Tunnel Invert Research Articles

Centrifuge modelling of the dynamic response of twin tunnels under train-induced vibration load

The impact of train-induced vibrations originating from underground tunnels has emerged as a significant environmental issue within urban areas. A multitude of studies, encompassing both numerical analyses and experimental investigations, have been undertaken to explore and address this concern. In the experimental tests, the dynamic characteristics of tunnels and soil has generally been studied using physical models with a single tunnel under a 1 g (gravity) environment. However, twin tunnels are commonly constructed in the field, and the stress of the soil is unrealistically simulated in 1 g models. In this paper, the dynamic characteristics of twin tunnels were studied by centrifuge testing. In this paper, results are presented from scaled model tunnel tests conducted at 50 g for four different conditions: a single tunnel, vertical twin tunnels with 60 mm spacing, horizontal twin tunnels with 60 mm and 120 mm spacing. Train load and sweep load were applied by a parallel pre-stressed actuator at the tunnel invert. Accelerometers were employed to gauge the dynamic response of both the tunnels and the surrounding soil. The experimental results illustrate that the interaction between twin tunnels has a clear amplification effect on the dynamic response of the loading tunnel, with the maximum peak particle acceleration (PPA) increasing by up to 43 %. This amplification phenomenon is reduced as the space between the twin tunnels is increased. The experimental results also indicate that the interaction between twin tunnels has a comparatively lower impact on the dynamic response of the surrounding soil when contrasted with the dynamic response of the tunnels themselves.

Simple approach to assessing excess pore water pressure induced by shield tunneling in saturated-unsaturated clay soil

Excess pore water pressure (EPWP) induced by shield tunneling has a significant influence on the stability of the tunnel face, post-construction settlement, and the mechanical behavior of the tunnel lining. However, the three-dimensional and unsaturated property of the soil field is seldom considered in current research. Considering the non-uniform radial convergence model, a modified three-dimensional displacement solution induced by shield tunneling was established first. Then based on unsaturated EPWP elastic theory, a reliable and efficient method is developed to expedite the evaluation of EPWP distribution in three-dimensional saturated and unsaturated clay soil. The validity of the method is confirmed through comparison with field test and numerical outcomes. The analysis examples demonstrate that negative and positive EPWP are generated above the tunnel crown and beneath the tunnel invert, respectively. In the vertical direction, the negative EPWP exhibits a decreasing trend ahead of the heading face and an increasing trend behind it. Along the longitudinal direction, the influence zone of EPWP extends to 1D ahead of and 6D behind the heading face. With the decrease of soil saturation, the EPWP values tend to diminish. The maximum EPWP values observed in saturated conditions can be 16.13 times higher than those under unsaturated conditions.

Thermal performance of geothermal energy tunnel in unsaturated soils

Energy tunnel provides an innovative and efficient approach to harvesting geothermal energy. Understanding its performance and identifying the key influential factors are important to the application of this sustainable technology. In practice, soils surrounding an energy tunnel are often unsaturated, while previous studies either focus on fully saturated conditions (FS analysis) or simplify the soils above the water table as completely dry (CD analysis). These analyses may lead to inaccurate evaluation of thermal performance in unsaturated conditions because soil's thermal properties are moisture-dependent. Moreover, the effects of soil moisture conditions on thermal performance are expected to depend on various factors like soil and operational conditions. To address these problems, this study developed a coupled thermo-hydraulic finite element code to investigate the thermal performance of energy tunnel in unsaturated soils. The effects of soil property, groundwater, tunnel’s internal airflow environment (TIAE), heat carrier fluid, and pipe conditions were investigated. Comprehensive results show that TIAE is one of the most important factors affecting the thermal performance in unsaturated soils. Another dominant factor is the groundwater flow velocity and fluid inlet temperature when the water table is relatively high (above tunnel crown) and low (below tunnel invert), respectively. Moreover, in the cases with a high water table and high TIAE (e.g., heat transfer coefficient ≥ 5.3 W/(m2∙K)), the conventional CD and FS analysis can give an acceptable performance evaluation for the sand and clay, respectively. In other cases, however, significant underestimation and overestimation, with a maximum value of 70 % and 130 %, are induced by the CD and FS analysis, respectively. These findings suggest that soil unsaturation should be properly considered in the design of energy tunnels.

