You are reading the online version of the LimitState:GEO manual, which is also available as a pdf.
Gilbert, M., Smith, C. C., Haslam, I. W. & Pritchard, T. J. 2009 Plastic limit analysis using discontinuity layout optimization (DLO), 17th UK Conference on Computational Mechanics (ACME-UK), Nottingham.
Smith, C. C. & Gilbert, M. 2007b New upper bound solutions for layered soil bearing capacity problems using discontinuity layout optimization, 10th Australia New Zealand Conference on Geomechanics, Brisbane, pp. 250–255.
Smith, C. & Gilbert, M. 2007a Application of discontinuity layout optimization to plane plasticity problems. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 463(2086), 2461–2484.