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Improving the diagnosis methodology for masonry tunnels
Tunnelling and Underground Space Technology 70 (2017) 55–64
Contents lists available at ScienceDirect
Tunnelling and Underground Space Technology journal homepage: www.elsevier.com/locate/tust
Improving the diagnosis methodology for masonry tunnels a,⁎
b
Daniel Llanca , Pierre Breul , Claude Bacconnet
MARK
b
a
Lombardi ingénierie SAS, 70, rue de la Villette, 69425 Lyon Cedex 03, France Polytech Clermont-Ferrand – Institut Pascal UMR CNRS 6602, Université Clermont Auvergne, Campus des Cézeaux, 2 avenue Blaise Pascal – TSA 60206 CS 60026, 63178 Aubière Cedex, France b
A R T I C L E I N F O
A B S T R A C T
Keywords: Tunnels diagnosis Masonry lining Site characterization Paris metro
The sustainability of transportation systems infrastructures remains a major challenge for managers in order to ensure safety and quality service to passengers. For example, the French company RATP transports up to 10 million passengers daily in Paris. Most of its underground structures are composed of masonry tunnels built several decades ago. However, at present, monitoring methodologies often remain incomplete or qualitative when evaluating the real condition of tunnels and proposing a diagnosis. This article focuses on a new monitoring methodology that complements visual inspections, based on a quantitative analysis of each tunnel component. Using a coupled analysis of the various data (qualitative, quantitative and expert) in our possession, we suggest establishing a score to qualify the actual condition of a tunnel and improve its diagnosis. The application of this methodology to carry out an evaluation of the masonry lining of the Paris Subway System shows that the proposed method and tools are particularly well adapted for characterizing and evaluating masonry lining.
1. Introduction
According to the seriousness of the defects located, additional and complementary survey actions can be performed. However, these interventions are complex and require mobilizing heavy and intrusive means that complicate their organization and execution in systems in service where the constraints of access and safety are very strong. In this context, we propose the development of a new monitoring methodology based on the quantitative analysis of each of the tunnel’s components. Using a multi-technical approach to obtain quantitative data, we suggest developing a method in addition to visual inspections to obtain a more complete evaluation of the real condition of the structure. Afterwards, we suggest establishing a scoring system to qualify the actual state of the structure, using a coupled analysis of the various data (qualitative, quantitative and expert) in our possession.
Guaranteeing the sustainability of transportation system infrastructures remains a major challenge for managers in order to ensure safety and quality service to passengers. For example, the French company RATP has to transport nearly 10 million passengers daily in Paris in its infrastructure network. The underground structures consist mainly of masonry tunnels built several decades ago (Idris et al., 2008) (Le Bras and Azria, 1989). In this context, the topic of diagnosis, maintenance and repair has become crucial. To optimize the maintenance of these structures, managers need tools to describe the condition of various components of the structure (tunnel lining, contact interface and surrounding soil) (Fig. 1) to assess the tunnel and prioritize the maintenance operations to be performed. However, the diagnosis methods currently available to managers are mainly based on continuous and periodic visual inspections which give rise to grading regarding defects and tunnel condition (Asakura and Kojima, 2003) (Richards, 1998). Visual tunnel inspections are necessary and provide essential information, though the latter is mainly qualitative information on the tunnel intrados. Consequently, the origin or the seriousness of the faults observed is sometimes complicated and the evaluation of the real condition of the tunnel remains incomplete (ITA-AITES, 1987; AFTES, 2005).
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2. New monitoring methodology 2.1. General methodology The Paris metro (RATP) current policy of tunnel’s diagnosis is based on periodic visual inspections. Non-exhaustive surveys are carried-out annually and a detailed inspection at least once every five years. Those surveys are performed by technical inspectors who visit all the elements and structures of the network. Each apparent default (crack, humidity,
Corresponding author. E-mail addresses: [email protected] (D. Llanca), [email protected] (P. Breul), [email protected] (C. Bacconnet).
http://dx.doi.org/10.1016/j.tust.2017.07.002 Received 31 October 2015; Received in revised form 29 June 2017; Accepted 4 July 2017 0886-7798/ © 2017 Elsevier Ltd. All rights reserved.
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or 3 bores/panel) are used to perform geoendoscopic and penetrometric tests and obtain the precise local characterization of the lining, the contact and the surrounding soil and calibrate geophysical soundings (Fig. 2). The analysis of the data collected provides an automatic physical and mechanical characterization of each tunnel component: local masonry lining degradation and the state of contact between the structure lining and the enclosing and surrounding soils, with low traumatic intrusion (Fig. 3). 2.2. Characterization of tunnel lining and contact layer The approach is aimed at replacing the traditional methodology for masonry qualification, which is time-consuming, requires investigation and drilling holes with diameters of about 60-mm with cumbersome and expensive procedures, by an analysis based on two non-destructive techniques. The latter are completed with punctual geo-endoscopic tests for the local analysis of tunnel linings performed in small size holes with image processing. Several campaigns to analyze sections of access tunnels in the Paris subway were carried out to test and calibrate the monitoring method proposed. In each analysis section, holes were drilled at points of interest to verify and calibrate the non-destructive measurement and obtain the local characterization of the lining and surrounding soils by geo-endoscopic and penetrometer tests. Similarly, in order to determine the local degradation of the masonry lining, additional analyses of the automated endoscopic images were performed. Several laboratory tests on the masonry core were also carried out to characterize the masonry materials (Llanca et al., 2013a,b).
Fig. 1. Masonry tunnel components.
…) is located, listed and given a score varying from 1 to 7 according its nature and seriousness: 1 for lower damage and 7 for important damage or structural defaults. The score given is the result of the combination of a class indicating the state of the structure and an optional index assessing the risk of the anomaly. Once the defaults are recorded, a score of the structure’s general health is established (global score). In general, the global score is correlated to the most frequent default score. This global health score is attributed to tunnels, corridors and stations. It varies from 1 to 6 (where 1 characterizes the state of a new structure, 6 that of a state close to ruin). According to the global health score, a decision regarding the maintenance operation to be performed can be taken. When major disorders of the structure are detected, an exceptional detailed inspection based on soundings can be carried out to obtain further information. The monitoring methodology proposed is complementary to visual inspection. This methodology is based on diagnosis using several tools (geophysical testing, endoscopic and penetrometric tests) (Fig. 2). First, a geophysical characterization of the lining based on ground penetration radar and mechanical impedance tests is performed on a panel 15 m long and 3 m high. These tests are designed to provide rapid mapping of structures to identify areas with variations of physical and mechanical characteristics. The identification of these areas can influence the choice of location of small diameter bores (2 cm in diameter) which are carried out in the second step. These small diameter bores (2
2.2.1. Local mechanical characterization of the masonry lining and contact by endoscopy The local characterization of the masonry lining was performed by an endoscopic inspection of the tunnel lining and contact interface layer inside small size boreholes (ɸ = 22 mm). Automatic image processing was used to detect anomalies (voids, cracks, etc.) in the lining and the presence (or absence) of contact between the lining and the surrounding soil. The result provided a local analysis of lining thickness and deterioration. (Haddani, 2002; Haddani et al., 2005; Llanca and Breul, 2011). The presence of discontinuities in masonry affects the mechanical behavior of the entire lining of an underground structure (Barton and Choubey, 1977). It is therefore necessary to take these discontinuities into account in order to evaluate the deterioration of the masonry at the local level. To this end, Llanca et al. (2013) proposed a methodology to assess the local condition of the lining of an underground structure. It is
Fig. 2. Monitoring methodology: example of panel of investigation, geophysical tests (ground penetration radar and impedance), endoscopic and penetrometric tests.
