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Estimating jacking force in vertical-curved microtunneling
Agustini, Hayati
Agustini, Hayati
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2025
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Abstract
Subsurface construction methods, such as microtunneling, are effective in minimizing surface disruptions during installation of pipelines or other utilities. As urban environments become increasingly complex, Vertical-Curved Microtunneling (VC-MT) has emerged as a viable solution for navigating subsurface obstacles, natural or manmade, while reducing the required depth of launch / receiving shafts, potentially lowering the cost of the project and project completion time. A critical aspect of VC-MT design and execution is the accurate estimation of jacking force (JF), which involves additional complexities compared to traditional Straight-Line Microtunneling (SL-MT). However, limited studies have been conducted on this topic, mainly due to limited availability of field data for VC-MT.
This study presents analysis of limited available data on VC-MT to develop predictive models for JF estimation using empirical method and machine learning techniques. Data from seven VC-MT projects were used in the analysis. Additionally, 23 datasets from SL-MT projects were analyzed and applied to the testing data for comparison. The proposed models were further evaluated against existing jacking force equations from Pellet (2002), Najafi (2004), Staheli (2006), Ma (2008), and Cheng (2017), which seem to overestimate JF by a notable amount.
The best-performing model incorporated key factors such as drive length (L), pipe diameter (D), depth of cover (Hs), unit weight of the soil (γ), height of groundwater (Hw), and frictional coefficient (μ). The proposed model achieved the highest coefficient of determination (R² = 0.822) and demonstrated the smallest deviation from actual jacking force values observed in the field when applied to testing data.
The findings indicate that the proposed VC-MT model in this study offers a more accurate and reliable estimation of jacking force, with reduced overestimation compared to existing equations. The results could help the industry in sizing the jacking equipment as well as a more realistic assessment of the need for the intermediate jacking stations (IJS) which could ultimately reduce the cost and risks involved in microtunneling operations. The analysis also showed that additional efforts have to be made to characterize and estimate the frictional coefficient between pipe and the ground for more accurate estimation of jacking forces.
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