Experimental study of the effects of contact loss under a shield tunnel invert

Experimental study of the effects of contact loss under a shield tunnel invert

Evaluation of the collapsible deformation of surrounding rock of loess hydraulic tunnel considering ground stress variation

BackgroundUneven settlement will occur as a result of the collapsible deformation of the loess strata, and the hydraulic tunnel lining structure will also fail. In this work, laterally confined compression tests were carried out on loess and the double-line method was employed to evaluate the loess collapsibility. The deformation of the surrounding rock of a loess hydraulic tunnel under various ground stresses and its effect on the lining structure was modeled.ResultsThree stages were noted in the collapsible deformation of loess. The critical point between the former two stages corresponds to the pre-consolidation pressure of saturated loess and that between the latter two is taken as the structural yield pressure of unsaturated loess.ConclusionFrom the relationship between the collapsibility coefficient and vertical stress, the deformation of the tunnel under ground seepage primarily originates from two sources, i.e., the collapsible and compressive deformation. The latter source accounts for the deformation of loess adjacent to the lining when the seepage depth is low, while both sources are included when the bottom of the tunnel invert is infiltrated. The collapsible deformation is lower than that of the original stratum due to the stress relaxation during tunnel excavation. The tensile and compressive stresses of tunnel lining increase linearly with the seepage depth, with the maximum appearing at a position of 20 m away from the midline of the collapse and non-collapse domains. The results will provide a theoretical reference to the design and construction of hydraulic tunnels in collapsible loess stratum.

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.

Coupled Eulerian-Lagrangian simulation of progressive failure in shield tunnels induced by developing contact loss

Contact loss may develop between a shield tunnel and the surrounding ground due to various factors. This study evaluated the deformation and failure of shield tunnels caused by contact loss using the Coupled Eulerian-Lagrangian (CEL) method. Three-dimensional finite element models considering the behavior of segment joints were established. The CEL method for simulating contact loss and the segmental tunnel model were validated through two existing experiments. The shield tunnel structure responses, including convergent displacement of linings, dislocation between tunnel rings and joint failure process, were analyzed under typical cases of contact loss developing circumferentially and longitudinally. In addition, the impact of contact loss location was investigated. The results show that significant joint dislocation may occur at the boundary of the contact loss region. When contact loss develops to a certain level, the tunnel deformation may increase sharply, and many segment joints fail suddenly. Additionally, more joints fail when the contact loss is located at the tunnel crown than when contact loss is located at the tunnel invert and springline due to the assembled method of shield tunnel in this study in which the key segments were all positioned at the tunnel crown.

Evaluation of segmental lining response during shield tunnel construction based on field measurements and 3D FEM simulation

Lining safety can be threatened more severely at the construction stage than at the service stage, because the loads at the construction stage are larger. This study presents an in-situ experiment for measuring the loads acting on the lining and the internal forces of the lining to investigate the lining response during both the construction and service stages. A three-dimensional (3D) finite element method (FEM) model that could simulate the main relevant components of the shield tunnel construction process was employed to gain further insight into the mechanisms of the lining response. The influences of the key segment position and assembly sequence on the lining behavior were examined through a comprehensive parametric analysis. The results showed that during the assembly stage, the insertion of a key segment resulted in the most significant increase in the axial force, followed by the assembly of an adjacent segment. The lining responses were significantly influenced by the key segment, particularly during the construction stage, whereas the assembly sequence had a limited effect on the lining responses. During the construction stage, the closer the key segment to the tunnel invert, the greater was the axial force and the smaller was the bending moment of the lining. During the construction stage, the closer the key segment to the tunnel invert, the smaller was the axial force of the tunnel lining and the greater was the bending moment. The circumferential compressive stress reached its maximum value at the joint interfaces. Finally, the jack thrust force was the greatest at the tunnel invert. The key segment should not be placed at this location.

