Pavement Systems with Geocell and Geogrid

Abstract

The present invention relates to a pavement system and method for suitable pavement in a location accommodating a generally soft subbase having a California Bearing Ratio (CBR) of 4 or less. The pavement system comprises: a first geogrid layer disposed directly on the subbase; a first granular layer on the first geogrid layer having a thickness of 0.5 to 20 times the opening distance of the geogrid layer; a first geocell layer on the first granular layer comprising a geocell and a filler material; and a capping layer on the geocell layer. A second geocell / geogrid layer may be disposed below the capping layer if necessary. An optional surface layer may be applied on the capping layer if required. The final pavement system provides long-term support for the pavement applied on the pavement system.

Description

Technology Field

[0001] This application claims priority to U.S. provisional application No. 61 / 884,231 filed on September 30, 2013, the contents of which are incorporated herein by reference.

[0002] The present invention relates to a pavement system suitable for use on soft subgrades, native soil, expansive clay, or soils susceptible to frost heaving during the cold season. These pavement systems are positioned on subgrades and are used for various applications such as roads, park roads, sidewalks, and railways. These pavement systems are particularly suitable for soft subgrades. Background Technology

[0003] In transport engineering, several layers are recognized as components of a paved road. These layers include a subbase layer, a sub-base layer, a base layer, and a surface layer. The subbase layer is the raw material and serves as the foundation for the paved road. An optional sub-base layer is placed on top of the subbase. The sub-base and base layers are used to support loads and dissipate these loads to a level applicable to the surface layer. Depending on the required use of the paved road, another layer may be placed on top of the base layer, and this layer may be known as the paved road base layer. The surface layer is placed on top of the paved road and is the exposed layer on the surface of the paved road. The surface layer may be, for example, asphalt (for roads or parking areas), concrete (for sidewalks), ballast (for example, on which railway tracks are subsequently laid), or compacted granular material (for unpaved roads).

[0004] A soft subbase is a subbase that has a California Bearing Ratio (CBR) of 4 or less, or typically 3 or less, when wetted with water. Soft subbases have low stiffness and low resistance to load. A particularly soft subbase has low stiffness and low resistance to load if the subbase is an expansive clay or soil susceptible to frost heave during the cold season. Frost heave is the upward swelling of soil caused by the formation of ice below the surface. The presence of water causes several processes that can significantly damage pavements. First, water molecules can cause soil particles to swell and reduce the cohesion between said soil particles. Second, swelling caused by water can cause soil expansion, increasing upward pressure on the pavement. Third, water expands while freezing and, in combination with hardening caused by ice formation, can damage the pavement. These upward stresses generated during expansion (e.g., swelling of clay or soil) can be significantly greater than the stress generated by vehicles on soft subgrades. Pavements installed on such soft subgrades will be permanently damaged.

[0005] In many situations where the subbase is soft and shallow, the subbase is removed and replaced with a stronger and more dimensionally stable granular material. However, in other situations, this is not possible because: (a) the soft soil of the subbase is very deep; or (b) stronger and more dimensionally stable granular material is not locally available, or the shipping cost of such material is very high. Examples of these situations can be found in peat ponds in northern Russia, expansive clay beds in Texas, and muskeg beds in Canada and Siberia.

[0006] An example of a paved road is illustrated in FIG. 1. The paved road comprises a soft subbase (2), a crushed stone base (4), and a surface layer (6). In other words, the soft subbase may be soft soil, expansive clay, or soil sensitive to frost heave. Typical failures include the formation of wheel tracks (formation of grooves or wheel tracks in the paved road), cracking in the asphalt or concrete surface layer of the paved road, misalignment or warping of railway tracks laid on ballast, and pumping out of the base layer beneath the surface layer. These failure modes are caused by irreversible deformation of the base and / or sub-base due to (1) tensile strength; (2) stiffness (modulus); (3) interfacial strength between the layer and the subbase; and / or (4) bending moment (resistance to bending).

