Soil-tunnel Interaction Research Articles

Soil-tunnel interaction under the effect associated with the longitudinal direction

Longitudinal structural analysis of shield tunnels is studied by considering the tunnel as a Timoshenko beam based on elastic foundations under Vlasov's theory. This article presents the structural behavior of a Timoshenko-Vlasov beam jointly, using a single differential system that brings together all the equilibrium and deformation equations. Solving the presented formulation, shield tunnels can be covered under any type of action, ground pressure and support or boundary conditions. This new compacted notation facilitates the possibility of expressing the interaction between soil and structure by introducing the variability of longitudinal support conditions on the elastic springs. This differential system is resolved with the numeric procedure named Finite Transfer Method. To verify the effectiveness of the procedure followed, the structure of the subway tunnel in Shanghai has been modeled and the results obtained have been compared with those offered in the literature. The proposed model has been exemplified by introducing the variability of longitudinal elastic spring conditions representing actual soil behavior.

Study on the Effect of Burial Depth on Selection of Optimal Intensity Measures for Advanced Fragility Analysis of Horseshoe-Shaped Tunnels in Soft Soil

Seismic intensity measures (IMs) can directly affect the seismic risk assessment and the response characteristics of underground structures, especially when considering the key variable of burial depth. This means that the optimal seismic IMs must be selected to match the underground structure under different buried depth conditions. In the field of seismic engineering design, peak ground acceleration (PGA) is widely recognized as the optimal IM, especially in the seismic design code for aboveground structures. However, for the seismic evaluation of underground structures, the applicability and effectiveness still face certain doubts and discussions. In addition, the adverse effects of earthquakes on tunnels in soft soil are particularly prominent. This study aims to determine the optimal IMs applicable to different burial depths for horseshoe-shaped tunnels in soft soil using a nonlinear dynamic time history analysis method, and based on this, establish the seismic fragility curves that can accurately predict the probability of tunnel damage. The nonlinear finite element analysis model for the soil–tunnel interaction system was established. The effects of different burial depths on damage to horseshoe-shaped tunnels in soft soil were systematically studied. By adopting the incremental dynamic analysis (IDA) method and assessing the correlation, efficiency, practicality, and proficiency of the potential IMs, the optimal IMs were determined. The analysis indicates that PGA emerges as the optimal IM for shallow tunnels, whereas peak ground velocity (PGV) stands as the optimal IM for medium-depth tunnels. Furthermore, for deep tunnels, velocity spectral intensity (VSI) emerges as the optimal IM. Finally, the seismic fragility curves for horseshoe-shaped tunnels in soft soil were built. The proposed fragility curves can provide a quantitative tool for evaluating seismic disaster risk, and are of great significance for improving the overall seismic resistance and disaster resilience of society.

Analysis of mechanical response and failure characteristics of tunnels crossing active faults considering axial force and geometrical nonlinearity

Tunnels subjected to active fault dislocation may experience significant damage. This paper establishes a novel methodology and solution procedure for analyzing the mechanical response and failure characteristics of tunnels subjected to active fault dislocation based on an elastic foundation beam model. The proposed methodology includes axial, transverse, and vertical soil-tunnel interaction terms, in addition to geometrical nonlinearity and axial force terms in the governing equation. This approach has a significantly extended application range, effectively addressing the problems encountered in tunnels crossing active faults with diverse crossing angles, dip angles, and fault types. The proposed methodology is verified by comparison to a 3D FEM model with various fault types, experimental tests, and on-site case, and the results are in excellent quantitative and qualitative agreement with the numerical, experimental, and on-site results. When fault displacement is below 0.5 m, disregarding geometric nonlinearity results in calculation errors of approximately 10% to 17% for peak axial force (Nmax), 18% to 22% for peak shear force (Vmax), and 20% to 30% for peak bending moment (Mmax). Finally, the responses caused by different factors, i.e., fault type, fault displacement, tunnel stiffness, and tunnel diameter, are investigated in detail to better understand tunnels crossing active faults. The results show that amongst the various fault types, the Vmax and the Mmax experienced by tunnels subjected to oblique slip-fault dislocation surpass those of other fault types, accompanied by the most extensive failure range. The augmentation of fault displacement, tunnel stiffness, and tunnel diameter precipitates a corresponding escalation in the Nmax, Vmax, Mmax, and failure range. Under oblique-slip fault dislocation, the tunnel undergoes an initial phase of shear failure, followed by tension-bending failure, delineated by distinct fault displacement thresholds of 0.1 m and 0.2 m, respectively. The proposed methodology provides the advantage of reliable stability analysis and design of tunnels crossing active faults.

