Lime-soil improved roadbed structure

Abstract

The application discloses a lime soil improved roadbed structure, which comprises, from bottom to top, a gravel cushion layer, a lime soil layer, an asphalt pavement layer and multiple water permeation units which are arranged in the roadbed structure at intervals, wherein each water permeation unit comprises a bottom frame which is horizontally arranged on the gravel cushion layer, multiple water permeation piles which are arranged in the lime soil layer and a connecting layer which is filled between the water permeation piles and the lime soil layer, wherein the upper end of the water permeation pile is arranged in the asphalt pavement layer, the lower end of the water permeation pile is connected to the bottom frame, the water permeation pile is a prefabricated pile, multiple convex edges are arranged on the outer side wall of the water permeation pile, the connecting layer has water resistance, the bottom frame is a prefabricated frame and the bottom frame has water permeability. The application has the beneficial effects of significantly improving the frost resistance of the roadbed, accelerating the drainage speed of the roadbed, reducing the settlement and uneven settlement of the roadbed and reducing the diseases of the pavement.

Description

Technical Field

[0001] This invention relates to the field of roadbed construction technology. More specifically, this invention relates to a lime-soil improved roadbed structure. Background Technology

[0002] Although the population in northern my country is sparse, a large number of highways need to be built in the Northeast Plain in order to improve economic development. However, there are two major construction challenges in the Northeast Plain: First, there is a shortage of sand and gravel materials, and the construction of highways requires the long-distance transportation of sand and gravel from the south, resulting in excessively high construction costs; Second, the Northeast Plain is a seasonally frozen area, and is severely affected by factors such as freeze-thaw conditions, groundwater, and traffic loads.

[0003] a. The problem of uneven settlement of the foundation caused by traffic loads or construction loads is more pronounced;

[0004] b. It is susceptible to the influence of groundwater level, which reduces the bearing capacity of the roadbed;

[0005] c. Ensuring that the roadbed working area is in a dry or moderately moist condition has become a prominent challenge;

[0006] d. The strength of the roadbed decreases significantly under freeze-thaw cycles;

[0007] e. Reduced subgrade strength leads to large additional stress in the pavement structure layer, inducing pavement distress.

[0008] Therefore, given the unfavorable external factors of scarcity of sand and gravel materials, how to improve the strength and compressive resilient modulus of the fill material in the roadbed working area, and reduce uneven settlement, improve water stability and frost resistance of the roadbed structure are problems that need to be solved when constructing highways in the Northeast Plain. Summary of the Invention

[0009] One object of the present invention is to solve at least the above-mentioned problems and to provide at least the advantages that will be described later.

[0010] To achieve these objectives and other advantages according to the present invention, a lime-soil improved roadbed structure is provided, comprising, from bottom to top, a compacted crushed stone cushion layer, a lime-soil layer, an asphalt pavement layer, and a plurality of permeable units spaced apart within the roadbed structure, wherein each permeable unit comprises:

[0011] The system comprises a base frame laid on the crushed stone subbase, multiple permeable piles inserted into the lime-soil layer, and a connecting layer filling the space between the permeable piles and the lime-soil layer. The upper end of each permeable pile extends into the asphalt pavement layer, and the lower end is connected to the base frame. The permeable piles are precast piles, and multiple protruding ridges are provided on the outer side wall of each permeable pile. The connecting layer is waterproof, and the base frame is a precast frame with permeability.

[0012] Preferably, the permeable pile is formed by pouring permeable concrete, wherein 0.3-0.5% of polyethylene water-resistant fiber and 0.1-0.3% of glass fiber are mixed and stirred in the permeable concrete, and the length of the polyethylene water-resistant fiber is 10-15 mm.

[0013] Preferably, the diameter of the seepage pile is 500-800mm, and the interval between adjacent seepage piles is 2-5m.

[0014] Preferably, the connecting layer is formed of cast-in-place concrete, and the concrete used in the connecting layer is impermeable concrete.

[0015] Preferably, the lime soil formula of the lime soil layer is: soil material, quicklime and glass powder, wherein the quicklime and glass powder are 3-5% and 5-8% of the weight of the soil material, respectively, and the particle size of the glass powder is less than 10 mesh.

