In this paper, the steady-state and transient heat transfer processes of functionally graded materials (FGMs) are analyzed using a coupled thermo-mechanical model in a GPU parallel multiphysics finite–discrete element software, namely MultiFracS. First, the coupled model to handle the heat transfer problem of heterogeneous materials is verified. Then, the advantages and disadvantages of FGMs and composite materials in response to thermal shock loads are compared and the results indicate that FGMs can overcome extreme environments better than composite materials. Finally, the influence of the geometric distribution characteristics of the double-edge cracks in the gradient material plate on the crack propagation is analyzed. The simulation results show that the interaction between the cracks affects the crack propagation path under the thermal load. The inclination angle and spacing of double-edge cracks greatly influence crack propagation. Specifically, a larger inclination angle and spacing can lead to a smaller crack propagation angle. The approach in this paper provides a new quantitative tool for investigating the thermal, elastic, and cracking of functionally graded materials.

The design of cutter parameters plays a key role in the successful cutting of large-diameter reinforced concrete building piles by shield machines. However, the cutting mechanism of the shield machine in cutting rebar is not clear. Based on the shield pile cutting project of Wuhan Metro Line 12, the finite-discrete element method (FDEM) numerical models of rebar cutting are established. The cutting force, rebar failure and stress evolution of rebar in linear cutting with different blade angles (a) are analyzed. By calculating the cutting area and cutting work, the relationship between the cutting specific energy and the a is obtained. Results indicate that the maximum peak cutting force increases as a increases and the maximum principal stress and shear stress are concentrated in the rebar near the cutter. As a increases, both the cutting surface roughness and cutting work increase, and the number of tensile and shear cracks also increases. However, the cutting specific energy decreases first and then increases with the increase of a, which has the lowest value and the highest cutting efficiency with a of -10°. The simulation results indicate that a of -10° can effectively improve the shield machine performance, which is also supported qualitatively by the project case.

Soil-rock composite strata are frequently encountered during shield tunneling for underground projects such as metros, railways, and other underground building facilities. The strong heterogeneity and abrupt variations in soil and rock mechanical properties often induce excavation instability, thereby adversely affecting construction safety and efficiency. Based on an urban shield tunneling project, the interface effects on cutting force and the failure characteristics of soil–rock composites under shield cutter penetration are investigated in this study using the finite–discrete element method (FDEM). Firstly, the FDEM input parameters are calibrated, after which the cutting force, crack number, acoustic emission (AE), breaking process, displacement, and stress fields with different interface inclinations (a) during penetration are analyzed. The influence of the interface strength reduction factor (λ) on the cutting force and failure mode is then discussed. The results indicate that the cutting force–penetration curves can be classified into two phases: in stage I, the cutting force grows smoothly, and some cracks are initiated in the sandstone layer with a few AE events; in stage II, the cutting force drops with violent fluctuation, and both tensile and shear cracks develop rapidly in the sandstone layer, accompanied by many AE events. Generally, cracks mainly propagate in the sandstone layer, and less shear failure occurs in the silty clay layer. As a increases, the peak force of cutter A increases, while that of cutter B decreases. Additionally, tensile cracks between the cutters are connected when a is 30° and 45°, resulting in rock bridge breakage. However, a larger λ leads to a greater peak cutting force. The total crack length tends to decrease with increasing α and λ with an a of 30°, indicating that larger interface inclinations and higher interface strengths are associated with less damage to the composite specimens. These findings provide new insights into the fragmentation mechanisms of soft–hard composite ground and can contribute to the efficient construction of underground building and transportation infrastructure.