Impact Of Lateral Swell Pressure On Retaining Structure Design Using Expansive Cohesive Backfill

Abstract

Since cohesive soils are difficult to drain once becoming saturated, in order to reduce lateral earth pressures exerted by saturated cohesive soils on retaining structures, retaining wall designs most always specify use of drainable granular backfill. However, costs for the importation of granular backfill materials continues to increase due to depletion of these materials in certain areas, and to the ever-increasing costs for material transportation, largely related to increased labor and fuel prices. These factors, together with the costs of removing replaced cohesive materials, and coupled with resource and environmental conservation concerns, are driving efforts to develop reasonable and prudent design methods for retaining structures using on-site cohesive soil backfill. Traditional design using non-expansive cohesive backfill is well established. However, certain cohesive fill materials exert lateral swell pressures as soil moisture contents increase. If these pressures are not accommodated in the structure design, the stability of the structure will be reduced, perhaps to the point of failure. This thesis study reviews certain properties of cohesive soils and their impact on retaining structure design, reviews relevant research pertaining to the determination of lateral swelling pressure performed by others, and attempts to correlate the implications of the previous research with the properties of cohesive soils in order to assess the impact of lateral swelling pressure on external structure stability. This effort was undertaken as a precursor to the development of a method for predicting the magnitude of the lateral swelling pressure component of lateral earth pressure for use in developing new and prudent design methodologies for retaining structures. The recommendations suggested in Chapter 7 have been formulated with this end result as the central focus.