Buried Tunnel Research Articles

Research on spatiotemporal patterns of ground deformation caused by shallow buried tunnel construction in urban areas based on three-dimensional numerical simulation

According to incomplete statistics, since 2018, there have been as many as 15 geological safety accidents caused by urban subway construction in Guangzhou, resulting in significant loss of people’s lives and property and social impact. The main reason for this is insufficient research on the spatiotemporal patterns of ground deformation caused by shallow buried and underground excavation tunnel construction in complex disaster-prone environments and a lack of targeted geological risk prevention measures. This study combines various methods such as statistical analysis, on-site investigation and monitoring, and numerical simulation to reveal the spatiotemporal deformation laws of the ground caused by the construction of shallow buried and underground tunnels in cities. The results obtained can provide a reference for reducing or preventing ground accidents caused by urban subway construction, thereby better ensuring the safety of people’s lives and property.

Role of foliation occurrence and stress orientation on asymmetric failure in foliated rock tunnel: insight from numerical simulation

The failure problem of deep-buried foliated rock tunnel is very prominent, which often presents asymmetry. Moreover, this failure is closely related to foliation occurrence and in-situ stress, and its mechanism is still unclear at present. In this study, a deep buried foliated rock tunnel in a hydropower station was taken as a case, and its failure mechanism was studied by using CASRock software embedded with three-dimensional equivalent continuous mechanical model of foliated rock. On this basis, the relationship and mechanism between the failure of deep-buried foliated rock tunnel and foliation occurrence, in-situ stress and tunnel axis were systematically studied. The results indicate that when the angle between the foliation strike and the tunnel axis (γ) is small, the surrounding rock will experience a larger range of failure. As the γ increases, the depth and degree of failure will significantly decrease. The dip angle of foliation (θ) and the orientation of maximum principal stress determine the failure location of tunnel section. When designing foliated rock tunnels, the angle between the foliation strike and the tunnel axis (γ) should be minimized as much as possible. When the γ is small, more attention should be paid to the orientation of the stress concentration area and its angle with the foliation on the tunnel section after excavation, and support should be strengthened for the small angle parts. This study has important guiding significance for the design, understanding of failure mechanisms, and disaster prevention and control of foliated rock tunnels.

Tunnel construction in shallow soft rock using the pipe shed support

In order to clarify the impact mechanism of shallow buried soft rock tunnel excavation on the upper existing highway, as well as the mechanism of pipe shed reinforcement, a combination of theoretical analysis and on-site monitoring was used to conduct in-depth research on the Diantou Tunnel Crossing the existing highway project of Dayong Expressway. The impact of shallow buried soft rock tunnel crossing construction on the existing highway and safety control issues were studied, a new deformation control index, namely deformation difference rate, was introduced. The results show that the main lateral area of influence of rock deformation is within a distance of one diameter, and the overall area of influence is within a distance of twice the diameter. From the perspective of axial tunnel deformation, the deformation of surrounding rock tends to be stable when the excavation face passes through the monitoring section about twice the tunnel diameter. Effectively controlling rock deformation depends on the total amount of settlement deformation, the change rate of deformation, and the difference rate of deformation. For V-class shallow buried tunnel surrounding rock, in order to prevent cracks on the surface, the cumulative deformation of the surrounding rock needs to be less than 50 mm, the change rate needs to be less than 3 mm/day, and the difference rate needs to be less than 5 mm/m. Finally, the proposed control standard for surface subsidence is given for similar engineering reference.

Analysis of dynamic behavior and damage mode of shallow buried tunnel due to underwater explosions

In order to explore the dynamic behavior and damage mode of shallow buried tunnel induced by underwater explosions (UWEPs), a fully coupled numerical model of a shallow buried tunnel based on Arbitrary Lagrangian and Eulerian (ALE) method was established. The strain rate effects of concrete and steel bar under explosion load, the explosion wave propagation, the interaction between fluids and solids, and the nonlinear response of the structure were considered. The reliability of the numerical method was verified by comparing the experimental and analytical results. The damage process and damage mechanism of submerged shallow buried tunnel due to UWEPs were investigated. The effects of saturated soil covering, explosive weight, buried depth and water depth on the dynamic behavior and damage mode of the tunnel were discussed. Finally, the dimensional analysis was used to obtain the functional relationship between the peak displacement, charge weight, buried depth and water depth. The results show that the saturated soil covering can effectively reduce the impact of explosion load on the tunnel. Increasing the buried depth can mitigate the blast effects on the structure, and the failure modes switch from local damage to global failure. The response of the tunnel increases with the increasing water depth, but the influence of water depth decreases gradually. The damage modes of shallow buried tunnel can be classified into local punching or spalling damage, global bending failure accompanied by spalling damage, and global bending failure.

