Assessment of non-linear rock strength parameters for the estimation of pipe-jacking forces. Part 2. Numerical modeling.

In the earlier companion paper (Ong and Choo, 2018), direct shear tests were performed on reconstituted tunneling rock spoils for the development of equivalent tangential cohesion, c' t,p and friction angle, ϕ' t,p. These equivalent rock strength parameters were used in assessing jacking forces, which were measured from three pipe-jacking drives negotiating the highly weathered lithologies from the Tuang Formation, Malaysia. The measured jacking forces were back-analyzed, leading to the development of frictional coefficient, μ avg and the vertical stress at the tunnel crown, σ EV. In this paper, the reliability of using the parameters, c' t,p , ϕ' t,p , μ avg and σ EV was assessed through the use of three-dimensional finite element modeling of the studied pipe-jacking drives. The peak tangential strength parameters, c' t,p and ϕ' t,p were applied to the modeled rock mass and the strength parameters of the pipe-rock interface were developed from μ avg. Arching ratios were developed from σ EV , which were subsequently used for post-analysis assessment of the results from numerical modeling. There was sound agreement between the resulting pipe-rock interface shear stresses, τ 1 and reaction loads, Σ F y from the numerical analysis against the field measured jacking forces, thus demonstrating the reliability of the use of developed equivalent rock strength parameters, c' t,p , ϕ' t,p , μ avg and σ EV in the assessment of pipe-jacking forces through highly weathered lithologies. Unlabelled Image • Jacking forces were backanalyzed using tangential parameters, c' t,p and ϕ' t,p. • The reliability of c' t,p and ϕ' t,p was assessed using finite element modeling. • Backanalyzed μ avg was used to model the strength of pipe-rock interface elements. • Arching ratios were developed from σ EV for post-analysis of modeling results. • The simulated results were in reasonable agreement with measured jacking forces. [ABSTRACT FROM AUTHOR]