US2211649A - Roadway - Google Patents

Description

J. D. DRURY Aug 13, 1940.

ROADWAY Filed NOV. 28, 1938 i H mw m W@ m mm A @v Patented Aug. 13, 1940 UNITED STATES PATENT OFFICE 4 Claims.

This invention relates to roadways.

More particularly it relates to foundations for pavements of roads and other outdoor areas, and to processes for making such foundations.

The invention provides at relatively low cost an improved artificial foundation or sub-base, which, being laid on a natural foundation of duly sub-graded ground suitable for a road, and carrying any suitable superstructure courses of base, and bedding, binder, or other courses, and Wearing `face surface, should have ability to withstand all ordinary disturbing influences which may assail the road from any direction-such as stresses from traffic, weather or Water from above, moisture penetrating from sides or below, and effects of freezing and thawing.

The importance has long been recognized that the foundation should be permanent in form and in strength. But in many instances each of such constructions has been found imperm-anent, and has soon become unsatisfactorily unstable.

The present invention solves the problems of stability and permlanence by providing a stout waterproof septum completely enveloping and surrounding the artificial foundation. The term foundation, as hereinafter used, refers to an artificial course under the pavement, unless the context indicates otherwise. This septum comprises a combination having a flexible stout woven fabric impregnated with and encased in a viscid or strongly coherent waterproof substance, and it is laid all around the foundation,- bottom, sides and ton-so as to seal within the septum all of that body of earth or other road material which comprises the foundation, Waterproofness is thus combined with tensile strength of enclosure. The fabric holds: the waterproof adhering substance in a continuous sheet, flexible but unbroken by bends or stresses. The strength is sufficient in all directions to resist whatever divisive movement may tend to occur in the granular material which it encloses, While it can flexibly permit sufficient movement for its becoming solidly packed against courses below or above, 'without a breakage of the fabric, and therefore without a breakage of the continuity of the thick water seal which the fabric carries. The whole constitutes an enduring barrier to all passing of moisture to or from. the compacted material comprised in the foundation.

Illustratively the material for a septum may be a woven strong cloth of jute impregnated with asphalt and coated on both sides with asphalt. However, other fibrous material might be used, as cotton; and other water-repelling sealing material, as resin or rubber. The septum is to be built into an envelope around the artificial part of the road foundation. This may be done by first, laying strips of it, in mutually lapping formation, on the sub-grade surface of the natural foundation, after that has been suitably prepared and compacted. These strips may be laid with edge portions out-reaching beyond the sides of the excavation, and there turned up. Then, after l the foundation has been installed, the remaining edge parts of the turned-up edge portions are to be turned back over the top of the foundae tion; and other strips are to be laid onthe top and lapped so that the whole of the top is thus covered. Whatever more, if any, of base is del sired for the pavement, and the courses for bedding or binding the wearing surface material, and the pavement, are to be built above the foundation thus enveloped and sealed.

Illustratively, the combination of fabric and sealing material constituting the septum may have a thickness less than an eighth of an inch. The material of the foundation, surrounded by this strong septum, may often be that ordinary earth of the region, or of the former road, which has been excavated for making the sub-grade.

The sealing material, being material which is not penetrated by water or by air, and being preferably viscid, at least at the timfe when it is applied, envelops the vegetable fibres of the fabric and permanently protects those fibres from den teriorating effects of water and oxygen, and from organisms living in air or water or in the earth. Preferably the septum is made of materials which retain flexibility at the temperatures. which are to be experienced. After it is installed, the considerable native tensile strength of the woven or other fabric is enhanced byr the pressing weight of roadmaterial above, and Weight of passing traic. The resulting compression of the fabric increases the internal frictional resistance of threads to slipping over each other, such as must occur before there can be a strain and a breakage. Any tendency of road material With-- in the foundation to slip sidewise under displacing pressure from above is resisted, first by the road material itself, which has inherent frictional resistance to side-slip,-indicated by the angle of repose of its granular element,-and second, that granular friction becomes greater under Weight imposed upon it, since the body of slippable material in the foundation is confined laterally. Resistance to movemlent is enhanced by the tight circumscribing effect of the stout fabric, and the fact that traffic weights are applied as forces which tend to flatten the iigure and therefore to tighten the septum which circumscribes the contents. In consequence of this frictional inhibition of internal movement of the encased granular particles, the stress actually experienced by the fabric is greatly diminished from that imposed by traffic at the wearing surface of the road, and is brought well within the withstanding ability of the fabric.

The function of the septum, in preventing the entrance of moisture to the granular material of the foundation, cooperates to maintain the above-mentioned frictional resistance of that material, for such resistance is greatest when such material is dry. The described structural formation helps dissipate and reduce every ordinary stress which might ultimately become imposed on the fabric as a tensile breaking stress of the textile material. And the textile material both resists whatever stress ultimately reaches the septum and holds the sealing substance intact.

