Two-way tying construction method for the cutting and filling intersection area of a sloping excavation stepped subgrade

Abstract

The present invention discloses a two-way tying construction method for the filling and excavation intersection area of a sloping excavated stepped roadbed. By setting inclined steps to provide horizontal and vertical lapping operation platforms, geogrids are arranged on the horizontal and vertical lapping operation platforms. The inclined geogrids can provide force in both the horizontal and vertical directions of the operation platform, achieving the ability to improve the resistance to uneven settlement failure, and enhancing the horizontal, longitudinal, and vertical tying forces, thereby reducing the roadbed settlement amount at the filling and excavation intersection, reducing the possibility of road surface subsidence, cracking, and damage, and extending the service life of the road.

Description

Technical Field

[0001] The present invention relates to the technical field of subgrade construction at the cutting and filling junction, and particularly relates to a two-way tie construction method for the inclined excavation stepped subgrade cutting and filling junction area. Background Art

[0002] With the enhancement of the national economic strength and the rapid development of highway construction, the highway construction in China has experienced a transformation from low-level to high-level, from the large lanes of highways to the construction of high-grade and high-standard expressways and race tracks. During the road construction process, subgrade settlement is the most common and easily occurring quality defect. And the cutting and filling junction is the key and crucial part where settlement occurs. At present, the traditional construction method at the cutting and filling junction is to adopt stepped lapping, and a geogrid is laid flat at the junction of each step for connection to strengthen the integrity and uniformity between the cutting area and the filling area, improve the subgrade bearing capacity and reduce subgrade settlement. This construction treatment method can enhance the integrity between the cutting area and the filling area to a certain extent and improve the subgrade bearing capacity. However, for roads with high requirements for bearing capacity and flatness, this base treatment method for the cutting and filling junction area is not easy to meet the settlement requirements during long-term use. With the extension of the road service life and the continuous loads applied to the road surface during the road use process, there is a risk of excessive deformation.

[0003] The invention patent application with the application number CN202011218533.9 discloses a transverse new and old subgrade connection structure and construction method. Among them, a transverse new and old subgrade connection structure includes an old subgrade and a new subgrade fixedly connected to the old subgrade; a plurality of steps are gradually opened along the transverse direction on the slope of the old subgrade, and geogrids are laid on the steps. A reinforcement grid fixedly connected to the old subgrade is inclined on the slope of the old subgrade; the new subgrade is formed by gradually tamping a filling material containing a part of screened waste earth and stone materials. The construction method includes the following steps: measuring and setting out on the outside of the old subgrade; removing the topsoil, and gradually excavating steps on the old subgrade and the outside soil layer; screening the excavated waste earth and stone materials; laying geogrids and arranging the reinforcement grid; gradually backfilling and tamping the backfill material and the permeable subgrade filler. This application belongs to the technical field of road construction, and it can make the widened subgrade structure more stable and not easily damaged, and utilize waste earth and stone materials, playing the role of energy conservation and environmental protection. Using the construction method provided by this technical solution, it still cannot solve the problems of various subgrade quality defects such as road surface subsidence, cracking, and damage caused by subgrade settlement. Summary of the Invention

[0004] To solve the above problems, the present invention discloses a two-way tying construction method for the cut-fill intersection area of a slope-excavated stepped subgrade. By setting inclined steps to provide horizontal and vertical lapping operation platforms, geogrids are arranged on the horizontal and vertical lapping operation platforms. The inclined geogrids can provide forces both horizontally and vertically on the operation platforms, achieving the ability to improve the resistance to uneven settlement failure, and enhancing the horizontal, longitudinal, and vertical tying forces, thereby reducing the settlement amount of the subgrade at the cut-fill intersection, decreasing the possibility of pavement subsidence, cracking, and damage, and extending the service life of the road.

