Measuring the load–deformation response of rockfill columns by a full-scale field test on a natural riverbank

A full-scale field test loading of a riverbank stabilized with rockfill columns was used to measure the load–deformation characteristics of the reinforced slope. The test site is located on the natural banks of the Red River in the city of Winnipeg. Rockfill column technology has evolved from granular shear key methods for stabilizing slopes. The relatively weak lacustrine clays are stabilized with compacted columns of limestone rockfill. The columns typically extend through the clay stratum and are anchored in the underlying till. The project involved an extensive site investigation, and soils characterization program in preparation for the field test. Eleven 2.1 m diameter columns were tested by loading the bank with 1920 t of fill. The deformations were measured with standard and in-place inclinometers. The pore-water pressure response of the in situ soils was continuously monitored with vibrating wire piezometers. The results have shown that shear stresses are mobilized along the entire length of the column when subjected to loading, and that complete densification is important in minimizing deformations. This paper discusses the design and construction of the field test and presents the results of the monitoring programs.

Evaluating shear mobilization in rockfill columns used for riverbank stabilization

The major rivers within the City of Winnipeg are founded in glacial Lake Agassiz clay and silt sediments that have low shear strength. As such, riverbank instabilities are a common issue along many stretches of the rivers. The use of rockfill columns has become an increasingly utilized approach for stabilizing failing banks. Recent cases in Winnipeg have shown that movements can occur following installation of rockfill columns. Uncertainty regarding the magnitude of these movements that is required to mobilize shearing resistance in the rockfill columns has resulted in situations where the stability of riverbanks following remediation has been questioned. This has provided a need to improve our understanding about how much movement a stabilized slope must undergo before sufficient shear resistance of the rockfill column will be mobilized. The results of experimental testing conducted to assess the shear mobilization of rockfill column materials using a large-scale direct shear test apparatus are presented in this paper. The testing methodology is described along with the test results. The results show that the development of material specifications, construction, and placement methods and appropriate methods of analysis requires understanding of the stress–strain properties of the in situ soil and the rockfill material.