Low embankment structure of flood detention area and construction method

Abstract

The application relates to a low embankment structure of a flood detention area and a construction method, belonging to the technical field of road engineering, which comprises a gravel cushion layer, a first sand cushion layer, a first composite waterproof geotextile, a multi-layered composite waterproof roadbed, a second composite waterproof geotextile and a third sand cushion layer which are sequentially arranged from bottom to top along the cross section of the embankment; the multi-layered composite waterproof roadbed comprises two layers of C-type waterproof geotextile bagged soil layers and one layer of A / B-type waterproof geotextile bagged soil layer which are alternately arranged from bottom to top, second sand cushion layers are arranged between the waterproof geotextile bagged soil layers, and longitudinal and transverse geotextile rib belts are arranged on the A / B-type waterproof geotextile bagged soil layer; the fourfold cooperative system of the waterproof geotextile bagging layering packaging, the rib belt three-dimensional locking, the sand cushion alternating drainage and the check valve anti-backflow effectively solves the problems of strength attenuation and heaving and settlement caused by the capillary rise of underground water and flood soaking of the low embankment of the flood detention area, and the embankment is low in height, does not block water, is high in integrity and convenient in construction.

Description

Technical Field

[0001] This invention belongs to the field of road engineering technology, and specifically relates to a low-lying roadbed structure and construction method for flood detention areas. Background Technology

[0002] Flood detention areas are low-lying areas temporarily storing excess water to intercept floods exceeding standard flood levels. They are often located near rivers, lakes, or other flood storage and detention areas. When constructing highways within flood detention areas, flood control planning restricts the design elevation of the roadbed to avoid obstructing water flow and affecting the flood discharge cross-section and flood storage capacity. However, the engineering conditions of low-lying roadbeds present the following prominent problems: First, the groundwater level is high. The flood detention area is low-lying, and the groundwater level is close to or higher than the bottom of the roadbed all year round. The capillary water rises strongly, and the roadbed soil is in a state of moisture or saturation for a long time, which leads to a decrease in the roadbed's resilience modulus and insufficient bearing capacity. Under repeated vehicle loads, it is prone to diseases such as frost heave, subsidence, and network cracking.

[0003] Second, there is the periodic soaking effect of floods. During the flood season, when flood detention areas store floodwater, the water level may rise to the height of the roadbed or even submerge the road surface, directly soaking the roadbed fill. If the fill is made of non-water-resistant materials, its strength will drop sharply after soaking. After the flood recedes, if the water accumulated inside the roadbed cannot be drained quickly, it will remain in a state of excessive moisture for a long time, seriously affecting the normal use of the road.

[0004] Third, low roadbeds lack sufficient fill height to block capillary water. Conventional high embankments rely on fill heights of over 1.5m to keep the roadbed working area above the groundwater level and capillary rise height, while the fill height of low roadbeds in flood detention areas is usually only 0.5m to 1.0m, which cannot achieve natural water isolation through fill height alone.

[0005] Fourth, existing drainage solutions have limited effectiveness. Traditional low-lying roadbeds often use crushed stone drainage ditches or gravel cushion layers to lower the groundwater level. However, there is a lack of complete waterproof seal between the drainage ditches and the bottom of the roadbed, allowing groundwater to still seep into the roadbed through paths other than the drainage ditches. There is a lack of organized collection and drainage channels for surface seepage and seepage from pavement cracks. When floodwaters rise in flood detention areas, high external water levels may also backflow into the roadbed through the drainage system.

[0006] For example, Chinese patent CN203174454U discloses a bagged soil silt-displacing roadbed structure, which uses geotextile bags to densely pile up soil in layers to form a trapezoidal cross-section to achieve the silt-displacing effect. However, this solution uses permeable woven bags, and the bags themselves do not have waterproof functions, allowing groundwater and floodwater to freely seep into the soil inside the bags; moreover, there is no classification between the bags, no rib connection, and no alternating sand cushion layers, resulting in poor overall integrity and making it unsuitable for the water-proofing requirements of flood detention areas.

[0007] For example, Chinese patent CN202310012303.4 discloses a geotextile tube roadbed and its construction method, which uses long tubes with straight long sides and raised short sides to be filled with fluidized solidified soil, and is connected and positioned by iron rings and ropes, and stacked in an alternating manner. However, the tubes in this scheme are long tubes, and the iron ring and rope connections are flexible point connections, which cannot form a three-dimensional network of planar interweaving and interlayer locking; moreover, the tubes have no waterproof sealing and no water-stopping function, and cannot solve the problem of soaking in flood retention areas.

[0008] For example, Chinese patent CN113152186B discloses a composite embankment with seepage prevention and drainage functions, which adopts a layered combination of aggregate waterproof layer, geotextile thin layer, porous geotextile drainage board and geotextile thin layer, and the slope is covered with high-strength woven bags of organic soil for vegetation. However, this scheme uses granular seepage prevention and drainage layer as the main body, without bagged solidified soil bearing structure, no classification or rib locking between bags, and the slope bags are only used for vegetation rather than the main bearing of the roadbed.

[0009] Furthermore, Chinese patent CN202210448927.6 discloses a ground fixture prestress retention structure, in which a cross-shaped locking strap and a sling are provided outside the bag, and prestress is obtained through vibration and pressure. However, its cross-shaped strap wraps around the individual bags instead of connecting between bags, and there is no layered bag classification, no alternating sand pads, no planar interweaving, and no interlayer misaligned bonding.

[0010] Therefore, there is an urgent need to develop an integrated water-blocking and drainage structure suitable for low roadbeds in flood detention areas. This structure can block groundwater and flood infiltration from the bottom and top, achieve rapid drainage and overall locking between layers, prevent backflow of external water during flood season, and has a low roadbed height, does not obstruct water, has strong integrity, is easy to construct, and is economical in cost. Summary of the Invention

[0011] This invention provides a low-lying roadbed structure and construction method for flood detention areas, which can solve the problems pointed out in the background art.

[0012] A low-lying roadbed structure for flood detention areas includes, from bottom to top, a crushed stone cushion layer, a first sand cushion layer, a first composite waterproof geotextile, a multi-layered composite waterproof roadbed, a second composite waterproof geotextile, and a third sand cushion layer. The edges of the crushed stone cushion layer extend into the drainage blind ditch trenches on both sides of the roadbed and are connected to the drainage blind ditch; the first sand cushion layer is laid flat on the top surface of the crushed stone cushion layer; the first composite waterproof geotextile is fully laid on the top surface of the first sand cushion layer, with its outer edge extending into the inner side of the drainage blind ditch and overlapping and sealing with the waterproof geotextile filter layer laid on the top of the drainage blind ditch. The multi-layer composite waterproof roadbed includes, from bottom to top, two alternating layers of Class C waterproof tarpaulin soil and one layer of Class A / B waterproof tarpaulin soil. A second sand cushion layer is provided between the two layers of Class C waterproof tarpaulin soil and between the Class C waterproof tarpaulin soil and the Class A / B waterproof tarpaulin soil. The top surface of the top layer of Class A / B waterproof tarpaulin soil is covered with the second sand cushion layer. The upper and lower layers of Class C waterproof tarpaulin soil are laid in a staggered manner, and the adjacent layers of Class A / B waterproof tarpaulin soil are staggered. The Class C waterproof tarpaulin soil layer is composed of Class C waterproof tarpaulins filled with solidified soil, and the Class C waterproof tarpaulin soil layer is laid continuously along the longitudinal direction of the roadbed. The soil-filled layer of the A / B type waterproof tarpaulin bag consists of A type waterproof tarpaulin bags filled with solidified soil and B type waterproof tarpaulin bags filled with solidified soil. The A type waterproof tarpaulin bags and B type waterproof tarpaulin bags in the same layer are arranged alternately in the horizontal and vertical directions. The Class A waterproof liner bags are standard main bags, with a planar length and width of 75cm to 85cm, and are lined with a geogrid reinforcement layer. The geogrid reinforcement layer effectively restrains the lateral deformation of the solidified soil inside the bag, diffuses vehicle load stress, and improves the overall bearing capacity and deformation resistance of the roadbed. The Class B waterproof liner bags are caulking auxiliary bags, with a planar length and width of 65cm to 75cm, their size adapted to the corner gaps enclosed by four adjacent Class A waterproof liner bags. During installation, the corner seams of the four Class A waterproof liner bags overlap with the corner portions of the four Class A waterproof liner bags, filling the caulking gaps between the Class A waterproof liner bags and eliminating weak points of leakage at the intersection of the four bags through the corner overlap. The Class A and Class B waterproof liner bags are laid in a crisscross pattern on the same layer, eliminating large-area through seams between bags within the same layer.

