Physical model test on the support characteristic for quasi-NPR bolt under asymmetric stress

With the continuous increase in tunnel construction,the significant deformation of the surrounding tunnel rock is often difficult to predict and control.In addition,the lithology,structure,and various asymmetric large deformation of surrounding rock mass during operation and maintenance severely affect the ultimate bearing and stability of the tunnel.To explore the deformation mechanisms and failure modes of surrounding rock under large asymmetric stress and complex geological conditions,a physical model of a tunnel through granite was constructed based on the similarity theory.The model had 30°dip lithology under asymmetric stress and was emplaced a new quasi-negative Poisson’s ratio(NPR)bolt.By analyzing the variation law of displacement and axial force of the bolt under an asymmetric load,the asymmetric deformation and failure mechanism of the granite tunnel and the support effect of the quasi-NPR bolt were determined.The energy absorbed by the surrounding rock was analyzed,and the influence mechanism and control countermeasures of asymmetric stress on the granite tunnel were explored.This work provides a reference for the design of asymmetric support of tunnels with similar engineering backgrounds.

A novel method for simulating nuclear explosion with chemical explosion to form an approximate plane wave: Field test and numerical simulation

A nuclear explosion in the rock mass medium can produce strong shock waves,seismic shocks,and other destructive effects,which can cause extreme damage to the underground protection infrastructures.With the increase in nuclear explosion power,underground protection engineering enabled by explosion-proof impact theory and technology ushered in a new challenge.This paper proposes to simulate nuclear explosion tests with on-site chemical explosion tests in the form of multi-hole explosions.First,the mechanism of using multi-hole simultaneous blasting to simulate a nuclear explosion to generate approximate plane waves was analyzed.The plane pressure curve at the vault of the underground protective tunnel under the action of the multi-hole simultaneous blasting was then obtained using the impact test in the rock mass at the site.According to the peak pressure at the vault plane,it was divided into three regions:the stress superposition region,the superposition region after surface reflection,and the approximate plane stress wave zone.A numerical simulation approach was developed using PFC and FLAC to study the peak particle velocity in the surrounding rock of the underground protective cave under the action of multi-hole blasting.The time-history curves of pressure and peak pressure partition obtained by the on-site multi-hole simultaneous blasting test and numerical simulation were compared and analyzed,to verify the correctness and rationality of the formation of an approximate plane wave in the simulated nuclear explosion.This comparison and analysis also provided a theoretical foundation and some research ideas for the ensuing study on the impact of a nuclear explosion.