Stabilization of a typical clay riverbank in the Winnipeg area

Abstract

This thesis is an extension of previous studies of a typical failed clay riverbank in the Winnipeg area in order to recommend possible remedial measures once the causes of failure are known. From the re-examination of previously reported data, more recent data, static water well levels in a nearby well, daily precipitation and earlier work by others, it concluded that: l. residual shear strength values should be used in analyzing a failed river bank in clay and in the design of remedial measures, 2. a lowering of piezometric levels in the bank by drainage, especially at the toe, and improving the surface of the slope to facilitate the run off of surface water should result in improved stability, 3. stability of a clay bank may be maintained or improved by increasing the developed shear strength through decreasing the loads on the bank or increasing the resistance at the toe and preventing loss of soil at the toe. A review of existing literature indicated a number of possible methods of stabilizing a clay riverbank i.e. counterbalancing with a toe berm, reduction of the slope angle and/or height of bank, drainage of the embankment to reduce pore pressures, protection of the toe of the slope against scour, retaining structures, chemical stabilization and eliminating or reducing drawdowns. Where applicable local examples of some of the above remedial measures are referred to. Also photographs were taken of a number of existing remedial measures along the rivers and streams in Winnipeg, The relative success of the various remedial works is appraised in light of the conditions at Tache Avenue. Of the possible remedial and protective measures reviewed, counterbalancing the weight of the bank by means of a toe berm is considered most applicable. Chemical stabilization by means of electro-injection also appears applicable. However, because of the uncertainty of chemical stabilization in clays, it is recommended that it be initially considered for a test site. Counterbalancing and chemical stabilization are usually considered for relatively short reaches of riverbank. For a more general benefit to riverbanks throughout Winnipeg, it is recommended that consideration be given to a study of the feasibility of a fixed crest weir at Lockport to replace the present St. Andrews locks as a means of improving the stability of the riverbanks by eliminating the fall drawdown.