A method for treating a roadbed in a deep slag backfill area

Abstract

The application belongs to the technical field of roadbed treatment, and particularly discloses a roadbed treatment method for a deep and thick slag backfill area, which comprises the following steps: step 1, dividing the roadbed of the slag backfill area into an upper soil body and a lower soil body; step 2, measuring the physical parameters and uneven areas of the roadbed, and grouting the uneven areas of the lower soil body; step 3, cleaning and flattening the site, selecting the pile type of a reinforcing body according to the physical parameters of the roadbed, then performing pile position measurement and lofting, and placing the reinforcing body in the upper soil body; step 4, flattening and rolling the site, then laying a gravel cushion layer above the reinforcing body and rolling and compacting the gravel cushion layer, laying a layer of geogrid above the gravel cushion layer, and then layering and laying a gravel layer; and step 5, sequentially constructing an upper roadbed backfill layer, a roadbed backfill layer and a pavement structure layer; the application provides a roadbed treatment method for a deep and thick slag backfill area, which has low engineering cost and short construction period.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of roadbed treatment, and particularly relates to a roadbed treatment method for deep thick slag backfill area. BACKGROUND

[0002] In recent years, in the design and construction of newly-built or expanded and reconstructed highway engineering, the foundation of a mine pit backfill area is often crossed due to investment, terrain or route restrictions and the like, and the special foundation has uneven physical properties, poor stability, weak bearing capacity and large settlement deformation, which brings great difficulties to the design and construction of the engineering. Therefore, how to treat the special foundation so as to make the stability, differential settlement and post-construction settlement of the foundation meet the requirements of the specification and design and reasonably utilize resources has become a difficult problem to be solved in the field of highway engineering construction.

[0003] At present, the commonly used treatment methods for the roadbed of the mine pit backfill area and the like include the excavation and replacement method, the dynamic compaction method, the column hammer punching pile method and the pile foundation method and the like. However, for the deep thick mine pit backfill area, the excavation and replacement method has large engineering quantity, long construction period and high engineering cost, and the re-piling of slag will also cause secondary environmental problems; the dynamic compaction method is usually suitable for the treatment of shallow foundation; the composite foundation and pile foundation methods have good treatment effect, but the engineering cost increases significantly when the treatment depth is large. Therefore, how to propose an effective treatment method different from the traditional method according to the actual geological conditions and in the case of reducing the engineering cost and construction difficulty as much as possible is a problem to be solved for the roadbed treatment under complex geological conditions. SUMMARY

[0004] The application aims to provide a roadbed treatment method for deep thick slag backfill area with low engineering cost and short construction period.

[0005] In order to achieve the above-mentioned purpose, the application adopts the following technical scheme:

[0006] A roadbed treatment method for deep thick slag backfill area, comprising the following steps:

[0007] Step 1, the roadbed of the slag backfill area is divided into an upper soil body and a lower soil body; the thickness calculation method of the upper soil body is as follows:

[0008] (1)

[0009] (2)

[0010] In the formula, L is the thickness of the upper soil body; is the characteristic value of the bearing capacity of the lower soil body after depth correction; is the top surface width of the upper soil body; is the bottom surface width of the lower soil body; It is the design load for road vehicle load; It is the average unit weight of the upper soil mass; It is the average internal friction angle of the upper soil.

[0011] Step 2: Measure the physical parameters and uneven areas of the roadbed, and grout the uneven areas of the lower soil.

[0012] Step 3: Clear and level the site, select the type of reinforcement pile according to the physical parameters of the roadbed, then measure and lay out the pile positions, and place the reinforcement in the upper soil.

[0013] Step 4: Level and compact the site, then lay a crushed stone cushion layer on top of the reinforcement and compact it. Lay a geogrid on top of the crushed stone cushion layer, and then lay the crushed stone layer in layers.

[0014] Step 5: Construct the upper subgrade backfill layer, the roadbed backfill layer, and the pavement structure layer in sequence.

[0015] Furthermore, in step 2, the grouting method is as follows: drill delivery holes from the ground to the uneven area of ​​the lower soil, make perforated holes on the grouting pipe and wrap it with tape, then put the grouting pipe into the delivery hole until the grouting pipe reaches the bottom of the uneven area, and grout is injected into the uneven area through the grouting pipe.

