HDD Installation of Pressure Sewer Pipeline in Mine Subsidence Areas

Abstract

In this study, impacts of mine subsidence on the structural and hydraulic performance of polyethylene pipe in pressure sewer applications were investigated. Structural safety of PE pipe against mine subsidence was investigated and different design safety factors were considered for different methods of installation. For installation of pipelines both trenchless, particularly horizontal directional drilling, and open trench were utilised. A numerical simulation considering pipe-structure interaction effects is employed to estimate the stresses due to mine subsidence. Ground condition, pipe material properties and subsidence parameters were used as input to the numerical structural analysis. Estimated stresses are then checked and verified against allowable stresses given by “AS/NZS 4130:2009 Polyethylene (PE) pipes for pressure applications”. This study showed the induced mine subsidence stress can reduce the nominal internal pressure capacity of polyethylene pipe material. For instance, a PE100 PN16 pressure rating pipe has a standard dimensional ratio (SDR) in order to safely performing with an internal pressure of 1.6 MPa. In general, the SDR calculation is purely based upon on hoop stresses; however induced longitudinal stresses from mine subsidence can change the stress pattern in the pipe which would not allow the PE pipe to fully utilising its nominal internal pressure. This reduction is called capping reduction which is dependant to a number of factors such as pipe size, SDR rating, method of installation (HDD, or open trench). Outcome of this study showed that the capping reduction is very dependant to the type of installation and can vary between 28%-35% of nominal pressure rating of pipe.

Techniques