Free-draining granular base for prepared ground surface

Abstract

A prepared ground surface e.g. a pavement or roadway is provided with a free-draining aggregate layer between it and subsoil, there being positioned above and beneath the aggregate layer a water impervious barrier to prevent water entering the aggregate from passing downwardly into the subsoil or upwardly into the pavement or road surface material. In one embodiment the angle of the bottom impervious layer is such that water flows through beneath the roadway surface. In another embodiment water from either side of the roadway or pavement surface can flow to a central or midpoint and is the means for draining away water tending to collect therein. In one form the means comprises an interceptor section or gully conducting water longitudinally to a point of discharge.

Description

This invention relates to the construction of a free-draining granular or aggregate base for a prepared ground surface, e.g., a pavement or roadway. In one of its aspects the invention relates to a prepared surface upon a free-draining aggregate base.

In one of its concepts the invention provides a surface construction suitable for roadway, driveway, playground or parking lot the construction comprising a prepared surface upon a layer of aggregate and a water impervious barrier on top and below said aggregate whereby water finding its way into the aggregate as from the side of the prepared surface cannot drain down through the aggregate into the subsoil or work its way upwardly into the prepared surface. In another of its concepts the invention provides such a prepared surface, e.g., a roadway or pavement surface of asphalt cement layer (hot mix) supported upon an aggregate base laid upon the subsoil there being interpositioned between the subsoil and the aggregate base and the aggregate base and the asphalt surface a water impervious layer, the edges of the aggregate being open to receive and/or to discharge water which may reach the edges of the structure. In another of its concepts the subsoil and therefor the bottom surface of the aggregate is inclined from the edge or edges of the prepared surface or construction so that water received into the aggregate will drain through a focal point or place from which it can be drained away by suitable means, as further described herein.

In light load or traffic road construction, driveways or parking or playground lots, it is customary to compact the subsoil, cover it with 5-8 inches of rolled granular base and then apply 2-3 inches of an asphalt cement layer (hot mix). A basic weakness of this type of construction is the inability of the granular base to retain its structural strength because water intrusion washes out the fines portion of the aggregate. Further, if the compacted subgrade is clay or contains a major fraction of clay, the aggregate often sinks into the clay when it has been softened by water. The softened aggregate/clay subbase cannot support traffic passing over the thin asphalt cement layer and large sink holes and chug holes develop.

The deleterious action of intruding water and the submersion of the aggregate layer into the water softened subsoil is prevented by the creation of a barrier between the subsoil and the aggregate layer and between the asphalt cement traffic course and the aggregate layer, respectively.

We have conceived a structure which will permit intruding water to pass, in effect, through the prepared surface, pavement or roadway, etc., all the while preventing the water from passing downwardly into the subsoil or upwardly into the prepared surface. Thus the subsoil will not be subject to softening due to the water intrusion, nor to having due to freezing and thawing. Similarly, the water will not pass upwardly into the asphalt or other surface and there do damage likewise. The water impervious barrier now preferred essentially consists of a polyolefin fabric such as Petromat.sup.1 fabric. Petromat fabric is a non-woven fabric of polypropylene fibers and is available from Phillips Petroleum Company, Bartlesville, Oklahoma. Petromat fabric is available in rolls of up to about 15 feet width and lengths of up to about 300 lineal feet. Petromat fabric was a weight of about 4 to 6 ounces per square yard, a tensile strength in the "warp" direction of 80-90 pounds and a tensile strength in the fill or woof direction of about 90-100 pounds. Petromat fabric has been found to be superior to such materials as burlap mats, cotton fibers, woven cloth, etc., in this capacity for retention of asphaltic material.

Any sealant mixture of material which will render the fabric impervious can be used. Now preferred is an asphalt-asbestos mixture as described in copending application Ser. No. 207,800 filed Dec. 14, 1971, Clarence R. Bresson, et al. In said application for a patent there is described and claimed an impervious cover structure coated with a mixture containing asphalt and asbestos fibers. The asphalt and asbestos fibers coating mixture can be used upon a polyolefin fabric such as a polyproplene fabric here described.

The asphalt-asbestos mixture which is applied is usually applied as a cut-back asphalt. The cut-back asphalt is prepared from an air-blown asphaltic material having a penetration of about 20-50, preferably 25-35, a minimum ductility at 77.degree.F of 5, and a Ring and Ball softening temperature of 160.degree.-175.degree.F.

The cut-back solvent used to prepare the cut-back asphalt is selected from kerosene, cycle oil, Stoddard solvent or, in general a hydrocarbon based material having an initial boiling point in the range of 160.degree.-450.degree.F, preferably 200-300.degree.F.

