Tunnel Lining Structure Research Articles

Seismic Response and Security Assessment of Cross-Fault Hydraulic-Tunnel Lining Structures

The foundation of a seismic safety assessment of cross-fault hydraulic tunnels is an acceptable and accurate seismic response. A dynamic contact force algorithm that may take into consideration the interaction between the fault–surrounding rock–lining structure was devised in light of the contact characteristics of various media in cross-fault hydraulic tunnels under seismic activity. A quantitative instability criterion using a relative displacement ratio as the criterion was devised based on the cusp catastrophe model. By using the cross-fault hydraulic tunnel of the Lawa Hydropower Station as an example, it was possible to evaluate and assess the impacts of four working circumstances on the seismic response of the tunnel lining structure. The findings demonstrated that the lining haunch exhibited stronger stress and displacement responses when subjected to seismic activity. The consideration of fault–surrounding rock–lining interaction exacerbated the displacement and stress seismic responses of the lining structure. The haunch, bottom arch, and top arch of the lining’s characteristic parts—which ranged in size from large to small—responded more seismically as peak ground acceleration rose. Applying the aforementioned instability criterion, the haunch, bottom arch, and top arch of the liner structure could withstand maximum peak ground accelerations of 0.10 g, 0.20 g, and 0.35 g, respectively. The aforementioned technique offers a fresh perspective on how to evaluate the seismic response and seismic safety of the tunnel’s lining structure, and the study’s findings can serve as a guide for seismic design.

Research and Development of Self-Waterproofing Concrete for Tunnel Lining Structure and Its Impermeability and Crack Resistance Characteristics.

This research paper systematically investigates the combined influence of fly ash, cementitious capillary crystalline waterproofing (CCCW) materials, and polypropylene fibers on the mechanical properties and impermeability of concrete through comprehensive orthogonal tests. Microscopic morphological changes in the concrete induced by different composite materials are examined via scanning electron microscopy (SEM) and X-ray diffraction (XRD) testing. The objective is to facilitate a beneficial synergetic interaction among these materials to develop highly permeable, crack-resistant concrete. Key findings of this study are: (1) The study unveils the impact of the concentration of three additive materials on the concrete's compressive strength, tensile strength, and penetration height, thereby outlining their significant influence on the mechanical properties and impermeability of the concrete; (2) An integrated scoring method determined the optimal composite dosage of three materials: 15% fly ash, 2% CCCW, and polypropylene fibers at 1.5 kg/m3. This combination increased the concrete's compressive strength by 12.5%, tensile strength by 48.4%, and decreased the average permeability height by 63.6%; (3) The collective introduction of these three materials notably augments the hydration reaction of the cement, resulting in denser concrete microstructure, enhanced bonding between fibers and matrix, and improved concrete strength and durability.

Experimental and numerical evaluation for tunnel structural stability of fiber concrete lining with different crack features under train load

Cracks are prone to occur in the secondary tunnel lining with the action of train loads, which will cause tunnel failure and adversely affect the long-term safety of tunnels. This paper conducts a series of material tests and numerical simulations to investigate the stability of fiber concrete tunnel linings with different crack features under train load. Through material tests for three different fiber and conventional concrete, the crack extension rule is discovered by combing digital image correlation (DIC) technology. The plastic damage constitutive relation of concrete is used to obtain the damage parameters. Then, the three-dimension numerical model is established to evaluate the stress intensity factor and stable coefficient of safety of tunnel lining. Moreover, four cases are determined to indicate the effect of cracks on the failure mechanisms of the tunnel lining structure. The influence of stability of lining structure with crack at different location, depth, width, inclination angle, train speed and grade of surrounding rock is analyzed.