Assuming the work to be executed well, the strength and shape of fabric will be permanent; the exclusion of moisture will be permanent; and the road as a whole will be satisfactory, subject only to effects of traiiic experience on the wearing surface and the courses above the foundation.

For disclosing the principle, specifications are given below for a road embodying the invention; but it will be understood that the details thus given are illustrative rather than definitive or limiting.

It is intended that the patent shall cover, by suitable expression in the appended claims, whatever features of patentable novelty exist in the invention disclosed.

In the drawing:

Figure l is a transverse section through a roadway embodying the invention, with part broken out so as to make room for showing both edges of the finished road.

Figure 2 is a fragment of septum, enlarged, in section; and

Figure 3 is a transverse section of an edge portion of the road in process of construction.

For illustration, a location having been selected at which the road will have adequate natural foundation support at bottom and sides, the artiiicial part of the foundation to be built for the new road will comprise a mass of earth, stone or other body material lll and a septum l2, composite of fabric and sealing material, which rests on the compacted earth or other firm support I4 which constitutes the natural foundation. The said mass is engaged at its sides and top by more of the same septum I2, so that the mass is enveloped and sealed. Above the sealed envelope is a course of broken stone, coarse or fine, or whatever else is provided, herein called the base I6, to underlie a wearing top surface I8, if such a surface course of different construction is also present. An inch or so of gravel, pre-mixed with stone and asphalt, 29, may lie between this base i6 and the sealed foundation I0.

The materials, arrangement and dimensions of these various parts are subject to engineering judgment of the designer.

While it is expected that for most roads a base course will rest on the foundation, which will be the sealed element, there may be other road construction employing the invention by building the surface course directly upon the sealed element, or otherwise arranging the elements whilegetting the benefits of the sealing septum herein described.

The septum may be prepared by thoroughly saturating a strong fabric, preferably jute or cotton closely woven, with hot asphalt cement, the saturated fabric being rolled or compressed in order to assure the thorough entering of the asphalt into the fabric, between the threads, and the sealing of the mesh openings. Then the fabric while Wet from the saturation should receive a film of hot asphalt not less than 1,(,4 of an inch thick on each side of the fabric, over the entire area of the fabric, temperature of the asphalt cement during the saturation and the film application being maintained in the range 20D-225 F., making a septum which when in place will have a thickness of the order of 335 of an inch.

The septum is represented in Figure 2, where a is the textile fabric and b is the continuous body of waterproof adhesive plastic material, covering both surfaces and reaching in between threads and between fibres.

The septum having been prepared in strips which for convenience of handling are preferably not more than 120 inches wide, 50 to 100 yards in length, a strip of the septum is to be laid along the bottom of the excavation, extending out sidewise and upward over the slope ol' the shoulder suiiiciently to permit the ultimate folding back of this edge portion of the septum, over the tcp of the foundation to a substantial width, for which 18 inches is suggested as being sufficient, although much less would serve.

The next strip of septum is then placed on the sub-grade, lapping a few inches, for example, four inches, over the first strip and firmly cemented thereto with hot asphalt cement. This procedure is to continue across the roadbed until the bottom of the excavation has been covered and both sides have extensions sufficient for the folding back of the septum later, over the foundation, to the desired extent. Wooden mold forms, 22, may be set along the edges of the excavation as indicated in Figure 3 to shape the edges of the filling which is to constitute the road; the edge part of the septum strip l2 being bent up to line the mold, for vertical or other desired edge surface.

The material which is to constitute the foundation lll is then to be placed on the septum in the excavated area, shaped, brought to the specified grade, and thoroughly compacted. If earth or other granular material is employed for this the strength of the resulting foundation will be greater if it has low content of moisture when sealed, which may be attained or assured, if necessary, by heating it in open air just before puting it into the foundation. The edge portions of the septum which have been left extending over the side molds on both edges of the road are then to be folded back over the top of the foundation; and the septum is to be laid on that top in mutually overlapping strips, as at the bottom. Such base course and other courses as may be predetermined are then to be constructed above the upper septum. This can be constructed directly upon the septum, or, if it is to be of broken stone, an inch or so of earth or other cushioning material may be preferably first be laid on the septum. The ends of the project are to be sealed by enveloping the end of the foundation within the septum, like the sides.

A successful construction of fabric for the septum is found in a plain weave of cotton or jute, the yarns being single and Without sizing applied to any part of the fabric. Such a fabric vcontaining 180 ends in 12 inches and 144 picks in 12 inches may have an A. S. T. M. breaking strength averaging -100 pounds in the warp and like strength in filling. The asphalt used may be of the rapid curing type customary for sheet asphalt in pavements according to standard specication known as RC 3. Specifications of both may be varied.