[0016] Furthermore, in step 2, the bottom of the grouting pipe is the grouting section, and all the perforations are located on the grouting section. The length of the grouting section is greater than or equal to the height of the uneven area.

[0017] Furthermore, in step 2, the spacing between grouting pipes is 2m, the grouting pressure is not less than 2MPa, and the grouting area is larger than the uneven area of ​​the underlying soil.

[0018] Furthermore, the reinforcement body is one of CFG piles, cement-soil mixing piles, and dynamic compaction piles; the optimal and most economical reinforcement body pile type can be explored by comparing the interaction effects of CFG piles, cement-soil mixing piles, and dynamic compaction piles with slag soil. The treatment spacing of the reinforcement body can be determined by verifying the bearing capacity of the composite foundation.

[0019] Furthermore, in step 2, ground-penetrating radar is used to explore the lower soil to identify uneven areas in the lower soil.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1. This invention provides a novel method for treating deep backfilled mine pit subgrades by strengthening the upper subgrade with reinforcement and uniformly grouting the lower subgrade. This method effectively solves the problems of insufficient strength of slag backfill subgrades, unevenness and high compressibility of slag soil, and ultimately enables slag backfill subgrades to meet engineering application requirements.

[0022] 2. The subgrade structure consists of an upper shallow strongly treated zone and a lower undisturbed backfill weakly treated zone. The additional load above the subgrade is mainly borne by the upper strongly treated zone. As the depth increases, the additional stress borne by the lower zone gradually decreases. At the same time, during the early backfilling stage, due to the time effect and the self-weight load of the upper layer, the compressibility and bearing capacity of the lower backfill soil will be improved to a certain extent, so weak treatment or no treatment may be performed.

[0023] 3. Grouting is used to reinforce uneven sections of the lower soil layer, ensuring uniformity with the surrounding soil. This method fully utilizes the load-bearing characteristics of multi-layer backfill, allowing upper and lower layers to work in harmony and meet project requirements. The reinforcement effectively forms a consolidated hard shell with the upper soil layer, providing sufficient strength and compressibility.

[0024] 4. Compared with traditional methods, this invention does not require overall excavation or reinforcement, thus improving the level and efficiency of roadbed construction in slag backfill areas. This method avoids the disadvantages of high cost and long construction period in excavation and replacement methods and complete pile foundation methods. This application makes full use of the characteristics of slag backfill soil itself for in-situ shallow treatment, which avoids the disadvantages of high engineering cost and long construction period caused by large treatment depth and large amount of excavation in traditional treatment methods. It can effectively solve the problems of insufficient strength of slag backfill roadbed and the unevenness and high compressibility of slag soil, ultimately enabling slag backfill roadbed to meet engineering application requirements, saving land resources and reducing engineering costs. Attached Figure Description

[0025] Figure 1 This is a flowchart of the roadbed treatment method according to Embodiment 1 of the present invention;

[0026] Figure 2 This is a schematic diagram of the roadbed structure according to Embodiment 1 of the present invention;

[0027] Figure 3 This is a schematic diagram of the grouting pipe in Embodiment 1 of the present invention;

[0028] Figure 4 This is a schematic diagram of the overall road structure according to Embodiment 1 of the present invention;

[0029] Figure 5 This is a cross-sectional view of the test tube layout in Embodiment 1 of the present invention;

[0030] Figure 6 This is a plan view of the test tube layout in Embodiment 1 of the present invention;

[0031] Figure 7 This is a schematic diagram of the horizontal displacement test in Embodiment 1 of the present invention;

[0032] Figure 8This is a schematic diagram of the cross-sectional settlement test in Embodiment 1 of the present invention;

[0033] Figure 9 This is a schematic diagram of the horizontal displacement of the inclinometer tube 1 in Embodiment 1 of the present invention;

[0034] Figure 10 This is a schematic diagram of the horizontal displacement of the inclinometer tube 2 in Embodiment 1 of the present invention;

[0035] Figure 11 This is a schematic diagram of the horizontal displacement of the inclinometer tube 3 in Embodiment 1 of the present invention;

[0036] Figure 12 This is a schematic diagram of the cross-sectional settlement of the cross-sectional settlement pipe 1 in Embodiment 1 of the present invention;

[0037] Figure 13 This is a schematic diagram of the cross-sectional settlement of the cross-sectional settlement pipe 2 in Embodiment 1 of the present invention;

[0038] Figure 14 This is a schematic diagram of the cross-sectional settlement of the cross-sectional settlement pipe 3 in Embodiment 1 of the present invention.