[0013] Both Type A and Type B waterproof tarpaulins have several cross-shaped geotextile ribs on their top surfaces. The ribs are made of the same material as the bag body, with a single rib width of 5cm to 10cm. The geotextile ribs of Type A waterproof tarpaulins are continuous in length, extending 5cm to 8cm beyond the sides of the bag body at both ends. The geotextile ribs of Type B waterproof tarpaulins only extend beyond the sides of the bag body at the overlap with those of Type A waterproof tarpaulins. Adjacent bags in the same layer are bonded together by the overlapping geotextile ribs, forming a planar, interwoven overall structure. When laying soil layers of adjacent Type A / B waterproof tarpaulins, the geotextile ribs of the upper bag are staggered and overlapped with those of the lower bag, so that the layers not only rely on friction between the bag contact surfaces but also form a three-dimensional locking structure through the bonding of the geotextile ribs, significantly improving the integrity and anti-slip ability of the roadbed.

[0014] The second composite waterproof geotextile is fully covered on the top surface of the multi-layered waterproof roadbed, and the third sand cushion layer is laid flat on the top surface of the second composite waterproof geotextile. Drainage blind ditches, sump pits, and open drainage ditches are arranged vertically from bottom to top on both sides of the roadbed. The drainage blind ditches are located at the elevation of the crushed stone subbase and run longitudinally through the roadbed. The sump pits are arranged at intervals along the longitudinal direction of the roadbed above the drainage blind ditches, and the bottom of the sump pits is connected to the drainage blind ditches. The open drainage ditches are located outside the sump pits. The third sand cushion layer is equipped with transverse drainage pipes that are buried at intervals along the longitudinal direction of the roadbed. The outer ends of the transverse drainage pipes extend out of the roadbed slope and connect to the slope protection drainage ditch. The outlet of the slope protection drainage ditch is connected to the open drainage ditch.

[0015] Preferably, the crushed stone cushion layer has a thickness of 20cm to 40cm, using continuously graded crushed stone with a particle size of 5mm to 40mm, and a compaction degree of ≥96%. The crushed stone cushion layer evenly distributes the upper load, isolates the original soft soil, and simultaneously serves as a lateral drainage channel, collecting groundwater and seepage water from beneath the first composite waterproof geotextile into the drainage blind ditches on both sides. The edges of the crushed stone cushion layer extend into the drainage blind ditch trench and connect with the drainage blind ditch, allowing free water within the cushion layer to directly flow into the drainage blind ditch.

[0016] The first sand cushion layer has a thickness of 10cm to 20cm and is laid with clean medium-coarse sand with a compaction degree of ≥95%. The first sand cushion layer has three functions: first, to level the unevenness of the top surface of the crushed stone cushion layer, providing a flat base for laying the composite waterproof geotextile; second, to serve as a buffer and protective layer to prevent the sharp edges of the crushed stone from breaking through the waterproof membrane layer; and third, to utilize the capillary barrier effect of sand to block the capillary upwelling channels of groundwater together with the crushed stone cushion layer.

[0017] The thickness of the C-type waterproof tarpaulin bag soil layer and the A / B-type waterproof tarpaulin bag soil layer is 20cm to 30cm, and the thickness of the second sand cushion layer is 8cm to 10cm.

[0018] Preferably, the first composite waterproof geotextile is a composite structure of one geotextile and one membrane or two geotextiles and one membrane, with a unit area mass of 300g / ㎡~600g / ㎡ and a vertical permeability coefficient ≤1×10 -8 The first layer, with a diameter of cm / s, forms the main waterproof barrier at the bottom. The edges on both sides are turned up to a height of ≥30cm, connecting with the inner wall of the drainage ditch; adjacent sections overlap longitudinally by ≥20cm, and the overlap seams are sealed by heat fusion welding to ensure a waterproof seal with no leakage channels. The second composite waterproof geotextile is a one-layer or two-layer structure, with a unit area mass of 200g / ㎡~400g / ㎡. It is fully laid on the top surface of the top sand cushion layer, with both sides extending downwards along the slope and wrapped around and pressed into the inner wall of the slope protection drainage ditch for fixation, forming a top waterproof sealing layer to prevent surface water infiltration.

[0019] The second composite waterproof geotextile is a composite structure of one fabric and one membrane or two fabrics and one membrane, with a unit area mass of 200g / ㎡~400g / ㎡ and a longitudinal overlap width of ≥20cm between adjacent sections. The two sides of the second composite waterproof geotextile extend downward along the roadbed slope and are pressed and fixed to the inner wall of the slope protection drainage ditch.

[0020] Preferably, the Class A, Class B, and Class C waterproof bags used in the soil layer are all rectangular bags made of coated woven geomembrane or composite geomembrane; the rectangular bag material has a CBR puncture strength ≥3.5kN, a longitudinal tensile strength ≥20kN / m, and a vertical permeability coefficient ≤1×10⁻⁶. -8 cm / s, UV aging resistance retention strength ≥80%; bag seams are sealed with hot-melt welding or double-layer polyurethane sealant. The waterproof tarpaulin bag is one of the core innovations of this invention, its functions being: 1. To encapsulate solidified soil in layers within an impermeable bag, making each bag an independent water-resistant load-bearing unit, preventing water from seeping into the soil during flooding, fundamentally solving the problem of roadbed soil softening due to water immersion; 2. The bag itself has high tensile and puncture strength, which can restrain the lateral deformation of the solidified soil inside the bag, improving load-bearing capacity; 3. The bags are prefabricated in the factory and filled and stacked on-site, making construction convenient and quality controllable.

[0021] Preferably, the overlap width of the upper and lower layers of soil-filled C-type waterproof tarpaulin bags is ≥15cm, and the lateral offset distance between the seams of the upper and lower layers of C-type waterproof tarpaulin bags is ≥50cm. The C-type waterproof tarpaulin bags have a planar length and width of 100cm to 150cm and are continuously laid longitudinally to form the bottom two main load-bearing layers of the multi-layered composite waterproof roadbed. The C-type waterproof tarpaulin bags are larger than the A-type and B-type waterproof tarpaulin bags, with a larger coverage area per bag, allowing for rapid foundation laying. A second sand cushion layer is provided between the two layers of soil-filled C-type waterproof tarpaulin bags, with an overlap width of ≥15cm and a lateral offset distance of ≥50cm between the seams of the upper and lower bags to avoid forming a continuous vertical leakage channel.

[0022] Preferably, the dimensions of the Class A waterproof bag are 75cm to 85cm, and the dimensions of the Class B waterproof bag are 65cm to 75cm. The width of a single longitudinal and transverse geotextile rib 16 is 5cm to 10cm, and the length of the rib extending beyond the side of the bag body is 5cm to 8cm; the longitudinal and transverse geotextile ribs are fixed to the top surface of the Class A or Class B waterproof bag.

[0023] Preferably, the contact surfaces of the interlocking longitudinal and transverse geotextile ribs are roughened fiber surfaces; a two-component polyurethane adhesive layer 17 is provided at the overlap position of the longitudinal and transverse geotextile ribs, which is uniformly coated on both sides, with a single-sided adhesive layer thickness of 0.15mm to 0.25mm and a rib overlap width of 5cm to 8cm.

[0024] Preferably, the solidified soil is low-liquid-limit silt or low-liquid-limit clay, with a clay content of 10%–25%, an organic matter content of ≤3%, a maximum particle size of ≤20mm, and a free expansion rate of ≤40%. 2%–4% of cement or lime solidifying agent by dry weight is added to the solidified soil. After bagging and compaction, the soil compaction degree is ≥94%, and the moisture content is controlled at 14%–20%. Adding a small amount of cement or lime can improve the water stability and early strength of the soil, preventing the soil inside the bag from softening or disintegrating when exposed to water. Using a low-dose solidifying agent instead of a high-dose method balances economy and workability.