Time-series prediction of settlement deformation in shallow buried tunnels based on EMD-SSA-GRNN model

Tunnel settlement deformation monitoring is a complex task and can result in nonlinear dynamic changes. To overcome the disturbances caused by historical data and the difficulty in selecting input parameters during deformation prediction, a decomposition, reconstruction and optimization method for tunnel settlement deformation prediction is proposed. First, empirical mode decomposition (EMD) is used to decompose the in-situ monitoring data and reduce the interactions among information at different scales in sequences. Then, the monitoring data are decomposed into intrinsic mode functions (IMFs). Secondly, the smoothing factor of the generalized regression neural network (GRNN) is optimized by using the sparse search algorithm (SSA). An EMD-SSA-GRNN deformation prediction model is developed using the optimized GRNN algorithm and is used to predict the changes in the decomposed IMFs. Finally, using the measured deformation data from a shallowly buried tunnel along the Kaizhou-Yunyang Highway in Chongqing, China, the reliability and accuracy of different models are analysed. The results show that tunnel settlement deformation exhibited a trend and a slow change in the early stage, a rapid change in the middle stage and a slow change in the late stage, and the rate of change was significantly influenced by the excavation time and the upper and lower geological layers. The prediction accuracy of the EMD-SSA-GRNN model after EMD improved from 19.2 to 59.4% relative to that of the SSA-GRNN and single GRNN models. Moreover, we find that the three error evaluation indicators of the EMD-SSA-GRNN model are lower than those of the other models and that the results of the proposed model and are more strongly correlated with measured data.

Transport of nitrate-containing groundwater to coastal areas through buried tunnel valleys, Denmark

Nitrogen impact on the aquatic environment, including coastal areas, is too high in many countries worldwide, particularly in areas with intensive agriculture. Efficient mitigation initiatives demand that important pathways and the fate of nitrate in the hydrological cycle are known. In this study, we focus on groundwater nitrate contamination in two near-shore catchment areas in north-west Denmark. Groundwater in the area is mainly located in buried tunnel valleys, which are subsurface structures eroded by meltwater during Pleistocene glaciations in former glaciated areas. Groundwater samples from the aquifers inside the buried valleys reveal the presence of up to 120 mg/l nitrate down to 10 m below sea level and about 1 km down from the stream outlet towards the coast. We interpret the complex tunnel-valley infill to be responsible for the spatial heterogeneity of the groundwater geochemistry, where sandy geological windows create localised hydraulic pathways and complex redox structures. Groundwater and stream water chemistry in the study area clearly demonstrate the role of groundwater in nitrate transport within the catchment as well as the direct pathway to the coast bypassing the stream and riverine systems. Our results show that the buried tunnel valleys potentially contribute to submarine groundwater discharge and therefore could be responsible for a hitherto unaccounted input of nitrogen to the marine environment.

The infill of tunnel valleys in the central North Sea: Implications for sedimentary processes, geohazards, and ice-sheet dynamics

