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• Influence of joint deflection on the axial mechanical response of pipe jacking. • Distribution of eccentric strain of pipe wall induced by joint deflection. • Development of tensile stress and inelastic stress induced by joint deflection. The bell-and-spigot joints play a vital role in the axial mechanical response of pipe jacking. This paper investigates the influence of joint deflection on the axial stress distribution and jacking load transfer of concrete pipe jacking via full-scale tests and numerical simulation. The joint deflection contributes to the single-side eccentricity or diagonal eccentricity of the pipe segments. The increase in joint deflection influences the extension of axial stress concentration in the vertical direction near the joint, while the increase in jacking load enhances the maximum compressive stress of the pipe wall in the alignment direction. In addition, the nonlinear axial strain–stress property of the cushioning plank among the segments resulted in the nonlinear transfer of the jacking load. Moreover, the joint deflection also induces the visible tensile stress or inelastic stress of the pipe under diagonal loading mode, indicating a risk of structural damage. [ABSTRACT FROM AUTHOR]

• This paper presents a new method for evaluating rock excavation efficiency. • The new method uses the excavated surface to obtain the optimal cutting geometry. • Volumes of underbreaks and overbreaks vs s-p ratio yield a unique turning point. • The turning point represents the optimal cutting geometry of the tested geology. Efficient rock excavation requires an optimal s-p ratio, where adjacent cuts interact to completely plane the rock surface. Traditionally, the specific energy (SE) methodology has been used to determine this ratio, but its U-shaped curve is sometimes incomplete or absent, making it difficult to find the optimal s-p ratio. In this research, an alternative methodology is proposed. This methodology relies on the morphology of the excavated rock surface, specifically, the amounts of overbreaks. To evaluate the proposed methodology, full-scale rock cutting experiments were conducted in the laboratory. Numerical simulations were also conducted in 3D particle flow code (PFC3D) and the results were validated by the full-scale laboratory rock cutting experimental data. The study also involved conducting sensitivity analyses to evaluate the effectiveness of downscaling and upscaling the PFC3D-based model to obtain results for full-scale applications. Following the excavation, laser profilometry was employed to characterize the excavated rock surfaces, and the resulting profiles were used to calculate the volume of overbreaks. Plots of these volumes against the s-p ratio were generated to identify the optimal s-p ratio. The findings indicated the presence of a noticeable optimal s-p ratio in both the PFC3D-based simulations and full-scale laboratory experiments. This optimal s-p ratio was not evident when the specific energy methodology was employed. This proposed methodology exhibits considerable potential and can prove beneficial in determining cutting geometry that is optimal for site-specific and TBM-specific, as well as in the design and production of tunnel boring machines. [ABSTRACT FROM AUTHOR]

• A refined numerical model is developed for signal propagation in soils. • The detailed structure of buried sensor node is considered in the simulation. • An optimal frequency exists to minimize the signal path loss. • The proposed model can be applied to signal propagation in heterogenous soils. Wireless underground sensor networks (WUSN) have promising applications in the field of underground structural health monitoring. Signal path loss prediction is a great challenge in the design and onsite installation of WUSN. Existing wireless signal propagation models cannot well predict the total path loss due to the neglection of node detailed structure. This paper develops a numerical model in FEKO to simulate the signal propagation in soils considering the detailed structure of buried sensor node including linear shaped antenna, coaxial feeder, batteries and protecting PVC box. The developed numerical model is validated using the Friis equation in free space and results of outdoor signal propagation experiments. Compared to analytical propagation models, the developed numerical model can well consider the path loss induced by sensor node itself. The proposed numerical model is able to simulate the signal propagation in heterogeneous soils. Signal path loss fluctuates in heterogeneous soils due to the coupling of direct, reflected and refracted waves. Parametric studies are conducted to investigate the effects of soil properties, signal frequency, node orientation and soil heterogeneity on total path loss. An optimal frequency f optimal exists to minimize the signal path loss and f optimal is in the range of 0.56–0.65 GHz for the node in this paper. [ABSTRACT FROM AUTHOR]