Sufficient cut-back solvent is used to make the resultant blend applicable to the surface by hot application not exceeding about 250.degree.F., i.e., at a temperature which will not exceed the melting point of polypropylene and thus adversely affect the fabric or the asphalt may be applied by spraying or brushing techniques at ambient temperatures. Usually about 20-100 parts by weight of solvent, preferably about 40-70 parts by weight per 100 parts by weight of asphaltic material, are used.

The asbestos fiber is added to the cut-back asphalt in amounts from about 4-15 parts/100 parts by weight of cut-back asphalt. It can have a fiber length of about 0.01-0.1 in., preferably about 0.03-0.06 in. While the presence of longer fibers can be tolerated, the preferred range is more readily handled by the usual equipment and best improves the desirable properties of the asphalt, such as the penetration values.

It has been found that using an approximately 4 oz/yd.sup.2 fabric, a cut-back asphalt with an asbestos fiber content of about 6-8, or more, parts by weight/100 parts by weight of cut-back asphalt is preferred, while for a 5 oz. web an asbestos fiber content of about 5-6 parts by weight/100 parts by weight in the cut-back asphalt is sufficient. About 0.25 to 2 gallons of such cut-back asphalt sealant per square yard is applied to the surface and fabric.

It is within the scope of this invention to utilize, in addition to the now preferred asbestos containing cut-back asphalt, a cut-back asphalt without asbestos fibers or alternatively, a cationic or anionic asphalt emulsion generally available from commercial sources, provided, however that sufficient asphalt be deposited in the fabric to render same substantially impervious to water. A suitable cationic emulsion, for example, is described in U.S. Pat. No. 3,625,119 (Gayle et al.) (Dec. 7, 1971) the disclosure of which is included herein by reference.

Accordingly it is an object of this invention to construct a prepared surface. It is another object of this invention to construct a surface upon a grounding through which water can freely flow so that the structure drains rapidly remaining essentially water-free except for momentary intrusions of water. It is another object of this invention to so cover the ground with a prepared surface that water is prevented from entering into the subsoil or moving upwardly into the prepared surface. Further it is an object of this invention to provide a surface construction which is not subject to destruction by freezing of water to ice and thawing of the ice.

Other aspects, concepts, objects and the several advantages of this invention are apparent from this disclosure and the appended claims.

According to the present invention there is provided a prepared surface construction or structure comprising a prepared surface, a layer of aggregate therebelow there being interpositioned a water impervious barrier below the aggregate upon the substrate or ground and another water impervious barrier above the aggregate and below the prepared surface.

Preferably the impervious layers are formed by a polyolefin fabric impregnated with a water repellent sealant.

The invention being primarily directed to a method of constructing a roadway having improved drainage and stability it will be obvious to one skilled in the art having possession of this disclosure and having studied the same that the materials from which the two water penetration resistant or impervious barriers or elements are made, i.e., the membrane are incidental. Thus, in addition to the non-woven fabrics such as Petromat.sup.R fabric, there can be a used burlap, cotton cloth, rubber or plastic sheet which can be suitably treated; even heavily asphalted or rubberized paper might be suitable for some purposes.

Importantly, as a feature of the invention, the aggregate layer should be capable of percolating water, i.e., it should be free-draining, yet compacted. An aggregate with very little material smaller than about standard 40 mesh screen, i.e., 10 per cent of less fines is suitable. This aggregate may be untreated or as desired can be at least lightly treated with asphalt or Petroset RB(trademark) which is an oil-rubber-water emulsion can be used. The emulsion is further described in U.S. Pat. No. 3,788,883 (Jan. 29, 1974, F. S. Rostler et al.) the disclosure of which is incorporated herein by reference. Ordinarily the amount of asphalt or oil-rubber-water emulsion should not exceed about 3-6 weight per cent asphalt based on a weight of aggregate or 21/2-5 weight per cent of undiluted RB emulsion based on the weight of aggregate because thee aggregate must be kept largely open to permit sufficient water percolation, especially in heavy deluges. The invention and the claims thereto are not limited to any particular type of aggregate or sizing except that there should be the sufficient desired drainage as may be predetermined.

Essentially, whatever the shape of the structure it will be so made that water will be permitted to seek a low point such that the water drains from the aggregate rather rapidly. Thus, the two asphalted fabric layers effectively seal the aggregate layer on top and bottom but leave at least one of the sides of this layer open. Preferably both or all sides of the aggregate are left open. Water which flows from the high side of the prepared surface, pavement or the low side has a free drainage path through the relatively open aggregate layer. IN hilly country, the flow of water may be engineered along the length of the roadway with a drainage sump provided at the bottom as along the centerline.

