The explosion at the Abbeystead valve house in May 1984, with its attendant loss of life and injury, forcibly drew the attention of the public to the dangers of methane and other natural gases. It also reaffirmed to the water industry and engineering professions the pervasive nature of the gas and the need to take appropriate measures in the construction, design and operation of any scheme which involves a possible methane presence. The investigations into the source and mechanism of the methane gas ingress, and the design of the permanent repairs and modifications to the scheme, have illustrated many of the risks and problems associated with methane and the measures for dealing with them.
The paper describes the essential repairs and modifications which had to be carried out, the main lessons learned, and the recommendations which are felt to be applicable to new and existing water schemes where methane may be present.
The design and analysis of buried structures presents difficulties that cannot often be solved by closed-form solutions. Finite element methods (FEM) have increasingly become the tool of choice for advanced soil-structure interaction analysis, with three-dimensional FEM being required for irregular non-plane-strain cases. To accurately capture the stress and deformation of soils, complex material constitutive models are required. Several input parameters to these models must be determined from expensive soil testing, which is impractical for most applications. For two-dimensional FEM, good approximations of these parameters for a wide range of placed backfill soils have been developed and used in practice for many years in the computer program CANDE. It is the purpose of this paper to take these parameters, developed by Selig for use in CANDE, and convert them to equivalent parameters for the three-dimensional PLAXIS computer program’s Hardening Soil model.
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