Hydraulic and earth engineering – Earth treatment or control – Rock or earth bolt or anchor
Patent
1989-10-24
1991-07-23
Taylor, Dennis L.
Hydraulic and earth engineering
Earth treatment or control
Rock or earth bolt or anchor
405258, 405284, E02D 520
Patent
active
050339125
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention concerns improvements in or and more particularly, this invention relates to reinforcements relating to reinforcements for use in stabilized earth structures.
BACKGROUND OF THE INVENTION
The technique of stabilizing earth structures by incorporation of spaced flexible reinforcements in the earth mass has become well-established. The basic principles of this procedure were set out in British Patent No. 1039361 of Henri Vidal and a large number of structures of this kind have been build all over the world. The reinforcements stabilize the mass virtually completely by frictional forces, both between the reinforcements and the adjacent fill particles and between those particles and the remainder of the fill. The reinforcements are so spaced that such frictional forces are transmitted throughout the fill and tension generated in the reinforcements opposes significant horizontal movement of the fill particles.
The tensile strength of the reinforcements must be sufficient to withstand the horizontal forces generated by the weight of the fill and any loads placed thereon, such as a road and road traffic. In order to retain the elastic properties of the stabilized earth structure, it is necessary that any modified form of the reinforcement should be flexible, in order to retain frictional contact with the fill and accommodate earth movements. It has been found that an earth mass stabilized in this way can be built with vertical sides up to substantial heights and the earth behaves as a material having predetermined elastic properties capable of accommodating significant vertical settling movements without failure.
An unstabilized block of earth has a tendency to fail in the well known way first described by Coulomb along a plane from the foot of the block at an angle of .alpha.=.pi./4+.phi./2 (where .phi. is the angle of friction), normally about 63.degree. to the horizontal. The mass of earth above this plane is often termed the "Coulomb wedge" or "active wedge". In older techniques, where a vertical wall was required, this was provided by a relatively massive wall structure at the vertical face resisting overturning primarily by its weight. Using the techniques of British Patent No. 1069361, the vertical sides of the earth block merely need protection from erosion and are commonly provided with relatively thin cladding elements attached to the exposed ends of the reinforcements.
The reinforcements used in the technique of British Patent 1069361 are, most efficiently, strips but differently shaped reinforcements are possible provided they are capable of mobilizing frictional forces adequate to stabilize the mass. The strips or other reinforcements are generally incorporated in the fill in layers, the structure normally being built up by placing a layer of spaced strips on a flat compacted layer of earth, compacting a further layer of fill on top of the strips and placing a further layer of strips, this procedure being continued until the structure has reached the required height.
It is found that the presence of the reinforcements according to the Vidal technique changes the properties of the earth mass to the extent that the boundary of the active wedge is substantially nearer to the vertical face of the mass than in the case of unreinforced earth. Recent experiments have shown that, surprisingly, the position of the boundary of the active wedge, which is, in fact, the line of maximum tension in the reinforcements, runs almost parallel to the vertical face, except for the region near the foot of the structure. Thus it has been found that the boundary of the active zone lies, for the greater part of the structure, at a distance about 0.28 H (.+-.0.02 H) from the face (where H is the height of the structure).
In such a structure, the reinforcements have always had a length of at least 0.7 H which means that a length of reinforcement of at least 0.4 H extended beyond the active wedge into the resisting zone, i.e. the zone not liable to failure. In low or medium height walls,
REFERENCES:
patent: 1472917 (1923-11-01), Laird
patent: 2149957 (1939-03-01), Dawson
patent: 3464211 (1969-09-01), Andresen
patent: 4116010 (1978-09-01), Vidal
patent: 4710062 (1987-12-01), Vidal et al.
Japanese publication entitled "Foundation Practice", pp. 13, 16, 63, 105, 107, 116, Jul., 1988.
"Soil Reinforcement", Civil Engineering, vol. 839, No. 10, Oct. 1979, pp. 47-53.
"Reinforced Earth-application & development", Civil Engineering, vol. 839, Nov./Dec. 1985, pp. 53-57.
Societe Civile des Brevets de Henri Vidal
Taylor Dennis L.
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