Experimental study on dynamic response of rock tunnel subjected to train moving load

The tunnels might be suffered from damage and destruction under the dynamic loads generated by trains moving on the upper railways, which can in turn threaten the safety of the railways. Understanding the dynamic response of tunnel under the train moving load is of significance for maintaining the operation safety of both the tunnel and upper railway. However, there is currently a lack of relevant research on this topic, especially regarding model experiments. To address this gap, this paper conducts physical model experiments on the train-rail-bridge-shaking table test system to investigate the dynamic response of tunnels subjected to train moving load. The experiment results revealed that except for the average peak particle velocity (PPA) at tunnel vault, the average PPAs at other locations and the vibration dominant frequency (f0) at all locations increase as the train moving speed (vtr) increases. With the exception of some special cases, the average PPAs on tunnel spandrels are generally less than that on the tunnel vault and greater than that on the tunnel invert. When the vtr exceeds 7.03 m/s, except for the average PPA at tunnel invert, the average PPAs on the tunnel wall are generally larger than those inside the surrounding rock mass. As vtr increases, the average f0 on tunnel wall changes more obviously compared to average f0 inside the surrounding rock mass. When the vtr exceeds 10.54 m/s, the average f0 on tunnel wall are noticeably larger than those inside the surrounding rock mass. The high coefficients of determination obtained from the nonlinear regression analysis indicates a power relationship between the average PPA and vtr, while the average f0 shows an exponential association with vtr. The research findings hold great importance in ensuring the safe operation of tunnels and railways.

Experimental Study on Seismic Response of Underground Tunnel–Soil–Piled Structure Interaction Using Shaking Table in Loose Sand

The seismic response of structures can have a significant impact on adjacent structures’ response. Although several numerical studies have been applied in the field of tunnel–soil–pile interaction systems, there is a lack of experimental research specifically focused on the effects of this interaction on tunnel cross-section deformation and the existence of structure on encircling soil response. In this study, shaking table tests were conducted to examine the seismic response of a tunnel and the surrounding soil when an eight-story structure with piles was located in the vicinity of the tunnel. Four series of physical models were analyzed, including free-field soil (S), tunnel–soil (TS), soil-piled structure (SP), and tunnel–soil-piled structure (TSP), under sinusoidal vibration at three frequencies on loose sand. According to the results, the tunnel significantly impacts the surrounding soil response during seismic excitation with reduced acceleration at the tunnel invert and increased acceleration at the tunnel crown. In the TSP model, applied frequency affects the recorded acceleration amplitude at the tunnel invert. Although acceleration amplitude decreases at 3 Hz frequency excitation compared to the free field model, 8 Hz excitation resulted in bigger values in tunnel invert. Displacements are higher at the tunnel crown, indicating tunnel-induced soil deformation and maximum shear strain concentrated near the tunnel crown. The tunnel cross-section exhibited oval shape changes, with higher forces on the tunnel crown in the presence of piles.

Research on Deformation Monitoring of Invert Uplifts in Soft Rock Tunnels Based on 3D Laser Scanning

The soft surrounding rock in tunnels has the characteristics of low strength, easy softening after soaking, and poor self-stability, which makes the inverted arch structure in soft rock tunnels prone to uplift deformations. Therefore, a deformation monitoring method for inverted arch uplifts of soft rock tunnels based on 3D laser scanning technology is studied to improve deformation monitoring. A Leica Scan Station2 3D laser scanner is used to collect 3D point cloud data of soft rock tunnel inverts. Using the automatic matching method of public landmarks and the improved Rodrigues parameter method, the collected 3D point cloud data are spliced and through the Mallat algorithm, the 3D point cloud data are reconstructed and processed after splicing. The whole least square method is used to fit the reconstructed 3D point cloud data. Through the principal component analysis method, the normal vector of the fitting plane is estimated and the best datum plane of the soft rock tunnel invert is found. By calculating and extracting the geometric parameters of the slice point cloud, the monitoring of inverted arch uplift deformations in soft rock tunnels is completed. The experiment shows that this method can effectively collect 3D point cloud data of soft rock tunnel inverts, and complete point cloud stitching and reconstruction. This method can effectively monitor the uplift deformation of inverted arches at different grouting depths.

