In-Situ Modification of Active Clays for Shallow Foundation Remediation

Abstract

Damage to structures constructed on expansive clay soils occurs throughout the United States each year. The extent to which expansive clay soils can damage an individual foundation will depend largely on the amount and location of moisture change in the soil beneath that foundation as well as the foundation's stiffness. Significant changes in moisture levels typically occur from poor drainage and/or from large vegetation causing heave or shrinkage respectively. Once a structure has experienced damaging differential movements and repair is needed, an engineer must consider sources and magnitudes of previous and future movements in designing repairs. This paper presents a tested technique, which involves using an aqueous solution of potassium and ammonium ions to treat expansive clay soils in remediation of damaged structures. The technique relies on reactions between the solution ions and the clay soil to adjust rheological properties of the clay. Mechanisms by which potassium and ammonium treatment reduce swelling motions and pressures are described herein. A case history of a forty-five year old building damaged by both heave and shrinkage movements is presented. Identification of movement sources, reactivity laboratory testing of site soils with the aqueous solution, predicted injection and long-term movements, description of the injection modification technique, verification quality assurance testing and foundation performance are presented.