[0007] One method commonly used to prevent these modes of failure involves chemical modification of the subbase. The subbase is mixed with an inorganic binder (e.g., lime, cement, or fly ash) or an organic binder (e.g., a polymer emulsion). However, this method suffers from several undesirable characteristics, such as slow curing, poor performance in humid and cold climates, leaching of inorganic binders in humid climates, high cost of polymer binders, brittleness, poor quality due to difficulties in field mixing, poor resistance to freeze-thaw cycles, and difficulty in obtaining a uniform subbase over large areas (e.g., in texture or composition). The problem to be solved

[0008] A pavement system that provides enhanced performance when installed on soft subbases, original soil, expansive clay, or soil sensitive to frost heave may be desirable. Additionally, it may be desirable for such a pavement system to be configured with an economical and easy installation method. means of solving the problem

[0009] A pavement system and method for installing such a pavement system on a soft subbase having a California Bearing Ratio (CBR) of 4 or less, such as expansive clay or frost-sensitive soil, are disclosed in various embodiments. The pavement system generally comprises a geogrid layer, a first granular layer, and a geocell layer on the subbase. The first granular layer has a specified thickness or height. A surface layer may be applied directly onto the geocell layer, or an additional geocell or geogrid reinforced layer may be placed on the geocell layer prior to the application of the surface layer.

[0010] A pavement system to be installed on a soft subbase having a CBR of 4 or less, particularly on expansive clay or on frost-sensitive soil, is disclosed in several embodiments, said pavement system comprising: a first geogrid layer disposed on said subbase and made of at least one geogrid; a first granular layer disposed on said geogrid layer and containing a first granular material; a first geocell layer disposed on said granular layer and containing at least one geocell filled as a filler material; and optionally a covering layer disposed on said geocell layer and made of a compact second granular material; wherein each of said geogrids is made from intersecting rib members to form geogrid openings, and said first granular layer has an average distance of 0.5 to 20 times the opening distance of said geogrid layer.

[0011] The pavement system may further include a surface layer disposed on a first geocell layer or on an optional covering layer, said surface layer comprising granular material, asphalt or concrete, or ballast. In several embodiments, railway tracks and ties are installed on the pavement system.

[0012] The first granular material may be sand, gravel, or crushed stone. Generally, the first granular material also enters the geogrid openings of the first geogrid layer.

[0013] The filling material may be sand, crushed stone, gravel, or a mixture thereof.

[0014] The second granular material of the optional covering layer may be sand, gravel, or crushed stone.

[0015] The geogrid opening distance may be between about 10 millimeters and about 500 millimeters, and may also be between about 25 millimeters and about 100 millimeters.

[0016] The first geocell layer may have a shell height between about 50 millimeters and about 300 millimeters. The first geocell layer may have a shell size between about 200 millimeters and about 600 millimeters.

[0017] At least one geogrid can be made of polypropylene, polyethylene, polyester, polyamide, aramid, carbon fiber, textile, metal wire or mesh, glass fiber, fiber-reinforced plastic, multilayer plastic laminate, or polycarbonate.

[0018] In several embodiments, the first granular material has an average particle size larger than the filler material in the first geocell layer.

[0019] In several other embodiments, the pavement system further comprises: an optional second granular layer disposed on a first geocell layer; and a second geocell layer or a second geogrid layer disposed on the second granular layer or on the first geocell layer, wherein the covering layer is disposed on the second geocell layer or the second geogrid layer. The second granular layer may have a thickness of about 1 mm to about 300 mm.

[0020] In another embodiment, the pavement system further comprises a second geocell layer or a second geogrid layer disposed directly on a first geocell layer, wherein the covering layer is disposed on the second geocell layer or the second geogrid layer.

[0021] In another considered embodiment, the geotextile layer may be placed at any location between the subbase and the covering layer. Such a layer may be particularly useful if the pavement is used in a location where it has a large groundwater level, or in a location where it is subject to heavy rain or flooding, or in a location where fines can infiltrate upward or downward between the layers.

[0022] Additionally, a method for installing a pavement system on a soft subbase having a California Bearing Ratio (CBR) of 4 or less, such as expansive clay or frost-sensitive soil, is disclosed, said pavement system comprising: applying at least one geogrid to the subbase to form a geogrid layer; applying a sufficient amount of a first granular material onto the geogrid layer and subsequently compacting the first granular material to form a first granular layer having an average thickness of 0.5 to 20 times the opening distance of the geogrid layer; placing at least one geocell on the first granular layer; and filling at least one geocell as a filler material to form a first geocell layer. Optionally, the method comprises the steps of applying a second granular material to the first geocell layer and compacting the second granular material to form a covering layer having a thickness of 0 to about 500 mm on the geocell layer; wherein each of the geogrids is made of intersecting rib members to form geogrid openings. Optionally, the second geogrid or geocell layer may be disposed directly on the first geocell layer, or separated from the first geocell layer by a second granular layer made of the granular material.