Selection of optimal intensity measures for seismic performance evaluation of underground utility tunnel and internal pipeline system

Seismic intensity measures (IMs), which are closely related to both earthquake hazards and structural responses, play a critical role in the performance-based earthquake engineering (PBEE) framework. This paper aims to investigate and define the most representative IMs for probabilistic seismic demand model (PSDM) for the longitudinal utility tunnel and internal pipeline system. Similar to the requirements by the Chinese Code for seismic design of urban rail transit structures, the utility tunnel in this study is assumed being buried in four typical engineering site classes for the analyses. Soil-tunnel-pipeline interactions are simulated using a double-beam system resting on a nonlinear foundation. Soil-tunnel interaction, tunnel-pipeline interaction and joint connections are modeled as nonlinear springs with different mechanical properties. A series of 17 pairs of outcrop ground-motion records and 27 commonly used IMs are selected in the analyses. Engineering demand parameter (EDP) is defined based on the maximum joint opening and the maximum strain of the utility tunnel and internal pipeline, respectively. The selected IMs for predicting the seismic responses of tunnel-pipeline systems are tested using different criteria, i.e., correction, efficiency, practicality, and proficiency. The final decision-making procedure employs a fuzzy multi-criteria decision method. The numerical results indicate that: (1) The velocity-related IMs are the most representative IMs based on the four criteria for structures buried in four sites of different conditions; (2) The optimal seismic IMs vary with different criteria, site classes and structure types. According to the fuzzy multi-criteria decision approach, optimal IMs for the tunnel-pipeline system are PGV, PGV, EPV and HI for site classes I – IV, respectively. The proposed optimal IMs can be utilized to construct seismic fragility curves of utility tunnel, internal pipeline and tunnel-pipeline systems in four different site classes.

Seismic performance and vulnerability analysis for bifurcated tunnels in soft soil

This paper investigates the seismic performance of complex comprehensive interchange underground structures. As an example, the seismic performance of Nanjing underground bifurcated tunnels constructed in soft soil is analyzed. A three-dimensional (3D) numerical finite element analysis model is established considering soil-tunnel interaction to analyze the seismic response characteristics and failure mechanism of the bifurcated tunnels. The results show that the tunnel damage degree is closely associated with the deformation response, and that the inter-story drift ratio of the lower layer is significantly greater than that of the upper layer. The pushover analysis method is used to obtain the seismic performance curve of the tunnel, and inter-story drift ratio limits are defined. The IDA procedure is then used to conduct multiple non-linear dynamic time history analyses based on the 3D finite element model, and IDA curve clusters are drawn with peak ground acceleration (PGA) as the earthquake intensity measures and the peak inter-story drift ratio as the damage measures of tunnels. The corresponding IDA percentiles lines are calculated, and the seismic fragility curves of the bifurcated tunnels are established. The post-earthquake functional failure probability of the bifurcated tunnels is obtained under different seismic fortification performance level.

