Permafrost roadbed cooling structure for reducing differential settlement of road surface

Abstract

The utility model relates to a permafrost roadbed cooling structure for reducing differential settlement of a road surface. The permafrost roadbed cooling structure comprises a block stone extrusion layer arranged in a natural foundation, an embankment arranged on the block stone extrusion layer, ventilation bricks arranged on the embankment, a plurality of L-shaped hot rods, a U-shaped drainage ditch and a water seepage blind ditch. The natural foundation is a permafrost region road foundation; a transverse drainage slope is arranged at the bottom of the block stone extrusion layer, and waterproof geotechnical cloth I and a water guide pipe are laid on the transverse drainage slope; the embankment is formed by paving a cushion layer, filling soil and an asphalt pavement from bottom to top in sequence; waterproof geotextile III and permeable geotextile are laid on the cushion layer; waterproof geotechnical cloth II is laid on the slope surface of the filled soil; a reinforced grating and an insulation board are laid in the filling soil; the plurality of L-shaped hot rods are inserted into slope toes on two sides of the embankment; a U-shaped drainage ditch and a water seepage blind ditch are arranged on each of the two sides of the roadbed. According to the utility model, the problem of permafrost degradation below due to heat absorption of the roadbed in a permafrost region and the problem of longitudinal cracking of the pavement due to non-uniform deformation of the roadbed are effectively solved.

Description

Technical Field

[0001] The utility model relates to the technical field of temperature control of frozen soil roadbeds, in particular to a permafrost roadbed cooling structure for reducing uneven road surface settlement. Background Art

[0002] Permafrost is widely distributed on the Qinghai-Tibet Plateau, covering an area of ​​about 1.5 million square kilometers. As the Qinghai-Tibet Plateau is located in the middle and low latitudes, the permafrost distributed in this area is generally characterized by high temperature and small thickness, and is extremely sensitive to climate change. As the trend of global warming intensifies, the permafrost on the Qinghai-Tibet Plateau will continue to degrade. Since the strength and deformation of permafrost are significantly affected by temperature changes, the degradation of permafrost on the Qinghai-Tibet Plateau will cause thawing and settlement of the natural foundation, and the thawing and settlement of the natural surface will cause the roadbed to sink. As a result, potholes, transverse cracks and longitudinal cracks will occur on the road surface. This poses a huge challenge to the stability of road infrastructure in permafrost areas.

[0003] The construction of the roadbed will change the thermophysical properties of the natural surface, making the roadbed show the characteristics of heat absorption. The roadbed continuously heats the permafrost below, causing the degradation of permafrost. Under the action of temperature gradient and gravity potential, the meltwater of permafrost transfers to the frozen soil layer, further expanding the range of heat conduction, causing a larger area of ​​permafrost degradation and then causing settlement. In addition, affected by the direction, slope and sun angle of the road, the heat absorption of the sunny slope of the roadbed is much greater than that of the shady slope. This phenomenon is called the yin-yang slope effect. Affected by the yin-yang slope effect, the settlement of the sunny side of the roadbed is much greater than that of the shady side, causing longitudinal cracks in the road surface. Although there are many protective measures available to reduce the temperature of the roadbed, such as reflectors, insulation boards and ventilation pipes, in actual applications, due to their own defects, pavement diseases still occur from time to time, especially longitudinal cracks caused by uneven settlement of the roadbed. This shows that the current cooling structure is still unable to complete the protection of the road surface well. Studies have shown that the damage of the road surface is closely related to the distribution of the permafrost temperature field under the roadbed. When the temperature distribution of permafrost under the roadbed is uneven, the uneven settlement caused by permafrost degradation is the main factor leading to road damage.

[0004] Based on the above considerations, it is urgent to seek new cooling structures to protect the permafrost under the roadbed from degradation on the one hand, and to eliminate the uneven temperature distribution of the permafrost under the roadbed on the other hand, so as to reduce the uneven settlement of the road surface caused by the degradation of permafrost, thereby ensuring the stability of roads in permafrost areas. Utility Model Content

[0005] The technical problem to be solved by the utility model is to provide a permafrost roadbed cooling structure which has a significant effect in reducing uneven road surface settlement.