[0023] The method may further include the step of applying a surface layer onto a covering layer, said surface layer comprising asphalt, concrete, or ballast. The method may further include the step of removing soil to expose a soft subgrade.

[0024] In a particular embodiment, the method further comprises the steps of: forming a second granular layer on a geocell layer; and placing another geocell or geogrid on the first geocell layer / on the second granular layer to form a second geocell layer or a second geogrid layer below a covering layer. The second geocell layer or the second geogrid layer may be separated from the first geocell layer by a distance of 0 to about 500 mm.

[0025] Additionally, an improved pavement system suitable for long-term performance on a relatively soft subgrade is disclosed, said pavement system comprising: a subgrade having a CBR of less than 4 in sequence from bottom to top; a geogrid disposed directly on said subgrade or incorporated within a layer of granular material; a layer of granular material on the top of said geogrid; a geocell filled with sand, crushed stone, gravel, ash, RAP (recycled asphalt pavement), quarry screening, or a mixture thereof; optionally another layer of granular material disposed on a second geocell or a second geogrid; a covering layer made of compact crushed stone, gravel, or sand; and optionally, an asphalt-based, concrete-based, or ballast-based surface layer; wherein the thickness of said layer varies from 0.5 to 20 times the geogrid opening distance.

[0026] These and other exemplary features of the present invention are described in more detail below.

[0027] It will be understood that the details described below are for a brief description of the drawings, and that these drawings are intended to illustrate exemplary embodiments disclosed in this specification and are not intended to limit embodiments of the present invention. Brief explanation of the drawing

[0028] FIG. 1 is a cross-sectional view of a conventional paved road system that does not include a geocell layer or a geogrid layer. FIG. 2 is a perspective view of the geocell in a unfolded state. Figure 3 is an enlarged perspective view of the polymer strip of the geocell of Figure 2. Figure 4 is a plan view of a part of the geogrid. FIG. 5 is a drawing of a paved road system of the present invention having a geogrid layer and a geocell layer. FIG. 6 is a drawing of another paved road system having a geogrid layer, then a first geocell layer, then a second geocell layer on the first geocell layer. FIG. 7 is a drawing of another paved road system having a first geogrid layer, a geocell layer, and a second geogrid layer on the geocell layer. Figure 8 shows the base layer (E V2-T A base layer (H) of a conventional unreinforced design product as a function of the CBR of the subgrade to obtain the required elastic modulus of ) SUB-A This is a graph showing the calculated thickness of ). Specific details for implementing the invention

[0029] The components, processes, and devices disclosed in this specification will be more fully understood by referring to the accompanying drawings. These features are depicted schematically merely to facilitate and conveniently explain the invention, and are therefore not intended to limit or define the scope of exemplary embodiments and / or to indicate the relative sizes and dimensions of the components or devices of the invention.

[0030] Although specific terms have been used in the detailed description below for clarification, these terms are intended to describe only specific structures of the embodiments selected for description in the drawings and are not intended to limit or restrict the scope of the invention. In the drawings and detailed description below, it will be seen that the same reference numerals indicate components having the same operation.

[0031] Even if a term described in this specification is expressed in the singular, it will be understood that the term may include a plural meaning unless specifically stated otherwise.

[0032] It will be understood that the numerical values ​​described in the specification and claims of this application include the same numerical value when reduced to a number of significant values ​​that are different from the mentioned value, such that the experimental error of the conventional measurement technique of the type described in this application for determining the value is smaller.

[0033] All ranges disclosed in this specification include the mentioned endpoints and can be independently merged (for example, the range “2 mm to 10 mm” includes the endpoints, 2 mm and 10 mm, and all intermediate values).

[0034] Values ​​modified by terms such as "about" and "substantially" may not be limited to specific exact values. The modifier "about" may also be considered to initiate a range defined by the absolute values ​​of two endpoints. For example, the expression "about 2 to about 4" also indicates a range of "2 to 4".

[0035] When CBR (California Bearing Ratio) is referenced in this specification, the provided value is measured when the layer is saturated with water.