• Experiments were conducted to investigate rock breaking using high-pressure, high traverse speed water jets, matching the movement speed of the TBM disc cutter. • The relationship between traverse speed and the depth of water jet cutting was examined. • A deeper groove depth than penetration depth leads to a more effective rock-breaking outcome. • A water jet zoning arrangement method for eight-meter class TBM cutters is introduced. The disc cutting load of a TBM is insufficient to induce crack propagation in hard rock tunnels due to the high strength of the rock. High-pressure water jets, considered an auxiliary rock-breaking method, enhance the disc cutter's capacity to penetrate cracks by creating pre-existing fissures. In order to examine the correlation between cutting depth achieved by a high-pressure water jet operating at high traverse speeds and the penetration capability of TBM disc cutters, we conducted rock cutting experiments employing varying traverse velocities for the water jet. Additionally, we performed linear disc cutting experiments using full-size disc cutters equipped with grooves. These experiments were conducted using high-strength granite from China's Bei Shan region. We utilized the Discrete Element Software PFC2D to construct a rock breaking model based on Tyson polygons, enabling us to investigate the microfine influence mechanism of grooves with symmetry. The experiments involving high-pressure water jet grooving at high traverse velocities revealed a logarithmic decrease in groove depth as the nozzle's traverse velocity increased. These findings suggest that when high-pressure water jets are employed as an auxiliary method in TBM operations, increased distance from the center of the disc hob leads to higher traverse velocities, resulting in less efficient rock breaking. Nonetheless, increasing the nozzle diameter can enhance the rock-breaking effect. Linear disc cutting experiments indicate that, at a penetration depth of 4 mm, grooves with depths less than 4 mm have minimal impact on assisting in disc cutter rock breaking. However, when the groove depth exceeds 4 mm, there is a noticeable improvement in the disc cutter's breaking performance. The numerical simulation results provide initial validation for the linear disc cutting experiment. Lastly, considering the specific conditions of the Beishan tunnel, we propose a design scheme that involves the zoned arrangement of water jets. Additionally, we recommend appropriately reducing the rotational speed when employing high-pressure water jets as an auxiliary method for rock breaking. The research findings presented in this paper can serve as valuable references for the design and implementation of high-pressure water jet-assisted TBM cutter rock breaking. [ABSTRACT FROM AUTHOR]

Bolt/cable support technology is widely used in the rock engineering protection field to limit large deformations of surrounding rocks, improve the anti-explosion and anti-impact mechanical properties of engineering rock mass, and increase stability and safety. The underground protective cavern suffers significant damage due to the powerful impact produced by the explosion. This paper studies the macro static and dynamic mechanical properties of the negative Poisson's ratio (NPR) constant resistance and large deformation anchor cable. In addition, an in-situ blasting test scheme is proposed to simulate the approximate plane wave generated by a nuclear explosion in the field. Hence, the anti-explosion and anti-impact properties of the NPR anchor cable support system and failure mode of ternary structure (rod body, anchor body, and rock mass) under explosion influence can be obtained. Finally, numerical modeling is utilized to validate the NPR anchor cable support and PR anchor bolt support under the high vibration condition with the same blasting equivalent. The findings showed that the cavern supported by the NPR anchor cable revealed better overall stability under strong impact and vibration than the PR anchor bolt. [Display omitted] • Multi-hole simultaneous blasting is proposed to simulate approximate plane waves. • The blasting effect depends on the synchronism of multi-hole blasting. • Large deformation resistance of 1G-NPR anchor cable is verified by blasting tests. • The anti-explosion effects of 1G-NPR and PR anchor cable are compared and analyzed. Bolt/cable support technology is widely used in the rock engineering protection field to limit large deformations of surrounding rocks, improve the anti-explosion and anti-impact mechanical properties of engineering rock mass, and increase stability and safety. The underground protective cavern suffers significant damage due to the powerful impact produced by the explosion. This paper studies the macro static and dynamic mechanical properties of the negative Poisson's ratio (NPR) constant resistance and large deformation anchor cable. In addition, an in-situ blasting test scheme is proposed to simulate the approximate plane wave generated by a nuclear explosion in the field. Hence, the anti-explosion and anti-impact properties of the NPR anchor cable support system and failure mode of ternary structure (rod body, anchor body, and rock mass) under explosion influence can be obtained. Finally, numerical modeling is utilized to validate the NPR anchor cable support and PR anchor bolt support under the high vibration condition with the same blasting equivalent. The findings showed that the cavern supported by the NPR anchor cable revealed better overall stability under strong impact and vibration than the PR anchor bolt. [ABSTRACT FROM AUTHOR]

