BTSYM | SOIL TRANSITION MODELS
CONCLUSIONS
The field validation using EPBM operation data demonstrates the capability of geostatistical modeling in identifying soil transitions. The geostatistics-based probabilistic approach
provides improved understanding and a quantifiable characterization of soil transition locations over the qualitative interpretations from the GBR. Such geostatistics-based probabilistic methodologies can be applied during many stages – planning,
QUESTIONS AND ANSWERS
Following the lecture, Rajat Gangrade took questions from attendees to the live online event, facilitated by the BTS chair. Below is a report on the Q&A session, selected and edited, and abbreviated, for clarity and space
Q: How and why are sinkholes formed? Rajat Gangrade (RG): Sinkholes result from sudden void formed at the ground surface due to ground volume loss during tunneling. Mechanized tunneling involves volume loss at the TBM face, shield gap, and the tail void. If the ground is not supported during excavation this volume loss at the TBM transcends to volume loss at the surface resulting in ground settlement. Such ground deformation could occur due to improper regulation of minimum required face support pressures, groundwater inflow, overcut volume, improper grout injection pressures, and lack of soil at the face and along the shield.
Q: TBM tunneling technology must be able to deal with all the variable ground conditions. How is your work contributing to the state-of-the-art practice? RG: Though TBM tunneling technology is advancing to deal with a variety of ground conditions, the machine operation needs to be regulated based on expected ground conditions and behaviour of ground on excavation (observational method). Currently, 2D ground profiles are used to demarcate risk allocation between the tunnel project owner and the contractor and to resolve DSC claims/litigations. Probabilistic assessment of ground conditions in 3D, built on spatial variability measures, provides a comprehensive review of ground conditions. The work advances the current industry practice by capturing the ground uncertainties into the design process, the construction means and methods, and risk mitigation strategies.
Q: Were the ground models developed using geostatistics adapted by a client or a tunneling contractor to save money? RG: During my Ph.D., the research group at the Colorado School of Mines collaborated with a tunneling contractor in North America to predict tool wear rates and ground deformation on a five-mile long tunnel project situated in a complex urban environment. Geostatistics based methodologies were applied to develop a 3D model of geological conditions and geotechnical parameters of interest. The research outcome predicted the tool wear rates
for guidance on interventions, and face support pressures required to keep ground deformations below the contractual requirements. Our recommendations were accepted by the tunneling contractor, and we were successful in saving one TBM intervention, resulting in schedule and cost savings (Gangrade, RETC 2021).
Q: What programs are used to generate the ground models using geostatistics? RG: Open source packages in R and Python are available to visualize and process the geotechnical data. The Stanford Geostatistical Modeling Software (SGeMS), Spatial Analysis and Decision Assistance (SADA), Geostatistical Software Library (GSLIB) are a few examples of free software available to analyze the point cloud data. The open source and free software provides an opportunity to gain experience in ground spatial variability modeling before investing in licensed tools, such as Geovariances Isatis, LeapFrog, Surfer, or ArcGIS, respectively.
Q: Is machine learning capable enough to predict the ground conditions ahead of the TBM? RG: Yes, a few researchers have investigated using artificially intelligent models to predict and update the ground conditions ahead of the TBM. Geostatistical models can be updated using as-encountered ground data to update predictions of ground conditions ahead of TBM (Yu and Mooney, 2021).
tendering, construction, and post-construction to help analyze disputes and claims. The flexibility of applying geostatistical techniques at
multiple stages allows for effective risk management and decision-making for contractors, designers, and owners. Although, geostatistics is a powerful tool for investigating the influence of ground uncertainties, it is essential to remember that the results derived from geostatistics are based on the given input of limited geotechnical data.
REFERENCES ● Gangrade, R., Zheng, H., Yu, H., Mooney, M., and Nebbia, D. (2021)
NEBT Project: The Application of Artificial Intelligence to Improve TBM Operations. Proc. Rapid Excavation Tunneling Conference (RETC), Las Vegas, June 2021
● Yu, H., & Mooney, M. (2021). Logging the as-encountered ground condition with EPBM data using supervised and semi-supervised learning. Tunnelling and Underground Space Technology.
50 | Fall 2023
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