Mechanical response and failure characteristics of tunnels subjected to reverse faulting with nonuniform displacement: Theoretical and numerical investigation

Tunnels subjected to reverse fault dislocation undergo severe structural damage, and their mechanical response and failure characteristics play a key role in seismic fortification efforts. This paper investigates the mechanical responses and failure characteristics exhibited by tunnels subjected to reverse faulting using theoretical analysis and numerical simulations. A theoretical model is established for analysing the bending moment, shear force, and safety factor of the tunnels under reverse fault dislocation. The nonuniform fault displacement, fault zone width, and nonlinear soil-tunnel interaction is applied in the proposed theoretical model, significantly improving the analysis accuracy and range of applicability. The corresponding numerical simulation based on the XFEM (extended finite element method) is carried out, and the proposed theoretical model is verified by the numerical results. The theoretical results demonstrate excellent agreement with the numerical results when nonuniform fault displacement is considered. A parametric analysis is presented in which the effects of the maximum fault displacement, fault zone width, and ratio of the maximum fault displacement of the footwall to the hanging wall are investigated. The results show that the ultimate fault displacement for compression-bending failure of the tunnel subjected to reverse fault dislocation is estimated to be approximately 30 cm, while the ultimate displacement for shear failure stands at 20 cm. Variations in the fault displacement ratio yield alterations in the distribution pattern and peak values of internal forces, together with shifts in the potential failure ranges of the footwall and hanging wall. Additionally, an initial crack emerged on the tunnel crown near the fault plane, followed by a second crack on the tunnel invert. Upon reaching a fault displacement of approximately 40 cm, the crack fully traverses the entire tunnel lining.

Numerical investigations on the dynamic responses of metro tunnel-soil-ground building under oblique incidence of seismic wave

With the development of urban rail transits, the metro tunnels frequently underpass the above-ground buildings, and understanding the dynamic responses of metro tunnel-soil-ground buildings experiencing oblique incidence of seismic waves is of crucial importance. Considering that the seismic waves in the near-field seismic area are mostly obliquely incident to the ground at a certain angle, a two-dimensional numerical model for tunnel-soil interaction system and tunnel-soil-above ground structure was established by Abaqus software, in which the viscoelastic boundary and equivalent nodal forces were adopted to simulate the ground motion. The effects of tunnel burial depth, tunnel spacing, and tunnel frame spacing on the seismic responses of metro tunnel-soil and metro tunnel-soil-above ground building were analyzed under oblique incidence of SV wave with different incident angles. It was found that the tunnel depth has a significant effect on the lining dynamic bending moment and axial force peak, and its influence is closely related to the site category. The tunnel spacing has a minor impact on the dynamic response of the lining structure. The incident angle has a significant effect on the peak value of the dynamic shaft force of the lining. The application of the frame on the ground has a significant impact on the tunnel. The influence of above-ground buildings and tunnel burial depth should be considered when tunnel design is carried out.

Improved analytical solution for forecasting overlying excavation-induced tunnel response

It is inevitable that deep excavation will induce free movement of the surrounding soil, which will further greatly influence the response of the underlying existing tunnel. Most theoretical studies are concerned with the mechanical equilibrium analysis of tunnel units, ignoring adopting the energy method to simulate tunnel-soil interaction, and further obtain the explicit solutions of tunnel response. On this basis, from the perspective of the energy relation, the existing tunnel’s deformation is simulated using the Rayleigh-Ritz method. Further, its potential energy equation is established based on Pasternak foundation. The minimum potential energy principle is selected to solve the variational tunneling energy solution, and then analytically solving for the overlying excavation-induced deformation on the existing tunnel. The proposed method’s rationality is tested against a series of finite element (FE) results as well as a field case study extracted from previous studies. Compared with the Winkler foundation model degraded from the suggested method, the corresponding results become closer to the measurement data. Additional parameter studies show that the soil elastic modulus, the excavation’s aspect ratio, and the tunnel axis depth are significant factors inducing the response of tunnel. Our proposed theoretical solution is beneficial to predicting the existing tunnels’ latent danger due to overlying excavation in related projects.