[0025] Preferably, both the second and third sand cushion layers are laid with clean medium-coarse sand, with a mud content ≤5%, and the overall thickness of the cushion layers is uniform, ranging from 8cm to 10cm. The second sand cushion layer is laid between adjacent bagged soil layers. The functions of the sand cushion layer include: 1. leveling the unevenness of the top surface of the lower bag body, providing a uniform support surface for the upper bag body; 2. serving as an interlayer drainage channel, guiding any small amount of water that may seep in from the seams between the bags laterally to the sides of the roadbed for discharge; 3. the internal friction angle of the sand particles forms a large embedding friction force between the sand and the surface of the waterproof bag, assisting in interlayer anti-slip. The waterproof bags and sand cushion layers are alternately stacked to form a functional layer sequence of "waterproof-drainage-waterproof".

[0026] Preferably, transverse drainage pipes are installed longitudinally at intervals of 5m to 10m within the topmost second sand cushion layer. These pipes are perforated HDPE corrugated pipes or PVC pipes with a diameter of 80mm to 150mm, featuring a 2% to 4% outward slope. The outer end extends at least 20cm beyond the slope surface and connects to the slope protection drainage ditch. The slope protection drainage ditch is a cast-in-place concrete or masonry structure, installed along the slope surface. Its upper end connects to the transverse drainage pipe opening, and its lower end connects to an open drainage ditch. A stilling basin or erosion-resistant paving is installed at the outlet. Seepage from the road surface is blocked by the second composite waterproof geotextile and flows into the top sand cushion layer, then is systematically discharged through the transverse drainage pipes to the slope drainage ditch, and finally into the open drainage ditch.

[0027] Preferably, the drainage ditch is located at the elevation of the crushed stone cushion layer and runs longitudinally through it. The cross-section is rectangular or trapezoidal. The ditch is filled with graded crushed stone, and the outer side of the graded crushed stone is entirely wrapped with a permeable geotextile filter layer. A longitudinally perforated drainage pipe is installed inside the drainage ditch. The pipe runs longitudinally through the roadbed. The inner wall of the drainage ditch is connected to the crushed stone cushion layer. A waterproof geotextile is laid at the bottom of the ditch and sealed with the first composite waterproof geotextile, so that groundwater and seepage water can only flow into the ditch and be discharged without seeping back from the bottom of the ditch.

[0028] Preferably, the water collection wells are longitudinally spaced 30m to 50m above the drainage blind ditch, and are cast-in-place or precast reinforced concrete structures. A sedimentation pit is provided at the bottom of the well, and a water inlet is reserved at the junction of the well wall and the blind ditch. A one-way check valve is installed at the connection point between the drainage blind ditch and the water collection well, with an opening head of 3cm to 8cm. When the seepage head inside the roadbed is higher than the external water level, the check valve opens under internal water pressure, and the seepage flows through the blind ditch into the water collection well for discharge. When the flood detention area rises and the external water level is higher than the internal roadbed, the check valve automatically closes under external water pressure, preventing floodwater from flowing back into the roadbed.

[0029] A one-way check valve is installed at the connection point between the drainage blind ditch and the sump well. The opening head of the one-way check valve is 3cm to 8cm.

[0030] A method for constructing low-lying roadbeds in flood detention areas includes the following steps: S1. Roadbed excavation: Clear, level, and compact the roadbed area in the flood detention area. The compaction degree of the base should not be less than 90%. Excavate the roadbed and the drainage blind ditches and side ditches on both sides according to the design cross-section.

[0031] S2. Laying crushed stone subbase: Spread continuous graded crushed stone on the bottom surface of the roadbed, level and compact it in layers to the designed thickness, with a compaction degree ≥96%, and extend the two sides of the edge into the blind ditch trench.

[0032] S3. Laying the first sand cushion layer: Spread clean medium-coarse sand on the top surface of the crushed stone cushion layer, sprinkle water to level it and compact it to the designed thickness.

[0033] S4. Laying the first composite waterproof geotextile: Fully lay one layer of geotextile and one membrane or two layers of geotextile and one membrane composite waterproof geotextile on the top surface of the first sand cushion layer, with the membrane facing upwards. The longitudinal overlap of adjacent sections should be ≥20cm and hot-melt welded. The edges on both sides should be turned up ≥30cm and extended to the inner wall of the blind drain.

[0034] S5. Layered and composite waterproof subgrade construction: Preparation of solidified soil: Select low liquid limit silt or low liquid limit clay, add 2% to 4% cement or lime, and mix evenly at the optimum moisture content of 14% to 20%; fill the bags into Class C, Class A, and Class B waterproof bags respectively, with the Class A waterproof bags lined with a geogrid reinforcement layer, and the top surface of the Class A and Class B waterproof bags is prefabricated and fixed with cross-shaped longitudinal and transverse geotextile ribs; seal the bags after filling, and seal the bag opening seams with hot melt welding or polyurethane sealant. ② First, lay two layers of soil-filled Class C waterproof bags: Class C waterproof bags are laid continuously in the longitudinal direction, and a second sand cushion layer is laid between the layers. The two layers are staggered and overlapped by ≥15cm, and the joints of the upper and lower layers are staggered by ≥50cm in the transverse direction. The layers are compacted by using a plate vibratory tamper or a light vibratory roller. ③ Then, alternately lay A / B type waterproof cloth bag soil layer and second sand cushion layer: A type waterproof cloth bag and B type waterproof cloth bag are laid in a crisscross pattern in the same layer, and B type waterproof cloth bag is placed across the corner joint of four adjacent A type waterproof cloth bags and partially overlapped; after the ribs of adjacent bags overlap, they are fixed by two-component polyurethane adhesive; pressing ≥30s, static curing ≥2h; upper and lower bag soil layers are staggered and the ribs are staggered and bonded; after each bag soil layer and the second sand cushion layer (5) are laid, the whole is compacted and the flatness deviation is ≤15mm / 3m; layer by layer are stacked to the design height.

[0035] S6. Laying the second composite waterproof geotextile: Fully lay the composite waterproof geotextile on the top surface of the second sand cushion layer, with adjacent widths overlapping by ≥20cm and hot-melt welded. Extend the edges on both sides down the slope to wrap around and press them into the inner wall of the slope protection drainage ditch for fixation.

[0036] S7. Laying horizontal drainage pipes: Perforated HDPE or PVC horizontal drainage pipes are installed in the second sand cushion layer at intervals of 5m to 10m. The pipes are designed with an outward cross slope of 2% to 4%, and the pipe ends extend ≥20cm beyond the side slope.

[0037] S8. Drainage system construction: Drainage blind ditches (waterproof geotextile is laid at the bottom of the ditch and connected to the first composite waterproof geotextile, graded crushed stone is filled in the ditch and wrapped with a filter layer, and a longitudinal perforated pipe is installed in the middle), sump wells (settling pits are set at the bottom of the wells and water inlet holes are reserved in the well walls), open drainage ditches and slope protection drainage channels are constructed in sequence; one-way check valves are installed at the connection between the blind ditches and sump wells; all drainage facilities are connected together.

[0038] S9. Construct the pavement structure layer to complete the roadbed construction.

[0039] Preferably, in step S5, the solidified soil mix ratio and performance parameters are the same as above, the waterproof bag material parameters are the same as above, and the construction parameters for the crushed stone cushion layer and the first sand cushion layer are the same as above; the bagged soil layer is compacted by a plate vibratory tamper or a light vibratory roller, and it is prohibited to use heavy compaction equipment to directly compact the bag structure; the joints of the upper and lower bagged soil layers are staggered by a distance of ≥50cm, and the overlapping positions are staggered with each other, and there are no through vertical gaps inside the roadbed.

