Deformation of a retaining wall by ground freezing

Field measurements were made of the horizontal movement of a large retaining wall in Hopkinton, NH, USA. The reinforced concrete retaining wall is part of an earthen dike on the downstream side of an earth-filled dam. The dike is used to separate an existing wood-cribbed dam and its associated forebay pool from the outlet channel of the earth dam. The wall, completed in 1963, is 71 m long and varies in height from 5.7 to 10.7 m. Previous surveys have indicated that outward displacements at the top of the wall occur during the winter and rebound partially during the spring. Observations of the wall show severe, permanent deformation. The owner of the dam-the US Army Engineer Division, New England-is concerned about the stability of the wall and plans on doing remedial work shortly. Prior to the 1995-96 winter season, the US Army Cold Regions Research and Engineering Laboratory installed various sensors on and behind the wall to continuously measure these displacements and to provide information for the repair strategy. The measurements indicate that the movement is frost related. Horizontal movement at the top of the wall of 20 mm, and increased earth pressure behind the wall of almost 200 kPa, were measured during the period of frost penetration. As the frost subsided in the spring, the earth pressure approached pre-winter values. Although the displacement at the top of the wall did rebound, it did not recover completely. This paper will present and discuss data recorded during the 1995-96 winter. These will include temperatures on the face of the wall, as well as the soil behind it, pressure between the wall and backfill material, lateral displacement at the top of the wall, and the angle of rotation along the face of the wall.