An in-situ reconstruction and expansion structure for embankment and its construction method

Abstract

The present invention discloses an in-situ reconstruction and expansion structure for an embankment and a construction method thereof. The in-situ reconstruction and expansion structure for the embankment includes a stepped surface, which is excavated on the original slope. The slope of the stepped surface is the same as that of the expanded slope, and the stepped surface intersects with the top and bottom planes of the original slope respectively. Using the toe of the original slope as the toe of the expanded slope, the slope of the expanded slope is determined according to the toe position and the expansion width. The outer side of the stepped surface is filled with a geogrid reinforced layer in layers, and a slope protection structure is arranged on the outer side of the geogrid reinforced layer to form an expanded slope. A drainage system is provided at the bottom of the expanded slope for discharging the internal seepage water of the expanded structure. The present invention improves the stability, reduces the uneven settlement, reduces the floor area, does not conduct a full excavation, and reduces the project cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of highway slopes, and relates to an in-situ reconstruction and expansion structure and construction method for embankments. Background Technique

[0002] With the rapid development of society and economy and the gradual update of people's consumption concepts, cars have become an indispensable means of transportation in human society; with the continuous increase in the number of cars, the traffic demand is constantly increasing, but limited by the early design concepts and design levels, most existing expressways cannot meet the growing traffic demand; in this case, the upgrade and reconstruction of the original expressways have become a research hotspot in the traffic field.

[0003] At present, the commonly used methods for highway expansion include the geogrid splicing method or the method of combining anchoring with geogrid splicing. The geogrid splicing method is to excavate the old roadbed to form surface steps, then lay geogrids on the steps and fill the new roadbed, so as to achieve highway expansion. However, the traditional method requires full excavation of the embankment, which is likely to cause instability during construction, and then engineering accidents and casualties. Some existing studies conduct fill expansion parallel to the original slope during highway expansion, increasing costs; there are no corresponding solutions for areas where expansion cannot be carried out.

[0004] Chinese Patent Invention No. CN102619150A discloses an anchoring method for widening roadbeds, which uses anchor rod technology to reinforce the slope of the excavated old roadbed. At the same time, according to the fixed steel bars in the anchor rods being connected to the geogrids, although it effectively avoids the sliding of the geogrids on the steps of the old roadbed and improves the stability of the new and old roadbeds, the use of anchor rod anchoring increases the steel consumption and the construction cost.

[0005] Chinese Patent Invention No. CN107386031A discloses a treatment method for the joint part of highway reconstruction and expansion projects. After the original slope is excavated downward to form an inclined plane, geogrids are laid and reinforcing ribs are set, and gravel piles are set at the joint of the new and old roadbeds as permanent supports. Although it effectively reduces the possibility of cracks between the new and old roadbeds, a large area of excavation is required to have a construction site for driving the gravel piles, which will cause great disturbance to the original embankment and is prone to engineering accidents during construction.

[0006] In summary, the existing methods for highway expansion have the following problems:

[0007] (1) Non-in-situ expansion of the embankment is likely to cause a large amount of land waste and low land utilization rate.

[0008] (2) Full excavation during construction is prone to instability failure and cause engineering accidents.

[0009] (3) The measures such as adopting anchor rods, reinforcing bars and anti-slide piles in combination with geogrids are used to splice the new and old roadbeds, and the project cost is relatively high. Summary of the Invention

[0010] In order to solve the above problems, the present invention provides an in-situ reconstruction and expansion structure for an embankment, which improves stability, reduces uneven settlement, reduces the occupied area, does not conduct a full excavation, reduces the project cost, and solves the problems existing in the prior art.

[0011] Another object of the present invention is to provide a construction method for an in-situ reconstruction and expansion structure of an embankment.

[0012] The technical solution adopted by the present invention is an in-situ reconstruction and expansion structure for an embankment, including a stepped surface, the stepped surface is excavated on the original slope, and the slope of the stepped surface is the same as that of the expanded slope. The stepped surface intersects with the top and bottom planes of the original slope respectively; the toe of the original slope is used as the toe of the expanded slope, and the slope of the expanded slope is determined according to the toe position and the expansion width;

[0013] The outside of the stepped surface is filled with geogrid reinforced layers in layers, and a slope protection structure is arranged outside the geogrid reinforced layers to form an expanded slope;

[0014] A drainage system is provided at the bottom of the expanded slope for discharging the internal seepage water of the expanded structure.

[0015] Further, the excavation of the stepped surface starts from the toe of the original slope and extends towards the inside of the embankment to divide the embankment into multiple sub-construction areas. Before excavating the stepped surface, steel sheet piles are driven into the top of the corresponding sub-construction area at the end, and grouting pipes are prefabricated at the corners of the steel sheet piles.