[0036] The present application refers to a paved road system located on the ground. The present application also refers to different layers located "above," "on the upper side," or "above" each other. Where a second layer is described as being located in relation to a first layer using these terms, the first layer is located deeper in the ground than the second layer, or, in other words, the second layer is closer to the surface than the first layer. There is no requirement for the first layer and the second layer to be in direct contact with each other; another layer may be located between the first layer and the second layer. Furthermore, each layer has a length, width, and height / depth / thickness. Length and width will refer to the dimensions of the layer in the ground. The terms height, depth, and thickness will be used interchangeably to refer to the vertical dimensions of the layer.

[0037] Geogrids are used to heal the failure modes described above. Geogrids can be made of polymers (e.g., polyester or extruded polymers) arranged in a network of ribs and openings to provide uniaxial or biaxial tensile reinforcement to the soil. Geogrids may include coatings that provide additional chemical and mechanical advantages. Alternatively, sheets can be punched to form geogrids and subsequently drawn, which is performed by Tensar Corporation. Polyester or polypropylene rods or straps can also be ultrasonically bonded together in a grid pattern or laser heated to form geogrids. Geogrids are generally mechanically and chemically durable, allowing them to be installed in intrusive soils or aqueous environments. Geogrids have a two-dimensional structure, no effective height, and a flat planar structure.

[0038] Geocells are also being integrated into pavement systems to prevent failure modes. A geocell (also known as a cellular confinement system (CCS)) is an array of containment cells similar to a "honeycomb" structure filled with filler. While a CCS is a three-dimensional structure with internal force vectors acting within each shell for every wall, a geogrid is only two-dimensional. However, when geocells are used to reinforce a base or sub-base on a soft subbase, the pavement still fails due to the "flow" of filler outward from the bottom of the geocell and downward toward the soft subbase, and due to insufficient tensile strength. This causes undesirable differences in tensile strength and modulus between the base / sub-base and the subbase, resulting in poor tensile performance along these interfaces.

[0039] Research has been conducted on combining geocells and geogrids within shared pavement systems. For example, one system places geogrids in the subbase layer, then places geocells directly on the geogrid-reinforced subbase layer (i.e., in the subbase), and then fills the geocells with excavated material. These layers are then compacted and raised (0.75 inches high) as a layer of clean stone. However, such systems using a geogrid subbase layer equipped with a geocell top layer only partially address the identified problems associated with failure modes in pavement systems. Due to the high stiffness of the geocell layer, the geogrid-reinforced layer is subjected to small strain. Since the geogrid requires significant deformation to contribute to substantial tensile reinforcement, the geogrid consequently cannot provide significant reinforcement to the overall system.

[0040] Accordingly, the present application relates to an improved pavement system suitable for long-term performance on soft subbases having a California Bearing Ratio (CBR) of 4 or less, on expansive clay, or on frost-sensitive soils (i.e., frost-sensitive soils). These soils may include organic clay, peat, musque, montmorillonite soils, and bentonite soils. The pavement system of the present invention comprises a geogrid-reinforced layer separated from a geocell-reinforced layer by a layer of granular material. Another geogrid layer or geocell layer may be placed on top of the first geocell-reinforced layer. These systems are also very suitable for use where stress is applied from below (i.e., upward) the pavement.

[0041] Geocells (also known as cellular confinement systems (CCS)) are three-dimensional geosynthetic products available for many geoengineering applications, such as soil erosion control, channel lining, components of reinforced soil retaining walls, and supports for pavements. A CCS is an array of containment shells similar to a "honeycomb" structure filled with filler, which can be non-cohesive soil, sand, gravel, ballast, or any other type of aggregate. CCS is used in civil engineering applications to provide lateral support, such as retaining walls for soil, or to prevent erosion, as an alternative to sandbag walls or gravity walls, and as an alternative to road, pavement, and railway foundations. While geogrids are generally flat (i.e., two-dimensional) and used for planar reinforcement, CCS is a three-dimensional structure with internal force vectors acting within each shell for every wall. CCS also provides effective reinforcement for relatively fine-grained fillers such as sand, high-quality soil, and quarry waste.