[0040] Preferably, in step S5, before bonding the longitudinal and transverse geotextile ribs, the overlapping contact surfaces are roughened and cleaned; two-component polyurethane adhesive is evenly applied to both sides, and the overlapping positions are aligned and pressed together for a pressing time of not less than 30 seconds; after bonding, the surface is allowed to cure for not less than 2 hours before the upper structure paving construction can be carried out; Class A waterproof bags are laid according to the grid positioning, and Class B waterproof bags are laid with overlapping joints, with the flatness deviation of the bag body ≤15mm / 3m.

[0041] Compared with the prior art, the present invention has the following beneficial effects: (1) Layered sealing to prevent water seepage, fundamentally solving the problem of soaking and softening. This invention encapsulates the solidified soil in layers within impermeable waterproof bags (vertical permeability coefficient ≤ 1×10). -8 (cm / s), each bag is an independent waterproof bearing unit, preventing water from seeping into the bag during flood immersion, fundamentally solving the problem of soil softening and sudden strength drop in the subgrade. Compared with the fully permeable and water-resistant granular material solution, low liquid limit silt or clay can be sourced locally, with only 2% to 4% cement or lime added, significantly reducing material costs.

[0042] (2) The corners of the A / B main and auxiliary bags are fitted together to eliminate weak points of leakage. The size of the B-type waterproof bag is 65cm to 75cm, which just spans the corner seams of the four adjacent A-type waterproof bags (75cm to 85cm) and partially overlaps. This fills the gap between the A-type waterproof bags and covers the weak points of leakage where the four bags meet, so that there are no large-area through seams in the same layer.

[0043] (3) Cross-rib three-dimensional locking significantly enhances the overall integrity. The continuous ribs of the Class A waterproof bag and the overlapping ribs of the Class B waterproof bag are bonded to the same layer to form a planar crisscross network. The upper and lower ribs are staggered and bonded to form a three-dimensional locking structure, connecting the independent bag bodies into an overall force-bearing system. The interlayer shear strength is improved from pure friction to a triple mechanism of "friction + adhesive bonding + rib interlocking", which effectively resists interlayer slippage and uneven settlement caused by vehicle load.

[0044] (4) The "waterproof-drainage-waterproof" function alternates, and the drainage between layers is smooth. The waterproof bag (waterproof) and the sand cushion layer (drainage) are alternately stacked. A small amount of water seeping in from the seam between the bags can be guided laterally to the blind drains on both sides through the sand cushion layer and will not stagnate between the layers. The bottom first composite waterproof geotextile blocks capillary water, and the top second composite waterproof geotextile blocks the infiltration of road surface water, forming a full-section closure.

[0045] (5) Check valve prevents backflow and adapts to the rise and fall of water level in the flood detention area. A one-way check valve (opening head 3cm~8cm) is installed at the water inlet of the drainage blind channel. Internal seepage can be discharged while external flood cannot backflow, adapting to the bidirectional water level change requirements of the flood detention area of ​​"internal water discharge and external water no backflow".

[0046] (6) The roadbed is low and does not obstruct water, making construction convenient. The thickness of a single layer of bagged soil is only 20cm to 30cm, which can be flexibly stacked to a low roadbed height of 0.5m to 1.0m, meeting the flood control height limit requirements of flood detention areas; the bags are prefabricated in the factory and filled and stacked on site, without the need for large special equipment, and the construction speed is fast and the quality is controllable. Attached Figure Description

[0047] Figure 1 This is a schematic cross-sectional view of the low-lying roadbed structure in the flood detention area of ​​this invention; Figure 2This is an enlarged schematic diagram of the interlayer structure of the multi-layer composite waterproof roadbed of the present invention; Figure 3 This is an enlarged schematic diagram of the interlayer structure of the multi-layer composite waterproof roadbed of the present invention; In the diagram: 1- Crushed stone cushion layer; 2- First sand cushion layer; 3- First composite waterproof geotextile; 4- Class C waterproof geotextile bagged soil layer; 5- Second sand cushion layer; 6- Class A / B waterproof geotextile bagged soil layer; 7- Blind drain; 8- Water collection well; 9- Open drainage ditch; 10- Second composite waterproof geotextile; 11- Third sand cushion layer; 12- Transverse drainage pipe; 13- Slope protection drainage ditch; 14- Class A waterproof geotextile bag; 15- Class B waterproof geotextile bag; 16- Longitudinal and transverse geotextile ribs; 17- Polyurethane adhesive layer. Detailed Implementation

[0048] The following detailed description of a specific embodiment of the present invention is provided in conjunction with the accompanying drawings. However, it should be understood that the scope of protection of the present invention is not limited to the specific embodiment.

[0049] Example 1: As Figure 1-3 As shown in the figure, the embodiment of the present invention provides a low roadbed structure for flood detention areas, which is set in an excavated roadbed. Along the cross section of the roadbed, from bottom to top, there are a crushed stone cushion layer 1, a first sand cushion layer 2, a first composite waterproof geotextile 3, a multi-layer composite waterproof roadbed, a second composite waterproof geotextile 10, and a third sand cushion layer 11.

[0050] The crushed stone subbase 1 is 30cm thick, made of continuously graded crushed stone with a particle size of 5mm to 40mm and a compaction degree of ≥96%. It is laid on the bottom of the roadbed, and the two sides extend into the drainage blind ditch 7 base trench and are connected to the blind ditch.

[0051] The first sand cushion layer 2 is 15cm thick, made of clean medium-coarse sand with a mud content of ≤3% and a compaction degree of ≥95%, and is laid on top of the crushed stone cushion layer 1.

[0052] The first composite waterproof geotextile 3 has a two-layer fabric and one-layer membrane structure (long-fiber geotextile + PE membrane + long-fiber geotextile), a unit area mass of 400g / ㎡, a membrane thickness of 0.3mm, and a vertical permeability coefficient ≤1×10 -9 cm / s, CBR puncture strength ≥3.0kN, tensile strength at break ≥20kN / m. The first composite waterproof geotextile 3 is fully laid on the top surface of the first sand cushion layer 2 with the membrane surface facing upwards. The two sides are turned up 40cm high and extended to the inner wall of the drainage blind ditch 7. The longitudinal overlap width of adjacent widths is 25cm, and the overlap seam is double-sealed by heat fusion welding.

[0053] The multi-layered waterproof roadbed, from bottom to top, comprises two layers of Class C waterproof tarpaulin-filled soil 4, four sets of alternating Class A / B waterproof tarpaulin-filled soil 4, and a second sand cushion layer 5. In this embodiment, the total thickness of the multi-layered waterproof roadbed is approximately 0.8m.

[0054] The soil layer consists of two layers of Class C waterproof tarpaulin bags, each measuring 120cm x 120cm. These bags are constructed from coated woven waterproof fabric (PP woven fabric + PE coating) and have a CBR bursting strength of 4.2kN, a longitudinal tensile strength of 25kN / m, and a vertical permeability coefficient ≤5×10⁻⁶. -9 cm / s, seams are sealed by hot-melt welding. Class C waterproof tarpaulins are filled with solidified soil, each layer 25cm thick, laid continuously along the longitudinal direction. A second sand cushion layer 5, 10cm thick, is placed between two layers of Class C waterproof tarpaulins. The soil layers 4 of the two Class C waterproof tarpaulins overlap with a 20cm width, and the seams of the upper and lower bag layers are staggered laterally by 60cm.

[0055] Four groups of Class A / B waterproof tarpaulin bags filled with soil (6) and a second sand cushion layer (5) are laid alternately: each group includes one layer of Class A / B waterproof tarpaulin bags filled with soil (66) and one layer of second sand cushion layer (5). Class A waterproof tarpaulin bags (14) are 80cm x 80cm in plan view, using the same coated woven impermeable fabric as Class C waterproof tarpaulin bags, with a bidirectional geogrid reinforcement layer (fiberglass geogrid, longitudinal and transverse tensile strength ≥50kN / m, mesh size 25mm x 25mm) inside. Class B waterproof tarpaulin bags (15) are 70cm x 70cm in plan view, made of the same material, without a geogrid reinforcement layer. Both Class A waterproof tarpaulin bags (14) and Class B waterproof tarpaulin bags (15) are filled with solidified soil, with a single layer thickness of 25cm.