Tunnel valleys are widespread in formerly glaciated regions such as the North Sea and record sediment transport beneath ice sheets undergoing deglaciation. However, their complex infill architecture often makes their implications for ice-sheet processes difficult to unravel. Here, we use high resolution 3D (HR3D) seismic-reflection data, improved-resolution conventional 3D seismic-reflection data, and geotechnical information from industry-acquired boreholes to image the infill architecture of buried Quaternary tunnel valleys in the North Sea in unprecedented detail. Ten cross-cutting generations of tunnel valleys are mapped beneath the seafloor of the North Sea where only seven were visible previously. Each generation of tunnel valleys potentially reflects a different glaciation, although our evidence may imply that it is possible to rapidly erode and infill multiple generations of tunnel valleys within a single glacial cycle. The infill of the oldest tunnel valley generations reflects sedimentation during relatively gradual ice-sheet retreat, with occasional episodes of overriding by re-advancing grounded ice. Tunnel valleys formed in more recent glaciations are characterised by more variable sedimentation patterns that reflect dynamic fluctuations of the ice margin, including readvances and stagnation, during valley filling and ice retreat. Numerous subglacial landforms are also imaged within the tunnel valleys; these sometimes contain shallow gas accumulations that represent geohazards for seafloor infrastructure installations. In addition, we document examples where salt diapirism has caused fluids to migrate upwards from depth through faults and into the near-surface tunnel valleys. In instances where this occurs, the relatively porous and often highly continuous subglacial landforms present within their infill may allow these fluids to spread laterally for kilometres or even escape from the seafloor; it is therefore important to consider tunnel valleys when monitoring possible CO2 leakage from carbon capture and storage efforts.

Effect of rock nonlinear mechanical behavior on plastic zone around deeply buried tunnel: An efficient semi‐analytical solution

AbstractAdopting the novel proposed unified strain‐hardening and strain‐softening (UHS) model and finite difference method, an efficient semi‐analytical solution is proposed to study the influence of the nonlinear behavior of rock on ground reaction. The proposed solution eliminates stress vibrations of the classical method that occurred in the strain‐hardening zone, because it judges the elastic or plastic state of the calculation nodes before calculating the ground reaction; compared with the iterative solution, the proposed solution avoids iteratively solving for the plastic internal variables at each calculated node, resulting in that its computational efficiency is improved by more than 10 times. The proposed solution was verified by comparing it with the iterative solution, and numerical solution. Moreover, the effects of initial yield strength, peak strength, residual strength, and supporting pressure on ground reaction after tunnel excavation are studied. The results show that increasing the initial yield strength and residual strength will obviously decrease the plastic zone (PZ) and sub‐zones. The peak strength of rock has limited influence on the radius of PZ, which mainly adjusts the ratio of each sub‐zone in PZ. In addition, increasing the support pressure is an effective means to control the radius of PZ and sub‐zones in deep buried tunnels.

Experimental study on stress distribution characteristics of a shield tunnel under passive failure

Urban rail transit construction will inevitably encounter tunnel working conditions with extremely complex surrounding environment and buried deep shield tunnel, and the stability of the tunnel surface cannot be ignored. A series of passive instability geotechnical model tests were carried out on the tunnel faces at different burial depths. The earth pressure, lateral earth pressure coefficient and soil arch area evolution law caused by passive instability of the tunnel face in sandy cobble stratum were studied. Once the preset position is reached, the rotation is stopped using the cutterhead and the screw excavator and the shield machine continues the jack, simulating passive instability of the tunnel face. The results show that the soil pressure in the horizontal earth pressure is significantly more affected by the passive instability of the tunnel face than the vertical direction. The soil in front of the excavation caused by the ejection of the shield machine is squeezed and moved forward, resulting in a decrease in horizontal earth pressure perpendicular to the direction of shield tunnel excavation. The results of the passive instability region obtained by numerical simulation are larger than those obtained by model experiments, because the numerical simulation method fails to consider the compacting effect caused by the extrusion of sandy cobble formations. It can be found that the uplift value of C/D = 1.0 is significantly greater than that of C/D = 1.5, which also confirms the conclusion that the instability area with a relatively small burial depth is larger and develops farther to the front of excavation.

The submerged Palaeo-Ems River in the Quaternary stratigraphic context of the German North Sea

During the Late Pleistocene, the Palaeo-Ems system (PES) was one of the major tributary channels feeding the Elbe Palaeovalley (EPV) and formed an important part of the drainage system of the continental northwestern Europe unglaciated hinterland. In this study, a detailed interpretation of high-resolution 2D sub-bottom profiler and Boomer grids were used to map the overall course of the submerged PES channel, as well as its spatial and stratigraphic relationships with other Quaternary geological units in the German North Sea. Mapping of buried tunnel valleys, a lacustrine-fill unit, straight channel structures was also carried out. The sedimentary record of the PES is represented by a low gradient and meandering channel which branched into two major pathways as it approached the EPV western flank. Its upstream to downstream trends, coupled with seaward decreasing gradient and sinuosity, are similar to those visible in present-day river deltas. Both the PES and EPV subsequently formed a combined depositional system, which was successively drowned due to the fast-rising relative sea level that overwhelmed the adaptation capabilities of the joint drainage system. For the first time, this study sheds light onto the PES/EPV morpho-stratigraphic relationships which played a key role in the coastal landscape architecture of the German North Sea since the Late Pleistocene.