[0006] In order to solve the above problems, the utility model discloses a permafrost roadbed cooling structure for reducing uneven settlement of the road surface, characterized in that the structure comprises a block stone extrusion layer placed in a natural foundation, an embankment placed on the block stone extrusion layer, and ventilation bricks, a plurality of L-shaped heat rods, a U-shaped drainage ditch and a seepage blind ditch arranged on the embankment; the natural foundation is a highway foundation in a permafrost area; the top of the block stone extrusion layer is flush with the surface of the natural foundation, and the bottom is a herringbone-shaped lateral drainage slope of 4% on both sides, and the lateral drainage slope is paved with impermeable geotextile I; a water guide pipe is laid on the lateral drainage slope and is connected to the seepage blind ditch; the embankment is composed of a cushion layer, fill soil, and asphalt pavement laid in sequence from bottom to top, and the overall shape is a symmetrical trapezoid that is narrow on the top and wide on the bottom, and the slope of the slope is 1:1.5; the upper surface of the cushion layer is paved with impermeable geotextile III, and the lower surface is paved with permeable geotextile; the The slope of the fill is paved with impermeable geotextile II; reinforced grids and insulation boards are laid in the fill; a plurality of L-shaped heat rods are inserted at the left and right slope feet of the embankment, and are composed of an evaporation section and a condensation section connected through each other; the evaporation section is bent and connected with the condensation section, and the direction of the evaporation section is perpendicular to the direction of the embankment and is obliquely buried in the natural foundation and the block stone extrusion layer, and the condensation section is vertically arranged and exposed to the air; a U-shaped drainage ditch and a seepage blind ditch are arranged on each side of the roadbed; the directions of the U-shaped drainage ditch and the seepage blind ditch are parallel to the direction of the embankment; the top of the U-shaped drainage ditch is flush with the surface of the natural foundation, and the surface of the natural foundation on the side of the U-shaped drainage ditch away from the embankment is piled with water-retaining soil; the upper part of the seepage blind ditch is connected to the bottom of the U-shaped drainage ditch, and the center is on the same vertical line as the U-shaped drainage ditch.

[0007] The slope of the water conduit is consistent with the slope of the lower surface of the block stone extrusion layer.

[0008] The thickness of the block stone extrusion layer is 1.5~2.0 m, the block stone particle size is selected to be 150~300 mm, the minimum side length is greater than 150 mm, the slenderness ratio is less than 3, the strength is not less than 30 MPa, the crushing value is not more than 25%, and the porosity is not less than 25%.

[0009] The ventilation bricks are in a concave shape and are laid randomly on the embankment slope. The surface exposed to the air is painted white. The thickness of the sunny slope is twice that of the shady slope. The top is flush with the asphalt pavement and the bottom is connected to the cushion layer.

[0010] The angle between the L-shaped heat rod and the natural foundation is 5~10°, and the length of the evaporation section is 8~9 m; the horizontal spacing between the ends of the evaporation sections on both sides of the embankment is 1.0~1.5 m, and the longitudinal spacing is 1.5~2.5 times the effective cooling radius of the L-shaped heat rod.

[0011] The cushion layer is made of natural gravel or medium-coarse sand, with a thickness of not less than 300 mm and a mud content of not more than 5%.

[0012] The reinforced grid is single-layer or multi-layer, and is laid at different positions of the fill; two adjacent reinforced grids are connected by U-shaped steel bars, the steel bar spacing is 2 m, and are wrapped 2 m on the slope of the embankment.

[0013] The insulation board is buried 150 cm below the asphalt pavement and has a thickness of 10 cm.

[0014] The U-shaped drainage ditch uses C30 concrete prefabricated blocks, with exposed lines set at 5 mm chamfers, impermeable geotextile IV laid on both sides of the ditch wall and the bottom of the ditch, and cement mortar cushion layers poured on both sides of the ditch wall and the bottom of the ditch.

[0015] A C20 concrete cushion layer is poured at the bottom of the seepage blind ditch and filled with coarse granular filler; an impermeable geotextile V is arranged on the ditch wall and the bottom of the seepage blind ditch.

[0016] Compared with the prior art, the utility model has the following advantages:

[0017] 1. The ventilation bricks in this utility model have the characteristics of "thermal semiconductor".

[0018] In the cold season, the natural convection of air in the ventilation bricks allows the heat in the embankment to be discharged from the embankment, cooling the frozen soil below. In the summer, the natural convection of air in the ventilation bricks stops, and the air with low thermal conductivity in the ventilation bricks prevents heat from entering the roadbed, protecting the permafrost below. At the same time, the ventilation bricks painted with white paint have the ability to reflect solar radiation, which can effectively reduce the absorption of heat by the embankment slope and reduce the degradation of permafrost below the embankment. In addition, the ventilation bricks with different thicknesses on the sunny and shady sides can regulate the yin and yang slope effects of the embankment, solve the uneven settlement of the sunny and shady slopes of the roadbed, and avoid the problem of longitudinal cracks caused by uneven deformation.

[0019] 2. The reinforced grille in the utility model has a locking effect.

[0020] The reinforced grid can absorb part of the strain energy, reduce the lateral displacement of the embankment fill, and thus cause the embankment to deform laterally more slowly, thereby improving the overall strength of the embankment, inhibiting the generation and development of cracks to a certain extent, improving the bearing capacity and stability of the embankment, and extending the service life of the road.

[0021] 3. The utility model is provided with an insulation board with a heat-insulating effect. On the one hand, the insulation board can prevent the heat absorbed by the road surface from being conducted downward into the permafrost layer below; on the other hand, it can prevent the cold energy brought into the permafrost layer by the heat pipe from being transferred to the external environment, thereby effectively protecting the permafrost.

[0022] 4. The utility model effectively utilizes the drainage function of the U-shaped drainage ditch and the seepage blind ditch.

[0023] U-shaped drainage ditches and seepage blind ditches can drain surface water and active layer groundwater in layers, discharge external precipitation and permafrost meltwater out of the strata, avoid the transfer of permafrost meltwater to the frozen soil layer under the influence of temperature gradient and gravity potential, and reduce the thermal impact range of meltwater.