[0042] FIG. 2 is a perspective view of the geocell in an expanded state. The geocell (10) comprises a plurality of polymer strips (14). Adjacent strips are joined together along separate physical seams (16). Joining can be performed by bonding, sewing, or welding, but is generally done by welding. The portion of each strip between two seams (16) forms the shell wall (18) of an individual shell (20). Each shell (20) has a shell wall made of two different polymer strips. When the strips (14) are joined together and expanded, a honeycomb pattern is formed from the plurality of strips. For example, an outer strip (22) and an inner strip (24) are joined together at regularly spaced seams (16) along the length of the strips (22 and 24). A pair of inner strips (24) are joined together along a seam (32). Each seam (32) exists between two seams (16). As a result, when a plurality of strips (14) are stretched or unfolded in a direction perpendicular to the surface of the strips, the plurality of strips are bent in a sinusoidal manner to form a geocell (10). At the edge of the geocell where the ends of two polymer strips (22, 24) meet, an end weld (26) (also considered as a joint) is made at a short distance from the end (28) to form a short tail (30, tail) that stabilizes the two polymer strips (22, 24). Such a geocell may also be referred to as a part, particularly when combined with another geocell over an area larger than that which can actually be covered by one part.

[0043] FIG. 3 is an enlarged perspective view of a polymer strip (14) showing the length (40), height (42), and width (44), wherein the seam (16) is shown for reference. The length (40), height (42), and width (44) are measured in the indicated directions. The length is measured when the geocell is in its folded or compressed state. In the compressed state, each shell (20) may be considered to have no volume, whereas the unfolded state generally refers to when the geocell is unfolded to its maximum possible capacity. In the embodiment, the geocell height (43) is about 50 millimeters (mm) to about 300 mm. The geocell shell size (measured as the distance between the seams in the unfolded state) may be about 200 mm to about 600 mm.

[0044] Geocells can be made of linear low-density polyethylene (PE), medium-density polyethylene (MDPE), and / or high-density polyethylene (HDPE). The term "HDPE" refers to polyethylene characterized by a density greater than 0.940 g / cm³. The term medium-density polyethylene (MDPE) refers to polyethylene characterized by a density greater than 0.940 g / cm³ from 0.925 g / cm³. The term linear low-density polyethylene (LLDPE) refers to polyethylene characterized by a density between 0.91 and 0.925 g / cm³. Geocells can also be made from polypropylene, polyamide, polyester, polystyrene, natural fibers, woven textiles, blends of polyolefins with other polymers, polycarbonates, fiber-reinforced plastics, textiles, or multilayer plastic laminates. The strips used to make the geocell are welded together using an offset method, and the distance between the welded seams is about 200 mm to approximately 600 mm.

[0045] The width of the typical strip wall for the geocell is 1.27 millimeters (mm) and varies in the range of 0.9 mm to 1.7 mm. The shell wall may be perforated and / or embossed.

[0046] FIG. 4 is an enlarged plan view of a portion of a geogrid (60). The geogrid is made from rib members (62) that intersect each other to form a geogrid opening (64). The geogrid may be made of polypropylene, polyethylene polyester, polyamide, aramid (e.g., kevlar), carbon fiber, textile, metal wire or mesh, glass fiber, fiber-reinforced plastic (e.g., blend or alloy), multilayer plastic laminate, or polycarbonate. As disclosed herein, the geogrid opening is rectangular, but the geogrid opening may generally be any shape including square, triangle, circle, etc. Any geometric structure may be used. The rib members are smaller than 50% of the geogrid area, or in other words, the open area of ​​the geogrid is larger than 50%.

[0047] Each geogrid opening has an opening distance which is the average length of the ribs surrounding the opening. As described herein, for example, in a rectangular opening, the opening distance is the average length of the shorter rib member (66) and the longer rib member (68). In an embodiment, the opening distance for the geogrid is about 10 mm to about 500 mm, or about 25 mm to about 100 mm.

[0048] Geocells and geogrids can be distinguished by the vertical thickness of their respective strip and rib members. Geocells have a vertical thickness of at least 20 mm, whereas geogrids have a vertical thickness of about 0.5 mm to 2 mm.

[0049] FIG. 5 is a cross-sectional view of an exemplary pavement system of the present invention. Generally, the geogrid-reinforced layer is spaced from the geocell-reinforced layer by the amount of the layer of granular material.

