This paper presents the results of a comprehensive research study to determine the potential causes for an inordinate distress developed on a shotcrete liner material of a tunnel located near Dallas, TX. This tunnel was originally founded on a limestone material. Distress locations were identified where possible delamination of shotcrete layer and moisture leaks were either suspected or noticed. As a part of the research, rock cores and white powderlike substance behind the liner were collected around the distressed locations, and these cores and powder material were subjected to chemical, mineralogical, and engineering tests to understand the potential causes of this distress. Mineralogical tests, in particular, X-ray powder diffraction analysis on a powder material and gel-like substances collected on the liner, showed the presence of anhydrite, gypsum, and ettringite traces. High amounts of sulfate measurements in chemical and energy dispersive X-ray spectroscopy studies also showed that both gypsum and ettringite formations were possible in and around the limestone material. Upon hydration, mineral expansion of ettringite and anhydrite led to heaving and subsequent cracking of the adjacent shotcrete layer. Engineering characterization tests including unconfined compression strength (UCS), indirect tensile strength (ITS), and triaxial tests on rock cores embedded with a powder type sulfate material revealed that low strength cores were obtained near high distress zones and high strength cores were collected at low distress zones. The UCS values ranged from 6.2 (high distress) to 13.8 MPa (low distress) whereas the ITS values of the cores varied from 0.5 to 1.1 MPa for the same distress locations. This indicates the potential loss of strength of these rock materials from the presence of gypsum material in them. Possible methods to mitigate this heaving problem behind the liner are also discussed.

Forensic Investigations to Evaluate Sulfate-Induced Heave Attack on a Tunnel Shotcrete Liner

L'etude de l'equilibre a long terme du tunnel revetu suscite un interet important. D'un point de vue mecanique, il s'agit d'un probleme d'interaction complexe entre deux structures de comportement tres different : le massif avec la cavite d'une part, le soutenement d'autre part. Les effets differes qui apparaissent dans un massif sont principalement lies a deux phenomenes qui peuvent etre couples : - la viscosite du squelette solide du massif ; - la diffusion du fluide interstitiel au sein du massif. On commence par presenter une etude bibliographique assez generale concernant les differentes etapes d'etude, de conception et de realisation d'un projet de tunnel profond. Dans la seconde partie du memoire, on etudie l'influence de l'histoire du chargement (vitesse de creusement et instant de pose du soutenement) sur l'equilibre d'un tunnel soutenu creuse dans un massif monophasique a comportement viscoplastique. Une methode simplifiee de dimensionnement des tunnels dans de tels milieux a ete elaboree. On a egalement aborde les effets de couplage entre comportements hydraulique et mecanique dans le cadre des tunnels profonds creuses dans un milieu poreux sature isotherme ayant un comportement poro-elastique ou poro-elasto-plastique. Une etude analytique du tunnel 1D revele l'influence de l'histoire du chargement mecanique et des conditions aux limites hydrauliques imposees en paroi. Des simulations numeriques de creusement de tunnel en geometrie 2D axisymetrique sont menees. L'etude analytique permet, grâce a la generalisation de la notion de contrainte fictive de soutenement, de localiser le point d'equilibre du tunnel soutenu dans le plan (convergence en paroi - contrainte appliquee en paroi). Ces resultats permettent d'aborder le calcul en deformation plane des tunnels creuses en milieux biphasiques avec plus de rigueur.

Etude des effets différés dans les tunnels profonds

The proposed Gibraltar Strait tunnel will cross two zones with breccia consisting of a chaotic mixture of blocks and stones embedded in a clay matrix. The breccia is saturated, has a high porosity and exhibits poor mechanical properties in the range between hard soils and weak rocks. The overburden and high in situ pore pressures in combination with the low strength of the breccia may lead to heavy squeezing. The crossing of the breccia zones thus represents one of the key challenges in the construction of the tunnel. In order to improve our understanding of the mechanical behaviour of the breccias, a series of triaxial compressions tests were carried out. Standard rock mechanics test equipment was not adequate for this purpose, because it does not provide pore pressure control, which is important in the case of saturated porous materials. Pore pressure control is routine in soil mechanics tests, but standard soil mechanics equipment allows only for relatively low nominal loads and pressures. In addition, the low hydraulic conductivity of the breccias demands extremely low loading rates and a long test duration. For these reasons, we re-designed several components of the test apparatus to investigate the mechanical behaviour of the breccia by means of consolidated drained and undrained tests. The tests provided important results concerning the strength, volumetric behaviour, consolidation state and hydraulic conductivity of the breccias. The present paper describes the test equipment and procedures, provides an overview of the test results and discusses features of the mechanical behaviour of the breccias which make them qualitatively different from other weak rocks such as kakirites—a typical squeezing rock in alpine tunnelling. The paper also demonstrates the practical importance of the experimental findings for tunnelling in general. More specifically, it investigates the short-term ground response to tunnel excavation from the perspective of elasto-plastic behaviour with the Mohr–Coulomb yield criterion. The computational results indicate that the breccias will probably experience very large deformations already around the advancing tunnel heading, which can be reduced considerably, however, by advance drainage. The analyses additionally show that plastic dilatancy is favourable with respect to the short-term response, thus highlighting the importance of the constitutive model when it comes to theoretical predictions.