Seismic vulnerability of shield tunnels in interbedded soil deposits: Case study of submarine tunnel in Shantou Bay

This paper presents a numerical approach for deriving seismic fragility curves for a submarine shield tunnel subjected to transverse ground shaking in interbedded soil deposits. To simulate the nonlinear behavior of soils, PM4Sand and HS-small constitutive models were adopted. In contrast, the closed-form elastic design method or elastic–plastic design method was used for modeling the shield tunnel lining considering the effect of joints on the seismic performance of structures. Fully coupled numerical analyses provided a satisfactory interpretation of the seismic responses of soil–structure systems considering the effects of groundwater level and soil–tunnel interaction. Subsequently, free-field peak ground acceleration was selected as the intensity measure. The ratio of maximum bending moment to capacity bending moment or permanent joint rotation of the tunnel lining was selected as the damage measure, combined with incremental dynamic analysis, a series of fragility curves were generated. In this study, one-dimensional equivalent-linear earthquake site response analysis was implemented to validate the nonlinear dynamic analysis under weak earthquakes. However, the analysis overestimates the amplitude periodic vibrations in interbedded soil deposits under strong earthquakes. Additionally, numerical results show that the examined tunnel is prone to slight or moderate damage under ground shaking, and its joints are more vulnerable to damage than its segments. The fragility curves constructed were compared with existing fragility curves, highlighting the significant effects of local soil profiles, groundwater conditions, soil–tunnel interaction, and segmental joints on the seismic vulnerability of shield tunnels in a submarine environment. The developed fragility functions contribute to the prediction of seismic damage to submarine shield tunnels of similar characteristics, enabling the rapid and efficient response of structures to disasters in ocean engineering.

An isoparametric element permutation method for railway tunnel–soil interaction modeling in train–track–tunnel–soil dynamic analysis

For evaluating the ground vibration involving metro tunnel operation, it is of necessity to extend the train-track-tunnel near-filed vibration to the train-track-tunnel-soil far-filed vibration in viewpoint of numerical analysis. It therefore becomes a key technology to achieve the tunnel-soil coupling simulation. In this work, a isoparametric element permutation method is proposed, where the 6-node triangular prismatic elements and 8-node spatial isoperimetric elements have been effectively integrated to achieve the finite elemental modelling of the soil system with the tunnel penetrating. The tunnel and soil subsystems are coupled by the spring-dashpot elements. Once the tunnel satisfies symmetrical property in geometry, the proposed method can be applied to build the tunnel-soil interaction by parametric finite element modelling. Through a combination of this proposed tunnel-soil interaction model and the train-track-tunnel dynamic model, a unified model for characterizing the train–track–tunnel–soil dynamic interaction analysis is constructed within the finite element framework. By comparing the simulation results to the measurements in site, the effectiveness of this model is validated, through which track, tunnel, and ground vibrations can be assessed in an entirely coupled way. Through the numerical studies, it is known that both the number of tunnel lines and the number of trains in operation and their running modes hold significant influence and show different vibration attenuation law on ground vibrations, and quantitative analysis can be achieved through this present work.

A Three-Stage Prediction Method for Track Displacement During Shield Tunneling

Track displacement is an important factor of track irregularity. Existing researches related with track displacement prediction generally ignore the influence from underground construction engineering such as shield tunneling, resulting in inaccurate estimation of track displacement. To fill this gap, we propose a three-stage framework to predict the track displacement when the shield tunnel under crosses the existing tunnel. Firstly, by considering the curved shield tunneling, a three-dimensional model is constructed to estimate the total ground displacement during the whole tunneling process. Furthermore, the soil-tunnel interaction model is established to estimate the deformation of the existing tunnel. To tackle the issue of unknown node displacements, cubic splines are used to interpolate the unknown values of tunnel displacements. On this basis, the direct stiffness method is used to estimate the track displacement and to calculate the track irregularity. Finally, the effectiveness of the proposed method is verified and the prediction performance on the track irregularity is evaluated using a real engineering case and the finite element simulation. The main contributions of this article lie in the modeling of the curved scenario for the estimation of the ground loss, as well as the combination of cubic splines and direct stiffness method, which improve the accuracy of the track displacement estimation during shield tunneling.