[0050] Initially, a geogrid layer (60) is formed on the subgrade layer (50). The geogrid layer is formed from at least one geogrid. It will be known that the subgrade may be a native subgrade, or may be chemically modified (e.g., with lime, cement, polymer, or fly ash), or physically modified (e.g., replaced with a more stable granular material). The modified portion of the subgrade may have a thickness that varies from about 50 mm to about 1000 mm.

[0051] Next, a first granular layer (70) is placed on the geogrid layer (60). The first granular layer comprises a first granular material, which may be sand, gravel, or crushed stone. The first granular layer has a thickness (75) of 0.5 to 20 times the opening distance of the geogrid layer. It will be seen that the first granular material may fall into or enter the geogrid opening of the geogrid layer (60). If necessary, the first granular layer is compact.

[0052] Since the opening distance of a geogrid layer is typically the same as the opening distance of the geogrids forming the geogrid layer, it is presumed that all of the geogrids are identical. When different geogrids having different opening distances are used in a geogrid layer, the opening distance of the geogrid layer can be calculated as an average opening distance weighted by the surface area covered by each geogrid.

[0053] Next, a geocell layer (80) is placed on the first granular layer (70). The geocell layer is formed from at least one geocell (82) filled with a filler material (84). The filler material compacts (packs) the filler to reinforce it. Exemplary filler materials include sand, crushed stone, gravel, and mixtures thereof. Other granular materials of finer grades may also be included in the filler material if necessary. In this regard, in several embodiments, the first granular material of the first granular layer has a larger average particle size compared to the average particle size of the filler material.

[0054] A combination of the first granular layer (70) and the geogrid layer (60) is required to develop tensile and shear forces and for the appropriate performance of the geocell layer (80). The combination of the geogrid layer and the first granular layer provides: (1) a rigid and impermeable "floor" that enables the development of large rigidity in the geocell layer while compactly filling the fill material; (2) a barrier against the upward filling of fine granules from the subbase into the geocell layer; (3) an interface for high shear forces; and (4) mechanical separation between the subbase and the geocell layer so that the geocell layer can perform rigid and elastic beams while limiting strain to an elastic range.

[0055] Optionally, a covering layer (90) is subsequently placed on the geocell layer (80). This layer is formed from a compact material such as crushed stone, gravel, or sand. This layer may be considered to be made of a second granular material.

[0056] Optionally, the surface layer (100) may be placed on a covering layer (90) distributed on the geocell reinforced layer (80). The surface layer may comprise asphalt, concrete, or ballast.

[0057] This design allows the geogrid layer (60) to deform, thereby enabling the geogrid layer to harden and reinforce the first granular layer (70) located beneath the geocell layer (80). This configuration significantly further reduces stress and deformation passing through the interface between the subbase and the sub-base and through the subbase (50). The geogrid layer (60) and the first granular layer (70) also provide a rigid foundation for the geocell layer (80) by improving the tensile strength and shear strength performance of the best zone of the subbase (50). The geogrid layer (60) helps increase the fatigue resistance of the subbase and reduces downward "leakage" of fill from the geocell layer during the service life of the pavement system. To clarify, the first granular layer (70) separates the geogrid layer (60) from the geocell layer (80); The geogrid and geocell do not come into contact with each other when assembled.

[0058] The geocell layer (80) acts as a hard and rigid mattress that helps avoid localized excessive stress and distributes stress over a wide area of ​​the pavement system. These localized excessive stresses are the main cause of failure of pavement systems installed on soft subgrades. The filler material may be sand, gravel, crushed stone, or a mixture thereof.

[0059] A synergistic relationship is created between the geogrid layer and the geocell layer when separated by the first granular layer. The geogrid layer (60) is positioned below the geocell layer (80) at a sufficiently deformable distance along the geogrid layer, thereby allowing the subbase to be tensilely rigid against stress created by the expansion of the subbase. The design of the present invention can absorb large mechanical stress elastically with great fatigue resistance. In particular, the pavement system of the present invention exhibits enhanced resistance to multiple periodic mechanical loads, multiple expansion-contraction cases of the subbase, and freeze-thaw cycles over long time intervals.

[0060] It is believed that placing only one or more geogrid layers on the subgrade, not limited to theory alone, fails to adequately and successfully stiffen the subgrade layer due to (1) insufficient bending moment; and (2) geogrid layers with insufficient stiffness. Similarly, using only geocell layers on the subgrade may not be successful due to (1) insufficient tensile strength; and (2) an upward / downward yielding filling tendency caused by soil expansion-contraction or pressure applied by vehicles.