[0024] 5. The utility model utilizes L-shaped heat rod evaporation condensation to achieve permafrost cooling.

[0025] In winter, the heat pipes start working, and the heat in the permafrost layer is discharged to the outside environment by evaporation and condensation of the working fluid in the heat pipes, which cools the permafrost below. In summer, the heat pipes stop working, and the heat from the outside can only be transferred to the permafrost below through the embankment fill. Compared with the heat pipes discharging the heat in the permafrost to the outside environment in winter, the heat transfer from the embankment fill to the permafrost in summer is much slower, so the heat pipes play a role in protecting the permafrost.

[0026] 6. The utility model is provided with a block stone extrusion layer, and the block stone extrusion layer has the natural convection effect of air and the heat insulation effect.

[0027] In winter, the air in the rock squeeze layer will undergo natural convection, and during the process of air convection, the cold energy brought into the permafrost by the heat pipe will be quickly and evenly distributed to the stratum, keeping the temperature of the permafrost stable. In summer, the air in the rock squeeze layer will not undergo natural convection, and the heat from the outside needs to be transferred through the air with low thermal conductivity in the rock squeeze layer to enter the permafrost. Therefore, the rock squeeze layer also plays a role in protecting the permafrost below.

[0028] 7. The structure of the utility model can effectively solve the problem of degradation of the permafrost below due to heat absorption of the roadbed in permafrost areas and the problem of longitudinal cracking of the road surface due to uneven deformation of the roadbed. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The specific implementation of the utility model is further described in detail below with reference to the accompanying drawings.

[0030] Figure 1 It is a cross-sectional view of a permafrost roadbed cooling structure for reducing uneven road surface settlement in an embodiment of the utility model.

[0031] Figure 2 It is a top view of a permafrost roadbed cooling structure for reducing uneven road surface settlement in an embodiment of the utility model.

[0032] Figure 3 It is a cross-sectional view of the drainage ditch and the seepage blind ditch in the embodiment of the utility model.

[0033] Figure 4 It is a schematic diagram of ventilation bricks in an embodiment of the utility model.

[0034] Figure 5 This is a schematic diagram of the buried connection of the L-shaped heat rod in the embodiment of the utility model.

[0035] Figure 6 It is a schematic diagram of the reinforced grille in the embodiment of the utility model.

[0036] Figure 7 The utility model is a flow chart of the construction method of the permafrost roadbed cooling structure for reducing uneven road surface settlement.

[0037] Figure 8 This is the temperature field distribution diagram of the traditional heat pipe roadbed.

[0038] Fig. 9 This is a temperature field distribution diagram of an embodiment of the utility model.

[0039] Fig.10 It is the deformation of the positive slope shoulder, the center of the roadbed and the negative slope shoulder of the traditional heat pipe roadbed.

[0040] Fig.11 It is the deformation of the positive slope shoulder, the center of the roadbed and the negative slope shoulder of the roadbed in the embodiment of the utility model.

[0041] In the figure: 1—natural foundation; 2—block squeezed layer; 3—embankment; 4—cushion; 5—reinforced grid; 6—insulation board; 7—fill; 8—asphalt pavement; 9—ventilation brick; 10—L-shaped heat rod; 11—U-shaped drainage ditch; 12—seepage blind ditch; 13—water guide pipe; 14—impermeable geotextile I; 15—permeable geotextile; 16—coarse particle filler; 17—C20 concrete cushion; 18—cement mortar cushion; 19—water retaining soil twist; 20—impermeable geotextile II; 21—impermeable geotextile III; 22—impermeable geotextile IV; 23—impermeable geotextile V. DETAILED DESCRIPTION

[0042] like Figures 1 to 6 As shown, a permafrost roadbed cooling structure for reducing uneven settlement of the road surface includes a block stone extrusion layer 2 placed in a natural foundation 1, an embankment 3 placed on the block stone extrusion layer 2, and ventilation bricks 9, a plurality of L-shaped heat rods 10, a U-shaped drainage ditch 11 and a seepage blind ditch 12 arranged on the embankment 3.