[0005] The technical solution adopted by the present invention is as follows:

[0006] The present invention discloses a two-way tying construction method for the cut-fill intersection area of a slope-excavated stepped subgrade, including a cutting area and a filling area, and comprising the following steps:

[0007] Construction preparation step: Prepare the construction materials and tools required for construction, and prepare geogrids and fixing nails for fixing the geogrids.

[0008] Step excavation step: Before excavating the steps, remove the unqualified soil. After completion, release the excavation line of each step and mark it with lime. The step excavation is carried out in the cutting area, and the construction tools are used to excavate layer by layer from bottom to top, and the slope-excavated steps are initially excavated and formed.

[0009] Slope excavation step: A number of continuous steps are formed by excavation in the cutting area. Each step includes a step plane and a step slope. The step plane is set as an inclined cross slope, and the cross slope inclines towards the inside of the step, and the inclination angle is set to 1.5 - 2.5%. The step slope is connected to the step plane to form a continuous slope, and the step slope inclines towards the outside of the step. The step slope and the step plane form an inclined slope with an angle of 120°, and the slope-excavated steps are completed and formed.

[0010] Geogrid laying step: Clean the slope-excavated steps after excavation and formation. Lay geogrids on the slope-excavated steps after cleaning, including a geogrid fixing net formed by longitudinal and vertical laying. The overlapping length of the longitudinally laid geogrids on the upper and lower platforms of the slope-excavated steps is 30 cm, and the overlapping part is tied and connected with binding wires.

[0011] Geogrid anchoring step: Lay the geogrids on the step plane according to the width design. When the geogrids are paved, they should be straightened and smooth, and be closely attached to the step plane. The overlapping part of the geogrids on the step plane is fixed with fixing nails or connectors.

[0012] Earthwork backfilling step: Complete the earthwork backfilling in the filling area. The earthwork backfilling is carried out layer by layer from bottom to top. After the geogrids of the current step are laid, backfilling can be carried out. When backfilling the bottom layer of earthwork, compact the original ground, and after the compaction degree is detected to be qualified, the earthwork backfilling can be carried out.

[0013] Steps for setting the transition section: After the compaction degree is qualified, set the transition section. The transition section is a longitudinal plane connection geogrid at the step junction. The geogrid here is fixed with fixing nails. Repeat the above steps to complete the step construction from bottom to top until the construction at the excavation and filling junction is completed.

[0014] Furthermore, set the length of the transition section to 4H + 5m, and the length of the transition section is not less than 10m; the H is the filling height from the first - level step to the bottom of the roadbed.

[0015] Furthermore, in the step of laying the geogrid, each step plane includes longitudinally laying a 3 - m - wide geogrid as an overlap, and laying a 3 - m - wide geogrid along the vertical direction of the step together.

[0016] Furthermore, the fixing nails are U - shaped nails, which are made of φ8 steel bars. Set the width of the U - shaped nails to 5 - 7cm and the length to 14 - 16cm.

[0017] Furthermore, the geogrid is a bidirectional plastic - steel geogrid. Set the tensile strength of the bidirectional plastic - steel geogrid ≥60kn / m, the node peel resistance ≥100n, and the elongation at break ≤3%.

[0018] Furthermore, the transition section is provided with a double - layer geogrid, a lower roadbed, an upper roadbed, and a pavement structure layer from bottom to top. First, construct the excavation and filling transition section, and then fill the adjacent embankment section after the construction is completed.

[0019] Furthermore, the geogrid of the transition section is a double - layer steel - plastic geogrid, which is set across the full width of the transition section horizontally. The double - layer geogrid is overlaid 3m on both sides of the transition section.

[0020] The technical effects of the present invention are as follows:

[0021] The present invention discloses a two - way tie - in construction method for the excavation and filling junction area of a sloping - excavation step - type roadbed, which effectively solves the problems of various quality diseases such as road surface settlement, cracking, and damage caused by roadbed settlement, directly affecting the road use quality.

