BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to a method of roadway construction and, more particularly, but not by way of limitation, it relates to an improved method of forming a roadway base to a controlled depth for deposition of earth material cut and processed in situ.
2. Description of the Prior Art
The prior art includes various teachings directed to utilization of native or other earth material in forming support structure for overlay of roadway surfaces. Prior attempts at "in place" stabilization were characterized by an inability to maintain reliably a specified depth or base line and, therefore, a proper thickness of the stabilized base layer; and, deleterious effects to finished roadways containing such base layer have necessitated outlawing of such practices in many states. That is, earth material may have been cut, ground and whatever for placement as base material and then leveled off to a neat line to form the base layer; however, the prior methods allowed no way whereby it could be ascertained that the base layer was uniform in thickness, i.e. the roadway bottom or base line was not cut to a controlled level or depth.
SUMMARY OF THE INVENTION
The present invention contemplates a method of road construction utilizing native or prepared earth material for base material wherein the earth material is cut, comminuted and layered automatically at a controlled depth and having a controlled thickness. In a more limited aspect, the invention consists of cutting the earth material to a predetermined base line as automatically controlled from a preselected external reference line, and comminuting the earth material to a desired consistency or maximum particle size for placement on the cut roadway above the base line to a desired thickness also controlled from the reference line. It is further contemplated to inject stabilizing additives, either liquid or dry in form, to the cut earth material for mixture therewith to adjust the stabilization properties such that the stabilized base is optimally processed to receive additional roadway material for support thereon.
Therefore, it is an object of the present invention to provide a method for building roadways from the base structure upward while utilizing native earth materials for stabilization.
It is also an object of the invention to provide a method of forming roadway base structure from earth material wherein each interface of the base structure is automatically formed at a controlled depth.
It is a further object of the invention to enable utilization of native earth material in forming reliable, controlled depth roadway base where the physical characteristics of the native earth material will permit.
Finally, it is an object of the present invention to provide a method of roadway construction which enables great economy with little or no reduction in strength and reliability of roadways.
Other objects and advantages of the invention will be evident from the following detailed description when read in conjunction with the accompanying drawings which illustrate the invention.
DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts a section of earth surface with a layer of cut native earth material as might be formed by conventional roadbuilding machinery utilized for grade cutting;
FIG. 2 depicts a section of paved roadway formed along the same earth section as shown in FIG. 1;
FIG. 3 depicts a section of earth surface having a cut and comminuted native material base layer formed thereon to a controlled depth and thickness in accordance with the present invention;
FIG. 4 is a partial block diagram of apparatus which may be utilized in carrying out controlled depth stabilization in situ in accordance with the present invention;
FIG. 5 is a side elevation of one form of apparatus which may be utilized in carrying out the method of the invention;
FIG. 6 is a front view of the apparatus shown in FIG. 5;
FIG. 7 is an enlarged, front elevation of a cutter as may be utilized in the apparatus of FIGS. 5 and 6;
FIG. 8 is a section of the cutter as taken along lines 8-8 of FIG. 7; and
FIG. 9 is a front view of roadbuilding apparatus similar to that of FIGS. 5 and 6 but being adapted for single-land usage with increased cutter speed.
DETAILED DESCRIPTION OF THE INVENTION
The method of the present invention enables construction of roadway utilizing native or prepared earth materials in situ as base support layer, and the method brings reliability to such practice through the employ of automated profile roadbuilding techniques. That is, recent advances in automated profile roadbuilding is based upon the premise that you build a roadway from the bottom up and not from the top down as has been done since early days of road construction with less than desirable results. Such latter day techniques have been brought about primarily through the capabilities of recent construction equipment innovations as best exemplified by the teachings of U.S. Pat. application Ser. No. 446,239 entitled "Road Construction Method and Apparatus" and filed on Apr. 7, 1965 in the name of George W. Swisher et al., now U.S. Pat. No. 3,423,859, and copending U.S. Pat. application Ser. No. 749,823 entitled "Control Systems for Road Construction Machinery" filed on Aug. 2, 1968 in the name of George W. Swisher, Jr., et al.