/pdf/experimental-investigations-into-the-mechanical-behaviour-of-1ahm6bu44l.pdf

Experimental Investigations into the Mechanical Behaviour of the Breccias Around the Proposed Gibraltar Strait Tunnel

Shallow landslide susceptibility map at a regional scale (Asturias, NW Spain). A heuristic-driven approach

Mass movements represent one of the most significant geohazards worldwide. The aim of this research is to highlight the potential and limitations of the European Ground Motion Service (EGMS) in detecting and monitoring mass movements at a local scale, especially in cases where data from in situ instrumental devices are unavailable. The study area corresponds to the La Miera landslide, located in Asturias (NW Spain). The multidisciplinary methodology applied involved the following steps: (1) downloading, acquiring, and analyzing Sentinel-1 A-DInSAR datasets (2015–2021) through the EGMS; (2) conducting a detailed geomorphological map and identifying evidence of movement; (3) classifying building damage by means of a damage inventory; (4) compiling and analyzing daily rainfall records with respect to deformation time series. Sentinel-1 A-DInSAR results revealed maximum LOS and East–West velocities of −11.6 and −7.9 mm/yr related to the landslide activity. Geomorphological mapping allowed for the updating of the landslide boundaries and its characterization as an active, complex movement. Registered building damage, which ranged from moderate to serious, was correlated with LOS and East–West velocities. The displacement recorded by the EGMS closely corresponds with rainfall periods, while periods of reduced rainfall coincide with the stabilization and recovery phases of displacement. This emphasizes a noteworthy quantitative correlation between rainfall events and EGMS data, evident both spatially and temporally. This work highlights that areas in which the EGMS data indicate deformation but lack in situ instrumental records, geomorphological techniques, and building damage surveys can provide spatial validation of the EGMS displacement, while rainfall records can provide temporal validation. 

Potential and Limitations of the New European Ground Motion Service in Landslides at a Local Scale

A tunnel project under the straits of gibraltar

Gravitational processes on inaccessible cliffs, especially in coastal areas, are difficult to study in detail with only in situ techniques. This difficulty can be overcome by the complementary application of remote sensing methods. This work focuses on an active complex landslide affecting the slope of the Tazones Lighthouse (Cantabrian coast, North Iberian Peninsula), which has been monitored since June 2018. The aim of this research is to establish a conceptual model of the internal structure of the slope. A remote multitechnique approach was applied, including landscape deformation analysis from photogrammetric surveys, ground motion detection applying A-DInSAR techniques and Sentinel-1 satellite data, and electrical resistivity tomography. The obtained results showed the great potential of some of the remote techniques, such as UAV photogrammetry and electrical tomography, and the ineffectiveness of others, such as A-DInSAR, which failed to provide adequate results due to the profuse vegetation. This work made it possible to establish a geological model of the functioning of the slope of the Tazones Lighthouse and to deduce the surface extent of the destabilized mass (70,750 m2), the rupture surface shape (stepped), its in-depth extent (10–50 m), the volume of materials involved (~3,550,000 m3) and the type of landslide (complex including a predominant translational slide). The combination of field and remote sensing data significantly increased the possibility of reaching a comprehensive geological interpretation of landslides on rocky coasts.

/pdf/using-remote-sensing-methods-to-study-active-geomorphologic-2337xahm.pdf

Using Remote Sensing Methods to Study Active Geomorphologic Processes on Cantabrian Coastal Cliffs

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A tunnel project under the straits of gibraltar

Using Remote Sensing Methods to Study Active Geomorphologic Processes on Cantabrian Coastal Cliffs