US 1969267 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
Aug. 7, 1934. P. HUBBARD 1,969,267
` METHOD 0F PREPARING SUBGRADES FOR ROADS AND HIGHWAYS v Filed-March 17, 1930 @fyi . Y Z 4a Y 4@ v w \\v n v 05 104 fl 104] 1066z l0! 104a 105 ATTORNEY Patented Aug. 7, 1934 METHOD oF PREPARING `SUBGRADESYFOR ROADS AND HIGHWAYS Prevost Hubbard, White Plains, N. Y.
Application March 17, 1930, Serial N0. 436,525
` 4 Claims.
My invention consists in the novel features hereinafter described. reference being had to the accompanying drawing which illustrates an embodiment of my invention selected by me for 5 purposes of illustration, and a slight modification thereof, and said invention is fully disclosed in the following description and claims.
The efficiency of any road or highway must depend, to a greater or less extent, upon the support alforded by the subgrade or natural soil upon which the roadway proper rests. The major problem which soil subguards for highways presents is the .variation in moisture content. Most dry soils, when properly compacted, will sustain the loads to which highways are subjected, so long as they can be maintained free from excess moisture. `Water linds its Way into subgrade soil mainly by 1. Direct precipitation,
2. Run off and side infiltration 3. Capillary rise from accumulation of water which may be drawn upward into the upper portions of the subgrade from depthsV very considerably belowthe surface.
25 The provision of a waterproof wearing surface and the installation of adequate drains andculverts will serve to protect the subgrade against the infiltration of water from the rst two or of these sources, but will have no effect whatgrade with excess Water. by capillary action from below, which, especially at certain periods of the year, or by frost action, frequently softens the subgrade material to such an extent as to cause failure of the entire road structure carried upon it under tralic loads. k
In an attempt to prevent the breaking down cf the road structure locally, due toexcess'moisture drawn into the subgrade soil by capillary action, it has been deemed necessary in the more important highways to adopta pavement of such thickness and character as to support the traffic loads even when the subgrade soil contains the maximum excess of water due to capillary action. This often involves enormous expense. of initial construction throughout' the j entire length of the road or highway, and even such roads may fail at certain points where unusual or unexpected quantities of water are drawn into the subgrade soil by capillary action. Obviously such expensive types of highways are rinapplicable to thousands of miles of roads which must be maintained, and where the provision of adequatefunds for the more expensive ,types oi roadco'n'struction is impracticable.
ever in preventing the saturation of the subvious that the surface treatment, that is to say,
Athe road is subjected, when in moderately dry and compact condition, and to prevent the rise of moisture by capillary action to said layer by 'interposing between it and the body of soil be- 55 low, an impervious septum whichwill prevent f the access of waterthereto bycapillary action,
the said dry compact layer of subgradematerial being further protected from moisture of precipitation by a water-proof wearing surface or pavement, and from side infiltration by proper drains or ditches, so constructed that the level of water therein shall be below the level of the septum. In some instances, where it may be found necessary or desirable, a plurality of im- 'I5 pervious septums may be employed at different distances below the upper surface of the final subgrade soil, in which case the water level of the drainage ditches will ordinarily bebelow the lowest septum, but for ordinary road con- ,3 0 struction, and especially for firm roads and the like, a single septum below a layer of dry oompact subgrade soil of suitable rdepth will be suiicient. l
In carrying out my invention, it will be ob- 8,5
the actual pavement or roadway which protects the subgrade layer from moisture of precipita- Vtion and supplies the necessary surface wearing course, to prevent indentation by the wheels of 90 Vehicles, may be comparatively thin since the traflic loads are supported directly by the subgrade material itself, and the cost of road structure is thereby vastly decreased. It is to be understood, however, that my invention is also 95 applicable to the more expensive types of road as it will not only relieve them from the present menace of accumulationof water in the subgrade soil by capillary action, but will permit of the use of a pavement of less depth, and
greatly decrease the cost of building the more f expensive types of roadways, such for example,
as those of concrete, cement, or other like constructiomand those composed of granular stone combined with asphalt, orr other binders, also brick and block.
Referringr to the accompanying drawing, which illustrates onemanner in which my invention may be carried into effect, and a slight modiiication thereof,
Fig. l represents a cross section of the subgrade for a road or highway prepared in accordance with my invention.
Fig. 2 represents the same subgrade construction, with a relatively thin wearing course or pavement of waterproof character thereon.
