The Effect of Initial Bed Height on the Behaviour of a Soil Bed Due to Pipe Leakage Using the Coupled DEM-LBM Technique

Abstract

Leakage from underground pipes could result in foundations being undermined, surface subsidence, and damage to infrastructures. Soil particles surrounding the leaking area may be mobilised, raised, and even washed apart from the soil matrix by the leaking fluid, generating a subsurface cavity. Two-dimensional numerical simulations using a coupled Discrete Element Method (DEM) and Lattice Boltzmann Method (LBM) were used to investigate the bed behaviour due to a local leakage from a buried pipe. In this technique, the DEM was used for the modelling of the soil particles and the LBM for the modelling of the fluid. Immersed Moving Boundary (IMB) scheme was adopted for the treatment between the solid and fluid phases. A parametric study was carried out with various values of initial bed height. Time evolutions of the pore pressures along the bed height and cavity development were explored. From the results, it is identified that the initial bed height influences neither the initial orifice pressure, nor the angle of the wedge at the onset of fluidisation which should be a property of the soil. However, it can be concluded that a soil bed with a deeper initial height leads to a slower decrease in the orifice pressure and a slower developing rate of the cavity. It is also worth noting that the cavity size at any particular moment relates linearly to the initial bed height, which may be of special importance in predicting cavity size at a particular moment with the initial bed height specified.