[0016] Further, a tree-shaped geogrid is laid in the soil layer of the geogrid reinforced layer. The tree-shaped geogrid is provided with a strengthening part in the vertical direction. The first geogrids are arranged in a staggered manner on both sides of the strengthening part. The first geogrids are laid between each layer of soil in the geogrid reinforced layer. The strengthening part is laid upward in a stepped shape and matches the stepped surface.

[0017] Further, the thickness of the strengthening part is 2-3 times the thickness of the first geogrid.

[0018] Further, the slope of the expanded slope is between 1:1.5 and 1:1.

[0019] Further, the slope protection structure includes:

[0020] Hollow bricks, the hollow bricks are installed in a staggered manner on the stepped surface outside the geogrid reinforced layer;

[0021] The second geogrid, one end of which is fixed inside the hollow brick and the other end extends into the soil layer of the geogrid reinforced layer.

[0022] Furthermore, upper and lower lapping structures extending vertically outwards are respectively provided at the diagonals where each hollow brick contacts the adjacent upper and lower hollow bricks.

[0023] Furthermore, a temporary intercepting ditch is dug in the upper part of the top end of the steel sheet pile, and a water-proof geotextile is laid on the surfaces of the original slope and the temporary intercepting ditch.

[0024] Furthermore, a soil platform is provided on one side of the temporary intercepting ditch close to the steel sheet pile, and the soil platform inclines 3°-6° towards the temporary intercepting ditch; a water-proof geotextile is laid on the surfaces of the original slope, the temporary intercepting ditch and the soil platform.

[0025] Furthermore, it is characterized in that the drainage system includes:

[0026] A water-proof layer which is arranged on the surface of the step surface;

[0027] A gravel layer which is laid on the water-proof layer;

[0028] A bottom-of-slope drainage ditch which is arranged at the bottom of the embankment.

[0029] A construction method for an in-situ reconstruction and expansion structure of an embankment, comprising the following steps:

[0030] S1: Sort out the original embankment, remove surface sundries, make an auxiliary line parallel to the expanded slope from the top of the original slope, and divide the embankment into multiple sub-construction areas by starting from the toe of the original slope and extending inwards to the embankment;

[0031] S2: Drive steel sheet piles at the top of the end of the sub-construction area closest to the starting point;

[0032] S3: Horizontally and stepwise excavate the step surface from top to bottom along the auxiliary line in the sub-construction area, lay a water-proof layer on the surface of the step surface, and lay a gravel layer on the water-proof layer;

[0033] S4: Layer by layer fill the geogrid reinforced layer on the gravel layer, and install a slope protection structure during the filling process;

[0034] S5: Carry out wetting pre-settlement construction on the backfill soil in the sub-construction area;

[0035] S6: Pull out the steel sheet piles in a segmented and spaced manner, and at the same time inject slurry into the gaps left after the steel sheet piles are pulled out through a grouting pipe. Stop grouting when the bottom of the grouting pipe is flush with the top of the constructed geogrid reinforced layer;

[0036] S7: Construction is carried out on all sub - construction areas from bottom to top in sequence according to steps S2 - S6; when the horizontal distance of the sub - construction area from the top of the original slope is less than the horizontal advancement distance, it is not necessary to drive steel sheet piles.

[0037] S8: Compact the geogrid reinforcement layer 3m - 5m away from the slope top.

[0038] S9: Build a bottom drain at the slope bottom.

[0039] Further, the specific content of S2 is as follows:

[0040] S21: Install a guide frame at the top of the sub - construction area.

[0041] S22: Connect multiple steel sheet piles into sections, lock the joints between adjacent sections of steel sheet piles, drive the steel sheet piles in each section in a stepped shape, set a reserved sectional interval of 15cm - 30cm between each section of steel sheet piles and the adjacent section, and the driving depth of the steel sheet piles is 6m - 8m; a grouting pipe is pre - fabricated at the trapezoidal top angle of the steel sheet pile, and the bottom of the grouting pipe extends out of the steel sheet pile.

[0042] S23: Excavate a temporary intercepting ditch above the steel sheet piles. A soil platform is provided on the side of the temporary intercepting ditch close to the steel sheet pile, and the soil platform inclines 3° - 6° towards the temporary intercepting ditch. A water - proof geotextile is laid on the surface of the original slope, the temporary intercepting ditch and the soil platform.

[0043] Further, in S3, the laying method of the geogrid reinforcement layer and the slope protection structure: Clean and level the subgrade bed, lay the first inner soil layer at the set position and compact it, lay the first geogrid on one side of the tree - shaped geogrid on the top of the first inner soil layer, and lay the strengthening part on the top and side of the first inner soil layer. Lay the first outer soil layer on the side of the strengthening part far from the step surface and compact it. Trim the outside of the first outer soil layer for placing hollow bricks. Lay the second geogrid embedded in the hollow bricks to the preset position in the first outer soil layer, and continue to fill and compact to complete the first outer soil layer; lay the first geogrid on the other side of the tree - shaped geogrid on the top of the first outer soil layer; repeat in this way, lay the geogrid reinforcement layer in layers, and the strengthening part is laid upward in a stepped shape, matching the step surface; the hollow bricks are arranged staggered on the surface steps of the geogrid reinforcement layer, and the hollow bricks in the upper and lower adjacent layers are buckled with each other, and fill the hollow bricks with soil mixed with green plant seeds.

