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, phi(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, mu(avg) and the vertical stress at the tunnel crown, sigma(EV). In this paper, the reliability of using the parameters, c(t,p)', phi(t,p)', mu(avg) and sigma(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 phi(t,p)' were applied to the modeled rock mass and the strength parameters of the pipe-rock interface were developed from an. Arching ratios were developed from sigma(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, tau(1) and reaction loads, Sigma 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)', phi(t,p)', mu(avg) and sigma(EV) in the assessment of pipe-jacking forces through highly weathered lithologies.