Since water can drain freely either across or along the aggregate layer, it acts as its own culvert and fewer of these structures will be required. Additionally, the aggregate will remain relatively dry at all times and in freezing whether, no frost heave or buckling of this layer will take place.

In another embodiment, lengthwise flow only is contemplated. The aggregate layer is in a 3/4 envelope which separates it from the compacted subsoil and the sides of the trench type road course. The traffic course is a so-called upon graded surface course. Here the aggregate layer will also act as a drain for the surface layer to prevent water build-up and to minimize hydroplaning, but the water intrusion from the subsoil is prevented. On inclined roadways, walks, ramps, this type of construction would be particularly useful. A suitable drain would have to be provided at the low point or line of such a road structure.

Referring now to the drawing, FIG. 1 is a view of a roadway according to the invention showing a cross-section cut. FIG. 2 is a view of a different roadway according to the invention also showing a cross-section cut.

Referring now to FIG. 1 there is shown subsoil 1 upon which there has been positioned water impervious layer 2, upon which has been positioned aggregate layer 3 upon which has been positioned impervious layer 4 on top of which the prepared road surface 5 has been placed. Water draining from hill 6 and from the surface of the roadway passed down into aggregate 3 from alongside the road as along the base of the hill 6 indicated at 7 follows the arrows and exits from the aggregate layer at 8.

Referring now to FIG. 2 where it is seen that there are hills to both sides of the portion of the roadway shown, i.e., hills 10 and 11 from which the water flows in from both sides of the structure, which is essentially like that of FIG. 1 but in this distance there is provided a drainage channel 12. The water follows the arrows toward the centerline of the aggregate into channel 12 from which it is drained away to a suitable sump or sewer or to a place where it can be allowed to emerge from the aggregate onto a drainage plane or hill and therefore away from the aggregate. By suitably structuring the channel it is possible to have it drain free of water in a relatively short time.

At the same time, water draining through the open-graded surface flows laterally into the aggregate shoulder or envelope and thence into drainage channel 12.

Reasonable variation and modification are possible within the scope of the foregoing disclosure of the drawing and the appended claims of the invention, the essence of which is that there has been provided a prepared surface as herein described said surface being positioned upon a layer of aggregate laid upon a subsoil there being interpositioned between the subsoil and the aggregate on the one hand and the aggregate and the prepared surface on the other, at each interface, a water impervious barrier.

Claims

We claim:

1. A traffic-bearing construction structure having improved drainage and stability comprising a traffic-bearing surface and a subsoil underlying said surface, said surface and said subsoil having positioned therebetween a free-draining layer of aggregate capable of receiving some surface water, said layer of aggregate and said subsoil having therebetween a water-impervious barrier positioned such that water in the subsoil cannot pass upward into the aggregate and such that water in the aggregate drains away from both edges of the traffic-bearing surface toward some low point under said surface and passes through a drainage means which discharges the water to some point away from the subsoil underlying the aggregate.

2. A structure according to claim 1 wherein the aggregate layer is open for water flow on both sides of the edges of the traffic-bearing surface.

3. A structure according to claim 2 wherein there is a water-impervious barrier positioned between the traffic-bearing surface and the aggregate layer.

4. A traffic-bearing construction structure having improved drainage and stability comprising a traffic-bearing surface and a subsoil underlying said surface, said surface and said subsoil having positioned therebetween a free-draining layer of aggregate capable of receiving some surface water, said layer of aggregate and said subsoil having therebetween a water-impervious barrier positioned such that the water in the subsoil cannot pass upward into the aggregate and such that the water in the aggregate cannot pass into the subsoil but will accumulate on said barrier and run to a point of drainage which insures that the water will not flow downward into the subsoil underlying the aggregate, and said aggregate and said traffic-bearing surface having positioned therebetween another water-impervious barrier.

5. A traffic-bearing construction structure having improved drainage and stability comprising a water-permeable traffic-bearing surface and a subsoil underlying said surface, said surface and said subsoil having positioned therebetween a free-draining layer of aggregate capable of receiving some surface water, said layer of aggregate and said subsoil having therebetween a water-impervious barrier positioned such thta the water in the subsoil cannot pass upward into the aggregate and such that water in the aggregate cannot pass into the subsoil but will accumulate on said barrier and run to a low point where there is located a drainage means which discharges the water which accumulates on the water-impervious barrier to some point away from the subsoil underlying the aggregate, said water-impervious barrier being extended upward to the edges of the traffic-bearing surface so that the only water which enters the aggregate is the water which has passed through the water-permeable traffic-bearing surface.