The prior attempts at utilization of native earth material for placement in situ as roadway base layer was generally unreliable due to an inability to maintain a uniform depth after compaction of the base layer along a right-of-way. FIG. 1 depicts such a prior attempt to rearrange earth material in situ. Grade-cutting machinery 10, such as conventional bulldozers, motorgraders, and various other cutting and loading machinery, might be utilized in one or more units to remove native earth material from the earth 12 having a surface 14. The grade-cutting machinery 10 would attempt to move a certain top depth of the earth 12 to redeposit loosened or broken up earth material 16 along the right-of-way. While the grade-cutting machinery 10 could continually cut down to a base line 18, there has been no known practice whereby the base line 18 could be maintained uniformly level to the roadway neat line such that it would also insure uniformity of base layer 16 when compacted thereon. For example then, when the base line 18 experiences an undulation peak 20 the base layer 16 in the area 22 would, of necessity, constitute a thinner layer since the upper surface 24 of the base layer 16 will be compacted and smoothed to the roadway neat line.
FIG. 2 shows the manner in which a faulty section of finished roadway might result from the attempt at inplace stabilization or utilization of native earth material as depicted in FIG. 1. The base layer 16 will have been smoothed and compacted such that upper surface 24 will equal the grade neat line; thereafter, a suitable form of base material 26 might be deposited in uniform layer and/or a paving material slab 28 will next be supported to provide the roadway surface. The employ of base 26, e.g. bituminous aggregate or other well-known base material, as well as the thicknesses of base 26 and paving material 28 will vary with the exigencies of different applications as well as requirements of building specifications in the locale.
In any event, core samples taken at spaced intervals along the roadway as depicted in FIG. 2 will show variations in the base layer 16, some of which can be extremely detrimental to roadwear and the ability to withstand normal temperature changes. A core sample taken at area 22, shown by dash lines 30, will show that the base layer 16 is of much less thickness than the same base layer 16 as sampled by a core taken along dash lines 32.
As shown in FIG. 3, the method of the present invention enables utilization of earth material as a stable base layer which can be uniformly extruded along a right-of-way having an automatically controlled depth. Thus, a suitable form of cutting and comminuting machinery 32 is moved along a surface 14 of earth 12 to cut and comminute the native earth material for deposition in a base layer 34 of uniform thickness and density. The stabilization properties of the native earth material may be adjusted to provide best function as a pavement base layer. Thus, it may be desirable to adjust the plasticity index, i.e. the difference in moisture content of soil between the liquid and plastic limits as expressed in percentage, so that the base capabilities may be altered to an optimum value. A suitable stabilizer material 35, e.g. lime, water, oil, and other well-known additives, may be interjected into cutting and comminuting machinery 32 for thorough mixture throughout the native earth material prior to its being deposited as uniformly thick base layer 34.
Automated profile control is maintained over the cutting and comminuting machinery 32 such that it cuts down to a uniform base line 36 which is continually maintained at a uniform distance from some external reference, thus, controlled depth as will be further described below. Similarly, the cutting and comminuting machinery 32 has the capability of leaving the base surface 38 at a uniform distance above the base line 36, it too being controlled from the external reference source. Such automatic profile control enables the guidance and cutting depth control of the cutting and comminuting machinery 32 to deposit base layer 34 of native earth material along the right-of-way. Such automatic profile control is the particular subject matter of the aforementioned Pat. applications, U.S. Ser. Nos. 446,239 (now U.S. Pat. No. 3,423,859) and 749,823. While description is directed more to the techniques of utilizing the native earth material, it should be understood that the present method is equally applicable to controlled depth cutting with preparation of imported or prepared base material. The use of native material is desirable for obvious reasons, but not always possible for obtaining required results.
