Slope stability and settlement analysis for dry bulk terminal at mozambique: a case study.

Abstract

Stability of man-made soil slopes is an important issue for long term performance of any bulk terminal storage facilities and it becomes more critical for very heavy material storage like iron ore, coal etc. In most of the cases, it is observed that the parent (original) in-situ sub-soil formations are not capable to support such heavy bulk storage material. Hence, ground improvement techniques are usually recommended for such soft soil sites, in addition to maintain the stability of the slope of the stack itself. Present case study describes the design of three types of stacks for a proposed bulk terminal site at Beira, Mozambique for storage of iron ore and coal. The site consists of thick soft to very soft clay layers resting on interbedding of the sandy/silty sand layers. The geotechnical characterization was carried out through drilling 16 boreholes and conducting 9 cone penetration tests. Since the subsoil stratum was not capable enough to take the expected pressure from the bulk storage, the ground improvement is proposed in form of wick drain/strip drains in order to accelerate the consolidation and gain in strength. In order to optimize the cost and construction time, staged construction method was adopted and strength gain during each construction phase was monitored. To limit the foundation settlement and to estimate the expected lateral thrust on the reclaimed foundation; detailed slope stability analysis and settlement analysis are carried out at each construction stage. It was observed that under the 10m of stacking height of iron ore; the ground may settle more than 3m and the differential settlement of more than 1.5m may influence the stacker reclaimer foundations. Both the rotational slip failure mode and translational failure mode are checked to obtain the limiting displacement for foundation failure. Staged construction program along with safe heights for material handling in each construction stage are finally recommended based on the detailed slope stability and settlement analysis.