Reinforced
Soil

The concept of earth reinforcement is not new, the basic principles are demonstrated abundantly in nature by animals and birds and the action of the roots.

The earliest remaining examples of soil reinforcement are the ziggurat of the ancient city of Dur-Kurigatzu, now known as Agar-Quf, and the Great Wall of China. The Agar-Quf ziggurat, which stands five kilometers north of Baghdad was constructed of clay bricks varying in the thickness between 130-400 mm, reinforced with woven mats of reed laid horizontally on a layer of sand and gravel at vertical spacings varying between 0.5 and 2.0 m. Reeds were also used to form plaited ropes approximately 100 mm in diameter which pass through the structure and act as reinforcement. The Agar-Quf structure is now 45 m tall, originally it is believed to have been over 80 m high; it is thought to be over 3000 years old. The Great Wall of China, parts of which were completed circa 200 BC, contains examples of reinforced soil, in this case use was made of mixtures of clay and gravel reinforced with tamarisk branches.

The modern concept of earth reinforcement and soil structures was proposed by Casagrande who idealized the problems in the form of a weak soil reinforced by high-strength membranes laid horizontally in layers. The modern form of earth reinforcement was introduced by Vidal in the 1960s. Vidal's concept was for a composite material formed from flat reinforcing strips laid horizontally in a frictional soil, the interaction between the soil and the reinforcing members being solely by friction generated by gravity. This material he described as 'Reinforced Earth', a term that has become generic in many countries, being used to described all forms of earth reinforcement or soil structures.