Referring now to FIG. 4, the apparatus 40 exemplifies a form of device or mechanical structure which is suitable for carrying out the method of the invention. The apparatus 40 may consist of a frame 42, of suitable shape as necessitated by design requirements, which is movably supported on forward mobile support means 44 and rearward mobile support means 46. The respective support means 44 and 46 are connected via extendable support members 48 and 50, respectively, to the frame 42, and each of extendable support members 48 and 50 is operative under the control of respective height controls 52 and 54. Height controls 52 and 54 are individually controlled from respective height sensors 56 and 58 which derive height or level indication from an external reference, in this case, a stringline 60. Level sensing of stringline 60 for input to control the respective height control sensors 56 and 58 may be by various well-known means such as are described in the aforementioned U.S. Pat. applications Ser. Nos. 446,239 and 749,823; and such controls are the particular subject matter of a U.S. Pat. application Ser. No. 683,256 entitled "Line Tracer Control Device" filed Nov. 15, 1967 in the name of Steele et al.
The frame 42 may then carry a succession of operating elements such as a rotary cutter 62. The rotary cutter 62 may consist of a rotating shaft 64 carrying a plurality of cutter arms 66, each of which supports a cutter tooth 68 on the end thereof. The rotary cutter 62 is supported from a support member 70 which is adjustably connected to a cutter support 72 supported by the main frame 42. A suitable reservoir or storage tank may be secured to the main frame 42 for the purpose of holding stabilizer material for injection via a suitable input conduit 76 into the general area of comminution about rotary cutter 62. A mold board 78 is suspended from a mold board support 80 which is adjustably affixed to the main frame 42. Similarly, a rotary distributing auger 82 is supported from an elongatable support member 84 which is suspended from frame 42 by means of an auger support 86, and a rear moldboard support 88 extends rear moldboard 90 downward to the rear of rotary auger 82.
The frame 42 has its level adjusted in response to height control sensors 56 and 58 which control the operations of height controls 52 and 54 to vary the elongation of the respective support members 48 and 50. Each of the rotary cutters 62, moldboard 78, auger 82 and rear moldboard 90 is individually adjustable as to depth of operation below frame 40 by the adjustment of their respective cutter support 72, moldboard support 80, auger support 86 and rear moldboard support 88. For an initial setting of the relative displacement of the operating elements, i.e. the setting of rotary cutter 62 at a preset depth and with moldboard 78, rotary auger 82 and moldboard 90 relatively displaced at a higher level, the frame 42 may be moved along the right-of-way with support members 44 and 48 set at a level which is determined in relation to the stringline 60. Continual adjustment of the level of frame 42 relative to stringline 60 also serves to adjust the depth of cutting at base line 36 as well as the base surface 38 which is displaced a predetermined distance thereabove.
One form of automatic profile machinery which is suitable for employ in carrying out a stabilization in situ method as disclosed herein is shown in FIG. 5. This apparatus is similar to that disclosed in the aforementioned U.S. Pat. application Ser. No. 446,239 with the exception that the rotary cutter is altered as will be described below. The construction machine 100 is essentially a dual lane automatic grade-cutting machinery as disclosed in the prior application; however, alteration of rotary cutter 102 such that it includes an increased number of individual cutter arms 104, each being somewhat longer than the conventional cutter elements, will enable function in accordance with the method of the present invention. Construction machinery 100 consists of a main frame 106 which is supported by a pair of forward support legs 108 and rearward support legs 110 disposed in quadrature array. The forward support legs 108 are secured to respective forward vertical supports 112 which, in turn, are connected to yoke members 114 which are attached for support above mobile track units 116. The rear support legs 110 connect to respective rear vertical supports 118 which extend from yokes 120 and rear mobile track units 122. Forward and rearward steering is effected through tension bars 124 and 126 in a manner which is disclosed at length in the aforementioned U.S. Pat. application Ser. No. 446,239.