[0061] The present invention also includes a method for installing a paved road system on a soft subbase. Generally, soil is removed to expose the soft subbase. Next, at least one geogrid is applied to the subbase to form a geogrid layer. A sufficient amount of a first granular material is then applied onto the geogrid layer to form a first granular layer having an average thickness of 0.5 to 20 times the opening distance of the geogrid layer. At least one geocell is placed on the first granular layer and then filled with a filler material to form a geocell layer. A second granular material is applied onto the geocell layer and then compressed to form a covering layer on the geocell layer. If necessary, a surface layer is then applied onto the covering layer.

[0062] FIGS. 6 and FIGS. 7 are cross-sectional views of two additional embodiments of a paved road system including additional layers.

[0063] In FIG. 6, the paved road system comprises, as described above, a geogrid layer (60) formed on a subgrade layer (50), a first granular layer (70) disposed on the geogrid layer (60), and a geocell layer (80) disposed on the first granular layer (70). The first granular layer (70) has a thickness (75). A second granular layer (110) is subsequently disposed on the geocell layer (80). This second granular layer may be made from the same material as the first granular layer (70) or from the filling of the geocell layer. The second granular layer may be considered to be formed from a third granular material (as described above, the covering layer is formed from the second granular material). The second granular layer has a thickness (115) that may be about 10 mm to about 500 mm. The second geocell layer (120) is subsequently disposed on the second granular layer (110). This second geocell layer is also formed from at least one geocell and filled with a filler material, as described above in relation to the geocell layer (80). A covering layer (90) is subsequently disposed on the second geocell layer (120), and optionally, a surface layer (100) may be disposed on the covering layer (90). The covering layer and the surface layer may be made as described above in FIG. 5. The second geocell layer (120) provides additional tensile strength to the system, resisting bending from the subgrade that may occur during clay expansion or during freeze-thaw cycles.

[0064] In FIG. 7, the paved road system comprises, as described above, a geogrid layer (60) formed on a subgrade layer (50), a first granular layer (70) disposed on the geogrid layer (60), and a geocell layer (80) disposed on the first granular layer (70). The first granular layer (70) has a thickness (75). A second granular layer (110) is subsequently disposed on the geocell layer (80), having a composition as described above. The second granular layer has a thickness (115) that may be about 1 mm to about 300 mm. A second geogrid layer (130) is subsequently disposed on the second granular layer (110). The second geogrid layer is formed from at least one geogrid. The covering layer (90) is subsequently placed on the second geogrid layer (130), and optionally, the surface layer (100) may be placed on the covering layer (90). The covering layer and the surface layer may be made as described above in FIG. 5. The material used to form the covering layer may fall into the opening of the second geogrid layer (130). The second geogrid layer (130) also provides additional tensile strength to the system, resisting bending from the subgrade that may occur during clay expansion or during freeze-thaw cycles.

[0065] In another considered embodiment, the second geogrid layer or the second geocell layer may be placed directly on the first geocell layer after the filling in the first geocell layer has been compacted. The second granular layer is not required. The distance between the first geocell layer and the second geogrid layer or the second geocell layer can be adjusted accordingly from nearly 0 to about 500 millimeters as needed to obtain the required total pavement modulus and fatigue resistance.

[0066] Furthermore, as required, the geotextile layer may be placed anywhere in the pavement system between the top layer of the pavement system and the subbase (i.e., the geotextile layer is never the top layer of the system). The geotextile is a two-dimensional permeable textile that may be woven or nonwoven and is used to prevent the upward penetration or loss of fine particles into the surface of the pavement. The geotextile may differ from a geogrid in that the geotextile is not permeable to soil, whereas the openings of a geogrid are large enough to allow soil strike-through from one side of the geogrid to the other. The geotextile layer is preferably used in areas subject to flooding, heavy rain, or high groundwater levels. The geotextile layer may be made from fabric having a specific weight of 50 grams per square meter (g / m²) to 3000 g / m².

[0067] It will be understood that the present invention also presents only exemplary working examples below, and these examples are for illustrative purposes only, and the present invention is not limited to materials, conditions, process parameters, and those mentioned herein.