Dynamic response and progressive damage modes of fault-crossing tunnels simulated using similar materials

Tunnels are widely constructed because they can effectively withstand seismic loads and avoid tunnel collapse in high-intensity seismic zones. However, in the case of fault-crossing tunnel, the fault crossing tunnel will be seriously damaged in seismic activities because the tunnel lining follows the deformation of surrounding rock. Therefore, the researches of the dynamic response and failure modes of fault-crossing tunnel are highly significant. In this study, quartz sand, cement and detergent were used to simulate similar materials of surrounding rock. A gypsum-based materials have been selected as similar materials for tunnels. The shaking table model tests were conducted on fault-crossing tunnel and conventional tunnel based on the Xianglushan Tunnel. The dynamic response characteristics of the fault-crossing tunnel were analyzed, and draw the conclusions: The acceleration amplification coefficients of the two sets of tests exceeded 1. The acceleration dynamic response of the fault-crossing tunnel was greater than the conventional tunnel, and the acceleration dynamic response at the fault was greater than the monitoring surface on both sides, rendering the acceleration dynamic response at the fault abrupt. Compared to other cross sections, tunnel lining structures at faults had the strongest dynamic response. The maximum peak strain value of the fault-crossing tunnel was magnified 4.4 times, and the bending moment value was magnified 2.3 times, relative to those of the conventional tunnel. The fault markedly increased the strain peak and bending moment values, causing cracks and damage even at a small peak acceleration value, weakening the seismic capacity of the tunnel. The lining at the fault was dominated by longitudinal cracks, and dislocation occurred. The degree of destruction and development of tunnel at faults was greater than that of other cross sections. The research results and conclusions could provide a reference to prevent the destruction of fault-crossing tunnel in an earthquake.

Seismic Response Analysis of Secondary Lining Polymer Grouting Debonding Repair for Tunnel Construction Based on Parameter Inversion

The void phenomenon behind the tunnel lining has become the main cause of tunnel disease, easily triggering tunnel lining structure damage, shedding, water seepage, and other diseases that seriously threaten the normal operation of the tunnel. The void area behind the lining seriously reduces the seismic capacity of the tunnel. In this paper, the mechanical parameters of the surrounding rock are calculated by optimizing the inversion of the improved system identification sensitivity analysis method, and the numerical model of the tunnel’s dynamic response is optimized using the improved inversion results to study the repair effect and seismic capacity of the Longmenshan tunnel using polymer grouting to repair the void area behind the lining under the action of a seismic load. The results show that the displacement and stress at the top of the tunnel secondary lining void area are significantly reduced and close to normal after the repair of polymer grouting; however, the stress and displacement at the top of the secondary lining are significantly different under the action of seismic waves at the same peak at different site conditions, which indicates that the dynamic response of this tunnel model has obvious sensitivity to the seismic wave spectrum.

Durability Evaluation of Hydraulic Tunnel Lining Structure Based on Set Pair Analysis and Extension Coupling Model

A series of water diversion projects to address the uneven distribution of water resources in China have involved the construction of a large number of hydraulic tunnels. As the lining structure is there to maintain the stability and durability of the tunnels, durability damage can easily occur in the operation process, thus affecting the safety of water transmission and water supply capacity. Therefore, it is important to evaluate the durability of hydraulic tunnel lining structure. Considering the randomness and fuzziness of the factors affecting the durability of hydraulic tunnel lining structure, this paper proposes a comprehensive evaluation model based on the coupling of set pair analysis and extension. The G1 method and the simple correlation function method are used to determine the subjective and objective weights of the evaluation indexes, respectively, and the combination weight of them is assigned based on the principle of minimum entropy; next, the set pair analysis principle is used to establish the linkage affiliation function, which can calculate the comprehensive linkage affiliation of the object to be evaluated, and then the maximum affiliation principle is used to judge the durability level of the hydraulic tunnel lining structure. Finally, taking a section of hydraulic tunnel as an example, the model proposed in this paper is used to calculate its durability grade as Class III, with the set pair potential SHI(H) = 7.5856, which is consistent with the actual engineering practice, and a comparative study is done in combination with the AHP-Extenics method. It is verified that the evaluation model can scientifically and reasonably evaluate the durability of hydraulic tunnel lining structure, providing a basis for subsequent maintenance and reinforcement.