[0044] Further, in S3, the number of excavation levels n of the sub - construction area is determined by the height h of the sub - construction area and the vertical spacing t of the first geogrid, and the calculation formula is .

[0045] Further, the laying thickness t of the first geogrid is 0.1 - 1m.

[0046] The beneficial effects of the present invention are as follows:

[0047] (1) In the embodiments of the present invention, multiple sub - construction areas are divided for the original slope. The anchoring system, drainage system, and the tree - shaped geogrid with a specific structure cooperate with each other, achieving the completion of the entire reconstruction and expansion efficiently, safely, at low cost, and with less land occupation. The slope gradient after expansion is larger than that before expansion. Compared with the non - in - situ expansion of the roadbed, the restrictions of surrounding buildings and terrain on the expansion project are reduced.

[0048] (2) In the embodiments of the present invention, the construction in sub - areas uses steel sheet piles as temporary supports, and grouting is carried out during the process of pulling out the steel sheet piles, reducing the disturbance to the original slope stability structure during the excavation process and the horizontal lateral displacement of the original slope caused by the pulling out of the steel sheet piles; during the construction period, measures such as temporary intercepting ditches and water - isolating geotextiles are set at the upper part of the top of the steel sheet piles, reducing the adverse effects on the slope caused by rainfall during the construction period.

[0049] (3) The present invention fully protects the embankment during the reconstruction and expansion construction process and the embankment during the operation period, which can greatly improve the safety of the embankment slope during the construction period and operation period, achieving the purpose of safe construction; it overcomes the problems of instability failure and engineering accidents easily caused by full - scale excavation during the construction period.

[0050] (4) In the currently widely used technologies for embankment reconstruction and expansion, anchor bolts, reinforcement bars, and anti - slide piles all need to cooperate with geogrids to splice the new and old roadbeds. Since the full - scale step excavation is adopted at the interface between the new and old roadbeds, the excavation area is large and the involved scope is wide. In the embodiments of the present invention, the tree - shaped geogrid is strengthened in the vertical direction. Compared with ordinary geogrids, it solves the problem that the embankment may slide between the two layers of geogrids; at the same time, the weak positions at the fill - cut intersection zone of the embankment are accurately reinforced through the tree - shaped geogrid, reducing the labor cost and material cost caused by a large amount of laying of geogrids.

[0051] (5) In the embodiments of the present invention, wetting pre - settlement construction is carried out on the backfill soil in the sub - construction area, greatly reducing the post - construction settlement of the new roadbed and reducing the non - uniformity of the settlement between the new and old roadbeds. Description of the Drawings

[0052] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following - described drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0053] Figure 1 It is the overall side view of the expanded structure in the embodiments of the present invention.

[0054] Figure 2 It is the drawing of the original slope sub - level construction area division in the embodiment of the present invention.

[0055] Figure 3 It is the side view during the construction of the first sub - level construction area in the embodiment of the present invention.

[0056] Figure 4 It is the top view of the steel sheet piles driven in a stepped shape in the embodiment of the present invention.

[0057] Figure 5 It is the three - dimensional view of the steel sheet piles driven in a stepped shape in the embodiment of the present invention.

[0058] Figure 6 It is the construction schematic diagram when the steel sheet piles are driven in the embodiment of the present invention.

[0059] Figure 7 It is the side view after the installation of the fork - shaped geogrid in the embodiment of the present invention.

[0060] Figure 8 It is the side view of the fork - shaped geogrid when leaving the factory in the embodiment of the present invention.

[0061] Figure 9 It is the side view of the slope protection structure in the embodiment of the present invention.

[0062] Figure 10 is Figure 9 the sectional view taken along line I - I in

[0063] Figure 11 It is the layout drawing of the hollow bricks in the embodiment of the present invention.

[0064] Figure 12 It is the side view after the construction is completed in the embodiment of the present invention.

[0065] Figure 13 It is the data graph of the reduced land occupation area and filling volume per kilometer in the embodiment of the present invention.

