Stabilization of Natural Clay Riverbanks with Rockfill Columns: A Full-Scale Field Test and Numerical Verification

Abstract

Rockfill columns have been used to stabilize the clay riverbanks in the Winnipeg area for over two decades. The construction methods used in Manitoba are uniquely adapted to the local soil conditions. The performance of rockfill columns in Manitoba has generally been satisfactory, except that in some cases significant deformations have occurred during and after construction (Yarechewski and Tallin 2003). This thesis will discuss the full-scale test loading of a riverbank that was stabilized with rockfill columns. The purpose of the test was to measure the load-deformation characteristics of a reinforced slope in order to further the understanding of rockfill column behaviour. Rockfill column technology has evolved from granular shear key methods for stabilizing slopes. The relatively weak and soft lacustrine clay is reinforced with compacted columns of stronger and stiffer limestone rockfill.

The research test site is located along the natural banks of the Red River in The City of Winnipeg. The project involved an extensive site investigation, and soils characterization program in preparation for the field test. Eleven columns, 2.1 m in diameter were tested by surcharging the slope with 1920 tonnes of fill. The deformations were measured with standard and in-place inclinometers while the porewater pressure response of the in-situ soils was continuously monitored with vibrating wire piezometers.

The research further investigated the mobilization of resistance along the length of the rockfill columns with finite element models. The analysis of the model results illustrated the mobilization of shear resistance within the rockfill and the development of stresses across the column cross section. The important engineering characteristics of rockfill are discussed in the context of rockfill column design and the importance of effective compaction is highlighted. The results of this research are used to develop recommendations for rockfill column design, analysis and construction.