The top surface of main frame 106 serves as an operating platform 128 and an operator's console 130 is disposed at the forward edge thereof while a central power source 132 is supported at the rear. The rotary cutter 102 is supported from cutter support 134 which is vertically movably supported beneath main frame 106. While various power input forms may be employed to supply drive to the rotary cutter 102, a suitable form of hydraulic drive is employed which is capable of providing continuous control of rotary cutter 102 between 0 and 80 r.p.m. A moldboard 136 is also vertically adjustably supported beneath main frame 106 at a position just to the rear of rotary cutter 102 to provide both baffling and distribution function. A rotary auger 138 is supported from a support member 140 in vertically adjustably manner similar to that for rotary cutter 102, and a similar hydraulic drive is also utilized to provide revolution control. A rear moldboard 142 is then vertically adjustably supported to the rear of auger 138.
Stabilization material such as lime, water, or other stabilizing compounds may be retained in storage tanks 144 and 146 which are suitably secured across the front of the construction machine 100. The storage tanks 144 and 146 may include respective control structures 148 and 150 for distributing the dried or liquid-stabilizing material across the length of rotary cutter 102. Respective left and right stringlines 152 and 154 are also shown as they may be contacted by the various steering and level control-sensing devices.
Thus, a right front level control 156 derives indications from a movable sensing arm 158 to control the vertical extension of vertical support member 112 relative to stringline 152, the external reference source which in most cases would be constant to grade line of the right-of-way. A similar sensor (not specifically shown) would be disposed at the right rear to control vertical extension of vertical support member 118. On the left side (right side of FIG. 6), a control device 160 derives level control indications through position of sensing arm 162 as urged by stringline 154, and steering sensing is derived from a control device 164 and sensing arm 166. Similar level and steering control devices would be disposed adjacent the left rear of construction machine 100. It should also be understood that the steering control sensing can be carried out on either side as a matter of choice. Such control sensing is described in greater detail in the aforementioned U.S. Pat. applications, Ser. Nos. 446,239 and 749,823.
Referring now to FIG. 7, the rotary cutter 102 is shown in greater detail. The cutter 102 consists of a plurality of radially extending cutting members 104. Each of cutter members 104 consists of a cutter arm 170 which is welded to and radially extending from a central shaft 172. The cutter members 104 in one case may be arrayed in three intertwined helical flights, and that is the array as depicted in FIGS. 7 and 8. Thus, noting FIG. 8, the cutting members 104 are arrayed as three equally displaced helical flights as exemplified by particular cutter members 172, 174 and 176 which are attached in coplanar affixure to the center shaft 172. Each cutter arm 170 supports a cutter head 180 at its outward end, as has been found desirable in practice, the cutter heads 180 are so formed that they receive removable, hardened steel cutter teeth (not specifically shown) therein.
The rotary cutter 102 is primarily characterized by having an increased number of cutter members 104 disposed in greater density therealong so that cutter 102 has the capability of applying an extremely thorough chopping or cutting action to earth material as it moves along the right-of-way. In addition to the density of cutting members 104, the rotary cutter 102 is also controllable over a wide range of rotary speeds to enable further adjustment as to the degree and uniformity of comminution of the native earth material. With standard rotary control systems as present in conventional forms of construction machine 100, the operator may have the capability of controlling rotation of cutter 102 between 0 and 80 r.p.m. Still greater speeds approaching 120 r.p.m. are attainable when utilizing a single-lane type of machine as shown in FIG. 9.
A construction machine 190, another commercially available type of automatic grade control machine, is highly similar to the construction machine 100 of FIGS. 5 and 6 with the exception that it is built around a more narrow frame 192 which carries single-lane working or operating elements. In this case, a rotary cutter 194, which is similar to rotary cutter 102 in tooth structure and density but about one-half as long, is employed at higher revolutional speeds. This is enabled by applying similar hydrostatic drive, but greater rotational speeds are realized since the two drive systems required by rotary cutter 102 (FIG. 6) are both applied to control the single-lane rotary cutter 194. It is capable of continuous control between 0 and 120 r.p.m.
