Stabilization of Retaining Walls and Embankments using Rammed Aggregate Piers TM

Abstract

Highway construction often requires the placement of embankments and earth retaining walls to facilitate grade separations. Instability and settlement occur when these structures are placed on top of weak and compressible soils. Historically, the severity of these problems have been reduced using toe berms and surcharging. More recently, Rammed Aggregate Piers have been used to avoid the need for extending large right-of-ways required for toe berm construction or for time-consuming surcharging. The installation of Rammed Aggregate Piers reinforces weak and compressible foundation soils prior to construction of earth embankments and walls. The installation of Rammed Aggregate Piers increases the factor of safety against slope stability as a result of the high angle of internal friction (48 to 52 degrees) achieved during ramming and reduces the magnitude and time of settlement by increasing the overall stiffness of the foundation soils and providing a drainage pathway for dissipation of excess pore water pressure. This paper presents analytical methods used to design Rammed Aggregate Piers to reinforce weak soils and control settlements below highway and railroad retaining walls and embankments. The analytical methods are illustrated by a case history for a Mechanically Stabilized Earth (MSE) wall support project near Houston, Texas. This work is of particular significance because it presents design methodologies and a case history for an effective ground reinforcement technique increasingly used to support highway embankments and walls.