[0066] In the figure: 1. The first sub - level construction area, 2. The second sub - level construction area, 3. The third sub - level construction area, 4. The fourth sub - level construction area, 5. The original slope, 6. The expanded equivalent slope, 7. The steel sheet piles, 8. The grouting pipes, 9. The reserved sectional interval, 10. The guide frame, 11. The temporary intercepting ditch, 12. The soil platform, 13. The water - proof geotextile, 14. The step surface, 15. The water - proof layer, 16. The gravel layer, 17. The geogrid reinforcement layer, 18. The slope protection structure, 19. The first geogrid, 20. The strengthening part, 21. The hollow bricks, 22. The second geogrid, 23. The soil, 24. The green plants, 25. The upper lapping structure, 26. The lower lapping structure, 27. The water supply pipe, 28. The sprinkler head, 29. The tamping area, 30. The slope bottom drainage ditch, 31. The starting point of the sub - level construction area division. Specific embodiments

[0067] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. Embodiment

[0068] An in-situ reconstruction and expansion structure for an embankment, as Figure 1 shown, includes a stepped surface 14 excavated on the original slope 5. The slope of the stepped surface 14 is the same as that of the expanded slope. The stepped surface 14 intersects with the top and bottom planes of the original slope 5 respectively. The slope of the expanded slope is determined according to the position of the slope toe and the expansion width, and the slope toe of the original slope 5 is used as the slope toe of the expanded slope. A geogrid reinforced layer 17 is filled in layers outside the stepped surface 14, and a slope protection structure 18 is arranged outside the geogrid reinforced layer 17 to form an expanded slope.

[0069] The excavation of the stepped surface 14 starts from the starting point 31 of the sub-level construction area division, and the embankment is divided into multiple sub-level construction areas by taking a certain horizontal distance inward from the embankment. Before excavating the stepped surface 14, sheet piles 7 are driven into the top of the end of the corresponding sub-level construction area. A grouting pipe 8 is prefabricated at the top corner of the sheet pile 7. A temporary intercepting ditch 11 is excavated above the top of the sheet pile 7. A water-proof geotextile 13 is laid on the surfaces of the original slope 5 and the temporary intercepting ditch 11. A soil platform 12 is arranged on the side of the temporary intercepting ditch 11 close to the sheet pile 7, and the soil platform 12 inclines 3°-6° towards the temporary intercepting ditch 11.

[0070] The geogrid reinforced layer 17 is an area surrounded by the embankment bottom surface, the highway pavement, the excavated stepped surface 14 and the stepped surface on the surface of the expanded slope. The geogrid reinforced layer 17 and the slope protection structure 18 constitute an anchoring system, and the sheet pile 7, the temporary intercepting ditch 11 and the water-proof geotextile 13 constitute a temporary support system; a drainage system is arranged at the bottom of the expanded slope to discharge the internal seepage water of the expanded structure; the anchoring system, the drainage system and the temporary support system cooperate with each other.

[0071] In some embodiments, a tree-shaped geogrid is laid in the soil layer of the geogrid reinforced layer 17, as Figures 7 - 8 shown. The tree-shaped geogrid is provided with a strengthening part 20 in the vertical direction. The first geogrids 19 are arranged in a staggered manner on both sides of the strengthening part 20. The first geogrids 19 are laid between each soil layer of the geogrid reinforced layer 17. The strengthening part 20 is laid upward in a stepped shape and matches the stepped surface 14. The tree-shaped geogrid increases the shear strength of the embankment and avoids the embankment from undergoing instability failure.

[0072] The first geogrid 19 is an ordinary geogrid, and the thickness of the reinforcement part 20 is 2-3 times the thickness of the first geogrid 19. The width of a single first geogrid 19 is preferably 6m, the ultimate tensile strength is not less than 80kN / m, and the overlap length between the two first geogrids 19 along the longitudinal direction of the embankment is not less than 0.5m.

[0073] like Figure 1 , Figures 9 - 11 As shown, the slope protection structure 18 includes hollow bricks 21 and a second geogrid 22. The hollow bricks 21 are arranged on the step surface outside the geogrid reinforcement layer 17. The diagonals where each hollow brick 21 contacts the upper and lower adjacent hollow bricks 21 are respectively provided with an upper overlap structure 25 and a lower overlap structure 26 extending vertically outward; the hollow bricks 21 are filled with soil 23 mixed with green plant seeds, and green plants 24 can grow; one end of the second geogrid 22 is pre-buried in the hollow bricks 21, and the other end extends into the soil layer of the geogrid reinforcement layer 17; the second geogrid 22 can adopt a steel-plastic geogrid, and the ultimate tensile strength is not less than 80kN / m.

[0074] The hollow brick 21 is 0.28m high, 0.335m wide and 0.4m long. The upper overlapping structure 25 and the lower overlapping structure 26 are both rectangular parallelepipeds of 0.03m×0.03m×0.4m. The bottom wall thickness of the inner groove of the hollow brick 21 is 0.04m, the wall thickness close to the upper overlapping structure 25 is 0.06m, and the wall thickness of the other three sides is 0.03m.