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Fig. 3. Methodology and analysis of tunnel components.
or damage areas. Zone 2 – damaged masonry (thickness t2): This layer is defined as an area where the masonry can be deteriorated and presents discontinuities. In this case, a reduction of mechanical properties is assumed as a function of the frequency of discontinuities and the condition observed in this layer. A method has been proposed to obtain the homogenized values for the main parameters studied: Uniaxial Compressive Strength (UCS) and Young’s modulus (Em) of this zone. Zone 3 – disaggregated masonry thickness (thickness t3). This layer
based on the discontinuities observed using geoendoscopy and a realistic estimation of the mechanical parameters by sectioning the lining thickness. This assessment is based on the values of the parameters obtained from the mechanical tests on core samples and taking into account the local state of degradation. This approach consists in defining three sub-layers linked to the rate of degradation of the lining (Fig. 4): Zone 1 – undamaged masonry (thickness t1): This masonry layer corresponds to the thickness of the structure with no discontinuities
Fig. 4. Local characterization of the masonry lining by endoscopy and simplified masonry model.
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of the masonry lining is completely disaggregated and has no mechanical continuity and consequently no cohesion. This phenomenon is observed in the areas close to the extrados of tunnels. We consider that this area is no longer part of the lining. This layer starts at the end of zone 2 and is defined as a transition zone between the tunnel lining and the surrounding soil. In practice, the mechanical parameters applied to this area will be those of a loose granular soil. The application of this method results in the definition of the concept of ‘‘effective thickness’’ (teff = t1 + t2) of the structure lining at the local scale. This thickness corresponds to the thickness of the structure lining ensuring the structural resistance of the tunnel. 2.2.2. Geophysical characterization The geophysical characterization of the tunnel lining is based on ground penetration radar tests and the impulse-response method. These tests are designed to provide the thickness profile and a rapid mapping structure to identify areas with their physical characteristics and/or different mechanical properties.
Fig. 6. Principal Component Analysis of impedance and sounding parameters.
materials, thickness and variable geometry. To do this we analyzed the results of in-situ tests (4 subway stations - 846 survey points) through a comparative analysis of the results of the impedance test and the analysis of the lining’s condition. A multi-variable study was conducted to assess the contribution of each impedance parameter in the global assessment of the structure. It sought to highlight the possible relationships between the different parameters obtained from the impedance test and the possible link between the impedance settings and parameters obtained from core drilling. The parameters used are as follows:
2.2.2.1. Impulse-response test. The impulse-response test was developed from the vibration method for pile integrity testing. The method was later extended to the inspection of other kinds of concrete structures, particularly plate-like elements such as floor slabs, walls, and large cylindrical structures (Davis et al., 2005). The method is based on the analysis of characteristics of stress propagation waves in the element tested. A low-strain impact is applied by a hammer equipped with a force sensor; the response to the input stress is measured by using a velocity transducer (Fig. 5). The result is a transfer function referred to as the “Mobility of the element under test” (the velocity/force signal ratio: |V/F| expressed as a function of frequency). The test graph of mobility plotted against frequency from 0 to 800 Hz contains information on the condition and integrity of the concrete in the element under test (see Fig. 6). To improve the interpretation of the impedance test and understand the physical meaning of these measurements, 3 parameters obtained using this test were analyzed (Llanca, 2014). These are the parameters that provide the most representative information: Slope ∗ Mobility (S × M), Void Index (IdV) defined as the ratio of the peak mobility below 100 Hz to the average mobility and Dynamic Stiffness (R), defined as the inverse of the slope of the mobility plot for the portion with a frequency less than 50 Hz. The objective is to analyze the relationship between these parameters and the lining status, taking into account specific conditions such as the heterogeneity of component coating
– RQD (Rock Quality Design) – t1 (undamaged masonry thickness as defined in 1.2.1) – UCS (Uniaxial Compressive Strength) A distribution can be observed along the two main axes distinguishing three groups of variables. The first corresponds to the S × M (Slope ∗ Mobility) variables, UCS and t1, with the first two being correlated quite closely. The second axis corresponds to the void index (IdV) and the stiffness (R) to a lesser extent. Finally, RQD seems related to the third component. The impedance test is strongly influenced by the mechanical continuity of the medium. This result led us to assume that the S × M parameter was closely related to the mechanical
Fig. 5. Mechanical Impedance.
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the thickness and the transit time of the wave corresponding to each sampling line. It should be noted that the calibration was performed on the effective thickness of the lining (i.e. teff = t1 + t2 as defined at § 2.2.1) Secondly, a blind analysis was carried out by using the dielectric constant found at the first step. Fig. 10 shows the comparison of the thicknesses evaluated by endoscopy and GPR at the same place in different subway stations.Fig. 11 Ground penetrating radar was used to estimate the effective thickness of the masonry with an accuracy of ± 6 cm/m. However, account had to be taken of the highly heterogeneous nature of the material studied, with considerable geometrical (variations of thickness) and physical (humidity conditions) variations that significantly influence the values of the main dielectric constant. It was observed that the value of the dielectric constant could be defined for a large tunnel section from the correlation with geoendoscopic tests.
Fig. 7. Relation S × M and t1.
characteristics of the materials of the first layer of healthy coating and to the mechanical continuity of the medium. Therefore we focused on the study of possible correlations between the S × M impedance parameter and the undamaged masonry thickness (t1) observed through the geoendoscopic tests. The study was carried out using the surveys of 3 stations. Fig. 7 shows the relationship obtained for both parameters t1 (undamaged masonry thickness) and Ln (S × M) (logarithm of the parameter “SlopexMobility”). Despite a significant dispersion for the t1 thickness values higher than 50 cm, a linear trend can be noticed. These two parameters are linked by the function:
t1 (m) = 1,64−0,47∗Ln (S × M )
2.3. Characterization of surrounding soils The study of the in-service facility showed the extent to which the evolution of the tunnel lining is related to changes in the surrounding environment. These changes can result from the evolution of the surrounding soils, a change in environmental conditions or modifications in groundwater conditions (leached fine elements of soils, reduction of mechanical characteristics when water conditions become more severe, swelling due to the hydration of certain types of clays and rocks, etc.). The influence of these pathologies can increase without an efficient drainage system, which is the case in many ancient structures. Here, the need for information on the geological and geotechnical environment is evident. To perform a rapid and efficient characterization of enclosing soils, we used the light-weight penetrometer test combined with the endoscopic analysis of soils from the underside of the tunnel. Llanca and Breul (2011) and Llanca-Vargas et al. (2015) demonstrated that it was possible to obtain an in-situ material characterization and elasticity modulus estimation with minimal intrusion and at lower cost. This method is also of great interest for estimating the spatial variability of soil mechanical parameters at different scales (monitoring, tunnel or station section).
