of loess usually bring great difficulties to the construction of tunnel invert, and it is very easy to cause subsidence at the tunnel base, uneven subsidence at the tunnel bottom, and cracks in the road and lining. The use of jet-grouting piles to strengthen the weak loess foundation is an effective method to improve the geological characteristics of loess. To investigate the effect of jet-grouting piles on the reinforcement of the tunnel foundation in weak loess areas, centrifugal model tests were used to analyze the subsidence and structural mechanics response characteristics of the tunnel base under the influence of jet-grouting pile length and pile diameter. Research shows that subsidence at the tunnel bottom can be reduced effectively and the adjustment time of the surrounding rock stress can be shorten significantly when using jet-grouting piles to reinforce the tunnel foundation. The length of the jet-grouting pile is better than the diameter in improving the strength of the foundation. However, with the improvement in the strength of jet-grouting piles, the efficiency of foundation reinforcement is reduced, the surrounding rock pressure and lining stress gradually increase, and the construction economy and structural safety are gradually reduced. When selecting parameters of jet-grouting pile, consideration should be given to safety, economy, and ease of construction. 

Effects of Jet-Grouting Piles on Loess Tunnel Foundation with Centrifugal Model Tests

Experimental study on the collapse evolution law of unlined tunnel in Boulder-Cobble mixed formation

Tunnel distress occurs often. Tunnel leakage, segment dislocation, and section deformation seriously affect tunnel construction safety and normal operation. Currently, mainly the traditional monitoring technology is used in tunnel distress monitoring. This kind of technology has the problems of low monitoring efficiency, slow speed, inaccurate measuring points, and so on. With the development of science and technology, three-dimensional laser scanning monitoring technology (3D LSMT) has fast acquisition speed, a comprehensive monitoring range, and high acquisition accuracy. This review collected the world’s more advanced monitoring technologies, such as optical fiber sensing technology (OFST), photogrammetry (PT), and so on. Firstly, these technologies were introduced and compared with 3D LSMT. Then the theoretical basis of 3D LSMT was analyzed. Three-dimensional LSMT uses the captured high-density point cloud to extract the tunnel structure information and realizes the rapid processing of point cloud data through automated software. Finally, the use of 3D LSMT for segment dislocation, tunnel deformation, and seepage water was discussed and analyzed further to understand the status of 3D LSMT in tunnel monitoring and provide a reference for tunnel distress monitoring. 

A State-of-the-Practice Review of Three-Dimensional Laser Scanning Technology for Tunnel Distress Monitoring

Rainfall deformation characteristics and influencing factors for a large deep level landslide in tuff grounds in Zhejiang, China

Local buckling characteristic of hollow π-type steel-concrete composite support in hilly-gully region of loess tunnel

Abstract The single-screw extruder with a perturbation baffle is a novel piece of equipment for polymer processing, in which the polymer melts undergo complex chaotic mixing. In this paper, from a new Lagrangian perspective, the fluid transporting mechanism in chaotic flow of the unwound screw channel was analyzed based on the finite element method. Firstly, two-dimensional velocity distributions in the unwound screw channel were calculated based on the mesh superposition technique. Fluid particle evolution processes in the extruder were tracked based on the fourth-order Runge-Kutta scheme. The numerical method used in this paper was validated by grid independence and experiments obtained from literature. Moreover, the finite-time Lyapunov exponent (FTLE) and Poincaré sections were adopted to discuss the chaotic mixing in the novel single-screw extruder. The effects of baffle width and height on the manifold structures in the flow dynamic system were analyzed. The results show that the homoclinic point of the manifold structure can give rise to chaotic mixing in the single-screw extruder. The height of the baffle is an important parameter to control the chaotic strength. In a way, increasing the height of the baffle can enlarge the kink scale and increase the stretching and folding actions, which results in the decrease of regular regions and an increase of the mixing efficiency in the single-screw extruder.

Jian Liu

Papers

Local buckling characteristic of hollow π-type steel-concrete composite support in hilly-gully region of loess tunnel

Chaotic mixing analysis of a novel single-screw extruder with a perturbation baffle by the finite-time Lyapunov exponent method

Lift-drag characteristics of S-shaped hydrofoil under different cloud cavitation conditions

Experimental and theoretical study of dynamic mechanical behavior of concrete subjected to triaxial confining and impact loads