The multi-factor influence of frost resistance and prevention effect of tunnel thermal insulation layer in cold areas

To figure out the thermal insulation effect of tunnel thermal insulation layer under the action of different factors in cold areas, the heat transfer analysis module in ABAQUS software was used for the Jiangluling Tunnel to numerically simulate the temperature change of the lining. The said thermal insulation effect under different insulation layer laying methods, insulation material heat conductivity coefficients, insulation layer thickness values, and air temperature conditions was analyzed based on the range of Heat Regulation Circle (HRC), and the empirical equation proposed by Japanese Scholar Kurokawa Yoshinori was employed to calculate the laying length of thermal insulation layer, which was then verified by the safety coefficient of tunnel lining structure. The research results showed that, after the thermal insulation layer had been set, the radial depth of annulus of HRC decreased significantly, indicating that the convective heat transfer of cold air had been suppressed; from high to low, the thermal insulation performance of thermal insulation layer installed by different laying methods was: double-layer style, wall-attaching style, composite filler style, and wall-detaching style. When installing thermal insulation layer for the Jiangluling Tunnel, the wall-attaching style thermal insulation layer is suggested; the thickness of thermal insulation layer should not be less than 5.5 cm; the thermal insulation material should take a thermal conductivity coefficient between 0.025 and 0.04 (W/m.k) and be laid throughout the entire tunnel; when the temperature drops below −17 °C, extra thermal insulation measures should be taken to ensure the frost resistance and prevention ability of the tunnel structure.

Structural Behaviors of Large-Section Mine Tunnels Undercrossing Existing Metro Lines

To meet the operational requirements of a new metro line in Guangzhou, China, a complex tunneling project was undertaken in a business area surrounded by high-rise buildings and underground utility pipelines. Two large-section mine tunnels, with a maximum excavation span of 15.6 m, were constructed, crossing beneath the existing metro line 7 in close proximity. To ensure construction safety, extensive field monitoring was conducted, investigating the deformation and stress characteristics of the newly built tunnel lining structures and settlement of existing tunnels during various construction stages. The findings indicate that the structural integrity of the newly built tunnels may be compromised by the ground pressure resulting from deep-hole grouting, which is aimed at protecting the existing metro line above. The primary lining of the new tunnels is particularly susceptible to stress at the arch waist, where it experiences significantly higher stress compared to the arch crown and arch foot. While constructing the secondary lining before removing temporary diaphragm supports can be advantageous in controlling ground settlement, the stress levels within the secondary lining can fluctuate significantly once the temporary supports are removed. Once the tunnels are completed as closed loops, the stress conditions in both the primary and secondary lining tend to stabilize. The secondary lining primarily undergoes flexural stress, with internal force diagrams roughly symmetrical to the cross-section center line, and the most vulnerable position being at the left arch waist or invert. This investigation provides valuable insights for the design and construction of similar engineering projects in the future.

Research on the Design and Construction of Inclined Shafts for Long Mountain Tunnels: A Review

In recent years, inclined shafts have been widely used in long mountain tunnels, but the corresponding design and construction technical specifications need to be improved. By means of literature statistics and actual cases, a comprehensive and systematic review is made on the tunnel profile, lining structure, construction and operation ventilation, construction methods, and machinery of inclined shafts for long mountain tunnels. The results show that: (1) The design of a gentle slope section of an inclined shaft with large longitudinal slope needs to be further improved; (2) When an inclined shaft is only used for ventilation in the operation stage, it is necessary to make full use of the natural wind and eliminate its adverse effects; (3) It is suggested to study the supporting parameters of an inclined shaft in order to realize the standardised design of the supporting parameters; (4) The space of an inclined shaft is narrow, and it has practical demand in improving the automation, intelligence, management, and dispatching level of transport vehicles. In the future, it is an inevitable trend for electric vehicles to replace fuel vehicles. It is necessary to carry out further research on inclined shaft longitudinal slope design, construction and operation ventilation design, and transportation mode.

Thermal Insulation, Antifreeze, and Anti-Drainage Technology for Tunnels in the Cold Area of Jinpen Bay

There are a large number of tunnels built in permafrost regions every year in China. When investigating the road tunnels that have been in operation in cold regions, it was found that most of these tunnels have various freezing damages. Therefore, in the design, construction, operation, and maintenance of tunnels in cold regions, there are still many technical problems that need to be solved urgently. Among them, the problems of heat preservation, anti-freezing, and anti-drainage are the key technical problems to determine whether the tunnels in cold regions are affected by freezing damage. The project was based on the completed highway tunnels in Inner Mongolia. Given a series of special problems faced by the construction and management of tunnels in cold regions, a large number of reference documents were consulted. This paper designed thermal insulation, antifreeze, and anti-drainage technology for tunnels in the cold area of Jinpen Bay. The research in this paper can effectively reduce the probability of the occurrence of tunnel freezing damage, ensure the safety of the long-term operation of the tunnel lining structure, and greatly reduce maintenance costs, which have good economic and social benefits.