[0043] The natural foundation 1 is a highway foundation in a permafrost region; the top of the block stone squeeze layer 2 is flush with the surface of the natural foundation 1, and the bottom is a herringbone lateral drainage slope of 4% on both sides, and the lateral drainage slope is paved with an impermeable geotextile I14 to prevent water from seeping downward into the natural foundation 1. A water guide pipe 13 is laid on the lateral drainage slope and is connected to the seepage blind ditch 12 to drain the water accumulated on the impermeable geotextile I14 to the seepage blind ditch. The embankment 3 is the main body of the roadbed, which is composed of a cushion layer 4, a fill 7, and an asphalt pavement 8 laid in sequence from bottom to top. The overall shape is a symmetrical trapezoid that is narrow at the top and wide at the bottom, and the slope is 1:1.5; the upper surface of the cushion layer 4 is paved with an impermeable geotextile III 21, and the lower surface is paved with a permeable geotextile 15; the slope surface of the fill 7 is paved with an impermeable geotextile II 20; a reinforced grid 5 and an insulation board 6 are laid in the fill 7; a plurality of L-shaped heat rods 10 are inserted at the left and right sides of the embankment 3, and are composed of an evaporation section and a condensation section connected through; the evaporation section is connected to the condensation section in a bent manner, and the direction of the evaporation section is aligned with the embankment 3. The drainage ditch 11 is vertical and obliquely buried in the natural foundation 1 and the block stone extrusion layer 2, and the condensation section is vertically arranged and exposed to the air; a U-shaped drainage ditch 11 and a seepage blind ditch 12 are arranged on both sides of the roadbed 3; the directions of the U-shaped drainage ditch 11 and the seepage blind ditch 12 are parallel to the direction of the embankment 3; the top of the U-shaped drainage ditch 11 is flush with the surface of the natural foundation 1, and the surface of the natural foundation 1 on the side of the U-shaped drainage ditch 11 away from the embankment 3 is piled with retaining soil 19; the upper part of the seepage blind ditch 12 is connected to the bottom of the U-shaped drainage ditch 11, and the center is on the same vertical line as the U-shaped drainage ditch 11.

[0044] The slope of the water pipe 13 is consistent with the slope of the lower surface of the block stone extrusion layer 2, and a HPPE pipe or a sandless concrete pipe can be used.

[0045] The thickness of the rock extrusion layer 2 is 1.5~2.0 m, the rock particle size is 150~300 mm, the minimum side length is greater than 150 mm, the slenderness ratio is less than 3, the strength is not less than 30 MPa, the crushing value is not more than 25%, and the porosity is not less than 25%.

[0046] The ventilation bricks 9 are in a concave shape and are laid randomly on the slope of the embankment 3 as slope protection. The surface exposed to the air is painted white. The thickness of the sunny slope is more than twice the thickness of the shady slope. The top is flush with the asphalt pavement 8, and the bottom is connected to the cushion layer 4. The compressive strength of the ventilation bricks 9 is not less than 5MPa, and the freeze-thaw resistance is not less than 3.5MPa. The thickness of the top surface and the brick belly is 5 cm, and the outer contour is a cube with a side length of 30 cm.

[0047] The angle between the L-shaped heat rod 10 and the natural foundation 1 is 5-10°, and the length of the evaporation section is 8-9 m; the horizontal spacing between the ends of the evaporation sections on both sides of the embankment 3 is 1.0-1.5 m, and the longitudinal spacing is 1.5-2.5 times the effective cooling radius of the L-shaped heat rod 10. The L-shaped heat rod 10 is calculated according to the use requirements and geological conditions to determine the corresponding specifications and shapes, and is generally required to have a service life of no less than 30 years.

[0048] The cushion layer 4 is made of natural gravel or medium-coarse sand with a thickness of not less than 300 mm and a mud content of not more than 5%.

[0049] The filling material of fill 7 must comply with the requirements of relevant specifications and relevant design documents, and frozen soil shall not be used as filling material.

[0050] The reinforced grid 5 is a single layer or multiple layers, which is laid at different positions of the fill 7 to strengthen the integrity of the embankment 3. Two adjacent reinforced grids 5 are connected by U-shaped steel bars, with a steel bar spacing of 2 m, and are reversed by 2 m on the slope of the embankment 3. The reinforced grid 5 adopts a composite geogrid, which meets the requirements of node thickness ≥3.5 mm, mid-rib aspect ratio ≥1.0, radial tensile secant modulus at 2% strain ≥130 kN / m, oxidation resistance strength retention rate ≥90%, UV resistance strength retention rate ≥90%, and acid and alkali resistance strength retention rate ≥90%.

[0051] The insulation board 6 is buried 150 cm below the asphalt pavement 8 and has a thickness of 10 cm. It is made of a board with high strength and good toughness such as molded polystyrene foam (EPS), polyurethane foam (PU) or extruded polystyrene foam (XPS).

[0052] The U-shaped drainage ditch 11 uses C30 concrete prefabricated blocks, with 5 mm chamfers set on the exposed lines, impermeable geotextile IV 22 laid on both sides of the ditch wall and the bottom of the ditch, and cement mortar cushion layers 18 poured on both sides of the ditch wall and the bottom of the ditch.

[0053] The bottom of the seepage blind ditch 12 is poured with a C20 concrete cushion layer 17 and filled with coarse-grained filler 16; the wall and bottom of the seepage blind ditch 12 are provided with an impermeable geotextile V23. The coarse-grained filler 16 is made of clean gravel, coarse sand, crushed stone and flaked stone, of which the content of fine particles less than 2.36 mm shall not be greater than 5%.

[0054] like Figure 7 As shown, a construction method of a permafrost roadbed cooling structure for reducing uneven road settlement comprises the following steps:

[0055] (1) Excavate the working surface on the ground of natural foundation 1, take the center point of roadbed 3 as the axis of symmetry, excavate a herringbone drainage slope of 4% on both sides at the bottom, and level and compact the excavated working surface slope.

