Hydraulic and earth engineering – Earth treatment or control – Compaction
Patent
1986-07-03
1987-10-13
Taylor, Dennis L.
Hydraulic and earth engineering
Earth treatment or control
Compaction
404133, 405258, E02D 302
Patent
active
046995463
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and apparatus for deep compacting soil, and preferably such a method and apparatus for compacting soil at its natural frequency or one of its overtones.
In a method generally known today for deep compacting of soil strata there is used a rod or pipe, which is several meters long and over its entire length provided with one or a plurality of radially projecting fins or brackets. The arrangement is driven down as a unit into the soil stratum. A vibrator is mounted at the upper end of the rod with the aid of a crane or the like. The vibrator operates at constant frequency, usually around 20 Hz, a certain compaction taking place of a region having the shape cover a cone with its apex downwards and concentric with the rod and fins, as these cause the soil to accompany them in their movement.
The disadvantages with the known method and apparatus, which is still known under the designation "vibro-wing method" are that compaction proceeds relatively slowly, that the effective surface over which the vibrations are propagated is small, in turn resulting in that the volume of compacted material will be limited to the extent of the fins, that the rods or pipes must be arranged close to each other with a spacing of approximately 1,5-2 meters, that compaction takes place at a constant frequency demanded by the vibrators available on the market today and which do not take into account the special properties of the soil stratum, and in that it may be difficult to withdraw the rod or pipe from the soil after compaction, because the compacted is terminated stratum effectively locks the radially projecting fins. Since large volumes of soil, e.g. sand or silt, are to be compacted, it is important that the number of compaction means be kept to a minimum, i.e. the spacing of the rods or pipes driven into the ground should be as large as possible without deteriorated compaction resulting, and that the compaction time should be as short as possible. Furthermore, the apparatus should be implemented so that the compaction means can easily be withdrawn from the soil stratum.
The DE-A-No. 27 27 880 describes an apparatus for compaction of a soil stratum at the natural frequency thereof. As with the apparatus already described, this apparatus includes a pipe which can be driven into the ground. A vibrator is mounted on the upper end of the pipe, on the surface of which are arranged axially extending fins. The vibrator is connected to the pipe at a certain angle in relation to the longitudinal axis of the pipe and/or eccentrically to this axis, the tube thus being given a radial, oscillating deflection during operation. Compaction thus takes place by the radial deflection of the pipe and not, as is the case with the present invention, by combined movements in the axial direction of the pipe. Since the pipe of the known apparatus is provided with axially distributed radially extending fins a stiffening of the pipe is obtained which contributes to the deterioration of the compacting properties thereof.
In the method and apparatus in accordance with the invention the above mentioned disadvantages are mitigated, while compaction is made more efficient. According to the invention, compaction of soil strata takes place with the aid of a rod or pipe (hereinafter designated "bar") driven into the ground, the bar varying in its axial extension both before and in conjunction with the compaction operation. It is preferable to oscillate the bar by a vibrator at the natural frequency of the earth stratum or at one of its overtones, thus providing the most effective compaction result. The axial stiffness of the bar can thus be adjusted so that it is favourably suited to the stiffness of the soil stratum. When the bar oscillates at the natural frequency of the soil stratum, the soil will also begin to oscillate at its natural frequency while using low vibration energy, without fins or brackets being needed along the bar to grip and cause the soil to accompany the movements thereof. The vibrations will propaga
REFERENCES:
patent: 3162102 (1964-12-01), Juneau
patent: 3282055 (1966-11-01), Landau
patent: 3309877 (1967-03-01), Degen
patent: 3865501 (1975-02-01), Kniep
patent: 4186197 (1980-01-01), Tetsuo
patent: 4397590 (1983-08-01), Friesen et al.
patent: 4504176 (1985-03-01), Lindberg et al.
S.A. Compagnie Internationale
Taylor Dennis L.
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