Failure mechanism of underwater shield tunnel: An experimental and theoretical study

This study proposes a plastic hinge-based approach to investigate the failure mechanism of underwater shield tunnel lining structures. Joint plastic hinge and segmental plastic hinge are defined based on the observed failure patterns. The rotational demands of the plastic hinges are obtained through theoretical and numerical methods, and the locations of potential plastic hinges are determined based on the displacement requirement of the structure. A damage index model is used to evaluate the damage of the plastic hinges. Full-scale tests are conducted on two types of shield tunnel lining structures: straight-joint assembly structure (STRJS) and staggered-joint assembly structure (STGJS) under high-water pressure loading conditions. The test results indicate that the assembly method is found to significantly affect the failure pattern, with STRJS and STGJS failing through longitudinal joints and concrete segments, respectively. Furthermore, the STRJS and STGJS exhibit comparable load-bearing capacities, with ultimate loads of 2912 kN and 2867 kN, respectively. The plastic hinge approach is used to compare the failure mechanisms of STRJS and STGJS, revealing that STGJS has fewer joint plastic hinges than STRJS at the ultimate state of the shield tunnel lining structure. The failure of STRJS and STGJS is caused by the joint and segmental plastic hinges exceeding their rotation capacity, respectively. The study highlights the importance of considering the assembly method and the type of plastic hinge in the design of underwater shield tunnel lining structures.

Novel Reinforcing Techniques and Bearing Capacity Analysis for Tunnel Lining Structures with Extensive Corrosion

Affected by the erosive environment, tunnel lining concrete in the long-term service zprocess often exhibits engineering diseases such as concrete corrosion degradation and loss of strength, decreasing the stability of the tunnel lining structure and the traffic safety. Based on HTG tunnel project, the basic distribution rule of tunnel lining corrosion and macro mechanical properties of corroded concrete were explored in this paper through engineering disease site investigation. Then, on this basis, aiming at large-scale corrosion of tunnel lining structure, two reinforcement and repair schemes are proposed, corrugated steel plate reinforcement method and channel steel reinforcement method. Indoor component tests are carried out on the two reinforcement schemes. The failure characteristics and stress and deformation law of tunnel lining members after reinforcement and repair were verified. The analysis showed that the failure process of the reinforced specimens on the tensile side could be divided into the non-cracking stage and the working stage with cracks, and the cracking load and failure load of the specimens were significantly increased. The bearing capacity of the reinforced specimens was divided into the ultimate bearing capacity against cracking and the ultimate bearing capacity during failure. Finally, the calculation methods of the bearing capacity of the channel steel reinforcement method and the corrugated steel plate reinforcement method were derived. Comparative analysis shows that the results of numerical simulation, experimental testing and theoretical simplification methods are close to each other, and the maximum deviation is less than 8%. The established method for calculating the bearing capacity of corroded components after reinforcement is reliable and can be used for the design calculation of corroded lining reinforcement.

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.

Numerical investigations on dynamic responses of subway segmental tunnel lining structures under internal blasts

Numerical simulation of segmental lining tunnel subjected to internal explosive loading is carried out in this paper based on the arbitrary-Lagrangian-Eulerian (ALE) and finite element (FE) coupled algorithms. A high-fidelity FE model considering assembled features of segmental lining structure is established, and the mapping technique is adopted to accurately simulate the explosion process. The calculated overpressure histories and failure modes of the lining structure fit well with field test results of full-scale specimens, indicating the applicability and accuracy of the numerical model. A more comprehensive numerical model considered the practical service state of segmental lining tunnel is further built based on the verified model. Influences of mechanical properties and pressure levels of surrounding soils on dynamic responses of tunnel structure under internal explosion are investigated. Numerical results show that dominated deformation modes of the segmental lining tunnel under the action of internal explosion include opening deformation at the segmental joints of the charged ring and shear deformation between the adjacent rings. The modest explosion caused by terrorist bombing attacks may severely harm the shield tunnel structure and impair its service performance, especially if the tunnel is buried in soft soil at a shallow depth