[0056] (2) After laying impermeable geotextile I14 on the slope of the working face after excavation, throw the blocks into the working face and extrude them layer by layer. At the same time, bury the evaporation section of the L-shaped heat rod 10, and expose the top 1 m of the block extrusion layer 2 by bending the connecting opening.

[0057] ⑶ Level the top of the block stone extrusion layer 2, lay the permeable geotextile 15, and then lay the cushion layer 4. After completion, lay a layer of impermeable geotextile III 21 on the top surface of the cushion layer 4.

[0058] (4) Hoist the condensing section of the L-shaped heat rod 10, clamp the top groove of the L-shaped heat rod 10 with a bayonet hoist (1 / 4 D-type shackle G-210 of Beijing Feiying Hoisting and Sling Co., Ltd.), lift it with a crane with an arm length of more than 15 m, align it with the bent connection opening of the L-shaped heat rod 10 exposed on the surface of the cushion layer 4, and then connect and install it.

[0059] (5) Seal the hole gap between the L-shaped heat rod 10 and the cushion layer 4 with cement mortar.

[0060] (6) Fill the soil 7 in layers. When the soil reaches the designed elevation of the reinforced grid 5 and the insulation board 6, lay the reinforced grid 5 and the insulation board 6. Fill the embankment 3 in sections. When filling the junction of two sections at the same time, overlap and compact the layers. When filling at different times, make steps with a height not more than 1 m and a width not less than 1.5 m in the first filled section.

[0061] ⑺ Use bulldozer for initial leveling and grader for final leveling, with the principle that there should be no obvious local unevenness on the top surface of embankment 3. Then, the top surface of embankment 3 is made into a 4% lateral drainage slope on both sides.

[0062] ⑻ Use heavy-duty vibratory rollers to compact the embankment 3 along the longitudinal direction of the line from both sides to the middle; the first pass is static compaction, then from slow to fast, from weak vibration to strong vibration. When rolling, the intersections of each section overlap and compact.

[0063] ⑼ After repairing the slope of the fill 7, removing loose soil, filling pits and making the slope flat, lay impermeable geotextile II 20 along the entire longitudinal section of the slope of the fill 7; then lay ventilation bricks 9 from bottom to top on both sides of the embankment 3; after the slope protection is laid, paint the surface of the ventilation bricks 9 exposed to the air white.

[0064] ⑽Use a trencher + excavator in frozen soil areas to excavate the seepage blind ditch 12 and the U-shaped drainage ditch 11.

[0065] ⑾ Drill holes in the ditch wall of the seepage blind ditch 12 near the embankment 3 to add a water guide pipe 13, and at the same time lay impermeable geotextile V23 on the left and right sides of the seepage blind ditch 12 to form an anti-filtration layer A; pour a C20 concrete cushion layer 17 at the bottom of the seepage blind ditch 12, and after sealing the bottom, lay a layer of impermeable geotextile V23 to form an anti-filtration layer B, and then fill the seepage blind ditch 12 with coarse granular filler 16; finally, apply impermeable geotextile IV22 on the top of the seepage blind ditch 12.

[0066] ⑿ Lay impermeable geotextile IV 22 on the wall of the U-shaped drainage ditch 11, then pour the cement mortar cushion layer 18, and assemble the overall prefabricated block U-shaped drainage ditch 11 on site.

[0067] ⒀The excavated soil is piled up to form a water retaining soil pile 19.

[0068] Example:

[0069] A permafrost roadbed cooling structure for reducing uneven road settlement, comprising a natural foundation 1, a stone layer 2, an embankment 3, ventilation bricks 9, an L-shaped heat rod 10, a U-shaped drainage ditch 11, and a seepage blind ditch 12. Among them:

[0070] The natural foundation 1 is the highway foundation in the permafrost area.

[0071] The top of the block extrusion layer 2 is flush with the surface of the natural foundation 1, and the bottom is a herringbone lateral drainage slope of 4% on both sides. The lateral drainage slope is paved with an impermeable geotextile Ⅰ14 to prevent water from seeping down into the natural foundation 1. A water pipe 13 is laid on the lateral drainage slope and connected to the seepage blind ditch 12.

[0072] The embankment 3 is composed of a cushion layer 4, a fill 7, and an asphalt pavement 8, which are laid in sequence from bottom to top. The overall shape is a symmetrical trapezoid that is narrow at the top and wide at the bottom, and the slope is 1:1.5. Reinforced grids 5 and insulation boards 6 are laid in the fill 7; the reinforced grids 5 are laid in a single layer 200 cm below the asphalt pavement 8 to strengthen the integrity of the roadbed, and the insulation board 6 is buried 150 cm below the pavement with a thickness of 10 cm. Impermeable geotextile II 20 is laid on the slope of the fill 7. The thickness of the asphalt pavement 8 is 0.15 m.

[0073] Ventilation bricks 9 are laid randomly on the slope of embankment 3 for slope protection. The surface exposed to the air is painted white. The thickness of the sunny slope is 0.8 m and the thickness of the shady slope is 0.4 m. The top is flush with the asphalt pavement 8 and the bottom is connected to the cushion layer 4.