Fig. 3 represents a slight modincation of my invention. in which a plurality 'of impervious septums below the drycor'npact subgrade layer are shown. l'
In carrying my invention into effect, a surface of natural soil, indicated at 1, is prepared, repre-f sented by the dotted line,'l -;c, in Figs. 1 and 2, at a predetermined distance below the upper level of the subgrade soil material upon which the pavement or roadway proper isl to be constructed. rIhis will ordinarily be vaccomplished by excavating the roadway to the required depth and removing the natural subgrade material therefrom, but obviously where filling is necessary, the level indicatedby the dottedline, m-."c, must be obtained in the usual manner. V1Upon thesurface of the soil, 1, at the level indicated by the dotted line, x--:c, I provide an impervious septum, which is indicated at 2, extending-over the entire surface beneath the roadway, and be tween the drainage ditch, indicated at 3, with which the .subgrade is tobe provided. I have found that capillary rise of water in soils of high capillary action can be checked by a relatively thin layer of bituminous material, or soil mixed l.with or impregnatedwith bituminousmaterial,
and under lordinary circumstances the impervious septum, 2, may be provided in this manner. For example, I may employ aV cheap grade of asphaltum road oil, such as is` commonly used for the surface treatment of earth roads, but I may` use other bituminous compounds with or without admixture to soil or other materials.
My invention, however, includes any type of impervious septum whichwillvprevent the rise vof water therethrough by capillary action, suchas .impervious sheet'material of any kind which will not become disintegrated by the action ofthe surrounding earth. Suitable sheetrmaterial provided with a `protecting coating on one or both Ysidesto insure against disintegration or to render it impervious may also be employed, but as one of the objects of my invention istoprovide an exceedingly inexpensive and yet durable and satisfactory roadway, I prefer to employa septum composed mainly or entirely of bituminous material, or such material ,mixed with soil or other granular material. The `dry subgrade material, indicated at '4, is superimposed upon the septum, 2, to the desired depth. Ifthe level, indicated by the ldotted line, .r-, has been obtained by removing the subgrade material, this same material may be replaced andthe drainage ditches, 3, are providedfof such depth that the normal water level therein will not atvany time rise aboveV the level ofthe septum, 2. The depth of the dry subgrade material, 4, which .will ordinarily' be of exactly the' same character as the soil, 1, below the septum, will depend upon the character of the subgrade soil. Ordinarily the subgrade material will be replaced above the septum, 2, in exactly the same condition in which it was before its removal. Obviously, however, in some instances, additions of sandor clay may be made, if desired, butthis will not ordinarily ber'rnecessary. The. dry subgrade material will be graded and compacted inany ordinary or preferred manner, with or without the laddition of water, and the shoulders, indicated at 4a, will preferably be given a suicient inclination toward the respective drainage ditches, to facilitate drainage of precipitated moisture. This dry compact subgrade material is then covered with a road surface, or pavement, which preferably should be of a water-proof character. In Fig. 2, for example, I have showna thin road surface, indicated at 5, which may be composed of bituminous material, with or without inely` divided stone or other suitable material, and all in desired depth. The shoulders, 4a, may also be coated with water-prooi material, as indicated at V5a, if desired, `although when properly constructed and given the requisite inclination toward the drainage ditches, little infiltration is to be feared from this source. In the finished roadway, the vwearing course or nished pavement, whatever its character may be, is supported'upon a substantially thick subgrade material composed of reasonably dry compact subgrade soil. beneath which is animpervious 'sepa ,tumv extending the full width of the roadway, between the side ditches or drains, but at an elevation above that of any standing water that might be expected to accumulate within them. The dry compact subgrade material, 4, is therefore protected from capillary moisture in the earth, 1, below it by the impervious septum, 2,
"and, is further protected from accumulation of excess water or precipitation or lateral infiltration so thatit will remain through the seasons in ics the same condition, and will at all times provide the necessary support for road traffic.
all directions, including' infiltration from the bottom by capillary action, forms no part of the pavement of the roadway, whether comprising It `will be understood that the dry subgrade lmaterial soprotected from excess moisture in merely an impervious surface treatment of comparatively little thickness, or a thicker stratain- Vcluding what may lbe termed foundation material surmounted by an impervious surface'wear-f ing courseyall of which if used Vwill be located above and rest upon the dry subgrade fmaterial so 'protected against moisture.
The depth of the dry compact subgrade layer above the, septum will vary in different soils land 'in Vdifferent localitiesand climates. `The septum, 2, may be located either adjacent to or below the normal frost line, if considered necessary, or in many cases, it may be located of a plurality of septumsat different distances from the upper surface of the subgrade, if this is necessary or desirable, and in Fig. 3 I have `lshown a slight modiiicationy of my invention in which theparts corresponding to those shown Yin Figs. l and 2 arey given the same reference numeralswith the addition of 100.