[0022] The specific content is as follows:

[0023] 1. The present invention adopts the method of sloping - excavation steps, with closer and firmer connection between upper and lower layers, and it is convenient for the paving of the geogrid during construction, improving the construction operation efficiency, reducing the operation cost and construction period.

[0024] 2. Compared with the vertical step excavation construction, the inclined step excavation construction adopted in the present invention has a relatively high stiffness for geogrids with better materials. The vertical step excavation method cannot integrate the horizontal and vertical geogrids, and they can only be cut and connected by tying, which cannot achieve the stress-bearing effect. The inclined step excavation construction of the present invention provides an inclined laying of geogrids, enabling the operation platform to bear stress both horizontally and vertically.

[0025] 3. The inclined laying of geogrids adopted in the present invention can share the horizontal and vertical forces simultaneously. The horizontal force increases the integrity of the two originally staggered layers of geogrids, and the vertical force makes up for the lack of vertical force in traditional construction, increasing the stability between soil layers. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic diagram of vertical step excavation construction;

[0027] Figure 2 is a schematic diagram of the inclined step excavation construction of the present invention;

[0028] Reference numerals in the figures: 1 - excavation area, 2 - filling area, 3 - geogrid, 4 - step plane, 5 - step slope, 6 - transition section, 601 - double-layer geogrid, 602 - lower roadbed, 603 - upper roadbed, 604 - pavement structure layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] The present invention will be described in detail below with reference to the accompanying drawings.

[0030] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0031] In this embodiment, the data adopted are preferred solutions, but they do not limit the present invention.

[0032] In this embodiment, when the longitudinal ground slope, that is, the ground line slope, is steeper than 1:5, the original ground is excavated to form an inclined step with a width of 2 m, an inward slope of 2% and an outward slope of 120°, which is convenient for the laying of geogrids, and the step height is set to be less than or equal to 0.4 m.

[0033] As Figure 1 shown, the prior art adopts vertical step construction. The bearing capacity and longitudinal tensile force of the subgrade in this scheme cannot be guaranteed, and it is easy to cause subgrade settlement. Moreover, the mechanical cost invested in this construction method is relatively high, and the economic benefit does not meet the construction requirements.

[0034] As Figure 2 shown, this embodiment provides a two-way tie construction method for the cut-fill intersection area of an inclined step subgrade, including an excavation area and a filling area, and the following steps:

[0035] Construction preparation steps: Prepare construction materials and tools required for construction, and prepare geogrids and fixing nails for fixing geogrids.

[0036] Step excavation steps: Before excavating the steps, remove unqualified soil, excavate to the ground line of hard soil layer or rock layer. After completion of the removal, release the excavation line of each step and mark it with lime. The step excavation is carried out in the cut area. The step excavation is carried out layer by layer from bottom to top by construction tools. The inclined excavation steps are initially excavated and formed. The width of the initially excavated and formed steps is 2m and the height is 40cm.

[0037] Slope excavation steps: A number of continuous steps are set up by excavation in the cut area. Each step includes a step plane and a step slope. The step plane is set as an inclined cross slope, and the cross slope inclines towards the inside of the step. The inclination angle is set to 1.5 - 2.5%; The step slope is connected to the step plane to form a continuous slope. The step slope inclines towards the outside of the step. The step slope and the step plane form an inclined slope with an angle of 120°. The inclined excavation steps are completed and formed after excavation.

[0038] Geogrid laying steps: Clean the inclined excavation steps after excavation and forming. Lay geogrids on the cleaned inclined excavation steps, including a geogrid fixing net formed by longitudinal and vertical laying. The overlapping length of the longitudinally laid geogrids on the upper and lower platforms of the inclined excavation steps is 30cm, and the overlapping part is tied and connected with binding wire; Fixed with U-shaped nails, finally making the vertically connected geogrids form a whole. Thereby improving the bearing capacity of the foundation and controlling the settlement amount at the intersection of cutting and filling.