Tunnelling in soft soil conditions, especially with a shallow overburden, faces the risk of face instability due to blowout. Although several blowout models have been proposed to estimate the blowout pressure, mostly based on limit analysis or limit equilibrium, there is a significant gap between the allowable blowout pressures predicted by these models and the values observed in case studies, laboratory experiments and numerical simulations. This paper proposes a compact blowout model, which is more compact compared to a model proposed by Balthaus (1991). This new blowout model is able to predict blowout pressures more closely to the value observed by centrifuge testing, reduced scale experiments and case studies, whilst staying conservative. Its application on the Hochiminh Metroline No. 1 project in this study resulted in a smaller support pressure in the boring stage to avoid the occurrence of a blowout. • A new compact blowout model for stability analysis when tunnelling with shallow overburden. • Validation with experimental data including centrifuge tests and reduced scaled experiments. • Validation with two blowout case studies. • Case study at Hochiminh Metro shows smaller support pressures should have been applied. [ABSTRACT FROM AUTHOR]

• Energy dissipation rate (EDR) criterion was developed for rockburst risk evaluation. • EDR contour map can reveal potential damaged zones of rockbursts. • Rockbursts in Jinping II drainage tunnel were evaluated and understood using EDR. • Joints may increase intensity, delay occurrence and affect locations of rockbursts. Risk evaluation of rockbursts is crucial for ensuring the safety and stability of deep-tunnel construction. Structural planes play an important role in the potential for rockbursts to occur, and more related studies are needed. In this paper, a new rockburst criterion based on energy dissipation rate (EDR) index was developed and the role of structural planes in rockburst potential was studied. Firstly, a method of generating structural planes and a viscoplastic constitutive model with internal variables were introduced for numerical simulation using FLAC3D. Then, tunnelling under different hydrostatic pressures was simulated to obtain the values of EDR index and stress-strength/strength-stress ratio indices, and EDR criterion was estimated based on stress-strength/strength-stress ratio criteria. The results show that EDR criterion is: 0∼1 Pa/s (no risk), 1∼3 Pa/s (low risk), 3∼6 Pa/s (medium risk), >6 Pa/s (high risk). Subsequently, the case study of rockbursts in the drainage tunnel of Jinping II hydropower station was conducted considering a nearby fault to validate EDR criterion. The simulation results using EDR are basically consistent with actual rockbursts in terms of the potential location, intensity and time. Finally, the numerical simulations of tunnel excavation considering a joint set with different dip angles were implemented, and the influences of joints on rockbursts were investigated using EDR. Analysis results show that rockbursts are prone to occur on tunnel walls parallel and perpendicular to joints; potential rockburst locations are controlled by local joints and are less affected by geostress distribution. Joints may increase the intensity, delay the occurrence time, and control the pit boundaries of rockbursts. Obtained EDR contours can be used to infer damaged zones of strainbursts and strain-structure slip rockbursts and understand inducing mechanism of rockbursts in Jinping II drainage tunnel. The findings of this study provide insight into the role of structural planes on rockbursts. The presented methodology can be applied to rockburst evaluation and prevention during the construction of deep tunnels. [ABSTRACT FROM AUTHOR]

• Flexural behavior of segmental joint containing oblique bolts is investigated. • CDP model is used to capture the distribution of damage zone of concrete. • The bolt arrangement effect is highlighted via a series of numerical simulations. As the width of segments increases, segmental joints containing three oblique bolts are increasingly used while their flexural behavior is still not clear. Therefore, this paper presents a comprehensive investigation on the flexural behavior of such joints; and the effects of bolt arrangement are also highlighted. A series of full-scale experiments and numerical simulations are first performed to reveal the typical flexural behavior and failure characteristics of the joint with one single oblique bolt. Then, the verified numerical model is extended to investigate the influence of different oblique bolt arrangements (i.e. number and direction) on the joint flexural behavior under different axial forces. Five bearing stages can be identified during the whole loading process of joints, and they are separated by the bolts tension, concrete severe damage, contact of the segment top, and joint failure. Under small axial force, the joint failure under the positive moment is dominated by the tensile damage of concrete around bolt holes; while the compressive damage of concrete at the same position controls the joint failure under the negative moment. The concrete damage area changes to the compression zone as the axial force increases. The oblique bolt arrangement has little effect on the identification of five-stage bearing process of such segmental joints, but increasing the number of bolts can improve the flexural stiffness and ultimate bearing capacity of joints. Moreover, the joint containing three cross oblique bolts has a stronger flexural capacity than that containing three parallel bolts under small axial forces, which is because the change of the bolt direction avoids the connection of tensile damage zones around the bolt holes. However, these effects of bolt arrangement fade away as the axial force increases. [ABSTRACT FROM AUTHOR]