Study on Seismic Response and Vibration Reduction of Shield Tunnel Lining in Coastal Areas

The construction of subway tunnels in the coastal section is affected by special soil quality, with complex construction conditions of unstable soil and vulnerability to groundwater corrosion. The design difficulty of subway tunnels is greatly increased, and the safety performance in the event of an earthquake is greatly reduced. To study the changes in shield tunnel lining structure under earthquake and propose damping measures, ANSYS software is used to conduct tunnel soil numerical simulation. Firstly, static analysis and modal analysis are carried out, and it is found that the maximum displacement deformation occurs at 3.8 cm of the arch crown, and the maximum stress occurs at 2.6 × 107 Pa of the left and right wall corners, 8 easily deformed points are obtained at the same time. Input EI_Centro EW forward 19 s seismic wave is used to analyze the displacement, acceleration and stress vibration characteristics of tunnel lining. The upper part of the lining is more vulnerable to earthquake, and the right arch waist is subject to the maximum stress, reaching 1.37 × 10−4 Pa, the maximum displacement deformation point is 3.65 × 10−10 m at the right wall. To reduce the impact of earthquakes on tunnel lining, the damping scheme of adding an isolation layer is adopted. Using foam concrete isolation material can reduce the stress of the arch waist by 74.6%, and rubber isolation material can reduce the stress by 80%. In consideration of groundwater corrosion and subsequent engineering construction, it is recommended to use foam concrete as the material for the isolation layer. This study can provide a theoretical basis for the design of metro tunnels in offshore areas.

Risk analysis and countermeasures of TBM tunnelling over the operational tunnel

To study the risk and control countermeasures of the TBM tunnel construction adjacent to the operational railway tunnel, based on the TBM tunnel project of Chongqing Rail Transit Line 5, this paper first evaluates the quality health degree of the operational tunnel lining (OTL) structure according to the on-site structural inspection. Then, the displacement, internal force, and proximity influence scope influenced by the metro TBM tunnel construction are studied using numerical simulation. Finally, the corresponding control countermeasures are proposed. The results show that: (1) The adjacent construction of the upper TBM tunnel will lead to the uplift deformation trend of the lower operational tunnel, and the uplift deformation of the vault is greater than that of the ballast bed. The influence scope is roughly a parallelogram, with the long axis parallel to the operational tunnel and the short axis parallel to the new TBM subway tunnel. (2) TBM tunnelling over the operational tunnel will cause the transformation of the mechanical mode of the OTL structure from the small eccentric compression mode to the large eccentric compression mode. The OTL structure between the left and right lines of TBM is unfavorable. (3) The longitudinal curve of the bending moment and axial force of the OTL fluctuates greatly within the influence range. The bending moment and axial force are reduced in operational tunnel construction joints. Based on field evaluation and numerical analysis, this paper puts forward some risk control countermeasures, such as TBM tunnelling parameters control, pea-gravel backfilling, backfill grouting, and bottom grouting, which can effectively solve the risk of the operational tunnel structure in the adjacent construction. This study has important reference value for risk control and safety assessment of tunnel in complex adjacent tunnel construction.

Experimental study on forced response characteristics and anti-dislocation performance of articulated tunnel structure under dislocation action of normal fault

The stick–slip dislocation of normal faults will produce large permanent displacement. The tunnel lining structure crossing active normal faults is easily affected by fault dislocation. It is necessary to study the mechanical behavior of tunnel lining structure under fault dislocation. Therefore, taking the subway tunnel of Urumqi Rail Transit Line 1 crossing the Jiujiawan fault project as an example, based on the optimal mix ratio determined by the indoor similar material ratio test, the self-designed large-scale active fault dislocation simulation loading system is used to carry out the stick–slip dislocation model test of normal fault with 60° dip angle. The mechanical behavior difference between the conventional tunnel structure and the flexible articulated tunnel structure is compared and analyzed, and the cracking range, damage characteristics and failure mode of the tunnel lining structure are defined. The results show that: (1) The failure modes of the conventional tunnel structure and the flexible articulated tunnel structure are basically the same, including the large eccentric failure of the inverted arch and the wall foot, and the compression shear failure at the fault plane, which are longitudinal cracks and oblique cracks respectively. In addition, there are longitudinal cracks in the inner side of the invert and the lateral side of the wall foot, but few circumferential cracks. (2) Because the flexible articulated structure increases the overall longitudinal flexibility of the tunnel, the flexible joints between segments can share part of the fault dislocation displacement, so the deformation range, failure degree and number of cracks of the articulated tunnel structure are significantly reduced compared with the conventional tunnel structure, and the anti-dislocation performance is better. (3) Considering the influence of fault dislocation on tunnel structure, the loose area and empty area should be investigated and repaired in the rapid repair and reinforcement of post-disaster tunnel. At the same time, the case study ideas and test methods in this paper can provide some reference value and guidance for other similar tunnel engineering studies in the future.