[0074] There are multiple L-shaped heat rods 10, which are placed at the left and right slope feet of the embankment 3, and are composed of an evaporation section and a condensation section that are connected through each other; the evaporation section and the condensation section are connected in a bending manner, and the direction of the evaporation section is perpendicular to the direction of the embankment 3 and is obliquely buried in the natural foundation 1 and the block stone squeeze layer 2, and the condensation section is vertically arranged and exposed to the air.

[0075] A U-shaped drainage ditch 11 and a seepage blind ditch 12 are arranged on both sides of the embankment 3, and their directions are parallel to the direction of the embankment 3. The top of the U-shaped drainage ditch 11 is flush with the surface of the natural foundation 1, and the upper part of the seepage blind ditch 12 is connected to the bottom of the U-shaped drainage ditch 11, and the center is on the same vertical line as the U-shaped drainage ditch 11.

[0076] The thickness of the rock compression layer 2 is 1.5 m, the rock particle size is 200 mm, the minimum side length is greater than 150 mm, the slenderness ratio is less than 3, the strength is not less than 30 MPa, the crushing value is not more than 25%, and the porosity is not less than 25%.

[0077] The cushion layer 4 is made of natural gravel with a thickness of 300 mm and a mud content of no more than 5%. At the same time, an impermeable geotextile III 21 is laid on the upper surface of the cushion layer 4 and a permeable geotextile 15 is laid on the lower surface.

[0078] The reinforced grid 5 adopts composite geogrid, which meets the requirements of node thickness of 3.5 mm, mid-rib aspect ratio ≥1.0, radial tensile secant modulus at 2% strain ≥130kN / m, oxidation resistance strength retention rate ≥90%, UV resistance strength retention rate ≥90%, and acid and alkali resistance strength retention rate ≥90%. U-shaped steel bars are used for the connection of reinforced grid 5, with a steel bar spacing of 2 m and a 2 m reverse wrap of the embankment slope.

[0079] The material of the insulation board 6 is molded polystyrene foam (EPS).

[0080] The fill material of the fill 7 is pebble soil.

[0081] The compressive strength of the ventilation brick 9 is not less than 5MPa, the freeze-thaw resistance is not less than 3.5MPa, the shape is concave, the outer contour is a cube with a side length of 30 cm, and the thickness of the top surface and the brick belly is 5 cm.

[0082] The angle between the L-shaped heat rod 10 and the natural foundation 1 is 10°, and the length of the evaporation section is 8-9 m; the horizontal spacing between the ends of the evaporation sections on both sides of the embankment 3 is 1.3 m, and the longitudinal spacing is twice the effective cooling radius of the L-shaped heat rod 10. The L-shaped heat rod 10 is calculated according to the use requirements and geological conditions to determine the corresponding specifications and shapes, and is generally required to have a service life of no less than 30 years.

[0083] The U-shaped drainage ditch 11 uses C30 concrete prefabricated blocks, with 5 mm chamfers on the exposed lines, impermeable geotextile IV22 laid on both sides of the ditch wall and the bottom of the ditch, and cement mortar cushion 18 poured on both sides of the ditch wall and the bottom of the ditch. In the U-shaped drainage ditch 11, the surface of the natural foundation 1 away from the side of the embankment 3 is piled with water retaining soil 19.

[0084] The bottom of the seepage blind ditch 12 is poured with a C20 concrete cushion layer 17 and filled with coarse-grained filler 16; the wall and bottom of the seepage blind ditch 12 are provided with an impermeable geotextile V23. The coarse-grained filler 16 is made of clean gravel, coarse sand, crushed stone and flaked stone, of which the content of fine particles less than 2.36 mm shall not be greater than 5%.

[0085] The water pipe 13 is used to connect the block stone squeeze layer 2 and the seepage blind ditch 12. The slope is consistent with the slope of the lower surface of the block stone squeeze layer 2. Sandless concrete pipes can be used.

[0086] The construction method is as follows:

[0087] (1) Excavate the working surface on the ground of natural foundation 1, take the center point of roadbed 3 as the axis of symmetry, excavate a herringbone drainage slope of 4% on both sides at the bottom, and level and compact the excavated working surface slope.

[0088] (2) After laying impermeable geotextile I14 on the slope of the working face after excavation, throw the blocks into the working face and extrude them layer by layer. At the same time, bury the evaporation section of the L-shaped heat rod 10, and expose the top 1 m of the block extrusion layer 2 by bending the connecting opening.

[0089] ⑶ Level the top of the block stone extrusion layer 2, lay the permeable geotextile 15, and then lay the cushion layer 4. After completion, lay a layer of impermeable geotextile III 21 on the top surface of the cushion layer 4.

[0090] (4) Lift the condensing section of the L-shaped heat rod 10, clamp the top groove of the L-shaped heat rod 10 with a bayonet lifter, lift it with a crane with an arm length of more than 15 m, align it with the bent connection opening of the L-shaped heat rod 10 exposed on the surface of the cushion layer 4, and then connect and install it.

[0091] (5) Seal the hole gap between the L-shaped heat rod 10 and the cushion layer 4 with cement mortar.