Modeling Railway Track Mechanical Behavior with Under Tie Pads and Under Ballast Mats

Under tie pads (UTPs) and under ballast mats (UBMs) are used in rail track construction to reduce track stiffness and increase the size of the ballast contact area where it meets track support elements either above the ballast (ties) or below the ballast (e.g., subgrade, bridge deck, or tunnel invert). Limited information on the in-track performance of UTPs or UBMs is available. The University of Florida recently completed a research program to monitor track performance and track support changes using a UBM and UTPs in the Virginia Avenue Tunnel in Washington, DC. Researchers measured parameters to estimate the effect of a UBM and UTPs on tunnel invert pressure, tie bottom pressure, and track deflection. A control condition without a UBM or UTPs was not available for testing; however, Volpe developed a finite element track model for estimating track behavior without a UBM or UTPs. The modeling results highlighted the individual contributions of both a UBM and UTPs to stress reduction on the ties and tunnel floor. The model included features that simulate the load chains that can develop in clean granular materials leading to high peak stresses and ballast and structure degradation. The modeling results revealed that a UBM and UTPs might reduce the average stress on the ties and tunnel floor by 5% to 20% when the ballast was well compacted. The peak stresses from ballast load chains, or edges, may be reduced by 50% or more.

Research on the Influence of Tunnel Invert Excavation on the Rheological Deformation of Different Levels of Surrounding Rock

The closed section of the inverted arch, formed by the surrounding rock, acts as a bearing ring. Combined with the upper initial support, it ensures stable initial support. However, excavating the inverted arch can disturb the original balance, significantly affecting the tunnel’s stability. To determine the optimal exposure length and excavation length of the elevation arches at different rock levels, numerical analyses were conducted. These analyses used the classical Burgers creep intrinsic structure model for the three-step excavation mode. Various closure distances and exposure distances of the elevation arch were considered. The study aimed to investigate the influence of these factors on the stability of the primary lining, comparing it with the maximum displacement of the vault. The results indicate that the strength of the surrounding rock primarily affects the displacement of the arch crown. Lower rock strength corresponds to greater arch crown displacement. Additionally, increasing the closure distance of the inverted arch leads to increased arch displacement. On the other hand, the exposure distance of the inverted arch has minimal impact on arch displacement. Longer exposure distances result in greater arch displacement. These findings can serve as a basis for improving current standards and adapting them to meet the spatial requirements of large-scale mechanized operations.

Failure mechanism of the deep-buried metro tunnel in mixed strata: Physical model test and numerical investigation

Lining cracking is a typical damage phenomenon during the construction of metro tunnels, especially in the mixed strata with soft upper and lower hard rock, which severely affects the safety of the tunnel. In this paper, the physical model test was conducted to investigate the failure mechanism of metro tunnels. The full-face excavation apparatus was used to simulate tunnel excavation. The pressure cells, displacement transducers, strain gauges, and quartz sand marking method were adopted to monitor the mechanical response of the tunnel. Moreover, the failure evolution process of tunnel lining was recorded. The effectiveness of the model test was verified by numerical simulation. Meanwhile, the influences of the soil mechanical parameters, tunnel geometry, and lining stiffness on the failure behaviors of the tunnel were systematically discussed. The test results indicate that the tunnel excavation induced a slight deep soil disturbance. At buried depths ranging from 50 to 500 m, the soil settlement near the tunnel entrance was significant due to the uneven longitudinal compression, and the settlement decreased with increasing depth. The attenuation magnitude of the ground pressure in the vertical direction was greater than that in the horizontal direction. For the spring line, it was most affected by the coupling of axial compression and bending moment. The bearing capacity of the lining reached the limit when the buried depth was 150 m. The damage of the tunnel invert was the most severe, followed by the crown and the spring lines. In addition, the damage of the left part of the lining was more severe than that on the right part due to asymmetrical pressure. The entrance of the tunnel had little convergence, while the convergence at the end of the tunnel was the most significant.