[0056] In the same layer, Class A waterproof fabric bags 14 and Class B waterproof fabric bags 15 are arranged in a staggered pattern both horizontally and vertically: Class A waterproof fabric bags 14 are positioned according to an 80cm × 80cm grid, and Class B waterproof fabric bags 15 are positioned at the corner gaps enclosed by four adjacent Class A waterproof fabric bags 14. Class B waterproof fabric bags 15 span the corner seams of four Class A waterproof fabric bags 14 and overlap the corners of each of the four Class A waterproof fabric bags 14 by approximately 5cm. The circumferential butt joint of the Class A waterproof fabric bags 14 and Class B waterproof fabric bags 15 in the same layer extends horizontally.

[0057] Both Class A waterproof liner bags 14 and Class B waterproof liner bags 15 have two cross-shaped geotextile ribs 16 sewn onto their top surfaces. The ribs are made of the same coated woven geotextile material as the bag body, with a single rib width of 8cm. The ribs of Class A waterproof liner bags 14 are continuous, crossing the center line of the bag body, with each end extending 6cm beyond the side of the bag body. The ribs of Class B waterproof liner bags 15 only extend 6cm beyond the bag edge at the four corners where they overlap with Class A waterproof liner bags 14; they do not extend in other directions. When adjacent bags are laid in the same layer, the extended ribs overlap each other. The overlapping surfaces are pre-treated with fiber roughening (sanding and roughening), cleaned, and then coated with two-component polyurethane adhesive 47 on both sides, with a single-sided adhesive layer thickness of 0.2mm. The rib overlap width is 6cm, and the surfaces are pressed together for 40 seconds before bonding. The ribs of the adjacent A / B type waterproof cloth bag soil layers 6 are staggered (the direction of the upper ribs is rotated 45° relative to the lower layer and intersects), and are staggered and overlapped to form a three-dimensional interlayer locking structure.

[0058] Both the second sand cushion layer 5 and the second sand cushion layer 11 are made of clean medium-coarse sand with a mud content of ≤4% and a thickness of 10cm. The second sand cushion layer 5 is laid between the two layers of Class C waterproof liner bags and between each group of Class A / B waterproof liner bag soil layers 6. The circumferential butt joints of adjacent Class A / B waterproof liner bag soil layers 6 are staggered by 60cm laterally, and the overlapping positions are also staggered, with no through vertical gaps.

[0059] The substrate for the solidified soil is low-liquid-limit silt with a clay content of 18%, an organic matter content of 1.5%, a maximum particle size of 15mm, and a free expansion rate of 25%. 3% (dry weight) of PO 42.5 ordinary Portland cement is added and mixed evenly at an optimum moisture content of 17%. After bagging and compaction, the compaction degree is ≥95%.

[0060] The second composite waterproof geotextile 5 is a one-layer geotextile-one-membrane structure (long-filament geotextile + PE membrane), with a unit area mass of 300g / ㎡, a membrane thickness of 0.2mm, and a vertical permeability coefficient ≤1×10. -9 cm / s, fully laid on the top surface of the second sand cushion layer 5, with a longitudinal overlap width of 20cm between adjacent sections, and the overlap seam is hot-melted welded; the two sides extend down the roadbed slope for a length of 60cm and are pressed into the inner wall of the slope protection drainage ditch 13 and fixed with cement nails.

[0061] Drainage blind ditch 7, water collection well 8 and open drainage ditch 9 are set up on both sides of the roadbed from bottom to top.

[0062] Drainage blind ditch 7 is located at the elevation of crushed stone cushion layer 1, running longitudinally with a trapezoidal cross-section, a bottom width of 40cm, and a depth of 60cm. The ditch is filled with graded crushed stone with a particle size of 20mm–40mm, and the crushed stone is wrapped with a permeable geotextile filter layer (equivalent pore size O). 95 =0.2mm, permeability coefficient ≥1×10 -2(cm / s). A perforated PVC drainage pipe with a diameter of 150mm, a hole diameter of 10mm, an opening rate of 3%, and a longitudinal slope of 0.5% is installed longitudinally in the middle of the blind drain. The inner wall of the blind drain is connected to the crushed stone cushion layer 1, and the bottom of the drain is covered with waterproof geotextile and sealed with the first composite waterproof geotextile 3.

[0063] One water collection well (8) is installed every 40m along the longitudinal direction. It is a cast-in-place C25 reinforced concrete structure with an inner diameter of 80cm and a depth of 120cm. A sedimentation pit with a depth of 25cm is set at the bottom of the well. A water inlet hole (20cm×20cm in size, with the bottom of the hole flush with the bottom of the drainage ditch 7) is reserved at the junction of the well wall and the drainage ditch 7. A cast iron manhole cover is installed on the top of the well, with the top surface of the manhole cover flush with the road shoulder.

[0064] A one-way check valve is installed at the connection point (inlet) between the drainage blind ditch 7 and the water collection well 8. It is a flap-type check valve with an opening head of 5cm. When the water head inside the roadbed is more than 5cm higher than the external water level, the valve flap opens to drain water under the action of internal water pressure; when the external water level is higher than the internal water level, the valve flap closes tightly against the valve seat under the action of external water pressure to prevent flood backflow.

[0065] The open drainage ditch 9 is located outside the water collection well 8. It has a trapezoidal cross section and is protected by C20 cast-in-place concrete. The longitudinal slope of the bottom of the ditch is 0.5%.

[0066] A transverse drainage pipe 12 is installed every 8m along the longitudinal direction inside the top layer of the second sand cushion layer 5. The transverse drainage pipe 12 is a perforated HDPE double-wall corrugated pipe with a pipe diameter of 100mm, a pipe hole diameter of 8mm, an opening rate of 2.5%, and the pipe slopes towards the outside of the roadbed at a 3% transverse slope. The outer end extends 25cm out of the slope surface, and the pipe end is sealed and connected to the side wall of the slope protection drainage ditch 13.

[0067] The slope protection drainage channel 13 has a trapezoidal cross section and is constructed with C20 cast-in-place concrete. The longitudinal slope of the channel bottom is consistent with the slope ratio of the roadbed side slope (1:1.5). The upper inlet of the drainage channel is connected to the end of the transverse drainage pipe 12, and the lower outlet leads to the open drainage ditch 9. A C20 concrete stilling basin (80cm long × 60cm wide × 30cm deep) is set at the outlet.

[0068] The construction method for the aforementioned low-lying roadbed structure in the flood detention area includes the following steps: S1. Roadbed excavation: Clear, level and compact the surface, with a base compaction degree ≥90%. Excavate the roadbed and drainage blind ditches and side ditches on both sides according to the design cross-section.

[0069] S2. Laying crushed stone cushion layer: Spread continuous graded crushed stone in two layers, each layer 15cm, level and compact to a compaction degree ≥96%, extending to the blind ditch foundation trench on both sides.

[0070] S3. Lay the first sand cushion layer: Spread 15cm thick clean medium-coarse sand, sprinkle water to level it, and lightly vibrate and compact it.

[0071] S4. Laying the first composite waterproof geotextile: Fully lay two layers of composite waterproof geotextile with the membrane facing upwards, overlap longitudinally by 25cm and heat-melt weld, and turn up 40cm on both sides to the inner wall of the blind drain.

[0072] S5. Layered and composite waterproof subgrade construction: ① Preparation of solidified soil: Take low liquid limit silt, add 3% cement, and mix evenly at a moisture content of 17%; fill the bags into Class C waterproof bags (120cm×120cm), Class A waterproof bags 14 (80cm×80cm, lined with fiberglass geogrid), and Class B waterproof bags 15 (70cm×70cm); prefabricate cross ribs on the top surface of Class A waterproof bags 14 and Class B waterproof bags 15; heat-seal the bags after filling. ② Lay two layers of Class C waterproof bags: Class C waterproof bags are arranged continuously in the longitudinal direction, with a 10cm sand cushion layer between the layers, staggered by 20cm, and the seams staggered by 60cm. Compact with a flat vibratory tamper. ③ Alternately lay A / B type waterproof liner bags 6 and the second sand pad layer 5: A type waterproof liner bags 14 are positioned according to an 80cm grid, and B type waterproof liner bags 15 are positioned at the four corners with an overlap of 5cm; the overlapping surfaces of the ribs are sanded, cleaned, and coated with polyurethane adhesive (0.2mm thick) on both sides, overlapped by 6cm, pressed for 40s, and allowed to cure for 2.5h; the upper and lower layers are staggered and overlapped, and the ribs are staggered at 45° and bonded; each layer is compacted by vibratory compaction, with a flatness ≤15mm / 3m; a total of 4 sets of A / B type waterproof liner bags 6 + sand pads are laid, with a total height of about 0.8m.

