Evaluation of Tunneling-induced Downdrag on End-bearing Piles

J. S. Yang

Professor of Civil Engineering, Changsha Communications University, Hunan, China. Presently, Visiting Scholar in the Department of Civil & Environmental Engineering, The Pennsylvania State University - University Park, PA, USA

M. C. Wang

Professor of Civil Engineering, Department of Civil & Environmental Engineering The Pennsylvania State University - University Park, PA, USA

  ABSTRACT

Ground loss induced by soft-ground tunneling may result in considerable down-drag loading on nearby piles. This paper presents a method for estimating the tunneling-induced down-drag loads on end-bearing piles. The method of analysis involved determinations of ground settlement profile and distribution of negative skin friction followed by integration of the negative skin friction over the entire pile length. In the analysis, the negative skin friction was assumed to increase linearly with soil settlement along pile shaft to a constant maximum value. The total down-drag load was determined using the Eulerís integration method. The computed down-drag loads were non-dimensionalized by expressing in terms of total positive shaft resistance. The dimensionless ratios were related graphically with the ratios of tunnel depth to pile length as well as horizontal distance between tunnel and pile to tunnel diameter. The relations were developed for three levels of ground loss with a broad range of soil properties. These graphical relations are useful for estimating the tunneling-induced down-drag loading on end-bearing piles nearby tunnel constructions.

KEYWORDS: Downdrag, End-Bearing Pile, Soft Ground Tunnel, Negative Skin Friction, Shaft Resistance, Ground Loss, Analysis

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