The demand for land in the hilly terrain of Hong Kong means there is increasing pressure for developments to enc roach onto the natural terrain. This paper examines some salient aspect s of the design of barriers against natural terrain landslides and channelized debris flows. The various approaches suggested in the literature in evaluating the impact load are re viewed. The authors suggest that the impact pressure due to the landslide debris could be taken as three times that given by the equation based on the consideration of the rate of loss o f momentum of an equivalent fluid impacting onto a rigid surface. The impact load due to boulders in the debris could be estimated using the flexural stiffness method or taken to be nominally one-tenth of that given b y the Hertz equation.


The kinetic energy of the boulder is equated to the work done t o deform some of the structural component soft the barrier. Generally, the maximum energy -absorbing capacity of the barrier system is designed to be mobilised assuming that the barrier undergoes permanent deformation rather than elastic deformation; otherwise, very massive structural members will be needed (Ch an et al. 19 86). Proprietary rock fences are also available to meet different energy-absorbing requirements. The force approach tends to be adopted in the design of barriers which act as permanent structures, particularly where a structural wall or a mass barrier has been used. Two methods have been used to estimate the impact force: one assumes that the entire debris mass will move with the barrier as a unit upon impact and the unit will then decelerate at a rate controlled by the sliding resistance at the base of the barrier.

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