In this Yinstance the surface earth isv exca- :v
vated to a greater depth than heretofore described, to wit, toa level indicated bythe Vdotted line,` y-;1/. The lateral drainage ditches,
103, are carried to a greater depth so that the water level therein will be below thelevel of the dotted line represented ^by y-y; yThe entire with an impervious septum, indicatedat 102e, in any of the ways previously described. YApportion of the dry subgrade' soil, indicated at`104b,
surface between the ditches is then provided is then placed on top of the septum, 192e, to any desired depth and compacted in any usual or well known manner. A second septum, indicated at 102, is then provided above the layer of dry subgrade material, 10411, extending the entire distance between the drainage ditches, and the remaining portion of the subgrade material is applied above the upper septum, 102, and compacted and graded to the desired subgrade level. The water-proof Wearing course, 105, or roadway, is then applied over the top of the subgrade material, 104, and may be of any desired depth and of any desired character, whether merely a water-proof wearing course of bituminous material admixed with earth or broken stone, or any other desired form of pavement may be erected upon the upper layer of subgrade soil, 104. The shoulders, 104e, may also be protected by Water-proof material, as indicated at 105e, extending. downwardly past both of the layers of dry compact subgrade material, 104 and 104].
While this embodiment of my invention involves additional expense, itis obvious that it affords a double protection against infiltration by capillary action, as any water from thatr source would have to pass through both the septums, 102 and 102, in order to reach the upper course, 104.
While my invention is especially adapted to the preparation of subgrade for roads and highways, it will be understood that it may be applied to the preparation of subgrade for any sort of pavement, road, airport runway, taxiway,
landing strip or landing field, or in any other connection in which a supporting surface is to be provided. My invention is especially adapted for use in connection with preparation of subgrades for country roads and the like where a cheap and durable roadway is desired and where the enormous cost of cement and other expensive roadways makes it impracticable to divert large sums of money to such purposes.
While I have referred to the subgrade material above the septum or septums as being dry, this does not necessarily mean bone dry, but includes a condition in which the material may have a moderate degree of moisture which will not decrease its load carrying capacity. It will also be understood that should any excess water penetrate into the subgrade material above a septum, it will tend to drain out through the shoulders to the lateral drains, and
" the waterproof protection for the shoulders, in-
dicated at 5a and 105e, where employed may be of such character as to facilitate the passage over them of precipitated water without hermetically sealing the surfaces. The surface over which the septum or septums is or are laid may also be crowned, as indicated for example in Fig. 3, or inclined or otherwiseconstructed so as to facilitate drainage from the superimposed subgrade material should excess water nd access thereto,v at any time.
What I claim and desire to secure by Letters Patent is:-
1. The method of forming a supporting bed, which consists in placing an impervious substantially horizontal septum upon the subgrade soil at a predetermined depth below the normal subgrade level, then placing a bed of natural subgrade or soil material susceptible to capillary action on said septum, having its upper surface below the normal subgrade level, placing an impervious substantially horizontal septum upon said bed of natural subgrade or soil material, placing another bed of natural subgrade or soil material susceptible to capillary action upon said second septum, providing drainage adjacent to the lateral margins of said beds of a character to prevent a water level adjacent thereto higher than the first mentioned septum, and applying an impervious wearing surface over said last mentioned bed.
2. A roadway comprising an impervious septum supported in natural subgrade soil below the normal subgrade level, a substantially dry supporting bed of naturalsubgrade soil susceptible to capillary action on said septum, an impervious wearing surface mounted on the supporting bed, drainage ditches at the opposite lateral extremities of said septum having a depth suii'icient to prevent a water level above said septum, and a protective coating on the walls of said ditches above and adjacent to the septum for preventing lateral inltration into said bed.
3. The method of forming a roadway which consists in placing an impervious substantially horizontal septum upon subgrade soil at a predetermined depth below the normal subgrade level of the road, superimposing upon said septum a layer of untreated natural subgrade soil of suflicient thickness to support the normal traflic loads when in a dry condition and providing said layer with lateral drainage slopes and providing a protective coating upon the upper surface of said layer of untreated soil, said protective coating extending over said lateral drainage slopes to their lines of intersection with the plane of the septum, so as to protect it from water of precipitation and lateral inltration of water.
4. A roadway comprising an impervious septum supported on natural subgrade soil below the normal subgrade level, a substantially dry supporting bed of natural subgrade soil susceptible to capillary action on said septum, an impervious septum supported by said bed below the normal subgrade level, a substantially dry supporting bed of natural subgrade soil susceptible to capillary action on the upper septum, an impervious wearing surface mounted on the upper supporting bed, drainage ditches at the opposite lateral extremities of said septums having a depth suicient to prevent a water level above the lower of said septums, and a protective coating on the walls of said ditches above and adjacent to the lower septum for preventing lateral infiltration into said beds.
` PREVOST HUBBARD.