A bending-shear-torsion resistant beam foundation model for segmental tunnels in longitudinal direction

Segmental tunnels constructed by Shields / TBMs are easily subjected to uneven longitudinal cross-sectional torsion because of asymmetric external loads or deformations along the tunnel. However, the conventional models for soil-tunnel interaction in the longitudinal direction generally regard the tunnel as a one-dimensional beam on elastic springs, ignoring its cross-sectional torsion. To mitigate this gap, the paper proposed a bending-shear-torsion-resistant beam foundation model to explore the effects of cross-sectional torsion on tunnel performance. Firstly, an analytical solution for the longitudinal bending-shearing-torsion stiffness of a segmental tunnel was derived, then a soil-tunnel interaction model based on torsional Timoshenko beam on Winkler foundation was proposed with three-dimensional soil reactions incorporated. The present model is verified by comparing it with the Finite Element program and other published methods based on two case studies. The new contributions and findings are as follows: (1) The longitudinal torsional stiffness is proposed, and it is found that it is greatly affected by the number of bolts and segment size. (2) The governing differential equations and the closed-form solution for the soil-tunnel interaction model under bending-shear-torsion mode are derived, regarding arbitrary loading and two typical boundary conditions. (3) By considering the sectional torsion and three-dimensional soil reactions, the proposed method is proved to be actually more reasonable than the existing analytical methods. (4) A parametric analysis for the proposed solution was conducted to investigate the influence of key parameters on the torsional performance of segmental tunnels, which revealed the effect of torsional stiffness, soil resistance and elastic boundary conditions. The proposed solution and results could promote tunnel engineers better understand the anti-torque behaviors of segmental tunnels and improve the tunnel design in case of complicated circumstances.

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 8 °C to 18 °C), 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.

On the simplified method for evaluating tunnel response due to overlying foundation pit excavation

Foundation pit excavation may cause excessive uplift displacement and structural damage to the underlying shield tunnel. In this paper, the rationality of the excavation-induced inputs in the current force-based and displacement-based methods is analyzed theoretically and verified by comparing the elastic finite element method (FEM) and the elastic continuum solution. Then, the force input is modified by the load amplification factor to obtain a reasonable tunnel response, and the calculation method of the load amplification factor is given. Based on the mechanism of tunnel-soil interaction, the difference between Winkler subgrade moduli under active and passive conditions is analyzed. It is recommended that the active and passive Winkler subgrade moduli should be adopted under the force and displacement inputs, respectively. By comparing the elastic continuum solution and the Winkler solution, the validity of the Winkler subgrade moduli under active and passive conditions is verified. Thus, a force-based Winkler solution with modified force input is proposed. Finally, the proposed method is applied to a case study, and its applicability is verified by comparing the measured results and the FEM analysis with the HS-Small model.

Experimental investigations on the influence of embedment depth and frequency on the dynamic behaviour of tunnels under repeated shaking events

ABSTRACT Recently, occurrence of repeated shaking events such as the Kobe earthquake (1995), the Wenchuan earthquake (2008), the Chi-Chi earthquake (1999) and the Kumamoto earthquake (2016), Kahramanmaras earthquake (2023), etc., posed a severe threat to the safety of infrastructures. Studies on the influence of repeated shaking events on underground structures are minimal. Considering the above, tunnel-soil interaction under repeated shaking events is attempted in the study. One-gram shaking table tests were conducted in this study by varying loading frequency (5 Hz, 10 Hz) and tunnel embedment depth (H/W − 0.85 and 1.2 where H is the tunnel embedment depth and W is the width of the tunnel) and subjected to incremental shaking conditions, i.e. 0.2 g, 0.3 g and 0.4 g. A tunnel-embedded ground with 60% relative density was prepared and instrumented with conventional sensor schemes and a non-contact-based 2D digital image correlation technique. It was observed that the loading frequency and tunnel embedment influences tunnel’s performance during repeated shaking events. About 37% to 62.4% increment in tunnel displacement was observed in the case of H/W-0.85, and 20% to 29% increment in tunnel displacement was observed for H/W-1.2 when subjected to incremental acceleration shaking, i.e. 0.2 g to 0.4 g for varying embedment depth conditions.

