Hydraulic and earth engineering – Earth treatment or control – Ground stabilization or reinforcement
Reexamination Certificate
1999-11-05
2002-02-05
Bagnell, David (Department: 3673)
Hydraulic and earth engineering
Earth treatment or control
Ground stabilization or reinforcement
C405S259100, C405S262000, C428S098000
Reexamination Certificate
active
06343895
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a soil reinforcing resin net and its production method, and also relates to a drawn product of polyethylene based resin which may preferably be used as a soil reinforcing net particularly suitable for preventing slip of filling-up soil or reinforcing soft soil.
In recent years, there is a tendency of filling-up marshy area or low level area for developing residential, industrial or roadway sites. In such site development, since buildings are constructed on the filling-up soil, it is required to prevent collapse of the filling-up soil. To meet such a requirement, filling-up of soil for developing residential site or the like has been made by repeating the step of laying synthetic resin-made reinforcing nets on underlying soil at specific intervals and banking soil thereon to a thickness of several tens cm. Specifically, in recent years, to meet strong demands to increase construction of dwelling houses, there is a tendency to prepare residential site on filling-up soil or soft soil. In this case, the slip of such residential site must be perfectly prevented. In general, to prevent the slip of site and stabilize the filling-up soil, there has been adopted a method of arranging layered nets in soil. The net is generally made from polyethylene which is subjected to uniaxial or biaxial drawing for realizing molecular orientation thereby increasing the strength of polyethylene.
The above soil reinforcing net has a large number of holes. When the net is laid in soil, upper and lower filling-up soil layers arranged with the net put therebetween are jointed to each other through the holes of the net, to prevent collapse the filling-up soil. To effectively prevent collapse of filling-up soil, the net is formed of a sheet of a resin having a high drawability such as high density polyethylene, which sheet is drawn uniaxially or biaxially for making the molecular orientation linear. To be more specific, the sheet is drawn in such a manner that the molecular orientation of the sheet is matched with the direction in which collapse of filling-up soil is anticipated to occur, to prevent elongation of the net when a slip force is applied from filling-up soil to the net, thereby keeping the strength of the net.
FIG. 13
is a schematic view of such a reinforcing resin net
30
. The resin net
30
is produced by punching a polyethylene sheet
20
shown in
FIG. 14
to form round or rectangular holes
21
therein, and drawing the sheet
20
in a uniaxial direction. By drawing the sheet
20
, each hole
21
becomes an elongated hole
31
having a pair of opposed ribs
31
a
and a pair of opposed bars
31
b
. In
FIG. 13
, reference numeral
40
designates a non-punched portion;
40
a
is a drawn rib portion: and
40
b
is a non-drawn bar portion.
The resistance force of the net of this type for preventing collapse of filling-up soil is generally tested by laying soil below and above the net
30
to specific thicknesses, pulling the net
30
out of the soil, and taking the pull-out resistance as the resistance force of the net. Such a pull-out resistance has been substantially determined by a thickness of the bars
31
b
extending in the direction transverse to the pulling direction, that is, the area against the pulling direction. Accordingly, to increase the resistance force of the net
30
, there has been taken a countermeasure of increasing the thickness of the sheet
20
as a base of the net
30
or making short the vertical gap, that is, the amount of soil between the two adjacently laid nets
30
. The increased thickness of the sheet
20
, however, is inconvenient for raising the construction cost. Further, since the boundary between the non-drawn portion and the drawn portion forms a smooth slope, even if the thickness of the non-drawn portion is increased, it is difficult to ensure a desired pull-out resistance.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a soil reinforcing resin net capable of improving pull-out resistance in soil, and its production method.
Another object of the present invention is to provide a drawn product of polyethylene based resin with improved creep characteristic and increased strength, which is suitable for soil reinforcement.
According to a first aspect of the present invention, there is provided a soil reinforcing resin net including hole portions arranged in the longitudinal and transverse directions of the resin net, each of which is formed by a pair of opposed ribs and a pair of opposed bars, wherein projecting portions formed typically into fillet shapes are fixed on bar portions, preferably, in the direction transverse to the drawing plane of the hole portions. The projecting portions may be fixed on the bar portions by vibrational fusion, ultrasonic fusion or hot plate fusion.
According to a second aspect of the present invention, there is provided a method of producing a soil reinforcing resin net, including the steps of: punching a resin sheet to form hole portions arranged in the longitudinal and transverse directions of the resin sheet; drawing the resin sheet having the hole portions in the uniaxial direction, to form elongated hole portions each having a pair of opposed ribs and a pair of opposed bars; and fixing projecting portions on bar portions by vibrational fusion, ultrasonic fusion or hot plate fusion. In this method, the projecting portions may be fixed on the bar portions in the direction transverse to the drawing direction of the hole portions.
According to the soil reinforcing resin net of the present invention, since the projecting portions, for example, fillet portions are fixed on the bar portions extending in the direction transverse to the drawing direction of the net, it is possible to significantly increase the pull-out resistance in soil of the resin net.
The soil reinforcing resin net is generally made of a high corrosion resisting polypropylene or polyethylene sheet which is little compatible with adhesive, and therefore, it has been difficult to fix separate projecting portions to bar portions of the sheet by adhesive joint.
According to the present invention, however, the bar portion is fused by vibration, ultrasonic waves, or hot plate, and the projecting portions are fixed on the bar portion thus fused. To be more specific, the projecting portions are brought into press-contact with the bar portions, and are fixed thereto by the above-described fusing means such as vibration. In other words, according to the present invention, the projecting portions can be fixed to the bar portions not by using the chemical adhesive bonding mechanism but by using the mechanical fixing mechanism. For example, the fixing of the projecting portions to the bar portions of the resin net by vibrational fusion is performed by bringing the projecting portions into press-contact with the bar portions of the resin net, applying fine vibration to the press-contact portions to give an energy to the bar portions, being press-contact with the projecting portions, of the resin net thereby softening them, and re-hardening the softened bar portions of the resin net in a state in which the softened bar portions surround the projecting portions. Additionally, the projecting portions can be fixed to the bar portions of the net in the state before drawing.
The projecting portion is mainly made from the same material as that of the resin net, such as polypropylene or polyethylene. The shape of the projecting portion is not particularly limited and, for example, it may be a columnar, three-dimensional or groove shape. The length of the projecting portion can be also arbitrarily selected.
According to a third aspect of the present invention, there is provided a method of producing a soil reinforcing resin net, including the steps of: punching a resin sheet to form hole portions arranged in the longitudinal and transverse directions of the resin sheet and simultaneously forming, by pressing, a plurality of projections on bar portions between the hole portions at specific inte
Eguchi Shinichi
Ino Fumitaka
Iwasaki Shinichi
Yamada Kotaro
Bridgestone Corporation
Mayo Tara L.
Sughrue & Mion, PLLC
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