[0073] S6. Laying the second composite waterproof geotextile 10: Fully lay one layer of geotextile and one layer of membrane, overlap by 20cm and heat-melt weld, and press into the drainage ditch for fixation on both sides along the slope for 60cm.

[0074] S7. Laying horizontal drainage pipes 12: Install φ100 perforated HDPE pipes every 8m in the top sand cushion layer, with a 3% cross slope and the outer end extending 25cm out of the slope.

[0075] S8. Drainage system construction: Drainage blind ditch 7 (waterproof geotextile is laid at the bottom of the ditch and connected to the first composite waterproof geotextile, filled with crushed stone and wrapped with a filter layer, and φ150 perforated PVC pipe is placed) → Water collection well 8 (one every 40m, with a 25cm sand pit at the bottom of the well, a 20cm×20cm water inlet hole on the well wall, and a flap valve-type check valve installed, with a water head of 5cm when opened) → Open drainage ditch → Slope protection drainage channel 13 (C20 concrete, with a stilling basin at the outlet); All facilities are connected together.

[0076] S9. Construct the road structure layer (base course + surface course) above the second composite waterproof geotextile 10 and the third sand cushion layer 11 to complete the construction.

[0077] Example 2: This example has a structure that is basically the same as that of Example 1, except that: The multi-layered waterproof roadbed has a total thickness of approximately 0.6m, comprising two layers of Class C waterproof tarpaulin-filled soil (4) and three sets of Class A / B waterproof tarpaulin-filled soil (6) (one less than in Example 1). Each single-layer tarpaulin-filled soil layer is 20cm thick, and the sand cushion layer is 8cm thick. The Class C waterproof tarpaulin bags are 100cm x 100cm in plan, the Class A waterproof tarpaulin bags (14) are 75cm x 75cm, and the Class B waterproof tarpaulin bags (15) are 65cm x 65cm. The corners of the Class B waterproof tarpaulin bags (15) and Class A waterproof tarpaulin bags (14) overlap by approximately 4cm.

[0078] The solidified soil is made of low liquid limit clay with a clay content of 22%, mixed with 2% lime as a solidifying agent, a moisture content of 16%, and a compaction degree of ≥94%.

[0079] The first composite waterproof geotextile 3 adopts a one-layer geotextile and one-layer membrane structure, with a unit area mass of 300g / ㎡. The second composite waterproof geotextile 10 adopts a one-layer geotextile and one-layer membrane structure, with a unit area mass of 200g / ㎡.

[0080] The horizontal drainage pipe 12 is made of PVC pipe with a diameter of 80mm, a longitudinal spacing of 10m, and a cross slope of 2%.

[0081] The drainage blind ditch has a bottom width of 30cm and a depth of 40cm, with a longitudinally perforated PVC pipe diameter of 100mm. The water collection wells are spaced 50m apart, with an inner diameter of 60cm and a depth of 80cm. The check valve opens with a water head of 3cm.

[0082] This embodiment is applicable to low-grade roads with shallow flooding depth and a roadbed fill height of about 0.6m.

[0083] Example 3: This example has a structure that is basically the same as that of Example 1, except that: The multi-layered waterproof roadbed has a total thickness of approximately 1.0m, comprising two layers of Class C waterproof tarpaulin-filled soil (4) and six sets of Class A / B waterproof tarpaulin-filled soil (6). Each single-layer tarpaulin-filled soil layer is 30cm thick, and the sand cushion layer is 10cm thick. The Class C waterproof tarpaulin bags are 150cm x 150cm in plan, the Class A waterproof tarpaulin bags (14) are 85cm x 85cm, and the Class B waterproof tarpaulin bags (15) are 75cm x 75cm. The corners of the Class B waterproof tarpaulin bags (15) and Class A waterproof tarpaulin bags (14) overlap by approximately 6cm.

[0084] The solidified soil is made of low liquid limit silt with a clay content of 12%, 4% cement, a moisture content of 19%, and a compaction degree of ≥96%.

[0085] The waterproof geotextile bags are made of composite geomembrane (two layers of fabric and one layer of membrane, 600g / ㎡), with a CBR puncture strength of 4.5kN, a longitudinal tensile strength of 30kN / m, and a vertical permeability coefficient ≤1×10⁻⁶. -10 cm / s, and the joints are sealed with double-layer polyurethane sealant.

[0086] The first composite waterproof geotextile 3 uses two layers of fabric and one layer of membrane, with a strength of 600g / ㎡; the second composite waterproof geotextile 10 uses two layers of fabric and one layer of membrane, with a strength of 400g / ㎡.

[0087] The horizontal drainage pipe 12 is made of HDPE corrugated pipe with a diameter of 150mm, a longitudinal spacing of 5m, and a cross slope of 4%.

[0088] The drainage blind ditch has a bottom width of 50cm, a depth of 80cm, and a longitudinal perforated pipe diameter of 200mm. The sump pits are spaced 30m apart, with an inner diameter of 100cm and a depth of 150cm. The check valve opens at a head of 8cm.

[0089] The longitudinal and transverse geotextile ribs 16 have a rib width of 10cm, an extension length of 8cm, an overlap width of 8cm, and a polyurethane adhesive layer 17 with a single-sided thickness of 0.25mm. The bonding process is 60s, followed by static curing for 3 hours.

[0090] This embodiment is applicable to trunk highways with large flood retention depths and high traffic load levels.

[0091] Comparative Example 1: The difference between this comparative example and Example 1 is that the bag body is made of ordinary permeable woven bag (non-woven needle-punched geotextile, equivalent pore size O). 95 =0.15mm, vertical permeability coefficient ≥1×10 -2 (cm / s), and is not waterproof. The rest of the structure is the same as in Example 1.

[0092] Comparative Example 2: The difference between this comparative example and Example 1 is that the type B waterproof liner 15 is omitted, and only type A waterproof liner 14 is used arranged in a regular grid, with the gaps between the type A waterproof liner 14 filled with loose solidified soil. The rest of the structure is the same as in Example 1.

[0093] Comparative Example 3: The difference between this comparative example and Example 1 is that the longitudinal and transverse geotextile ribs 16 and the polyurethane adhesive bonding are omitted, and the bags are only overlapped by friction between the contact surfaces. The rest of the structure is the same as in Example 1.

[0094] Comparative Example 4: The difference between this comparative example and Example 1 is that the one-way check valve is removed, and the drainage blind ditch 7 is directly connected to the sump well 8. The rest of the structure is the same as in Example 1.

[0095] Performance testing The following performance tests were conducted on the roadbed structures of Examples 1-3 and Comparative Examples 1-4: (1) Waterproof performance: The water tank on one side of the roadbed is filled with water to submerge the top surface of the roadbed by 0.5m. After soaking for 7 days, the bag is cut open to detect the change in the water content of the soil inside.

[0096] (2) Interlayer shear strength: In-situ direct shear test was conducted at the interface between each layer of bag body and sand cushion layer to determine the interface shear strength.

[0097] (3) Overall bearing capacity: Benkelman beam deflection test and bearing plate test were carried out on the top surface of the roadbed to determine the resilient modulus and deflection value.

[0098] (4) Drainage performance: Water was injected into the top sand cushion layer to simulate the seepage of the road surface, and the drainage response time of the transverse drainage pipes and blind drains was measured.

[0099] (5) Backflow protection: Fill the outside of the water well with water to 0.3m higher than the water level inside the well, and continue for 24 hours to check whether there is backflow of water into the blind ditch and the roadbed.