Simplified method for evaluating mechanical interactions between tunnel and soil due to adjacent excavation

Excavations disrupt the original stress field and may have harmful effects on in-service shield tunnels. Therefore, a rational assessment of the responses of existing shield tunnels to construction of excavation is a significant challenge. Current analytical methods for evaluating the mechanical interactions between the excavation and the tunnel generally utilize Winkler’s model, which considers only the plane strain and ignores the spatial effect between the tunnel and the excavation. In this analysis, a new elastic analytical method that uses the Pasternak elastic model is presented to simulate mechanical interactions between the lateral soil and the tunnel when subjected to the unloading pressure of the bottom and surrounding walls of the excavation. The space-effect of excavation and spatial effects of tunnel-soil interaction are both under consideration. The responses of the tunnel to the construction of excavation were assessed by a two-stage analysis method. First, the imposed unloading load at the tunnel location was calculated based on elastic solutions. Second, vertical displacement of the tunnel caused by the corresponding load was evaluated using the finite difference method. In addition to the proposed analytical approach, six analytical approaches were developed for the elastic model. The applicability of the proposed method was validated by comparisons with numerical simulations and field monitoring data. Furthermore, the predictions of the six analytical approaches for the elastic model were compared with those of the proposed method.

Analytical method for predicting tunnel heave due to overlying excavation considering spatial effect

Deep excavations have significant influence on existing metro tunnels. Currently, there is still a lack of practical and simple assessment approaches for predicting this influence. In this paper, a new analytical method is developed that uses a continuous Euler-Bernoulli beam to simulate shield tunnel behavior due to overlying basement excavation. Firstly, the excavation-induced greenfield displacement at the tunnel axis is obtained with the application of Mindlin’s solution. Secondly, the longitudinal response of the tunnel due to the ground movement induced by excavation is computed using a finite difference method. The effectiveness and applicability of the proposed method are validated by three high-quality case histories, including field measurement, FEM method, and semi-analytical method. Different from previous studies, the tunnel-soil interaction behavior is studied based on the displacement coupling condition in the proposed method, capable of accurately considering tunnel-soil interaction behavior. Subsequently, with the verified proposed analytical solution, further parametric studies are performed to investigate the spatial factors affecting tunnel behavior including tunnel buried depth, excavation-tunnel relative distance, excavation geometry, skew angle between tunnel axis, short side of the excavation, and excavation depth, yielding abundant artificial data. Then, a semi-empirical formula considering spatial effect is established for directly predicting the maximum vertical displacement of the tunnel with adequate engineering accuracy and applicability. The proposed analytical method can be applied to predict the potential risk of existing tunnel due to nearby excavation.

Improved Theoretical Solutions for Estimating the Tunnel Response Induced by Overlying Excavation

As a result of China’s urbanization, it has been a common phenomenon that adjacent deep excavations were constructed near underground structures, which can have a series of detrimental effects on existing tunnels. Thus, it is crucial to assess the tunnel response induced by the overlying excavation, with the aim of maintaining the safety and serviceability of operating tunnels. The shield tunnel is idealized as an infinite beam lying upon a three parameter Kerr-model and the vertical force equilibrium equation of the tunnel element is established. Then, a theoretical solution is derived for capturing the soil–tunnel interaction. To prove the accuracy of the proposed method, the calculation results are compared with field measurements, along with the data of finite element studies. Thereafter, a parametric analysis will be conducted to assess some characteristic factors for tunnel responses caused by overlying excavations, such as tunnel-excavation horizontal distance, tunnel bending stiffness, and the buried depth of the tunnel. The results indicate that the increase in the bending stiffness and the buried depth of tunnel, as well as the tunnel-excavation horizontal distance, will significantly alleviate the tunnel deformation. However, the inner force will be increased when increasing the tunnel bending stiffness.