(1)
Carrying out the impedance test made it possible to evaluate the undamaged masonry thickness (t1) for a panel. It is clear that because of the limitations of the tool, the greater the thickness of the masonry, the lower the accuracy of the mobility measurements. Despite this, the method is very useful for obtaining a spatial view across the panel to assess the evolution of thickness t1. 2.2.2.2. Ground penetration radar (GPR). GPR employs electromagnetic waves emitted by an antenna. When a signal emitted passes through a solid propagation medium (structures), its intensity is gradually weakened (Haack et al., 1995). The electromagnetic waves passing through the lining medium are principally influenced by two properties: material conductivity and dielectricity. The antenna emits and receives high frequency electromagnetic pulses through the material. The signal is partially or entirely reflected when it encounters a discontinuity. A discontinuity corresponds to a change of the dielectric properties, and the signal is entirely or partially reflected. Using GPR provides a qualitative study of the lining condition, changes in the nature of the materials, structural abnormalities (voids, caverns), and the analysis of the structure’s constituents, among other things (AFTES, 2005). Here, we used GPR to identify the extrados lining profile (or the lining thickness). The frequencies should allow analyzing large lining thicknesses ranging from 0.5 to 1.5 m. It was found that the lower frequency antenna was poorly suited for studying thick coatings beyond 1-m. Henceforth, the results presented include those obtained only from the 400 MHz antenna, which is better suited to coatings of old underground structures. The thickness of the masonry was estimated using the wave reflection time measurements, and the dielectric constant of the medium (Fig. 8). To evaluate the capacity of the GPR to provide the lining thickness, in situ test campaigns were carried out to compare the thickness estimation provided by the GPR and those provided by endoscopy at the same place. Initially, to improve the accuracy of the GPR measurements, it was necessary to combine the use of geoendoscopy. Thus, by using the real local thickness of the masonry obtained by geoendoscopic tests, the GPR settings were calibrated for this value by setting it at the corresponding dielectric constant. As can be seen in Fig. 9, we obtained
3. Scoring and diagnosis The monitoring method proposed in this paper provides a set of quantitative information summed up below: – – – –
Thickness of the undamaged masonry (t1), Effective thickness of masonry (teff), Status of the contact between the lining and enclosing soil, Physical and mechanical characterization of the surrounding soil.
The data collected with the new monitoring method must be aggregated to propose a score for the fault or tunnel section before diagnosing the tunnel. This scoring system enables updating the score obtained for these tunnel sections during previous investigations and visual inspections. 3.1. Parameters taken into account for scoring In order to assign a score to the tunnel sections investigated, we propose taking into account the parameters presented below: ● For masonry: – t1: thickness of the undamaged masonry. Value obtained from endoscopic and impulse-response test – teff and t2: effective thickness and thickness of the damaged masonry defined from endoscopic and GPR tests (teff = t1 + t2) 59
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Fig. 8. Estimation of masonry lining thickness (εR = 10, VM = 0.1 m/ns).
● Contact status: C: contact status evaluated from the punctual endoscopic test. ● For the surrounding soil: – Identification: characterization of the soil from image processing – Hydric status evaluated from endoscopic images – Mechanical status evaluated from the analysis of endoscopic images and cone resistance obtained with the light penetrometer test. 3.1.1. Threshold values for the masonry To grade the thickness of the masonry, we suggest comparing the effective thickness teff (teff = t1 + t2) of the masonry with the initial total thickness (tinit) of the construction obtained from endoscopic measurements or from the plans of the works. In agreement with the RATP experts and based on numerical simulation works (Kamel et al., 2012, 2013a,b, 2014), three thresholds have been defined according to the ratio between the effective and the initial total thickness:
Fig. 10. Graphics of correlation between GPR and geoendoscopic thickness evaluation.
approach based on the local evaluation obtained from the endoscopic analysis. Thus on a panel, three thresholds have been defined: – contact exists in 100% of the endoscopic tests, – contact exists in 50% of the endoscopic tests, – contact exists in 0% of the endoscopic tests.
1. teff > 2/3 tinit: considering that the old masonry tunnels were oversized, we accept that a part of the masonry no longer participates in the structural resistance of the structure without having an impact on its global behavior. 2. ½ tinit < teff < 2/3 tinit: masonry is relatively modified and the thickness degraded is substantial. This situation can lead to a redistribution of stresses, leading to a loss of structural resistance or an adaptation of the lining (cracks, displacement, strain, etc.). 3. teff < ½ tinit: In this case, we consider that a large part of the masonry thickness is modified. If this limit value is reached, the grading will not take into account the contact and the surrounding soil status. The score assigned will reflect the state of the structure and the urgency of intervention.
3.1.3. Evaluation of surrounding soil The evaluation of the surrounding soil is dependent on: ● the kind of existing material estimated by the endoscopy (Haddani et al., 2009), ● soil compaction evaluated by the cone resistance of the penetrometric test (Chaigneau et al., 2000), ● the estimation of hydric state: 3 states have been defined from the visual analysis of endoscopic images. Based on these three data, the condition of the surrounding soil is declared “evolving” (or risky), or “non evolving”. For example, a clay in
3.1.2. Threshold values for contact status The evaluation of the ground-structure contact status uses a binary
Fig. 9. Sampling line on tunnel lining by geoendoscopic and GPR tests.
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Fig. 11. In-situ test and results for soil surrounding a tunnel.
intervention). Fig. 12 provides the flowchart of the grading. From the local scores obtained for each measurement point, a panel score was defined as follows: If more than 20% of the local scores are equal to 6 or 7 then the panel score is equal to 7, otherwise, the panel score is equal to the average of the local scores. Finally, it is necessary to aggregate the scores obtained with the new monitoring method with the scores of visual inspections assigned by the RATP inspectors. 3 scenarios are possible and the final score attributed is defined in the following way:
a humid hydric state and with weak cone resistance will be declared “evolving or risky soil”. On the contrary, compacted sand will be declared “non evolving soil”.
3.2. Scoring From the threshold established for each parameter, aggregation is necessary to propose a grading of the fault or tunnel status as well as a diagnosis of the tunnel. To be in accordance with the scores assigned to defects detected by the RATP inspectors during their visual survey, we defined a scoring scale from 1 to 7 (1 excellent state and 7 critical state - immediate
Fig. 12. Score flow chart.
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Fig. 13. Results of the Impulse-response test and estimation of undamaged masonry thickness (t1).
– If we only have a visual inspection score, then the final score will be this score. – If we have a visual inspection score and a score resulting from the new monitoring method at the same place, then the final score will be that resulting from the new monitoring method. – At last, if we only have a score resulting from the new monitoring method, then this score will be the final score.
because the score takes account of all the tunnel’s components. The scores obtained with the new diagnosis method are sometimes lower or equal to those obtained by the visual inspection when the extension of the defect is limited. But the scores obtained with the new method of diagnosis are often higher than those obtained by the visual inspection because they are more quantitative and because they provide the condition of both the intrados and the structure extrados. Finally, the diagnosis obtained with this new methodology is more complete and objective than visual inspections. Moreover, it is possible to use this methodology to control regeneration works as presented in Fig. 16.
