Hydraulic and earth engineering – Drainage or irrigation – Porous waterway – e.g. – sand drain – etc.
Reexamination Certificate
2002-09-03
2004-10-12
Will, Thomas B. (Department: 3671)
Hydraulic and earth engineering
Drainage or irrigation
Porous waterway, e.g., sand drain, etc.
C405S302700, C404S028000, C404S031000
Reexamination Certificate
active
06802669
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to means and methods for extending the life of paved structures such as highways and airport runways by providing improved and novel drainage systems of geosynthetic elements that can be installed economically with conventional road building and construction equipment.
BACKGROUND OF THE INVENTION
Water is a principal cause of distress and damage to paved structures such as roadways, airport runways and parking lots. Therefore, drainage systems are often provided in such structures in order to remove water from the paved surface or its foundations to thereby extend the useful life of the pavement surface. In some drainage methods, drainage systems are incorporated between the native soils or “subgrade” upon which a roadway or other large structure is situated and the overlying pavement surfaces. The present invention relates generally to synthetic void-maintaining structures with high permittivity and high transmissivity that are capable of extending the life of pavement by maintaining voids of sufficient dimensions to permit the timely egress of undesirable fluids. In conventional roadbuilding, natural stone and aggregate materials are placed to form a drainable layer that is commonly called an Open Graded Base Course, or “OGBC.” OGBC's are typically used underneath the surfaces of highways, airport runways, roads, and parking lots that are paved with bituminous materials such as asphalt or cementitious materials such as concrete. The present invention comprises a Synthetic Drainable Base Course (“SDBC”) of polymeric material and related methods for constructing paved surfaces such that the need for an OGBC can be eliminated or minimized.
Pavement surfaces are highly engineered layered structures. Because of this, pavement structures require engineered materials that are selected based upon factors such as their density, particle or aggregate size, compressibility or other engineering parameters of the soil, stone and aggregate-based products that are required as structural fill that typically is installed in layers beneath pavement surfaces.
Two types of structural fill are the base course and, typically immediately beneath the base course, a subbase course. Fluids such as water that become trapped or retained within structural fill cause damage to roadways and, over time, subsequently greatly reduce the useful life of a pavement system. These destructive phenomena occur even when asphalt additives, waterproofing techniques and conventional geosynthetics are used to improve the road.
The cause of many premature pavement failures has been traced to inadequate subsurface drainage. Typically, fluids enter the subsurface layers of pavement systems from surface infiltration through joints and cracks in the pavement, as well as pores in the pavement itself, seepage from the sides of the paved surface, and from rising groundwater beneath the road surface, either by capillary action or the upward movement of water in vapor form. In fact, the FHWA discovered that over 50% of all rainfall reaching a mature pavement surface enters underlying structural portions of the pavement through infiltration. In northern tier states, the destructive nature of water trapped in the structural base is exacerbated by freeze-thaw cycles, and particularly during spring thaw as ice lenses melt to create water-filled voids and very soft, water-saturated soils which lose a substantial amount of their compressive strength. In turn, these phenomena result in extensive damage to the highway system. These and related drainage-based structural issues are now well-recognized in the road and runway building industries.
When there is a high fluid content within soil or other layers supporting pavement that carries vehicular traffic, reduced bearing capacity can occur, resulting in deformation of the contour of the road surface, wheel rutting, and premature collapse or failure of the roadway. The American Association for Safety and Highway Transportation Officials (AASHTO) issued design methodologies in 1993 that underscore the observation that damage to roadways occurs when fluid such as water is retained. In promulgating standards for quantifying the drainage performance of highways and other paved surfaces, AASHTO rates pavement drainage performances from “excellent,” where water is removed from the roadway system within two hours, to “poor,” where water is removed within one month. Drainage coefficients corresponding to these ratings are often used as direct design parameters in highway construction. For example, the drainage coefficient corresponding to an “excellent” drainage system in a roadway section would typically be at least two times greater than the corresponding drainage coefficient for “poor” drainage system in a similar section of roadway. In general, a drainage system having a higher drainage coefficient increases the corresponding effective structural rating of a section of roadway. Therefore, higher drainage coefficients generally correspond to a longer or extended service life, or result in the reduction of the overall structural cross-section, and therefore the amount of engineered materials, necessary to support a particular load.
Other engineering parameters reflect the importance of sufficient drainage to roadways. For example, the presence of water in pavement causes a reduction of the resilient modulus, which reduces the ability of a pavement surface to support traffic loads. In 1993, AASHTO reported that water saturation can reduce the dry modulus of asphalt paving by 30% or more. Moreover, added moisture in unbound aggregate base and subbase layers was estimated to result in a loss of stiffness on the order of 50% or more. With water retention, a modulus reduction of up to 30% can be expected for an asphalt-treated base as well as an increased erosion susceptibility of cement or lime-treated bases. In addition, with inadequate drainage, saturated fine-grain road-bed soil may experience modulus reductions of over 50%. Furthermore, the presence of fluids often causes the buildup of hydraulic pore pressure that, in turn, reduces the effective stress capacity of the soil materials that were placed to support the pavement system.
Premature failure of pavement systems results in unacceptably high life-cycle costs for highways and other large paved structures. One conventional approach to the prevention of such premature failure from occurring has been directed toward developing means and methods for waterproofing roads. After years of expense and effort, however, waterproofing paved surfaces sufficiently to extend their useful life has proven to be quite challenging and somewhat unsuccessful. At the present time, industry focus has shifted from attempts at preventing water from entering the pavement surface to developing ways for removing water from the subbase and other base materials underlying the pavement. This shift in focus has been the subject of a number of publications in the field. One such publication is
Drainage of Highway and Airfield Pavements
, H. R. Cedegren (1987, R.E.K. Publishing Co.). In his book, Cedegren emphasizes that proper base and subbase drainage are considered to be more essential than paved surface waterproofing with respect to assuring that a pavement structure will perform for the duration of its design life. Cedegren projects that pavement useful life can be extended up to three times (e.g., a service life can be extended from 15 years, to 45 years) if adequate subsurface drainage systems are installed and maintained. The benefits of good drainage are also recognized in many current roadway design methodologies published in the early 1990's by AASHTO and the U.S. Army.
Other published studies support this view. In one of them, “
The Economic Impact of Pavement Subsurface Drainage
,” R. A. Forsyth (1987, Transportation Research Record 1121, National Research Council, Washington, D.C.), the author reports at least a 33% increase in service life for asphalt pavement and a 50% increase for PCC pavem
Capra Giovanni
Ianniello Peter J.
Zhao Aigen
Pechhold Alexandra K.
Shaffer, Esq. Gary L.
Will Thomas B.
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