Burial is an effective approach to offshore pipeline protection for impact loads. However, few studies address the influences of inherent soil spatial variabilities on failure behaviour of soil covers and pipelines, causing deviations. Therefore, a random field-large deformation finite element analysis framework is developed to explore the failure mechanisms of buried pipelines in spatially varying soils. The failure mode of soil cover is conformed to a local mode, where the failure path is insensitive to soil variability. The failure mechanism of pipelines depends on the competition mechanism between soil strengths and pipe-soil interactions, based on which two typical failure modes are summarized. Soil variability not only aggravates the impact damage but also stimulates the diversity of structural responses. Correlations between probabilistic damage degrees and multiple influential factors are discussed. Further, inspired by the principle of energy dissipation, an integrated quantitative risk assessment model is derived to reveal the failure risk evolution, where uncertainties from soil variabilities and structure-related factors are considered. The latter shows a significant influence, which may pose an additional failure probability of over 50 %. Different safety design approaches are compared, and spatial failure probability surfaces are configured for burial depth determination.

Unsupported excavations are frequently performed in several geological and geotechnical projects, particularly for constructing roads and railways, and they are often carried out in different materials. The design of such cuts in soils needs the determination of representative values of its mechanical properties, particularly of the strength parameters, and the application of adequate safety factors. The procedure should ensure a sustainable design of those cuts, allowing for economical solutions that guarantee a low probability of geological-geotechnical failure. This paper assesses the reliability of unsupported cuts in soils, under drained conditions, assuming a Mohr-Coulomb strength criterion. Statistical meshes are generated considering the spatial variability of the friction angle and of the true effective cohesion, which are assumed to be uncorrelated. In this process, typical values of the coefficients of variation and of the horizontal and vertical scales of fluctuation are applied. Soil characterisation is simulated in each statistical mesh, and the characteristic values of the strength parameters are determined using statistical methods. Unsupported cuts of different heights and inclinations are designed using typical safety factors. Slope stability analyses are carried out using Random Finite Element Limit Analysis. The uncertainty in the actions is considered, and the probability of failure is determined by direct reliability analysis. The results show the relevance of the ratio between the scale of fluctuation and the excavation depth, the slope inclination, and the characteristic value of the soil strength parameters on the probability of failure. Values of adequate safety factors are proposed towards obtaining an appropriate probability of failure, compatible with the sustainable design of the cuts.