[0016] Preferably, the soil is cohesive, with a plasticity index of 10-20 and an organic matter content of no more than 10%.

[0017] Preferably, the thickness of the crushed stone subbase is 10-15cm, the thickness of the lime-soil layer is 45-75cm, and the thickness of the asphalt pavement layer is 18-35cm.

[0018] Preferably, the base frame includes a pair of arched transverse ribs and an arched longitudinal rib connecting the pair of transverse ribs.

[0019] Preferably, the seepage piles on each seepage unit include vertical seepage piles arranged in a vertical state and inclined seepage piles arranged in an outward inclined state, wherein the bottom of the inclined seepage piles is provided with connecting piles, and the lower end of the connecting piles is fixed to the transverse reinforcement.

[0020] The present invention has at least the following beneficial effects:

[0021] First, the crushed stone cushion layer is used to accelerate drainage, absorb the traffic load transmitted by the above lime-soil layer, and alleviate the deformation caused by changes in the subgrade base below, thereby reducing uneven settlement of the subgrade and reducing the water content of the subgrade.

[0022] Secondly, the addition of glass fiber enhances the freeze-thaw resistance, thereby reducing the expansion caused by freeze-thaw changes. The main principle is that the freeze-thaw changes of the lime-soil layer are absorbed by the seepage piles, thus significantly reducing the freeze-thaw changes of the entire roadbed from a macroscopic perspective.

[0023] Third, the connecting layer is used to connect the lime-soil layer and the seepage pile, so that the seepage pile and the lime-soil layer are organically connected as one, and jointly resist load deformation and freeze-thaw deformation.

[0024] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0025] Figure 1 This is a partial longitudinal sectional view of the roadbed structure according to one of the technical solutions of the present invention;

[0026] Figure 2 This is a transverse cross-sectional view of the seepage pile according to one of the technical solutions of the present invention;

[0027] Figure 3 This is a top view of the base frame according to one of the technical solutions of the present invention. Detailed Implementation

[0028] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0029] It should be noted that, unless otherwise specified, the experimental methods described in the following embodiments are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified. In the description of this invention, the orientation or positional relationship indicated by the terms is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. It does not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0030] like Figures 1-3 As shown in the accompanying drawings, the reference numerals in this invention are interpreted as follows: 1. Crushed stone cushion layer; 2. Lime-soil layer; 3. Asphalt pavement layer; 4. Permeable pile; 5. Connecting layer; 6. Base frame; 7. Transverse reinforcement; 8. Longitudinal reinforcement; 9. Connecting pile.

[0031] like Figures 1-3 As shown, the present invention provides a lime-soil improved roadbed structure, comprising, from bottom to top, a compacted crushed stone cushion layer 1, a lime-soil layer 2, an asphalt pavement layer 3, and a plurality of permeable units spaced apart within the roadbed structure, wherein each permeable unit includes:

[0032] The system comprises a base frame 6 laid on the crushed stone subbase 1, multiple permeable piles 4 inserted into the lime-soil layer 2, and a connecting layer 5 filling the space between the permeable piles 4 and the lime-soil layer 2. The upper end of each permeable pile 4 extends into the asphalt pavement layer 3, and the lower end is connected to the base frame 6. Each permeable pile 4 is a precast pile, and multiple protruding ridges are provided on the outer side wall of the permeable pile 4. The connecting layer 5 is waterproof, and the base frame 6 is a precast frame with permeability.

[0033] The crushed stone cushion layer 1 is used to accelerate drainage, absorb the traffic load transmitted by the upper lime-soil layer 2, and mitigate deformation caused by changes in the underlying subgrade, thereby reducing uneven settlement and water content in the subgrade. Specifically, the thickness of the crushed stone cushion layer 1 is 10-15 cm.

[0034] Furthermore, the combination of the crushed stone cushion layer 1 and the permeable piles 4 further enhances the drainage capacity of the roadbed, reduces the amount of water entering the lime-soil layer 2, and prevents the lime-soil layer 2 from becoming too wet, even exceeding its liquid limit, thereby increasing the strength of the roadbed and reducing deformation.

[0035] Furthermore, the permeable pile 4 is formed by pouring permeable concrete, wherein 0.3-0.5% of polyethylene water-resistant fiber and 0.1-0.3% of glass fiber are mixed and stirred in the permeable concrete. The length of the polyethylene water-resistant fiber is 10-15mm. Specifically, the diameter of the permeable pile 4 is 500-800mm, and the interval between adjacent permeable piles 4 is 2-5m.