[0092] (6) Fill the soil 7 in layers. When the soil reaches the designed elevation of the reinforced grid 5 and the insulation board 6, lay the reinforced grid 5 and the insulation board 6. Fill the embankment 3 in sections. When filling the junction of two sections at the same time, overlap and compact the layers. When filling at different times, make steps with a height not more than 1 m and a width not less than 1.5 m in the first filled section.

[0093] ⑺ Use bulldozer for initial leveling and grader for final leveling, with the principle that there should be no obvious local unevenness on the top surface of embankment 3. Then, the top surface of embankment 3 is made into a 4% lateral drainage slope on both sides.

[0094] ⑻ Use heavy-duty vibratory rollers to compact the embankment 3 along the longitudinal direction of the line from both sides to the middle; the first pass is static compaction, then from slow to fast, from weak vibration to strong vibration. When rolling, the intersections of each section overlap and compact.

[0095] ⑼ After repairing the slope of the fill 7, removing loose soil, filling pits and making the slope flat, lay impermeable geotextile II 20 along the entire longitudinal section of the slope of the fill 7; then lay ventilation bricks 9 from bottom to top on both sides of the embankment 3; after the slope protection is laid, paint the surface of the ventilation bricks 9 exposed to the air white.

[0096] ⑽Use a trencher + excavator in frozen soil areas to excavate the seepage blind ditch 12 and the U-shaped drainage ditch 11.

[0097] ⑾ Drill holes in the ditch wall of the seepage blind ditch 12 near the embankment 3 to add a water guide pipe 13, and at the same time lay impermeable geotextile V23 on the left and right sides of the seepage blind ditch 12 to form an anti-filtration layer A; pour a C20 concrete cushion layer 17 at the bottom of the seepage blind ditch 12, and after sealing the bottom, lay a layer of impermeable geotextile V23 to form an anti-filtration layer B, and then fill the seepage blind ditch 12 with coarse granular filler 16; finally, apply impermeable geotextile IV22 on the top of the seepage blind ditch 12.

[0098] ⑿ Lay impermeable geotextile IV 22 on the wall of the U-shaped drainage ditch 11, then pour the cement mortar cushion layer 18, and assemble the overall prefabricated block U-shaped drainage ditch 11 on site.

[0099] ⒀The excavated soil is piled up to form a water retaining soil pile 19.

[0100] In order to verify the application effect of the permafrost roadbed cooling structure for reducing uneven road settlement in this embodiment, numerical simulation and comparison were conducted on the stratum temperature field and deformation process of the traditional heat pipe roadbed and the permafrost roadbed cooling structure for reducing uneven road settlement in the embodiment of the utility model:

[0101] like Figure 8 and Fig. 9 As shown in the figure, the upper limits of permafrost on the sunny shoulder, the center of the roadbed and the shady shoulder of the traditional heat pipe roadbed are respectively -0.78, 1.14 and 0.28 m, and the permafrost temperature distribution line under the roadbed is obviously asymmetric and uneven, which can easily cause uneven deformation of the road surface. After adopting the permafrost roadbed cooling structure of the utility model for reducing uneven settlement of the road surface, the upper limits of permafrost on the sunny shoulder, the center of the roadbed and the shady shoulder of the roadbed are respectively -0.81, -0.71 and -0.94 m, and the permafrost temperature distribution line under the roadbed is symmetrical and flat. Compared with the traditional heat pipe roadbed, although the upper limit of frozen soil under the roadbed after adopting the utility model is lower than that of the traditional heat pipe roadbed, the upper limit of frozen soil under the roadbed after adopting the utility model is still higher than the original natural frozen soil upper limit, indicating that the utility model can still protect permafrost. The outstanding feature of the utility model is that the distribution of ground temperature isotherms under the roadbed can be obviously symmetrical and flat.

[0102] like Fig.10 and Fig.11As shown, in the 20th year of operation of the traditional heat pipe roadbed, the deformations of the sunny shoulder, the center of the roadbed and the shady shoulder can reach -23.37, 5.43 and -15.73 cm respectively, and the differential settlement of the sunny shoulder and the center of the roadbed is 29.00 mm; after adopting the permafrost roadbed cooling structure of the utility model for reducing uneven settlement of the road surface, in the 20th year of operation, the deformations of the sunny shoulder, the center of the roadbed and the shady shoulder are -9.15, -12.92 and -14.80 mm respectively, and the differential settlement of the shady slope-sunny slope is 5.65 mm.

[0103] Compare Figure 8 and Fig. 9 ,as well as Fig.10 and Fig.11 It can be concluded that the utility model can protect permafrost and make the temperature distribution line of permafrost under the roadbed symmetrical and flat, effectively reducing the uneven settlement of the road surface.

[0104] The above content is only for explaining the technical idea of ​​the utility model and cannot be used to limit the protection scope of the utility model. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the utility model shall fall within the protection scope of the claims of the utility model.