[0068] Examples

[0069] The railway trail was stretched on an expansive clay subgrade having a CBR of 3 when wetted with water. Periodic maintenance of the trail was required, and train speeds were limited on this subgrade. The conventional design was compared with an alternative design as described in the present invention.

[0070] FIG. 8 shows the base layer (H) as a function of the CBR of the subgrade to obtain the required elastic modulus of the base layer. SUB-AThis is a graph showing the calculated thickness of ). For example, to obtain an elastic modulus of 100 kPa with a subgrade CBR of 3, the thickness of the base layer would need to be 750 mm. This elastic modulus is sufficient for conventional railway pavement designs in Israel.

[0071] Conventional designs were first prepared using sand or lime to stabilize a 600 mm subgrade. Next, 920 mm of crushed stone was applied and compacted, and subsequently, 300 mm of gravel was applied and compacted. Ballast and trackway ties were then placed on the pavement system.

[0072] An alternative design was constructed as described below. The combination coefficients of the geogrid-reinforced layer and the geocell-reinforced layer were measured separately on a model pavement, and said layer was installed on a subbase having a known CBR on said model pavement. A pressure shell was positioned beneath the geogrid layer. Increasing pressure was applied to the top of the geocell layer by a plate or vehicle wheel until plastic (irreversible) deformation occurred. Based on the pressure drop curve, the layer coefficient was recalculated. Based on the plastic deformation after a series of repeated loading applications, the degree of "immunity" to long-term stress was evaluated.

[0073] At the site, the alternative design was prepared by first leveling the subgrade. A first geogrid layer was applied and covered by a 200 mm thick layer of crushed stone. A first geocell layer was subsequently applied over the crushed stone layer. The first geocell layer had a height of 150 mm, and the geocells had a distance of 330 mm between seams. The fill material was crushed stone. A second granular layer 50 mm thick was subsequently applied over the first geocell layer, and a second geocell layer with the same composition as the first geocell layer was applied. Ballast and trackway ties were subsequently placed on the second geocell layer.

[0074] The difference in required materials was very clear between the two designs. The conventional design required 1220 mm of granular material followed by 600 mm of sand or lime treatment. In contrast, the alternative design required only 750 mm of granular material and provides significant cost savings.

[0075] A one-year study of the performance of two designs was conducted in Israel. The conventional design experienced continuously increasing plastic twisting over time. The result was that train speeds were slower and maintenance was required at short intervals. An alternative design using a geogrid and two geocell layers exhibited pure elastic performance without irreversible twisting.

[0076] It will be understood that the embodiments of features and operations described above and other features or alternatives thereto may be incorporated into many other different systems or applications. It will also be understood that various currently unforeseen or unforeseen alternative embodiments, modifications, changes, or improvements in the present invention may also be made by those skilled in the art within the scope of the claims set forth below.

Claims

Claim 1 A pavement road system installed on a soft subbase having a California Bearing Ratio (CBR) of 4 or less, wherein stress due to freeze-thaw cycles of the subbase is applied upward and downward from the subbase, and which is disposed on the said subbase and has 50 g / m² 2 Up to 3000g / m² 2 A geotextile layer made of a two-dimensional permeable fabric having a weight; a first geogrid layer disposed on the geotextile and made of at least one geogrid, wherein each geogrid is made of a rib member intersecting to form a geogrid opening; a first granular layer disposed on the first geogrid layer and containing a first granular material; a first geocell layer disposed on the first granular layer and containing at least one geocell filled as a filler material; a second granular layer disposed on the first geocell layer and containing the same material as the first granular material; a second geogrid layer disposed on the second granular layer; A paved road system comprising: a covering layer disposed on the second geogrid layer; wherein the first and second granular layers have an average thickness of 0.5 to 20 times the opening distance of the first geogrid layer. Claim 2 A paved road system according to claim 1, wherein the first granular material is sand, gravel, or crushed stone. Claim 3 A paved road system according to claim 1, wherein the opening distance is 10 millimeters to 500 millimeters. Claim 4 A paved road system according to claim 1, wherein the first geocell layer has a cell height of 50 millimeters to 300 millimeters. Claim 5 A paved road system according to claim 1, wherein the first geocell layer has a cell size of 200 millimeters to 600 millimeters. Claim 6 A paved road system according to claim 1, wherein the first granular material has an average particle size larger than that of the filler material.

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