Dynamic response of water-rich tunnel subjected to plane P wave considering excavation induced damage zone

The stability analysis of a deep buried tunnel subjected to dynamic disturbance is an important issue. In this study, the transient response has been obtained by establishing a water-rich tunnel model considering excavation damage zone (EDZ). Based on Biot’s two-phase dynamic theory and wave function expansion method, the analytical solution of dynamic response around the water-rich tunnel containing EDZ subjected to P wave is derived. Moreover, Fourier transform and Duhamel’s integral technique is introduced to calculate the transient response, and the equivalent blasting curve is adopted to input excitation function. The dimensionless parameters thickness N and shear modulus ratio μ∼ are defined to characterize the degree of damage in the surrounding rock, investigating the influencing factors, such as the parameters and the incident source frequencies. The results indicate that the dynamic stress concentration factor (DSCF) gradually decreases as the dimensionless parameters increase. Additionally, it is observed that the DSCF is more sensitive to changes in the thickness parameter N. Finally, the influence of the waveform parameters has been taken into account in the analysis of transient response, and the stress state and transfer process in each time stage of the EDZ are analyzed. This study establishes a theoretical foundation for comprehending the mechanical behavior and support design considerations associated with a deep-buried water-rich tunnel containing EDZ.

Coupled FEM–DEM analysis of mountain tunnels subjected to explosion-induced landslide

In this study, the onset of a landslide induced by an explosion within a shallow buried mountain transit tunnel was simulated using a coupled finite-element–discrete-element method (FEM–DEM). Two cases of mountain tunnels were considered for the investigation: a continuous tunnel passing through the mountain body and the terminal end of the tunnel. The effect of the location of the explosion inside the tunnel and the angle of slope on the dynamic response of the tunnel and landslide mechanism were investigated. The initiation of landslide and the location of mobilisation of overlying soil varied as the location of the explosion was changed. Time of initiation increased when the explosive was positioned away from the mouth of the tunnel. Changing the location of the explosive also affected the tunnel's response. Highest displacement and acceleration were observed at the crown in the tunnel section where the explosive was positioned. However, regardless of the location of the explosive, substantially high displacement and acceleration were still observed at the mouth of the tunnel. Early triggering of a landslide occurred when the slope angle was increased for the same location of explosion. However, the effect of slope angle on the response of the tunnel was minimal.

An analytical approximate solution for stress and displacement around a shallow circular tunnel excavated under concave slope topography

For shallow buried tunnels under slope, overloading on the ground surface and unloading of excavation both significantly influence the stability of the tunnel surrounding rock and slope. This study proposes an analytical approximate solution for the stress and displacement around shallow buried circular tunnel under slope boundary. In derivation process, the original problem is divided into two models: Model A is a slope plane without any holes subjected to gravity and surcharge load along the ground surface, and Model B is a tunnel contained in a slope plane loaded by released stresses along the tunnel boundary. Furthermore, Model B is decomposed into another two models: Model B1 represents a slope without holes subjected to virtual surface force along the ground surface, and Model B2 is an infinite domain containing a tunnel loaded by another virtual surface force along its boundary. Two sets of virtual surface forces are then achieved by an iterative calculation. The solution, which strictly meets all stress boundary and compatibility conditions of the original problem, are ultimately solved by superposing the solution of Models A, B1 and B2, respectively obtained by the method proposed by the authors (Models A, B1) and complex variable theory (Model B2). The convergence of iteration process and good agreement between the derived and numerical results under the same assumptions verify the correctness of the proposed solution. Furthermore, a parametric investigation is performed to investigate the influence of surcharge load position, slope topography and tunnel position on the stress and displacement around the tunnel and near the ground. The proposed solution is of great value for the conceptual understanding of mechanical behavior of shallow tunneling in slope terrain and for verifying the numerical models. Moreover, the solution is useful for the preliminary design of tunnels at shallow depth under slope topography.