[0036] The addition of water-resistant polyethylene fiber enhances the shear strength of the seepage pile 4.

[0037] The addition of glass fiber enhances the freeze-thaw resistance, thereby reducing the expansion caused by freeze-thaw changes. The main principle is that the freeze-thaw changes of the lime-soil layer 2 are absorbed by the seepage piles 4, thus significantly reducing the freeze-thaw changes of the entire roadbed from a macroscopic perspective.

[0038] The connecting layer 5 is used to connect the lime-soil layer 2 and the seepage pile 4, thereby organically connecting the seepage pile 4 and the lime-soil layer 2 into one unit, jointly resisting load deformation and freeze-thaw deformation. Specifically, the thickness of the lime-soil layer 2 is 45-75cm.

[0039] Furthermore, the connecting layer 5 is formed by cast-in-place concrete, and the concrete used in the connecting layer 5 is impermeable concrete. This can reduce the infiltration of water from the seepage pile 4 into the lime-soil layer 2, and the water is quickly guided from the roadbed surface to the crushed stone cushion layer 1 for discharge through the seepage pile 4.

[0040] The base frame 6 supports the permeable piles 4 and connects multiple permeable piles 4 together, thereby improving the overall roadbed's anti-settlement performance. Specifically, the base frame 6 includes a pair of arched transverse ribs 7 and arched longitudinal ribs 8 connecting the pair of transverse ribs 7, forming a combined I-shaped and arched structure, significantly improving stability. Furthermore, the base frame 6 is permeable, specifically pre-cast using the same formula as the permeable piles 4, allowing water introduced by the permeable piles 4 to be discharged to both sides through the base frame 6, improving the roadbed structure's drainage capacity.

[0041] Specifically, each seepage unit includes vertically arranged vertical seepage piles 4 and inclined seepage piles sloping outwards. The bottom of each inclined seepage pile has a connecting pile 9, the lower end of which is fixed to the transverse reinforcement 7. This forms a slope shape, which, in conjunction with the arched structure of the base frame 6, forms a load-bearing structure, improving the roadbed's resistance to settlement. It can also quickly guide water from inside the roadbed to both sides. Specifically, the longitudinal reinforcement 8 is 2-3m long and 100-120mm in diameter, with a spacing of 500-1000mm between adjacent seepage units along the roadbed direction. Specifically, the base frame 6 is first formed by welding arched tie bars to create an I-shaped structure, and then concrete is poured through a formwork until the specified strength is achieved.

[0042] Furthermore, the specific formula for the lime-soil layer 2 is as follows: soil, quicklime, and glass powder, wherein the quicklime and glass powder account for 3-5% and 5-8% of the weight of the soil, respectively, and the particle size of the glass powder is less than 10 mesh. The increase in glass powder can reduce the frost resistance of the lime-soil layer 2 to a certain extent, i.e., reduce the expansion caused by freeze-thaw cycles. Specifically, the soil is cohesive, with a plasticity index of 10-20, and the organic matter content in the soil is no more than 10%.

[0043] Furthermore, the thickness of the crushed stone subbase 1 is 10-15cm, the thickness of the lime-soil layer 2 is 45-75cm, and the thickness of the asphalt pavement layer 3 is 18-35cm, forming a low embankment lime-soil subgrade structure, which can significantly reduce the amount of construction materials used and lower construction costs.

[0044] A construction method for lime-soil improved roadbed structure is provided, including the following steps:

[0045] S1. Select a test section of the roadbed. Specifically, select a 100m long test section of the roadbed to test the lime-soil formula, roadbed composition, and related properties. When it meets the specified standards, it can then be used for formal roadbed construction.

[0046] S2. Take soil samples from near the construction section, preferably within a 500m radius of the construction section. Test the soil properties, specifically including particle density, plastic limit, plasticity index, liquid limit, and organic matter content. Silty clay is preferred, with the plasticity index controlled between 10 and 20.

[0047] S3. Take soil material, crush it, control the particle size to be less than 10mm, and air dry it until the content is less than 10%, and set it aside for later use.