• Model test of shield tunnelling adjacent pile group was established to study pile response. • Computed results of nonlinear FEM were systematically compared with model test results. • Displacement and inner force of pile group induced by shield tunnelling was evaluated. The shield tunnelling adjacent pile group was a common phenomenon in urban metro construction, and additional internal force and displacement field of pile group was disadvantageous to existing superstructure. In this paper, a micro shield machine was invented to simulate the shield tunnelling process, and a series of physical scale model tests and 3-D nonlinear FE models were employed to investigate the pile group (2 × 2) response with different minimum distance between pile group and the tunnel central line (H m) in clay. The results indicated that large additional bending moment and axial force was induced by shield tunnelling, the maximum bending moment was near the tunnel center line, and the amplitude of maximum bending moment in the lateral section (M y) was three to five times of that in the longitudinal section (M x). The maximum lateral displacement emerged at the tunnel central line, and the vertical displacement distributed uniformly along pile length. The negative shaft resistance between pile group and surrounding soil obviously reduced the axial bearing capacity. The shielding effect of the front pile on the rear pile greatly reduced its internal force and displacement, but it gradually weakened with increase of H m. The internal force and displacement of pile group decreased quickly with increased of H m. The research results in this paper can provide a reference for the design and construction of shield tunnels near pile group. [ABSTRACT FROM AUTHOR]

• Developed a 3D visualization and assembleable geomechanical model test system. • Conducted the model test of the construction of super span and small clearance tunnels. • Simulated the construction process of super span and small clearance tunnels based on FDM. • Revealed the construction mechanics response of super span and small clearance tunnels. • Provide a reference to the safe construction of the super span and small clearance tunnels. In order to study the mechanics response law of lager span and small interval tunnels during the construction process, this paper took the Jinan Southeast Second Ring Engineering-Daling Tunnel as the research object, and developed a large-scale 3D visible and assemble geomechanical model test system. Based on that, we carried out a model test and numerical simulation of the construction progress of the Daling Tunnel, and we studied the mechanics response law by monitoring the deformation and stress changes of the surrounding rock in real time. Combined with the results of the model test and the numerical simulation, the mechanical characteristic response law of the construction process of the lager span and small interval tunnels was revealed, and we found that: 1) The deformation of the surrounding rock of the lager span and small interval tunnels showed a change law of "slow settlement-rapid settlement-tending to be gentle". And the stress release of surrounding rock shown a change law of "load accumulation-load release-tending to be stable"; 2) The excavation of the section ③ caused the largest settlement of the vault surrounding rock, which accounted for about 18.5% of the settlement value. The order of the influence degree of the surrounding rock deformation of the vault was ③＞②＞④＞①, which were almost the same with the law of the stress release of the surrounding rock; 3) The excavation of the tunnel ② caused the largest convergent deformation of the surrounding rock of the side wall, accounting for about 26.4% of the total convergent deformation. The order of the degree of influence of excavation on the deformation of the surrounding rock of the side wall was: ②>④>③>①, which were almost the same with the law of the stress release of the surrounding rock. The technical methods and conclusions formed in this experiment have important guidance and reference significance for related projects. [ABSTRACT FROM AUTHOR]

• The integrity of push–pull airflow influences the smoke control effect greatly. • When the momentum ratio R ≥ 6.5, the smoke control efficiency exceeds 90%. • Smoke accumulation is easy to occur within 5 m near the air curtain. • The escape door should be settled outside 10 m of the air curtain. A new type of push–pull air curtain was designed, and the smoke control effect was verified by carrying out a small-scale smoke control experiment in a model tunnel. The experimental results show that when the air volume of the system is the same, the smoke control effect of the push–pull air curtain is better than that of exhausting smoke from the side wall of the tunnel. The greater the velocity of the push air, the better the smoke control effect of the air curtain, and the effect of the jet velocity is greater than the cross-sectional area of the air curtain. FDS was used to numerically simulate the influence of factors such as air curtain spacing, air curtain width, push–pull airflow velocity in a tunnel of actual size on the effect of smoke control. The calculation results show that the smoke control ability of air curtain depends on the integrity of the air flow composed of incoming smoke and push–pull air flow. The smoke control efficiency E increases with the increase of momentum ratio R between push air flow of the curtain and incoming smoke flow. For the fire scene given in the paper, when the air curtain spacing is 80 m, the width of the push outlet and pull inlet are 0.6 m and 1.2 m, and the speed of push and pull air speed are 16 m/s and 23 m/s respectively; the momentum ratio R is greater than 6.5, and the smoke control efficiency E of the air curtain can exceed 90%. [ABSTRACT FROM AUTHOR]