4. Contribution of the new methodology: comparative study on a real case This methodology was tested in 8 Paris subway stations in order to validate and evaluate its applicability. We present the analysis of one station section below. Fig. 13 provides the results of the impulse-response test. A test was performed on a panel at each point of a mesh 1 m in length and 0.60 m in height. Then, a map of the main parameters extracted from the test was drawn. The white zones on the map correspond to areas where tests were not carried out because of the presence of objects (advertising panel, electrical devices, etc.) on the wall. Then, using the relationship (Eq. (1)), the impedance test was used to evaluate the undamaged masonry thickness (t1) The GPR tests were carried out on 3 profiles (low, intermediate and upper) on the surface of the panel. From the results obtained, an estimation of the effective masonry thickness teff was performed by using the calibration of the dielectric constant with the endoscopic tests (Fig. 14). Fig. 15 provides the classical results obtained from endoscopic and penetrometric test results (2 or 3 tests were performed for each panel). From these results, we were able to characterize the contact and the surrounding soil. In this example, contact was detected in 100% of the endoscopic tests and the surrounding soil was estimated as “evolving soil” because it was soft soil with high cone resistance but in the presence of water. The effective thickness (teff) is higher than 2/3 tinit (initial thickness) which is equal to 0.9 m. Based on the diagnosis flow chart shown in Fig. 12, the score of this section is 2. In this case, the score provided by the RATP inspectors according to their visual inspection was also 2. Table 1 proposes a comparison of the scores obtained with the new monitoring method and those obtained from the visual inspection by the RATP inspector at the same place for different sections in this subway station (Table 1). As can be seen, the scores obtained from the new diagnosis methodology are often different from those obtained with the visual inspection. The range of the scores is wider for the new diagnosis method
5. Conclusions An improvement of the diagnosis methodology for masonry tunnels was proposed. This methodology is based on a new monitoring method used to assess the three main components of a tunnel: masonry lining, contact and surrounding soil. This monitoring method is rapid, well adapted to the conditions of underground in-service structures and relatively non-destructive. The monitoring methodology is based first on geophysical characterization using Ground Penetration Radar and the impulse-response test. We showed that GPR can provide the effective masonry thickness, but calibration with the geoendoscopic test is necessary. One of the parameters of the impulse-response test is directly linked to undamaged lining thickness (t1). The second stage of the monitoring method is based on the use of geoendoscopic and light penetrometric monitoring that provide the mechanical quality of the masonry, the contact status and the characterization of the surrounding soil. Testing results highlight the fact that separately the proposed tools of the method do not allow to conclude on the global state of the tunnel. In fact, each tool need for calibration or to make hypothesis to obtain correctly data and results, gives partial information and only on located zones of the lining or surrounding soil. That is why the advantage of the proposed methodology in this paper is to overcome these drawbacks by providing a complete and integrated tunnel diagnosis. Testing results highlight how by separate, the proposed tools of the method do not allow to conclude on the global state of the tunnel. In fact, each tool need for calibration or to make hypothesis to obtain correctly data and results, gives partial information and only on located zones of the lining or surrounding soil. That is why the advantage of the proposed methodology in this paper is to overcome these drawbacks by providing a complete and integrated tunnel diagnosis. Using the data collected with the new monitoring method, a 62
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Fig. 14. Results of the GPR test on a profile and estimation of the masonry effective thickness teff.
methodology for scoring and diagnosing tunnels was proposed by aggregating the different data. To be in accordance with scores assigned to the anomalies detected by RATP inspectors during their visual surveys, we defined a scoring scale from 1 to 7. The thresholds and the methodology proposed were validated by the RATP’s experts and by numerical simulation works. The method was tested in 8 subway stations in Paris and the score grading obtained was compared with the grading obtained from classical visual inspections. This comparison highlights that the new monitoring methodology proposed completes and improves the classical diagnosis method as it is more complete, more quantitative and more objective than visual inspections. Moreover, we showed it is possible to use this methodology to control regeneration works. Finally, the methodology focuses only on the grading of a section of tunnels. The aggregation of different scores of different sections to
Table 1 Comparison of scores obtained from the visual inspection (RATP score) and from the new diagnosis method. No section
RATP score
Score obtained with the new diagnosis method
1 2 3 4 5 6 7 8 9
2 2 2 3 3 2 2 2 2
2 4 2 2 4 3 4 4 5
Fig. 15. Endoscopic and penetrometric test results.
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Fig. 16. Comparison of the evolution of the lining status before and after regeneration. 526–536. Idris, J., Verdel, T., Heib, M.Al., 2008. Numerical modelling and mechanical behaviour analysis of ancient tunnel masonry structures. Tunn. Undergr. Space Technol. 23, 251–263. ITA Working Group on Costs-Benefits of Underground Urban Public Transportation, 1987. Examples of benefits of underground urban public transportation systems. Tunn. Undergr. Space Technol. 2, 15–54. Kamel, T., Pellet, F., Silvani, C., Goirand, P., 2012. Numerical modeling of the time dependent degradation of the mechanical properties of a metro underground gallery. In: 1st Eastern European Tunneling Conference (1EECT) – Budapest – 2012. Kamel, T., Limam, A. Silvani, C., 2013. Modeling of the strength’s loss and void appearance in the underground structures of Paris Metro, 5iYGEC Paris. Kamel, T., Limam, A. Silvani, C., 2013. Masonry weathering of the Metro de Paris gallery: modeling via a continuum approach - EURO: TUN 2013, in: 3rd International Conference on Computational Methods in Tunnelling and Subsurface Engineering Ruhr University Bochum. Germany. Kamel, T., Limam, A., Silvani, C., 2014. Modeling the degradation of old subway galleries using a continuum approach. Tunn. Undergr. Space Technol. 04, 77–93. Le Bras, A., Azria, E., 1989. Methods for diagnosing the condition of structures at the RATP. Revue Travaux. FNTP 5 (643), 1–11. Llanca, D., 2014. Caractérisation de tunnels anciens en maçonnerie par des techniques d’auscultation non conventionnelles – Application au réseau RATP, PhD Thesis Blaise Pascal University, Clermont-Ferrand, France. Llanca D., Breul, P. 2011. Characterization of composants of an underground structure in service for the evaluation of its status. In: 13th AFTES International Congress, Underground Spaces for Tomorrow. Llanca, D., Breul, P., Bacconnet, C., Sahli, M., 2013a. Characterization of the masonry lining of an underground structure by geoendoscopy. Tunnel. Undergr. Space Technol. 38, 254–265. http://dx.doi.org/10.1016/j.tust.2013.07.009. Llanca, D., Breul, P., Haddani, Y., Goirand, P., 2013. Methodology of diagnosis of urban tunnels in service. World Tunnel Congress, May–June 2013, Geneva, Switzerland. Llanca-Vargas, D., Breul, P., Bacconnet, C., 2015. Modulus estimation of surrounding soils of underground structures in service. GTJ 38 (4), 452–460. Richards, J.A., 1998. Inspection, maintenance and repair of tunnels: international lessons and practice. Tunnel. Undergr. Space Technol. 4 (13), 369–375.
obtain a global tunnel grading, and the optimization of the monitoring emplacements will be the subjects of a future article. Acknowledgements These studies were carried out with the support of the National Research Agency (ANR) France. References AFTES, 2005. Recommendations on rehabilitation for underground structures. Tunnels et ouvrages souterrains, HS 3, Association Française des Tunnels et l’Espace Souterrain. Asakura, T., Kojima, Y., 2003. Tunnel maintenance in Japan. Tunnel. Undergr. Space Technol. 18, 161–169. Barton, N., Choubey, V., 1977. The shear strength of rock joints in theory and practice. Rocks Mech. 10, 1–54. Chaigneau, L., Gourves, R., Bacconnet, C., 2000. Penetration test coupled with a geotechnical classification for compaction control. International conference on geotechnical and geological engineering, GeoEng, 2000, Melbourne, Australia, 19–24 November. Davis, A.G., Lim, M.K., Petersen, C.G., 2005. Rapid and economical evaluation of concrete tunnel linings with impulse response and impulse radar non-destructive methods. NDT & E Int. 38, 181–186. Haack, A., Schreyer, J., Jackel, G., 1995. State-of-the-art of nondestructive testing methods for determining the state of a tunnel lining. Tunnel. Undergr. Space Technol. 10 (4), 413–431. Haddani, Y., 2002. Geoendoscopy: application to soil investigation and diagnostic in urban area. JNGG 2002, 8 et 9 October 2002, Nancy, France. Haddani, Y., Breul, P., Gourvès, R., 2005. Diagnostic Des Tunnels Par Couplage Des Techniques Complémentaires. AFTES International Congress, Chambéry. Haddani, Y., Breul, P., Bonton, P., Gourvès, R., 2009. Learning method for in situ soil classification based on texture characteristics. ASTM Geotech. Test. J. 32 (6),
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Tunnelling and Underground Space Technology journal homepage: www.elsevier.com/locate/tust
Improving the diagnosis methodology for masonry tunnels a,⁎
b
Daniel Llanca , Pierre Breul , Claude Bacconnet
MARK
b
a
Lombardi ingénierie SAS, 70, rue de la Villette, 69425 Lyon Cedex 03, France Polytech Clermont-Ferrand – Institut Pascal UMR CNRS 6602, Université Clermont Auvergne, Campus des Cézeaux, 2 avenue Blaise Pascal – TSA 60206 CS 60026, 63178 Aubière Cedex, France b
A R T I C L E I N F O
A B S T R A C T
Keywords: Tunnels diagnosis Masonry lining Site characterization Paris metro
The sustainability of transportation systems infrastructures remains a major challenge for managers in order to ensure safety and quality service to passengers. For example, the French company RATP transports up to 10 million passengers daily in Paris. Most of its underground structures are composed of masonry tunnels built several decades ago. However, at present, monitoring methodologies often remain incomplete or qualitative when evaluating the real condition of tunnels and proposing a diagnosis. This article focuses on a new monitoring methodology that complements visual inspections, based on a quantitative analysis of each tunnel component. Using a coupled analysis of the various data (qualitative, quantitative and expert) in our possession, we suggest establishing a score to qualify the actual condition of a tunnel and improve its diagnosis. The application of this methodology to carry out an evaluation of the masonry lining of the Paris Subway System shows that the proposed method and tools are particularly well adapted for characterizing and evaluating masonry lining.