[0075] The main function of the hollow brick 21 is to protect the slope surface and prevent rainwater from eroding the slope surface; it also has the function of preventing rainwater from penetrating into the inside of the embankment, and can plant green plants to beautify the slope; it can be replaced by a structure with the same function as the hollow brick 21.

[0076] In some embodiments, the drainage system includes an aquiclude 15, a gravel layer 16, and a slope bottom drainage ditch 30. The aquiclude 15 is arranged on the surface of the step surface 14, and the aquiclude 15 is made of waterproof geotextile; the gravel layer 16 is laid on the aquiclude 15; and the slope bottom drainage ditch 30 is arranged at the bottom of the embankment.

[0077] In some embodiments, the horizontal surface of the step surface 14 is excavated at an angle of 3° to 6° toward the outside of the embankment in the lateral direction and at an angle of 2° to 5° in the longitudinal direction to quickly drain the water produced during the wet sedimentation construction process; the height of the step surface 14 is the laying thickness t of the first geogrid 19.

[0078] The upper surfaces of all hollow bricks 21 on the surface of the geogrid reinforcement layer 17 are set at an overall slope angle of 3°~6° in the transverse direction, and the upper surfaces of the overlapped hollow bricks 21 are set at a slope angle of 2°~5° in the longitudinal direction, so as to quickly guide away rainwater falling on the embankment surface. Example

[0079] A construction method for an in-situ modified and reinforced embankment expansion structure is carried out according to the following steps:

[0080] S1: Sort out the original embankment, remove the sundries on the slope surface, determine the expansion width to be 4m, draw an auxiliary line parallel to the expanded equivalent slope 6 from the top of the original slope, and take the intersection of the auxiliary line and the bottom plane of the slope as the starting point 31 of the sub-level construction area division towards the inner side of the embankment, and divide the embankment into multiple sub-level construction areas by taking a certain horizontal advancing distance; considering the embankment stability and construction efficiency, the horizontal advancing distance is taken as 3m; the step surface 14 and the first geogrid 19 are both laid along this auxiliary line. If starting from the toe of the original embankment, the horizontal advancing distance of the first sub-level construction area 1 is taken as 7m, and the advancing distances of the remaining several sub-level construction areas are taken as 3m; the advancing distance of the first sub-level construction area 1 needs to consider the expansion width.

[0081] S2: As Figure 2 shown, from the toe of the slope towards the inner side of the embankment, it is successively divided into the first sub-level construction area 1, the second sub-level construction area 2, the third sub-level construction area 3, and the fourth sub-level construction area 4. The division of the sub-level construction area is carried out by the positions where the steel sheet piles 7 need to be driven. When the spacing of the steel sheet piles 7 on the embankment section is smaller, the embankment stability during construction is higher, but the construction efficiency is lower; when the spacing is larger, the construction efficiency is higher, but the embankment stability during construction will decrease. After comprehensively considering the embankment stability and construction efficiency during construction, the spacing of the steel sheet piles on the embankment section is selected to be 3 meters.

[0082] As Figure 3 shown, drive the steel sheet piles 7 at the top of the first sub-level construction area 1, excavate a temporary intercepting ditch 11 above the top of the steel sheet piles 7, and lay a water isolation geotextile 13 on the surfaces of the original slope 5 and the temporary intercepting ditch 11. The specific operations are as follows:

[0083] S21, install a guide frame 10 at the top of the first sub-level construction area 1;

[0084] S22, for the convenience of construction, as Figures 4 - 5 shown, take 10 - 20 steel sheet piles 7 as a section, connect the lock joints between adjacent steel sheet piles 7 in each section, and use equipment such as a three-point guide rod type crawler pile driver and a vibrating hammer to drive the steel sheet piles 7 in each section in a stepped shape; a reserved section interval 9 of 15 cm to 30 cm is set between each section of steel sheet piles 7 and the adjacent section of steel sheet piles 7, as Figure 6As shown in the figure, the driving depth of the steel sheet pile 7 is 6m to 8m; grouting pipes 8 are prefabricated by welding at the two top corners of the trapezoid formed by the steel sheet pile 7. The bottom of the grouting pipe 8 extends 0.3m below the bottom of the steel sheet pile 7. The grouting pipe 8 is made of a steel pipe with an inner diameter of 19mm to 38mm and a wall thickness of not less than 5mm. The pipe tip is a cone with a thread for connecting to the grouting pipe 8. There are four rows of staggered holes at a distance of 0.2m from the bottom end of the grouting pipe 8. The hole spacing is about 50mm, and the hole diameter is 1mm to 3mm. The width B of the steel sheet pile 7 is 400mm, the height H is 240mm, and the thickness t is 9.2mm.

[0085] S23: Excavate a temporary intercepting ditch 11 at 2 - 3 meters above the steel sheet pile 7. A soil platform 12 is provided on the side of the temporary intercepting ditch 11 close to the steel sheet pile 7. The soil platform 12 slopes 3° to 6° towards the temporary intercepting ditch 11. A water - proof geotextile 13 is laid on the surfaces of the original slope 5, the temporary intercepting ditch 11, and the soil platform 12.

