Time-dependent isotache behaviour observed in physical soil-pipe interaction model tests – its practical implications on pipeline performance evaluation

ABSTRACT: Pipelines for the transport essential natural resources are often constructed at shallow depths through different geologic terrains. Permanent ground deformations can occur in actively moving slopes, landslides, surface faulting and ground subsidence, which impose external load on buried pipes. Large strains may be accumulated in the buried pipes and may affect their performance over time. The external load exerted on the pipe by the ground movement is dependent on the soil resistance mobilized in soil-pipe interaction. Recent available pipeline design guidelines (e.g., American Lifelines Alliance (ALA) and Pipeline Research Council International (PRCI)) provide recommendations on soil ultimate resistances for different soil types in drained and undrained loading conditions. However, these guidelines do not consider the effect of soil displacement rate on the soil ultimate resistance in soil-pipe interaction. This paper proposes to use the concept of “isotache” behavior to quantify the relationship between the soil-pipe relative displacement rate and the soil ultimate resistance on the pipe in compacted clays. The relationship is developed based on results measured in physical soil-pipe interaction models. Practical examples are presented to illustrate the use of this relationship to evaluate the performance of buried pipelines subjected to short- and long-term ground movements.