1. Introduction
According to the seriousness of the defects located, additional and complementary survey actions can be performed. However, these interventions are complex and require mobilizing heavy and intrusive means that complicate their organization and execution in systems in service where the constraints of access and safety are very strong. In this context, we propose the development of a new monitoring methodology based on the quantitative analysis of each of the tunnel’s components. Using a multi-technical approach to obtain quantitative data, we suggest developing a method in addition to visual inspections to obtain a more complete evaluation of the real condition of the structure. Afterwards, we suggest establishing a scoring system to qualify the actual state of the structure, using a coupled analysis of the various data (qualitative, quantitative and expert) in our possession.
Guaranteeing the sustainability of transportation system infrastructures remains a major challenge for managers in order to ensure safety and quality service to passengers. For example, the French company RATP has to transport nearly 10 million passengers daily in Paris in its infrastructure network. The underground structures consist mainly of masonry tunnels built several decades ago (Idris et al., 2008) (Le Bras and Azria, 1989). In this context, the topic of diagnosis, maintenance and repair has become crucial. To optimize the maintenance of these structures, managers need tools to describe the condition of various components of the structure (tunnel lining, contact interface and surrounding soil) (Fig. 1) to assess the tunnel and prioritize the maintenance operations to be performed. However, the diagnosis methods currently available to managers are mainly based on continuous and periodic visual inspections which give rise to grading regarding defects and tunnel condition (Asakura and Kojima, 2003) (Richards, 1998). Visual tunnel inspections are necessary and provide essential information, though the latter is mainly qualitative information on the tunnel intrados. Consequently, the origin or the seriousness of the faults observed is sometimes complicated and the evaluation of the real condition of the tunnel remains incomplete (ITA-AITES, 1987; AFTES, 2005).
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2. New monitoring methodology 2.1. General methodology The Paris metro (RATP) current policy of tunnel’s diagnosis is based on periodic visual inspections. Non-exhaustive surveys are carried-out annually and a detailed inspection at least once every five years. Those surveys are performed by technical inspectors who visit all the elements and structures of the network. Each apparent default (crack, humidity,
Corresponding author. E-mail addresses: [email protected] (D. Llanca), [email protected] (P. Breul), [email protected] (C. Bacconnet).
http://dx.doi.org/10.1016/j.tust.2017.07.002 Received 31 October 2015; Received in revised form 29 June 2017; Accepted 4 July 2017 0886-7798/ © 2017 Elsevier Ltd. All rights reserved.
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or 3 bores/panel) are used to perform geoendoscopic and penetrometric tests and obtain the precise local characterization of the lining, the contact and the surrounding soil and calibrate geophysical soundings (Fig. 2). The analysis of the data collected provides an automatic physical and mechanical characterization of each tunnel component: local masonry lining degradation and the state of contact between the structure lining and the enclosing and surrounding soils, with low traumatic intrusion (Fig. 3). 2.2. Characterization of tunnel lining and contact layer The approach is aimed at replacing the traditional methodology for masonry qualification, which is time-consuming, requires investigation and drilling holes with diameters of about 60-mm with cumbersome and expensive procedures, by an analysis based on two non-destructive techniques. The latter are completed with punctual geo-endoscopic tests for the local analysis of tunnel linings performed in small size holes with image processing. Several campaigns to analyze sections of access tunnels in the Paris subway were carried out to test and calibrate the monitoring method proposed. In each analysis section, holes were drilled at points of interest to verify and calibrate the non-destructive measurement and obtain the local characterization of the lining and surrounding soils by geo-endoscopic and penetrometer tests. Similarly, in order to determine the local degradation of the masonry lining, additional analyses of the automated endoscopic images were performed. Several laboratory tests on the masonry core were also carried out to characterize the masonry materials (Llanca et al., 2013a,b).
Fig. 1. Masonry tunnel components.
…) is located, listed and given a score varying from 1 to 7 according its nature and seriousness: 1 for lower damage and 7 for important damage or structural defaults. The score given is the result of the combination of a class indicating the state of the structure and an optional index assessing the risk of the anomaly. Once the defaults are recorded, a score of the structure’s general health is established (global score). In general, the global score is correlated to the most frequent default score. This global health score is attributed to tunnels, corridors and stations. It varies from 1 to 6 (where 1 characterizes the state of a new structure, 6 that of a state close to ruin). According to the global health score, a decision regarding the maintenance operation to be performed can be taken. When major disorders of the structure are detected, an exceptional detailed inspection based on soundings can be carried out to obtain further information. The monitoring methodology proposed is complementary to visual inspection. This methodology is based on diagnosis using several tools (geophysical testing, endoscopic and penetrometric tests) (Fig. 2). First, a geophysical characterization of the lining based on ground penetration radar and mechanical impedance tests is performed on a panel 15 m long and 3 m high. These tests are designed to provide rapid mapping of structures to identify areas with variations of physical and mechanical characteristics. The identification of these areas can influence the choice of location of small diameter bores (2 cm in diameter) which are carried out in the second step. These small diameter bores (2
2.2.1. Local mechanical characterization of the masonry lining and contact by endoscopy The local characterization of the masonry lining was performed by an endoscopic inspection of the tunnel lining and contact interface layer inside small size boreholes (ɸ = 22 mm). Automatic image processing was used to detect anomalies (voids, cracks, etc.) in the lining and the presence (or absence) of contact between the lining and the surrounding soil. The result provided a local analysis of lining thickness and deterioration. (Haddani, 2002; Haddani et al., 2005; Llanca and Breul, 2011). The presence of discontinuities in masonry affects the mechanical behavior of the entire lining of an underground structure (Barton and Choubey, 1977). It is therefore necessary to take these discontinuities into account in order to evaluate the deterioration of the masonry at the local level. To this end, Llanca et al. (2013) proposed a methodology to assess the local condition of the lining of an underground structure. It is
Fig. 2. Monitoring methodology: example of panel of investigation, geophysical tests (ground penetration radar and impedance), endoscopic and penetrometric tests.
