Prediction of structural integrity of the ground using numerical simulation of soil erosion around a leaking pipe

Monzer, Ali ORCID: 0000-0002-8808-2308 (2023). Prediction of structural integrity of the ground using numerical simulation of soil erosion around a leaking pipe. University of Birmingham. Ph.D.

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Abstract

Underground buried pipes are extensively used in water and sewer networks to fulfil domestic and agricultural demands. Leakage is a common issue associated with underground water networks that occurs due to cracks and holes in pipes which can lead to economic, environmental, health, and safety predicaments. Leakage can induce soil fluidisation resulting in severe consequences to the urban environment where pipes are commonly buried in and supported by the ground. Soil fluidisation is the process of transition of soil particles from solid-like to liquid-like behaviour that can eventually lead to the failure of the surrounding ground and buried utilities. Understanding and predicting the initiation and propagation mechanisms of soil fluidisation around a leaking pipe is of particular importance for risk assessment of ground and buried assets. In addition, it is essential to determine the crucial parameters contributing to the fluidisation process to prevent severe damage and fatal consequences.

There have been considerable studies in the field of soil fluidisation process; however, majority of these research concentrated on the initiation of soil fluidisation around defective pipes, lacking fundamental studies addressing the soil-fluid interaction during the progression of soil fluidisation until it reaches the ground surface. The onset and progress of the soil fluidisation mechanism are significantly detrimental in identifying the severity of pipe leakage, maintenance of underground pipes, support of the ground, and transportation infrastructure. Therefore, a thorough understanding of soil fluidisation due to leakage should be achieved via a robust modelling method that properly addresses the influence of different soil and pipe parameters on fluidisation phenomenon. Physical modelling is expensive and time consuming whilst analytical modelling cannot be used to analyse complex problems. As such, often, numerical simulation is the preferred approach. Meanwhile, numerical simulation of pipe leakage problems often entails several challenges due to complexity of modelling associated with large deformations, soil-fluid interaction, and mesh distortions associated with traditional numerical methods such as the standard Lagrangian Finite Element Method (FEM). To overcome this, advanced computational approaches such as Material Point Method (MPM) can be used. This method has proven to be a powerful technique in simulating large deformations in various multi-material and multi-phase geotechnical and hydraulic problems.

In this research, the soil fluidisation mechanism induced by a pressurised leaking pipe embedded in fully saturated soil is numerically modelled using MPM formulations, namely two-phase single-point (2P-SP) and two-phase double-point (2P-DP) approaches. Additionally, advanced inflow/outflow Boundary Conditions (BCs) are implemented in the double-point formulation to prescribe a velocity-controlled inflow of water into the domain.

The capabilities of two MPM approaches to simulate the onset and progression of soil fluidisation are presented and discussed. Displacement field and failure mechanism around a leaking pipe are analysed in terms of change in pore water pressure and soil porosity. The results have demonstrated that the 2P-SP MPM formulation is applicable for identifying the leak pressure required for the initiation of the local fluidisation in the vicinity of the orifice. The results of 2P-SP MPM approach were compared against standard FEM for reference which revealed both are not capable of capturing the post-local fluidisation mechanism due to numerical instabilities. However, the 2P-DP MPM formulation has proven to be an effective tool in capturing the progression of this phenomenon until it reaches the ground surface.

This thesis has successfully replicated an experimental pipe leakage problem using 2P-DP MPM approach. The observed results and fluidisation mechanism are consistent with the experimental data. The model is further developed to conduct an extensive parametric assessment of the impacts of different soil and pipe parameters on the soil fluidisation process. It has shown that the inflow velocity required for the onset and development of fluidisation decreases with the increase in orifice size and soil porosity. The bed height increases the resistance of the soil bed against fluidisation. Furthermore, the onset and progression of soil fluidisation are controlled by the flow direction and the burial depth of the pipe.

The numerical model presented in this thesis provides useful information that buried utilities companies and asset managers can utilise to improve and evaluate aspects associated with maintenance, operations, and remediation of pipe leakage problem and the supporting ground.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):

Supervisor(s)	Email	ORCID
Faramarzi, Asaad	UNSPECIFIED	orcid.org/0000-0001-6964-5577
Chapman, David	UNSPECIFIED	orcid.org/0000-0001-8729-3966
Yerro Colom, Alba	UNSPECIFIED	orcid.org/0000-0002-2819-1289