[0039] In the diagram: 1. Reinforcement; 2. Grouting pipe; 3. Uneven area; 4. Natural ground; 5. Subsoil; 6. Upper soil; 7. Geogrid; 8. Crushed stone cushion layer; 9. Subgrade backfill layer; 10. Roadbed backfill layer; 11. Pavement structure layer; 12. Hole. Detailed Implementation

[0040] Example 1

[0041] A method for roadbed treatment in deep slag backfill areas, such as Figure 1 As shown, it includes the following steps:

[0042] Step 1: Divide the roadbed in the slag backfill area into upper soil 6 and lower soil 5, with the natural ground 4 above the roadbed; (e.g., ...) Figure 2 As shown, the subgrade structure consists of an upper shallow strongly treated zone and a lower undisturbed backfill weakly treated zone. The additional load above the subgrade is mainly borne by the upper strongly treated zone. With increasing depth, the additional stress borne by the lower layer gradually decreases. Simultaneously, during the early backfilling stage, due to the time effect and the self-weight load of the upper layer, the compressibility and bearing capacity of the lower backfill soil will increase to some extent, allowing for weak treatment or no treatment. The upper soil mass 6 is the strongly treated zone, i.e., the upper embankment; the lower soil mass 5 is the weakly treated zone, i.e., the lower embankment. The thickness of the upper soil mass 6 is calculated as follows:

[0043] (1)

[0044] (2)

[0045] In the formula, L is the thickness of the upper soil body 6; It is the characteristic value of the foundation bearing capacity of the lower soil 5 after depth correction; It is the width of the top surface of the upper soil mass; It is the width of the bottom surface of the lower soil mass; It is the design load for road vehicle load; It is the average unit weight of the upper soil mass; It is the average internal friction angle of the upper soil. The thickness Z of the lower soil is the total fill thickness of the slag backfill area minus the thickness L of the upper soil.

[0046] Step 2: Measure the physical parameters of the slag fill and use ground-penetrating radar to conduct a comprehensive survey of the soil in the area to determine the location of the uneven region 3 of the slag fill. Uneven region 3 is a loose or cavitary area of ​​the fill. Then, grouting is performed on the uneven region 3 of the lower soil body 5 of the slag fill: Drill a conveying hole from the ground to the uneven region 3 of the lower soil body 5. The bottom of the grouting pipe 2 is set as the grouting section, such as... Figure 3 As shown, a perforated hole 12 is opened in the grouting section, and the length of the grouting section is greater than or equal to the height of the uneven area 3. The perforated hole is wrapped with tape, and then the grouting pipe 2 is placed into the delivery hole until the grouting pipe 2 reaches the bottom of the uneven area 3. Grout is injected into the uneven area 3 through the grouting pipe 2. The grouting pipe 2 is a DN32 PVC pipe, the spacing of the grouting pipe 2 is 2m*2m, the grouting pressure is not less than 2Mpa, and the grouting area is larger than the uneven area of ​​the lower soil, so that the uneven area of ​​the lower soil is located within the grouting area.

[0047] Step 3: Combining the physical properties of slag, compare the interaction effects of CFG piles, cement-soil mixing piles, and dynamic compaction piles with slag soil to explore the optimal and most economical reinforcement type 1. Calculate the design parameters for reinforcement 1 in the backfill soil above the mine pit to determine the optimal pile length, diameter, and spacing. The treatment spacing of reinforcement 1 can be determined through composite foundation bearing capacity verification.

[0048] Step 4: Clear and level the site, measure and set out the pile positions, and carry out construction according to the selected pile type and design parameters of the reinforcement body 1. Insert the reinforcement body 1 into the upper soil 6.

