Reducing the Intrusion: Instrumentation and Monitoring for Urban Excavation with Non-Contact Technologies

L.T. Galisson

In the proceedings of: GeoEdmonton 2018: 71st Canadian Geotechnical Conference; 13th joint with IAH-CNC

Session: Risk Management in Geotechnical Projects

ABSTRACT: The Instrumentation and Monitoring Program (IMP) is becoming a critical aspect of project scope due to the increasing complexity and sensitivity of the environment surrounding deep urban excavations. The items monitored include the ground, shoring structures, adjacent buildings, roads surfaces as well as underground utilities. However, there are also constraints on the deployment of an IMP such as the congestion of the construction sites, the difficult access to the instruments, the (lack of) coordination among multiple players, the myriad of permits and clearances required, the continuous traffic of vehicles and of pedestrians, etc. It is very common that the implementation of the IMP gets delayed, that its scope gets reduced, or that the continuity of the monitoring data is jeopardized, increasing the overall geotechnical and structural risk associated to the project. This paper introduces state-of-the art IMP technologies. Focus will be on the advantages and limitations of those technologies by demonstrating how they can individually be beneficial for the success of the project (safety, reliability, productivity, competitiveness, etc..).

RÉSUMÉ: L™importance du Programme d™Instrumentation et d™Auscultation de travaux souterrains urbains accroit avec la complexification des villes et la volonté croissante à limiter les nuisances pour la population. De tels programmes permettent de conserver en état les bâtiments adjacents, les routes, les réseaux enfouis. Ils génèrent cependant des nuisances (interruption de la circulation, accès à des propriétés privées, etc.) et sont soumis à des contraintes de site (permis, préservation du patrimoine, etc.) qui rendent leur déploiement laborieux. Cela peut induire des délais, voire une réduction du programme, au détriment de sa pertinence et de sa performance. Dans cet article, nous présentons des solutions innovantes d™instrumentation pour des travaux urbains souterrains, qui ont l™avantage de réduire les nuisances tout en améliorant la performance du programme (sécurité, précision, intervalle de mesure, temps de réponse, résolution spatiale). 1 CHALLENGES OF URBAN EXCAVATIONS 1.1 You said intrusion? Underground work happens frequently in urban environments: excavations for vertical constructions, utility work, micro-tunnels, extensions of buildings below ground, transportation and transit tunnels, sewers and combined sewers/overflows (CSO), etc. In most cases, the disruption of the ground induces collateral movements involving deformations of adjacent structures (buildings, aerial structures, vaults, etc.), of the surrounding ground (road surfaces, rails tracks, airports runways, subgrade, utilities, etc.), of existing underground structures (underground spaces, tunnels, sewers and collectors) and of the temporary retaining structures (shoring walls, supports of excavations, etc.). Because urban environments are structurally dense and sensitive, they often require numerous monitoring devices, combining different types of technologies to ensure redundant collection of information from the site. The number and the concentration of measurement points, as well as the time interval between consecutive readings, increases with the geotechnical risk and the level of controversy of the project and risk-mitigation culture of the project team. The process is usually intense and invasive. The more sensors on the ground combined with a higher frequency of readings results in a higher rate of intrusion caused by the project. This applies to private spaces, public spaces and construction sites. By intrusion, reference is made to recurrent lanes closures, traffic interruption or rerouting, random access to private buildings for the collection of readings (manual probes, survey points), co-activity on construction sites, synchronization of critical path construction activities, damages to pavements and buildings for the installation (and removal) of sensors or reflectors, and routine calibrations or maintenance of those sensors and reflectors. 1.2 Reassure but don™t cause discomfort There is no question about the relevance of an Instrumentation and Monitoring Program (IMP) for urban underground work. The program provides accurate information in a timely manner to mitigate the geotechnical, environmental, and structural risks. This also constitutes a very efficient tool to adjust the working methods or design criteria in the field. Changes are based on the response of the ground, structures, and environment under continuous measurement. The serenity provided by the IMP is also used by projects owners, to demonstrate that the project is

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