A new method and application of groundwater prediction along the direction of tunnel excavation in karst strata

Abstract Tunnel construction in karst strata with abundant water causes changes in the surrounding groundwater environment, which can easily trigger geological disasters such as mud and water inrush. How to accurately predict the groundwater ahead of tunnel excavation face is a highly challenging problem. In order to improve the detection accuracy of groundwater during the construction of a deep buried tunnel, the transmission and reflection process of seismic waves at the interface and the relationship between the reflection coefficient and seismic wave signal have been analyzed on the basis of a two-phase medium theory in this paper. The expression of seismic wave stress–response relationship associated with the instantaneous amplitude and instantaneous phase and frequency is established. Then the relationship between seismic wave attributes and groundwater seepage potential energy is derived by combining the fluid mechanics theory, which is used as the basis for the determination and identification of groundwater volume and classified, and a new technology of an advanced detection of groundwater by seismic waves is established. This method has been applied to the Zhanghuai Railway in China and quantitatively predicted the karst water and caves in the Tianqiaoshan Tunnel before excavation. The engineering test proves the reliability and advancement of this technology.

Thermomechanical performance of energy retaining pile influenced by surrounding utility tunnel via the regression tree model

The thermomechanical performance of energy retaining pile differs from that of axisymmetric energy pile due to utility tunnel excavation. This study presents four field tests of energy retaining pile conducted before and after utility tunnel construction. A regression tree (RT) model for predicting the thermally induced stress of energy retaining pile was established based on the measured water temperature, pile temperature and previous stage thermally induced stress to evaluate the effect of shallow buried utility tunnel on the thermomechanical performance of adjacent energy pile. The established thermally induced stress RT prediction model could acceptably predict the thermally induced stress of the future short-team. Surrounding utility tunnel excavation alters the distribution of the axial thermally induced stress. The axial thermomechanical response of the energy retaining pile after utility tunnel construction is approximately 50% that before utility tunnel construction. The asymmetrical boundary conditions cause a limited bending moment of the energy retaining pile at the top or bottom of the utility tunnel, which is not enough to threaten the pile safety. Moreover, the thermal performance of the energy retaining pile slightly increases due to the heat exchange between the pile and the air in the surrounding utility tunnel.

Tunnel Lining Stability and Structural Damage Threshold under Seismic Loading

To analyze the damage distribution characteristics and ultimate bearing capacity of tunnel linings under seismic action, damage variables were introduced into the Mohr-Coulomb constitutive model. Thus, an incremental elastic–plastic damage constitutive model for concretewas constructed. Uniaxial tensile and compressive tests were performed to verify model reliability, and the damage thresholds for different strength classes of concrete under the test conditions were numerically obtained when destruction occurred. These damage thresholds were considered as the criteria for material failure to solve the ultimate bearing capacity and failure form of the tunnel structure. Calculation results demonstrate that as the peak ground acceleration increases, the shallowly buried tunnel structure presents the three following stages: elastic bearing, local instability, and overall instability. If the compression or tensile damage values of an element exceed the threshold value, the element is regarded as destroyed. The failure of any element of a structure can be used as a criterion for local instability. If the volume of the destroyed elements exceeds 10% of the overall volume of elements, and the proportion of destroyed elements in the lining shoulders and side walls begins to abruptly increase, the structure can generally be regarded as unstable.

Test and damage assessment of shallow buried RC tunnel under explosion

As a major element of the transportation network, tunnels are unavoidably threatened by accidental loads such as vehicle bombs and tank truck explosions. The goal of this research is to explore the dynamic characteristics and damage assessment of tunnel structures under contact blast loads. First, three scaled-down reinforced concrete tunnel models were made, and the explosion test and static loading test were carried out successively to evaluate the axial residual bearing capacity, axial displacement and failure mechanism of the tunnel. Secondly, the finite element model is built by utilizing LS-DYNA, and the reliability of the finite element method is confirmed by comparing the data of the explosion test with the static loading test. At the same time, the calculation method for damage coefficient and the classification criteria for damage grade based on axial residual bearing capacity are presented. Then, based on the finite element method, the propagation process of the explosion shock wave in the tunnel and the damage mechanism of the tunnel are investigated. Finally, seven explosion scenarios are developed, the damage degree of these seven tunnels under the blast load is quantitatively analyzed, and further anti-blast design ideas are put forth. The study in this article may give an intended reference for the damage assessment, anti-explosion design and strengthening work of reinforced concrete tunnels.