• The influence of dilatancy angle on the limit support pressure and the failure zone is analyzed. • A 3D theoretical model in cohesive–frictional soils is proposed. • The accuracy of the proposed model is validated by comparing with other approaches. This paper aims at analyzing the influence of non-associated flow rule on face instability of a circular tunnel in cohesive–frictional soils. A series of three-dimensional numerical simulations are performed to analyze the influence of dilatation angle on the limit support pressures and the failure zones. The dilatation angle significantly influences the limit support pressure and the failure zone. Then, a three-dimensional failure mechanism that consists of the ellipsoid and the multi-block is proposed based on the upper-bound theorem. Finally, the limit support pressures and failure zones obtained from the new mechanism are compared with those given by existing approaches of limit analyses, numerical simulation and centrifuge tests. The results indicate that the presented model is more effective in analyzing the face stability of tunnels. [ABSTRACT FROM AUTHOR]

• The previous constitutive law of the pile elements was improved with the tri-linear constitutive relation. • Credibility of the modified numerical model was confirmed with physical pull results. • Loading behaviour of bolts under the in-situ condition was studied with the modified numerical model. This paper modified the original structural elements of pile in FLAC3D to analyse the performance of rock bolts. For the contact surface between the bar and the binding grout, bonding behaviour was modelled using the tri-linear constitutive relation. Pull tests were used to testify the effectiveness of the modified pile elements. A satisfactory correlation was acquired between the modelling and physical results. This testified that the improved pile elements can successfully analyse the performance of bolts. Then, a numerical coal roadway was established and reinforced with the modified pile elements. After equilibrium, a non-uniform force distribution occurred along bolts. The axial force around the middle was maximal and the tensioning force at two ends of the bolt was minimal. A parametric analysis was performed to analyse the effect of relevant factors on performance of bolts. The results showed that with the bonding strength of the bolt surface raising, the neutral point shifted towards the excavation direction. Moreover, when the applied vertical stress was beyond a limit, the axial force in the bolts installed in the roadway side reduced dramatically. However, for the bolts installed in the roof, the axial force in the bolts was still raising. [ABSTRACT FROM AUTHOR]

• Influence of dilation angle on tunnel face passive instability was investigated. • A new analytical model considering partial failure and dilation angle was proposed. • The accuracy of the proposed model was validated by comparing with other models. This paper aims at analyzing the influence of non-associated flow rule on passive face instability for shallow shield tunnels. The influence exerted by dilation angle on the limit support pressures, the failure zones and partial failure ratios is investigated by numerical simulations. Based on the failure zone obtained from numerical simulation, a log-spiral mechanism is proposed. The upper-bound theorem is employed to acquire the limit support pressures, failure zones and partial failure ratios. The analytical results indicate that dilation angle has a significant influence on the limit support pressure and failure mechanisms. Finally, by comparison with the numerical models and existing analytical models, the results indicate that the proposed log-spiral model has a certain accuracy in analyzing the face instability of blow-out. [ABSTRACT FROM AUTHOR]

• 32 loading levels in 3 physical models with different σ max direction are conducted. • The smaller the angle of σ max direction and tunnel axial, the tunnel is more stable. • If σ max direction is perpendicular to the tunnel axial, spalling is occurred. • If σ max direction is parallel, ring-like failure is occurred when σ max is large. • With increase of σ max , the effect of its direction increases. The major principal stress direction of the tunnel is one of the most important factors affecting the stability of an underground tunnel. This paper is devoted to the quantitative analysis of the effect of the major principal stress direction respect to the tunnel long axis on the stability of an underground tunnel. A total of thirty-two loading levels with three physical models combined with the numerical simulation were conducted. The results indicated that, with the decrease of the angle between the major principal stress direction and the long axis of the tunnel, the tunnel becomes more stable. For the load at which cracks begin to occur in the tunnel, when the major principal stress direction is parallel to the tunnel axis, there are no cracks in the tunnel until the load reaches approximately twice as much that of perpendicular. When the major principal stress direction is perpendicular to the tunnel axis, the failure involves spalling. The cracks initially occur at the corner of the tunnel, and then propagate along the sidewall in the form of a parabola. When the major principal stress direction is parallel to the tunnel axis, the failure involves ring-like damages. Cracks appear at the top and bottom of the tunnel, and connect with the cracks on the sidewall. With the increase of the principal stress, the effect of the major principal stress direction increases. [ABSTRACT FROM AUTHOR]