A Finite Element Method Integrated with Terzaghi’s Principle to Estimate Settlement of a Building Due to Tunnel Construction

This study presents the application of the finite element method integrated with Terzaghi’s principle. The definition of a model in oedometric or confinement conditions for settlement estimation of a building after the construction of a tunnel, including the effect of Terzaghi’s principle, is an unresolved problem. The objectives of this work include the demonstration of the need for a minimum of three methodological states to estimate said settlement. For this, a specific methodology is applied to a case study, with eight load steps and four types of coarse-grained soils. In the studied case, two layers of 50 m and 5 m with different degrees of saturation are overlaying an assumed impermeable rock layer. The excavation of a tunnel of 15 m in diameter at a depth of 30 m with drainage lining inside the tunnel is assumed. The minimum distance from the tunnel’s outline to the mat foundation is 15.8 m. It is determined that the settlement, according to Terzaghi’s principle, is around 11% of the total settlement for the most compacted soil types, reaching 35% for the loose soil type, from the tunnel’s outline. In the mat foundation, it implies an increase in the differential settlement of up to 12%. It shows a nonlinear relationship between some of the variables in the analysis. To detect the collapse due to uplifting the tunnel invert, it was determined that it was not appropriate to model in oedometric conditions. The novelty of the investigation relies on identifying and determining the need for a minimum of three states for methodological purposes for a proper quantification of the total settlement: (i) before the construction of the tunnel, (ii) immediately after the excavation of the tunnel, but without groundwater inflow into the tunnel, and (iii) after the tunnelling, with stabilised groundwater inflow into the tunnel.

The effect of internal structure on dynamic response of road-metro tunnels under train vibration loads: An experimental study

The environmental vibration caused by train induced vibration loads has received considerable research attention. However, the dynamic response characteristics of tunnels with large diameter and complex internal structures, such as road-metro tunnels, remains unknown. In this study, physical model tests have been carried out to study the dynamic response characteristics of road-metro tunnels under train vibration loads and the effect of internal structure on the dynamic response of the tunnel linings and surrounding soils. A road-metro tunnel model (RTM) and a simple tunnel model (STM) were tested under train vibration loads and sweep frequency loads applied to the tunnel invert of each model. The dynamic response of tunnel linings and surrounding soils at different positions were measured by accelerometers and analyzed in both time and frequency domains. The experimental results show that the internal structure can significantly reduce the dynamic response of tunnel linings and surrounding soils. The maximum ratio of the peak particle acceleration (PPA) of the tunnel linings in the two tunnel models is about 275%, while the ratio of PPA of soils in the two tunnel models is greater than 90%. The vertical acceleration level (VAL) of tunnel linings in STM test is always greater than that in RTM test at the near field, whereas for the tunnel linings at the far field, the VAL in STM test is clearly larger than that in RTM test in the frequency range of 80–250 Hz. The difference between the VAL of surrounding soils in these two models is not obvious at lower frequencies (<63 Hz). The obvious dynamic response on the upper lane decks was also studied. The study demonstrates that failure to consider the internal structure of road-metro tunnels can lead to an overestimate of the dynamic response of tunnel linings and surrounding soils and that special attention should be paid to the obvious dynamic response of lane decks.

Numerical Investigation on the Dynamic Response of Fault-Crossing Tunnels under Strike-Slip Fault Creep-Slip and Subsequent Seismic Shaking

Tunnels built in geologically active areas are prone to severe damage due to fault dislocation and subsequent earthquakes. Using the Ngong tunnel in the East African Rift Valley as an example, the dynamic response of a fault-crossing tunnel and the corresponding sensitivity are numerically simulated by considering four factors, i.e., tunnel joint stiffness, isolation layer elastic modulus, strike-slip fault creep-slip and earthquakes. The results show that a valley-shaped propagation of peak displacement at the tunnel invert occurs in the longitudinal axis direction under an earthquake alone. Then, it transforms into an S-shaped under strike-slip fault creep-slip and subsequent seismic shaking. The tunnel invert in the fault zone is susceptible to tensile and shear failures under strike-slip fault creep-slip movements of less than 15 cm and subsequent seismic shaking. Furthermore, the peak tensile and shear stress responses of the tunnel invert in the fault zone are more sensitive to fault creep-slip than earthquakes. They are also more sensitive to the isolation layer elastic modulus compared to the joint stiffness of a segmental tunnel with two segments. The stress responses can be effectively reduced when the isolation layer elastic modulus logarithmic ratio equals −4. Therefore, the isolation layer is more suitable to mitigate the potential failure under small strike-slip fault creep-slip and subsequent seismic shaking than segmental tunnels with two segments. The results of this study can provide some reference for the disaster mitigation of fault-crossing tunnels in terms of dynamic damage in active fault zones.