Claims

1. A permafrost roadbed cooling structure for reducing uneven road settlement, characterized in that: The structure comprises a block stone squeeze layer (2) placed in a natural foundation (1), an embankment (3) placed on the block stone squeeze layer (2), and ventilation bricks (9), a plurality of L-shaped heat rods (10), a U-shaped drainage ditch (11) and a seepage blind ditch (12) arranged on the embankment (3); the natural foundation (1) is a highway foundation in a permafrost region; the top of the block stone squeeze layer (2) is flush with the surface of the natural foundation (1), and the bottom is a herringbone lateral drainage slope of 4% on both sides, and the lateral drainage slope is paved with an impermeable geotextile. Ⅰ (14); a water pipe (13) is laid on the transverse drainage slope and is connected to the seepage blind ditch (12); the embankment (3) is composed of a cushion layer (4), fill (7), and asphalt pavement (8) laid in sequence from bottom to top, and the overall shape is a symmetrical trapezoid that is narrow at the top and wide at the bottom, and the slope is 1:1.5; the upper surface of the cushion layer (4) is laid with an impermeable geotextile III (21), and the lower surface is laid with a permeable geotextile (15); the slope surface of the fill (7) is laid with an impermeable geotextile II (20); the fill (7) A reinforced grid (5) and an insulation board (6) are laid in the middle; a plurality of L-shaped heat rods (10) are inserted at the left and right slope feet of the embankment (3), and are composed of an evaporation section and a condensation section that are connected through; the evaporation section and the condensation section are connected in a bent manner, and the direction of the evaporation section is perpendicular to the direction of the embankment (3) and is obliquely buried in the natural foundation (1) and the block stone extrusion layer (2), and the condensation section is vertically arranged and exposed to the air; a U-shaped drainage ditch (11) and a water seepage blind ditch are respectively arranged on both sides of the embankment (3) (12); the directions of the U-shaped drainage ditch (11) and the seepage blind ditch (12) are both parallel to the direction of the embankment (3); the top of the U-shaped drainage ditch (11) is flush with the surface of the natural foundation (1), and the surface of the natural foundation (1) on the side of the U-shaped drainage ditch (11) away from the embankment (3) is piled with retaining soil (19); the upper part of the seepage blind ditch (12) is connected to the bottom of the U-shaped drainage ditch (11), and the center is on the same vertical line as the U-shaped drainage ditch (11).

2. A permafrost roadbed cooling structure for reducing uneven road settlement as claimed in claim 1, characterized in that: The slope of the water conduit (13) is consistent with the slope of the lower surface of the block stone extrusion layer (2).

3. A permafrost roadbed cooling structure for reducing uneven road settlement as claimed in claim 2, characterized in that: The thickness of the block stone extrusion layer (2) is 1.5-2.0 m, the block stone particle size is selected to be 150-300 mm, the minimum side length is greater than 150 mm, the slenderness ratio is less than 3, the strength is not less than 30 MPa, the crushing value is not greater than 25%, and the porosity is not less than 25%.

4. A permafrost roadbed cooling structure for reducing uneven road settlement as claimed in claim 1, characterized in that: The ventilation bricks (9) are in a concave shape and are laid randomly on the slope of the embankment (3). The surface exposed to the air is painted white. The thickness of the sunny slope is more than twice the thickness of the shady slope. The top is flush with the asphalt pavement (8) and the bottom is connected to the cushion layer (4).

5. The permafrost roadbed cooling structure for reducing uneven road settlement as claimed in claim 1, characterized in that: The angle between the L-shaped heat rod (10) and the natural foundation (1) is 5 to 10 degrees, and the length of the evaporation section is 8 to 9 meters; the horizontal spacing between the ends of the evaporation sections located on both sides of the embankment (3) is 1.0 to 1.5 meters, and the longitudinal spacing is 1.5 to 2.5 times the effective cooling radius of the L-shaped heat rod (10).

6. The permafrost roadbed cooling structure for reducing uneven road settlement as claimed in claim 1, characterized in that: The cushion layer (4) is made of natural gravel or medium-coarse sand, has a thickness of not less than 300 mm, and a mud content of not more than 5%.

7. The permafrost roadbed cooling structure for reducing uneven road settlement as claimed in claim 1, characterized in that: The reinforced grid (5) is single-layer or multi-layer and is laid at different positions of the fill (7); two adjacent reinforced grids (5) are connected by U-shaped steel bars with a steel bar spacing of 2 m, and are wrapped 2 m on the side slope of the embankment (3).

8. The permafrost roadbed cooling structure for reducing uneven road settlement as claimed in claim 1, characterized in that: The insulation board (6) is buried 150 cm below the asphalt pavement (8) and has a thickness of 10 cm.

9. The permafrost roadbed cooling structure for reducing uneven road settlement as claimed in claim 1, characterized in that: The U-shaped drainage ditch (11) is made of C30 concrete prefabricated blocks, with exposed lines having a 5 mm chamfer, impermeable geotextile IV (22) laid on both sides of the ditch wall and the ditch bottom, and a cement mortar cushion layer (18) poured on both sides of the ditch wall and the ditch bottom.

10. The permafrost roadbed cooling structure for reducing uneven road settlement according to claim 1, characterized in that: A C20 concrete cushion layer (17) is poured at the bottom of the seepage blind ditch (12) and filled with coarse granular filler (16); an impermeable geotextile V (23) is provided on the wall and bottom of the seepage blind ditch (12).

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