Numerical Analysis of Grouting of Water-Enriched Karst Highway Tunnel Based on Critical Water-Enriched Height

The occurrence state of groundwater in a karst area has a significant impact on the tunnel lining structure. The impact on the groundwater is more significant during construction. This paper used numerical simulation to study the grouting reinforcement range of the Liaoshan Tunnel. This was based on the critical water rich height. Under Grade IV and Grade V surrounding rock, the critical points of grouting reinforcement were 230 m and 240 m deep, respectively. The vertical and horizontal stress and seepage flow of the tunnel arch crown and invert decreased as the circumferential grouting reinforcement range increased. In the case of no grouting reinforcement, 1/4 circumferential grouting reinforcement, 1/2 circumferential grouting reinforcement, and all circumferential grouting reinforcement, the seepage flow was 7 m3/dm, 4 m3/dm, 3 m3/dm, and 0 m3/dm, respectively. With Grade V surrounding rock, when the groundwater level was 260–270 m away from the tunnel arch crown, two schemes could be adopted: 1 m radial grouting reinforcement and 1/2 circumferential grouting reinforcement. The results have guiding significance for developing a construction scheme of a karst water rich tunnel.

Large-Scale Model Test on Water Pressure Resistance of Lining Structure of Water-Rich Tunnel

In order to solve the problem of testing the water pressure resistance of lining structures of water-rich tunnels and the difficulty of implementing the existing model tests, a large-scale model test method was proposed relying on the New Yuanliangshan Tunnel threatened by high pressure and rich water. This method creatively transformed the external water pressure of the lining structure into internal water pressure, and the conversion coefficient of water resistance of lining under different sizes and loading modes was obtained by numerical calculation. Results showed that the ultimate water pressure resistance of the lining structure under an external uniformly distributed water pressure and local water pressure was 1.44 and 0.67 times of that obtained from the large-scale model tests, respectively. By conducting the large-scale model tests and combining with the conversion coefficient, the water pressure resistance of the actual tunnel lining could be obtained. Research indicated that water pressure resistance of K2.0 (bearing water pressure of 2.0 MPa) type lining at the transition section of karst caves and K3.0 (bearing water pressure of 3.0 MPa) type lining at the section of karst caves of the New Yuanliangshan Tunnel was 3.33 MPa and not less than 4.36 MPa, respectively, and the high reliability of the large-scale model tests was verified by numerical calculation, implying that the model test method could be extended to similar tunnel projects.

High-speed train induced vibration measurements in fresh tunnel shotcrete layer

Existing coastal railway track has been undergoing for renovation and improvement work aiming to raise train speed and shorten the travel time between Turku and Helsinki. The track has 16 existing tunnels of which 14 has been renovated between 2019 and 2021. Majority of the tunnels have been reinforced by system and shotcrete and rock bolts. The water seepage control has been solved by using PE sheets with additional 100 mm fibre shotcrete layer as fire protection layer. After the track and tunnel improvements, the track was test driven with two different trains: a high speed SM train unit and a two storey intercity train unit. The speeds used were higher than the current allowed speeds aiming to study the potential to increase the travel speed. One of the most restrictive parameters for the increase is the pressure shock of high speed train entering the tunnel. Too high pressure shock will cause inconvenience for the passengers and can cause damage in tunnel lining structures. Also currently no clear guideline exists what speed limits need to be used for trains entering tunnels with curing shotcrete. To study these matters the test run train units were instrumented including with pressure sensors. The conclusions about the pressure shocks are investigated briefly in the paper.