Search Results (9)

Tunnels are critical components of transportation networks. Explosions caused by accidents or terrorist attacks can severely damage tunnel linings and even cause structural collapse. This paper develops the validated simulation model for single-channel tunnels into a twin-channel tunnel model. Subsequently, a simulation study investigates the damage state and vulnerability of the twin-channel tunnel under single-sided internal blasting. The results suggest that the supporting effect of the soil can improve the blast resistance of the outer wall of the tunnel. An explosion within a single channel can induce changes in the relative bearing capacity of the twin-channel lining. Under the influence of earth pressure, the relative bearing capacity of the twin-channel lining is further weakened, thereby affecting the overall failure state of the tunnel. Longitudinal plastic strain is primarily distributed at the ends and center of walls and floors, and it spreads as the charge mass increases. The charge location has a significant impact on the damage state of the outside walls of the uncharged channel of the tunnel. Placing explosives on tunnel walls will increase the damage level of the twin-channel tunnel. When the charge weight exceeds 1000 kg and 3000 kg, respectively, the exceedance probability for minor damage and severe damage to the tunnel approaches 1. The strengthening of the blast protection level of the center wall is the key to preventing tunnel collapse. Full article

Accurate assessment of aerodynamic resistance in mine ventilation networks is essential for ensuring operational safety and energy efficiency, yet traditional measurement approaches remain time-consuming and prone to uncertainty. This study presents a novel methodology for constructing digital ventilation models of underground mine workings using markerless LiDAR scanning combined with automated data processing. The proposed procedure includes segmentation of point clouds into sections, calculation of geometric parameters, and direct determination of resistance coefficients, which are subsequently exported to VentSim software. The approach was validated through a case study conducted in a Polish coal mine, where a 369 m ventilation siding was scanned and analyzed. The comparison between numerical simulations and in situ measurements demonstrated strong agreement, with differences not exceeding ±5% for airflow velocity, pressure drop, and total flow rate, while larger deviations were observed for cross-sectional area (+5.1%). The method is limited by potential inaccuracies in determining excavation geometry, which can lead to errors in calculating resistance coefficients, particularly at excavation intersections and at the beginning and end of scanning sections. Point cloud analysis, determination of resistance coefficients for individual sections (segments), spatial transformation, and point cloud reduction, along with integration with VentSim, are based on Python scripts. Calculation results can be easily exported to other computational programs. The proposed approach enables integration with various sensors and allows for assigning this value directly to a given section (segment of the excavation). The method can support the construction of digital twins for mines or underground tunnels. The implementation codes of the developed algorithms have also been made available for educational and scientific purposes under the Modified GNU General Public License v3 (GPLv3). Full article

Shallow-buried, closely spaced tunnels under bias loading often encounter stability challenges due to excavation-induced interaction effects. These effects are particularly significant in the middle rock pillar zone. To evaluate the influence of face lag distance on tunnel stability, the Georgia No. 1 Tunnel was selected as a case study. Numerical simulations and field monitoring were combined to analyze the deformation and stress evolution under different face lag distances. The analysis focused on ground surface settlement, vault displacement, and tunnel clearance convergence. The results indicate that ground surface settlement decreases notably as the face lag distance increases. When the face lag distance increased from 0.5 D to 2.0 D, the maximum settlement decreased by about 11.9%, with the absolute maximum measured value of approximately 3.48 mm. Stress concentration occurred mainly within 15 m behind the excavation face, suggesting that a face lag distance exceeding this range can effectively mitigate tunnel interaction effects. The biased tunnel side experienced greater vault settlement and convergence, requiring closer monitoring. An insufficient face lag distance amplifies deformation superposition, whereas an excessive one causes additional horizontal fluctuations. For the geological and structural conditions of the Georgia No. 1 Tunnel, a face lag distance of approximately 2.0 D provides an optimal balance between stability, safety, and construction efficiency. These findings offer practical guidance for the design and safe construction of shallow-buried twin tunnels under bias loading. Full article

The development of urban areas has led to an increase in the use of subsoil for installing transportation networks. These systems usually comprise the construction of side-by-side twin running tunnels built sequentially and in close proximity. Different studies have demonstrated that under such conditions, there is an interaction between tunnels, leading to greater settlements compared with those obtained if the tunnels were excavated separately. Supported by those findings, several analytical methods have been proposed to predict the settlements induced by the excavation of the second tunnel. This paper examines the applicability of these proposals across multiple case studies published in the literature by comparing the analytical predictions with the reported monitoring data of 57 sections. The results indicate that, regardless of the different soil conditions and geometrical characteristics of the tunnels, a Gaussian curve accurately describes the settlements in greenfield conditions and those induced by the second tunnel excavation, although with the curve becoming eccentric in this case. Despite some significant scatter observed, most methods predict the settlements induced by the second tunnel with reasonable accuracy, with Hunt’s method presenting the best fit metrics. The obtained findings confirm that existent methods can be a valid tool to predict the settlements induced by twin tunnelling during the early stages of design, although do also contain limitations and pitfalls that are identified and discussed throughout the paper. Full article

