A post-peak dilatancy model for soft rock and its application in deep tunnel excavation

The dilation angle is the most commonly used parameter to study nonlinear post-peak dilatancy(PPD)behavior and simulate surrounding rock deformation;however,simplified or constant dilatancy models are often used in numerical calculations owing to their simple mathematical forms.This study developed a PPD model for rocks(rock masses)based on the Alejanoe-Alonso(A-A)dilatancy model.The developed model comprehensively reflects the influences of confining pressure(σ_(3))and plastic shear strain(γ^(p)),with the advantages of a simple mathematical form,while requiring fewer parameters and demonstrating a clear physical significance.The overall fitting accuracy of the PPD model for 11 different rocks was found to be higher than that of the A-A model,particularly for Witwatersrand quartzite and jointed granite.The applicability and reliability of the PPD model to jointed granites and different scaled Moura coals were also investigated,and the model was found to be more suitable for the soft and large-scale rocks,e.g.deep rock mass.The PPD model was also successfully applied in studying the mechanical response of a circular tunnel excavated in strain-softening rock mass,and the developed semi-analytical solution was compared and verified with existing analytical solutions.The sensitivities of the rock dilatancy to γ^(p) and σ_(3) showed significant spatial variabilities along the radial direction of the surrounding rock,and the dilation angle did not exhibit a monotonical increasing or decreasing law from the elasticeplastic boundary to the tunnel wall,thereby presenting the σ3-or γ^(p)-dominated differential effects of rock dilatancy.Tunnel deformation parabolically or exponentially increased with increasing in situ stress(buried depth).The developed PPD model is promising to conduct refined numerical and analytical analyses for deep tunneling,which produces extensive plastic deformation and exhibits significant nonlinear post-peak behavior.

Research progress of electronic nose technology in exhaled breath disease analysis

Exhaled breath analysis has attracted considerable attention as a noninvasive and portable health diagnosis method due to numerous advantages,such as convenience,safety,simplicity,and avoidance of discomfort.Based on many studies,exhaled breath analysis is a promising medical detection technology capable of diagnosing different diseases by analyzing the concentration,type and other characteristics of specific gases.In the existing gas analysis technology,the electronic nose(eNose)analysis method has great advantages of high sensitivity,rapid response,real-time monitoring,ease of use and portability.Herein,this review is intended to provide an overview of the application of human exhaled breath components in disease diagnosis,existing breath testing technologies and the development and research status of electronic nose technology.In the electronic nose technology section,the three aspects of sensors,algorithms and existing systems are summarized in detail.Moreover,the related challenges and limitations involved in the abovementioned technologies are also discussed.Finally,the conclusion and perspective of eNose technology are presented.

Study on the long-term performance of shield tunnel passing through the gas-bearing strata

When the shield tunnel passes through the gas-bearing strata,gas and water leakage may occur depending on the sealing performance of the segment joints.This process involves the complex multiphase seepage flow phenomenon in unsaturated soil.In this study,a fully coupled solid-liquid-gas model of the GIL Utility Tunnel was established to investigate the influence of the high-pressure gas on the mechanical properties of the tunnel segments and joints.The constitutive model of the Extended Barcelona Basic Model was imple-mented to simulate the effect of the seepage process on soil deformation.The results show that significant upward displacement occurred in the gas reservoir and its overlying strata,and the maximum displacement reached 30 mm.In addition,during the leakage of the gas and the water,an increase in the average soil effective stress was observed.It would induce a reduction in the suction and expansion of the yield surface.The tunnel tended to be stable from 20 years onwards,thus the soil deformation due to the water leakage only occurred at the early stage.In addition,the joint opening under the most unfavorable internal force combination was 0.69 mm,and the correspond-ing bolt stress was 119.5 MPa,which is below the yield limit.The results of this study help to understand the influence of high-pressure gas on tunnel safety and the sealing performance of the joints.

Numerical and experimental analyses of methane leakage in shield tunnel

Tunnels constructed in gas-bearing strata are affected by the potential leakage of harmful gases,such as methane gas.Based on the basic principles of computational fluid dynamics,a numerical analysis was performed to simulate the ventilation and diffusion of harmful gases in a shield tunnel,and the effect of ventilation airflow speed on the diffusion of harmful gases was evaluated.As the airflow speed increased from 1.8 to 5.4 m/s,the methane emission was diluted,and the methane accumulation was only observed in the area near the methane leakage channels.The influence of increased ventilation airflow velocity was dominant for the ventilation modes with two and four fans.In addition,laboratory tests on methane leakage through segment joints were performed.The results show that the leakage process can be divided into“rapid leakage”and“slight leakage”,depending on the leakage pressure and the state of joint deformation.Based on the numerical and experimental analysis results,a relationship between the safety level and the joint deformation is established,which can be used as guidelines for maintaining utility tunnels.

Optimization of pipe circuits in energy tunnels

Geothermal energy is a kind of green and renewable energy.Conventionally,ground source heat pumps can be used to harvest geothermal energy from the subsurface.To reduce the initial investment,a good solution is to use tunnel linings as heat exchangers to extract/dump heat.This special infrastructure is called an energy tunnel.In addition to the thermal performance,the impact of pipe network configuration on thermal efficiency is still challenging in the design of energy tunnels.To solve this problem,this study makes the first attempt to carry out research on the optimization of pipe circuits in energy tunnels by a series of numerical analyses.A fully coupled thermo-hydraulic 3D finite element model is established to investigate the response of tunnel-soil interaction under cyclical thermal loading(initial soil temperature varies from 8C to 18C),as well as the thermal transient interactions among air,absorber pipe,tunnel linings and ground,to quantify the amount of useful heat that can be extracted from the tunnel and the ground.On the other hand,the influence of 3 various heat-carrying pipes layout is also investigated.It is found that higher heat transfer efficiency can be obtained when the entrance and exit of pipelines are located below the tunnel in the study.The spatial location of pipelines will also affect the exchanged heat output.