Research on Construction Sequences and Construction Methods of the Small Clear-Distance, Double-Arch Tunnel under an Asymmetrical Load

A small clear-distance, double-arch tunnel under an asymmetrical load combines the characteristics of small clear-distance, tunnels and double-arch tunnels, and the influence of an asymmetrical terrain must be considered. Its construction stability is a problem worth studying. This paper used the Wengcun tunnel as the engineering background. Midas/GTS finite element analysis software was used to study the effects of eight excavation sequences and two excavation methods on tunnel stability. The results showed that the deformation and force of the tunnel were asymmetric under the asymmetrical terrain. Both middle partition walls were deformed towards the shallowly buried side, and the shallowly buried side was deformed to a greater extent. Excavating shallow side tunnels first can effectively mitigate the impact of asymmetric terrain. The arch settlement of the Center Diaphragm Excavation Method is 1.33 cm, which is smaller than the three-step excavation method of 1.48 cm; however, this difference is not significant. The Three-bench Excavation Method was more efficient. Based on the conclusion of a numerical simulation, the construction site adopted the construction sequence of excavating the shallowly buried side tunnel first and adjusted the excavation method to the Three-bench Excavation Method.

Calculation of Rock Pressure in Loess Tunnels Based on Limit Equilibrium Theory and Analysis of Influencing Factors

The research on the calculation method of tunnel envelope pressure is a key issue in the design of tunnel engineering support structure. Based on the limit equilibrium theory, this paper proposes a method to calculate the surrounding rock pressure in shallow buried loess tunnels. Firstly, based on the investigation of the damage mode of the loess tunnel surrounding rock and the field measurement results of the surrounding rock pressure, the damage mode of the loess tunnel is proposed, and then a method of calculating the surrounding rock pressure applicable to the shallow buried loess tunnel is derived according to the limit equilibrium condition of the tunnel square soil body and the side wedge; the basic mechanical parameters are known in this method, so only the rupture angle β needs to be determined, and the rupture angle calculation model in the shallow buried loess tunnel is proposed Three assumptions are made in the rupture angle calculation model, and the rupture angle calculation formula is derived according to the stress state on the slip surface of the surrounding rock; the pressure of the surrounding rock in the loess tunnel obtained by this method is compared with four methods, namely, the pressure theory of the surrounding rock in the existing loose body of Taishaki, the pressure formula of the deeply buried surrounding rock in the railroad tunnel design code, the Beer Baumann method, and the Xie Jiayi method, in order to verify the correctness and validity of the calculation method used, and to analyze the influence of different parameters on the surrounding rock pressure. The innovation of this paper lies in the derivation of a method for calculating the pressure in the surrounding rock of a shallow buried loess tunnel using the limit equilibrium theory, and also further proposes a formula for calculating the rupture angle. The pressure of surrounding rock decreases with the increase of static earth pressure coefficient, lateral pressure coefficient, friction angle and cohesion in soil, but the static earth pressure coefficient has a greater influence on the surrounding rock pressure. With the increase of sagittal span ratio, tunnel burial depth and soil weight, the surrounding rock pressure peaked with the increase of tunnel burial depth, and the surrounding rock pressure curve increased first and then decreased.

Blast test and probabilistic vulnerability assessment of a shallow buried RC tunnel considering uncertainty

The purpose of this investigation is to analyze the failure probability of a blast in a shallow RC tunnel. The field blast tests are carried out, and a refined finite element model (FEM) is established based on LS-DYNA. To account for blast uncertainty, the Monte Carlo method is used to determine 150 blast conditions. A failure evaluation method based on a mechanical performance index is proposed. The probabilistic blast demand model (PBDM) and the probabilistic blast capacity model (PBCM) are established. Finally, a probability assessment framework based on the structural performance index and the vulnerability curve for shallow tunnels are established. According to the findings, when the mass of TNT in the tunnel exceeds 300 kg, the tunnel is in danger of collapsing. At this moment, it is suggested that people enter the tunnel cautiously. The vulnerability curve predicts the failure probability of a tunnel under various blast loads. At the same time, it could assess its structural performance after the disaster.