[0048] Take glass waste, crush it, and control the particle size to be less than 10 mesh, then set it aside.

[0049] The content of effective CaO and MgO in quicklime is greater than 70%, and the performance of quicklime should meet the technical requirements of Grade III lime.

[0050] Add 3-5% quicklime and 5-8% glass powder to the soil, mix and stir evenly, then let it sit for about 40 hours to obtain lime-soil. Prepare corresponding samples / specimens of lime-soil according to the test requirements for relevant tests.

[0051] S4, Sample Testing

[0052] The dry density of the samples was tested using an electric compactor, and the dry density ranged from 1.75 to 1.91 g / cm³. 3 Within the range;

[0053] The moisture content of lime-soil was tested, with a liquid limit of 40.5–42.3%, a plastic limit of 27.6–29.8%, and a plasticity index of 10.7–14.7.

[0054] The unconfined compressive strength of the specimens was tested using a triaxial apparatus. The specimens were 50mm x 50mm in size and cured for 10 days, reaching 2.07–2.35 MPa.

[0055] Using the bearing plate method, the sample compaction degree was 96%. During the pre-compression test, a pressure of 175 kPa was applied for 1 min, followed by unloading for 1 min, and then the sample was loaded in stages. The CBR was found to be 196.3-205.7%.

[0056] The rebound modulus was tested and found to be 300–315 MPa, which is much higher than the value specified for highways.

[0057] By testing the internal temperature difference of existing roadbeds in the Northeast Plain during the freeze-thaw season within the range of -20 to 25℃, specimens measuring 50mm*50mm were prepared and placed directly into a DW-40 temperature-controlled freezer. Ten freeze-thaw cycles were performed, each lasting 24 hours, with freeze-thaw cycles at -20℃ and 25℃. Under a confining pressure of 150kPa, the peak strengths of the specimens before and after freeze-thaw were measured to be 254.8–267.6kPa and 253.9–260.3kPa, respectively, significantly improving the freeze-thaw resistance.

[0058] The above sample tests show that the lime-soil formula meets the specified requirements and is even better than expected.

[0059] S5. Carry out foundation treatment in the roadbed test section, clean the foundation surface according to the prescribed standards, and excavate the foundation surface downward to a certain depth;

[0060] Lay a crushed stone cushion layer 1 into the base and compact it. Specifically, the thickness of the crushed stone cushion layer 1 should be controlled at 10-15cm.

[0061] A prefabricated base frame 6 is laid on the crushed stone cushion layer 1, so that the two ends of the transverse reinforcement 7 are inserted into the crushed stone cushion layer 2;

[0062] According to the lime-soil formula determined in step S4, a suitable amount of lime-soil is prepared. Then, a bulldozer is used to spread the lime-soil on the crushed stone subbase 1, cover the base frame 6 and fill the gaps. The top roller is used to compact and level the lime-soil layer 2 so that the compaction degree of the lime-soil layer 2 is not less than 95%. After curing for 10 days, the thickness of the lime-soil layer 2 is controlled at 45-75cm.

[0063] During the curing period, a required number of permeable piles 4 are prefabricated. Specifically, the length of the permeable pile 4 is 5-10 cm greater than the thickness of the lime-soil layer 2, and the diameter of the permeable pile 4 is controlled between 500 and 800 mm. Improved permeable concrete is prepared using permeable concrete, 0.3% or 0.5% polyethylene water-resistant fiber, and 0.1% or 0.3% glass fiber. Then, it is poured using a formwork. After reaching the specified strength, the permeable pile 4 with raised ridges is obtained. The length of the polyethylene water-resistant fiber is 10-15 mm. The specific formula of the permeable concrete is as follows:

[0064] The cement is P·O42.5 grade ordinary Portland cement. The coarse aggregate is recycled aggregate crushed by a crusher, with particle sizes of 9.5–16 mm and 4.75–9.5 mm. The water-cement ratio is 0.3, and the mix proportion is: 730 kg / m³ for particles with particle sizes of 9.5–16 mm and 4.75–9.5 mm. 3 The cement content is 330 kg / m³. 3 .