[0100] The test results are shown in the table below:

[0101] Test results show that: (1) The waterproof bags in Examples 1 to 3 have excellent water-proof performance. After soaking for 7 days, the water content of the soil inside the bag changes by only 0.2% to 0.4%. In contrast, the water content of the soil in Comparative Example 1 increased by 18.5% after using a permeable woven bag. The soil was severely softened by water immersion, with a rebound modulus of only 68 MPa and a deflection value as high as 380 (0.01 mm). This proves that the water-proof sealing of the waterproof bag is the core functional basis of the present invention.

[0102] (2) The interlayer interface shear strength of Example 1 was 85 kPa, which is 2.0 times that of Comparative Example 3 (without rib bonding, 42 kPa), proving that the three-dimensional locking structure formed by the planar interlacing of cross ribs and the interlayer staggered bonding significantly improves the interlayer shear capacity and the overall integrity of the subgrade. The deflection value of Comparative Example 3 was 260 (0.01 mm), which is much larger than that of Example 1 (125), indicating that the overall stiffness of the subgrade is insufficient without rib bonding.

[0103] (3) After removing the Class B waterproof bag 15 in Comparative Example 2, the gap between the Class A waterproof bags 14 was filled with loose soil, and the drainage response time was extended to 8 minutes (3 minutes in Example 1). The deflection value of 175 was greater than that of 125 in Example 1, which proved that the corner fitting of the Class B waterproof bag 15 accelerated the interlayer drainage (continuous sand cushion layer) and improved the overall integrity.

[0104] (4) After the check valve was removed in Comparative Example 4, the floodwaters flowed back 0.3m through the blind ditch under the external high water level conditions, proving that the check valve is indispensable for preventing backflow in the flood detention area.

[0105] (5) Example 3 uses a higher dose of curing agent (4% cement), a larger bag size and a higher specification waterproof membrane, and has the best performance in all aspects, making it suitable for high-grade roads; Example 2 has lower parameters but still meets the requirements for use on low-grade roads, proving that the parameters of this invention can be flexibly adjusted according to the load level.

[0106] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A low-lying roadbed structure for flood detention areas, characterized in that: The roadbed consists of a crushed stone cushion layer (1), a first sand cushion layer (2), a first composite waterproof geotextile (3), a multi-layer composite waterproof roadbed, a second composite waterproof geotextile (10), and a third sand cushion layer (11), laid sequentially from bottom to top along the cross section of the roadbed. The edges of the crushed stone cushion layer (1) extend to the drainage blind ditch (7) on both sides of the roadbed and are connected to the drainage blind ditch (7); the first sand cushion layer (2) is laid flat on the top surface of the crushed stone cushion layer (1); the first composite waterproof geotextile (3) is fully laid on the top surface of the first sand cushion layer (2), with its outer edge extending to the inner side of the drainage blind ditch (7) and overlapping and sealing with the waterproof geotextile filter layer laid on the top of the drainage blind ditch (7); The multi-layer composite waterproof roadbed consists of two alternating layers of Class C waterproof tarpaulin soil (4) and one layer of Class A / B waterproof tarpaulin soil (6) from bottom to top. A second sand cushion layer (5) is provided between the two layers of Class C waterproof tarpaulin soil (4) and between the Class C waterproof tarpaulin soil (4) and the Class A / B waterproof tarpaulin soil (6). The top surface of the top layer of Class A / B waterproof tarpaulin soil (6) is covered with the second sand cushion layer (5). The upper and lower layers of Class C waterproof tarpaulin soil (4) are laid in a staggered manner, and the adjacent layers of Class A / B waterproof tarpaulin soil (6) are staggered. The C-type waterproof tarpaulin soil layer (4) is composed of C-type waterproof tarpaulins filled with solidified soil. The C-type waterproof tarpaulin soil layer (4) is laid continuously along the longitudinal direction of the roadbed. The A / B type waterproof tarpaulin soil layer (6) consists of A type waterproof tarpaulin (14) filled with solidified soil and B type waterproof tarpaulin (15) filled with solidified soil. The A type waterproof tarpaulin (14) and B type waterproof tarpaulin (15) in the same layer are arranged alternately in the horizontal and vertical directions. The Class A waterproof tarpaulin bag (14) is a standard main bag with a geogrid reinforcement layer inside; the Class B waterproof tarpaulin bag (15) is a caulking auxiliary bag, with a single Class B waterproof tarpaulin bag (15) spanning the corner seam of four adjacent Class A waterproof tarpaulins (14) and partially overlapping with the corners of the four Class A waterproof tarpaulins (14). The top surfaces of both the Class A waterproof liner (14) and the Class B waterproof liner (15) are provided with several cross-shaped geotextile ribs (16); the cross-shaped geotextile ribs (16) of the Class A waterproof liner (14) are set along the entire length, with both ends extending out of the side of the bag body; the cross-shaped geotextile ribs (16) of the Class B waterproof liner (15) only extend out of the side of the bag body at the overlap position with the Class A waterproof liner (14); adjacent bags in the same layer are bonded together by the cross-shaped geotextile ribs (16) to form a planar cross-shaped overall structure. The second composite waterproof geotextile (10) is fully covered on the top surface of the multi-layer composite waterproof roadbed, and the third sand cushion layer (11) is laid flat on the top surface of the second composite waterproof geotextile (10). Drainage blind ditches (7), water collection wells (8), and open drainage ditches (9) are arranged vertically from bottom to top on both sides of the roadbed. The drainage blind ditches (7) are located at the elevation of the crushed stone cushion layer (1) and are arranged longitudinally along the roadbed. The water collection wells (8) are arranged at intervals above the drainage blind ditches (7) along the longitudinal direction of the roadbed, and the bottom of the water collection wells (8) is connected to the drainage blind ditches (7). The open drainage ditches (9) are arranged outside the water collection wells (8). The third sand cushion layer (11) is provided with transverse drainage pipes (12) buried at intervals along the longitudinal direction of the roadbed. The outer end of the transverse drainage pipe (12) extends out of the roadbed slope and connects to the slope protection drainage ditch (13). The outlet of the slope protection drainage ditch (13) is connected to the open drainage ditch (9).

2. The low-lying roadbed structure in the flood detention area according to claim 1, characterized in that: The crushed stone cushion layer (1) has a thickness of 20cm to 40cm, is laid with continuously graded crushed stone with a particle size of 5mm to 40mm, and has a compaction degree of ≥96%; the first sand cushion layer (2) has a thickness of 10cm to 20cm, is laid with clean medium-coarse sand, and has a compaction degree of ≥95%. The thickness of the C-type waterproof tarpaulin bag soil layer (4) and the A / B-type waterproof tarpaulin bag soil layer (6) is 20cm to 30cm, and the thickness of the second sand cushion layer (5) is 8cm to 10cm.

3. The low-lying roadbed structure in the flood detention area according to claim 1, characterized in that: The first composite waterproof geotextile (3) is a composite structure of one fabric and one membrane or two fabrics and one membrane, with a unit area mass of 300g / ㎡~600g / ㎡, the height of the two sides turned up is ≥30cm, the longitudinal overlap width of adjacent widths is ≥20cm, and the overlap seam is sealed by hot melt welding. The second composite waterproof geotextile (10) is a composite structure of one fabric and one membrane or two fabrics and one membrane, with a unit area mass of 200g / ㎡~400g / ㎡ and a longitudinal overlap width of ≥20cm between adjacent sections. The edges of the second composite waterproof geotextile (10) extend down along the roadbed slope and are pressed and fixed to the inner wall of the slope protection drainage ditch (13).

4. The low-lying roadbed structure in the flood detention area according to claim 1, characterized in that: The Class A waterproof tarpaulin bag (14), Class B waterproof tarpaulin bag (15), and Class C waterproof tarpaulin bag used in the soil layer (4) are all rectangular bags made of coated woven impermeable fabric or composite geomembrane; the rectangular bag has a CBR puncture strength ≥3.5kN, a longitudinal tensile strength ≥20kN / m, and a vertical permeability coefficient ≤1×10 -8 cm / s, UV aging resistance retention rate ≥80%; rectangular bag body splicing seams are sealed by hot melt welding or double polyurethane sealant.