Shallow tunnels induce surface displacements which can cause damage to existing structures; an adequate evaluation of their settlement trough is of paramount importance. Nowadays, it becomes even more critical when dealing with an underground occupation where the green stress field has already been disturbed by previous excavations. Since the end of the last century, many researchers have explored the subject. Some empirical methodologies have been developed based on data from actual cases, sometimes associated with numerical analysis. The present work used plane strain numerical analysis of different geometric arrangements of side-by-side twin tunnels for different depths and distances between tunnel axes to evaluate its compatibility with some of the proposed methods to adjust the settlement profile of the second cavity. It was observed that the discussed methodologies have similar results for maximum settlement and its eccentricity. Nevertheless, the behavior of the trough width parameter from the semi-empirical methods has shown discrepancies. Full article

The effect of a blasting vibration from an excavating tunnel on an adjacent excavated tunnel is of great importance for the stability and security of twin tunnels. Due to the relatively small distance between the tunnel face of the excavating tunnel and the concrete lining of the excavated tunnel, the impact of blasting could be significant and should be considered in a practical project. In order to control the blasting scales during the excavation of one tunnel and minimize the effect of blasting on the adjacent one, research based on field-blasting tests performed on twin tunnels is presented in this study. The particle velocities on the concrete lining of the excavating tunnel caused by blasting from the adjacent excavated tunnel were measured and analysed during six rounds of blasts. According to the measured vibration waves, it was clear that the peak particle velocity (PPV) from each blast was always induced by cut blasting, therefore, the maximum vibration due to each blast was mainly dependent on cut blasting. The measured maximum PPV for all the blasts was 15.55 cm/s, corresponding to a maximum tensile stress of 1.44 MPa observed on the concrete lining, which was smaller than the tensile strength of the concrete lining, in accordance with the one-dimensional elastic-wave theory. Moreover, the attenuation of the vibration waves varied in different regions, and they could be utilized to demonstrate the impact characteristics of the blasting; e.g., the particle velocities in the region along the excavating direction were 1.12 to 1.79 times larger than those in the region opposite to the excavating direction, and the difference increased with the increasing distance to the blasting source. The particle velocities on the side of the excavated tunnel close to the excavating tunnel were larger than those on the other side of the excavated tunnel. However, the particle velocities of the two aforementioned regions were similar when the distance between the measuring point and the blasting source was more than 6 m in the longitudinal direction of the tunnels. Furthermore, the measured vibration waves could be used to evaluate and improve the blast designs of tunnelling with the drill-and-blast method. Full article

Cross-river twin tunnels are prone to deformation and uneven settlement of the surrounding soil due to the complexity of the strata crossed, which has a negative impact on the tunnel structure. A numerical calculation model was established using the COMSOL Multiphysics to study the effects of twin tunnel excavation in composite strata on the ground settlement and the ground settlement pattern. The results indicated that after the construction of the twin tunnels is completed, the ground settlement above the first tunnel is slightly larger than the ground settlement above the second tunnel. The further the spacing between the two tunnels before and after excavation, the smaller the amount of ground settlement and the impact on the surrounding soil. The ground settlement value increases with the increase in burial depth, and the ground settlement curve gradually changes from a W-shaped curve to a V-shaped curve. As the distance between the two tunnels increases, the maximum settlement value of the settlement curve gradually decreases, and the ground lateral settlement curve changes from V-shaped to W-shaped. The higher the water level on the riverbed side, the greater the settlement value of the ground. Full article

Excavation near or above existing shield tunnels often results in adverse impacts on tunnel stability. To ensure the serviceability of existing tunnels, this paper presents experimental and numerical studies with reference to a foundation pit case history excavated above twin-tube shield tunnels in soft soils. The experimental tests were firstly applied to study the deformation characteristics and structural response of the shield tunnels. Thereafter, an extensive numerical investigation was performed to determine the influence of some factors such as cover-to-excavation depth ratio, length-to-depth ratio, and unloading ratio on tunnel displacement behaviors. It was demonstrated that the tunnel heaves as the excavation proceeds, and heaves and horizontal displacements reach their maximum values when the excavation is finished. The earth pressure around the tunnels is symmetrically distributed in a gourd shape, with a larger reduction at the tunnel crown and invert and a smaller reduction at tunnel side walls. Additionally, the earth pressure at the tunnel crown and invert changes more significantly than that at other parts. The tunnel moment increment is significantly affected by the tunnel excavation depth. The axial force at or near the side walls of the tunnel is the most sensitive to the unloading effect induced by the excavation activity. Full article

This paper aims at influence analysis of approaching excavation on adjacent segments for twin tunnels with variable clear spacing located in Beijing, China. A series of numerical simulations have been conducted to investigate the influence of approaching excavation on ground displacements and mechanical responses of segments. What’s more, on-site monitoring was conducted at the position of the minimum spacing between the twin tunnels. It is found that the deformation of the measured segment presents a pronounced asymmetric ovalization when the second tunnel approaches the measured cross-section. During the approaching excavation of the second tunnel, the normal force increases gradually, whereas the bending moment first decreases and then increases. The maximum increments of internal forces in the measured segment are both located at the regions near the second tunnel, in which the springline and shoulder of the segment are mainly subject to the effect of the circumferential compression and axial tension. The approaching excavation reduces the horizontal displacements of the ground between twin tunnels and increases the ground settlements as well as the horizontal displacements of the ground on both sides. The actual tunneling case of first along the curved trajectory and then along the straight-line trajectory can reduce internal forces of the segment. Full article