[0049] Step 5: Level and compact the site. After the pile head is compacted, lay a 0.2m thick crushed stone cushion layer on top of the pile and compact it. Figure 4 As shown, a geogrid 7 is laid on top of the crushed stone cushion layer 8, and then a 0.3m thick crushed stone layer is laid in layers. During the entire construction process, it should be ensured that the crushed stone is not contaminated by the surrounding soil.

[0050] Step 6: Construct the upper subgrade backfill layer 9, the roadbed backfill layer 10, and the pavement structure layer 11 in sequence.

[0051] Example 2

[0052] The method described in this application has been successfully applied in the construction of national highways. The subgrade treatment method for deep slag backfill areas in bauxite mines includes the following steps:

[0053] Step 1: Measure the data of the deep slag backfill area. The measurement results are as follows: average backfill depth is approximately 25m, upper embankment top width B1 = 20m, and the characteristic value of the foundation bearing capacity f of the lower soil 5 after depth correction. a =180kPa, soil weight in the upper strongly treated zone =20 kN / m 3 ; Angle of internal friction of the upper soil 6 =20°; Road load =31 kPa. Substitute the measurement result into the following two equations:

[0054] (1)

[0055] (2)

[0056] The calculations show that the depth of the upper strong treatment zone is L=8m, the width of the lower embankment bottom is B2=31.5m, and the thickness of the lower soil 5 is Z, which is the total fill thickness of the slag backfill area minus the thickness L of the upper soil 6, Z=17m.

[0057] Step 2: Measure the physical parameters of the slag fill and use ground-penetrating radar to conduct a comprehensive survey of the soil in the area to determine the location of the uneven area 3 of the slag fill. The length, width, and height of the uneven area are 5m, 4m, and 3m, respectively. Uneven area 3 is a loose or cavitary area of ​​the fill. Then, grouting is performed on the uneven area 3 of the lower soil 5 of the slag fill: Drill a conveying hole from the ground to the uneven area 3 of the lower soil 5. The bottom of the grouting pipe 2 is set as the grouting section. Holes 12 are opened in the grouting section. The length of the grouting section is set to 3.5m. The length and width of the grouting area are 5.5m and 4.5m, respectively. Wrap the holes with tape and then put the grouting pipe 2 into the conveying hole until the grouting pipe 2 reaches the bottom of the uneven area 3. Grout is injected into the uneven area 3 through the grouting pipe 2. Cement grout with a water-cement ratio of 0.5 is used for grouting. The amount of cement injected is not less than 500kg / hole. The spacing between the grouting pipes is 1.5m×1.5m.

[0058] Step 3: Combining the physical properties of slag, compare the interaction effects of CFG piles, cement-soil mixing piles, and dynamic compaction piles with slag soil. Based on the characteristics of the bauxite slag backfill area, CFG piles are adopted for reinforcement body 1. The design parameters of reinforcement body 1 in the backfill soil above the mine pit are calculated. According to the existing "Technical Specification for Foundation Treatment of Buildings" (JGJ79-2012), formulas 7.5.1-2, 7.5.1-3, and 7.1.6-1 are converted to determine that the pile spacing is 1.5m x 1.5m, the pile length is 8m, and the piles are arranged in a square.

[0059] Step 4: Clear and level the site, measure and mark the pile positions, and carry out construction according to the design parameters of CFG piles. Insert reinforcement 1 into the upper soil 6.

[0060] Step 5: Level and compact the site. After the pile head is compacted, lay a thick crushed stone cushion layer on top of the pile and compact it. Figure 4 As shown, a geogrid 7 is laid on top of the crushed stone cushion layer 8, and then a thick crushed stone layer is laid in layers. During the entire construction process, it should be ensured that the crushed stone is not contaminated by the surrounding soil.

[0061] Step 6: Construct the upper subgrade backfill layer 9, the roadbed backfill layer 10, and the pavement structure layer 11 in sequence.