Such speed capability and control enables a most thorough cutting and comminuting operation of earth material, and this also allows more thorough mixture of stabilizing material throughout the comminuted earth material prior to its deposition or extrusion as the base layer along the right-of-way. Stabilizing material may be retained in a suitable storage tank 196 which is affixed across the forward edge of frame 192 and which includes a suitable form of distribution structure 198 for leading stabilizing material down for controlled release into the comminution area about rotary cutter 194.
In operation, and utilizing various of the apparatus capable of automatic profile control earth-working, or controlled depth cutting and comminution, the construction machinery is first set up relative to an external level reference such that the various operating elements are disposed at a preset depth. Thus, and referring to FIG. 4, stringline 60 serves as the external reference line along a right-of-way and the cutter support 72 and support member 70 are adjusted so that rotary cutter 62 will cut to the elevation level of a predetermined base line 36 within the earth 12. Similarly, the respective moldboard support 80, auger support 86 and moldboard support 88 are preadjusted so that they will extend their respective operating elements to a preset level relative to reference or stringline 60. The construction machine 40 can then proceed along a right-of-way cutting and comminuting the portion of earth material 12 above base line 36 for deposition in situ as a uniform base layer 34. The base line 36 as well as the upper surface 38 of base layer 34 is automatically maintained at a controlled depth and thickness relative to the stringline 60.
Depending upon the qualities of the native earth material, selected additives may be applied, e.g. through storage tanks 74 and injection line 76, for the purpose of stabilizing the native earth material so that optimum base characteristics are achieved. For example, it may be desirable to add dry commercial lime at a certain rate to lower the plasticity index of the native earth material 12 to increase its ability to support a paving slab and the attendant loads thereon. A prior qualitative analysis of the native earth material 12 will indicate the type and degree of stabilization and stabilizer material which must be added. Amounts of stabilizer material injected through line 76 may be released by metering in accordance with stabilization requirements versus the speed of traverse of mobile support means 44 and 46 along the surface 14 of earth 12.
While some native soils may require lime additive to bring about proper stabilization characteristics, it is contemplated that other applications may utilize oil or water or still other compounds as additives to the native earth material. Proper stabilization having been effected, the base layer 34 will be extruded out as a uniform layer with both base line 36 and surface 38 disposed at a constant distance from the external reference or stringline 60. The base layer 34 can then be compacted by following equipment, the uniformity of base layer 34 being maintained due to the initial uniformity of deposition and particle size, whereupon it may be further prepared for additional base material and/or a topmost-paving material to provide the finished roadway.
In cases where native material is unsuitable for base purposes, such material will have to be imported. Thus, after cutting the roadway base line to a predetermined base or depth line relative to an external reference, imported material is deposited in the roadbed for controlled depth distribution. Native earth material must be completely removed above the certain prescribed depth line. There is still the assurance that the bottom of the roadway bed is true and uniform at a preset level relative to the grade line.
The foregoing discloses a novel method of constructing roadways wherein native earth material is used to best advantage as pavement base support. While the use of native soil is not novel in itself, the formation of a native earth material base layer with required stabilization as extruded or laid down in uniform thickness upon a base line which is true to the roadway grade line does constitute new and useful practice which effects great economy in the building of improved quality roads. Economies are enabled not only from savings in hauling, distributing and wastage of nonnative, prepared base materials, but also in job time and man hours per roadway unit distance.
Changes may be made in the combination and arrangement of steps and/or elements as heretofore set forth in the specification and shown in the drawings; it being understood that changes may be made in the embodiments disclosed without departing from the spirit and scope of the invention as it is defined in the following claims.