[0065] Drill holes in the well-maintained lime-soil layer 2, including inclined holes, straight holes and cross holes. Then insert the seepage pile 4 into the hole. The seepage pile 4 is 25-10cm higher than the lime-soil layer. Then pour impermeable concrete between the seepage pile 4 and the hole wall of the lime-soil layer 2 to form a connecting layer 5. Specifically, the diameter of the drilled hole is 5-8cm larger than the diameter of the seepage pile 4.

[0066] Specifically, the impermeable concrete uses high-strength cement concrete with the following formula: P·O 42.5 grade ordinary Portland cement, coarse aggregate of 5-20mm crushed stone, fine aggregate of Grade II natural sand, admixtures of fly ash and silica fume, water-reducing agent of type NF-2, and air-entraining agent of type CAS-I. The mixing ratio is: fly ash and silica fume in a 1:1 ratio, and sand content of 670kg / m³. 3 The crushed stone is 1250 kg / m³ 3 The cement usage is 360 kg / m³ 3 The dosages of water-reducing agent and air-entraining agent are 1% and 0.1%, respectively.

[0067] After the connecting layer 5 reaches the specified hardness, asphalt concrete is laid to form asphalt pavement layer 3, with a compaction degree of not less than 95%. The roadbed test section is cured for 28 days. Specifically, the thickness of asphalt pavement layer 3 is controlled between 18 and 35 cm.

[0068] S6. Core sampling was conducted on the test section of the roadbed, avoiding sampling from seepage pile 4 and base frame 6. The unconfined compressive strength and resilient modulus of the roadbed were found to be 956.8–1000.5 kPa and greater than 300 MPa, respectively. The resilient modulus was much greater than the specified 30 MPa and even better than expected.

[0069] Simulated traffic loads were applied to the roadbed test section, and single-point settlement gauges were installed. The settlement of the roadbed test section was found to be less than 10 cm.

[0070] S7. Carry out the roadbed laying according to the formula and laying method determined in steps S1 to S6.

[0071] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A lime-soil improved roadbed structure, characterized in that, It includes, from bottom to top, a compacted gravel cushion layer, a lime-soil layer, an asphalt pavement layer, and multiple permeable units embedded at intervals within the roadbed structure, wherein each permeable unit includes: The system comprises a base frame laid on the crushed stone subbase, multiple permeable piles inserted into the lime-soil layer, and a connecting layer filling the space between the permeable piles and the lime-soil layer. The upper ends of the permeable piles extend into the asphalt pavement layer, and the lower ends are connected to the base frame. The permeable piles are precast piles, and multiple protruding ridges are provided on the outer walls of the permeable piles. The connecting layer is waterproof, and the base frame is a precast frame with permeability. The permeable pile is formed by pouring permeable concrete, and the permeable concrete is mixed with and stirred with 0.3~0.5% polyethylene water-resistant fiber and 0.1~0.3% glass fiber, and the length of the polyethylene water-resistant fiber is 10~15 mm. The base frame includes a pair of arched transverse ribs and an arched longitudinal rib connecting the pair of transverse ribs; Each seepage unit includes vertical seepage piles that are set vertically and inclined seepage piles that are set outwards. The bottom of the inclined seepage piles is provided with connecting piles, and the lower end of the connecting piles is fixed to the transverse reinforcement.

2. The lime-soil improved roadbed structure as described in claim 1, characterized in that, The diameter of the seepage pile is 500~800 mm, and the interval between adjacent seepage piles is 2~5 m.

3. The lime-soil improved roadbed structure as described in claim 1, characterized in that, The connecting layer is formed by cast-in-place concrete, and the concrete used in the connecting layer is impermeable concrete.

4. The lime-soil improved roadbed structure as described in claim 1, characterized in that, The specific formula of the lime soil layer is as follows: soil material, quicklime and glass powder, wherein the quicklime and glass powder account for 3-5% and 5-8% of the weight of the soil material, respectively, and the particle size of the glass powder is less than 10 mesh.

5. The lime-soil improved roadbed structure as described in claim 4, characterized in that, The soil is cohesive, with a plasticity index of 10-20 and an organic matter content of no more than 10%.

6. The lime-soil improved roadbed structure as described in claim 1, characterized in that, The thickness of the crushed stone subbase is 10-15 cm, the thickness of the lime-soil layer is 45-75 cm, and the thickness of the asphalt pavement layer is 18-35 cm.

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