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Fig. 3. Methodology and analysis of tunnel components.
or damage areas. Zone 2 – damaged masonry (thickness t2): This layer is defined as an area where the masonry can be deteriorated and presents discontinuities. In this case, a reduction of mechanical properties is assumed as a function of the frequency of discontinuities and the condition observed in this layer. A method has been proposed to obtain the homogenized values for the main parameters studied: Uniaxial Compressive Strength (UCS) and Young’s modulus (Em) of this zone. Zone 3 – disaggregated masonry thickness (thickness t3). This layer
based on the discontinuities observed using geoendoscopy and a realistic estimation of the mechanical parameters by sectioning the lining thickness. This assessment is based on the values of the parameters obtained from the mechanical tests on core samples and taking into account the local state of degradation. This approach consists in defining three sub-layers linked to the rate of degradation of the lining (Fig. 4): Zone 1 – undamaged masonry (thickness t1): This masonry layer corresponds to the thickness of the structure with no discontinuities
Fig. 4. Local characterization of the masonry lining by endoscopy and simplified masonry model.
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of the masonry lining is completely disaggregated and has no mechanical continuity and consequently no cohesion. This phenomenon is observed in the areas close to the extrados of tunnels. We consider that this area is no longer part of the lining. This layer starts at the end of zone 2 and is defined as a transition zone between the tunnel lining and the surrounding soil. In practice, the mechanical parameters applied to this area will be those of a loose granular soil. The application of this method results in the definition of the concept of ‘‘effective thickness’’ (teff = t1 + t2) of the structure lining at the local scale. This thickness corresponds to the thickness of the structure lining ensuring the structural resistance of the tunnel. 2.2.2. Geophysical characterization The geophysical characterization of the tunnel lining is based on ground penetration radar tests and the impulse-response method. These tests are designed to provide the thickness profile and a rapid mapping structure to identify areas with their physical characteristics and/or different mechanical properties.
Fig. 6. Principal Component Analysis of impedance and sounding parameters.
materials, thickness and variable geometry. To do this we analyzed the results of in-situ tests (4 subway stations - 846 survey points) through a comparative analysis of the results of the impedance test and the analysis of the lining’s condition. A multi-variable study was conducted to assess the contribution of each impedance parameter in the global assessment of the structure. It sought to highlight the possible relationships between the different parameters obtained from the impedance test and the possible link between the impedance settings and parameters obtained from core drilling. The parameters used are as follows:
2.2.2.1. Impulse-response test. The impulse-response test was developed from the vibration method for pile integrity testing. The method was later extended to the inspection of other kinds of concrete structures, particularly plate-like elements such as floor slabs, walls, and large cylindrical structures (Davis et al., 2005). The method is based on the analysis of characteristics of stress propagation waves in the element tested. A low-strain impact is applied by a hammer equipped with a force sensor; the response to the input stress is measured by using a velocity transducer (Fig. 5). The result is a transfer function referred to as the “Mobility of the element under test” (the velocity/force signal ratio: |V/F| expressed as a function of frequency). The test graph of mobility plotted against frequency from 0 to 800 Hz contains information on the condition and integrity of the concrete in the element under test (see Fig. 6). To improve the interpretation of the impedance test and understand the physical meaning of these measurements, 3 parameters obtained using this test were analyzed (Llanca, 2014). These are the parameters that provide the most representative information: Slope ∗ Mobility (S × M), Void Index (IdV) defined as the ratio of the peak mobility below 100 Hz to the average mobility and Dynamic Stiffness (R), defined as the inverse of the slope of the mobility plot for the portion with a frequency less than 50 Hz. The objective is to analyze the relationship between these parameters and the lining status, taking into account specific conditions such as the heterogeneity of component coating
– RQD (Rock Quality Design) – t1 (undamaged masonry thickness as defined in 1.2.1) – UCS (Uniaxial Compressive Strength) A distribution can be observed along the two main axes distinguishing three groups of variables. The first corresponds to the S × M (Slope ∗ Mobility) variables, UCS and t1, with the first two being correlated quite closely. The second axis corresponds to the void index (IdV) and the stiffness (R) to a lesser extent. Finally, RQD seems related to the third component. The impedance test is strongly influenced by the mechanical continuity of the medium. This result led us to assume that the S × M parameter was closely related to the mechanical
Fig. 5. Mechanical Impedance.
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the thickness and the transit time of the wave corresponding to each sampling line. It should be noted that the calibration was performed on the effective thickness of the lining (i.e. teff = t1 + t2 as defined at § 2.2.1) Secondly, a blind analysis was carried out by using the dielectric constant found at the first step. Fig. 10 shows the comparison of the thicknesses evaluated by endoscopy and GPR at the same place in different subway stations.Fig. 11 Ground penetrating radar was used to estimate the effective thickness of the masonry with an accuracy of ± 6 cm/m. However, account had to be taken of the highly heterogeneous nature of the material studied, with considerable geometrical (variations of thickness) and physical (humidity conditions) variations that significantly influence the values of the main dielectric constant. It was observed that the value of the dielectric constant could be defined for a large tunnel section from the correlation with geoendoscopic tests.
Fig. 7. Relation S × M and t1.
characteristics of the materials of the first layer of healthy coating and to the mechanical continuity of the medium. Therefore we focused on the study of possible correlations between the S × M impedance parameter and the undamaged masonry thickness (t1) observed through the geoendoscopic tests. The study was carried out using the surveys of 3 stations. Fig. 7 shows the relationship obtained for both parameters t1 (undamaged masonry thickness) and Ln (S × M) (logarithm of the parameter “SlopexMobility”). Despite a significant dispersion for the t1 thickness values higher than 50 cm, a linear trend can be noticed. These two parameters are linked by the function:
t1 (m) = 1,64−0,47∗Ln (S × M )
2.3. Characterization of surrounding soils The study of the in-service facility showed the extent to which the evolution of the tunnel lining is related to changes in the surrounding environment. These changes can result from the evolution of the surrounding soils, a change in environmental conditions or modifications in groundwater conditions (leached fine elements of soils, reduction of mechanical characteristics when water conditions become more severe, swelling due to the hydration of certain types of clays and rocks, etc.). The influence of these pathologies can increase without an efficient drainage system, which is the case in many ancient structures. Here, the need for information on the geological and geotechnical environment is evident. To perform a rapid and efficient characterization of enclosing soils, we used the light-weight penetrometer test combined with the endoscopic analysis of soils from the underside of the tunnel. Llanca and Breul (2011) and Llanca-Vargas et al. (2015) demonstrated that it was possible to obtain an in-situ material characterization and elasticity modulus estimation with minimal intrusion and at lower cost. This method is also of great interest for estimating the spatial variability of soil mechanical parameters at different scales (monitoring, tunnel or station section).