Study on the time-varying fatigue reliability of the invert structure of subway tunnel under the action of train loads

Introduction: The present study examines the fatigue reliability of subway tunnel invert structures subjected to train-induced loads, a critical factor in ensuring the safety and longevity of these vital infrastructures.Methods: By integrating higher-order moment theory, fatigue equations, and cumulative damage theory, this research analyzes the impact of train loads on invert structures, taking into account factors such as tension stress, compression stress, train axle weight, speed, and lining thickness.Results: The findings indicate that the reinforcement of the invert structure is required under tension stress, while it is not necessary for compression stress. Notably, the train’s axle weight and speed exert a significant influence on the fatigue reliability index, with speed displaying a marginally greater effect than axle weight. Conversely, the lining thickness demonstrates a negligible impact on the reliability index. As time progresses, the fatigue reliability index diminishes, resulting in an elevated probability of failure.Discussion: In light of these findings, it is imperative to conduct regular inspections and maintain the tensile state of the invert structure, which warrants the most attention. To safeguard the safety and longevity of subway tunnel invert structures, it is essential to concentrate on the aspects related to tensile stress and closely monitor train loads, specifically axle weight and speed.

Testing and Analysis of the Vibration Response Characteristics of Heavy-Haul Railway Tunnels and Surrounding Soil with Base Voids

This paper discusses research on the dynamic response characteristics of a heavy-haul railway tunnel and the surrounding soil under the conditions of substrate health and a base void. The detection results of the base condition of 20 double-track tunnels for a heavy-haul railway show the main distribution law of base voids. Based on this, a 1:20 scale test model of a heavy-haul railway tunnel is established. The vibration load of the train is established by a vibration exciter arranged at the tunnel invert. The dynamic response and attenuation law of a heavy-haul railway tunnel lining structure and the surrounding soil are tested using acceleration sensors, strain gauges, and soil pressure boxes. The research results show that most of the diseases are concentrated below the heavy-haul line. The base void causes the peak acceleration of the nearby tunnel invert to increase by 55.6%. Tunnel annular construction joints reduce the conductivity of the vibration waves in the axial direction of the tunnel. The acceleration attenuation rate of the soil above the tunnel invert is significantly less than that under the invert. The base void reduces the acceleration of the nearby soil layer by 19.4% and increases the stress on the surface of the nearby tunnel invert by 21.3%, and the stress change amplitude increases by 0.55%. The tunnel structure in the area of the base void experiences fatigue damage. The base void causes the compaction and bearing capacity of the nearby soil to decrease and the softening speed of the tunnel basement soil layer to increase. Therefore, for the basement damage to heavy-haul railway tunnels, “early detection, early treatment” should be performed.

Testing of a GPR equipment to assess the integrity condition of a subway tunnel located under groundwater level

AbstractDetermining the condition of underground concrete tunnels is fundamental for ensuring continuity and safety of operations, as well as for deploying efficient maintenance plans. The increased traffic volumes in early infrastructures, which are characterized by outdated construction techniques and potential approximated realization, as well as rising groundwater levels due to variations in urban industrialization patterns, are among the main causes of current concerns regarding their performance. Such uncertainties and constraints push towards the use of non‐destructive techniques, rather than direct methods, to gather the required knowledge on the actual status of structures. This study presents the results of a ground penetrating radar (GPR) investigation carried out in a subway tunnel segment to characterize the thickness of its underlying concrete elements, namely the tunnel invert and the concrete filling, deemed necessary after relevant flooding events prompted the evaluation of its overall integrity condition. A preliminary step was performed to define the optimal frequency and polarimetric antenna configuration, given the resolution and penetration requirements and considering the high electromagnetic interference characterizing the site. The selected configuration was then assembled in a dedicated survey platform, and an entire 650 m long segment surveyed, producing a high resolution delineation of the concrete elements thickness. The accuracy of the estimation has been validated through nine core samples, demonstrating the reliability and consistency of the conceptualized GPR platform.