[0039] Geogrid anchoring steps: Lay geogrids on the step plane according to the width design. When the geogrids are spread, they should be straightened and smooth, and be set closely against the step plane. The overlapping part of the geogrids on the step plane is fixed with fixing nails or connectors.

[0040] Earthwork backfilling steps: Complete the earthwork backfilling in the filling area. The earthwork backfilling is carried out layer by layer from bottom to top. After the geogrid laying of the current step is completed, the backfilling can be carried out. When backfilling the bottom layer of earthwork, compact the original ground. After the compaction degree is detected to be qualified, the earthwork backfilling can be carried out.

[0041] In this embodiment, the loose paving coefficient should be determined first when backfilling the earthwork, select qualified fillers, and unqualified fillers such as plowed soil and humus soil are strictly prohibited from being used for backfilling. The maximum particle size of the fillers should not exceed 2 / 3 of the layer thickness during backfilling.

[0042] After the earthwork backfilling of each step is completed, it is compacted densely by a 20t roller. When compacting, it should be light first and then heavy, and the speed should be moderate. To ensure the uniformity of compaction, the compaction speed cannot be too fast, first fast and then slow, and the driving speed is controlled within 2km / h.

[0043] The number of rolling passes shall be determined according to requirements of compaction degree, layer thickness, water content of backfill soil, rolling machinery, etc., generally being 6 - 8 passes. It shall be determined through a rolling test section at the initial stage of construction and used as the basis for rolling construction. After the earthwork backfill compaction is completed, compaction degree detection shall be carried out;

[0044] Steps for setting the transition section: After the compaction degree detection is qualified, set the transition section. The transition section is a longitudinal plane connection geogrid at the step intersection. Here, the geogrid is fixed with fixing nails. Repeat the above steps to complete the step construction from bottom to top until the construction at the excavation and filling junction is completed.

[0045] Preferably, the filled area is filled and rolled in layers with well - graded gravel and sandy soil to the bottom of the roadbed, and the compaction degree is not less than 96%.

[0046] In this embodiment, the length of the transition section is set to 4H + 5m, and the length of the transition section is not less than 10m; the H is the filling height from the first - level step to the bottom of the roadbed, so as to strengthen the integrity and uniformity between the soil masses in the excavation area and the filled area.

[0047] In this embodiment, in the step of laying the geogrid, each step plane includes longitudinally laying a 3 - m - wide geogrid for lapping, and laying a 3 - m - wide geogrid along the vertical direction of the step together.

[0048] In this embodiment, the fixing nails are U - shaped nails made of φ8 steel bars. The width of the U - shaped nails is set to 5 - 7cm, and the length is 14 - 16cm.

[0049] In this embodiment, the geogrid is a bidirectional plastic - steel geogrid. The tensile strength of the bidirectional plastic - steel geogrid is set to ≥60kN / m, the node anti - peeling force is ≥100N, and the elongation at break is ≤3%; in the prior art, a convex - node steel - plastic geogrid is selected for vertical step construction. The tensile strength of the convex - node steel - plastic geogrid is ≥100kN / m, the node anti - peeling force is ≥400N, and the elongation at break is ≤3%.

[0050] In this embodiment, the transition section is provided with a double - layer geogrid, a lower roadbed, an upper roadbed, and a pavement structure layer from bottom to top. First, construct the excavation and filling transition section, and then fill and construct the adjacent filled - area section after the construction is completed. The transition section is filled and rolled in layers with gravel and sandy soil having higher strength, better water stability and gradation, and the thickness of each layer for compaction is not more than 40cm.

[0051] Preferably, the lower roadbed is arranged 50cm below the upper roadbed and filled with gravel; the upper roadbed is arranged 30cm below the pavement structure layer and filled with graded crushed stone;

[0052] In this embodiment, the geogrid in the transition section adopts a double-layer steel-plastic geogrid. The double-layer steel-plastic geogrid is arranged across the entire width of the transition section, and the double-layer geogrid is overlaid by 3 m on both sides of the transition section.

