Laboratory Testing

Internal Stability Testing

Internal stability testing evaluates a soil's susceptibility to suffusion — the migration of finer particles through the coarser soil matrix under seepage.

Evaluating Internal Stability

Broadly graded and gap-graded soils may be internally unstable where the pore spaces within the coarser fraction are large enough to allow finer particles to migrate.

Gradation-based methods, including Kenney and Lau (1985), are commonly used to assess internal stability. Laboratory studies by Skempton and Brogan (1994) also showed that internally unstable soils can experience particle movement at hydraulic gradients well below those associated with heave.

Laboratory testing allows this behaviour to be evaluated directly by applying controlled seepage to a prepared soil specimen while monitoring hydraulic response and particle migration.

Hydraulic Loading and Particle Migration

Hydraulic loading is progressively increased to identify the onset and progression of particle migration and critical gradient. The results can be used alongside gradation-based empirical methods to assess whether a soil is susceptible to suffusion and the hydraulic conditions under which migration occurs.

Applications to Embankment Dams

Internal stability testing can be used to evaluate broadly graded or gap-graded materials within embankment dams and their foundations, including core, transition, and foundation soils.

The results can support a broader internal erosion assessment together with filter compatibility, seepage conditions, dam zoning, and other relevant information.

Test Program Development

Stratem develops each testing program around the materials being evaluated and the engineering questions the testing is intended to address.