[0062] The post-construction monitoring results are as follows:

[0063] To verify the effectiveness of the above treatment methods, on-site monitoring was conducted at the construction site. For example... Figures 5-6 As shown, the main methods for testing the settlement and horizontal displacement of the embankment are to install cross-sectional settlement pipes on the upper part of the embankment and inclinometer pipes on the right edge of the embankment. Cross-sectional settlement pipes include cross-sectional settlement pipes, cross-sectional settlement pipes, and cross-sectional settlement pipes, while inclinometer pipes include inclinometer pipes, inclinometer pipes, and inclinometer pipes.

[0064] The test began on June 18, 2020, after the embankment construction was completed, and ended on October 15 of the same year, lasting four months. The monitoring process and results of horizontal displacement and cross-sectional settlement displacement are detailed below. Figures 7-14 .

[0065] Depend on Figures 9-11 The horizontal displacement monitoring results show that the increase gradually over time, mainly due to post-construction consolidation deformation of the embankment soil. The horizontal displacement curve also approximates a "C" shape, and its pattern is basically consistent with the numerical calculation results. Furthermore, the maximum horizontal displacement of 30.5 mm in the inclinometer tube is not significantly different from the calculated result of 28.7 mm. Figures 12-14The monitoring results of the cross-sectional settlement show that the cross-sectional settlement gradually increases over time, and its variation pattern is consistent with the numerical calculation results. Furthermore, the cumulative settlement of the cross-sectional settlement tube (28.6 mm) is not significantly different from the calculated 23.3 mm. Simultaneously, the values ​​measured by the tube are larger than those of other tubes for both horizontal displacement and cross-sectional settlement, mainly due to the constraint effect of the boundary on the tubes (the cross-sectional settlement tube and the inclined tube are collectively referred to as the measuring tubes). Based on the above monitoring results, the method proposed in this paper is feasible.

Claims

1. A method for roadbed treatment in deep slag backfill areas, characterized in that, Includes the following steps: Step 1: Divide the roadbed of the slag backfill area into upper soil and lower soil; the thickness of the upper soil is calculated as follows: L≥(f a B2-P0B1) / γB2 (1) In the formula, L is the thickness of the upper soil mass; f a B1 is the characteristic value of the foundation bearing capacity after depth correction of the subgrade soil; B2 is the width of the top surface of the upper soil; P0 is the design load of road vehicle load; γ is the average unit weight of the upper soil. It is the average internal friction angle of the upper soil mass; Step 2: Measure the physical parameters and uneven areas of the roadbed, and grout the uneven areas of the lower soil. Step 3: Clear and level the site, select the type of reinforcement pile according to the physical parameters of the roadbed, then measure and lay out the pile positions, and place the reinforcement in the upper soil. Step 4: Level and compact the site, then lay a crushed stone cushion layer on top of the reinforcement and compact it, lay a geogrid on top of the crushed stone cushion layer, and then lay the crushed stone layer in layers. Step 5: Construct the upper subgrade backfill layer, the roadbed backfill layer, and the pavement structure layer in sequence.

2. The subgrade treatment method for deep slag backfill areas as described in claim 1, characterized in that, In step 2, the grouting method is as follows: drill delivery holes from the ground to the uneven area of ​​the lower soil, make perforated holes on the grouting pipe and wrap it with tape, then put the grouting pipe into the delivery hole until the grouting pipe reaches the bottom of the uneven area, and grout is injected into the uneven area through the grouting pipe.

3. The subgrade treatment method for deep slag backfill areas as described in claim 2, characterized in that, In step 2, the bottom of the grouting pipe is the grouting section, and all the perforations are located on the grouting section. The length of the grouting section is greater than or equal to the height of the uneven area.

4. The subgrade treatment method for deep slag backfill areas as described in claim 3, characterized in that, In step 2, the spacing between the grouting pipes is 2m, the grouting pressure is not less than 2MPa, and the grouting area is larger than the uneven area of ​​the underlying soil.

5. The subgrade treatment method for deep slag backfill areas as described in claim 4, characterized in that, The reinforcement is a CFG pile, a cement-soil mixing pile, or a dynamic compaction pile.

6. The subgrade treatment method for deep slag backfill areas as described in claim 5, characterized in that, In step 2, ground-penetrating radar is used to explore the lower soil and identify uneven areas in the lower soil.

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