(1)
Carrying out the impedance test made it possible to evaluate the undamaged masonry thickness (t1) for a panel. It is clear that because of the limitations of the tool, the greater the thickness of the masonry, the lower the accuracy of the mobility measurements. Despite this, the method is very useful for obtaining a spatial view across the panel to assess the evolution of thickness t1. 2.2.2.2. Ground penetration radar (GPR). GPR employs electromagnetic waves emitted by an antenna. When a signal emitted passes through a solid propagation medium (structures), its intensity is gradually weakened (Haack et al., 1995). The electromagnetic waves passing through the lining medium are principally influenced by two properties: material conductivity and dielectricity. The antenna emits and receives high frequency electromagnetic pulses through the material. The signal is partially or entirely reflected when it encounters a discontinuity. A discontinuity corresponds to a change of the dielectric properties, and the signal is entirely or partially reflected. Using GPR provides a qualitative study of the lining condition, changes in the nature of the materials, structural abnormalities (voids, caverns), and the analysis of the structure’s constituents, among other things (AFTES, 2005). Here, we used GPR to identify the extrados lining profile (or the lining thickness). The frequencies should allow analyzing large lining thicknesses ranging from 0.5 to 1.5 m. It was found that the lower frequency antenna was poorly suited for studying thick coatings beyond 1-m. Henceforth, the results presented include those obtained only from the 400 MHz antenna, which is better suited to coatings of old underground structures. The thickness of the masonry was estimated using the wave reflection time measurements, and the dielectric constant of the medium (Fig. 8). To evaluate the capacity of the GPR to provide the lining thickness, in situ test campaigns were carried out to compare the thickness estimation provided by the GPR and those provided by endoscopy at the same place. Initially, to improve the accuracy of the GPR measurements, it was necessary to combine the use of geoendoscopy. Thus, by using the real local thickness of the masonry obtained by geoendoscopic tests, the GPR settings were calibrated for this value by setting it at the corresponding dielectric constant. As can be seen in Fig. 9, we obtained
3. Scoring and diagnosis The monitoring method proposed in this paper provides a set of quantitative information summed up below: – – – –
Thickness of the undamaged masonry (t1), Effective thickness of masonry (teff), Status of the contact between the lining and enclosing soil, Physical and mechanical characterization of the surrounding soil.
The data collected with the new monitoring method must be aggregated to propose a score for the fault or tunnel section before diagnosing the tunnel. This scoring system enables updating the score obtained for these tunnel sections during previous investigations and visual inspections. 3.1. Parameters taken into account for scoring In order to assign a score to the tunnel sections investigated, we propose taking into account the parameters presented below: ● For masonry: – t1: thickness of the undamaged masonry. Value obtained from endoscopic and impulse-response test – teff and t2: effective thickness and thickness of the damaged masonry defined from endoscopic and GPR tests (teff = t1 + t2) 59
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Fig. 8. Estimation of masonry lining thickness (εR = 10, VM = 0.1 m/ns).
● Contact status: C: contact status evaluated from the punctual endoscopic test. ● For the surrounding soil: – Identification: characterization of the soil from image processing – Hydric status evaluated from endoscopic images – Mechanical status evaluated from the analysis of endoscopic images and cone resistance obtained with the light penetrometer test. 3.1.1. Threshold values for the masonry To grade the thickness of the masonry, we suggest comparing the effective thickness teff (teff = t1 + t2) of the masonry with the initial total thickness (tinit) of the construction obtained from endoscopic measurements or from the plans of the works. In agreement with the RATP experts and based on numerical simulation works (Kamel et al., 2012, 2013a,b, 2014), three thresholds have been defined according to the ratio between the effective and the initial total thickness:
Fig. 10. Graphics of correlation between GPR and geoendoscopic thickness evaluation.
approach based on the local evaluation obtained from the endoscopic analysis. Thus on a panel, three thresholds have been defined: – contact exists in 100% of the endoscopic tests, – contact exists in 50% of the endoscopic tests, – contact exists in 0% of the endoscopic tests.
1. teff > 2/3 tinit: considering that the old masonry tunnels were oversized, we accept that a part of the masonry no longer participates in the structural resistance of the structure without having an impact on its global behavior. 2. ½ tinit < teff < 2/3 tinit: masonry is relatively modified and the thickness degraded is substantial. This situation can lead to a redistribution of stresses, leading to a loss of structural resistance or an adaptation of the lining (cracks, displacement, strain, etc.). 3. teff < ½ tinit: In this case, we consider that a large part of the masonry thickness is modified. If this limit value is reached, the grading will not take into account the contact and the surrounding soil status. The score assigned will reflect the state of the structure and the urgency of intervention.
3.1.3. Evaluation of surrounding soil The evaluation of the surrounding soil is dependent on: ● the kind of existing material estimated by the endoscopy (Haddani et al., 2009), ● soil compaction evaluated by the cone resistance of the penetrometric test (Chaigneau et al., 2000), ● the estimation of hydric state: 3 states have been defined from the visual analysis of endoscopic images. Based on these three data, the condition of the surrounding soil is declared “evolving” (or risky), or “non evolving”. For example, a clay in
3.1.2. Threshold values for contact status The evaluation of the ground-structure contact status uses a binary
Fig. 9. Sampling line on tunnel lining by geoendoscopic and GPR tests.
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Fig. 11. In-situ test and results for soil surrounding a tunnel.
intervention). Fig. 12 provides the flowchart of the grading. From the local scores obtained for each measurement point, a panel score was defined as follows: If more than 20% of the local scores are equal to 6 or 7 then the panel score is equal to 7, otherwise, the panel score is equal to the average of the local scores. Finally, it is necessary to aggregate the scores obtained with the new monitoring method with the scores of visual inspections assigned by the RATP inspectors. 3 scenarios are possible and the final score attributed is defined in the following way:
a humid hydric state and with weak cone resistance will be declared “evolving or risky soil”. On the contrary, compacted sand will be declared “non evolving soil”.
3.2. Scoring From the threshold established for each parameter, aggregation is necessary to propose a grading of the fault or tunnel status as well as a diagnosis of the tunnel. To be in accordance with the scores assigned to defects detected by the RATP inspectors during their visual survey, we defined a scoring scale from 1 to 7 (1 excellent state and 7 critical state - immediate
Fig. 12. Score flow chart.
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Fig. 13. Results of the Impulse-response test and estimation of undamaged masonry thickness (t1).
– If we only have a visual inspection score, then the final score will be this score. – If we have a visual inspection score and a score resulting from the new monitoring method at the same place, then the final score will be that resulting from the new monitoring method. – At last, if we only have a score resulting from the new monitoring method, then this score will be the final score.
because the score takes account of all the tunnel’s components. The scores obtained with the new diagnosis method are sometimes lower or equal to those obtained by the visual inspection when the extension of the defect is limited. But the scores obtained with the new method of diagnosis are often higher than those obtained by the visual inspection because they are more quantitative and because they provide the condition of both the intrados and the structure extrados. Finally, the diagnosis obtained with this new methodology is more complete and objective than visual inspections. Moreover, it is possible to use this methodology to control regeneration works as presented in Fig. 16.