[0086] S3: Determine the number of excavation levels n in the first - level construction area 1, and conduct horizontal stepped excavation from top to bottom within the first - level construction area 1 to form a stepped surface 14. The number of excavation levels n in the first - level construction area 1 is determined by the height h of the first - level construction area 1 and the laying thickness t of the first geogrid 19. The calculation formula is , the height h of the first - level construction area 1 is 2.7m, the laying thickness t of the first geogrid 19 is 0.5m, and the number of excavation levels n is 5. A water - proof layer 15 is set on the stepped surface 14 of the first - level construction area 1. The water - proof layer 15 uses a water - proof geotextile; a layer of gravel layer 16 is laid on the water - proof layer 15. The gravel layer 16 uses single - sized crushed stones with a particle size of 2cm and a thickness of 10cm.

[0087] The laying thickness t of the first geogrid 19 is 0.1 to 1m. Considering the slope stability, the smaller the laying thickness t, the more stable it is. However, considering the construction period and project cost, the smaller the laying thickness t, the longer the construction period and the higher the project cost. After comprehensively considering the slope stability, construction period, and project cost, the laying thickness t of the first geogrid 19 in the embodiment is selected as 0.5m; the width of the stepped surface 14 is 0.55m, which is determined by the slope of the embankment after expansion and the laying thickness t.

[0088] S4: Layer - by - layer fill the geogrid - reinforced layer 17 on the gravel layer 16, and install the slope protection structure 18 during the filling process. The specific operations for filling the geogrid - reinforced layer 17 and installing the slope protection structure 18 are as follows:

[0089] S41: Clean the debris on the underlying layer, level the underlying layer, use equipment such as excavators supplemented by manual labor to lay the first inner soil layer, and use machinery to compact it. Lay the first geogrid 19 on one side of the tree-shaped geogrid on the top of the first inner soil layer, and lay the strengthening part 20 on the top and side of the first inner soil layer.

[0090] S42: Lay and compact the first outer soil layer on the side of the strengthening part 20 away from the step surface 14, trim the outside of the first outer soil layer for installing the hollow bricks 21, lay the second geogrid 22 embedded in the hollow bricks 21 to the preset position in the first outer soil layer, continue to fill and compact to complete the first outer soil layer; lay the first geogrid 19 on the other side of the tree-shaped geogrid on the top of the first outer soil layer; repeat in this way, layer by layer fill the geogrid reinforced layer 17, and the strengthening part 20 is laid upward in a stepped shape to match the step surface 14. When filling and compacting, the remaining part of the first geogrid 19 can be rolled up first. When constructing the inner soil layer, place the rolled-up part on the outer soil layer, and place it on the inner soil layer when constructing the outer soil layer; the tree-shaped geogrid is laid at the bottom of the geogrid reinforced layer 17.

[0091] S43: Fill and compact the geogrid reinforced layer 17 from bottom to top and from left to right, install the slope protection structure 18 until it is fully covered; manually interlock and connect two adjacent first geogrids 19 on the left and right; stagger the hollow bricks 21 on the surface steps of the geogrid reinforced layer 17 by manual laying method, and the hollow bricks 21 in the upper and lower adjacent layers are buckled with each other, and fill the hollow bricks 21 with soil 23 mixed with green plant seeds, as Figure 11 shown.

[0092] S5: Carry out wetting pre-settlement construction on the backfill soil in the first sub-construction area 1; set up a water supply pipe 27 on the top of the slope protection structure 18 in the first sub-construction area 1, and set a sprinkler head 28 every 3 - 7 meters along the longitudinal direction of the road on the water supply pipe 27, spray water to the top of the backfill soil and the slope protection structure 18 through the water supply pipe 27 and the sprinkler head 28, and then discharge it through the gravel layer 16 laid at the bottom of the backfill soil to make the backfill soil pre-settle. After the construction is completed, remove the water supply pipe 27 and the sprinkler head 28.

[0093] S6: Use machinery such as a vibrating hammer and a crane to pull out the steel sheet piles 7 in batches at segmented intervals, inject slurry into the gaps left by pulling out the steel sheet piles 7 through the grouting pipe 8, and stop grouting when the bottom of the grouting pipe 8 is flush with the top of the constructed geogrid reinforced layer 17.

[0094] S7: Construction is carried out on the second-level construction area 2, the third-level construction area 3, and the fourth-level construction area 4 in sequence from bottom to top according to steps S2 - S6; when the lateral horizontal distance between the sub-level construction area and the original slope top is less than the horizontal advance distance (3 m), it is not necessary to drive the steel sheet piles 7; that is, construction is carried out on the fourth-level construction area 4 according to steps S3 - S5.