Jute or cotton is suggested for the fabric be-4 cause these are bases to which asphalt cement vwill adhere, and which have strength to retain the asphalt in place as a water barrier regardless of the nature of the soil, and will provide a strong and flexible septum which will be able to withstand the stresses occasioned by differential movements, and by impact of trafic. The ultimate requirement is that the septum be waterproof, tough and durable, having a breaking strength greater than is ordinarily to be imposed horizontally upon it by any stresses in the higher courses of the road, or by any stresses arising between the artificial foundation and the soil below which constitutes the natural foundation. It will be observed that if the latter is stable, the septum resting on it becomes adhesively and frictionally secured both to it and the articial foundation which the septum envelope, and is itself subject ordinarily only to compressive stresses. Stresses emanating from any particular point of heavy pressure on the surface of the road become considerably spread and distributed, and so are minimized in intensity, before they reach the septum; and such stresses are resisted by neighboring portions of the foundation and septum as well as by those portions which are more directly underneath the point whence the stress emanates. This secure strength never becomes reduced by the entry of water into the foundation by capillary attraction from below, or by infiltration from above or beside, even under extremes of climatic or temperature conditions. The applying of pressure at any point on the surface of the top course of the septum tends to deform the contained mass into a thinner rectangle, whose perimeter would be greater, so that, theoretically, if any movement within the septum were to occur, tension would thereby be generated in the septumy to resist such movement, and the mass automatically increases its friction to arrest such a movement. Therefore it is not necessary to use expensive cracked stone or gravel for the foundation, but the same soil which has been excavated from the pre-existing road can be used to constitute the foundation because, when so located, the septum will keep it free from water and will contribute to its stabilization.

Asphalt has been mentioned for the waterproof seal as it has the needed qualities, is of low cost, and is a familiar and abundant road material; but rubber and resins each may be used, being taken in suitable consistency for penetration, adhesiveness, and ultimate waterproofness, and so may any other materials having the requisite described qualities.

In either case, and in either process of construction above indicated, a watertight bond is eiected between the sealed course, and the subgrade or course, if any, below it, and between the sealed course and the material placed upon it.

The excluding of water from the sealed artificial foundation makes less dangerous the presence of water in the natural foundation under it; therefore some sub-drainage heretofore necessary in preparing the sub-grave can be omitted.

The invention thus makes savings in cost, over practices hitherto prevalent, in that its requirements are less both in excavation, in drainage, inexpense of foundation material, in base course material, and in maintenance costs. v

The embodiment of the invention herein illus tratively presented may be considered as having the septum in four sections, two of which are the under and upper. courses of septum and two of which are those which stand upright at the sides of the road, the best form of the invention being that in which the entire artificial foundation is surrounded and sealed against moisture passing in or out. The side sections, those at the edges of the road, are not necessarily so perfectly upright as are represented in the drawing. In some cases, if the terrain is reasonably dry, and especially if the side edges of the foundation are otherwise protected against the entrance of moisture, these upright sections may be omitted, and a measure of envelopment, probably suiicient for the middle part of the road, will be had from the overlying and underlying horizontal septum layers.

The invention has been illustratively described as it may be applied in roadway construction, this being the field in which its use would probably be most extensive; ybut it will be understood that it can also be used with advantage for pavements of other areas, as driveways, yards and courts, including tennis courts, public squares, and all p-laces exposed to Weather and to infiltration of water from beside or below; also for revetments on river banks, banks at road cuts and other banks exposed to wash by water; and also in connection with foundations for buildings where packed granular material is used,

I claim as my invention:

1. In a pavement structure having a plurality of superimposed courses of road making material, that improvement in which an under one of said courses is a conned body of loose earthy or the like road material with constant content of moisture; there being a permanent, conning septum, sealed completely around that said body and its moisture; said septum comprising a flexible sheet, having a continuous body of material which is inert to the chemical properties and biological content of ordinary earth and is impervious to moisture, and said sheet having toughness and tensile strength oi an order suitable for flexibly withstanding the deformation stresses to which the said course is normally subject from imposed weights and tran-lc and from movements of subadjacent earth, whereby the septum is of permanent nature and maintains constant the moisture f content of the surrounded earthy material.

2. In a pavement structure, an improvement as in claim 1 in which the septum is a woven strong fabric combined with a plastic substance of a nature impervious to moisture and to microorganisms, spread over both sides of the woven fabric, adhering thereto and coalesced thereon.

3. In a pavement construction, a combination as in claim 1, in which the septum is a composite sheet comprising a strongly cohering woven fabric sheet and a coating of viscid waterproof material adhering thereto.

4. In a pavement construction, a combination as in lclaim l, in which the septum is a composite sheet comprising a. woven fabric and asphalt adhering thereto; the fabric sheet being both impregnated with asphalt and coated on both sides with asphalt,

JOHN D. DRURY.

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