[0053] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A two-way tie construction method for the cut-fill intersection area of a slant-excavated stepped roadbed, comprising an excavation area (1) and a filling area (2), characterized in that, It includes the following steps: Construction preparation step: Prepare construction materials and tools required for construction, and prepare geogrid (3) and fixing nails for fixing geogrid (3). Step excavation step: Before excavating the steps, remove unqualified soil. After removal, release the excavation line of each step and mark it with lime. The step excavation is carried out in the excavation area (1). The step excavation is carried out layer by layer from bottom to top by construction tools, and the inclined excavation steps are initially formed. Slope excavation step: A number of continuous steps are set in the excavation area (1). Each step includes a step plane (4) and a step slope (5). The step plane (4) is set as an inclined cross slope, and the cross slope inclines towards the inside of the step, and the inclination angle is set to 1.5 - 2.5%. The step slope (5) is connected to the step plane (4) to form a continuous slope. The step slope (5) inclines towards the outside of the step, and the step slope (5) and the step plane (4) form an inclined slope with an angle of 120°. The inclined excavation steps are completed and formed. Geogrid laying step: Clean the inclined excavation steps after excavation and forming. Lay geogrid (3) on the cleaned inclined excavation steps, including a geogrid (3) fixing net formed by longitudinal and vertical laying. The longitudinally laid geogrid (3) has a lap length of 30 cm on the upper and lower platforms of the inclined excavation steps, and the lap joint is tied and connected with binding wire. Each step plane includes longitudinally laying 3 m wide geogrid (3) as a lap, and laying 3 m wide geogrid (3) along the vertical direction of the step together. Geogrid anchoring step: Lay geogrid (3) on the step plane (4) according to the width design. When the geogrid (3) is paved, it should be straightened and smooth, and closely attached to the step plane. The lap joint of the geogrid (3) on the step plane (4) is fixed with fixing nails or connectors. The fixing nails are U-shaped nails made of φ8 steel bars. The width of the U-shaped nails is set to 5 - 7 cm, and the length is 14 - 16 cm. The geogrid (3) is a bidirectional plastic steel geogrid (3). The tensile strength of the bidirectional plastic steel geogrid (3) is set to ≥60 kn / m, the node peel resistance is ≥100 n, and the elongation at break is ≤3%. Earthwork backfilling step: The earthwork backfilling in the filling area (2) is completed. The earthwork backfilling is carried out layer by layer from bottom to top. After the geogrid (3) of the current step is laid, backfilling can be carried out. When backfilling the bottom layer of earthwork, the original ground is compacted, and earthwork backfilling can be carried out only after the compaction degree is detected and qualified. Transition section setting step: After the compaction degree is detected and qualified, set the transition section (6). The transition section (6) is the longitudinal plane at the step intersection connecting the geogrid (3). Here, the geogrid (3) is fixed with fixing nails. Repeat the above steps to complete the step construction from bottom to top until the construction at the excavation and filling intersection is completed. Set the length of the transition section (6) to 4H + 5 m, and the length of the transition section (6) is not less than 10 m. The H is the filling height from the first step to the bottom of the roadbed.

2. The two-way tie construction method for the cut-and-fill transition zone of the inclined excavation stepped subgrade according to claim 1, characterized in that The transition section (6) is provided with a double-layer geogrid (601), a lower roadbed (602), an upper roadbed (603) and a pavement structure layer (604) from bottom to top. First, the excavation and filling transition section (6) is constructed, and after the construction is completed, the adjacent filling area (2) section is filled.

3. The two-way tying construction method for the cutting and filling intersection area of the inclined excavation step-type roadbed according to claim 2, wherein, The geogrid (3) of the transition section (6) adopts a double-layer steel-plastic geogrid, and the double-layer steel-plastic geogrid is arranged across the full width of the transition section (6). The double-layer geogrid (601) is overlaid 3 m on both sides of the transition section (6).

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