Tunnelling induces stress change and displacement in the ground. The excavation of a new tunnel in stratified soil can trigger different patterns of stress redistribution, which may adversely influence nearby tunnels. Research on multi-tunnel interaction has mainly been performed on the assumption of a uniform ground. The effects of different soil stratifications on tunnelling interaction remain poorly understood. In this paper, threedimensional numerical parametric studies verified by previous centrifuge tests were carried out to analyse the twin tunnelling effects in two-layered soil. An advanced hypoplastic constitutive model that can capture stress-, path-, and strain-dependency of soil behaviour is adopted. Numerical cases investigated include perpendicular twin tunnelling in two sand layers with different relative densities and the location of the interface between the two sand layers. It is revealed that larger settlements and a wider surface settlement trough occur when tunnelling in two-layered soil strata than in a uniform ground. This is because of the wider and larger soil arch induced in two-layered soil strata. The structural response including tunnel deformation, induced bending moment, and induced hoop stress of the existing tunnel can be greater when tunnelling in layered soil strata than in a uniform ground owing to larger stress relief. Moreover, the combination of bending moment and hoop stress can exceed the M-N failure envelope of the structure in layered soil. A conventional simplified assumption of a uniform ground can underestimate of the influence of new tunnel excavation on existing tunnels, resulting in unsafe designs.

The extended duration of mulching in Xinjiang cotton fields leads to a significant decline in the tensile strength of plastic film. When recycling is in operation, the soil and the spring teeth of the machinery used can easily cause secondary damage and fracture the residual film. Establishing appropriate working parameters for recycling is essential to enhance the overall quality of collection efforts. By analyzing the motion process of a chain-tooth residual film pickup device, we identified key working parameters that significantly impact the efficiency of recycling. Employing the finite element method (FEM) and a coupled algorithm incorporating smooth particle hydrodynamics (SPH), we developed a coupled finite element model representing the interaction among spring teeth, soil, and residual film. Through simulation and analysis of the process of inserting the spring teeth into the soil to collect film, we derived the governing rules for residual film stress and deformation changes. Utilizing forward speed, rotational angular velocity, and angle of entry into the soil of the spring teeth as test factors and selecting the residual film stress and the residual film deformation as test indices, we conducted a multi-factor simulation test. We established a mathematical model correlating test factors with test indices, and the influence of each factor on the test index was analyzed. Subsequently, we optimized the working parameters of the spring teeth. The results indicated that the optimal working parameters are forward speed of 1111.11 mm/s, rotational angular velocity of 25 rad/s, and angle of entry into the soil of 30 degrees. At these values, the average peak stress of residual film was 4.51 MPa and the height of residual film pickup was 84.48 mm. To validate the optimized the spring teeth impact on performance, field experiments were conducted with recovery rate and winding rate as test indices. The results demonstrated a 92.1% recovery rate and a 1.1% winding rate under the optimal combination of working parameters. The finite element model presented in this paper serves as a reference for designing and analyzing key components of residual film recycling machines.

In combination with the field monitoring data, PLAXIS3D finite-element software was used to numerically model the pull-pile supporting structure in a deep foundation pit. This structure was compared to the single-row pile support structure in order to learn more about the pull-pile supporting structure's force and deformation characteristics and how it works. The study found that the cumulative horizontal displacement curves of the supporting piles are integrated into an upward convex shape. The bendingmoment curve of the front-row piles presents an inverted S shape, and the bendingmoment curve of the back-pull piles presents a bow shape. The back-pull-pile effect can improve the unbalanced distribution of positive and negative bending moments in single-row piles by changing the stress condition of the soil. In other words, the pull-pile supporting structure has good safety and serviceability and can well control the lateral displacement of the foundation pit.