[0095] S8: Use mechanical equipment such as cranes and rammers to carry out heavy tamping construction on the tamping area 29 at the top of the geogrid reinforced layer 17; the width of the tamping area is 4 m, and the depth is 3 m - 5 m.

[0096] S9: Build a bottom slope drain 30 at the bottom of the slope, and the construction effect is as Figure 12 shown.

[0097] After calculation, compared with the existing non-in-situ expansion, when the unilateral widening is 4 m and the bilateral widening is 8 m, 12 mu of land occupation can be reduced per kilometer, and the volume of the filling body can be reduced by 80,000 m 3 , effectively improving the land utilization rate and reducing a large amount of land acquisition costs, as Figure 13 shown.

[0098] Through the anchoring system, drainage system, customized geogrids, and the entire construction process in the embodiments of the present invention, the entire reconstruction and expansion are completed on the premise of high efficiency, safety, low cost, and reduction of a large amount of land occupation. With the help of the strengthening part of the tree-branch-shaped geogrid, the shear strength of the embankment is improved, so that the embankment can remain stable even when the slope increases after the expansion. According to the different selected expansion widths, the slope range is between 1:1.5 and 1:1, reducing the additional land occupation area and additional filling body volume required for the expansion, and reducing the restrictions of the surrounding buildings and terrain on the expansion project.

[0099] The above is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A construction method for an in-situ reconstruction and expansion structure of an embankment, characterized in that, The in-situ reconstruction and expansion structure of the embankment includes a stepped surface (14), which is excavated on the original slope (5). The slope of the stepped surface (14) is the same as that of the expanded slope, and the stepped surface (14) intersects with the top and bottom planes of the original slope (5) respectively; Taking the toe of the original slope (5) as the toe of the expanded slope, the slope of the expanded slope is determined according to the toe position and the expansion width; The stepped surface (14) is filled with a geogrid reinforced layer (17) in layers on the outside, and a slope protection structure (18) is arranged outside the geogrid reinforced layer (17) to form an expanded slope; A drainage system is provided at the bottom of the expanded slope to drain the internal seepage water of the expanded structure; It includes the following steps: S1: Sort out the original embankment, remove the surface sundries, make an auxiliary line parallel to the expanded slope from the top of the original slope, and extend from the toe of the original slope (5) towards the inside of the embankment to divide the embankment into multiple sub-construction areas; S2: Drive steel sheet piles (7) at the top end of the sub-construction area closest to the starting point; S3: Horizontally and stepwise excavate the stepped surface (14) along the auxiliary line from top to bottom within the sub-construction area, lay a water-proof layer (15) on the surface of the stepped surface (14), and lay a gravel layer (16) on the water-proof layer (15); S4: Fill the geogrid reinforced layer (17) in layers on the gravel layer (16), and install the slope protection structure (18) during the filling process; S5: Carry out wetting pre-settlement construction on the backfill soil within the sub-construction area; S6: Pull out the steel sheet piles (7) in a segmented and spaced manner, and at the same time inject slurry into the gap left after pulling out the steel sheet piles (7) through the grouting pipe (8). Stop grouting when the bottom of the grouting pipe (8) is flush with the top of the constructed geogrid reinforced layer (17); S7: Carry out construction on all sub-construction areas from bottom to top in sequence according to steps S2 to S6; when the horizontal distance between the sub-construction area and the top of the original slope is less than the horizontal advancing distance, there is no need to drive steel sheet piles (7); S8: Compact the geogrid reinforced layer (17) at a distance of 3m to 5m from the slope top; S9: Build a bottom drain ditch (30) at the slope bottom.

2. The construction method of an in-situ reconstruction and expansion structure of an embankment according to claim 1, characterized in that, The specific content of S2 is as follows: S21: Install a guide frame (10) at the top of the sub-construction area; S22: Connect multiple steel sheet piles (7) in sections, lock the joints between adjacent steel sheet piles (7) in each section, drive the steel sheet piles (7) in each section in a stepped shape, and set a reserved segmented interval (9) of 15cm to 30cm between each section of steel sheet piles (7) and the adjacent section of steel sheet piles (7). The driving depth of the steel sheet piles (7) is 6m to 8m; a grouting pipe (8) is prefabricated at the trapezoidal top angle of the steel sheet piles (7), and the bottom of the grouting pipe (8) extends out of the steel sheet piles (7); S23: Excavate a temporary intercepting ditch (11) above the steel sheet piles (7). A soil platform (12) is provided on the side of the temporary intercepting ditch (11) close to the steel sheet piles (7), and the soil platform (12) inclines 3° to 6° towards the temporary intercepting ditch (11). Lay a water-proof geotextile (13) on the surfaces of the original slope (5), the temporary intercepting ditch (11) and the soil platform (12).