5. The low-lying roadbed structure in the flood detention area according to claim 4, characterized in that: The overlap width of the upper and lower layers of C-type waterproof tarpaulin bags containing soil (4) is ≥15cm, and the horizontal distance between the splicing seams of the upper and lower layers of C-type waterproof tarpaulin bags is ≥50cm; the length and width of the C-type waterproof tarpaulin bags are 100cm to 150cm.

6. The low-lying roadbed structure in the flood detention area according to claim 1, characterized in that: The A-type waterproof bag (14) has a planar length and width of 75cm to 85cm, and the B-type waterproof bag (15) has a planar length and width of 65cm to 75cm. The width of a single longitudinal and transverse geotextile rib (16) is 5cm to 10cm, and the length of the rib extending out of the side of the bag body is 5cm to 8cm; the longitudinal and transverse geotextile rib (16) is fixed to the top surface of the Class A waterproof bag (14) or the Class B waterproof bag (15).

7. The low-lying roadbed structure in the flood detention area according to claim 6, characterized in that: The contact surface of the interlocking longitudinal and transverse geotextile ribs (16) is a roughened fiber surface; a two-component polyurethane adhesive layer (17) is set at the overlap position of the longitudinal and transverse geotextile ribs (16), which is uniformly coated on both sides, with a single-sided adhesive layer thickness of 0.15mm to 0.25mm and a rib overlap width of 5cm to 8cm.

8. The low-lying roadbed structure in the flood detention area according to claim 1, characterized in that: The solidified soil is low liquid limit silt or low liquid limit clay, with a clay content of 10% to 25%, an organic matter content of ≤3%, a maximum particle size of ≤20mm, and a free expansion rate of ≤40%. 2% to 4% of cement or lime solidifying agent is added to the solidified soil, and after bagging and compaction, the soil compaction degree is ≥94%, and the moisture content is controlled at 14% to 20%.

9. The low-lying roadbed structure in the flood detention area according to claim 1, characterized in that: The second sand cushion layer (5) and the third sand cushion layer (11) are both laid with clean medium-coarse sand with a mud content of ≤5% and the overall thickness of the cushion layer is uniform. The transverse drainage pipe (12) is made of perforated HDPE corrugated pipe or PVC pipe with a diameter of 80mm to 150mm. It is set with an outward slope of 2% to 4%, and is laid at a spacing of 5m to 10m along the longitudinal direction of the roadbed. The outer end of the pipe extends ≥20cm beyond the slope surface.

10. The low-lying roadbed structure in the flood detention area according to claim 1, characterized in that: The drainage blind ditch (7) has a rectangular or trapezoidal cross section. The ditch is filled with graded crushed stone, and the graded crushed stone is wrapped with a permeable geotextile filter layer. The drainage blind ditch is equipped with a longitudinal perforated drainage pipe, which runs longitudinally along the roadbed.

11. The low-lying roadbed structure in the flood detention area according to claim 1, characterized in that: The water collection well (8) is a cast-in-place or precast reinforced concrete structure, and is arranged at intervals of 30m to 50m along the longitudinal direction of the roadbed; a sand settling pit is set at the bottom of the water collection well (8), and a water inlet hole is reserved at the connection position between the well wall and the drainage blind ditch (7); A one-way check valve is installed at the connection point between the drainage blind ditch (7) and the water collection well (8). The opening head of the one-way check valve is 3cm to 8cm.

12. A method for constructing low-lying roadbeds in flood detention areas, characterized in that, For constructing the low-lying roadbed structure in the flood detention area as described in any one of claims 1 to 11, the following steps are included: S1. Roadbed excavation: Clear, level and compact the construction site, excavate the shaped roadbed, and simultaneously excavate the drainage blind ditches (7) and side ditch foundation trenches on both sides of the roadbed. S2, Laying crushed stone cushion layer (1): Spread crushed stone on the bottom surface of the roadbed and compact it. The crushed stone cushion layer (1) extends on both sides into the drainage blind ditch (7) base trench and is connected to the drainage blind ditch (7). S3. Laying the first sand cushion layer (2): Spread medium-coarse sand on the top surface of the crushed stone cushion layer (1), level it, and then compact it. S4. Laying the first composite waterproof geotextile (3): The first composite waterproof geotextile (3) is fully laid on the top surface of the first sand cushion layer (2), with the cross-sections sealed. The edges of the geotextile extend to the inside of the drainage blind ditch (7) and overlap with the top waterproof geotextile of the drainage blind ditch (7) to form a filter layer. S5. Layered and overlapping construction of multi-layered waterproof subgrade: ① Prepare solidified soil and fill it into the interior of Class A waterproof tarpaulin bags (14), Class B waterproof tarpaulin bags (15) and Class C waterproof tarpaulin bags respectively; Class A waterproof tarpaulin bags (14) and Class B waterproof tarpaulin bags (15) are pre-lined with geogrid reinforcement layers, and cross-shaped geotextile ribs (16) are prefabricated and fixed on the top surface of the bags. ② Lay two layers of Class C waterproof burlap bags filled with soil (4), and spread a second sand cushion layer (5) between the two layers of Class C waterproof burlap bags. The upper and lower layers are staggered and compacted in layers. ③ The A / B type waterproof cloth bag soil layer (6) and the second sand cushion layer (5) are laid alternately from bottom to top; the A type waterproof cloth bag (14) and the B type waterproof cloth bag (15) in the same layer are laid in a crisscross pattern, and the B type waterproof cloth bag (15) is placed across the corner joint of the four adjacent A type waterproof cloth bags (14) and partially overlapped; the ribs of the adjacent bags are overlapped and fixed with two-component polyurethane adhesive; the upper and lower bag soil layers are staggered and the ribs are staggered and bonded; after each bag soil layer and the second sand cushion layer (5) are laid, the whole layer is compacted. After the construction is carried out layer by layer to the design elevation, the second sand cushion layer (5) is laid on the top surface of the top layer of A / B type waterproof bag soil layer (6) to complete the construction of multi-layer composite waterproof roadbed; S6. Laying the second composite waterproof geotextile (10): The second composite waterproof geotextile (10) is fully laid on the top surface of the multi-layer composite waterproof roadbed, with the widths overlapping and sealed by hot-melt welding. S7. Laying the third sand cushion layer (11) and transverse drainage pipe (12): The third sand cushion layer (11) is laid on the top surface of the second composite waterproof geotextile (10) and leveled and compacted. Transverse drainage pipe (12) is laid in the third sand cushion layer (11) according to the design spacing and slope, with the pipe end extending out of the roadbed slope. S8. Construct the drainage system: Construct drainage blind ditches (7), water collection wells (8), open drainage ditches (9) and slope protection drainage channels (13) on both sides of the roadbed in sequence to ensure that each drainage structure is interconnected; install one-way check valves at the connection points between drainage blind ditches (7) and water collection wells (8); S9. Construct the upper pavement structure layer to complete the overall roadbed construction.

13. The method for constructing low-lying roadbeds in flood detention areas according to claim 12, characterized in that: In step S5, the solidified soil mix ratio and performance parameters meet the requirements of claim 8, the waterproof bag material parameters meet the requirements of claim 4, and the construction parameters of the crushed stone cushion layer (1) and the first sand cushion layer (2) meet the requirements of claim 2. The bagged soil layer is compacted by a flat vibratory tamper or a light vibratory roller, and it is prohibited to use heavy rolling equipment to directly roll the bag structure. The joints of the upper and lower bagged soil layers are staggered by a distance of ≥50cm, and the overlapping positions are staggered with each other. There are no through vertical gaps inside the roadbed.

14. The method for constructing low-lying roadbeds in flood detention areas according to claim 12, characterized in that: In step S5, before bonding the longitudinal and transverse geotextile ribs (16), roughen and clean the overlapping contact surfaces; apply two-component polyurethane adhesive evenly on both sides, align the overlapping positions and apply pressure to bond them together, with a pressing time of not less than 30s; after bonding, allow the surface to stand and cure for not less than 2 hours before the upper structure can be laid; lay Class A waterproof bags (14) according to the grid positioning, and lay Class B waterproof bags (15) in alignment and overlap, with the flatness deviation of the bag body ≤15mm / 3m.

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