Predictive Models to Evaluate the Interaction Effect of Soil-Tunnel Interaction Parameters on Surface and Subsurface Settlement

Nowadays, the need for subway tunnels has increased considerably with urbanization and population growth in order to facilitate movements. In urban areas, subway tunnels are excavated in shallow depths under densely populated areas and soft ground. Its associated hazards include poor ground conditions and surface settlement induced by tunneling. Various sophisticated variables influence the settlement of the ground surface caused by tunneling. The shield machine's operational parameters are critical due to the complexity of shield-soil interactions, tunnel geometry, and local geological parameters. Since all elements appear to have some effect on tunneling-induced settlement, none stand out as particularly significant; it might be challenging to identify the most important ones. This paper presents a new model of an artificial neural network (ANN) based on the partial dependency approach (PDA) to optimize the lack of explainability of ANN models and evaluate the sensitivity of the model response to tunneling parameters for the prediction of ground surface and subsurface settlement. For this purpose, 239 and 104 points for monitoring surface and subsurface settlement, respectively, were obtained from line Y, the west bond of Crossrail tunnels in London. The parameters of the ground surface, the trough, and the tunnel boring machine (TBM) were used to categorize the 12 potential input parameters that could impact the maximum settlement induced by tunneling. An ANN model and a standard statistical model of multiple linear regression (MLR) were also used to show the capabilities of the ANN model based on PDA in displaying the parameter's interaction impact. Performance indicators such as the correlation coefficient (R2), root mean square error (RMSE), and t-test were generated to measure the prediction performance of the described models. According to the results, geotechnical engineers in general practice should attend closely to index properties to reduce the geotechnical risks related to tunneling-induced ground settlement. The results revealed that the interaction of two parameters that have different effects on the target parameter could change the overall impact of the entire model. Remarkably, the interaction between tunneling parameters was observed more precisely in the subsurface zone than in the surface zone. The comparison results also indicated that the proposed PDA-ANN model is more reliable than the ANN and MLR models in presenting the parameter interaction impact. It can be further applied to establish multivariate models that consider multiple parameters in a single model, better capturing the correlation among different parameters, leading to more realistic demand and reliable ground settlement assessments. This study will benefit underground excavation projects; the experts could make recommendations on the criteria for settlement control and controlling the tunneling parameters based on predicted results. Doi: 10.28991/CEJ-2022-08-11-05 Full Text: PDF

2.5D FE-BE modelling of dynamic responses of segmented tunnels subjected to obliquely incident seismic waves

Segmented tunnels are widely used nowadays. However, most existing studies on the seismic response of underground tunnels are based on the model of continuous linings, without considering the segment joints. This paper presents a numerical study aiming to investigate the factors that affect the seismic response of segmented tunnels, with a step further than previously, considering obliquely incident seismic waves. The numerical simulation is carried out by a 2.5D coupled finite element-boundary element (FE-BE) model, which can properly simulate the soil-tunnel interaction for obliquely incident seismic waves and predicts both the transverse and longitudinal seismic responses of the tunnel. It is shown that the joint distribution is one of the critical factors that determine the seismic responses of the segmented tunnel, and the influence of the segment joints tends to be more pronounced when they are located near the positions of large transverse bending moments in the tunnel lining. Compared with the homogeneous tunnel, the reduction in the transverse bending moment and axial force of the segmented tunnel is significant, while it is minor in the longitudinal bending moment and axial force, and the effect of the segment joints highly depends on the soil-tunnel relative stiffness. In addition, the influence of the spectral characteristics of the input motions on the tunnel responses is highlighted.