3. The construction method of an in-situ reconstruction and expansion structure of an embankment according to claim 1, characterized in that, In S3, the laying method of the geogrid reinforcement layer (17) and the slope protection structure (18): Clean and level the subgrade, lay the first inner soil layer at the set position and compact it. Lay the first geogrid (19) on one side of the tree-shaped geogrid on the top of the first inner soil layer, and lay the strengthening part (20) on the top and side of the first inner soil layer. Lay the first outer soil layer on the side of the strengthening part (20) away from the step surface (14) and compact it. Trim the outer side of the first outer soil layer for placing the hollow bricks (21). Lay the second geogrid (22) pre-embedded in the hollow bricks (21) to the preset position in the first outer soil layer, and continue to fill and compact to complete the first outer soil layer. Lay the first geogrid (19) on the other side of the tree-shaped geogrid on the top of the first outer soil layer. Repeat in this way, layer by layer to fill the geogrid reinforcement layer (17). The strengthening part (20) is laid upward in a stepped shape to match the step surface (14). The hollow bricks (21) are staggered and arranged on the surface steps of the geogrid reinforcement layer (17), and the hollow bricks (21) in the upper and lower adjacent layers are buckled with each other. Fill the hollow bricks (21) with soil (23) mixed with green plant seeds.

4. The construction method of an in-situ reconstruction and expansion structure of an embankment according to claim 3, characterized in that, In S3, the excavation level of the sub-construction area n is determined by the height of the sub-construction area h and the vertical spacing of the first geogrid (19) t and the calculation formula is as follows 5. The construction method of an in-situ reconstruction and expansion structure of an embankment according to claim 3, characterized in that, The laying thickness of the first geogrid (19) t is 0.1 to 1 m.

6. The construction method of an in-situ reconstruction and expansion structure of an embankment according to claim 1, characterized in that, The excavation of the step surface (14) starts from the toe of the original slope (5) and extends towards the inner side of the embankment to divide the embankment into multiple sub-construction areas. Before excavating the step surface (14), drive steel sheet piles (7) at the top of the end of the corresponding sub-construction area. The steel sheet piles (7) are prefabricated with grouting pipes (8) at the corners.

7. The construction method of an in-situ reconstruction and expansion structure of an embankment according to claim 1, characterized in that, The soil layer of the geogrid reinforcement layer (17) is laid with a tree-shaped geogrid. The tree-shaped geogrid is provided with a strengthening part (20) vertically. The first geogrids (19) are arranged in a staggered manner on both sides of the strengthening part (20). The first geogrids (19) are laid between each layer of soil in the geogrid reinforcement layer (17). The strengthening part (20) is laid upward in a stepped shape to match the step surface (14).

8. The construction method of an in-situ reconstruction and expansion structure of an embankment according to claim 7, characterized in that, The thickness of the strengthening part (20) is 2 - 3 times the thickness of the first geogrid (19).

9. The construction method of an in-situ reconstruction and expansion structure of an embankment according to claim 1, characterized in that, The slope of the expanded slope is between 1:1.5 and 1:

1.

10. The construction method of an in-situ reconstruction and expansion structure of an embankment according to claim 1, characterized in that, The slope protection structure (18) includes: Hollow bricks (21), which are staggered and installed on the step surface outside the geogrid reinforcement layer (17); The second geogrid (22), one end of which is fixed inside the hollow brick (21), and the other end extends into the soil layer of the geogrid reinforcement layer (17).

11. The construction method of an in-situ reconstruction and expansion structure of an embankment according to claim 10, characterized in that, Each of the hollow bricks (21) is respectively provided with an upper lapping structure (25) and a lower lapping structure (26) that extend vertically outward at the diagonals in contact with the upper and lower adjacent hollow bricks (21).

12. The construction method of an in-situ reconstruction and expansion structure of an embankment according to claim 6, characterized in that, A temporary intercepting ditch (11) is dug on the upper part of the top of the steel sheet pile (7). The surfaces of the original slope (5) and the temporary intercepting ditch (11) are laid with water-proof geotextiles (13).

13. The construction method of an in-situ reconstruction and expansion structure of an embankment according to claim 12, characterized in that, A soil platform (12) is provided on one side of the temporary intercepting ditch (11) close to the steel sheet pile (7), and the soil platform (12) inclines 3°-6° towards the temporary intercepting ditch (11); a water-proof geotextile (13) is laid on the surfaces of the original slope (5), the temporary intercepting ditch (11) and the soil platform (12).

14. The construction method of an in-situ reconstruction and expansion structure of an embankment according to claim 1, characterized in that, The drainage system includes: a water-proof layer (15) which is arranged on the surface of the stepped surface (14); a gravel layer (16) which is laid on the water-proof layer (15); a bottom-of-slope drainage ditch (30) which is arranged at the bottom of the embankment.

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