BTSYM | SOIL TRANSITION MODELS
PROBABILISTIC AND AI GROUND MODELS TO PREDICT SOIL TRANSITIONS
Rajat Gangrade, Senior Tunneling Engineer in Arup’s San Francisco office, gave an online talk for the British Tunnelling Society Young Members’ (BTSYM) lecture in February 2022. He presented a methodology for quantitative assessment and probabilistic interpretation of soil transitions and other critical subsurface features important in tunneling. Here, he provides a summary of his presentation and also a brief update on ongoing research and applications
In presenting a methodology for quantitative assessment of soil transitions and critical subsurface features for tunneling, the online talk to BTSYM discussed a soft ground tunnel project (Anacostia River Tunnel) where geostatistics-based methodologies were used, enabling verification against, and so validation by, actual TBM data. The research grew out of a strong interest to develop
cutting-edge digital solutions that would help with risk management in design workflows, TBM data analytics, visualization of geotechnical data, and tunnel risk quantification. Studies and research has brought a PhD in
Underground Construction and Tunneling from Colorado from School of Mines, an MS in Geotechnical Engineering from Virginia Tech and interesting work with consultants Aecom (a geotechnical and tunnel engineer on Mumbai Metro Line 3, India) and CH2M (several US federal- and state-funded transport projects). Strong involvement in the industry includes being Chair of Underground Construction Association’s (UCA) Young Members’ committee.
MOTIVATION When considering the problem of quantifying soil transitions, the motivation for the research was to solve the problem for tunneling contractors faced with the question of soil transition occurrence in the longitudinal and transverse directions along a proposed tunnel alignment. The lack of knowledge of the soil transition zones could result in reduced TBM advance rates, improper regulation of face pressures, creation of sinkholes, and inrush of groundwater. The lack of sufficient detailed ground awareness can
result in severe damage to urban infrastructure, such as in the Kolkata metro project, in India, in 2020. Another instance – considered in a British Tunnelling
Society (2005) report and also research by Clough and Leca (1993) on Washington Metro Area Transit Authority (WMATA) – correlated lack of knowledge of mixed strata with ground deformations. In Changsha Metro Line 4, in China, about 50mm
of surface settlement was observed due to the lag in chamber pressure regulation as the TBM advanced from low to high permeability ground.
Clays Tunnel envelope
Sands Tunnel envelope Clays x-z plane Clays y-z plane
Above, figure 1 a) and (b): A schematic representation of the qualitative interpretation (‘?’) of uncertainty in transitions from deterministic ground profiles in the longitudinal direction (x-z plane) (c) Representation of stratigraphic transition in the cross-sectional frame (y-z plane). Dotted red lines indicate two possible spatial locations of the stratigraphic transitions
44 | Fall 2023
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