4. Contribution of the new methodology: comparative study on a real case This methodology was tested in 8 Paris subway stations in order to validate and evaluate its applicability. We present the analysis of one station section below. Fig. 13 provides the results of the impulse-response test. A test was performed on a panel at each point of a mesh 1 m in length and 0.60 m in height. Then, a map of the main parameters extracted from the test was drawn. The white zones on the map correspond to areas where tests were not carried out because of the presence of objects (advertising panel, electrical devices, etc.) on the wall. Then, using the relationship (Eq. (1)), the impedance test was used to evaluate the undamaged masonry thickness (t1) The GPR tests were carried out on 3 profiles (low, intermediate and upper) on the surface of the panel. From the results obtained, an estimation of the effective masonry thickness teff was performed by using the calibration of the dielectric constant with the endoscopic tests (Fig. 14). Fig. 15 provides the classical results obtained from endoscopic and penetrometric test results (2 or 3 tests were performed for each panel). From these results, we were able to characterize the contact and the surrounding soil. In this example, contact was detected in 100% of the endoscopic tests and the surrounding soil was estimated as “evolving soil” because it was soft soil with high cone resistance but in the presence of water. The effective thickness (teff) is higher than 2/3 tinit (initial thickness) which is equal to 0.9 m. Based on the diagnosis flow chart shown in Fig. 12, the score of this section is 2. In this case, the score provided by the RATP inspectors according to their visual inspection was also 2. Table 1 proposes a comparison of the scores obtained with the new monitoring method and those obtained from the visual inspection by the RATP inspector at the same place for different sections in this subway station (Table 1). As can be seen, the scores obtained from the new diagnosis methodology are often different from those obtained with the visual inspection. The range of the scores is wider for the new diagnosis method
5. Conclusions An improvement of the diagnosis methodology for masonry tunnels was proposed. This methodology is based on a new monitoring method used to assess the three main components of a tunnel: masonry lining, contact and surrounding soil. This monitoring method is rapid, well adapted to the conditions of underground in-service structures and relatively non-destructive. The monitoring methodology is based first on geophysical characterization using Ground Penetration Radar and the impulse-response test. We showed that GPR can provide the effective masonry thickness, but calibration with the geoendoscopic test is necessary. One of the parameters of the impulse-response test is directly linked to undamaged lining thickness (t1). The second stage of the monitoring method is based on the use of geoendoscopic and light penetrometric monitoring that provide the mechanical quality of the masonry, the contact status and the characterization of the surrounding soil. Testing results highlight the fact that separately the proposed tools of the method do not allow to conclude on the global state of the tunnel. In fact, each tool need for calibration or to make hypothesis to obtain correctly data and results, gives partial information and only on located zones of the lining or surrounding soil. That is why the advantage of the proposed methodology in this paper is to overcome these drawbacks by providing a complete and integrated tunnel diagnosis. Testing results highlight how by separate, the proposed tools of the method do not allow to conclude on the global state of the tunnel. In fact, each tool need for calibration or to make hypothesis to obtain correctly data and results, gives partial information and only on located zones of the lining or surrounding soil. That is why the advantage of the proposed methodology in this paper is to overcome these drawbacks by providing a complete and integrated tunnel diagnosis. Using the data collected with the new monitoring method, a 62
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Fig. 14. Results of the GPR test on a profile and estimation of the masonry effective thickness teff.
methodology for scoring and diagnosing tunnels was proposed by aggregating the different data. To be in accordance with scores assigned to the anomalies detected by RATP inspectors during their visual surveys, we defined a scoring scale from 1 to 7. The thresholds and the methodology proposed were validated by the RATP’s experts and by numerical simulation works. The method was tested in 8 subway stations in Paris and the score grading obtained was compared with the grading obtained from classical visual inspections. This comparison highlights that the new monitoring methodology proposed completes and improves the classical diagnosis method as it is more complete, more quantitative and more objective than visual inspections. Moreover, we showed it is possible to use this methodology to control regeneration works. Finally, the methodology focuses only on the grading of a section of tunnels. The aggregation of different scores of different sections to
Table 1 Comparison of scores obtained from the visual inspection (RATP score) and from the new diagnosis method. No section
RATP score
Score obtained with the new diagnosis method
1 2 3 4 5 6 7 8 9
2 2 2 3 3 2 2 2 2
2 4 2 2 4 3 4 4 5
Fig. 15. Endoscopic and penetrometric test results.
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Fig. 16. Comparison of the evolution of the lining status before and after regeneration. 526–536. Idris, J., Verdel, T., Heib, M.Al., 2008. Numerical modelling and mechanical behaviour analysis of ancient tunnel masonry structures. Tunn. Undergr. Space Technol. 23, 251–263. ITA Working Group on Costs-Benefits of Underground Urban Public Transportation, 1987. Examples of benefits of underground urban public transportation systems. Tunn. Undergr. Space Technol. 2, 15–54. Kamel, T., Pellet, F., Silvani, C., Goirand, P., 2012. Numerical modeling of the time dependent degradation of the mechanical properties of a metro underground gallery. In: 1st Eastern European Tunneling Conference (1EECT) – Budapest – 2012. Kamel, T., Limam, A. Silvani, C., 2013. Modeling of the strength’s loss and void appearance in the underground structures of Paris Metro, 5iYGEC Paris. Kamel, T., Limam, A. Silvani, C., 2013. Masonry weathering of the Metro de Paris gallery: modeling via a continuum approach - EURO: TUN 2013, in: 3rd International Conference on Computational Methods in Tunnelling and Subsurface Engineering Ruhr University Bochum. Germany. Kamel, T., Limam, A., Silvani, C., 2014. Modeling the degradation of old subway galleries using a continuum approach. Tunn. Undergr. Space Technol. 04, 77–93. Le Bras, A., Azria, E., 1989. Methods for diagnosing the condition of structures at the RATP. Revue Travaux. FNTP 5 (643), 1–11. Llanca, D., 2014. Caractérisation de tunnels anciens en maçonnerie par des techniques d’auscultation non conventionnelles – Application au réseau RATP, PhD Thesis Blaise Pascal University, Clermont-Ferrand, France. Llanca D., Breul, P. 2011. Characterization of composants of an underground structure in service for the evaluation of its status. In: 13th AFTES International Congress, Underground Spaces for Tomorrow. Llanca, D., Breul, P., Bacconnet, C., Sahli, M., 2013a. Characterization of the masonry lining of an underground structure by geoendoscopy. Tunnel. Undergr. Space Technol. 38, 254–265. http://dx.doi.org/10.1016/j.tust.2013.07.009. Llanca, D., Breul, P., Haddani, Y., Goirand, P., 2013. Methodology of diagnosis of urban tunnels in service. World Tunnel Congress, May–June 2013, Geneva, Switzerland. Llanca-Vargas, D., Breul, P., Bacconnet, C., 2015. Modulus estimation of surrounding soils of underground structures in service. GTJ 38 (4), 452–460. Richards, J.A., 1998. Inspection, maintenance and repair of tunnels: international lessons and practice. Tunnel. Undergr. Space Technol. 4 (13), 369–375.
obtain a global tunnel grading, and the optimization of the monitoring emplacements will be the subjects of a future article. Acknowledgements These studies were carried out with the support of the National Research Agency (ANR) France. References AFTES, 2005. Recommendations on rehabilitation for underground structures. Tunnels et ouvrages souterrains, HS 3, Association Française des Tunnels et l’Espace Souterrain. Asakura, T., Kojima, Y., 2003. Tunnel maintenance in Japan. Tunnel. Undergr. Space Technol. 18, 161–169. Barton, N., Choubey, V., 1977. The shear strength of rock joints in theory and practice. Rocks Mech. 10, 1–54. Chaigneau, L., Gourves, R., Bacconnet, C., 2000. Penetration test coupled with a geotechnical classification for compaction control. International conference on geotechnical and geological engineering, GeoEng, 2000, Melbourne, Australia, 19–24 November. Davis, A.G., Lim, M.K., Petersen, C.G., 2005. Rapid and economical evaluation of concrete tunnel linings with impulse response and impulse radar non-destructive methods. NDT & E Int. 38, 181–186. Haack, A., Schreyer, J., Jackel, G., 1995. State-of-the-art of nondestructive testing methods for determining the state of a tunnel lining. Tunnel. Undergr. Space Technol. 10 (4), 413–431. Haddani, Y., 2002. Geoendoscopy: application to soil investigation and diagnostic in urban area. JNGG 2002, 8 et 9 October 2002, Nancy, France. Haddani, Y., Breul, P., Gourvès, R., 2005. Diagnostic Des Tunnels Par Couplage Des Techniques Complémentaires. AFTES International Congress, Chambéry. Haddani, Y., Breul, P., Bonton, P., Gourvès, R., 2009. Learning method for in situ soil classification based on texture characteristics. ASTM Geotech. Test. J. 32 (6),
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