The compression and consolidation of weathered clays and mudstones beneath an instrumented trial embankment

The magnitude and rate of deformation of soils under load is influenced by their stiffness and hydraulic conductivity. This paper demonstrates the use of simple, analytical methods to interpret the deformation properties of heavily oversconsolidated weathered clays and mudstones beneath an instrumented trial embankment. Extensometer data were collected during and after construction of the embankment. The measurements were interpreted using the Asaoka (1978) observational approach and one-dimensional consolidation models. These enabled estimation of the operational drained Young’s modulus (E’), coefficient of consolidation (cv), and vertical saturated hydraulic conductivity (kv,sat) of the underlying ground. The results showed that E’ increased with depth and was consistent with estimates of the maximum shear modulus (G0) derived from geophysical measurements. The estimated kv,sat values decreased with depth within the weathered clay and mudstone. They were broadly consistent with both laboratory test data and independent back-analyses of porewater pressure data. The study shows that simple, analytical models can be used to understand and estimate the magnitude and rate of settlement of an embankment foundation, using independently-obtained geotechnical parameters based on in situ or laboratory tests. This will improve interpretation of ground conditions and parameters for design and construction of earthworks on weathered mudstone outcrops.